Low ripple low noise small power supply design

[VEGETA]

Dear EEVBlog members...

I am making a small PSU for the Dreamcast, it is linear with pre-regulator switching supply fed by 12v laptop\cheap power supply.

I made the design and it is final but it occurs to my thought using a capacitance multiplier to eliminate the ripple more, despite using 1000uf elec caps (+ other 10uf ceramic caps before and after linear ldo).

I assume these caps are good enough but capacitance multiplier seems to enhance it more as Dave showed, and low ripple low noise is important for me.

I searched and found this mosfet: PMV16XN -> https://datasheet.lcsc.com/szlcsc/Nexperia-PMV16XNR_C110920.pdf

which is low space and small size which is important to me.

can this withstand 1-3 amps? notice that it won't regulate anything but rather will be put before the linear regulator and Vgs will be 6v for one rail (5v one) and 8v for another (3.3v one) which is enough i guess.

So I figured it would be just the Rds on dropout voltage: 3 amps * 3 amps * 0.02 R = 0.18 watts.

So are my calculations correct?


thanks for help!

[Vovk_Z]

Voltage drop of a capacitance multiplier is related to Vgs but not to Rds. Rds is not a parameter for linear mode. So in linear mode a Mosfet transistor will dissipate up to 4V × 3 A = 12 W.
That needs TO220 transistor with large enough heatsink.

[VEGETA]

Voltage drop of a capacitance multiplier is related to Vgs but not to Rds. Rds is not a parameter for linear mode. So in linear mode a Mosfet transistor will dissipate up to 4V × 3 A = 12 W.
That needs TO220 transistor with large enough heatsink.

But this is a logic level mosfet where 4.5v Vgs is fully on, thus won't operate in linear mode right?

I will feed it Vgs of more than 4.5v so I guess it could be fully on. However, I thought that this is how load switches are, not capacitance multipliers. So I wanted to verify more.

Voltage drop of teh cap. mulitplier is not so important to me but rather the heat. I can adjust the switching regulator to compensate for any drop but wouldn't imagine it could be this big despite using > 4.5v on gate.

All this comes from the thought that 1000uF elec. cap + 5 of 10uf ceramics aren't enough to eliminate the ripple.

[Vovk_Z]

Ok, you may use logic level mostet too, of cause, but still 1..2 VDC voltage drop multyplied by 1-3 Ampere is 1..6 W. SOT23 case wan't help to dissipate such amount of power.

[BrianHG]

I am curious, why have you abandoned BJT?
Mosfets have a gradual turn on curve/knee making them poor at output regulation.
A BJT has a very sharp knee and turns on at around a 0.7v drop only.

Using an NPN transistor with a beta of ~100m under load in emitter-follower setup, tying the a 100 ohm resistor to V+ then to the base while having a 100uf cap at the base to GND would be equivilant to having something like a 10,000uf cap in circuit.  Say you place a 1000uf cap, this isn't a really large number, but, you would get something like a 0.1 farad cap output at the emitter, and unlike the mosfet, the transient load capabilities will be regulated in the mv with a change in load in the amps, not a half a volt like a mosfet.

Adding a pull-down resistor on the base, or a series diode in line with the 100ohm resistor would only give your filter an additional 0.7v drop/separation/headroom from the source VCC's ripple improving regulation in the case where you may need to clean a large 1v ripple.  2 diodes in series to clean a 1.5v ripple.  You have very precise control here unlike mosfets with their wide Vgs.

Note that with a voltage drop of 2v, 3 amps is still 6 watts of heat you will need to dissipate and I suspect you will need at least a TO-225 package transistor with a little heatsink, or a TO-220 to be safe.

Operating that tiny mosfet in the linear region, at 3 amps, there will be an around 2v drop from drain to source, meaning that sot-23 will need to dissipate 6 watts of heat.  At room temp, that device is only rated to dissipate 0.51watts (P_tot in table 5) at room temp.  When it heats up to 100 degrees C, (and it will with even @ 1 amp load), that drops to 40% according to the graph on Fig.1, meaning 0.2 watts.  Do I need to say 'up in a puff of smoke'?

[BrianHG]

The minimum transistor I would use is an MJE200.
Very good h_FE up to 3 amps.  IE expect 70x you capacitor figure up at a full load of 3 amps, 100x and below 2 amps.

BD437 also looks good.

[BrianHG]

For a mosfet in your application, in a linear voltage follower mode, the choice I would make would be the 'MCU90N02' by Micro Commercial Components.  With a 3 amp load, the Vgs will be around 1.6v.

It's in a DPAK case and I would still have good copper flood on my PCB to dissipate that heat from linear operation, or a tiny heatsink glued onto the device package will give you enough headroom.

Vishay's 'SQA410EJ' is in a much smaller package 'PowerPAK SC-70' and has better Vgs performance on par with your SOT-23 device, around 1.2v @ 3 amp.  However, make sure your PCB has a proper good plated surface area to cool the device and you will just make it.

[langwadt]

why would a Dreamcast need "low ripple low noise" ?

[VEGETA]

why would a Dreamcast need "low ripple low noise" ?

I am making a replacement PSU as I mentioned in the beginning of the topic.

Giving it noisy power may affect its output since this is analog video and audio we are dealing with. People came up with DreamPSU which uses switching regulators only which is noisy. Original PSU had several problem and it didn't age very well according to many many people especially when you hook the GDEmu device which makes the 12v no longer used... then 12v regulator is floating -> starts generating heat and so on... you could put 1k resistor as minimum load on it but this is not a professional solution right? still people report the heat and stuff from it.

My solution is this: a little PSU (50mm x 50mm) which takes 12v input from a laptop or chinese or whatever power plug as input, and outputs a cleaner voltage due to the fact that I used a switching pre-regulator with linear post-regulator with about 0.5v in between to save power and heat. this way I can provide a cheap device, low noise (as low as possible) and won't generate heat.

Then I knew or remembered the cap. multipler thing and thought it may enhance the performance more... however, the board is packed xD and no place on it. even sot-223 may not fit anymore. Since I will be using jlcpcb service to make the boards, at least for now.

I put 1000uf elec. + 5 of 10 uf ceramics at the output of each rail hoping it is enough, is it?

I am curious, why have you abandoned BJT?

I didn't, I just looked at dave's video without much thinking about it. My problem is with the heat, I don't want heatsinks at all and thought that maybe I could make a cap. multiplier to do the job without much heat and drop voltage which using very small components.

Here are some pictures of the design: https://slow.pics/c/iwFVoT81

[BrianHG]

I am curious, why have you abandoned BJT?

I didn't, I just looked at dave's video without much thinking about it. My problem is with the heat, I don't want heatsinks at all and thought that maybe I could make a cap. multiplier to do the job without much heat and drop voltage which using very small components.

Here are some pictures of the design: https://slow.pics/c/iwFVoT81

I can see how looking at an SOT23 with 2amps and think, hey, this device wont give off heat like a BJT.
The Virshay 'SQA410EJ' I listed is actually just about identical to you NXP PMV16XN, it only has slightly higher Rds ON figure of 28mOhm  VS 16mOhm, however where the Virshay wins is at room temp, it can dissipate 13watts, 4.5 watts at 125 degrees through it's package where NXP can only do 0.5watts, or, 1.2watts on a PCB with 6cm square (Well just read Table 5 in the datasheet) which goes down to 40%, IE 0.50 watts @ 125 degrees with PCB heat-sink.  Again, in NXP data sheet, see figure 1/2, the power de-rating curve.

For your project, you have a ripple being generated by a cheap PSU switching supply.  I assume that there is no modulating current in the load.

Feeding a mosfet gate with a cap multiplier, you can get away with 1uf or 10uf with a good series resistor like 1k instead of 100 ohm like the BJT.

Adding a 1k parallel resistor to a 12v to load a minimum 12ma isn't a big problem when the supply is capable of delivering over an amp.  I would just make sure it is a 1/4watt resistor.

As for switching noise, there do exist quality switching regulator designs which make really cleaner and tighter voltage outputs, though, this usually means more coils, or, higher frequency switching ICs.

Remember, a capacitance multiplier doesn't regulate, it only smooths out noise by slightly lowering voltage.
And that output will raise and lower depending on output load by a bit, IE there is no true voltage regulation at the output.

If I were to make this project, I would concentrate on filtering the 12v supply input and having a clean switcher for the 3 output voltages.  You have a really tight PCB and if you want 'Analog' grade voltage regulation, you might not be able to achieve that in that truly cramped space for 3amp, 3 outputs.  To get analog quality supply, this also means taking care about GND loops and power tracing locations and how the layout of the caping is located on your PCB, otherwise, the ringing EMI from switching supplies will go through the PCB circuitry as if it were an antenna designed to tune into those nasty spikes.

Now, if Q1,Q2,Q3,Q4 on your PCB are the NXP mosfets which are your capacitance multipliers, and that's all the space you got to release their heat, you are in trouble.

Also, if you have 12v input, from a dirty supply, only expect 10v output after the capacitance multiplier, maybe 11v at loads under an amp.

[BrianHG]

Have you though about the new modern low noise step down switching converters?

There are new 2MHz ICs which will give you a ~15mv P-P noise with 100ma load, and that shrinks down to ~3mv P-P when driving 4 amps.  This is so small it's even difficult for many scopes to measure.  And since it's up at 2MHz, all you would need is a second series output choke inductor or ferrite bead with a 1uf cap the erase that residue oscillation.  If you have any length of wire between your PCB and Dreamcast, ~10mv at 2Mhz wouldn't even make it to the Dreamcast as it's onboard caps would filter out such a weak high frequency noise over any length of wire, especially if you run that wire through a ferrite core.

The 0 load output regulation has also vastly improved on these new ICs.
At no load, you would expect a 5v output to be at 5.07v, dropping down to 5.00v at 500ma staying flat all the way up to 4 amps.  Even 4 amp linear regulators operate in this ballpark.

Take a look at TI's LM62440 here: https://www.ti.com/store/ti/en/p/product/?p=LM62440APPQRJRRQ1&HQS=OCB-tistore-invf-storeinv-invf-store-findchips-wwe

Using 2 of those on your PCB for 3.3 & 5v with a good choke filter to pass through the 12V input to output would simplify your PCB to 2 regulators and a few extra inductor chokes.

Or you can have a 15-24v source supply and use 3 switchers to get all 3 regulated outputs.

(Warning: to achieve the datasheet's noise levels, you need to follow the example PCB layout as close as you can.  Making changes, unless you know what you are doing may increase that ~5mv ripple (assuming moderate loads).)

[VEGETA]

For your project, you have a ripple being generated by a cheap PSU switching supply.  I assume that there is no modulating current in the load.

the 12v rail is a direct connection to the cheap psu which is not so critical.

However, the 3.3v and 5v are the important ones. I wanted a switching pre-regulator followed by linear post-regulator. I insist on linear being the final one.

When I return home I will give you the names of the ICs chosen.

Now, if Q1,Q2,Q3,Q4 on your PCB are the NXP mosfets which are your capacitance multipliers, and that's all the space you got to release their heat, you are in trouble.

No, those in the bottom are for minimum load for each rail... they get about 12 ma or so to solve the problem of floating supply rail and ensure stability.

Cap. multiplier doesn't exist in this design yet.

Have you though about the new modern low noise step down switching converters?

I will give you the name of my chosen IC when I return and oped KiCAD. I think it is AOZ1284, but I will verify soon. it is configurable from 200khz to 2mhz.

According to it's datasheet, the output ripple is about 5mv or so (rough reading from plot). This followed by a linear regulator + many caps... I think it would be enough? gotta check the kicad project!

Or you can have a 15-24v source supply and use 3 switchers to get all 3 regulated outputs.

this could be another solution but people are used to readily available 12v psus. I could make another version later on but I need to make this one works as intended.

The 12v rail is used only to drive the GD-ROM device which is maybe just the motors and so on to drive the assembly... nothing serious, so yeah... 12v could be noisy here. However, 3.3v and 5v are different, they are for the board itself which contains the output voltage.

as you know analog voltage is 0.7v p-p which is highly sensitive to noise.

[BrianHG]

For your project, you have a ripple being generated by a cheap PSU switching supply.  I assume that there is no modulating current in the load.

the 12v rail is a direct connection to the cheap psu which is not so critical.

However, the 3.3v and 5v are the important ones. I wanted a switching pre-regulator followed by linear post-regulator. I insist on linear being the final one.

When I return home I will give you the names of the ICs chosen.

Now, if Q1,Q2,Q3,Q4 on your PCB are the NXP mosfets which are your capacitance multipliers, and that's all the space you got to release their heat, you are in trouble.

No, those in the bottom are for minimum load for each rail... they get about 12 ma or so to solve the problem of floating supply rail and ensure stability.

Cap. multiplier doesn't exist in this design yet.

Have you though about the new modern low noise step down switching converters?

I will give you the name of my chosen IC when I return and oped KiCAD. I think it is AOZ1284, but I will verify soon. it is configurable from 200khz to 2mhz.

According to it's datasheet, the output ripple is about 5mv or so (rough reading from plot). This followed by a linear regulator + many caps... I think it would be enough? gotta check the kicad project!

Or you can have a 15-24v source supply and use 3 switchers to get all 3 regulated outputs.

this could be another solution but people are used to readily available 12v psus. I could make another version later on but I need to make this one works as intended.

The 12v rail is used only to drive the GD-ROM device which is maybe just the motors and so on to drive the assembly... nothing serious, so yeah... 12v could be noisy here. However, 3.3v and 5v are different, they are for the board itself which contains the output voltage.

as you know analog voltage is 0.7v p-p which is highly sensitive to noise.

If you are talking about audio, 2Mhz is outside the audio band.
(TI-Switcher, ~2amp load) In analog video, 0.003v P-P ripple @ 2.1Mhz may be seen if it is injected right into the video line, however, I doubt this could happen unless the there are no caps on the Dreamcast.
(AOZ1284 - ~2amp load) You are getting 0.01v P-P ripple at 600Khz.  A little more noise, however, this regulator also injects a nasty 0.2v P-P into your 12V supply coming in.  This is harder to get rid of especially at the lower 600Khz frequency.

If your problem is not these ripples, but load transient regulation, then this is a different problem and a mosfet capacitance multiplier will actually makes things much worse.  Even BJT will be much cleaner, and if your load is at a minimum say 250ma, going up to 3amp, a darlington transistor would near 0 high frequency ripple, with the cost that there will be a 1.7v drop from collector to emiter with the TI switcher, though, your 100uf cap with a 1k series resistor will look something like a 1 farad cap on the power supply line, better than a lead acid battery.  You are at a point where you might as well use no switchers and 2 darlingtons with zener diodes on the bases to GND creating your own super responsive linear regulators.  Though, powerup will take something like half a second as the caps on the base slowly charge to the zener diode point.

Example:
(TI Switcher, 2amp to 4amp transient on 5v)  A 0.1v positive or negative spike for 40us before it completely settles.  This correction is outside the audio band, you would not be able to hear it.

(AOZ1284 -  2amp to 4amp transient on 5v)  A 0.4v positive or negative spike for 100us before it completely settles.  (You can hear this as tin-type washy bit error sounding noise with heavy processing if these load changes are due to CPU/GPU current processing load as it will be in the 10Khz band.)

(Voltage drop across the PMV16XN when going from 1amp to 3 amp load) - A ~0.4v, not a spike, but a continuous drop which stays there until the load is released.  This will be heard throughout the audio band as there is no output feedback correction whatsoever.

The low noise TI switcher beats both the AOZ1284 and PMV16XN mosfet capacitance multiplier hands down.

Normal speed LDOs take up to 30us to settle from a 2 amp transient load at up to 0.3v spike.  The low noise TI switcher actually competes here where is has less ripple and is slightly slower at 40us to completely settle.

High Speed Linear LDO regulators like the LM323 can win here in that with a 2 amp load swing, or 2v Vin swing, they will deviate 0.2v, but, for only 1us, correcting their output in the 1Mhz band.

Now without knowing the setup and the source of the Sega Dreamcast noise, as it should have noise suppression on it's analog components, however, older gaming console may have not had such quality audio components, the low noise TI switcher will get you damn close to an linear supply.  And, if the original Dreamcast supply used old analog regulators like the 7805 series/similar, the TI switcher should outperform them.

The AOZ1284 switcher has transients and responses due to load change within the audio band.  This you may want to double regulate, however, just using a mosfet capacitance multiplier will reveal even more lower frequency noise since it's output drifts with current load.

I remember with really loud volume on my old Amiga 1000, there was ugly noises as I moved the mouse and when it's blitter processor rendered animation.  The +/-12v going into the op-amps weren't the problem.  Even the 5v coming out of the PSU wasn't too bad.  It was the routing to the sound IC (Paula) itself on the Amiga motherboard which had a noisy 5V since back in the day, it was a 2 layer PCB.  The only fix was t remove the IC, sit it on a breadboard IC socket with it's own 5v VCC supply separated from the rest of the computer motherboard, with GND referenced to that IC socket's GND and a dedicated 7805 for that 1 IC, I was able to erase all processing noise.  No capping or improvements to the main power supply could fix this problem since that noise was introduced on the motherboard itself.

[VEGETA]

Update:

I am using AOZ1284 with 20KOhm frequency set resistor... that means 2 MHz switching frequency.

I take the 12v into the AOZ1284 then output 3.8v for the 3.3v LDO and 5.5v for the 5v LDO (input of LDOs have 3x 10 uF ceramic caps). The LDOs are LM39302 (Chinese clones, cheap) which are followed by 1000uf elec. cap (10mm x 10mm one) + 5x 10 uF ceramic caps. The inductors are 10uH big size.

You guys mentioned 2MHz devices, well, here is one used... also followed by linear LDO with good amount of caps.

How much ripple do you think we get?

[BrianHG]

Did you check the 'LM39302' datasheet for the 'Line Transient response, power supply VS ripple rejection frequency range?

The 'lemon' range for those LDOs is 200Khz to 2Mhz.  Your 2MHz switcher ripple and transient load noise will basically only be lowered by only 15db at best if your PCB is perfect with a middle thick GND plane.  Combining a well chosen ferite bead with a good 1-10uf LOW-ESR cap would actually do a better job than adding a linear regulator, cost less and make no heat not to mention taking less PCB space.

Since you are combining technologies in a small footprint, not using a 4 layer board with a dedicated reference GND middle layer and a power GND layer poured in the right places on top, you will need to experiment as switching supply EMI noise tends to penetrate linear regulators.

The 'AOZ1284' wasn't designed or specified to be low-EMI radiating and it does place a lot of ripple back onto your +12v meaning 2 of them will make your 12v look nasty without isolation from each other.

The only true way to avoid all these issues it to purely go all linear, but, it seems if your 12v PSU may be a low quality switcher which you might not have control over, it's EMI might go right through the linear regulators if it has spikes in the 200Khz region.

If I were you, before spending money on a PCB, I would first make simple linear power supply (hand wired or quality linear bench supply) with >10000uf caps (paralleled with 1000uf & 100uf, the smaller ones closer to the Dreamcast) on the 3 lines powering the Dreamcast to make sure that the noise you are trying to eliminate will be gone, otherwise, this may be an exercise in futility.

As for the capacitance multipliers, for this app, I would scrap the linear regulators and just use darlington transistors at the output of the switcher if I had to take that route.

If the above 100000uf linear supply test performed the way I like, these would be my 2 strategies:

A) I would  just go with the high quality TI switcher, operate it in it's 'FPWM' mode, if you analyzed it's datasheet, you would have noticed a perfect voltage output at any load from 0 amps to full 4 amps.  Then filter it's output with an smd ferite bead & an ultra-low ERS 47uf cap & it would be as clean as any linear regulator.

B) I would go with the AOZ1284, tune the output voltage by ~2v, then feed an emitter follower darlington transistor buffer (1k to base, 47uf to GND) with a 200 ohm pulldown on the 5v output and 100ohm pulldown on the 3.3v output (1/4 watt) to cancel out the darlington's internal resistors and keep them switched on.

[langwadt]

seems like a discussion of whether an anti aircraft gun or an surface to air missile is the most appropriate for  killing a fly

[BrianHG]

If I were you, before spending money on a PCB, I would first make simple linear power supply (hand wired or quality linear bench supply) ...

I think testing a hand made 'nuclear bomb' first with on hand parts may be wise to make sure attempting such a supply will be effective.  Otherwise, if his Dreamcast still makes noise he doesn't like, the problem may lie elsewhere and no matter what kind of PSU he makes will solve the problem.

For example, if it's interference in the audio, no PSU may solve the problem, yet, adding a thick copper GND to a particular IC on the Dreamcast with a good 220uf ultra-low ESR cap to that same IC's VCC pin without anything else may completely erase the problem.  Maybe in combination with lifting that IC's VCC pin and placing an SMD ferite bead.

[Doctorandus_P]

I did not read all the post here.
For a capacitance multiplier, a BJT is usually a better / easier option than a MOSfet.

If it's for in between the pre-regulator and the linear regulator, then seriously consider adding an extra inductor, to make it a LC filter
Electronics are having trouble with reacting fast enough tho high frequency stuff, while inductors only get better at higher frequencies.

Not all inductors are equal though, and it's not just inductance and current saturation rating. For good HF filtering, it's got to keep its properties into MHz range. Low capacitive inter winding coupling probably also helps.

It's just speculation, but using a straight ferrite antenna core, and using regular plastic insulated wire around it may be an excellent choice The thick plastic insulation introduces distance, and therefore lower capacitance between windings. Straight rod inductors are used as filters in for example PC power supplies. I do not know how their properties relate to toroidal or potted cores though.

Another Idea I've thought of, but never experimented with is to put a wire through a stack of "carosserie" washers. This would not work well as an inductor, but the eddy currents may be excellent at dissipating the HF noise as heat. A piece of thick walled aluminum or copper pipe may be even better at this.

[Zero999]

Be careful with LC filters, they can ring and generate higher voltages, at certain frequencies. It's often desirable to add some resistance, in parallel wih the inductor, or in series with the capacitor. If possible, choose the core type for the inductor so it's lossy enough at the resonant frequency of your filter, to make it criticaly/over-damped.

[VEGETA]

My design is just 2 layers now and I thought it could be good enough.

I don't have high quality test gear, only a DIY switching psu with no oscilloscope. I intend to buy 1054Z in December when I got enough money and stuff. I really prefer a cheap used one if it is gonna save a lot of money.

I could make 10 of these boards now and send to to people to test it, if you don't mind having one when they arrive.

The original stock PSU is using linear design with transformer, but I don't know if it makes any switching or so before the linear stage. I got an idea before this, which is to use one of those meanwell AC-DC module (https://www.meanwell.com/productPdf.aspx?i=683#1) as a source instead of the cheap 12v psu but it is very pricey and heavy to ship here to Jordan, also it has about 150mv p-p ripple which is worse that cheap psus right?. The complete unit should sell for about 40$.

Also, maybe I forgot to tell, but my goal too is to exclusively use JLCPCB SMT service to make everything which is why I spent much time picking parts suitable to it... and it worked. All the items can be assembled by that service which also explains why no component exists on the bottom of the board.

B) I would go with the AOZ1284, tune the output voltage by ~2v, then feed an emitter follower darlington transistor buffer (1k to base, 47uf to GND) with a 200 ohm pulldown on the 5v output and 100ohm pulldown on the 3.3v output (1/4 watt) to cancel out the darlington's internal resistors and keep them switched on.

this would need a heatsink right? which is not suitable to this thing... I don't want heatsink, thus I made only 0.5v difference between linear and switching stages.

[BrianHG]

B) I would go with the AOZ1284, tune the output voltage by ~2v, then feed an emitter follower darlington transistor buffer (1k to base, 47uf to GND) with a 200 ohm pulldown on the 5v output and 100ohm pulldown on the 3.3v output (1/4 watt) to cancel out the darlington's internal resistors and keep them switched on.

this would need a heatsink right? which is not suitable to this thing... I don't want heatsink, thus I made only 0.5v difference between linear and switching stages.

You had linear regulators, correct?
Did they have heatsinks?
If you use a transistor in place of a linear regulator, the heat given off will be identical.

Take a look at the NPN MJB44H11T4-A.  If you were to use this transistor, it will multiply you capacitor capacitance and divide it's ESR by at least 200 all the way up to 3 amps.  It will also reject frequencies above 10Mhz as it is a single BJT.

If you wanted to multiply that capacitance by 40000, I would add a MMBT3904 in front of the base creating your own Darlington, with a emitter to base series resistor of ~10 ohm and a pulldown resistor on the 3904's emitter to gnd of ~470ohm.  This will keep that speed where as with a true darlington like the Fairchild/On-Semiconductor's 'FJB102TM' will give you 4k, but only at 2 amp load.  It has a weaker gain at lower currents because of the internal load resistors and their setup means the transistor will only reject frequencies above the 1MHz range.

If you do not want a capacitance multiplier, you should just use the Diode's Inc 'AZ1084CD-ADJTRG1' linear adjustable 5 amp regulator.  Study the datasheet's load transient response.  It is what you are looking for and it only needs a quality 10uf cap at the output.  Do not use Linear's LM1084 as it is over 10x slower and has 5x the voltage spikes on the graph.  It also happens to be the cheapest of the 5 amp linear regulators.  Though for rejecting RF, you cannot beat the MJB44H11T4-A / MMBT3904 combo.

If you studied the graphs on the 'AOZ1284' and the TI's 'LM62440-Q1', you would have noticed that the 'AOZ1284' is a piece of crap.  2 MHz isn't the important factor here.  Even running TI's  'LM62440-Q1' at 400KHz according to the charts completely obliterates the 'AOZ1284', IE TI's figure 58(400Khz) & 60(2Mhz) on page 40 VS aosmd's figure on the bottom left of page 6.   Only Diode's Inc linear regulator 'AZ1084C' puts TI's switcher to shame.

[BrianHG]

Give me a day on finding you a suitable PSU.  You shouldn't be paying more than 6$, 15 at most for 12v, 30 watts.

Quality noiseless switchers, with high mains isolation & UL/CE approvals already exist at the 25$-35$ price point from reputable sources like TDK & TrIIad which I've used in Hi-Fi audio & video equipment with studio grade performance.

However, it's the size as these would need to be in an external box and they have a metal frame.
Though, you already get 12v,5v,3.3v all in 1 package.

[VEGETA]

You had linear regulators, correct?
Did they have heatsinks?
If you use a transistor in place of a linear regulator, the heat given off will be identical.

the linear regulator will have 0.5v dropout only, so assuming 3A max current (which, typically would be only 1A or so), this will be 1.5W total. This transistor will get 2v dropout at least right? so this wouldn't be enough without heatsink.

If you do not want a capacitance multiplier, you should just use the Diode's Inc 'AZ1084CD-ADJTRG1' linear adjustable 5 amp regulator.

so this instead of my linear regulator (LM39302) will make a big difference? it is cheap and available at JLCPCB assembly service. however, why this one is significantly better than LM39302 here despite having the same input ripple?

Though for rejecting RF, you cannot beat the MJB44H11T4-A / MMBT3904 combo.

if I could find a way to put these before the linear regulator and still getaway without heatsink, I will look into it.

If you studied the graphs on the 'AOZ1284' and the TI's 'LM62440-Q1', you would have noticed that the 'AOZ1284' is a piece of crap.  2 MHz isn't the important factor here.  Even running TI's  'LM62440-Q1' at 400KHz according to the charts completely obliterates the 'AOZ1284', IE TI's figure 58(400Khz) & 60(2Mhz) on page 40 VS aosmd's figure on the bottom left of page 6.   Only Diode's Inc linear regulator 'AZ1084C' puts TI's switcher to shame.

Where exactly in the datasheet can I find these info? I mean to know which one is better at noise rejection and final output noise quantity... etc?

[VEGETA]

I have found these:

ON Semiconductor MJD44H11T4G.

MMBT3904

they are cheap and most importantly available at JLCPCB assembly service which is critical to me as mentioned. However the transistor is no -A but rather -G. the A is for automotive, does this really matter?

also the MJD44H11T4G has a junction-to-ambient temperature of 71.4 degrees per watt.. meaning if it has 2v of drop voltage at maximum current it will be 6 watts. 6 watts = around 450 degrees! but if we reduce the drop voltage to 1v this will be about 240 degrees which is still too much.

So if we wanted to use this approach then heatsink is a must?? this DPAK package can use heatsinks like this: https://www.fischerelektronik.de/fileadmin/fischertemplates/images/SMD_Bauteile/bild1.gif right?

if I wanted cheaper ones I could get a piece of Aluminum cut at a square shape then screw it to the pad. this could work but requires more money and labor. no way i can order these from outside! plus I don't think I can solder them with that thermal mass they have.

can we make this work without heatsinks? I am really ready to adjust the design altogether  if we can do it without heatsink.

My assumption is this:

12v source -> AOZ1284 -> Cap. multiplier -> LM39302 for 3.3v and 5v.

how much ripple and noise are expected after this?

[BrianHG]

I have found these:

ON Semiconductor MJD44H11T4G.

MMBT3904

they are cheap and most importantly available at JLCPCB assembly service which is critical to me as mentioned. However the transistor is no -A but rather -G. the A is for automotive, does this really matter?

also the MJD44H11T4G has a junction-to-ambient temperature of 71.4 degrees per watt.. meaning if it has 2v of drop voltage at maximum current it will be 6 watts. 6 watts = around 450 degrees! but if we reduce the drop voltage to 1v this will be about 240 degrees which is still too much.

So if we wanted to use this approach then heatsink is a must?? this DPAK package can use heatsinks like this: https://www.fischerelektronik.de/fileadmin/fischertemplates/images/SMD_Bauteile/bild1.gif right?

if I wanted cheaper ones I could get a piece of Aluminum cut at a square shape then screw it to the pad. this could work but requires more money and labor. no way i can order these from outside! plus I don't think I can solder them with that thermal mass they have.

can we make this work without heatsinks? I am really ready to adjust the design altogether  if we can do it without heatsink.

My assumption is this:

12v source -> AOZ1284 -> Cap. multiplier -> LM39302 for 3.3v and 5v.

how much ripple and noise are expected after this?

Do you have the Junction to ambient temperature of the 'LM39302'?  If it is in the same package, it is not much different.
Also, because of those 0.5v spikes coming from the AOZ1284, and the regulator dropout of ~500mv at top load, with a little regulation safe zone, you would still be powering the LM39302 with ~+1.3v, 3.75 watts of heat.

The transistor derating you are reading is the transistor not even mounted on a PCB, complete open air.  Even a PCB alone will drain away heat.

Why do you need the 'LM39302' when your cap multiplier becomes a linear regulator just by adding the right zener diode between the MMBT3904's base and GND in parallel with your say 10uf cap.

Ok, scrap the MMBT3904 and LM39302.

Just get the cheapest adjustable linear 100ma regulators (LM317 in SMD) which can go to at least 18v input and down to 3.3v out.
You will use the 100ma regulator's output to feed the base of the MJD44H11T4G, multiplying that supplied current by the transistor's current gain curve which could drive ~ 5amps, however, the sweet spot is at the 3amp mark where the transistor's gain is clearly above 100.

The trick to preventing your 12V supply's ripple from reaching the 2x 50ma linear regulators is use a 1/2watt 100 ohm resistor from 12v to the regulator's Vin, and at that Vin, have a good 10uf 25v cap to GND (The GND trace by the output connector).  This 1 resistor and cap can power both regulators simultaneously, or, if you want super separation, use 1 resistor and cap for each LM317.  (Remember, if the MJD44H11T4G is driving a full 3amp load, the regulator powering it's base is driving ~15ma + a minimum pulldown resistor = ~20ma total max.)  While each AOZ1284, remember it makes spikes up to 0.5v, plus you want a little headroom, should power the collector with 1.3v more than the output voltage.  ~4.6v for the 3.3v output and ~6.3v for the 5v output.

     However, the 2 problems with this circuit is output regulation unless you try something I never had.  Tune the LM317 resistors for the desired voltage, however, place the voltage output feedback divider resistor on the emitter output of the transistor instead of the output of the LM317 directly.  This may regulate/correct the temperature drift and load change on the output of the transistor which may have introduced a ~0.3v variance over temp and load conditions if the LM317 took it's feedback from it's output pin.  But you need to make sure that there is no power-up overshoot spike in this case.  You may wire your PCB to operate in both modes since it will only be the placement of 1 resistor or the other.

     The second problem is that there is no true over-current protection.  You will be relying on the maximum current of the AOZ1284 to limit the output power.

With this, since the 2 linear regulators and transistors should be close and share the GND on your output power connectors, and you can move the switchers and V+ traces which feed the collectors further away from everything else, you would do fine.

This wiring configuration relies on the MJD44H11T4G collector absorbing and not passing through all the switching noise to it's emitter.  For this, the output will need a minimum load with a small cap.  Otherwise down at 0ma, some ripple may make it through as the transistor's internal capacitance will transmit some signal through as a slight DC error offset on the output.  This shouldn't be bad as a single transistor like this can operate above 85MHz.

If you knew the individual currents for both 3.3v and 5v, a single switcher at 6.3v may be enough to feed both MJD44H11T4G, though, the 3.3v one may get really hot is all the current is on the 3.3v supply.  Same with the 5v, if it is only an ~1 amp load, you may get away with feeding it more voltage on it's collector.


It's too bad the collector is the tab and not the emitter.  The collector is where you are getting all the noise from the switching supply source and a hunk of metal heatsink and fat PCB power trace may act as an antenna.

As for your illustrated heatsink, for ~5watts of heat, that will be fine, though placing the heatsink under the PCB right under the transistor with stitched vias and a rectangular copper pour on both sides will get rid of the heat more effectively.  Just gluing/taping that heatsink right ontop of the transistor's plastic case may be enough.

If you want to truly maximum protect your transistor, a TO-220 version vertically mounted with a screwed on heatsink would be best, however, for ~5 watts, I don't think you need to go that route.


More powerful transistors exist than the 'MJB44H11T4-A', I just picked the cheapest which would meet your needs.

[BrianHG]

Here are all the possible MJD44H11 you can use.
https://www.findchips.com/search/MJB44H11
Some places have it as cheap at 37cents for 1.

LM317...
https://www.findchips.com/search/LM317
Or as low as 11cents for 1, but in TO-92.
37cents in SO-8 for 1, but in quantity, it goes down to 10cents.

[VEGETA]

Do you have the Junction to ambient temperature of the 'LM39302'?  If it is in the same package, it is not much different.
Also, because of those 0.5v spikes coming from the AOZ1284, and the regulator dropout of ~500mv at top load, with a little regulation safe zone, you would still be powering the LM39302 with ~+1.3v, 3.75 watts of heat.

I put some caps before the lm39302 to ensure no big spikes happen, 3x 10uf as i remember. plus, 0.5v isn't much to cause such heat. I didn't do any measurements to see actual stuff happening.

The transistor derating you are reading is the transistor not even mounted on a PCB, complete open air.  Even a PCB alone will drain away heat.

you mean junction-to-ambient? I keep reading people say that even putting some copper area for dissipation will not help or won't make a difference.

Just get the cheapest adjustable linear 100ma regulators (LM317 in SMD) which can go to at least 18v input and down to 3.3v out.
You will use the 100ma regulator's output to feed the base of the MJD44H11T4G, multiplying that supplied current by the transistor's current gain curve which could drive ~ 5amps, however, the sweet spot is at the 3amp mark where the transistor's gain is clearly above 100.

you want to use lm317 for its stable output? how will this affect the final 3.3v and 5v without a linear post-regulator?

The trick to preventing your 12V supply's ripple from reaching the 2x 50ma linear regulators is use a 1/2watt 100 ohm resistor from 12v to the regulator's Vin, and at that Vin, have a good 10uf 25v cap to GND (The GND trace by the output connector).  This 1 resistor and cap can power both regulators simultaneously, or, if you want super separation, use 1 resistor and cap for each LM317.  (Remember, if the MJD44H11T4G is driving a full 3amp load, the regulator powering it's base is driving ~15ma + a minimum pulldown resistor = ~20ma total max.)  While each AOZ1284, remember it makes spikes up to 0.5v, plus you want a little headroom, should power the collector with 1.3v more than the output voltage.  ~4.6v for the 3.3v output and ~6.3v for the 5v output.

so from 12v source to 100ohm (0.5w) resistor (+ caps to gnd) then to lm317 input... then lm317 output to gate of npn?

this way yes the resistor can tolerate such low currents.

however, 1.3v dropout still requires heatsink... damn. I don't mind soldering and fixing heatsinks but shipping them will be very expensive and I didn't really check any local Aluminum shop if they can supply the required material cut and drill the hole...

I really hope that the heatsink remains the final issue... then I can be optimistic.

anyway you mentioned that I shouldn't let the ripple reach... what? you mean the resistor + cap will eliminate the ripple? but it is still getting into lm317.

     However, the 2 problems with this circuit is output regulation unless you try something I never had.

yes, this.

with linear post-regulator you can be very safe and precise. with just a multiplier....?

doing this trick is tricky... no guarantees.

The second problem is that there is no true over-current protection.  You will be relying on the maximum current of the AOZ1284 to limit the output power.

no over-current issue will happen since the actual current draw will barely reach 1-1.2 amps at most... even with modded fans.

This wiring configuration relies on the MJD44H11T4G collector absorbing and not passing through all the switching noise to it's emitter.  For this, the output will need a minimum load with a small cap.  Otherwise down at 0ma, some ripple may make it through as the transistor's internal capacitance will transmit some signal through as a slight DC error offset on the output.  This shouldn't be bad as a single transistor like this can operate above 50MHz.

I can send you the full pdf of the schematic to see how i implemented minimum load for each rail.

so lm317 with resistor and caps makes the npn power transistor absorb all noise but never passes it?

It's too bad the collector is the tab and not the emitter.  The collector is where you are getting all the noise from the switching supply source and a hunk of metal heatsink and fat PCB power trace may act as an antenna.

I could make the copper area connected to the emitter pin instead. easy.

As for your illustrated heatsink, for ~5watts of heat, that will be fine, though placing the heatsink under the PCB right under the transistor with stitched vias and a rectangular copper pour on both sides will get rid of the heat more effectively.  Just gluing/taping that heatsink right ontop of the transistor's plastic case may be enough.

I thought of making a hole in the heatsink then screw it tightly to the board where it sits on the copper area (but not soldered). while the transistor will be in the other face of the board with its own copper area too.

[BrianHG]

I put some caps before the lm39302 to ensure no big spikes happen, 3x 10uf as i remember. plus, 0.5v isn't much to cause such heat. I didn't do any measurements to see actual stuff happening.

If you have a +0.5v input to a low dropout regulator, it's output transistor is basically almost nailed 'ON'.  Now in the 'AOZ1284' datasheet, even with it's recommended output caps, it's output dips by 0.4v when the load switches by 2 amps.  To filter this through a lm39302 you would want +1v above your output voltage instead of 0.5v.  If you had something like a 47000uf cap at the regulator input, then you probably could get away with 0.6v above your output voltage.  Just adding a capacitance multiplier inbetween means the drop there will just make more heat for it's theoretical minimum optimum drop of now 0.7v for the transistor + 0.5v drop for filtering 'AOZ1284's 0.4v drop + ripple noise meaning 1.2v drop.  Now you have 1.2v drop on cap multiplier + 0.5v optimum drop on linear regulator.  That's still a total 1.7v drop in heat being injected into your PCB.  We can do better and save money.

The transistor derating you are reading is the transistor not even mounted on a PCB, complete open air.  Even a PCB alone will drain away heat.

you mean junction-to-ambient? I keep reading people say that even putting some copper area for dissipation will not help or won't make a difference.

Yes, if the PCB has no cooling or air flow, the heat up will happen, it will just take a little longer as the PCB itself warms up.  The same is true of a heat sink.  Still, you don't need so much as each transistor will have a ~1.5v drop, 1.2 amps load each meaning a total of 3.6 watts to radiate away from those 2 transistors.  You can shave the 'AOZ1284' down to 1.1v above the desired output voltage, 2.7 watts of heat for both transistors, but, I would test and trim these.

Just get the cheapest adjustable linear 100ma regulators (LM317 in SMD) which can go to at least 18v input and down to 3.3v out.
You will use the 100ma regulator's output to feed the base of the MJD44H11T4G, multiplying that supplied current by the transistor's current gain curve which could drive ~ 5amps, however, the sweet spot is at the 3amp mark where the transistor's gain is clearly above 100.

you want to use lm317 for its stable output? how will this affect the final 3.3v and 5v without a linear post-regulator?

The LM317 + MJD44H11 creates an adjustable 5 amp linear regulator.  You don't need anything else.  And because of the way we are wiring it, you wont even need more than a 10uf cap on the output.

The 100 ohm + 10uf cap feeding the Vin input of the LM317 means no high frequency ripple reaches the regulator's reference or GND pin.
The regulator output pin has a parallel 1uf cap and 1K resistor to GND to prevent output oscillation and guarantee a minimum load.
That output through a series 10 ohm resistor to prevent transistor oscillation feeds the base of the MJD44H11.
The emitter output of the MJD44H11 goes through a feedback resistor to the ADJ pin on the LM317 and that pin has the second feedback resistor going to your GND reference.  Just like in the LM317 data sheet, except the R1 is taken from the transistor emitter, not the regulator's Vout.
On the MJD44H11 emitter, also add a 10uf cap to GND and a 220ohm resistor 1/4watt to GND to make sure the transistor stays on at 0 load.

This is a linear regulator where the output stage is buffered 200 fold at 2 amps, 100 fold at 3 amps according to the transistor datasheet's DC current gain chart.

The reason this setup wont transmit any noise from the 'AOZ1284' to your outputs is that the entire regulator circuit is running at ~12v, coming from a 100 ohm - 10uf RC filter.  Meaning that the regulator circuitry and reference only needs to deal with and filter out  frequencies below 1Khz at the Vin pin, it wont have to deal with 10Khz spikes & 1-2Mhz RF which typically would go right through it.  With 100uf on the LM317 V+ pin instead of 10uf, now the regulator will only have to deal with ripple noise below the ~100Hz range, a frequency range it was well designed for.

The sensitive regulator circuitry never sees all the RF EMI on the MJD44H11 collector pin coming from the 'AOZ1284' output & source switching supply so long as you carefully lay out your PCB while the 85MHz MJD44H11, at low currents like 0.5 amps will still reject much of frequencies above 10Mhz.  I doubt 2Mhz could be seen on the output unless it being picked up and amplified by a looping GND on the PCB.

This eliminates those pesky additional linear regulators and makes less heat and would probably deliver a much cleaner output.

[BrianHG]

You know if you have any old TO-92 LM317 lying around plus a basic NPN transistor, you can try it out on a breadboard.

Even a 2N3904 or 2N2222 will work, except your output will be limited to the capabilities of the transistor.

[VEGETA]

I have made a quick and dirty drawing of the idea... check it out here: https://slow.pics/c/5iWg8qwS

excuse my phone camera, it started to wiggle!

[BrianHG]

I cant see a block of fuzz above the emitter of the transistor, but, that basically correct.
You want 100uf at the LM317 Vin.
You want 1uf at the LM317 Vout.  (SMD ceramic is good here)
You want 10uf or 100uf at the Emitter of the BJT.
The cheapest electrolytic 100uf 25v will do.

You do not need multiple 10uf s anywhere.  As for the 'AOZ1284' switcher, design it to spec in the datasheet.  Use 1MHz like recommended or 2MHz, and the specified recommended caps.  Let the BJT clean up the crap.

Only that feeding the 'base', you have a 100ohm resistor.  This means the output series resistance at the emitter appear to be 100ohm / Hfe200 = 0.5 ohm.  If you truly want to nail that output, using 10 ohm here would mean a series output resistance of 0.05ohm.  This means little as the LM317 will compensate in both cases, just that with 10ohm, the required compensation is a less making the circuit respond a little faster to rapid load swings.

A simpler PCB like this with only 2 switchers and 2 BJT on output with SOT23 LM317 gives you a PCB with maybe a little breathing room if you keep the current size.  You may still want to ferrite bead then cap +12vin when feeding the Dreamcast's +12v so the noise put on that power line from the 2  'AOZ1284's will not propagate to you 12v line in the Dreamcast infecting all the analog lines & GND as well.

[VEGETA]

I will try to re-design the thing from scratch and give you the update... at least the main circuit for one rail.

I cant see a block of fuzz above the emitter of the transistor, but, that basically correct.

it is (current mirror for minimum load circuit), instead of putting a resistor. this is better right?

You want 100uf at the LM317 Vin.
You want 1uf at the LM317 Vout.  (SMD ceramic is good here)
You want 10uf or 100uf at the Emitter of the BJT.
The cheapest electrolytic 100uf 25v will do.

will take these notes.

shouldn't multiple values (100uf elec. cap + 10u ceramic +1n ceramic) together make better result for all frequencies?

parts consolidation is a big thing too, so why using 1uf where I have 10uf used elsewhere and it is better?

As for the 'AOZ1284' switcher, design it to spec in the datasheet.  Use 1MHz like recommended or 2MHz, and the specified recommended caps.  Let the BJT clean up the crap.

I did as datasheet, but with 2MHz option.

Only that feeding the 'base', you have a 100ohm resistor.  This means the output series resistance at the emitter appear to be 100ohm / Hfe200 = 0.5 ohm.  If you truly want to nail that output, using 10 ohm here would mean a series output resistance of 0.05ohm.  This means little as the LM317 will compensate in both cases, just that with 10ohm, the required compensation is a less making the circuit respond a little faster to rapid load swings.

ok, i will make it 10 ohms.

A simpler PCB like this with only 2 switchers and 2 BJT on output with SOT23 LM317 gives you a PCB with maybe a little breathing room if you keep the current size.

in a 50x50 mm board? hmmm maybe if I remove the current mirror transistors and replace them with resistors but still same or more components.

linear regulators are replaced by the power NPN transistors. we have extra components like lm317 and most importantly the heatsinks.

will the heatsinks get hot? I don't want heat inside the thing, this is important.

I don't think one heatsink can be used for both transistors, right?

You may still want to ferrite bead then cap +12vin when feeding the Dreamcast's +12v so the noise put on that power line from the 2  'AOZ1284's will not propagate to you 12v line in the Dreamcast infecting all the analog lines & GND as well.

on the output pin to the dreamcast?

putting all these extra components will make it crowd area.

___

BTW i am using large inductors (10x10mm), is it necessary with 2MHz switching? if I could get away with less size I can then make room for more stuff.

____

to my understanding, the capacitance multiplier here is implemented by the 10uf that is parallel to the 1k resistor right?

[VEGETA]

I have made a very quick kicad schematic. kindly check it

[BrianHG]

You only install R1a, or R1b, not both.
Use the LM317 resistor calculator to
get the values for R1 & R2.  Use 1% resistors.
Choose an R1 value close to desired V output * 100 in Ohms,
Fill in the desired output voltage and the calculator will give you
the best value for R2.

When using R1a, your output voltage target for the calculator will be exact.
When using R1b instead, you need to fill in a voltage 0.7v higher than your
desired output voltage.

LM317 Voltage calculator website:
https://circuitdigest.com/calculators/lm317-resistor-voltage-calculator

Choose the best R1 available in 1% at around 100 X Vout in ohms.
The make sure R2 is easily available at 1%.
You may need to move R1 up or down a little to find an optimum R2.
With both resistor values, the calculator will give you the exact voltage output.
You can then remove R1's value and increase the output voltage by 0.7v and
get a new value for R2b if you want to test.

I'm assuming that you did the feedback resistor calculations correct for the AOZ1284.

On the linear side where you have the 10uf and 100uf, you only need the 100uf.
Cheap electrolytic radial will do.
Use at least 25v for the +Vin on the LM317 since a 16v cap is a little close.

[BrianHG]

You want to really save, make this the 5.0v regulator and on the output of your switcher, place 2 smd 'S5MB R5G' or 'S5KBHR5G' or through-hole 'MUR460RLG' 4-5 amp diodes in series to feed the collector of the transistor of the 3.3v linear regulator section.

Only 1 switcher, though, that switcher needs to deliver enough amps for the 5v and 3.3v.
Mount the diodes at the opposite edge of the PCB so they don't heat the BJTs as much.
Through-hole diodes may send a bit less heat to the PCB.
@1.2 amps on the 3.3v output means each diode will radiate around ~1 watt of heat.

[BrianHG]

I've had good results with these TDK supplies in the past, but they are not PCB mounted:

TDK supplies

This one is also good and cheap:
Triad Magnetics 65watt

Not as well filtered output...
Meanwell board mount, 12v @ 5 amps:
https://www.digikey.com/product-detail/en/mean-well-usa-inc/IRM-60-12/1866-3063-ND/7704688
Meanwell 12v @ 2.5 amps:
https://www.digikey.com/product-detail/en/mean-well-usa-inc/IRM-30-12/1866-3043-ND/7704668

[BrianHG]

If you really want to save on the PSU, use a cheap switcher 3$ 15v, 3amp wallwart, and add a third linear regulator to make a clean 12v from that junky wallwart.

I doubt the 12v on the Dreamcast will take much current as it only power's the CD drive.  And you get a UL/CE approved enclosed switcher with a barrel jack which can plug into your filter regulator PCB.  15v at 3 amps will easily give your 6.5v @ 4amps using your onboard single switcher and since the LM317 & BJT comes in at around 1$ per regulator, now making 3 of them.  This would be a fraction of the 30$ Meanwell PSU which has exposed mains wires meaning no safety approvals for your project as there are exposed mains wiring involved.  The 15v also leaves regulation headroom for the length of cable coming out of the wallwart.

Higher quality 15v bricks (AC power chord wire -> box -> and DC output chord with barrel jack, like laptop power supplies) go for 12$usd.


Cheap example: 15v 3amp Wallwart
Better quality: 15v 5 amp Brick
Better quality chassis mount for 6$: Get 12v 3amp version @6$ and adjust the output to 13.8v with onboard trimpot (less heat on 12v linear reg)
The 6$ chassis mount unit is nowhere near as good as the TDK or Triad Magnetics supplies I listed above.
The TDK and Triad units have proper input power chokes, well isolated from the mains and they are well certified and have fully documented datasheets.  You get what you pay for...

[VEGETA]

If you really want to save on the PSU, use a cheap switcher 3$ 15v, 3amp wallwart, and add a third linear regulator to make a clean 12v from that junky wallwart.

I doubt the 12v on the Dreamcast will take much current as it only power's the CD drive.  And you get a UL/CE approved enclosed switcher with a barrel jack which can plug into your filter regulator PCB.  15v at 3 amps will easily give your 6.5v @ 4amps using your onboard single switcher and since the LM317 & BJT comes in at around 1$ per regulator, now making 3 of them.  This would be a fraction of the 30$ Meanwell PSU which has exposed mains wires meaning no safety approvals for your project as there are exposed mains wiring involved.  The 15v also leaves regulation headroom for the length of cable coming out of the wallwart.

Higher quality 15v bricks (AC power chord wire -> box -> and DC output chord with barrel jack, like laptop power supplies) go for 12$usd.


Cheap example: 15v 3amp Wallwart
Better quality: 15v 5 amp Brick
Better quality chassis mount for 6$: Get 12v 3amp version @6$ and adjust the output to 13.8v with onboard trimpot (less heat on 12v linear reg)
The 6$ chassis mount unit is nowhere near as good as the TDK or Triad Magnetics supplies I listed above.
The TDK and Triad units have proper input power chokes, well isolated from the mains and they are well certified and have fully documented datasheets.  You get what you pay for...

well, the cheap psu is on the users themselves, not mine. so no cost there xD.

I will just provide the small board with nice little psu + a 3d printed small part with a female dc jack on it (my idea is to use a little pcb with a hole in it instead -> 0$ solution per unit).

You can just see this product to see for yourself what I want to make: https://www.indiegogo.com/projects/dreampsu-making-your-dreamcast-cool-again#/



____

I will respond to your previous posts soon.

[BrianHG]

LM317 with available 1% resistor values in ohms:

R1 - R2   = #v.
510-1540 = 5.02v
432-1540 = 5.71v -> may need adjustment depending on Vbe of transistor.

340-560  = 3.31v
249-560  = 4.06v -> may need adjustment depending on Vbe of transistor.

[BrianHG]

well, the cheap psu is on the users themselves, not mine. so no cost there xD.

Ok, fair.  If you are not providing a PSU, then I recommend buying the 2 cheapest pieces of junk in the above link and verify that they deliver the results you will claim on your indiegogo campaign just to be sure.  And I recommend passing the PSU links to your users so you know they will get the same results you are getting.

I also recommend getting 12v adapter versions to see if they provide a good enough 12v to remove that third regulator.  However, you would want good ferrites and caps on the 12v line feeding the Dreamcast.

[VEGETA]

well, the cheap psu is on the users themselves, not mine. so no cost there xD.

Ok, fair.  If you are not providing a PSU, then I recommend buying the 2 cheapest pieces of junk in the above link and verify that they deliver the results you will claim on your indiegogo campaign just to be sure.  And I recommend passing the PSU links to your users so you know they will get the same results you are getting.

I also recommend getting 12v adapter versions to see if they provide a good enough 12v to remove that third regulator.  However, you would want good ferrites and caps on the 12v line feeding the Dreamcast.

That indigogo is not mine. That is a replacement psu which can be found here: https://github.com/PSUThings/PSU

it is pure switching supply using 2 of TPS54525PWPR switching regulators. So I decided to make one using linear stage and much cleaner output.

I have a cheap chinese adjustable psu that can be used, and I recently got another one from amazon. they are good enough to test the thing.

I will try my best to redesign the thing using our approach of lm317 + npn, despite fearing the lm317 behavior since I never took feedback from another point rather than its output.

Also, where exactly in our design that cap. multiplier is implemented?

Will a small smt heatsink be enough for one regulator rail? aside from the idea of using a diy one by cutting an Aluminum sheet (this one is last resort).

I hope that we can use one heatsink for the 2 regulators (if it is hooked on gnd, no shortings needed xD).

Since using 2 MHz switching frequency, do inductors need to be large (10x10 mm)? these 2 take the most space and they are 10uH to eliminate the ripple... datasheet did specify lesser value.

[BrianHG]

I will try my best to redesign the thing using our approach of lm317 + npn, despite fearing the lm317 behavior since I never took feedback from another point rather than its output.

Also, where exactly in our design that cap. multiplier is implemented?

Will a small smt heatsink be enough for one regulator rail? aside from the idea of using a diy one by cutting an Aluminum sheet (this one is last resort).

I hope that we can use one heatsink for the 2 regulators (if it is hooked on gnd, no shortings needed xD).

Since using 2 MHz switching frequency, do inductors need to be large (10x10 mm)? these 2 take the most space and they are 10uH to eliminate the ripple... datasheet did specify lesser value.

The LM317 will just raise the voltage of it's output until the 'ADJUST' input pin reaches 1.25v.  The ADJUST pin is like a negative feedback of an op-amp.  Once the emitter of the BJT gets high enough to make the ADJUST pin 1.25v, (through the resistor divider) the LM317 will stop raising the voltage at the base hence regulating the circuit.

The LM317 feeding the BJT will simulate a battery, not a cap, expect an equivilant 1 farad output with a 20 amp peak capability and an ESR of ~0.1ohm so long as your switcher continues to deliver more than 1v above the output voltage at the collector.  Basically the LM317 is buffering and multiplying it's 100uf at it's Vin (since it is a negative feedback op-amp circuit, this is a huge number) while the BJT takes that multiplied output and further multiplies by another 100.

For heatsinks, if you could press-fit one of these ontop of both BJTs, yes ontop of the plastic case as each will be radiating only 2 watts, it will probably work fine if you even need it.  The space in that Dreamcast is big and your PCB may not build up anywhere near the amount of heat the original linear supply did.

1 Heat Sink for both - mounting permitting
(Too bad it wasn't just a tad longer, you cannot beat 1 unit at 25cents for both.):
(Though 2 of them side-by-side would be perfect for length for 3 BJTs):
https://www.arrow.com/en/products/v5619a/assmann-wsw-components-inc
Individual heat sinks (Yes, each one costs more):
https://www.digikey.com/product-detail/en/assmann-wsw-components/V5618A/AE10819-ND/3511413

I'd say think about using 1 switcher and the 2 diodes.  You will only increase your radiating heat by ~2.5 watts on the opposite side of the PCB.  And the diodes are only  ~16 cents each (S5KBHR5G).  Though your switcher will need to have enough output current for both +5v and +3.3v together.

If you 3.3v supply draws 1.5 amps continuous, each diode will radiate ~1.25 watts + the BJT will radiate ~2.25 watts.
You haven't specified how much current the 5v takes.

[BrianHG]

Hmmm this changes things, Quote: https://bitbuilt.net/forums/index.php?threads/dreamcast-r-d-and-documenting.1368/

Main Voltage lines:
12v
-Not needed to boot
-Used by disc drive laser

5v
-Required to boot
-Uses .42a

3.3v
-Required to boot
-Uses 2.8a
-Powers the 2v and 2.5v lines
-Uses .4a when not feeding onboard linear regulators

It looks like you need the full 3 amps for the 3.3v.  I might tune your switcher to the bare safe minimum of 4.5v making your worst heat output 3.6 watts instead of 4.5 watts.

Now, 0.5amps for 5v, this would be 3.5 watts of heat if you just powered the 5v linear regulator from the 12v supply directly.
Your waste heat with 1 switcher will be ~7 watts.
With 2 switchers, your waste heat will be around 4.5 watts (including the minute added heat of the second switcher).
The difference is 2.5 watts of heat to include a second switcher.
Maybe look for a smaller 1amp switcher for the 5v which may use smaller components & lower power inductor.

The 'AOZ1280CI' looks tiny and dirt cheap giving you 1.2 amps, double what you need for 5v.
You will only need to heat-sink the 3.3v BJT (if at all, I mean I have un-heat-sinked fpgas drawing 5 watts and the PCB spreads out the heat wide enough to radiate it away air convection) as the 5v one will only dissipate 0.7 watts max.

[VEGETA]

Check this one please: https://www.beharbros.com/product-page/dreamcast-power-supply

this one is more modern than dreampsu and it seems to use a heatsink stuck on the regulators... how? how does this press-fit work? I mean can I do it myself? since the assembly service from jlcpcb will not.

I can buy either one heatsink for both transistors or one for each since either solution is gonna be just 1$ total.

this one for example has 48 degrees per watt, assuming say 3 watts from each transistor = 6 watts = 288 degrees? horrible. am I calculating wrong? the other one you posted has 80 degrees per watt.

while this one has only 18 degrees per watt -> 3x18 = 54 degrees as absolute max (real max might be less than half). this one is a bit pricey and i don't know how should i solder it.

check these out: https://lcsc.com/products/Heat-Sinks_441.html

we can drill 2 holes in one of these:

https://lcsc.com/product-detail/Heat-Sinks_XSD-XSD183-097-B_C286209.html
https://lcsc.com/product-detail/Heat-Sinks_XSD-XSD35-014_C286197.html

then screw it to the board to squeeze onto the regulators plastic... dunno if this works.

dirt cheap heatsinks! didn't know they exist there. anyone we could use?

I'd say think about using 1 switcher and the 2 diodes.  You will only increase your radiating heat by ~3 watts on the opposite side of the PCB.  And the diodes are only  ~16 cents each (S5KBHR5G).  Though your switcher will need to have enough output current for both +5v and +3.3v together.

I should search for equivalent on lcsc and jlcpcb.com/parts for this diode.

anyway, putting all items on one side of the board taken into consideration... this forces me to put these 2 very far from the npn transistors. One switcher will be limited to only 4 amps... it is enough though since the ENTIRE dreamcast psu is just 22 watts xD. assuming 6.3v @ 4 amps = 25.2 watts + the 12v sources is gonna be way more than original 22 watts.

but assuming diodes has 2 amps = 2 x 1.1 = 2.2 watts, could be more if used more than 2 amps. however this diode SS52 is better as it seems. It has 0.55 dropout at 5 amps which gives max of 1.65 watts at 3 amps which is about 83 degrees of temperature, so putting 3 of them in series will get the job done, even 4 is ok. price is mere 0.05$ for one.

4 of them = 2.2v drop --> 6.3 - 2.2 = 4.1v for the 3.3v regulator.


___________

The 'AOZ1280CI' looks tiny and dirt cheap giving you 1.2 amps, double what you need for 5v.

this one is about 30 cents which is 10 cents lower than 1284 variant... it is much tiny though.

people do mods for the DC like adding noctua fan (50 ma current @ 5v) and rgb leds... dunno if 1.2a will be good enough. I don't mind spending the extra 10 cents to get a way better switcher.

getting 2 switchers solution is about this:

aoz1284 x2 = 0.8$
npn transistor x2 = 0.5$
lm317 x2 = 0.3 $
10uH or so inductor x2 = 0.5$
caps (all) = ~2$
resistors (all) = ~1$
heatsinks = 2$ max

total = 7.1$

assuming board assembly + shipping + handling + customs + etc = 10$, then total will be 17.1$ assumed to be 20$ per board complete. I think I can sell it with 50$ but I wanted it to be less.

[BrianHG]

Check this one please: https://www.beharbros.com/product-page/dreamcast-power-supply

this one is more modern than dreampsu and it seems to use a heatsink stuck on the regulators... how? how does this press-fit work? I mean can I do it myself? since the assembly service from jlcpcb will not.

Those heatsinks are purchased with a thermal conductive tape/sticker on the bottom where you just peel off the back and press fit it on.
For heatsinks without stickers, suppliers of thermal conductive tape exist.

I did not know the Dreamcast uses 3 amps at 3.3v.  Do not use the diode idea.
As for 5v, even with added LED mods, if they are powered from 5v, ok just use another 4amp switcher again, except dont expect to draw more than an additional amp for LEDs.  5 watts of LEDs means ~50watts of equivilant incandescent light bulbs.  Are you trying to light up a room?  Still, the second BJT with an additional 1amp for LEDs will generate 1.8 watts of heat, half the 3.3v BJT. That's 4.2 watts, 5.4 watts with 1amp for leds, for both BJTs total if you tune each switcher to only supply +1.2v above the final output voltage.

I mean, tuning +1.1v above would be the absolute bottom and might let a occasional power dips, you would need to measure, but with this setup, you are now down to 3.9watts without LEDs, 5 watts with.  This ~0.4 watt savings is becoming silly as you might compromise the quality of what you are trying to achieve.

[BrianHG]

Thermal tape:

https://www.amazon.com/s?k=Heat+Sink+Thermal+Tape

It's double sided tape.  Since you only need a little square on each BJT D2PAK, those 2x25 meter rolls for 10$ will make you something like 5000 units.

Or you can buy heatsinks with the tape already on like here:
Heatsinks With Tape

[BrianHG]

Actually, I don't trust that Amazon tape, go for real 3M brand:
https://www.digikey.com/product-detail/en/3m-tc/1-2-5-8810/3M10315-ND/2649860

[BrianHG]

If you truly want to go massive on the heatsink, just place the connectors on the bottom edges of your PCB, and tape 1 huge rectangular heatsink over the entire bottom of the PCB and mount it with that side up in the Dreamcast.  This means not through-hole components anywhere in the middle of the PCB.  Gonna need one of those really wide rolls of thermal conductive tape.

[BrianHG]

The thermal epoxy (not glue) should do a better job than those Amazon blue tapes:
https://www.amazon.com/s?k=heatsink+thermal+epoxy&ref=nb_sb_noss

LOL, in the past, I used crazy glue in a pinch and for ~5 watts, it was fine for a year until the heatsink came loose.

The some of the authentic high temperature double sided thermal tapes have a super-thin screen wire mesh in them with a gooey white glue, but these tapes cost something like 150$ a roll.

[VEGETA]

kindly check the attached picture. Maybe this is the working main circuit, besides stuff like connectors and so on.

as for heatsinks with these pads, are they gonna stick nicely? I mean moving the device and so on, stop sticking and getting loose with time...etc.

If I get that tape, I will need to cut the pieces myself which may not be 100% the same area size of the plastic of the IC, is it ok?

Here is my little calculations:

3.3v rail has 4.6v inputs and 1.3v dropout -> expected consumption is 3 amps -> 3*1.3 = 3.9 watts.
5v rail has 6.24v input and 1.24v dropout -> absolute max is 3 amps -> 3*1.24 = 3.72 watts.

I think for maximum of 4 watts, these small heatsinks will do the job. I just don't want them to be very hot like frying eggs on them since that will be worse heat than original psu. what do you think?


we are talking about an absolute max of 7-8 watts total... will this be enough: https://lcsc.com/product-detail/Heat-Sinks_XSD-XSD183-097-B_C286209.html

enough for both?

like putting these 2 NPNs next to each other then stick this on top on their plastic.

[BrianHG]

Your feedback resistors of 10K and 16.5k are really high.
The LM317 ADJUST input has an input current and input capacitance.
The website LM317 calculator website I sent you does not take the input current on that pin into account.
This is why I said for R1, use 500Ohm or less to eliminate that figure.

If I had any LM317 on hand, I would have already tested this circuit with a 2N3904 as an NPN buffer to verify final output voltage.
Studying the way the reference works internally, it looks like you will need to add the 0.75v drop of the NPN transistor into your output voltage calculation.  IE 3.3v = set regulator for 4v.

Also, I would still add an R1a and R1b, and only mount 1 of them.
Placing the resistor at in the R1b position means the regulator feedback sees only 1/100 the current spikes since it needs to travel through the transistor emitter to the base.  This means the circuit is acting like a current multiplier VS more like a regulator.

Note we can switch the LM317 with an op-amp / voltage reverence and make a super precise regulated output, on par with a high quality audio amplifier driving a DC output.  This would guarantee dead exact output voltage no matter the load.  A dual opamp would replace both LM317s.  The voltage reference would be a 78L05 regulator.  This would make your output look like a battery with 0ohm ESR.  In the past, I have actually made this type of circuit, so I know it works really well and you may swap the BJT for a logic level mosfet here as the opamp will compensate for the Vgs and it's drift as the mosfet temperature changes.

As for your heat-sink.  No problem radiating 5 watts, but with 8 watts, it will get warm.

According to ON-Semiconductor's MJB44H11 datasheet, at 5 amps. the Vce saturation voltage is 0.2v. (Actually 0.11v at 3amps)
This means if you want 3.3v out, you can get away with 3.5v in, however, there is a little offset in linearity right at the edge.
Now, your switcher can dip it's output voltage by up to 0.4v during current spikes, so, 0.4v + 0.2 + 0.2 extra margin means minimum = 0.8v above target output voltage.
3 amps *0.8v = 2.4 watts heat *2 = 4.8watts heat total, assuming 2.5amps-12.5 watts of LEDs.
This is as low as I would attempt the circuit with obvious test verification.

Raising the extra margin to 0.4v:
3 amps * 1v = 3 watts heat * 2 = 6 watts heat total, assuming 2.5amps-12.5 watts of LEDs.

Radiating 6 watts will be like having one of those old 120v 5 watt outdoor Christmas light bulbs inside your Dreamcast.  If the old PSU had a linear transformer, that transformer alone would radiate that amount of heat at least.

Using the opamp with a mosfet in a DPAK/D2PAK case, you can go down to ~0.6v, ~0.2v above the switcher's worst voltage dip.  Since the op-amp will not need to drive current with a mosfet, that part of the circuit will run cooler & only needing a 0.6v headroom, the circuit will radiate a total of 3.6 watts, 1.8 watts per mosfet.  You wont need a heatsink here, but, the PCB will still get warm to the touch, but not too hot.  I would still prefer at least 0.8v headroom.

Just so we are clear, (3*3.3+3*5)*1.2(loss in switcher supplies) = 29.9 watts at 12v, or 2.5amps at 12V.  With no room for the CD drive's 12v supply if you are using a 30 watt 12v power supply.

I've attached an image of using an opamp circuit.  Obviously we would use a more modern opamp and something like the mosfet.
Cheap mosfet = IRLR8726TRPBF - (Crss=310pf) https://lcsc.com/product-detail/MOSFET_International-Rectifier_IRLR8726TRPBF_International-Rectifier-IR-IRLR8726TRPBF_C81137.html
Or any 50N03 variant should do, like https://lcsc.com/product-detail/MOSFET_KIA-Semicon-Tech-KIA50N03AD_C112249.html

You can also use a TO-220 Mosfet/BJT with a bolted heatsink mounted down on the PCB:
EG: https://lcsc.com/product-detail/Heat-Sinks_XSD-XSD-heat-sink15-5-10-5-24-Htype_C108928.html
https://lcsc.com/product-detail/Heat-Sinks_Made-in-China-Made-in-China-15-10-20-U_C361579.html (More difficult to accidentally short)
However, they will have active voltage unlike the taped SMD heatsink.

See attached circuit below: ( The + goes to the 78L05 output, for channel 2 on the opamp, 3.3v, well divide the 5v to 3.3v with 2 resistors)  This would be an op amp-corrected/compensated/buffered capacitance multiplier.
https://lcsc.com/product-detail/Dropout-Regulators-LDO_Diodes-Incorporated_AS78L05RTR-E1_Diodes-Incorporated-AS78L05RTR-E1_C90471.html
https://lcsc.com/product-detail/General-Purpose-Amplifiers_STMicroelectronics-MC4558CDT_C435907.html
Input latch-up protection diode not shown in circuit.
https://lcsc.com/product-detail/Switching-Diode_ON-Semiconductor-ON-MMBD914LT1G_C46523.html
Precision CMOS opamp:
https://lcsc.com/product-detail/General-Purpose-Amplifiers_Texas-Instruments_TLC272CDR_Texas-Instruments-Texas-Instruments-TLC272CDR_C9374.html

[VEGETA]

Note we can switch the LM317 with an op-amp / voltage reverence and make a super precise regulated output, on par with a high quality audio amplifier driving a DC output.

I was about to suggest this.

it is not required to be extremely precise like 5.0000v but rather very low noise. If we put 78L05 with 12v input, it will give 5v and we can get 3.33v using 10K//10+10K or so. However, ripple and noise will continue to exist right?

Now all of that will go into the OP-amp and eventually to the mosfet gate. How can this be anti-noise and ripple.

Radiating 6 watts will be like having one of those old 120v 5 watt outdoor Christmas light bulbs inside your Dreamcast.  If the old PSU had a linear transformer, that transformer alone would radiate that amount of heat at least.

The original PSU is here: https://d3nevzfk7ii3be.cloudfront.net/igi/NDTYlWMuiMCcR5nW.full

Using the opamp with a mosfet in a DPAK/D2PAK case, you can go down to ~0.6v, ~0.2v above the switcher's worst voltage dip.

let's assume 1v dropout: 3x1= 3 watts per rail. I don't know if we can get away without heatsink here. even with heatsink i would still get the cheapest ever one xD.

This would be an op amp-corrected/compensated/buffered capacitance multiplier.

it looks like a linear regulator, where is the cap multiplier part?

I mean where to put the R and C? on mosfet gate from the op-amp output? like 100R in series from op-amp to mosfet gate and 10uF ceramic to gnd?

Cheap mosfet = IRLR8726TRPBF

seems fine and available at jlcpcb parts.

I will re-design the circuit based on IRLR8726 + LM358 op-amp (used for both rails).

[BrianHG]

Ok, update your schematic and I will take a look tomorrow.
The 100r series for the gate drive is good.

The opamp VCC and 78L05 VCC will share the same series 100 ohm/100uf-10uf-0.1uf RC filter from the 12v supply.
This is what will separate your switcher's ripple noise from your linear amplifier and voltage reference section.

The mosfet Drain has a capacitance of 310pf to the Gate.
This is where the 2MHz switcher noise is coming from, it will be conducted by that 310pf cap from drain to gate where the op-amp output will be fighting it.  This should be manageable with a strategically chosen cap from gate to GND.  Not too large as to prevent the LM358 from regulating the output fast enough, yet large enough to mute most of the switching noise.  I would say a ~10nf cap would do and you may need to shrink the 100ohm opamp output to gate resistance in half.

With the MJB44H11, the base-collector capacitance was only 130pf, but the opamp would need to drive ~30ma at it's output.

[BrianHG]

I mean where to put the R and C? on mosfet gate from the op-amp output? like 100R in series from op-amp to mosfet gate and 10uF ceramic to gnd?

The 1uf at the + input of the op-amp is the cap which you are multiplying.
Since the op-amp has a 100na input current, this will be amplified a million fold.
Coming from the 5v regulator should be a 330ohm series resistor to the + input of the 5v side.
For the 3.3v side, use another 1k series resistor from the 5v and a 2k pull down to GND for 3.33v. (A little high, maybe add a 27ohm in series with the 1k for 3.30v) Don't forget the 1uf cap from that +input to GND.
These 1uf caps with the series ~330Ohm & ~333Ohm feed are your voltage source filters.

The 100Ohm between the +12v 100uf to GND at the 78L05 & LM358N V+in does the bulk filter removal from the switcher's noise.  It will also have a 1uf cap on the output.  I mean, you could place a 470uf or 1000uf cap in place of that 100uf cap if you want to.  Electrolytic, not ceramic as high uF value ceramic caps lower their capacitance value when run at higher DC voltages.

Don't forget, you still want the right SMD emi ferrite bead & cap between your switchers and 12v in, and again between the 12Vin and the rest of your analog output.  If the 12V feeding you Dreamcast has high frequency ripple on it, the power supply caps for the 12v in the CDRom drive will conduct that ripple back through the GND.

[VEGETA]

Here is the updated schematic. Might be missing some stuff though.

- I didn't find a reason to have 330 ohms in the +5v input of the opamp, and chosen 10k//(10K+10K) to consolidate stuff.

- input side of opamps has 10uF instead of 1uF, for consolidation... unless it is necessary to have 1uf.

- mosfet gate is 100R parallel to 1nF since I happened to use a 1nF.

what do you think?

[BrianHG]

Ok,
Blue arrows, get rid of those 100uf caps, they wont do anything good.
Green arrow at V_5->3.3k, This will make the 5v reference rise up and filter identical to the 3.3v reference.

Dark Green arrows at new 3.3k on the V_FB# - This separates the opamp -input from a harsh supply rail and also allows the 2 other green arrows with the new MMDB914 diodes at the opamp inputs to work.

The 2 new MMBD914 (or equivilant) diodes lifts the V_FB# inputs off the GND rail at powerup and also prevents the + & - inputs from the op-amp from getting too far from each other preventing latch-up on power-up or output inversion. (These are not guaranteed rail-2-rail input opamps.)

Having the 1nf directly on the op-amp output can make the op-amp oscillate.

The red arrows are errors or changes.

The black arrow shows how you need to wire the +12V input to the rest of your circuit.  According to the AOZ128 datasheet, at full load, the input VCC ripple becomes massive and this is what we don't want to transmit to the analog supply section, or, to the Dreamcast.  Choose a FB which has a good low DCR & Current, and cuts/high impedance @ 1-2MHz.

Your only additional improvement here is to use really expensive ultra-low ESR caps, and blindly placing them wont help, or it could make things worse.  Your board layout and trace paths have now become important.

The switchers should be on 1 side of the PCB with their own GND and VCC and power supply input.
The other side should be the analog with a dedicated GND path from the power input and the output of the second ferrite bead with decoupling caps.  That GND path should GND all the analog/linear components.

Additional, You may also use 2 ferrite beads, one for each switcher's VCC.

[BrianHG]

For the ferrite beads, you might be better off just using the same 10uh inductors.

[BrianHG]

Ooops, you are also missing a dummy load on the +3.3v out and the +5v out.
If you are consolidating parts, place a 100ohm on the 3.3v and 2 series 100ohm for the 5v.

[VEGETA]

Kindly check the drawing, I made all the fixes.

Notes:

- I used this ferrite bead: https://lcsc.com/product-detail/Ferrite-Beads-And-Chips_TDK_MPZ1608S600ATAH0_60R-25-at100MHz_C76816.html/?href=jlc-SMT since it is available at JLCPCB SMT service and still provide what we need.

- 100R dummy load for both rails.

- ferrite beads everywhere needed, or so I think.

For the ferrite beads, you might be better off just using the same 10uh inductors.

those 10uH inductors are very big, can't afford adding another one.

[BrianHG]

Ok, here you go.

The purple arrows are where you forgot your bus/wire ties.
The red arrows are the mistakes.
Note that only having a single 100Ohm on 5v will overheat a smd 0805 resistor.  Use 2 in series.

Note that you are already using 100nf for the BST pin on the switchers.  Might as well use them for decoupling the regulator and opamp instead of 1nf.

Green arrow adds 10uf on the +12v to Dreamcast.
If you are using ceramic non-polarized 10uf caps, be careful.  Read the complete data sheet as 12v DC will result in a lower capacitance and higher ESR as ceramics at these capacitance levels at higher voltages de-rate miserably.  So much so that a 1uf cap may do better.

Quote from AOZ datasheet:

For lower output ripple voltage across the entire
operating temperature range, X5R or X7R dielectric type
of ceramic, or other low ESR tantalum capacitor or
aluminum electrolytic capacitor may also be used as
output capacitors.

Finally the ferrite chip bead.  I will look for a better one in the next post.

[BrianHG]

I assume you are using a 10uh inductor like this:
https://lcsc.com/product-detail/Power-Inductors_Wenshan-YT0630-100M_C428419.html
7mmx6.6mm.  69mOhm 4.5amp sat.

Or, if you want a better efficient cooler switcher, you would be using this TDK inductor:
https://lcsc.com/product-detail/Others_TDK-SPM10040T-100M-HZ_C375968.html
11mmx10mm.  26.7mOhm. 5.8amp sat.

Last ugly monster:
https://lcsc.com/product-detail/Power-Inductors_MAGLAYERS-MMD-10DZ-100M-X2_C332199.html
11.5x10mm  27mOhm 7.5amp sat.

This is the largest (impedance increases more at the lower frequencies) affordable ferrite chip bead:
https://lcsc.com/product-detail/Ferrite-Beads_TAI-TECH-HCB2012KF-600T60_C369525.html
I see you placed a bunch all over.  However, the chip beads will only really knock out frequencies in the +10Mhz range.

Just using only 2 strategically placed of the first 7mmx6.6mm inductors would vastly cut out lower frequency transmition down at the +1MHz range.

That's overkill, just read the next message...

[BrianHG]

Just a single strategically placed 3.5mmX3mm 10uh power/choke inductor:

https://lcsc.com/product-detail/Power-Inductors_Cybermax_CMLF0302-100MTT_Cybermax-CMLF0302-100MTT_C405095.html

To deliver 12v to your Dreamcast & Linear regulator section will do much more than all of your 5 ferrite beads combined.

Assuming that the Dreamcast's 12v draws no more than 1amp.

[BrianHG]

Another mistake...
Your 'FSW' resistors are set to 20k.
This is not 2MHz....


  The bloody formula in the datasheet is completely F--KED UP!!! 

You will need to verify that the device is actually running at 2MHz.
Otherwise, there will be ripple going throughout your entire PCB.
The example listed figures don't even come close after fiddling with the decimal point.

[VEGETA]

The bloody formula in the datasheet is completely F--KED UP!!

yes but when you calculate it properly you will result in getting 20k resistors. there is no way we can verify that.

Just a single strategically placed 3.5mmX3mm 10uh power/choke inductor:

https://lcsc.com/product-detail/Power-Inductors_Cybermax_CMLF0302-100MTT_Cybermax-CMLF0302-100MTT_C405095.html

To deliver 12v to your Dreamcast & Linear regulator section will do much more than all of your 5 ferrite beads combined.

Assuming that the Dreamcast's 12v draws no more than 1amp.

well, you mean feeding the 78L05 and 12v to dreamcast pin? then yes, I guess 1A or so is ok since the entire dreamcast power supply is 22 watts.

I think this inductor is perfect: https://lcsc.com/product-detail/Power-Inductors_Sunlord-MWSA0603-100MT_C132141.html/?href=jlc-SMT

I will use it for the rails themselves, I wonder why I didn't see it in the first place and went for a huge 12.5x12.5 mm inductor! 4.5A is more than enough for each rail... heck, small size means we can put more of it on inputs too.

[BrianHG]

I think this inductor is perfect: https://lcsc.com/product-detail/Power-Inductors_Sunlord-MWSA0603-100MT_C132141.html/?href=jlc-SMT

I will use it for the rails themselves, I wonder why I didn't see it in the first place and went for a huge 12.5x12.5 mm inductor! 4.5A is more than enough for each rail... heck, small size means we can put more of it on inputs too.

Don't go crazy on inductors.  Obviously the switchers themselves need them in circuit and your priority is to isolate the Dreamcast's +12v and your linear supply from that nasty side with all the ripple noise.
If it can be done, a good 1000uf to 4700uf cap on the Dreamcast 12v side of the 10uh inductor would really be nice.

A fat flat one like this (10k hour):
https://lcsc.com/product-detail/Aluminum-Electrolytic-Capacitors-Leaded_Ymin-LKMI2001C472MF_C442801.html
Cheaper one (2k hour):
https://lcsc.com/product-detail/Aluminum-Electrolytic-Capacitors-Leaded_CX-Dongguan-Chengxing-Elec-4700uF-16V-16-20_C47896.html

However, due to size price and availability, using 2 of these 2200uf is a better deal...
https://lcsc.com/product-detail/Aluminum-Electrolytic-Capacitors-Leaded_CX-Dongguan-Chengxing-Elec-16V2200uF-10X20_C3328.html

[VEGETA]

Don't go crazy on inductors. 

I will just use the part I linked up instead of the old one, which saves 50% of space. + on more inductor for 12v output to DC. + 1 for isolating the 5v regulator and op-amp circuit. which means a total of 4.

If it can be done, a good 1000uf to 4700uf cap on the Dreamcast 12v side of the 10uh inductor would really be nice.

I think this cap (1000uF) is the way to go due to size and smt placement capability: https://lcsc.com/product-detail/Others_Lelon-VE-102M1C1010-TRO_C249474.html/?href=jlc-SMT

I could put smaller 100uF caps instead but won't be the same amount of capacitance and still takes place.

[BrianHG]

Yup, placing 3/4 of those 1000uf in parallel will do it.

I may be going out of town at the end of the week.
So if you want, it's a good time to finish up and get to the PCB.

Your switcher's 2 frequencies where it generates noise is up at 2Mhz and according to the response time on load transients, those 0.4v dips at 100us, in the 100KHz region.
According to Panasonic's basic 1000uf 16v electrolytic caps, at 100KHz, the cap looks like a 0.06Ohm resistor and can conduct 1.19 amps of current.

This is approximate: Your 1000uf cap
Hz - ~Series Impedance in Ohms
10Hz      - >10 Ohm
100Hz   - >1 Ohm
1Khz     - >0.2 Ohm  result curving due to internal resistance
10Khz   - >0.1 Ohm
100Khz - >0.06 Ohm  lowest resistance
1Mhz     - >0.1 Ohm   resistance is increasing due to lead inductance.
10Mhz   - >1 Ohm      resistance is increasing due to lead inductance.

So for example, if you placed 1 1000uf cap for the 78L05 & LM358, since it is being fed power through a 100 Ohm series resistor, ripple at 100KHz will be attenuated 10000:6.  At 100Hz, the attenuation will be 100:1.  The 78L05 is rated to reject the V+ input by around -60db at 100Hz, but at 1Khz, that's (going off of memory of old datasheets which had charts for this) -20db.  At 10Khz, this was around -10db, and no rejection at 100Khz and up.  Meaning, if you power the 78L05 at 10v with a 100KHz 2v sine wave, the V+ output will also modulate +/-1v at 100KHz.  This only using that RC filter will make those potential +/-0.4v ripples only 0.00024v ripples at the regulator V+ input.  To really rid of the 2MHz ripple, since electrolytics aren't good here, your 10uf/22uf need to be MLCC caps as shown in the table I've attached below.  The op-amp also has a power supply rejection value in it's data sheet as well.  But as you can see, the 100ohm / 1000uf cap + 10uf MLCC cap in parallel filter will leave a final overall ripple noise which you could not measure so long as your +12v input isn't conducting any current to your mains and through the GND pin of your scope.  Unless you scope can see without any noise less than ~0.0005v, or you have an amplified differential probe designed to see these types of signals.  I think the transistor noise alone in the 78L05 output is noisier than this anyways.

Your unknown source supply may also switch as low as 20KHz.

Image #1 has a 560uf Aluminum VS a 22uf MLCC.  Your best choice is a 1000uf plus a 10uf, or 22uf MLCC in parallel to choke out those switching spikes.

Make sure your 10uf caps are the right grade and size, don't go for the smallest.
See image #2 which shows how the capacitance value derates of a 4.7uf MLCC cap.  Both type ans size makes a huge difference.
As you can see, X7R 25v 1210 is your best bet as the 0805 versions at at 12v dropped to down to ~1uf.  And this is a 4.7uf cap.  A 10uf cap would be at least the same if not worse as you try to squeeze more capacitance in the same package.

[BrianHG]

Here is an X7R 25v 1206:
https://lcsc.com/product-detail/Multilayer-Ceramic-Capacitors-MLCC-SMD-SMT_SAMSUNG_CL31B106KAHNNNE_10uF-106-10-25V_C14860.html
Here is an X7R 25v 1210:
https://lcsc.com/product-detail/Multilayer-Ceramic-Capacitors-MLCC-SMD-SMT_SAMSUNG_CL32B106KAJNNNE_10uF-106-10-25V_C39232.html

A bit of a deal, 22uf X7R 16V 1210:
https://lcsc.com/product-detail/New-Arrivals_Taiyo-Yuden-EMK325B7226KM-PR_C412624.html



Because of the price difference, maybe just add 3 in parallel for the 12v and 2 in parallel for the 5v&6v.

[BrianHG]

I just found an EMI filter schematic for feeding the VCC of 2MHz 6 amp buck converters.
They recommend a 1uH 7.5amp power inductor with 2x2.2uf & 2x470nf caps before and after the inductor.
Using a 10uH inductor may dip too much.

This is all you need to separate each switcher's VCC supply feedback ripple from the 12V supply input:
https://lcsc.com/product-detail/New-Arrivals_Sumida-252012CDMCDDS-1R0MC_C492725.html
And they are small at 2.5x2mm.

[VEGETA]

I made a new update taking everything in consideration.

Maybe I went crazy on EMI stuff? well, this is what makes the psu in this application. 

I can re-arrange the schematic into multiple hierarchical sheets to fit the wide chain of stuff... later on when I finish the design. I picked parts suitable with jlcpcb smt service... 1206 of 10uf caps and 100nf caps + 1000uf caps (big enough). + nice 1uH inductor but bigger than yours.

[BrianHG]

Back in a few hours....
Yes, some overkill there in the wrong places.

[langwadt]

Back in a few hours....
Yes, some overkill there in the wrong places.

overkill? nooo, a medium sized tactical nuke is the proper tool for killing a fly

[BrianHG]

Here you go.  I think you are ready for the PCB part placement.

[BrianHG]

1 last addition, I would add 3-4x more 1000uf caps on the Dreamcast +12v side + a single 1000uf cap at the V+12 input.

[VEGETA]

100uF caps on NPN inputs

I really wanted to get rid of them, now is the chance. x3 of 10uF 1206 maybe save space compared with 100uF elec. cap.

_____

suggested small inductor

I know your suggested inductor is better, but it doesn't exist here: https://jlcpcb.com/parts . I really searched for smaller one but couldn't find it.

I know people say PCBWay offers similar service but JLCPCB one seems better at least for now.

1 last addition, I would add 3-4x more 1000uf caps on the Dreamcast +12v side + a single 1000uf cap at the V+12 input.

I wonder if all of those are gonna fit in a 50x50 board with all components on one side. 


____

So you removed the EMI circuit in the bottom for 5v and op-amp? you took them from the 12v output to the DC itself, wouldn't this cause noise and ripple to get into the 5v and op-amp?

____

[BrianHG]

So you removed the EMI circuit in the bottom for 5v and op-amp? you took them from the 12v output to the DC itself, wouldn't this cause noise and ripple to get into the 5v and op-amp?

There is no EMI there.
And if there were, it would be attenuated by a 100 ohm series resistor while on the other side, it would look like a <0.05 ohm short to GND at 100Hz thanks to the 1000uF cap.  It would look line a <0.0005 ohm short to GND @ above 500KHz thanks to the 10uF MLCC cap in parallel.  The attenuation in the high frequency EMI range is greater than 100000:1 while the regulator's and opamp's PSRR at 1KHz attenuate that by another 10 fold, not to mention at 100Hz they go bonkers and attenuate it by a good 60db (another 1000 fold) each, not to mention the 5v reference goes through a 3.3k series resistor and through another 10uF MLCC cap.  This is utterly insane.  if your current noise on the audio or analog video was 0.1vp-p, a mild visible annoyance, or continuous audio tone with the volume with loud headphones, the supply for the linear reference and opamp will be 5 orders of magnitude less, or 10000 times cleaner.  This is a tactical nuke eliminating a fly.

As for the 1uH, anything 3amps or above will work.
As for the 10uH,  the 1amp I listed will be fine.

As for the 3 or 4 1000uF.  I didn't notice how big they were.  Maybe using double @470uF.  Except for the linear section, 1x 470uF would still be fine as well as 1 at the +12v input.  I would use the extra space for placing additional 470uF caps on the Dreamcast's +12v.

[VEGETA]

There is no EMI there.

But it is taking 12v from a switching supply. Yes it is low frequency but still switching ripple and noise... right?

It would look line a <0.0005 ohm short to GND @ above 500KHz thanks to the 10uF MLCC cap in parallel.

how do you know these exact numbers? I know the RC filter removes ripple and noise to some degree but I cannot know details such as its performance at a certain frequency or so.

while the regulator's and opamp's PSRR at 1KHz

from the datasheet or where?

As for the 1uH, anything 3amps or above will work.

yes it is, but slightly bigger than your suggested one. I think it is the 6 mm package or so.

As for the 10uH,  the 1amp I listed will be fine.

1A? I could use the same part I used for the switching supplies since it is 6mm package... this way is cheaper I guess.

As for the 3 or 4 1000uF.  I didn't notice how big they were.  Maybe using double @470uF.  Except for the linear section, 1x 470uF would still be fine as well as 1 at the +12v input.  I would use the extra space for placing additional 470uF caps on the Dreamcast's +12v.

looking into jlcpcb smt parts, there seems to be all 10x10 mm parts except if you go really low like 100uf or so. 1000uf is the same size as 470: https://lcsc.com/product-detail/Others_Lelon-VE-102M1C1010-TRO_C249474.html/?href=jlc-SMT this one is 16v which is the biggest rating.

Hmmm so getting those 1000uf 10x10 seems to be the best solution since all the same size. getting many of 100uf isn't space-friendly.

[BrianHG]

It would look line a <0.0005 ohm short to GND @ above 500KHz thanks to the 10uF MLCC cap in parallel.

how do you know these exact numbers? I know the RC filter removes ripple and noise to some degree but I cannot know details such as its performance at a certain frequency or so.

This isn't too difficult if you look at the capacitor chart I posted on the previous page:



For simplicity sake, we will use the 470uf and 22uF MLCC caps.  IE, 1/2 the 1000uf cap and 2x 10uf caps in parallel.
The chart labels these as separate impedances, not both components in parallel which would be similar to adding 2 resistors in parallel.  I assume you know how to add 2 different parallel resistors together.

Let's concentrate on just the 22nF cap, the cyan-blue line on the left chart.
At 100Hz, you can see it is 100ohms.  This means if you place this cap after a 100ohm resistor to GND, feeding a 1v 100hz sine wave signal into the 100ohm resistor means on the other side, 100ohm -> cap which = 100ohm to GND @ 100Hz, your 1v 100Hz signal will now be 0.5v.

Now say we feed a 10Khz 1v sine wave into the 100ohm resistor, well now, the cap at 10Khz looks like a 1ohm resistor to GND.
The formula here is the same voltage attenuation formula, 1ohm/(100ohm + 1ohm)= 0.0099v 10Khz sine wave at the output of the resistor, or we can call that 0.01v.

Do the same for 1Mhz and it's 0.001ohm/(100ohm+0.001ohm) = 0.0000099999, or we can call this 0.00001, or 10000:1 attenuation.  Assuming I didn't get my decimal places incorrect.

For the purple 470uf trace, a 1000uf cap would run a little lower in resistance in the middle, but be ~half the resistance down at the 100hz location.

As for the regulator and opamp, there is a specification in their datasheet called PSRR, or power-supply-rejection-ratio or sometimes called 'Ripple Rejection'.  This tells you how much the device attenuates down the input signal at a given frequency.  The on-seminconductor MC78L05 datasheet says it's PSRR when powered at 10v driving 40ma is 49db @ 120hz.  (Not the best one, but ok.)  So going to this site, I put -49db into the calculator:

http://www.sengpielaudio.com/calculator-db.htm

And get: 0.00354.
Looking at an 100ohm to 1000uf cap at 100hz, it's a little less than 0.01, multiplied by that regulator's -49db PSRR 0.00354 gives you 0.0000354 of your original 100hz signal before all the in place filters to after the regulator.

If you old circuit generated a 1v 100hz hum, after all this, that 100hz hum would be ~0.00004v.
So, a 0.1v 100Hz hum would become ~0.000004v.

[BrianHG]

LM358 datasheet PSRR: Worst case 65db, normally 100db (between 0.00056 and 0.00001) :

[VEGETA]

I made the changes.

I hope I can fit all of those 1206 10uF caps + 1000uF elec. caps on that tiny board... and most importantly, leave place to mount the heatsink on the mosfets. Once we finish modifying everything I will think about the heatsink, most probably it is going to be press-fit. I just hope it conducts well and doesn't get loose over-time.

My understanding of PCB layout is this:

I put all switching stuff on one portion of the PCB, like the upper side... make its ground pour on its own. Then make the same for linear regulator mosfets, and another private gnd pour for the 5v regulator. Then  connect all grounds together via thick traces (since some will carry big current right?).

I guess by this we ensure switching current and its noise stays on its ground and never make it to linear side since it is lower resistance there than the trace to other grounds.

[BrianHG]

My understanding of PCB layout is this:

I put all switching stuff on one portion of the PCB, like the upper side... make its ground pour on its own. Then make the same for linear regulator mosfets, and another private gnd pour for the 5v regulator. Then  connect all grounds together via thick traces (since some will carry big current right?).

I guess by this we ensure switching current and its noise stays on its ground and never make it to linear side since it is lower resistance there than the trace to other grounds.

Everything looks good.

Excellent, you are aware of the impedance of the GND layer itself.
You got the right idea.

On the switching side, you need to keep that GND & VCC path from the switchers diode & Inductor as tight & well thick as possible while all the feedback and control paths can be thin.

Make sure when you order the PCB, choose 1.5oz or 2oz copper thickness.  If I remember, from JLPCB, on 10 PCBs, the price increase was only around 25c per PCB, but, that's more than double the thickness compared to the standard 0.5oz.

The thick copper means trace spacing, via angular ring and drill size needs to be a bit larger.  Something like 12 mil drill instead of 8mil.  (These figures are a few years out of date.)

For copper fills, I usually tend to make the clearance of 12-15mil.  Don't be the one who sees the PCB fab says their trace-trace clearance needs to be at least 7mil and the copper flood fill to that tiny 7mil.

The rest of the PCB is so few in traces that you cannot do wrong if you manually place & route the thing.

Remember to stitch GND vias all around the bottom fill and under the switchers & decoupling caps.  Some vias, occasional partial lemmons can have as much as a >1ohm impedance and pass QC test unless you have specified specific impedance matching quality PCB, not the cheap quick ones.  Having a bunch eliminates this threat as such a high impedance via is rare, but grows if you are pushing the drill hole size down to the lowest limit.

I like 1 side = switchers, 1 side = linear.
Try to get most tracing on the top of the PCB except for some extension to the bottom.

On the top switchers, you want to also try to get their GND trace to be 1 solid piece as well when concerned with VCC, IC, diode & coil caps.  Then via-stitch along the entire central mass.  As for any components or feedback signals which need to be tied to GND, you may tap the GND place below if so long as it is not a power switching load.  The AOZ1284PI datasheet should provide an example layout.

[BrianHG]

Have you looked at 47uf 16v X5R 1206/1210 caps?
You could use half the number of 10uf caps.

[VEGETA]

I like 1 side = switchers, 1 side = linear.
Try to get most tracing on the top of the PCB except for some extension to the bottom.

component placement will all be on one side, which is say top. However, traces can be of different planes. My suggestion meant that at the top face of the board where components are sitting... I could gather all switching stuff on one area while all linear stuff on the other one... and also do the switching traces on top and linear traces on bottom.

Have you looked at 47uf 16v X5R 1206/1210 caps?
You could use half the number of 10uf caps.

There are some options but double the price. I will see, if the 10uF ones fit the board then ok.

________

I want this to be fully functional using JLCPCB service... then when I plan to sell them I will look into making a small volume maybe from a different manufacturer and assembler. How much do you think it would cost approximately?

Like a panel of 280x280mm can have 25 of it. Let's make say 10 panels (can be done through jlcpcb service if you notice). This means 250 boards!

[VEGETA]

To make you laugh, please look at the PCB. Still nothing done but look at component size xD. what a joke... all components on one side 

[BrianHG]

  That's MAD! 

You will probably have to live with only 2x 1000uf.

Maybe cut the 10uf in half.

[BrianHG]

The linear and switching sides just need to be separated -(good luck)
Having the bottom almost all GND is your bigger + with regard to EMI and noise.
You just want a separate GND path from the +12v in and the linear GND and output power.
Basically a 'crack/channel' in the GND and the 10uH inductor sitting over that gap, with both decoupling caps on each side.

Same thing for each switching supply with their 1uH inductor.

It not about reserving a layer for linear/switching, it's just separating/channeling out each parts GND to make them appear as a separate module.

Also, just painting the entire bottom as GND may be the best solution if you cant do the channels.

[BrianHG]

Just in case, make sure the positioning of the 2 mosfets and other components around them will allow that 1 wide heatsink you found to be taped on-top.

[VEGETA]

I removed a lot of 10uF caps while converting the rest to 22uF using 1206 package + removing about 2-3 1000uF caps... STILL no way near fitting them as you can see!

I started thinking about putting all small components on one side of the board and let that be the one JLCPCB assembly service take care of... while I solder manually the big components on the other side of the board. How about that?

Gonna take a lot of time obviously but for 50x50mm board this is the only solution. TBH, the small components are too much, they are the ones clogging the board not the big components.

So stuff like 1000uF caps, 10uH inductors, even some 1206 caps can all go to the other side of the board while everything else can be SMT assembled.

BTW, do you know about PCBWay SMT assembly service? I saw people say it is like JLCPCB but better. Like getting colors and both sides assembly...etc but they source the materials.

[BrianHG]

Strategically, I would place the 10uH, 1000uf  and the 12vside 10uf associated with that 12v side filter on the bottom.
Maybe place that Dreamcast power connector on the bottom right, or move it down a bit so the the 2 plastic fingers may slightly go over the edge.

JLPCB were to wave a panel, then only wave compatible SMD components may go on the bottom.  You cant do that with the 1000uf caps.

As for the switchers, make sure both look wired equivilant.  I see their 10uh wired on different sides.

You can also go down to a SOT23 78L05 which only can drive 35ma if memory serves, but, you are only using a fraction of that.

Cutting 10uf in half is ok, except for the output of the switchers.  Keep 2 of them there instead of 3 of them.

[BrianHG]

A more sane solution would be to slightly lengthen the PCB so you get 4x5 = 20 on a panel.
Remember, a panel is 400x500, not 400x400, so in theory you can still lengthen the PCB slightly and still get 5x5 or a good bit larger 4x5 panel.

Also don't forget the 2oz on top and bottom layer is you want extra low impedance traces.

[VEGETA]

Strategically, I would place the 10uH, 1000uf  and the 12vside 10uf associated with that 12v side filter on the bottom.
Maybe place that Dreamcast power connector on the bottom right, or move it down a bit so the the 2 plastic fingers may slightly go over the edge.

JLPCB were to wave a panel, then only wave compatible SMD components may go on the bottom.  You cant do that with the 1000uf caps.

As for the switchers, make sure both look wired equivilant.  I see their 10uh wired on different sides.

You can also go down to a SOT23 78L05 which only can drive 35ma if memory serves, but, you are only using a fraction of that.

Cutting 10uf in half is ok, except for the output of the switchers.  Keep 2 of them there instead of 3 of them.

JLCPCB lets you decide which side you want to assemble... I will put all small stuff on bottom layer and let that be assembled.

Top side will have my logo and name..etc + 2 mosfets with their heatsink + all large caps and inductors. notice that 1uH inductors are 0603 so they are on bottom.

with this approach I can put more caps like before.

There are no 10uF caps now, all 22uF as you can see. output of switchers is now just x2 22uF 1206 ones. EMI filter now using x1 22uF before and after the inductor instead of x2 10uF.

As for heatsink, is the one I posted good enough? also, what should I buy to be able to stick it firmly so that it conducts well and doesn't get loose by time or by movement.

If we finalize this, I can start doing the PCB. If I wanted JLCPCB smt service only, I will be forced to put everything on one side + make the board taller which is not nice. hand solder stuff is easier, and I will get them in reels in quantity.

I think the only stuff needed to be hand soldered are:

1000uF caps (I can put more now xD).
2 mosfets (I can put them on assembly side but heatsink should be on top to get more air).
10uH inductors

Also don't forget the 2oz on top and bottom layer is you want extra low impedance traces.

isn't it 1.6 by default.

[BrianHG]

isn't it 1.6 by default.

Make sure.  I think that's 1oz copper + .6oz plating.
I was asking for 2oz copper + 0.6 plating.
The last PCBs I made had little impact on the price of double thick copper, something like 50cents a PCB.  However, they were 4 layers.

[BrianHG]

I hope you are testing a 1 or 2 PCBs before building 250pcs...

[langwadt]

isn't it 1.6 by default.

Make sure.  I think that's 1oz copper + .6oz plating.
I was asking for 2oz copper + 0.6 plating.
The last PCBs I made had little impact on the price of double thick copper, something like 50cents a PCB.  However, they were 4 layers.

so we are past the tactical nukes, Tsar Bomba is what it takes

[BrianHG]

isn't it 1.6 by default.

Make sure.  I think that's 1oz copper + .6oz plating.
I was asking for 2oz copper + 0.6 plating.
The last PCBs I made had little impact on the price of double thick copper, something like 50cents a PCB.  However, they were 4 layers.

so we are past the tactical nukes, Tsar Bomba is what it takes

I once got quoted on a 4oz copper PCB.
Pricey and the PCB fab recommended clearances >10mil, but, you better believe those traces where low in impedance.
It was a high power PSU & Stepper motor and solenoid driver board.

[tszaboo]

1 last addition, I would add 3-4x more 1000uf caps on the Dreamcast +12v side + a single 1000uf cap at the V+12 input.

Nah, he should add a bunch of 100.000 uF caps everywhere with a load of 1000uH inductors, because that schematic is not too big of an abomination already. And please make it star ground.

Seriously, can you guys please use some common sense?

[BrianHG]

1 last addition, I would add 3-4x more 1000uf caps on the Dreamcast +12v side + a single 1000uf cap at the V+12 input.

Nah, he should add a bunch of 100.000 uF caps everywhere with a load of 1000uH inductors, because that schematic is not too big of an abomination already. And please make it star ground.

Seriously, can you guys please use some common sense?

LOL.....
I only helped out with someone who 'Asked' for the death of all outputs...

Too bad those ultra-low EMI switchers from TI I listed 2-3 pages back weren't available.  Used with the 1uH emi filters at the input + another at the output would have been enough as their load regulation and ripple far out-performs the AOZ switcher almost 10fold even without the additional output filter.

[langwadt]

1 last addition, I would add 3-4x more 1000uf caps on the Dreamcast +12v side + a single 1000uf cap at the V+12 input.

Nah, he should add a bunch of 100.000 uF caps everywhere with a load of 1000uH inductors, because that schematic is not too big of an abomination already. And please make it star ground.

Seriously, can you guys please use some common sense?

https://images-na.ssl-images-amazon.com/images/I/61yK53-z0CL._AC_SL1004_.jpg

[BrianHG]

1 last addition, I would add 3-4x more 1000uf caps on the Dreamcast +12v side + a single 1000uf cap at the V+12 input.

Nah, he should add a bunch of 100.000 uF caps everywhere with a load of 1000uH inductors, because that schematic is not too big of an abomination already. And please make it star ground.

Seriously, can you guys please use some common sense?

https://images-na.ssl-images-amazon.com/images/I/61yK53-z0CL._AC_SL1004_.jpg

They didn't install one of these:
58f 16v cap
So it's pure junk...

[VEGETA]

I managed to place the components as discussed. I think now it is time to route.

The white square on top side is where the 25x25mm heatsink will go, I drew that to make sure no component come inside that area. I still need to fix the silk screen components of a lot of parts!

[BrianHG]

Nice except, I cannot tell where in the schematic one of the 1000uf is connected.
The Dreamcast side 1000uf should be on the linear side...

If both are after the 10uf choke, then both should be on the linear side.
That weird round path the GND need to take through one of the switcher's isn't good at all.
I know you tried to work with a 25x25mm heat sink, but that layout isn't sound in isolating the switching noise from the linear.
You linear GND needs to cross above or circle around below the switchers creating a fairly good antenna.

If you keep your connectors where they are, the only clean solution is having the 2 switchers at the top of the PCB and the all the linear at the bottom row. including the Dreamcast +12v 100uf cap.

There is just no space...

Moving J4/J5 and the power out closer to the edge might help.
If that power connector U plastic finger shape is plastic above the connector, you may over-hang that at the edge of the PCB as long as when being panel assembled, the plastic doesn't interfere with components on the adjacent panel.

You haven't seen any rectangular heatsinks, like the one I mentioned which was 12x25.


If you are trying to keep this layout, the only thing you can do is move C8 right next to C16/ swap those 2 around.
Route the 12v output of the choke around the outside of the PCB to C8.
Also move 1/2 of the output 10uf & 100nf filter caps from the 12v choke where C8 is.

If you are keeping the mosfets where they are, rotate them 180 degrees.

The 2 mosfet load output caps and resistors should be near/inbetween the mosfet and op-amps instead of by the connector.
Maybe even place them on the other side if that is the side you are wiring the output to your power connector.

The wiring between them and the connectors needs to be nothing more than a wire.

That's it for now...

[VEGETA]

I made a rough drawing (using mspaint) on grounds. C16 is for the 5v and op-amp, so it is on linear side.

blue is linear ground, green (and white) is switching ground. I could make another ground just for op-amp and 5v reg.

Opamp and 5v with all their stuff are just under their ground as you can see... I can just put a thick line from 12v to the connector pin and make it as far as possible from linear stuff.

MOSFET taps seems to be the inputs, so is it worth it to make that space under it with thermal vias even with using heatsinks? if 25x25 is too big, then what about those individual heatsinks, the small ones? I still don't know what thermal glue to use in order to stick it firmly.

[BrianHG]

The caps C8 and the ones post L1 are going to the wrong GND.
Especially C8 which may modulate with the switcher it is above.
Those need to be next to the Dreamcast's +12v output.

[BrianHG]

Your caps below the switchers also are painted into the wrong GND section.  Be careful how you pout the GND.  The, the mosfets don't need a GND for their drain.

[BrianHG]

Actually, if you keep this layout, rotating the mosfets 90 degrees may also work.

[VEGETA]

The caps C8 and the ones post L1 are going to the wrong GND.

they should be on the same gnd as the 5v and opamp? or their own?

I will move them to be very close to the output connector to DC (12v).

Your caps below the switchers also are painted into the wrong GND section.

which ones? if you mean those close to the switchers then it is ok, they will go to the switching gnd not the blue one but the drawing here was rough estimate.

The, the mosfets don't need a GND for their drain.

but they will be within the linear gnd plane as shown. I thought about making a small copper area around them with thermal vias to help the heatsink more.

Actually, if you keep this layout, rotating the mosfets 90 degrees may also work.

I will eventually let them face their 3.3v and 5v connector directly.

[BrianHG]

The caps C8 and the ones post L1 are going to the wrong GND.

they should be on the same gnd as the 5v and opamp? or their own?

I will move them to be very close to the output connector to DC (12v).

Moving the cap is more important than the inductor.
I'm talking about the caps after L1.  Their GND should be on the linear GND.
Everything else is ok.

[VEGETA]

Here is the re-arrangement.

- moved 5v\op-amp big elec. cap a little bit to the left.
- placed all the caps after L1 in its place near 12v connector.
- rotated mosfets so that a direct connection is doable.

Notice that under the mosfets still empty in order to make thermal vias... but should I be doing it on 3.3v + 5v rails or where their pads are (the input)? I can make a local copper pour there (even one per mosfet) but to which net? I kinda believe the press-fit heatsinks gonna be enough without any of this, which makes more room to re-arrange bottom parts better.

As for heatsink, I like this 20x20x10 one: https://lcsc.com/product-detail/Heat-Sinks_XSD-XSD271-294-B_C286198.html  what do you think?

can you please link the product you talked about which can stick them and still conduct heat very well without being slippery?

[BrianHG]

Heat Sink OK.

Cheap stuff:
https://www.amazon.com/s?k=Heat+Sink+Thermal+Tape

Better stuff:
Actually, I don't trust that Amazon tape, go for real 3M brand:
https://www.digikey.com/product-detail/en/3m-tc/1-2-5-8810/3M10315-ND/2649860

The heatsink wont slip off the tape (unless you applied it over dust and oily surfaces).  The difference between the cheap and good stuff is the thermal conductivity through the tape.  The really good stuff is cost prohibitive and only necessary to conduct away >25watt <75watt loads.

Some of the Amazon quotes are from people who tried the tape on their PC CPUs not realizing that the stuff wasn't designed to conduct away 150-300 watts of heat produced by a modern CPU.  These tapes should not be used in applications where you need to get rid of >10 watts of heat, they are nowhere near conductive like metal-on-metal with liquid thermal paste.

[VEGETA]

It is nice to know such cheap tapes are good enough, will buy them in time. As for heatsinks, I have many options one of them being individual heatsink per mosfet and the other is one for both. Another one is to locally make them from an Aluminum sheet by cutting it, I guess workshops will do it for very cheap.

Anyway, is the placement of parts ok now? I guess this is the best I can do in such small footprint. If so, then I will start routing.

[BrianHG]

Well, looking at your space constraints, I truly wished the bottom switcher was further away from the linear opamp...

As you layout, you may end up adjusting orientation.

Also, if the traces from the source's to the output pins are short, your opamp may take the feedback from the output pins making them the exact voltage, with the appearance of something like a 0 ohm impedance.

1 heatsink will do as it has a larger fin area and one of the regulators will in general get warmer than the other.  This allows the hotter one to dissipate the extra heat by a larger chunk of metal.

Test the module on a full load output without the heatsinks to see how bad things get first.  You may not need one.

JLPCB & PCBWay's PCB panels are rectangles, not squares.  Adding 10mm width to that PCB will make a nice clear 1cm break between switchers and linear maintaining the exact same layout you already made and you should still get the same 25 boards per panel making the end price identical.

Right now the op-amp is so close to one of the switchers, I hope mere EMI wont affect it.

[VEGETA]

Well, looking at your space constraints, I truly wished the bottom switcher was further away from the linear opamp...

I may be able to move it a bit further.

Also, if the traces from the source's to the output pins are short, your opamp may take the feedback from the output pins making them the exact voltage, with the appearance of something like a 0 ohm impedance.

the 3.3v and 5v. output?

JLPCB & PCBWay's PCB panels are rectangles, not squares.

really? I thought they do all sizes. No sign of this on their site. keeping it small is a feature.

Right now the op-amp is so close to one of the switchers, I hope mere EMI wont affect it.

as I said, I will try to move it away. Maybe under the 2 mosfets since we won't be making thermal pads? how about that? they will be far from the switchers.

[BrianHG]

JLPCB & PCBWay's PCB panels are rectangles, not squares.

really? I thought they do all sizes. No sign of this on their site. keeping it small is a feature.

Look:


You optimize costs by making your panel fit inside that area.
Also, remember you require space between PCBs.

If your PCB was designed with true clearance to have no space between them for V scoring, currently, you can place 8x10 on a panel, or 80 per panel.

Currently, I would expect something more like 7x9 for 50x50mm PCB with 5mm between PCBs, or, 7x7 for 50x65mm PCB with the 5mm spacing between PCBs.  (Careful bending these with V scoring as they will flex an may damage SMD components.  Using cut-able tabs may requires more than 5mm between PCBs.)

In both cases, more PCBs than your original 25 per panel.

Read the panelization tab.  They claim the true sizes of the break-away tabs and V-scoring sizes.

[BrianHG]

Also, if the traces from the source's to the output pins are short, your opamp may take the feedback from the output pins making them the exact voltage, with the appearance of something like a 0 ohm impedance.

the 3.3v and 5v. output?

Yes.  Though, the quality of the solder in the connector's through-hole may add noise to the circuit.

[VEGETA]

I have finished routing it, I hope it doesn't need much modifications.

[BrianHG]

OMG, so messy...

Also, you placed L1 above a switcher, it will act like an antenna and really pipe through some noise, or not.  Cant be sure, but that is not a safe place for it.

Your opamp is in a really bad place.  It is under one of the mosfet drains which contain the bulk noise from the switcher, not to mention loss of PCB heat sink plating area for the mosfet.  I would rather place the opamp in the bottom right corner and place the 5v regulator to the left of it under the 2 1000uf caps.

There should be no GND under the noisy mosfet drains.  They should have a rectangular copper plate via stitched to the surface layer to surface layer to add heat removal.

You are also feeding up to ~15 watts or more power through single vias at multiple places in your design.

You can do a whole lot better...

[VEGETA]

Also, you placed L1 above a switcher, it will act like an antenna and really pipe through some noise, or not.  Cant be sure, but that is not a safe place for it.

I will move it.

Your opamp is in a really bad place.  It is under one of the mosfet drains which contain the bulk noise from the switcher, not to mention loss of PCB heat sink plating area for the mosfet.  I would rather place the opamp in the bottom right corner and place the 5v regulator to the left of it under the 2 1000uf caps.

I thought it would be better to be away from switchers...I will try to put it back where it was on bottom right as you mentioned.

There should be no GND under the noisy mosfet drains.  They should have a rectangular copper plate via stitched to the surface layer to surface layer to add heat removal.

this rectangular copper area with vias... attached to what rail? the smt pad is the input... I can make a small copper area for each mosfet rail 5v and 3.3v.

You are also feeding up to ~15 watts or more power through single vias at multiple places in your design.

you mean the output connector? what exactly.

[BrianHG]

There should be no GND under the noisy mosfet drains.  They should have a rectangular copper plate via stitched to the surface layer to surface layer to add heat removal.

this rectangular copper area with vias... attached to what rail? the smt pad is the input... I can make a small copper area for each mosfet rail 5v and 3.3v.

Ok.

You are also feeding up to ~15 watts or more power through single vias at multiple places in your design.

you mean the output connector? what exactly.

See the attached image purple arrows.

You are driving 6v @ 3 amps through one of those vias, no to mention 4v @ 3 amps.  If you think you can rely on a single tiny via to live through that, you will get some PCB mysteriously dying in the field after a week to a few months of use.

For the switcher, did you follow the datasheet recommended layout?

Also, the red one, hun?  Power to the inductor, but also to the switcher from the inductor's Vin.  I guess thatch ok as well.

Never flood fill when designing you PCB, especially power supplies where current handling matters in some areas.

The flood fill is the last step before the gerber output.

I need higher resolution prints without flood fill and proper net names on as many spots as possible.

[VEGETA]

I removed all tracks and vias so I can start with placement only for now.

I have re-arranged all components and was as faithful to aoz datasheet placement as I can. Now there is enough space between linear and switching, there is no colliding anymore.

if this placement is ok, then I can start routing.

the only downside is that the heatsink now should be a bit smaller, 15mm in vertical length and good length in horizontal position.

[BrianHG]

That looks a lot better.


Rotate C16 so the the GND faces the connector.
Rotate L1 with +12 out facing down.  Feed it with a thick +12v trace following the top/round the corner to the right of the PCB.

The 2 1uH chokes + input side chokes which feed the switchers should be on the top of the PCB while at least 1 of their filter output caps, if not both should be on the bottom.  Those 2 chokes should be above each switcher VCC they feed.  Use at least 4 vias in a square along a thick trace to power the switchers at the output of those inductors.  The output side of those chokes needs to be as short as possible.

As for the moved 1uH chokes to the top of the PCB.  Larger ones here may help as a void for a GND filled path.  You may even consider using the same 10uH (not necessary, there is still routing room with 1uH as the output is a short trace.) from the switchers if you like since they appear to have a nice huge void.  C2 may be moved lower in between the switchers to accommodate the 1uH chokes on top of the PCB.

Rotate and center the opamp & 78L05 regulator portion 90 degrees.  You may need to swap the opamp A&B channel for routing optimization.
You may also need to swap Q1&Q2 as well as the switchers to avoid vias/crossing from their source output and the power output connector.

The switcher's outputs feed should stay on the bottom and feed a big box pad under each mosfet's drain.  That box should have via switching to the top layer under the mosfets to help dissipate heat through copper.

[VEGETA]

I will dig into it tonight.

The 2 1uH chokes + input side chokes which feed the switchers should be on the top of the PCB while at least 1 of their filter output caps, if not both should be on the bottom.

you mean top side of the board and bottom side? Since these are gonna be smt assembled, then they should be on top side.

I can move L4 and L5 to top since I will already hand solder a similar one (L1) there, but the small ones should stay where they are.

The switcher's outputs feed should stay on the bottom and feed a big box pad under each mosfet's drain.  That box should have via switching to the top layer under the mosfets to help dissipate heat through copper.

This was my plan, getting the 5v and 3.3v to have this copper box filled with vias. However, it cannot go under the mosfet since the mosfet has pad which is the input. So i can make it near the mosfet in a way that it doesn't touch the pad.

__________

I am thinking of changing the dimensions since maybe 50mm will not fit properly inside. so maybe 40x60 is a good choice, or even 45x55... the length is gonna get bigger on the expense of the width (meaning the horizontal dimension). this way I must re-arrange the components a little bit.

I hope I can fit the 50x50 one, gonna do some measurements. I could offset it a bit to the side.

[BrianHG]

Don't move the switcher's output inductors.  I'm talking about the tiny ones feeding the +12v.  This is due to EMI noise considerations.

As for the mosfets, yes, the Drain +v inputs at 4.3v and 6v are routed to the switcher outputs through the bottom of the PCB while the source outputs go to the +5/+3.3v output connector on the top of the PCB.  The 12v in to the 10uh inductor is also on top of the PCB with the other 2 input inductor chokes with their 2 input caps.

[VEGETA]

Don't move the switcher's output inductors.  I'm talking about the tiny ones feeding the +12v.  This is due to EMI noise considerations.

I know but the tiny ones supposed to be smt assembled. Is it necessary to move it to other side?

As for the mosfets, yes, the Drain +v inputs at 4.3v and 6v are routed to the switcher outputs through the bottom of the PCB while the source outputs go to the +5/+3.3v output connector on the top of the PCB.  The 12v in to the 10uh inductor is also on top of the PCB with the other 2 input inductor chokes with their 2 input caps.

You mean by top\bottom is the routes themselves not the actual placement of components right?

but why such separation of signals despite being far enough from each other?

[BrianHG]

Don't move the switcher's output inductors.  I'm talking about the tiny ones feeding the +12v.  This is due to EMI noise considerations.

I know but the tiny ones supposed to be smt assembled. Is it necessary to move it to other side?

It's where the source GND is tied to by the caps at the input of those inductors and at the output.  The inductors can be on the bottom.  You want the source caps for those 2 on top and the ones on the bottom feeding the switchers by the switcher's GND.

As for the mosfets, yes, the Drain +v inputs at 4.3v and 6v are routed to the switcher outputs through the bottom of the PCB while the source outputs go to the +5/+3.3v output connector on the top of the PCB.  The 12v in to the 10uh inductor is also on top of the PCB with the other 2 input inductor chokes with their 2 input caps.

You mean by top\bottom is the routes themselves not the actual placement of components right?

but why such separation of signals despite being far enough from each other?

I talking about which side you place the traces.  When driving 3 amps, you try to avoid any vias possible.  They are just too small.  This is why going to the mosfet drains, you get the capability of stitching something like 10 vias around the drain as both heatsink transfer of power to the drain.  Keep the output of the switchers on the bottom of the PCB all the way to the mosfet drains.   Keep the source outputs on the top all the way to the output connectors.  Keep the +12v on the top all the way to the 10uH, then to the 12v power output connector.

Most of the top of your PCB will be GND on the left above the 2 switchers and a separate linear gen from the power input going around the left and down side (top of PCB), opposite the 12v line to the linear section.

Sorry, I got top and bottom.  I know the bottom is your SMD side which will be manufactured up-side-down.
So, when I've been saying bottom, I means the SMD side.

[BrianHG]

Well, how is it going?
I hope my instructions were simple and clear enough...

[VEGETA]

Well, how is it going?
I hope my instructions were simple and clear enough...

Hello,

I am well 

However, real-life job stuff... and also, the stock dreamcast PSU got broken 

I have been trying to fix it but couldn't after hours of fixing problems one by one, still can't seem to work. So I ditched it and started making one from scratch using the awesome L200 regulator. 2 of it for each rail, DIY project that I will finish tomorrow or so... to be able to play.

The irony is that I am designing a PSU for dreamcast... the the stock PSU got burned 

[VEGETA]

Hello,

I have made some little tweaks:

- Rotated C16.
- Rotated 5v regulator + op-amp 90 degrees.
- Rotated L1.

However, I didn't move input inductors and little inductors to top side of the board since I want them to be SMT assembled. Also, Q1\Q2 placements seem fine to me.

If this is ok as placements, I can start routing next week.

[BrianHG]

Here are some of my ideas...
I pushed up J4 & J5.  Move the +3.3 output cap and R load.  Shifted over the opamp a little.

See the chosen power trace path.

If you do do a linear GND fill, avoid the +12v heading into the 10uH inductor.
On the switcher side, you have generous GND plane fill area as well as room for a hefty 12v trace to the 1uH 12v choke inductors.

!!! The switcher GND fill should not touch the GND trace I laid out which feeds the linear side's GND !!!

These were rough drawings, I'm sure you can make it much nicer in the cad.

[BrianHG]

So?

Did you decide to spend 1 night to finish up this board, make 2 test prototypes so you can get your Dreamcast up & working again the right way?

Or did you scramble and waste more time than that would have taken to finish the small PSU to Gerry-Rig a sub-par temporary fix over a few days which may be dangerous enough to damage your 1 only Dreamcast?

[VEGETA]

So?

Did you decide to spend 1 night to finish up this board, make 2 test prototypes so you can get your Dreamcast up & working again the right way?

Or did you scramble and waste more time than that would have taken to finish the small PSU to Gerry-Rig a sub-par temporary fix over a few days which may be dangerous enough to damage your 1 only Dreamcast?

I will get to do it for sure! no getting back from this, no surrender!

These weeks I've been travelling from work to home back and forth (200 KM) more than ever... this is the cause.

I will keep you posted for sure.

[VEGETA]

Hello,

long time no see!

I finally got the time to work on this, and here is the result.

Obviously I still need to do some polygon pours and vias...etc as well as art stuff. However, I wanna make sure I got the most important stuff done.

what do you think?

regards!!

[BrianHG]

Ouch, kinda messy and you are mixing you switching GND with your linear GND.

Ok, step 1, reset / swap the voltage on both switcher's rewire them to the mosfets.
See attached schematic.
This will get the switcher's output to match my layout recommendations a few posts back.
(See all red text)
(This is only a start, there is a lot to do...)


Please remove all GND traces and see if you can get me a high enough quality bitmap or print to see the more net labels on the pads of the SMD components.

[VEGETA]

So you want to re-locate the switcher circuit for both rails? I can do that but it takes time.

I still need to figure out how to wire the grounds so I will leave it to the last moment.


where exactly did I do wrong in terms of mixing grounds?

[VEGETA]

Here is the update.

I have re-wired the transistors to the other switchers as we agreed. Did the same wirings too but still didn't fully connect all the pads especially grounds... also no ground pours yet.

[BrianHG]

Without a painted rectangle under the mosfets, no heat will be drawn away from their metal drain tabs to the vias to the bottom of the PCB.

More to come.  I need to look more closely of the layout.
There is still too much spaghetti in your layout style.  There is room for much improvement just my moving & rotating a fer smd caps and resistors.

[VEGETA]

Without a painted rectangle under the mosfets, no heat will be drawn away from their metal drain tabs to the vias to the bottom of the PCB.

More to come.  I need to look more closely of the layout.
There is still too much spaghetti in your layout style.  There is room for much improvement just my moving & rotating a fer smd caps and resistors.

I guess I put rectangles in each layer under the mosfets and connected them with vias... or what exactly?

I tried to make the layout as clean as possible with having the same component placement.

looking forward to your further input. thanks

[VEGETA]

Looks like you've been away for quite some time.

I still didn't do further more as nothing is left but to finish the layout itself.

[BrianHG]

You will need to start by redoing the op-amp layout.  It is such a jumble, it has an added chance of oscillation just due to signals going around the IC.

The op-amp's position isn't too terrible maybe center it a little between the 2 mosfets, lower a little.
Place it's decoupling cap above pin 8 and parallel to the opamp.
The termination and resistor divider and feedback resistor for each amp should be on each side o the opamp while the series reference power feeding resistors may be below the opamp.

Your linear regulator mess also needs some cleaning up.
Also, the 5v out's power trace should not encompass the large 1000uf cap's + pin.

See photo, the purple is the switcher's GND fill and the green is the linear's and output's GND fill (All will be on the red layer).  However, do not fill them yet, I just wanted to show you the guide so you know where you will be getting all the GND via points from.  There is still things to clean up on the switcher side after you fix the linear side.

The added red copper by the mosfets is needed for heat sinking.  In fact, there should be a grid of un-tented vias under the tab of the mosfets.

[VEGETA]

You will need to start by redoing the op-amp layout.

Ok, I will do it.

However, why the series feeding resistor must be on the lower side? assuming the mosfets are on the upper side of the opamp?

Your linear regulator mess also needs some cleaning up.

like what? you mean the signals going into vias and long distances?

Also, the 5v out's power trace should not encompass the large 1000uf cap's + pin.

you mean it goes under the cap? if I move it to the left, then it and 3.3v output one will be above some switching components.

The added red copper by the mosfets is needed for heat sinking.  In fact, there should be a grid of un-tented vias under the tab of the mosfets.

I will add more vias there, easy.

[BrianHG]

The congestion around your linear side is making it hard for me to make anything out.
Move the components away from the op-amp and start again.
Do only 1 side at a time as the other side should almost look mirror like.

I'm assuming pins 1&8 should be facing toward the mosfets.  Maybe swap U4A and U4B.

First place D4 vertical next to the input pins.
Place R16 and C38 above next to the output pin, both partway to the mosfet gate.
Place R10/C33 by the input pin.
Place R18 can be a little further away.

See how this looks and see if you can mirror the layout on the other side of the opamp.

[VEGETA]

This is my attempt after hours of doing modifications.

However, some stuff still not connected and kicad shows mosfets square area  being overlapped (top and bottom) + a track (VCC) close to it.

[BrianHG]

You didn't rotate the opamp 180 degrees and swap U4A and U4B to make the routing easier.

Also, why did you change to the green layer for the flood fill GND on the switcher side?

You are also missing heat-sink vias for the switcher regulator ICs.

Also, look at the attached image of example vias under a SMD power transistor.
Use something between pattern 2&3.

[VEGETA]

You didn't rotate the opamp 180 degrees and swap U4A and U4B to make the routing easier.

Also, why did you change to the green layer for the flood fill GND on the switcher side?

You are also missing heat-sink vias for the switcher regulator ICs.

Also, look at the attached image of example vias under a SMD power transistor.
Use something between pattern 2&3.

I sent the response before your response.

what is wrong with the current opamp configuration? I moved a lot of components around to make traces straight and short.

the green layer? i think it is away from the linear gnd so i thought it is ok... I can put the red layer but it wont fill properly.. maybe then I need to put lots of vias to achieve that.

as of heatsinks, i tried putting some of them to make the connection between the red and green rectangle pour... however, i couldn;t place vias in all area of the rectangle. I can add more though.

what more can i do besides heatsink and vias? assuming the op-amp now is good. I really hope I don;t need to change it but i am ready to do so if absolutely necessary

[BrianHG]

There shouldn't be any GND traces on the green layer other than a short hop from SMD pads to VIAs to the red layer which should be a solid GND.

That green GND fill is all chopped and garbled up with no continuous solid 1 piece backbone to it.

Please identify the arrows in the attached image...

Turning around that opamp is the only way to get rid of the clutter of traces under it while eliminating those looping long green traces going in and around the resistors.

[VEGETA]

ok so i will turn the op-amp to try to wire them a better way. however, these signals are on the other side of the board anyway, so a long green wire is a must... just maybe not using red layer is the only improvement to gain.

to make a red gnd of switching side, i need to put lots of vias and connect ground to it from green layer (signals not pour). I will attempt that tomorrow... maybe not a solid perfect rectangle but i hope it is close to it.

i really hope we finish the design soon xD

thanks!

[VEGETA]

I did all of this, it is in attachment.

It is not so tidy, especially the vias under mosfets but tidying it up should be easy.

I have connected both grounds with one trace as agreed earlier.

All traces are as short as they can be, but still some of them had to travel but those are very few.

If anything isn't clear, I will send the project via PM.

[BrianHG]

You didn't swap U4A and U4B in the schematic.

Are you autorouting?  It should not be done for such a simple design...

If you followed all my instructions, there should only be 4 vias in the linear section, 1 for each gate and 1 for each source.

There will be a few vias for GND as well, but no jumpers to the red side.

There would also be 1/2 vias by the 1000uf caps, but nowhere else.  There are 100% complete straight paths everywhere else if you placed the SMD caps/resistors correctly.

Also, what is it with that oddly placed resistor I have the red arrow pointed to?

It beginning to look better.  You clearly have the space for cleaning everything up.  The switching side isn't too bad, though a little adjustment to feedback resistors and maybe a few traces too thick going onto the switcher's SMD pads.  And, the switcher IC's thermal case GND vias in the footprint underneath the IC are missing.

[VEGETA]

You didn't swap U4A and U4B in the schematic

I thought it would be not necessary if I rotate the op-amp. I will try it now hoping it won't require me to re-do everything.

Are you autorouting?  It should not be done for such a simple design...

No, I never did it and don't intend to.

If you followed all my instructions, there should only be 4 vias in the linear section, 1 for each gate and 1 for each source.

one for mosfet gate and one for mosfet source x2 ?? I will swap U4A and B to see this.

There will be a few vias for GND as well, but no jumpers to the red side.

I increased GND vias so that they share the current, despite being so little in the op-amp area.

There would also be 1/2 vias by the 1000uf caps, but nowhere else. 

I didn't understand this.

There are 100% complete straight paths everywhere else if you placed the SMD caps/resistors correctly.

What is wrong with some of the traces going a bit further or bend a little bit? I see it all the time in PCBs. Yes, straight and short is the best though.

Also, what is it with that oddly placed resistor I have the red arrow pointed to?

this one delivers the EN voltage to the switchers. and the pins of the switchers are very far in the next side and cannot be rotated as you can see. either put the resistor in linear side then do the big trace or the opposite.

I will try more now.

[VEGETA]

Here is the said changes, all done.

Now only very few vias exist, but I had to put one to connect the 2 grounds together since kicad keeps listing some of them as not connected.

I couldn't put vias under the mosfets because they will be on the pad itself which is probably not allowed in kicad.

the big cap signal had to go under the op=amp or it would rotate more distance, by this... it is very short distance.

[BrianHG]

I couldn't put vias under the mosfets because they will be on the pad itself which is probably not allowed in kicad.

Maybe you need to do it in the footprint editor?
I don't know since I do not use Kicad.
However, I've attached some additional photos to show you when it comes to 'thermal pads' on ICs and transistors, this is normal in the electronics industry.

also read here, simple google: https://forum.kicad.info/t/pad-holes-under-smt-for-heat-sinking-and-other-questions/3714/3

You are almost done with the PCB.  I need to do some things in the paint software...

[BrianHG]

This should help clean up a bit more:

After making my green and red changes, the movement of the mosfet source output traces at the top right should be obvious to get make the GND cover more area and reach that new GND via.  The elimination of the opamp's VCC on the red layer makes all that section 1 solid GND plane.

The red Xs by the lower switcher needs movement and cleaning so that it better resembles the red check marks on the top regulator.  You cant have the protective flyback diode wired the way you have it on the bottom switcher.  It will radiate excessive noise.

Don't forget the Kicad link I gave you earlier where it says that you need a footprint which contains the 'PADs' with drill holes and matching pad number to get the heat-sink relief.

[VEGETA]

I will try to clean it as much as possible, but maybe it will take time since I am busy this weekend.

The red traces on right side (opamp + Vreg)... do you mean they are on the red layer? but the pads are green smt ones, they will need vias to connect to red ground. they are straight connections though, so why do we need to change them?

The rest of your red traces are just re-located ground vias right?

why you put X on the trace connecting the 2 grounds? shouldn't they be connected with a trace? I mentioned that kicad continues to say unconnected traces until I do it.


as for the switcher in the bottom, I will slightly move these parts to the right to make room for all these mods needed. However, these caps and maybe even the diode will be under the linear 3.3 and 5v traces of the red layer... will this make effect?

i will try to modify the kicad pads... I actually thought about this but really didn't think it would be necessary.

I will update you on this once I manage to do it.

[BrianHG]

See my red trace on the bottom, this is a good place to merge the 2 GNDs.
Also, move the V+ trace at the top left so that a little more meat for the GND leaves the power input connector.

[VEGETA]

I enhanced the design further more.

Now I think all are ok.

[BrianHG]

Almost perfect.  I'll upload a few minor patches before I go to sleep tonight.

[BrianHG]

Ok, let's see if you can catch & replicate all my improvements.

(The purple under the mosfets means remove/disable the 'thermal reliefs'.  You want a solid copper fill over those pads.)

I removed some rows of vias around the mosfets.  This will allow you to move the power traces further away from the edge of the PCB.

If you catch every change, and the nets report all connected, after 1 final look over, you will be ready to go.

[VEGETA]

I have removed the thermal relief and it is now solid. I also cut the area so that the traces are not near the board edge.

however, I didn't do the other minor relocations... are they necessary?

I'll see what I can do when I have time.

[BrianHG]

Yes, the minor changes are all necessary.  All those changes concern the series resistance of the vias and the amount of current which you are pushing through them.  So especially on the green layer, take a careful look at my layout changes and the number and location of all the added vias around the switchers, power input, feedback, GND going to the bottom switcher's GND input & also on the +12v going to the dreamcast's +12v power out side.

Do this board right once and you wont have to debug unseen weird things with your scope from PCB to PCB.

[VEGETA]

DONE.

I believe I've done everything.

If all is good now, I will just re-arrange the silkscreen writings.

Then I will try to make a panel so that I can use JLCPCB smt service as a panel (10-30 panels) rather than single ones.

 

[BrianHG]

This should do it:

[VEGETA]

I will do it tomorrow,

by this, the 3.3 and 5 linear power signals will pass under the cap, is it ok?

[BrianHG]

I will do it tomorrow,

by this, the 3.3 and 5 linear power signals will pass under the cap, is it ok?

Yes, this is ok since these signals do not have a high frequency EMI radiating from the switcher.

[VEGETA]

Done.

I thought about doing very small green copper zones around Vcc and 12v pins but I used thick tracks to cover the area properly.

[BrianHG]

I think you got it.
It looks as simple, direct and clean as it will get.

[VEGETA]

Tomorrow I will make a panel of it, suitable for JLCPCB SMT service.

[BrianHG]

Tomorrow I will make a panel of it, suitable for JLCPCB SMT service.

Ask JLPCB first, they may prefer to panel it themselves.  Or, they may tell you how much space you need to place between panels so they are able to assemble the PCB.

Also ask about fiducial marks.

[BrianHG]

1 functional quality improvement.  Take a look at the change I made to R1 and how it's connected to C16.  This is important as the original single via's resistance will determine how well filtered the +12v will be for the linear section in our RC equation where the VIA adds a unpredictable series resistance between the cap's + leg and R1's output.  This essentially makes the cap look as if it has a lower ESR in the filter.

The change makes sure that the +12 goes to the C16 filter cap first.  The that output feeds the linear section off from the cap's + pad through a second via.

[VEGETA]

Done.

I've messaged JLCPCB.

I looked at their site and looks like they updated the service to be able to use black solder mask which is a good thing for me.

also, 50 is the max quantity now.

so I could make 300x300mm panel, get about 10 panels which will have 250 boards! 50x50mm x 5 columns x 5 rows.

I could get just 5 panels though as a start... dunno about the price, lets wait and see.

choosing panel by jlcpcb didn't work on their demo smt board.

btw, kicad penalization is not so smooth, one needs to do some manual stuff.

[BrianHG]

Nice on the cap.  Everything looks good.  Good luck with JLPCB.  I think to get their 5$ special, you have to send the PCB as a single & they will deliver a few PCBs for you.

[BrianHG]

Q: Isn't the vertical portion of that 3.3v and 5v trace a little close to each other?

[VEGETA]

Q: Isn't the vertical portion of that 3.3v and 5v trace a little close to each other?

KiCAD didn't say a thing about them being too close.

[BrianHG]

Don't forget to test with dummy loads of varying current...

[VEGETA]

Don't forget to test with dummy loads of varying current...

Actually my problem is that I don't have an oscilloscope nor electronic dummy load. I plan to buy a scope soon though. I wish if there is a used 1054z available.

[VEGETA]

I have made a panel our of it.

25 single boards with 280x280 panel.

next is dealing with BOM and with JLCPCB format.

[BrianHG]

Don't forget to test with dummy loads of varying current...

Actually my problem is that I don't have an oscilloscope nor electronic dummy load. I plan to buy a scope soon though. I wish if there is a used 1054z available.

A dummy load is a resistor.
Voltage can be measured with a volt-meter, but, a scope would be more useful to inspect everything including noise.

Get 10x 10ohm, 5 watts and 10x 6.2 ohm 5 watts.  Wired...  10 watts may be a better idea.
Get 1x 100 ohm, 5 watts for the 12v.

On the 5v, every 10 ohm resistor you add will add 0.5 amp load, 2.5 watts.
On the 3.3v, every 6.2 ohm resistor you add will add ~0.532 amps, ~1.8 watts.
On the 12v out, place the 100 ohm resistor to load 0.12amps, or ~1.5 watts

The resistors will get hot.
Match and go above the current load of the Dreamcast for each output all running in parallel.
See how hot the power supply board gets.


Note: locally, you cant even find an old used cheap old 10-20MHz CRT oscilloscope for 15$?

[VEGETA]

I can hook up resistors, but I wanted electronics load since it is kinda better.

Here there are no scopes like this except in universities and no one sells them.

[BrianHG]

I can hook up resistors, but I wanted electronics load since it is kinda better.

You would need 3 of them.  Or a triple channel one...

[VEGETA]

I have made a small change which is L2 and L3 of the EMI filter before the switchers... look like we got the wrong footprint! 0603 in kicad got a very small part which is not like the 06s in JLCPCB...

long story short: I changed it to SMD,2.5x2.0x1.2mm package (slightly bigger size) and it is now 2.2uH instead of 1uH. I updated the PCB and now doing the panel again

here is JLCPCB part: https://lcsc.com/product-detail/Power-Inductors_Sumida-252012CDMCDDS-2R2MC_C351245.html/?href=jlc-SMT

it is 3 amps so I guess it is fine.

[BrianHG]

I have made a small change which is L2 and L3 of the EMI filter before the switchers... look like we got the wrong footprint! 0603 in kicad got a very small part which is not like the 06s in JLCPCB...

long story short: I changed it to SMD,2.5x2.0x1.2mm package (slightly bigger size) and it is now 2.2uH instead of 1uH. I updated the PCB and now doing the panel again

here is JLCPCB part: https://lcsc.com/product-detail/Power-Inductors_Sumida-252012CDMCDDS-2R2MC_C351245.html/?href=jlc-SMT

it is 3 amps so I guess it is fine.

Yes, for filtering the input, that inductor will clear as the one for the 5v will max out at ~2 amps and less for the 3.3v side.  If it was for the switcher's output, that coil would saturate and you would loose efficiency and add ripple to your output.

[VEGETA]

I have made a small change which is L2 and L3 of the EMI filter before the switchers... look like we got the wrong footprint! 0603 in kicad got a very small part which is not like the 06s in JLCPCB...

long story short: I changed it to SMD,2.5x2.0x1.2mm package (slightly bigger size) and it is now 2.2uH instead of 1uH. I updated the PCB and now doing the panel again

here is JLCPCB part: https://lcsc.com/product-detail/Power-Inductors_Sumida-252012CDMCDDS-2R2MC_C351245.html/?href=jlc-SMT

it is 3 amps so I guess it is fine.

Yes, for filtering the input, that inductor will clear as the one for the 5v will max out at ~2 amps and less for the 3.3v side.  If it was for the switcher's output, that coil would saturate and you would loose efficiency and add ripple to your output.

the way I understood it is this:

5v*2 amps max = 10 watts. 10 watts/12v = 0.83 amps input current.
3.3v*3 amps max or so = about 10 watts = 0.83 amps input current.

but of course, switching current is gonna be more.

is it this case or not?

[BrianHG]

I have made a small change which is L2 and L3 of the EMI filter before the switchers... look like we got the wrong footprint! 0603 in kicad got a very small part which is not like the 06s in JLCPCB...

long story short: I changed it to SMD,2.5x2.0x1.2mm package (slightly bigger size) and it is now 2.2uH instead of 1uH. I updated the PCB and now doing the panel again

here is JLCPCB part: https://lcsc.com/product-detail/Power-Inductors_Sumida-252012CDMCDDS-2R2MC_C351245.html/?href=jlc-SMT

it is 3 amps so I guess it is fine.

Yes, for filtering the input, that inductor will clear as the one for the 5v will max out at ~2 amps and less for the 3.3v side.  If it was for the switcher's output, that coil would saturate and you would loose efficiency and add ripple to your output.

the way I understood it is this:

5v*2 amps max = 10 watts. 10 watts/12v = 0.83 amps input current.
3.3v*3 amps max or so = about 10 watts = 0.83 amps input current.

but of course, switching current is gonna be more.

is it this case or not?

No, you got it right, except needing to add the loss and quisient current of the switcher.
I was maximizing the output current to 3 amps on both 6v and 4.3v outputs.

So, 6v * 2 amp = 12 watts, or 1 amp at 12v.  Or, consider worst case 80% efficiency at high load, and then that source current goes up to ~1.2amps.  I did my ~math with ~3 amps at 6v feeding the linear regulator outputting 5v at 3 amps.  This would mean that @3amps, the mosfet will radiate ~3 watts of heat.

Remember, your switcher's output is +1v and whatever you draw from the linear side at -1v from there still has the same current draw on the switcher +1v side.

[VEGETA]

So according to this, I think about doing a future enhancement in BOM by using smaller and noticeably cheaper power inductors instead of that big one to reduce total cost. However this is in the future.

getting 2 of that small 2.2uH inductor instead of the big 10uH switching one seems ok in terms of current since each one tolerates 3 amps which makes it 6 amps total. However, 2.2+2.2 = 4.4uH instead of 10uH. I am afraid this won't remove ripple as much. getting 5 of it will be more than 10uH and still maybe less or similar footprint but more expensive.

I won't bother with this now though. Right now I am contacting JLCPCB for the panels.

the damn 22uF 1206 caps costs about 182$ (quantity of 4000 xD) for the 10 panels (250 boards). Big inductors about 77$.

[BrianHG]

So according to this, I think about doing a future enhancement in BOM by using smaller and noticeably cheaper power inductors instead of that big one to reduce total cost. However this is in the future.

getting 2 of that small 2.2uH inductor instead of the big 10uH switching one seems ok in terms of current since each one tolerates 3 amps which makes it 6 amps total. However, 2.2+2.2 = 4.4uH instead of 10uH. I am afraid this won't remove ripple as much. getting 5 of it will be more than 10uH and still maybe less or similar footprint but more expensive.

I won't bother with this now though. Right now I am contacting JLCPCB for the panels.

the damn 22uF 1206 caps costs about 182$ (quantity of 4000 xD) for the 10 panels (250 boards). Big inductors about 77$.

What does the datasheet say about the 10uh?  Don't you need 10uh to filter the ~2MHz?

Careful.  The filter to supply the switchers is different than the inductors at the switcher's output.  The inductors at the switcher's output needs to support the DC load current + drive input switching current without saturating.  This is why in the datasheet for the 4 amp switcher, they recommend a 6-8amp inductor when you draw the full 4 amps.

As for the source power inductors, you only need around 1-2.2uh to remove the high frequency spikes generated from the edge of the switching mosfet inside the switcher ICs.  The 10uf/22uf ceramics before and after are there to short as much as possible at high frequencies to the GND plane.

[VEGETA]

check the datasheet: http://aosmd.com/res/data_sheets/AOZ1284PI.pdf

it recommends 22uH but we chose 10uH. I think it is enough since I don't think final output current is gonna be that big... like 4 amp continuous.

[BrianHG]

check the datasheet: http://aosmd.com/res/data_sheets/AOZ1284PI.pdf

it recommends 22uH but we chose 10uH. I think it is enough since I don't think final output current is gonna be that big... like 4 amp continuous.

You went to 10uH because you increased the frequency.

[BrianHG]

Take a look at the trace I highlighted in RED.
Isn't that a feedback trace?
Isn't that long aster the resistor dividers, going under the second switcher's inductor?
Shouldn't the feedback divider resistors be near the feedback input pin?

[VEGETA]

Take a look at the trace I highlighted in RED.
Isn't that a feedback trace?
Isn't that long aster the resistor dividers, going under the second switcher's inductor?
Shouldn't the feedback divider resistors be near the feedback input pin?

is it necessary now to change it? I mean, we didn't notice that all along past reviews for some reason.

[BrianHG]

Take a look at the trace I highlighted in RED.
Isn't that a feedback trace?
Isn't that long aster the resistor dividers, going under the second switcher's inductor?
Shouldn't the feedback divider resistors be near the feedback input pin?

is it necessary now to change it? I mean, we didn't notice that all along past reviews for some reason.

It wasn't noticed because I cannot tell from just images as I didn't layout the components myself.
It is not necessary to move, it is just common practice when driving a feedback input that any high impedance signal is kept as short as possible for minimal noise.
It is your choice as the change wont affect the circuit's function.

[VEGETA]

Take a look at the trace I highlighted in RED.
Isn't that a feedback trace?
Isn't that long aster the resistor dividers, going under the second switcher's inductor?
Shouldn't the feedback divider resistors be near the feedback input pin?

is it necessary now to change it? I mean, we didn't notice that all along past reviews for some reason.

It wasn't noticed because I cannot tell from just images as I didn't layout the components myself.
It is not necessary to move, it is just common practice when driving a feedback input that any high impedance signal is kept as short as possible for minimal noise.
It is your choice as the change wont affect the circuit's function.

TBH, I lost focus from the various revisions I have done to the board, so couldn't notice these resistors to be the feedback ones. the irony is that the 2nd switcher is done better.

It is better to move them, but now I need to re-pannelize the board which is the real headache. I am gonna try though if I had time.

However, I think we are ok with this being the way it is since it is a switching regulator and even if some little noise got in the signal, it won't matter. The output of this regulator will have ripple due to being a switcher, and it is well above the post-regulator so no problem if it got a tiny extra.

I have learned a lot doing this project, thanks to you.

Here is a quick and not-so-accurate pricing for 125 boards (5 panels):

- boards assembled = 290$.
- shipping them = ~60$ or so.
- aoz1284 switchers (not in stock now) = 75$.
- 1000uf caps = 75$
- other through-hole connectors = 150$.
- mosfets = 40$ or so.
- top-side inductor = 25$.
- heatsinks = ~100$
- extra materials (thermal tape, packaging, solder, etc...) = 100$
- handling and customs = 100$

total = 1015$ -> make it 1000$.

Price for a complete ready-to-ship product = 8$. I planned to sell it for 50$ or similar, maybe 40$ at least.

I still have a lot to do like getting these through hole connectors, especially that stupid 6 pin molex one.

Plus, figuring out where to get the 3d printed connector part like this:

https://www.thingiverse.com/thing:4576696
https://www.thingiverse.com/thing:2779041

which is important to tightly fit the DC jack connector. I tried thinking about a small PCB instead of this but it is not good. How much does this thing cost in your experience? I could buy say 1000 piece at once, or at least 300.

[VEGETA]

As for the 3D printed part, I got an offer from local 3D printing service company. For 1000 part, I pay 250$ means 0.25$ per part which is hugely cheap! I will go with them for sure without thinking too much.

JLCPCB noticed a problem that only the first board had proper ground layer while the others are not... hence I must re-do it which is an opportunity to do the small fix you mentioned.

[VEGETA]

I've done the modification.

[BrianHG]

I've done the modification.

Nice, but separate this 1 trace from the connector's pad. it became so close and this is a stress point on the PCB as you have off PCB wires pulling at a random direction on the power connector pads.

[VEGETA]

Done.

finally the last ever change!

waiting JLCPCB to know how can I proceed. Also, the switcher is still out of stock!

[BrianHG]

finally the last ever change!

[VEGETA]

finally the last ever change!

Right? hhh

on a parallel timeline:

year 2020: vegeta starts the project.
Year 3020:

Vegeta: I think now we are ready.
BrianHG: hmm... look at that trace. I think we need to move this and that.

 

____

I will keep you posted on what happens further on.

[BrianHG]

2 mistakes... You have no connection to the bottom right red VIA and you lost the second top left red arrow via with it's connection to the same net.

That connection can be over an amp, so, 1 via to transfer the 12v power from the top layer to the bottom switcher isn't enough.  Earlier versions of the PCB, we had all 3 vias in parallel to do the job.

( Earlier version where they are wired: https://www.eevblog.com/forum/beginners/small-mosfet-for-capacitance-multiplier-in-a-small-psu/msg3352100/#msg3352100 )

[VEGETA]

done

[VEGETA]

BTW, I was checking what we have chosen for the mosfet and found this:

https://lcsc.com/product-detail/Transistors-NPN-PNP_ON-Semiconductor-ON-MJD44H11T4G_C38780.html

it is an NPN transistor not a MOSFET. DPAK package and pins are compatible.

Pin1 -> gate.
Pin2 -> input.
Pin3 -> output.

remind me of our choice if you remember.

[BrianHG]

Ok, now,

Red arrows, too close to the edge of the PCB.
Move C33 in a little.
As for the trace on the left, you can move C11 to the right a little and the big long +5v trace can be pushed in quite a bit and made vertical straight to the grid.

The 2 purple arrow VIAs are not needed.

The green arrow trace is a little close to your screw drill hole, just push it up a minuscule notch.

[BrianHG]

We switched to the mosfet awhile back.

We engineered a linear 'Source-follower' amplifier meaning the voltage we put into the 'gate' comes out the 'source' - the VGS drop.  The 'drain' has the + supply in this scenario.

I do believe that the 'Gate' is also pin 1 and the 'Source' is pin 3.

If the LM358 was strong enough to drive the base of the transistor, and in a lower power scenario it is, a linear 'emitter-follower' amp would achieve the same functionality with a -0.5v drop from base to emitter.

Dont forget to fix that trace on the left too close to the edge.

(Arrrrrrrrgggggg -> The page count is over 9000!!!!)

[VEGETA]

I think everything is perfect now. link in PM.

As for the mosfet, you are correct. it is due to op-amp. here are the 2 that we resulted into:

https://lcsc.com/product-detail/MOSFET_International-Rectifier_IRLR8726TRPBF_International-Rectifier-IR-IRLR8726TRPBF_C81137.html
https://lcsc.com/product-detail/MOSFET_KIA-Semicon-Tech-KIA50N03AD_C112249.html

I like the 2nd one due to huge availability and very low price. I think I will go for it unless a cheaper suitable one is available.

[BrianHG]

The KIA mosfet doesn't have any charts showing the Vgs curve.

Try this one : https://lcsc.com/product-detail/MOSFET_KIA-Semicon-Tech-KND3403A_C382143.html

Or you can trust the one you picked or find a data sheet with the Vgs curve table shown.

[BrianHG]

More errors.  Bad paste-mask for the switcher's footprint.

See the red arrows, the yellow pads are the openings on the paste mask to apply solder.  You have the paste on the heat-sink portion of the footprint instead of under the IC where it can bond with the IC.

Double check the footprint recommendations including paste-mask-opening and make sure you match them.

The green arrow is correct.

[VEGETA]

you mean the full pad should be exposed? I thought this was the case within the footprint itself...

looks like the part under the IC is not exposed while the one outside is... I think they both should be exposed so i can solder them manually if I want to. this is very easy to fix though, just modify the footprint.

What about the ones under the mosfets? should this be a little bit exposed so I can manually solder them since this is what I will do?

is there anything else besides this? so I can do them all together THEN panelize the board again.

[BrianHG]

What you see is not the exposed pad.  It is the SMT Paste stencil cut-out opening.  This is a large lazer cut metal sheet which JLPCB uses with a squeegee to apply solder-paste (like a silkscreen process) before the components are mounted.

There should only be an exposed pad right underneath the switcher IC as shown the switcher IC's data sheet.  Not that yellow rectangle you have above the center of the IC.

All the other solder-paste openings are correct.  Do not confuse this with the 'solder-mask' which removes the green protective paint layer to expose the PCB copper for connection.

[BrianHG]

you mean the full pad should be exposed? I thought this was the case within the footprint itself...

Glad you made me check, there are more errors.  (It's over 9000)

All the red arrows are errors, the green arrows are correct.

The purple is the exposed solder mask copper while the yellow on top is the solder paste stencil.

You have the switchers whose exposed pad AND solder paste stencil isn't under the 8 pin IC or the right size.
You have D3 by the opamp which for some reason doesn't have any solder paste.

And for the large power connectors, for some reason, the circular pads aren't solder-masked out, but the square pin 1 on them is properly solder masked out.

Now, my old gerber viewer has shown a D-code error on 2 files which may account for the bug, but you need to double check.

Once fixed, I would do a partial flood fill of the switcher IC's heatsink pad to the outer surrounding area above and below the IC to draw away some heat build up.

[BrianHG]

See the shaded green area as an example fill area for each switcher IC.
That shaded green copper fill should match the net of the exposed +VCC power pad beneath so it becomes 1 large filled blob.

[VEGETA]

I used this gerber viewer: http://mayhewlabs.com/webGerber/

and gave me different results. diodes are ok here. Also, I think the connectors are too since they are through hole parts and also solder masked... I remember in kicad that they are solder masked.

check a better render at this gerber viewer too: https://myproto.eu/resources/online-gerber-viewer/

both show the same results, and you got one correct thing which is the switcher heatsink pad.. since it is from the footprint library itself not some render difference.

That shaded green copper fill should match the net of the exposed +VCC power pad beneath so it becomes 1 large filled blob.

I can just create a small copper area (without pads or so) in the green (bottom) layer to do so. but it won't be perfect since the pads of components near it are also on green layer so I doubt it will be that useful. what do you think?

___

Edit: see here https://www.eevblog.com/forum/beginners/small-mosfet-for-capacitance-multiplier-in-a-small-psu/msg3348692/#msg3348692

it shows the through hole connectors being solder masker properly, also on the same page there is a 3d picture for the panel showing it correctly.

[BrianHG]

I can just create a small copper area (without pads or so) in the green (bottom) layer to do so. but it won't be perfect since the pads of components near it are also on green layer so I doubt it will be that useful. what do you think?

I don't know about Kicad, but in Altium, we would call this a 'Polygon Flood Fill', where I would set the fill's net name to the same as the IC's exposed pad and select the feature fill over same net & remove dead copper.  The PCB software would take my rectangular box as a guide and automatically flood fill in all the spare area I marked in green with copper connected to that exposed pad while removing any parts which can not be fitted or connected to that pad.

[VEGETA]

I can just create a small copper area (without pads or so) in the green (bottom) layer to do so. but it won't be perfect since the pads of components near it are also on green layer so I doubt it will be that useful. what do you think?

I don't know about Kicad, but in Altium, we would call this a 'Polygon Flood Fill', where I would set the fill's net name to the same as the IC's exposed pad and select the feature fill over same net & remove dead copper.  The PCB software would take my rectangular box as a guide and automatically flood fill in all the spare area I marked in green with copper connected to that exposed pad while removing any parts which can not be fitted or connected to that pad.

it is 100% in kicad as you said for altium. my point is that it won't be a perfect square due to pads of components near it...

kindly see my above post about gerber issues... what do you think? is it that your software is bad or what exactly? since kicad shows it correctly.

[BrianHG]

Except for the switcher ICs center exposed pad, everything else looks correct in those renderings.

As for the flood fill, all you want is maximum copper fill.  Let the fill hug all the corners and edges, as much as it safely can.

[VEGETA]

Except for the switcher ICs center exposed pad, everything else looks correct in those renderings.

As for the flood fill, all you want is maximum copper fill.  Let the fill hug all the corners and edges, as much as it safely can.

Alright, this is easy. I just need to return from work to do it.

copper zone under the switchers + modify the footprint in order to include solder stencil of the pad under the IC along with the outter portion.

[VEGETA]

Hi

i have modified the footprint to be exactly what we want. under the ic is solder masked + solder paste, while the pad outside is just solder masked without paste.

btw, should I do something similar to the mosfets to be able to solder them properly? I know I can just put them then use the pads and so on to solder them.

I tried making a copper area around the switchers as we agreed, but it didn't produce good results so I scraped it. it only put a little extra area in a random way since, as i said, the area is tight and full of pads on the same layer.

anything else we need? so I can panelize the boards.

I posted the single board gerbers for you on PM.

[BrianHG]

Hi

i have modified the footprint to be exactly what we want. under the ic is solder masked + solder paste, while the pad outside is just solder masked without paste.

You shouldn't have masked out copper above the footprint.  Also, redo the footprint to match the attached land pattern 'EXACTLY', including all 8 pads.  Your footprint is bleeding and oversized compared to the manufacturer's expressly recommended land pattern and it wont mount properly with excess solder everywhere.

btw, should I do something similar to the mosfets to be able to solder them properly? I know I can just put them then use the pads and so on to solder them.

The mosfets are correct.  In fact, that big ' + ' in the paste stencil (but not in the solder mask) in the middle of them is so that the stencil remains strong without gigantic holes and not too much solder will be deposited under them so they may solder down flat & properly.

The advantage of removing soldermask on the other side of the PCB is only beneficial if you were to solder a heatsink on that side of the PCB, but, you also create an open electrical circuit on that side.

You may turn off on the D2PAK's throug-hole pads the solder mask for the bottom side to get rid of that.

To make the flood-fill look better under the switchers, maybe try a smaller gap clearance constraint of something like 10mil and trace thickness of 6mil.  This will fill out and hug the contours around the SMD there much better.

[BrianHG]

I believe that the 'Exposed Pad' paste stencil should be shrunk by 50-80% according to this document.  Or, at least make a similar patter to what you have on the mosfets.  See below:  (Note, this is not the same EPAD SO-8, but a close example.  Approach #1 is the simplest.)

[VEGETA]

I adjusted the entire footprint to be exactly as datasheet. pads are 2.2mm x 0.8mm (was 2x0.6), the thermal pad under it is now as the datasheet says (+-0.01mm) and pretty much you can say it is identical now.

I did modify the tracks to go along with new sizes, not too much done so no problem.

Kindly see the attached images of the switcher footprint mask, paste, and copper. I believe this is correct.

Copper is not so important here as it is straight forward.

Mask is as it supposed to be, all copper pads and thermal pad are exposed (not covered by solder mask). that includes the extra portion of the thermal pad.

paste is the same as mask, although I wanted to exclude the extra portion but thought it won't hurt. What do you think?

_______

As for copper under the switchers, I don't think it is that necessary. we already have thick traces with small area as you see. making such small tolerances to fit a small little blob of copper is not that beneficial and might not be good with pcb manufacturer. scrap the idea.

[BrianHG]

There shouldn't be that extra rectangle pad above the IC.  In the datasheet on page 12 or 15, it says to copper flood fill as much area around the IC as possible.  You will get the most from filling the VCC with my above specifications.
The other pin which will draw heat away from the IC is the GND pad.  You can also do a small flood fill on the right to add copper to pull heat away from the switcher IC.  Copper/tin only pulls heat away if it is directly connected.  The PCB material is actually a good insulator of heat.

As for the paste stencil, shrink that center power tab by 50% in area as my documentation listed above.  If you do not, when JLPCB assembles this PCB, that IC will be floating on a bubble of solder.

[VEGETA]

Done.

I shrunk the under pad and now the extra portion is done. I have made copper filling as datasheet says, as long as I could do it. I didn't modify anything, I mean no trace tolerances or any of that. I don't know how to do it in kicad for a specific area of the board since the rest must be within spec.

anyway, I don't think it is necessary. what is done now should be enough. I believe if we keep looking we won't finish it.

if there are no major issues left, i will send the gerbers to you for final verification before panelization.

[BrianHG]

That looks correct except the paste pad need to shrink by 50-70% in ''square area'' (not length and width).

[VEGETA]

That looks correct except the paste pad need to shrink by 50-70% in ''square area'' (not length and width).

I don't understand.

what square area? I shrunk its size and thus the mask + paste.

[BrianHG]

That looks correct except the paste pad need to shrink by 50-70% in ''square area'' (not length and width).

I don't understand.

what square area? I shrunk its size and thus the mask + paste.

The paste needs to be smaller than the mask for this 1 pad.  The paste adds solder.  Too much solder means the IC will float on liquid metal when baked and will not sit flush on the PCB.  The mask you have is correct.

When I say square, this means if you shrink the paste horizontally by half and vertically by half, the size reduction is 75%.  IE, if your original pad is 4x4mm, it is 16 square mm.  If you make the paste half width by half height of the mask, making the middle 2x2mm, only 4 square mm, you can see you shrunk the square area by 75%, IE 16mm²*0.75 = 12mm², 16mm²-12mm²=4mm².

[VEGETA]

so to sum up, I should keep the current mask as is but make the paste a bit smaller. I don't know if I can match such precise measurements but at least close to them.

the current mask\paste is 2mmx3.5mm. what is the optimal dimensions?

I could make the copper + mask = 3.5x3.5, then make the paste 2.5x2.5 or even 2x2. what do you think?

[VEGETA]

I changed the pad size according to AOZ1284 datasheet (2.5x3.5), then made the mask as its size + a little bit more. Then made the stencil opening less... it is now about 2x2.5.

see the images below, especially the close-up of mask (bronze color)+stencil (cyan blue color).

so, I think this is what your previous datasheet and won't allow the IC to float on blob of solder.

also, the copper for the pad is very good now.

[BrianHG]

I changed the pad size according to AOZ1284 datasheet (2.5x3.5), then made the mask as its size + a little bit more. Then made the stencil opening less... it is now about 2x2.5.

Still a little big.  Make is around 1.7x2.4.

Also, take a look at the attached red arrow..

[VEGETA]

it is now about 1.7x2.4 and the trace is done.

[BrianHG]

 

[VEGETA]

at last we can go for it?

gonna send you the panel just in case xD 

when I start selling them, I will surely give you a cut. I insist and you deserve it.

[BrianHG]

at last we can go for it?

gonna send you the panel just in case xD 

when I start selling them, I will surely give you a cut. I insist and you deserve it.

Yes, go for it.
Relax, my help is free...

[VEGETA]

at last we can go for it?

gonna send you the panel just in case xD 

when I start selling them, I will surely give you a cut. I insist and you deserve it.

Yes, go for it.
Relax, my help is free...

Now it is in your PM.

I know you helped for free but I also like to give rights to those who deserve it. We'll wait and see what happens.

[VEGETA]

The KIA mosfet doesn't have any charts showing the Vgs curve.

Try this one : https://lcsc.com/product-detail/MOSFET_KIA-Semicon-Tech-KND3403A_C382143.html

Or you can trust the one you picked or find a data sheet with the Vgs curve table shown.

Why did you pick this particular mosfet? I need to know what is in the Vgs curve we need to look for.

gate voltage is 3.3 and 5v, so I assume it should be in the linear region at that voltage in order to regulate?

I have ordered the PCBs but still going to need to order the top board components... this is why I need to know the MOSFETs.

[VEGETA]

I realize I made a mistake in picking the inductor!

the inductor footprint is 7.3x7.3 but the one in the BOM (and paid for) is 12.5x12.5! it is the 10uH for both switchers and one in the top side.

I am searching for replacements but none are with enough current!


Edit:

I found these replacements:

3.3uH @ 4.2A current: https://lcsc.com/product-detail/Power-Inductors_YJYCOIN-YPRH0704-3R3M_C516316.html
2.2uH @ 6A current   : https://lcsc.com/product-detail/Power-Inductors_YJYCOIN-YPRH0704-2R2M_C514805.html
1.0uH @ 9A current   : https://lcsc.com/product-detail/Power-Inductors_YJYCOIN-YPRH0704-1R0M_C338840.html >> I presume this is too low of inductance.

I sent an email to their support telling them to change it to this:

https://lcsc.com/product-detail/Power-Inductors_Sunltech-Tech-SLH0704S2R2MTT_C216193.html
which is 2.2uH @ 6.2A since it was the only thing available.

this one is slightly bigger at 7.4x7.4mm:

https://lcsc.com/product-detail/Power-Inductors_Gotrend-Tech-GSDRK74P-4R7M_C142420.html

but it is 4.7uH @ 5A.


____

so picking the 2.2uH inductor here is some datasheet calculations:

ripple current = [V_out * (1-V_out/V_in)]/(frequency*inductance)

which equals to 0.680A if you plug 2MHz frequency and 2.2uH inductance with 6.24v and 12v.

inductor chosen can easily handle the maximum current but I am not really sure about the ripple in final output... both voltage and current ripple?!

notice that nothing we can do now since the boards are already paid for. Keep changing the thing made us not aware of the change in footprints.

[BrianHG]

The KIA mosfet doesn't have any charts showing the Vgs curve.

Try this one : https://lcsc.com/product-detail/MOSFET_KIA-Semicon-Tech-KND3403A_C382143.html

Or you can trust the one you picked or find a data sheet with the Vgs curve table shown.

Why did you pick this particular mosfet? I need to know what is in the Vgs curve we need to look for.

gate voltage is 3.3 and 5v, so I assume it should be in the linear region at that voltage in order to regulate?

I have ordered the PCBs but still going to need to order the top board components... this is why I need to know the MOSFETs.

It's the avalanche curve at ~2v, almost completely just at 3v at 100amps for that mosfet.  It is a low voltage logic level mosfet.  The cheaper mosfet you chose has no spec in the data sheet and I assume it is a cheap clone of:
IPD50N03 https://lcsc.com/product-detail/MOSFET_Infineon-Technologies-IPD50N03S2-07_C536767.html
or STD50N03.

Compare the voltage difference between gate and source when drawing ~5-10amps.

This tells you how many more volts the opamp needs to send to the gate compared to your desired output voltage when drawing ~5amps.  Note it may be a little higher since we are operating so close to the voltage at the Drain.

[BrianHG]

I realize I made a mistake in picking the inductor!

the inductor footprint is 7.3x7.3 but the one in the BOM (and paid for) is 12.5x12.5! it is the 10uH for both switchers and one in the top side.

I am searching for replacements but none are with enough current!


Edit:

I found these replacements:

3.3uH @ 4.2A current: https://lcsc.com/product-detail/Power-Inductors_YJYCOIN-YPRH0704-3R3M_C516316.html
2.2uH @ 6A current   : https://lcsc.com/product-detail/Power-Inductors_YJYCOIN-YPRH0704-2R2M_C514805.html
1.0uH @ 9A current   : https://lcsc.com/product-detail/Power-Inductors_YJYCOIN-YPRH0704-1R0M_C338840.html >> I presume this is too low of inductance.

I sent an email to their support telling them to change it to this:

https://lcsc.com/product-detail/Power-Inductors_Sunltech-Tech-SLH0704S2R2MTT_C216193.html
which is 2.2uH @ 6.2A since it was the only thing available.

this one is slightly bigger at 7.4x7.4mm:

https://lcsc.com/product-detail/Power-Inductors_Gotrend-Tech-GSDRK74P-4R7M_C142420.html

but it is 4.7uH @ 5A.


____

so picking the 2.2uH inductor here is some datasheet calculations:

ripple current = [V_out * (1-V_out/V_in)]/(frequency*inductance)

which equals to 0.680A if you plug 2MHz frequency and 2.2uH inductance with 6.24v and 12v.

inductor chosen can easily handle the maximum current but I am not really sure about the ripple in final output... both voltage and current ripple?!

notice that nothing we can do now since the boards are already paid for. Keep changing the thing made us not aware of the change in footprints.

Check these out.  Lower resistance, higher current, the better:
https://lcsc.com/product-detail/Power-Inductors_TAI-TECH-TMPA0605SV-100MN-D_C305195.html
https://lcsc.com/product-detail/_Chilisin-Elec-HPPC06030-100M-Q8_C329517.html
https://lcsc.com/product-detail/Power-Inductors_YJYCOIN-YSPI0750-100M_C718402.html
https://lcsc.com/product-detail/Power-Inductors_SXN-Shun-Xiang-Nuo-Elec-SMMS0650-100M_C149584.html

[VEGETA]

Check these out.  Lower resistance, higher current, the better:
https://lcsc.com/product-detail/Power-Inductors_TAI-TECH-TMPA0605SV-100MN-D_C305195.html
https://lcsc.com/product-detail/_Chilisin-Elec-HPPC06030-100M-Q8_C329517.html
https://lcsc.com/product-detail/Power-Inductors_YJYCOIN-YSPI0750-100M_C718402.html
https://lcsc.com/product-detail/Power-Inductors_SXN-Shun-Xiang-Nuo-Elec-SMMS0650-100M_C149584.html

these are 7.1*6.6mm but our footprint is 7.3x7.3mm.. will these be ok? even in smt assembly machine? I can solder them by hand though.

however, as a worst case scenario... is using that 2.2uH will cause harm to our final output?

mosfet choice

well, we will have a Vgs of 3.3v and 5v, this mosfet (https://lcsc.com/product-detail/MOSFET_KIA-Semicon-Tech-KND3403A_C382143.html) has high current at these VGS values to be fully on since it is a very low voltage logic level mosfet.

with our drain-to-source (Vds) voltage being about 2.5v~3v, it shows +60A on Vds vs I curve.

can you explain a bit more since I find it kinda acting like a fully on switch at gate voltage of 3.3v and 5v, not in Linear region which what regulation is all about.

[BrianHG]

Check these out.  Lower resistance, higher current, the better:
https://lcsc.com/product-detail/Power-Inductors_TAI-TECH-TMPA0605SV-100MN-D_C305195.html
https://lcsc.com/product-detail/_Chilisin-Elec-HPPC06030-100M-Q8_C329517.html
https://lcsc.com/product-detail/Power-Inductors_YJYCOIN-YSPI0750-100M_C718402.html
https://lcsc.com/product-detail/Power-Inductors_SXN-Shun-Xiang-Nuo-Elec-SMMS0650-100M_C149584.html

these are 7.1*6.6mm but our footprint is 7.3x7.3mm.. will these be ok? even in smt assembly machine? I can solder them by hand though.

Check if the pads will solder on from the cad drawings.
If not, enlarge your solder pads so you support more inductors in the same space.
I'd say make sure you can place all 4 of the ones I listed so you have plenty of stock to choose from.

however, as a worst case scenario... is using that 2.2uH will cause harm to our final output?

mosfet choice

well, we will have a Vgs of 3.3v and 5v, this mosfet (https://lcsc.com/product-detail/MOSFET_KIA-Semicon-Tech-KND3403A_C382143.html) has high current at these VGS values to be fully on since it is a very low voltage logic level mosfet.

with our drain-to-source (Vds) voltage being about 2.5v~3v, it shows +60A on Vds vs I curve.

can you explain a bit more since I find it kinda acting like a fully on switch at gate voltage of 3.3v and 5v, not in Linear region which what regulation is all about.

See example mosfet charts below...
Now, with the 5v out mosfet drawing 3 amps, can the op-amp give enough voltage to the gate of the second mosfet?

[VEGETA]

Check if the pads will solder on from the cad drawings.

yes it should fit as seen in attachment. the 7.3 full length of the inductor should cover the pads easily... thus, it is actually better to have 6.6mm width to save a bit of room.

I will make a slight modification in the next batch to make the solder pads a bit longer inside so it can fit smaller footprints too. this batch is already sent and paid for,  no surrender!!

See example mosfet charts below...
Now, with the 5v out mosfet drawing 3 amps, can the op-amp give enough voltage to the gate of the second mosfet?

here is what I think:

our op-amp takes the clean filtered 12v as power. so it can drive output voltage up to say 10v since it is not rail to rail or so good. that is why first mosfet is totally ok since all we need is 2 Vgs to achieve 5v output @ 3 amps maximum. that means 5v + 2v = 7 volts from op-amp... no worries.

as for 2nd mosfet... we need 4.5v Vgs, means 4.5v+5v = 9.5v from opamp... I say yes we can but kinda tight tolerance.

so first mosfet is the best choice.. and since I will buy components myself, then I will get other mosfets too to try them and see.

[BrianHG]

here is what I think:

our op-amp takes the clean filtered 12v as power. so it can drive output voltage up to say 10v since it is not rail to rail or so good. that is why first mosfet is totally ok since all we need is 2 Vgs to achieve 5v output @ 3 amps maximum. that means 5v + 2v = 7 volts from op-amp... no worries.

Our opamp is being powerd through a 100ohm series RC resistor cap to filter power.  Only expect it's VCC to have ~10v.

so first mosfet is the best choice.. and since I will buy components myself, then I will get other mosfets too to try them and see.

Just look at the mosfet's data sheet's Vgs transfer characteristics.  You will see the approximate voltage difference between Gate and Source at a specific current draw at usually 3 temperatures.

Your snapshot is that of a capacitor, not inductor.  Make clean snapshots of 1 layer for easier reading...

[VEGETA]

Our opamp is being powerd through a 100ohm series RC resistor cap to filter power.  Only expect it's VCC to have ~10v.

now 2nd mosfet won't work since 10v is the peak and this opamp is not rail to rail. we stick to first one and I will try to search for other alternatives although this one is very cheap in +100 quantity.

Just look at the mosfet's data sheet's Vgs transfer characteristics.  You will see the approximate voltage difference between Gate and Source at a specific current draw at usually 3 temperatures.

so my analysis above with little calculations are good? aside from the rail being 10v not 12v. we stick to our first mosfet since it works and cheap.

Your snapshot is that of a capacitor, not inductor.  Make clean snapshots of 1 layer for easier reading...

now attached for the inductor, it does fit.

actually, no need for any snapshot since the length is 7.3mm exactly as the footprint. the difference is only the width which is not important at all!

[BrianHG]

That all looks good...

[BrianHG]

So, does it work?

[VEGETA]

So, does it work?

I have problems with JLCPCB since they keep cancelling the order. One time cuz the wrong inductor part and the other one for small mouse bites, they want them to be 5mm. I did that and will send the offer again today xD.

I will keep you posted always.

[VEGETA]

and now I am up to another freaking problem, the new visa credit card classified my payment move to JLCPCB as "possible fraud" when paying via paypal or directly via the card! I am trying to see the solution but it will take until Sunday if I am lucky, but most likely won't be good.

the laughable thing is that the previous card is mastercard credit and it accepted the payment a week ago. from the same bank!! same central bank!!

I messaged pcbway to see what can they offer as a turnkey solution.

my hope for jlcpcb is if i can transfer money from my credit card to my paypal then use paypal's own money to pay directly to them. this worked well for me on a previous situation with hetzner. however i used to pay my friend then he refunds them to paypal... this will take losses which I cannot afford for +300$ payments.

I just cannot believe this is happening

[VEGETA]

Hello,

boards arrived and they are with DHL to be delivered to me within days.

Our chosen Mosfet (https://lcsc.com/product-detail/MOSFET_KIA-Semicon-Tech-KND3403A_C382143.html) is out of stock thus I searched and found these alternatives:

https://lcsc.com/product-detail/MOSFET_PUOLOP-PTD3006_C479048.html
https://lcsc.com/product-detail/MOSFET_PUOLOP-PTD15N10_C479050.html
https://lcsc.com/product-detail/MOSFET_SINO-IC-SE4020B_C396085.html

what do you think?

I will also get the 1000uF cap: https://lcsc.com/product-detail/Aluminum-Electrolytic-Capacitors-SMD_ROQANG-RVT1C102M1010_C72470.html

Let's pick a MOSFET soon, so I can order fast.

_______

The remaining items are the connectors and heatsink. Connectors from Mouser, I got all P\N needed. I will try to see what to do about heatsinks locally.

However, if you can, please search for a good thermal tape product on Mouser to be used to press-fit the heatsinks. I can't get stuff from digikey due to some problems, and since I am getting a big package from Mouser I will get all stuff from them. If you can't find cheap stuff on Mouser, then maybe I can get this one single item via ebay or amazon but I prefer mouser now.


_________

Meanwhile, I will test the thing with installing IRLIZ44N mosfets (through-hole). It should work since it requires 2v for maximum of 3 amps. I only need it to show that it works well, I have heatsinks I can bolt it on it if I really need to fully operate the thing.

However, I will still need to get the top-side inductor too... so I could just short the inductor terminals just to see if the whole thing works... regardless of output quality. good move right?


Also, what noise and ripple is expected to show on output? single digit uVs or more?

I really hope it works as intended. Do you honestly think it wouldn't work? this could be a nightmare for me really! Don't like to even think about it. However, I really don't think there are any reasons that it wouldn't work... what about you?

[BrianHG]

Hello,

boards arrived and they are with DHL to be delivered to me within days.

Our chosen Mosfet (https://lcsc.com/product-detail/MOSFET_KIA-Semicon-Tech-KND3403A_C382143.html) is out of stock thus I searched and found these alternatives:

https://lcsc.com/product-detail/MOSFET_PUOLOP-PTD3006_C479048.html
https://lcsc.com/product-detail/MOSFET_PUOLOP-PTD15N10_C479050.html
https://lcsc.com/product-detail/MOSFET_SINO-IC-SE4020B_C396085.html

what do you think?

I will also get the 1000uF cap: https://lcsc.com/product-detail/Aluminum-Electrolytic-Capacitors-SMD_ROQANG-RVT1C102M1010_C72470.html

Let's pick a MOSFET soon, so I can order fast.

_______

The remaining items are the connectors and heatsink. Connectors from Mouser, I got all P\N needed. I will try to see what to do about heatsinks locally.

However, if you can, please search for a good thermal tape product on Mouser to be used to press-fit the heatsinks. I can't get stuff from digikey due to some problems, and since I am getting a big package from Mouser I will get all stuff from them. If you can't find cheap stuff on Mouser, then maybe I can get this one single item via ebay or amazon but I prefer mouser now.


_________

Meanwhile, I will test the thing with installing IRLIZ44N mosfets (through-hole). It should work since it requires 2v for maximum of 3 amps. I only need it to show that it works well, I have heatsinks I can bolt it on it if I really need to fully operate the thing.

However, I will still need to get the top-side inductor too... so I could just short the inductor terminals just to see if the whole thing works... regardless of output quality. good move right?


Also, what noise and ripple is expected to show on output? single digit uVs or more?

I really hope it works as intended. Do you honestly think it wouldn't work? this could be a nightmare for me really! Don't like to even think about it. However, I really don't think there are any reasons that it wouldn't work... what about you?

I have no clue about the brand's reputation, but, based on the data sheets, only this mosfet has a very low Vgs.
https://lcsc.com/product-detail/MOSFET_SINO-IC-SE4020B_C396085.html

Meanwhile, I will test the thing with installing IRLIZ44N

What's the Vgs at 3-4amps?

I really hope it works as intended. Do you honestly think it wouldn't work? this could be a nightmare for me really! Don't like to even think about it. However, I really don't think there are any reasons that it wouldn't work... what about you?

It should.  I've seen fake LM358 oscillate on the output, but, without a scope, you would never know.  The average output voltage would still look fine on the volt-meter.  A temp solution is usually a pull-down resistor on the output or 1000pf to 10000pf cap on the output of the op-amp.
Assuming the switchers work fine, the problem I listed above is the worst case scenario unless we did not catch something in the schematic.

[VEGETA]

I have no clue about the brand's reputation, but, based on the data sheets, only this mosfet has a very low Vgs.
https://lcsc.com/product-detail/MOSFET_SINO-IC-SE4020B_C396085.html

This has the lowest Vgs on 3 amps, but the others are also the in the good range. At least similar to our original pick. what is their problem in your opinion?

What's the Vgs at 3-4amps?

Here is the datasheet: https://www.infineon.com/dgdl/Infineon-IRLIZ44N-DS-v01_02-EN.pdf?fileId=5546d462533600a401535664286325cb

it is less than 3v max so I guess it is ok.

It should.  I've seen fake LM358 oscillate on the output, but, without a scope, you would never know.

This is what I think too, it should work. However, I don't have a scope now. I am thinking of assembling one unit then send it to you via EMS to check and take photos of the signals and especially the noise. I can test some analog scopes of my company but it is gonna take a lot of time to get one out...

A temp solution is usually a pull-down resistor on the output or 1000pf to 10000pf cap on the output of the op-amp.
Assuming the switchers work fine, the problem I listed above is the worst case scenario unless we did not catch something in the schematic.

I don't think we missed anything in the schematic, no way.

the output of the opamp already has 100R resistor and a 1nF capacitor on its output, we did this to make sure it won't oscillate if you remember.

now the funny thing is... JLCPCB for some unknown reason, didn't solder the switchers!!!!!!!!!!!!!!! now I cannot test anything at all 

I will order the switchers with the mosfets and other components, solder them manually...

_______

On another matter, I got quotes from PCBway to fully turnkey manufacture the panels and solder all components on all sides... it was way more expensive than this approach. the components alone were about 750$ and their assembly service is 500$ or a little bit less while PCB manufacture is just 135$. Do find 135$ + 500$ reasonable to this situation? assuming soldering all smt and through hole components on both sides. I could get the components myself and deliver them directly to them to save a bit of that huge 750$ but the main service is the same regardless.

while on JLCPCB costs about 360$ so far without extra components... gonna collect all data once we finish.

Got a simple conversation of a certain Aluminum local supplier, he said he can do the required heatsink very easily and cheaply... about less than 70$ for the entire 125 pieces. It won't be finned heatsink of course, just a rectangular cube (1.5 cm thickness) cut to suit the board... maybe 2.5x2cm of area. so heatsink is solved.

[VEGETA]

any news from you?

[BrianHG]

any news from you?

I'm stuck in a quarantine lock-down...
Bored to death...

(Everything else you selected looks fine...)

[VEGETA]

I'm stuck in a quarantine lock-down...
Bored to death...

you guys still on that!? we have normal life but after 12:00 midnight no one is allowed.

(Everything else you selected looks fine...)

here are summery of my selections:

Mosfet: gonna get all these 3 but mainly your suggestion for the default position.

https://lcsc.com/product-detail/MOSFET_PUOLOP-PTD3006_C479048.html
https://lcsc.com/product-detail/MOSFET_PUOLOP-PTD15N10_C479050.html
https://lcsc.com/product-detail/MOSFET_SINO-IC-SE4020B_C396085.html

1000uF cap:

https://lcsc.com/product-detail/Aluminum-Electrolytic-Capacitors-SMD_ROQANG-RVT1C102M1010_C72470.html

Inductor:

https://lcsc.com/product-detail/Power-Inductors_Sunltech-Tech-SLO0630H100MTT_C207842.html

Output connectors: these 2 are the ones to go, one is an official replacement of the other.

https://www2.mouser.com/ProductDetail/538-09-48-4069/
https://www2.mouser.com/ProductDetail/538-09-48-3064/

3-position connector (2 are used):

 https://www2.mouser.com/ProductDetail/571-1-1123724-2/

2-position connectors:

https://www2.mouser.com/ProductDetail/5716404452/

need 375 for 125 boards. Now under restocking from Mouser, so I got these alternatives:

https://www2.mouser.com/ProductDetail/TE-Connectivity/640388-2/?qs=%2Fha2pyFadugQXFuu0XZrQDI83R0hWQJW3xfg4GqlfBI%3D

Total price for extra components:

Switchers: 144$
Mosfets: 23$ (I will get 5 of the other 2, not calculated here)
Capacitor: 35$
Inductor: 11$
Connectors: 46$ + 14$ + 126$
Shipping: 66$ + 0$

TOTAL: 465$

What I paid so far: 358$ (PCB) + 271$ (customs)

Expected expenditure: ~50$ for 3D printed small part + ~30$ for DC connector (panel mount on the 3D printed part) + 150$ for extra customs and fees.

GRAND TOTAL: 1325$
cost per part: ~10-11$

[BrianHG]

I'm stuck in a quarantine lock-down...
Bored to death...

you guys still on that!? we have normal life but after 12:00 midnight no one is allowed.

(Everything else you selected looks fine...)

here are summery of my selections:

Mosfet: gonna get all these 3 but mainly your suggestion for the default position.

https://lcsc.com/product-detail/MOSFET_PUOLOP-PTD3006_C479048.html

No...
https://lcsc.com/product-detail/MOSFET_PUOLOP-PTD3006_C479048.html

[gnuarm]

Update:

I am using AOZ1284 with 20KOhm frequency set resistor... that means 2 MHz switching frequency.

I take the 12v into the AOZ1284 then output 3.8v for the 3.3v LDO and 5.5v for the 5v LDO (input of LDOs have 3x 10 uF ceramic caps). The LDOs are LM39302 (Chinese clones, cheap) which are followed by 1000uf elec. cap (10mm x 10mm one) + 5x 10 uF ceramic caps. The inductors are 10uH big size.

I was reading through this thread waiting to find someone to explain that a capacitance multiplier won't do anything a linear regulator won't do.  Then I see that you are misusing your linear regulator which is why the output is not very well regulated.  You don't provide any spec you are trying to meet, so I can't offer a real solution, but I can point out that giving a 3.3 volt output linear regulator 3.8 volts input is not enough to allow it to regulate fully.  If you read the spec on the linear it will specify a minimum drop out voltage, but at some specified drop in output voltage that will likely not be acceptable if it appears as ripple. 

Boost the input voltage to your linear regulator to at least 4.5 volts and you will see a big improvement in the regulation.

You guys mentioned 2MHz devices, well, here is one used... also followed by linear LDO with good amount of caps.

How much ripple do you think we get?

If you mean a low frequency (<10 kHz) you should see ripple below 1 mV.  However, keep in mind many linear regulators have specific requirements on the capacitors and the effective series resistance (ESR) to prevent oscillations. 

Higher frequencies on the power rail are referred to as noise and a linear regulator can't do much about them as it is out of their pass band.  That requires small ceramic capacitors and potentially power planes.

I imagine someone has pointed out to you all this, but I'm not going to read 10 pages of this tread to find out.  Good luck.

[VEGETA]

I'm stuck in a quarantine lock-down...
Bored to death...

you guys still on that!? we have normal life but after 12:00 midnight no one is allowed.

(Everything else you selected looks fine...)

here are summery of my selections:

Mosfet: gonna get all these 3 but mainly your suggestion for the default position.

https://lcsc.com/product-detail/MOSFET_PUOLOP-PTD3006_C479048.html

No...
https://lcsc.com/product-detail/MOSFET_PUOLOP-PTD3006_C479048.html

you mean this one won't work? why? it has the required Vgs. I wanted to order 5 pieces of it, but I am gonna stick to the one you mentioned before.

gnuarm

I suggest you go from last pages backwards then see the first schematic you stumble upon. We made 4.6v for 3.3v linear stage and about 6.25v for 5.5v stage. Plus, we use Mosfets for power regulation instead of ready-to-use linear ICs.

Cap multiplier was chosen since I liked the idea of ultra low noise for retro console (Dreamcast) instead of available solutions which uses switching regulators only.

[gnuarm]

gnuarm

I suggest you go from last pages backwards then see the first schematic you stumble upon. We made 4.6v for 3.3v linear stage and about 6.25v for 5.5v stage. Plus, we use Mosfets for power regulation instead of ready-to-use linear ICs.

Cap multiplier was chosen since I liked the idea of ultra low noise for retro console (Dreamcast) instead of available solutions which uses switching regulators only.

That's ok.  What you are not addressing is what you expect the cap multiplier to do that the linear regulator won't do.  Have you built anything that you found to not be suitable?  You talk about having the cap multiplier in contrast to a switcher, but that's not the question I have.  What do you think a cap multiplier will do that a linear regulator won't? 

I found a schematic using the LM317 in place of the capacitor.  So you have dropped the idea of a capacitor multiplier and are using an NPN to boost the regulator output.  Fine, I hope someone has advised you about this potentially affecting the stability of the LM317.  So be aware of that.  I just wanted to dispel the idea that a capacitance multiplier is better at removing low frequency (audible) ripple than a properly designed linear regulator.  What you have now IS a linear regulator.  These can be found to handle your load current, so you could do the same thing in a single package without the NPN.

[VEGETA]

That's ok.  What you are not addressing is what you expect the cap multiplier to do that the linear regulator won't do.  Have you built anything that you found to not be suitable?  You talk about having the cap multiplier in contrast to a switcher, but that's not the question I have.  What do you think a cap multiplier will do that a linear regulator won't?

I found a schematic using the LM317 in place of the capacitor.  So you have dropped the idea of a capacitor multiplier and are using an NPN to boost the regulator output.  Fine, I hope someone has advised you about this potentially affecting the stability of the LM317.  So be aware of that.  I just wanted to dispel the idea that a capacitance multiplier is better at removing low frequency (audible) ripple than a properly designed linear regulator.  What you have now IS a linear regulator.  These can be found to handle your load current, so you could do the same thing in a single package without the NPN.

check the schematic in here: https://www.eevblog.com/forum/beginners/small-mosfet-for-capacitance-multiplier-in-a-small-psu/msg3331484/#msg3331484

it is the final one, but a bit more finalized in kicad.

Here is my little explanation of this:

I feed 12v from a cheap or not-so-good generic switching supply to this board. The board must filter it properly to deliver as clean as possible 5v and 3.3v (amperage different between them).

12v is taken through a 100R resistor with lots of caps (1000uF + 22uF +100nF) into the 7805 linear regulator which outputs 5v and 3.3v via resistor divider. This "reference" signal is very clean since it was taken from a resistor divider which is the cap multiplier part of this design. the cap multiplier here is taken from V_filtered which is about 10v due to the dropout... it is the signal fed to the supply of the op-amp and then will be delivered to the gate of the mosfets. We kept changing it until we reached this formula.

Getting all of that into the linear 7805 is very beneficial to attenuate low frequency noise as you stated which is a further plus along with high capacitance + inductance which takes care of high frequency noise.

the rest is straightforward, the op-amp is fed with 3.3v and 5v from the reference clean signal and outputs the necessary to make the linear regulator mosfet regulates.

the trick here is the cap multiplier at the op-amp stage.

So is this a linear regulator? yes of course, but it is powered or enhanced by capacitance multiplier + switching pre-regulator.

If you are gonna design such a thing, what are you going to do? what parts to use? me and Brian took this project to the maximum by keep changing it and enhancing it... till we wished it end xD

[BrianHG]

I'm stuck in a quarantine lock-down...
Bored to death...

you guys still on that!? we have normal life but after 12:00 midnight no one is allowed.

(Everything else you selected looks fine...)

here are summery of my selections:

Mosfet: gonna get all these 3 but mainly your suggestion for the default position.

https://lcsc.com/product-detail/MOSFET_PUOLOP-PTD3006_C479048.html

No...
https://lcsc.com/product-detail/MOSFET_PUOLOP-PTD3006_C479048.html

you mean this one won't work? why? it has the required Vgs. I wanted to order 5 pieces of it, but I am gonna stick to the one you mentioned before.

At room temp, the Vgs is 4v at 3 amps.  That's twice as high as the other mosfets.  We wanted as low as 3v.
If you sell this device into a cold temperature area, like 10 degrees C, that Vgs would even increase a bit.
Also, the graphs we are provided in the data sheets do have an error margin associated with them.  This is one area where bipolar have much tighter voltage base emitter voltages.

However, all the other chosen mosfets Vgs at around 2-2.5v are fine.

[VEGETA]

I'm stuck in a quarantine lock-down...
Bored to death...

you guys still on that!? we have normal life but after 12:00 midnight no one is allowed.

(Everything else you selected looks fine...)

here are summery of my selections:

Mosfet: gonna get all these 3 but mainly your suggestion for the default position.

https://lcsc.com/product-detail/MOSFET_PUOLOP-PTD3006_C479048.html

No...
https://lcsc.com/product-detail/MOSFET_PUOLOP-PTD3006_C479048.html

you mean this one won't work? why? it has the required Vgs. I wanted to order 5 pieces of it, but I am gonna stick to the one you mentioned before.

At room temp, the Vgs is 4v at 3 amps.  That's twice as high as the other mosfets.  We wanted as low as 3v.
If you sell this device into a cold temperature area, like 10 degrees C, that Vgs would even increase a bit.
Also, the graphs we are provided in the data sheets do have an error margin associated with them.  This is one area where bipolar have much tighter voltage base emitter voltages.

However, all the other chosen mosfets Vgs at around 2-2.5v are fine.

Ah ok. I will request the stuff soon.

anyway, I can in the meantime (next 2 weeks so I can get home to have the boards)... I can connect 12v from my switching lab power supply (I DIY it, on my channel) on the 12v input... as well as, about 6.25v for the input of the 5v stage and similar for 3.3v rail. I guess this can be sufficient since I don't have the switchers now. What do you think?

the expected result from this is to see 3.3v and 5v on output rails.

[VEGETA]

I have ordered all the parts from mouser and LCSC.

Only thing remaining is the heatsink which is locally made. And the thermal tape needed which I still don't know which part to get.

[gnuarm]

That's ok.  What you are not addressing is what you expect the cap multiplier to do that the linear regulator won't do.  Have you built anything that you found to not be suitable?  You talk about having the cap multiplier in contrast to a switcher, but that's not the question I have.  What do you think a cap multiplier will do that a linear regulator won't?

I found a schematic using the LM317 in place of the capacitor.  So you have dropped the idea of a capacitor multiplier and are using an NPN to boost the regulator output.  Fine, I hope someone has advised you about this potentially affecting the stability of the LM317.  So be aware of that.  I just wanted to dispel the idea that a capacitance multiplier is better at removing low frequency (audible) ripple than a properly designed linear regulator.  What you have now IS a linear regulator.  These can be found to handle your load current, so you could do the same thing in a single package without the NPN.

check the schematic in here: https://www.eevblog.com/forum/beginners/small-mosfet-for-capacitance-multiplier-in-a-small-psu/msg3331484/#msg3331484

it is the final one, but a bit more finalized in kicad.

Here is my little explanation of this:

I feed 12v from a cheap or not-so-good generic switching supply to this board. The board must filter it properly to deliver as clean as possible 5v and 3.3v (amperage different between them).

12v is taken through a 100R resistor with lots of caps (1000uF + 22uF +100nF) into the 7805 linear regulator which outputs 5v and 3.3v via resistor divider. This "reference" signal is very clean since it was taken from a resistor divider which is the cap multiplier part of this design. the cap multiplier here is taken from V_filtered which is about 10v due to the dropout... it is the signal fed to the supply of the op-amp and then will be delivered to the gate of the mosfets. We kept changing it until we reached this formula.

Getting all of that into the linear 7805 is very beneficial to attenuate low frequency noise as you stated which is a further plus along with high capacitance + inductance which takes care of high frequency noise.

the rest is straightforward, the op-amp is fed with 3.3v and 5v from the reference clean signal and outputs the necessary to make the linear regulator mosfet regulates.

the trick here is the cap multiplier at the op-amp stage.

So is this a linear regulator? yes of course, but it is powered or enhanced by capacitance multiplier + switching pre-regulator.

If you are gonna design such a thing, what are you going to do? what parts to use? me and Brian took this project to the maximum by keep changing it and enhancing it... till we wished it end xD

I see your schematic and I don't think you understand what a capacitor multiplier is.  The linear part of the circuit is just a home brewed linear regulator.  There is no capacitor multiplier.  What you are calling a capacitor multiplier is just a linear feedback control circuit with a capacitor on an internal node... that may well make the circuit unstable and oscillate.  I don't know this cap will cause instability, that would require an analysis of the circuit.  It would be as good to pick a good, low noise linear regulator and use it.  Your circuit is fine, but you need to understand it and design it properly.  Rather than using a regulator as your voltage reference you can get better results with a low noise voltage reference. 

BTW, R19 should be 6.7k to match the impedance of the V_3.3 voltage divider to minimize offset voltage.

[VEGETA]

I see your schematic and I don't think you understand what a capacitor multiplier is.  The linear part of the circuit is just a home brewed linear regulator.  There is no capacitor multiplier.  What you are calling a capacitor multiplier is just a linear feedback control circuit with a capacitor on an internal node... that may well make the circuit unstable and oscillate.  I don't know this cap will cause instability, that would require an analysis of the circuit.  It would be as good to pick a good, low noise linear regulator and use it.  Your circuit is fine, but you need to understand it and design it properly.  Rather than using a regulator as your voltage reference you can get better results with a low noise voltage reference.

BTW, R19 should be 6.7k to match the impedance of the V_3.3 voltage divider to minimize offset voltage.

I know the linear part of the circuit is a linear regulator, that is what we wanted to do.

at first we went with a traditional capacitance multiplier circuit, then we kept changing it until it became like this. I don't remember why and when it happened since that was a long time ago.

I think the effect of cap multiplier is still there, not as textbook circuit though. instead of connecting the R+C circuit of the cap multiplier circuit directly into the gate of the mosfet, we put a linear regulator just before that to further aid in low noise and stability and perhaps the price since I was using 2 linear regulators instead. it will also isolate the high freq noise due to the big emi filter before the 7805. this means all of that ripple and noise will never reach the linear part to begin with, so the linear part has to deal with low freq. noise.

thus the mosfets needed more dropout room due to this effect which is why I bumped it up a bit and it is therefore not a low dropout regulator = need a heatsink.

maybe "capacitance multiplier" alone is not good enough to describe our circuit. but still provide the same or better results


maybe Brian can put his opinion on this too.

but why you think this circuit will not work?

[BrianHG]

Vegeta's title: Small MOSFET for capacitance multiplier in a small PSU was there because he wanted to get rid of the ripple from a switching supply.

The ripple on the output of a switching supply begins at 200KHz with signals in the 2MHz switching range depending on load.

Linear regulators pass these signals right through as their PSRR is designed to have a high rejection down below 1KHz.  In fact, some linear regulators enhance the ripple to the output.

Using a basic BJT capacitance multiplier can work since the emitter-follower configuration can reject high frequency modulation on the power being fed into the collector, however, the circuit looses output regulation as the base has nothing more than an RC filter with a load.

My original recommendation was to use a brand new ultra-low ripple, ultra low EMI switcher IC made by TI all on it's own, however, it's availability was only by direct order from TI.

     ---Vegeta needed MORE POWER---

The choice of using an opamp & 78L05 as a reference was price and availability.  Powering those from 12v through a 100ohm, 1000uf RC filter and a load current on them of ~2ma was chosen so that a complete cut and replacement of power within 1/10th of a second wouldn't nudge the output let alone a 200KHz to 2MHz signal making it through that first series 100uh to 1000uf, the even more 100ohm, 1000uf+10uf+0.1uf cap to GND RC filter stage making sure even if the switchers injected noise into the +12 could not get through that initial filter stage.

The mosfets are wired in a source follower configuration with the drain target voltage at 1v above the desired output since the switcher's output ripple according to the data sheet can dip ~0.5v under transient loads.  Having the op-amp powered close to 12v means the driving of the gate voltage will always be high enough to allow the source to drive the desired voltage out.  The only transmittance between the switcher and the linear output side is the internal capacitance between drain & gate & source.  This circuit is no longer a capacitance multiplier though tying the gate to a reference voltage in a source follower configuration where that gate does not have any noise coming from the switcher is keeping close to the theme, except now, with an additional negative feedback & reference, we can assure a degree of precision voltage on the output even with a wide shift in current load.

[gnuarm]

I know the linear part of the circuit is a linear regulator, that is what we wanted to do.

at first we went with a traditional capacitance multiplier circuit, then we kept changing it until it became like this. I don't remember why and when it happened since that was a long time ago.

What I am trying to tell you is that this circuit is no longer a capacitive multiplier... period!  So you can forget that term.  It is just a linear regulator following a switcher.  The linear regulator has frequency limitations because of the opamp and the capacitor you have on the gate imposes more frequency limitations exacerbating the problem.  The only high frequency filtering you will see is due to the capacitors on switcher outputs and the linear outputs.  C38 and C39 are on the control loop in a way that is detrimental to performance. 

I think the effect of cap multiplier is still there, not as textbook circuit though. instead of connecting the R+C circuit of the cap multiplier circuit directly into the gate of the mosfet, we put a linear regulator just before that to further aid in low noise and stability and perhaps the price since I was using 2 linear regulators instead. it will also isolate the high freq noise due to the big emi filter before the 7805. this means all of that ripple and noise will never reach the linear part to begin with, so the linear part has to deal with low freq. noise.

What "big EMI filter"  I see a couple of 22uF caps.  That's a good start, but it won't reduce the EMI so much.  Looking at your PCB artwork it looks like you are running the ground and power on traces rather than planes.  These traces seem to be forming long loops which create EMI.  Switching regulators require careful attention to detail.  Get a data sheet for a Linear Technology part and read every detail.  The best way to eliminate noise is to not generate it.

thus the mosfets needed more dropout room due to this effect which is why I bumped it up a bit and it is therefore not a low dropout regulator = need a heatsink.

maybe "capacitance multiplier" alone is not good enough to describe our circuit. but still provide the same or better results


maybe Brian can put his opinion on this too.

but why you think this circuit will not work?

I am very worried about the impact of adding a capacitor to the control loop in your linear regulator.  As I've said several times, you will get a much better result if you just drop the idea of designing your own linear regulator and pick a chip that has a low noise specification.  I can't think why you feel professionally design voltage regulators won't do a good job. 

I don't mean to be rude, but you don't actually understand how to design a linear regulator.  The capacitor you think is helping to filter the output is actually preventing the regulator from working to remove noise.  The only thing in your favor is that the corner frequency of the RC is about 1.6 MHz.   So lower frequency noise will still be regulated.  Since this is above the LM358 bandwidth it may not actually be harming anything, but it clearly isn't helping anything as you seem to think it does. 

Consider how the control loop works.  If the output droops a bit it feeds back to the inverting input of the op amp.  That pushes the op amp output up a bit which drives the gate higher which pulls the FET source (the circuit output) up to the proper level again.  That's good.  Add the RC filter between the op amp and the gate and you get a delay between the op amp responding and the FET being driven higher.  This allows the output more time to drift.  Not good.  In the worst case the delay is long enough that the op amp has had time to drive a significantly larger amount higher on its output.  Then when the the circuit output finally changes and drives the op amp back it has now over driven the FET and the op amp output is further delayed in correcting that... producing an oscillation.  It is not unusual for designers to take special precautions on high speed circuits to minimize pF of stray capacitance so it doesn't cause oscillations.  They certainly do not add any capacitance.

If you want to produce a good power supply design, focus on implementing a good layout and add a section of LC filtering to the output of the switcher.  That will cut the high frequency noise significantly.  There should not be measurable low frequency noise after a proper linear regulator.  Also read the linear regulator data sheet carefully as they often have specifications on the input and output capacitors to prevent oscillation. 

[gnuarm]

The mosfets are wired in a source follower configuration with the drain target voltage at 1v above the desired output since the switcher's output ripple according to the data sheet can dip ~0.5v under transient loads.  Having the op-amp powered close to 12v means the driving of the gate voltage will always be high enough to allow the source to drive the desired voltage out.  The only transmittance between the switcher and the linear output side is the internal capacitance between drain & gate & source.  This circuit is no longer a capacitance multiplier though tying the gate to a reference voltage in a source follower configuration where that gate does not have any noise coming from the switcher is keeping close to the theme, except now, with an additional negative feedback & reference, we can assure a degree of precision voltage on the output even with a wide shift in current load.

Yes, I was able to sus out most of that from reading the schematic.  I didn't at first understand what you were saying about the input filtering, but now I get that you are isolating the noise from the op amp supplies.  They don't show up in the schematic I have, but I can see that would be a concern. 

The linear regulator is a basic configuration that is available in chip form, separate power sources for the internal circuits and the regulated output.  This is typically so the control circuit can work with a higher voltage to manage the control circuitry and use a lower voltage for the power path to minimize losses just as you are doing. 

You mention that the switching regulator creates noise starting at 200 kHz and that somehow the use of a FET will help to stop that from reaching the output.  That is the same circuit as used in many commercial regulators.  I'm not clear on how your circuit will improve on those designs.  The internal FET is just a FET.  It is the internal op amp that limits the performance frequency range, same as in your design.  Adding the capacitor can be detrimental to the operation of the feedback circuit.  Are you suggesting that it acts as a voltage divider for the high frequency noise that couples from the drain to the gate? 

Have you looked at any of the chip regulators that separate the two power connections for different voltages?  Do you have any expectations on how this circuit will work compared to those?  How do you expect to keep the control loop stable?

[VEGETA]

What I am trying to tell you is that this circuit is no longer a capacitive multiplier... period!

correct, but we can't change the name of the thread. also, we started wanting this to be a cap multiplier, then kept slowly changing it until it became like this. now we cannot change the name of the thread so there is that.

The linear regulator has frequency limitations because of the opamp and the capacitor you have on the gate imposes more frequency limitations exacerbating the problem.

the small capacitor (1nf) on mosfet gate plus the resistor is to ensure stability, especially the resistor.

What "big EMI filter"  I see a couple of 22uF caps.

by that I meant the filtering on 12v rail + the filtering before 7805 (op-amp supply). add to them the filtering before each switcher ic.

22uf is on op-amp positive input.

Looking at your PCB artwork it looks like you are running the ground and power on traces rather than planes.

maybe that is not the final layout since we stalled for months until we settled on on, literally tens of times we changed it. I can send the project to you on private if you want to see the final stuff.

I am very worried about the impact of adding a capacitor to the control loop in your linear regulator.

the 1nf one?

As I've said several times, you will get a much better result if you just drop the idea of designing your own linear regulator and pick a chip that has a low noise specification.

I already manufactured the boards and should be ready to be finalized soon when the rest of components arrive.

I actually started doing just that and I think I still have the schematic. it was like this: Switching regulator -> LC filter -> cap multiplier -> linear regulator with caps on the output. However the cap multiplier part got us where we are now until we changed the entire thing.

Consider how the control loop works.

well, we didn't design this to be like a bench power supply or anything with vastly changing loads and so on. the load pretty much won't change as it is a retro gaming console with only one thing to do continuously.

Add the RC filter between the op amp and the gate and you get a delay between the op amp responding and the FET being driven higher.

adding that 100R is necessary for op-amp and mosfet stability, and the mosfet gate itself is capacitive. we only put 1nF to ensure more stability as I used to suffer from such particular circuits oscillating due to no cap on that place.... but that is on a linear bench psu on ltspice.

you suspect that it could output the wrong voltage if a fast change happens?

if this is the only issue in the design and it caused a problem, i can simply remove that 1nF from the board very easily.

If you want to produce a good power supply design, focus on implementing a good layout and add a section of LC filtering to the output of the switcher.  That will cut the high frequency noise significantly.  There should not be measurable low frequency noise after a proper linear regulator.  Also read the linear regulator data sheet carefully as they often have specifications on the input and output capacitors to prevent oscillation.

trust me, we spent months on layout from datasheets and app notes... down to mm positioning of traces.

by "proper linear regulator" you mean those expensive ICs? I could buy 3~5$ one from Analog Devices but then it will cost a lot per board unlike the opamp+mosfet which is less than 0.5$ combined. I would need 2 of them for 2 rails which will be like 6-10$ per board just for 2 ICs.

I've been searching of ready-to-use switching and linear ICs for very low noise but they are all expensive as hell. I wanted to manufacture this on JLCPCB SMT service as much as possible too.

what output noise and ripple do you expect from this? how many micro\milli volts?
do you think it may not work at all? I paid a lot for these and will be disastrous if they didn't work.

[gnuarm]

What I am trying to tell you is that this circuit is no longer a capacitive multiplier... period!

correct, but we can't change the name of the thread. also, we started wanting this to be a cap multiplier, then kept slowly changing it until it became like this. now we cannot change the name of the thread so there is that.

I am responding to your repeated use of the term capacitor multiplier in conversation, not the title of the thread.  There is no capacitive multiplication going on in this circuit.

The linear regulator has frequency limitations because of the opamp and the capacitor you have on the gate imposes more frequency limitations exacerbating the problem.

the small capacitor (1nf) on mosfet gate plus the resistor is to ensure stability, especially the resistor.

If you had given any other reason that might have flown.  But "stability" is the one thing I can guarantee that cap will not provide.  It has the opposite effect in fact.  As I have observed, the corner frequency of the RC is above the unity gain of the op amp, so it may not add to the instability of the circuit, but it is assured to not improve stability.

What "big EMI filter"  I see a couple of 22uF caps.

by that I meant the filtering on 12v rail + the filtering before 7805 (op-amp supply). add to them the filtering before each switcher ic.

Yeah, the schematic I see does not identify a 12V rail, but I assume you are talking about the one labeled Vcc?  You might do better using a single filter on the input to the rest of the circuitry rather than two circuits on the two inputs to the two regulators. 

22uf is on op-amp positive input.

And on the output of the switchers on the schematic I see.

Looking at your PCB artwork it looks like you are running the ground and power on traces rather than planes.

maybe that is not the final layout since we stalled for months until we settled on on, literally tens of times we changed it. I can send the project to you on private if you want to see the final stuff.

No, that's ok.  I'm already involved in a project that is not going well.  A team is designing a ventilator and the coordination is very poor.  Rather than having set requirements we just work on stuff until we think something works.  It is going so badly I might leave.  I design a circuit and it gets tossed out.  I redesign it and it gets tossed out.  All because of poor planning. 

I'm not looking to pick up any more projects.

I am very worried about the impact of adding a capacitor to the control loop in your linear regulator.

the 1nf one?

Yes

As I've said several times, you will get a much better result if you just drop the idea of designing your own linear regulator and pick a chip that has a low noise specification.

I already manufactured the boards and should be ready to be finalized soon when the rest of components arrive.

I actually started doing just that and I think I still have the schematic. it was like this: Switching regulator -> LC filter -> cap multiplier -> linear regulator with caps on the output. However the cap multiplier part got us where we are now until we changed the entire thing.

Yeah, that might actually work a little bit better than the circuit you have now as the cap multiplier will have a higher frequency than the linear.  But the higher frequencies are responsive to filtering.  So it is not important to use an active device to remove the switching noise.

Consider how the control loop works.

well, we didn't design this to be like a bench power supply or anything with vastly changing loads and so on. the load pretty much won't change as it is a retro gaming console with only one thing to do continuously.

Add the RC filter between the op amp and the gate and you get a delay between the op amp responding and the FET being driven higher.

adding that 100R is necessary for op-amp and mosfet stability, and the mosfet gate itself is capacitive. we only put 1nF to ensure more stability as I used to suffer from such particular circuits oscillating due to no cap on that place.... but that is on a linear bench psu on ltspice.

you suspect that it could output the wrong voltage if a fast change happens?

if this is the only issue in the design and it caused a problem, i can simply remove that 1nF from the board very easily.

If you want to produce a good power supply design, focus on implementing a good layout and add a section of LC filtering to the output of the switcher.  That will cut the high frequency noise significantly.  There should not be measurable low frequency noise after a proper linear regulator.  Also read the linear regulator data sheet carefully as they often have specifications on the input and output capacitors to prevent oscillation.

trust me, we spent months on layout from datasheets and app notes... down to mm positioning of traces.

by "proper linear regulator" you mean those expensive ICs? I could buy 3~5$ one from Analog Devices but then it will cost a lot per board unlike the opamp+mosfet which is less than 0.5$ combined. I would need 2 of them for 2 rails which will be like 6-10$ per board just for 2 ICs.

Aren't you using chips for the switcher?  I don't typically use $5 regulators.  They can be found as cheap as $0.50.  Units with a split voltage are a subset, so you would need to check to see what they cost. 

I've been searching of ready-to-use switching and linear ICs for very low noise but they are all expensive as hell. I wanted to manufacture this on JLCPCB SMT service as much as possible too.

I don't know what your total costs are, but if the devices are "expensive as hell" then I suppose you should not use them.  But you should do a stability analysis on your circuit to see if it will work.

what output noise and ripple do you expect from this? how many micro\milli volts?
do you think it may not work at all? I paid a lot for these and will be disastrous if they didn't work.

I don't have a clue.  I would have simulated the design if I had specific design goals for noise and stability.  Have you heard of LTspice?  What is the expensive part?  I thought the rest of the design was not expensive???   If you have a model for the FET in your circuit you can model the effect of the capacitor on the gate. 

[BrianHG]

I am very worried about the impact of adding a capacitor to the control loop in your linear regulator.

the 1nf one?

Yes

This is a tune-able point.  I would prefer no cap and lowering the series resistor value below 100 ohms.  However, I only recently found out Vegeta doesn't have a scope yet.  For now, I would say 'DO NOT INSERT' the C38 & C39 1nf caps.

Can you suggest a linear regulator which rejects noise on the power source at 20KHz through 2MHz?
Also, has a 0.5v dropout with a 3.5 amps load continuous.
And costs less than 30 cents each?

Other part values on the PCB was Vegeta's attempt at resistor part value consolidation.  I could not convince him to use real values and single resistors at single points.

[VEGETA]

Yeah, the schematic I see does not identify a 12V rail, but I assume you are talking about the one labeled Vcc?  You might do better using a single filter on the input to the rest of the circuitry rather than two circuits on the two inputs to the two regulators. 

I sent the pdf to you on private. Yes vcc is 12v.

Aren't you using chips for the switcher?  I don't typically use $5 regulators.  They can be found as cheap as $0.50.  Units with a split voltage are a subset, so you would need to check to see what they cost. 

switchers are basic chips here not special. what do you suggest for linear regulator that is cheap? assuming low ripple low noise design that we went with,

Have you heard of LTspice? 

yes and I even made video about it, but I am not too skilled with it especially making a custom model.

I didn't think this circuit needs much simulation since it is kinda basic. load is nearly constant with no special requirements.

This is a tune-able point.  I would prefer no cap and lowering the series resistor value to 100 ohms or less.  However, I only recently found out Vegeta doesn't have a scope yet.

My concern is that the design works or not. if removing the cap is what it takes, then this is easy to do. if i could sell this product then I can afford getting the scope I need. this is the plan

Other part values on the PCB was Vegeta's attempt at resistor part value consolidation.  I could not convince him to use real values and single resistors at single points.

real values?

resistor consolidation doesn't affect the circuit. what resistor value do you think affects the circuit in wrong way.?

[gnuarm]

I am very worried about the impact of adding a capacitor to the control loop in your linear regulator.

the 1nf one?

Yes

This is a tune-able point.  I would prefer no cap and lowering the series resistor value below 100 ohms.  However, I only recently found out Vegeta doesn't have a scope yet.  For now, I would say 'DO NOT INSERT' the C38 & C39 1nf caps.

Can you suggest a linear regulator which rejects noise on the power source at 20KHz through 2MHz?
Also, has a 0.5v dropout with a 3.5 amps load continuous.
And costs less than 30 cents each?

Other part values on the PCB was Vegeta's attempt at resistor part value consolidation.  I could not convince him to use real values and single resistors at single points.

I can't give you a part number.  But upwards of 100 KHz it is not hard to filter noise with passives.  Most linear regulators only start to roll off in rejection towards 100 kHz.  Since there is no spec on the goal there is no way to pick one over another or even to design a passive filter. 

I got into this because Vegeta kept talking about the capacitor multiplier which is not even in the circuit anymore.  The linear regulator shown here has unity gain at 1 MHz, so is not usefully attenuating input noise until the same frequencies as most linear regulators.  If you want to get better regulation at higher frequencies a high frequency op amp is required.  It will also require careful design for stability.  I believe this is greatly facilitated using LTspice, but the learning curve is steep. 

It is an interesting idea to mitigate the gate-drain and gate-source capacitance by adding capacitance from the gate to ground.  But that way lies madness with the tradeoff as it impacts the feedback control loop making it ring or potentially oscillate.  Maybe you can find a happy medium where it helps. 

[BrianHG]

This is a tune-able point.  I would prefer no cap and lowering the series resistor value to 100 ohms or less.  However, I only recently found out Vegeta doesn't have a scope yet.

My concern is that the design works or not. if removing the cap is what it takes, then this is easy to do. if i could sell this product then I can afford getting the scope I need. this is the plan

Other part values on the PCB was Vegeta's attempt at resistor part value consolidation.  I could not convince him to use real values and single resistors at single points.

real values?

resistor consolidation doesn't affect the circuit. what resistor value do you think affects the circuit in wrong way.?

Best not to insert the cap.  The component was placed there in case you needed to add one, you wouldn't have to do a hand-wire job.  The lower the capacitance, the faster the response from the opamp.

As for the resistors, as an example, you place a numerous 10k in series to avoid placing a single 20k.  This took up PCB area, but somehow, we still managed to fit everything.

[VEGETA]

Best not to insert the cap.  The component was placed there in case you needed to add one, you wouldn't have to do a hand-wire job.  The lower the capacitance, the faster the response from the opamp.

the cap is already soldered on the board during assembly as you know. I could remove it if it affects performance, by hand.

As for the resistors, as an example, you place a numerous 10k in series to avoid placing a single 20k.  This took up PCB area, but somehow, we still managed to fit everything.

I admit I am a bit stiff for consolidating parts especially resistors 

However, board size is the only problem in this, and as you said, we managed to fit it.

The linear regulator shown here has unity gain at 1 MHz, so is not usefully attenuating input noise until the same frequencies as most linear regulators.

how did you know its unity gain at 1 MHZ? from op-amp?

you asked about design goals, here is what I have: low noise low ripple to never affect analog video and audio by any means. the problem is analog video\audio signals are about 1v p-p so any noise and ripple will affect them. so the lower noise\ripple the better.

on a side note: i managed to edit the topic title!! now gnuarm can rest xD. However, website thread link didn't change. It is ok, since no one looks at it but rather look at thread name.

[VEGETA]

on another side note, I found an analog oscilloscope locally: https://jo.opensooq.com/ar/search/139119964/

it is Texio cs-4125a, looks like a Kenwood. 20Mhz dual channel with very clean and nice condition. However, I read that its sensitivity is 1mV so would it be able to measure noise and ripple beyond 1mV? is it gonna benefit me here?

Price is 100 JOD (currently negotiating) which is about 140$. Do you think it is worth it?

[BrianHG]

on another side note, I found an analog oscilloscope locally: https://jo.opensooq.com/ar/search/139119964/

it is Texio cs-4125a, looks like a Kenwood. 20Mhz dual channel with very clean and nice condition. However, I read that its sensitivity is 1mV so would it be able to measure noise and ripple beyond 1mV? is it gonna benefit me here?

Price is 100 JOD (currently negotiating) which is about 140$. Do you think it is worth it?

It looks nice, but 140$us for a dual channel 20MHz CRO...
I do not think 1mv of noise on the power line can have any effect on the Dreamcast's output.  Remember, the worst case noise coming out of the AOZ switcher you are using is in the neighborhood of 400mv pulse 100us wide (~10-50Khz MHz region) (see bottom left hand graph on page 6 of AOZ data sheet.) during a 2 amp swing in output load.  (We engineered this module to deal with this worst case pulse which can happen on the 3.3v bus during a change in CPU processing load.)  A scope with 1mv sensitivity is 400 times more sensitive than that.

In the video signal, if it were a ~0.7v signal, 1mv would represent ~1/700th a luminance level.  Or, greater than 256 shades of grey which is what you have with a 24bit color image.  That is if 100% of your supply voltage noise entered into the video output signal, which it does not since the video output isn't the full 5 or 3.3 volts.  Even our circuit as well as the original Dreamcast power supply has more noise than 1mv on the output unless you slap a 10 farad capacitor on the output.

Hunt a little more before commiting.  Search and ask around here on eeveblog.
In your situation, I would offer $50 US.

[BrianHG]

https://www.amazon.com/OWON-Oscilloscope-2-Channel-Oscilloscopes-Bandwidth/dp/B07VPNFVMN/ref=sr_1_1

[VEGETA]

well, 400mV seems like a lot is not it? what about normal operation at 2.8A of 3.3v, what ripple and noise is expected?

I plan to get DS1054Z for sure, but right now I cannot do it because it is gonna take a lot of money. Shipping is not cheap and itself is not cheap. thus I saw locally offered items by chance and found this one. Still negotiating with him though.

So I could get this one, then wait and get the rigol one.

we'll see what happens

EDIT:

on AOZ page 6, full load operation continuous load seems to have very little ripple at 50mV\div. the graph is not so clear but that seems like about 5mV maximum, this is without linear stage or filters.

[VEGETA]

I've been searching for better parts in case I wanted to make v2 of this board, and other project I have in mind. I found this:

MIC94325: https://www.microchip.com/wwwproducts/en/MIC94325
it is very low power, not suitable for this application but certainly for my other project (RGB to component\composite\s-video converter). It claims "Active noise rejection over a wide frequency band ...    >50dB from 10Hz to 5MHz at 500mA load" by using their ripple blocker technology. so powering it from USB port 5v then stepping it down to 3.6 via simple buck converter delivers this performance. dunno if this is correct or not but its specs seems great.

the other interesting part is this:

TPS62913: https://www.ti.com/product/TPS62913

low voltage output but high current, suitable to this project. still very new part with only samples are available now. it claims this:

•  Low output 1/f noise < 20 μVRMS (100 Hz to 100kHz)
•  Low output voltage ripple < 10 μVRMS after ferritebead
•  High PSRR of > 65 dB (up to 100 kHz)

cuz it uses a ferrite beat or small inductor in its control loop but says 100hz to 100khz low noise while itself working on 1mhz or 2.2mhz range.

what do you think?

on a side note, I could make a version 1.1 of this board which includes removing op-amp 1nf + adding pi passive filters (1nf+100nf then 2.2uH then 1nf+100nF) after switchers and 1nf+100nf after linear regulators. I made another PCB with those made and wired them. will it help much?

[BrianHG]

I though 3 amp isn't enough.

You still need that Murata ferrite bead, you should probably use their same power inductor and you will need to match their second PCB layout exactly to achieve their specs.

Notice they gone through charting the high frequency ripple but make no mention of some of the basics, like transient load response.

[VEGETA]

I though 3 amp isn't enough.

You still need that Murata ferrite bead, you should probably use their same power inductor and you will need to match their second PCB layout exactly to achieve their specs.

Notice they gone through charting the high frequency ripple but make no mention of some of the basics, like transient load response.

3 amps is full load yes, did I say anything else? TPS62913 supports 3 amps as I see. I am not talking about that MIC part, that is just to see your opinion on it as a regulator for small load project.

is there any other switcher that could deliver very low noise and ripple that I can play with later on? something that can deliver < 1mV p-p ripple and noise with or without a simple linear reg.

I offered 40JDs (57$) for that analog scope, could go to 50JD (71$) tops. I will get it for sure, golden chance for me really.

I've sent v1.1 schematic to you, not final but yeah .. did it in 15 mins or so. gonna start working on it once i verify the boards... gonna take time

[gnuarm]

The linear regulator shown here has unity gain at 1 MHz, so is not usefully attenuating input noise until the same frequencies as most linear regulators.

how did you know its unity gain at 1 MHZ? from op-amp?

Yes, the op amp has a gain BW product of 1 MHz, the common emitter configuration is essentially a gain of 1 and the feedback is direct. 

you asked about design goals, here is what I have: low noise low ripple to never affect analog video and audio by any means. the problem is analog video\audio signals are about 1v p-p so any noise and ripple will affect them. so the lower noise\ripple the better.

Those are not  design goals unless you have numbers for "never affect...".   "Lower is better" is not a spec.  Not trying to rag on you, but concrete goals should be set as it's not really true that lower is always better.  Everything has a price.  You have indicated many times that dollars matter to you.  The cost should be part of the spec.  Specific noise figures should be part of the spec just as the current and voltage are part of the spec.  These are actually requirements, but it's to much work to explain requirements vs. specs and why it's important.  I've been fighting that battle for some time on the ventilator project I'm working on.

[VEGETA]

Those are not  design goals unless you have numbers for "never affect...".   "Lower is better" is not a spec.  Not trying to rag on you, but concrete goals should be set as it's not really true that lower is always better.  Everything has a price.  You have indicated many times that dollars matter to you.  The cost should be part of the spec.  Specific noise figures should be part of the spec just as the current and voltage are part of the spec.  These are actually requirements, but it's to much work to explain requirements vs. specs and why it's important.  I've been fighting that battle for some time on the ventilator project I'm working on.

The problem is that I don't have a scope. why? look at this product: https://www.ebay.com/itm/Sega-Dreamcast-ReDreamPSU-Power-Supply/303170616893?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

my product should be the same as this one, and all these PSUs are clones\replicas\similar to this one: https://github.com/PSUThings/PSU/blob/master/Dreamcast/PCB/DreamPSURev2-0.pdf

The ebay one I linked (I have it) it uses LM2596 buck + 33uH inductors on the output + 100uF for input and output. that is it, very minimal and straightforward. what noise\ripple do you expect from this?

the github one uses TPS54525 with copy-pasting datasheet circuit.

I wanted mine to be lets say 10 times better in terms of noise and ripple. since I don't have a scope to measure their output, then it is very hard for me to put noise figures.

kindly see their ICs datasheets and see what expect noise\ripple from them, and if our design here gives better or not. maybe this is the best approach now.

I could say I want 10uV ripple\noise but maybe this is just too hard to get, but i will be happy with beating these products by a good margin. if they offer 10mv and I can get 1mv, then I consider this a success.

[gnuarm]

well, 400mV seems like a lot is not it? what about normal operation at 2.8A of 3.3v, what ripple and noise is expected?

I plan to get DS1054Z for sure, but right now I cannot do it because it is gonna take a lot of money. Shipping is not cheap and itself is not cheap. thus I saw locally offered items by chance and found this one. Still negotiating with him though.

So I could get this one, then wait and get the rigol one.

we'll see what happens

EDIT:

on AOZ page 6, full load operation continuous load seems to have very little ripple at 50mV\div. the graph is not so clear but that seems like about 5mV maximum, this is without linear stage or filters.

You might see high speed spikes at 400 mV at the time the diode starts to conduct.  But you won't see anything that large with a frequency at the switching rate.  Nothing you might call "ripple".  The ripple is due to the switching between driving the choke from the line and the choke "coasting", driving the current through the diode and ground.  You should see ripple more like a few tens of millivolts, maybe even just 10 mV.  If you are seeing anything like 400 mV of ripple, you need to address the design issue in the switcher.

The high frequency stuff is well filtered by passives.  Most people are happy with what caps can do.  There should be a physically small cap with solid connections to the ground and power planes, short and direct, 100 nF is fine.  Then there should be a large value cap sized to match the load.  It can be a bulk cap such as an electrolytic, but should have as low ESR as possible.  Tantalums are good in this use, but some don't like their failure rate.  They require massive over rating, at least 2:1.  So a 5V regulator would require at least a 10 volt cap, preferably 16V. 

I would like to see the output waveform of the switcher if you do this filtering. 

Rather than a standard scope, why not consider a digital attached scope.  The 20 MHz band width is not hard to find with a 100 or 200 MHz sample rate.  I have one here somewhere.  A Hantek I ended up getting for free.  I couldn't get the software to work and when I contacted the supplier they found the tracking info said it was lost so I got my money back!  lol  I understand people have hacked them and there is open source software for it that actually works.  I'm not expecting much out of it, but it's something to get going. 

How do you plan to evaluate your supply?  Are there visible symptoms on using the poor supplies on the unit it powers?  Do you have them documented so you can check your unit in a comparison? 

[gnuarm]

I wanted mine to be lets say 10 times better in terms of noise and ripple. since I don't have a scope to measure their output, then it is very hard for me to put noise figures.

kindly see their ICs datasheets and see what expect noise\ripple from them, and if our design here gives better or not. maybe this is the best approach now.

I could say I want 10uV ripple\noise but maybe this is just too hard to get, but i will be happy with beating these products by a good margin. if they offer 10mv and I can get 1mv, then I consider this a success.

The ad you linked claims 30 mV.  Does that board not work?  As the listing says it depends on clean input from the 12V supply.  That's actually a bit specious.  One of the functions of a regulator is called line to load regulation meaning how much the output changes from a change in the input voltage.   It should be very low so the 12V supply should not matter much. 

If you can get 1mV noise from all sources, that will be very good indeed.  But since you have no way to measure it...

[VEGETA]

The one in ebay link (LM2596) is what I use. It outputs good quality picture but I use LCD monitor via VGA and I didn't make a proper comparison and so on to find artifacts. HOWEVER, I had 2 12v PSUs... one is bad and other is less bad. on the bad PSU, this product doesn't output nice picture! actually the picture is full of waves and garbage... like a lot! hence it requires a good power supply. I had to get a better 12v psu than the one I have in order for it to work. I don't know about dreampsu (github) but people in retro gaming industry said it is not good, check here: https://twitter.com/voultar/status/1248271361778253824?lang=en

I want mine to be better than those. if they offer 30mV, then I must do reasonably better... don't you think so?

If you can get 1mV noise from all sources, that will be very good indeed.  But since you have no way to measure it...

I will get that analog scope for sure, I cannot get digital one anytime soon. so analog is all we got.

how much noise\ripple do you expect from this? approximately?

[VEGETA]

Hello,

I have tested the board and the initial results are promising. Kindly see pictures of the setup here: https://imgur.com/a/xCkHsew

The setup is without the switcher ICs + MOSFETS since they didn't arrive yet, still in customs. I have used IRLIZ44 mosfets instead and hook the 12v voltage directly to mosfet drain instead of the lowered voltage which supposed to come from the switchers. This is very hard for the circuit since now it needs to source the entire current from 12v, not from lowered voltage which means the 12v supply should be capable of high amps @ 12v which mine isn't.

Anyway, I have made a big resistor (as in pics) which is about 3.6 ohms and the circuit regulates while using it, on both rails. without load the voltages are 5.1 and 3.5 but when putting load it gets a bit down.



I have 2 PSUs, one is DYI made from buck modules which is 2 amps max, so drop voltage is to be expected and happened. the other is a 12v adjustable wall adapter, good quality and works well with other dream psu products. However, despite being rated at 12v 3 amps, the board outputs 4.5v and 3.1v at 1.6 ohms resistor (put on each rail separately). will this drop voltage be gone when using proper reduced voltages?

as you see, I have soldered 3 of 1000uf where they should but put a jumper instead of 10uH inductor. the board outputs buzzing sound, is it from the inductors despite being bypassed in this setup? why is that? the sound is almost gone when putting big load.

I will try to upgrade the setup tomorrow by having 2 buck modules output the required voltages to mosfet drains instead of the 12v jumper and will update you about the results.

What do you think so far? what about the drop voltage?

regards

[BrianHG]

Hello,

I have tested the board and the initial results are promising. Kindly see pictures of the setup here: https://imgur.com/a/xCkHsew

Eww, long unpredictable thin wires...

The setup is without the switcher ICs + MOSFETS since they didn't arrive yet, still in customs. I have used IRLIZ44 mosfets instead and hook the 12v voltage directly to mosfet drain instead of the lowered voltage which supposed to come from the switchers. This is very hard for the circuit since now it needs to source the entire current from 12v, not from lowered voltage which means the 12v supply should be capable of high amps @ 12v which mine isn't.

OK.

Anyway, I have made a big resistor (as in pics) which is about 3.6 ohms and the circuit regulates while using it, on both rails. without load the voltages are 5.1 and 3.5 but when putting load it gets a bit down.

This shouldn't be unless there is some oscillation going on.
What voltage do you read on the opamp VCC?
What voltage do you read on the output of the 78L05?
Where is you voltmeter GND connected to?
Where are you reading the output voltage from?

I have 2 PSUs, one is DYI made from buck modules which is 2 amps max, so drop voltage is to be expected and happened. the other is a 12v adjustable wall adapter, good quality and works well with other dream psu products. However, despite being rated at 12v 3 amps, the board outputs 4.5v and 3.1v at 1.6 ohms resistor (put on each rail separately). will this drop voltage be gone when using proper reduced voltages?

as you see, I have soldered 3 of 1000uf where they should but put a jumper instead of 10uH inductor. the board outputs buzzing sound, is it from the inductors despite being bypassed in this setup? why is that? the sound is almost gone when putting big load.

So long as the opamp VCC is high enough, the mosfet VGS is low enough and the mosfet drain has enough supply voltage, there shouldn't be a drop in the first place.  Your wires look too thin for even 1 amp let alone 3.  Also, if you are measuring the voltage anywhere else than the output connector on your PCB, because of those thin long wires, do not expect to see the right voltages.  Also, try AC measurements with your voltmeter.  Thise thing long wires in the op-amp feedback circuit will cause oscillation.

I will try to upgrade the setup tomorrow by having 2 buck modules output the required voltages to mosfet drains instead of the 12v jumper and will update you about the results.

What do you think so far? what about the drop voltage?

regards

Right now it's hard to tell.  Those long thin wires in the circuit and unknown points where you have been probing your voltages, I cannot tell.

[VEGETA]

Eww, long unpredictable thin wires...

these are all I have right now, unfortunately. Maybe I could get thicker wires tomorrow from my company (1mm sq wires).

This shouldn't be unless there is some oscillation going on.
What voltage do you read on the opamp VCC?
What voltage do you read on the output of the 78L05?
Where is you voltmeter GND connected to?
Where are you reading the output voltage from?

voltage on op-amp.. I don't remember correctly but it was like 0.3-0.5v less than supply voltage. I guess 12.3v was the supply, and the op-amp was about 12v or so. I am not so sure but it is high enough.

7805 voltage is 5v as expected, not 5.0000v but few mV more.

Voltmeter and reading is on the final connector itself.

So long as the opamp VCC is high enough, the mosfet VGS is low enough and the mosfet drain has enough supply voltage, there shouldn't be a drop in the first place.

drop doesn't happen on low loads, but only on high loads. I suspected this because of the input supply itself but the 2nd input supply was capable of 12v @ 3 amps...

Your wires look too thin for even 1 amp let alone 3. 

well, will it cause problems other than high heat in the wire itself? do you think this contributes to the drop voltage? how?

Also, if you are measuring the voltage anywhere else than the output connector on your PCB, because of those thin long wires, do not expect to see the right voltages.

I measure on output connector. again, what is the cause of thin wires?

Also, try AC measurements with your voltmeter

hmm ac coupling for measuring ripple\noise?

Thise thing long wires in the op-amp feedback circuit will cause oscillation.

but thin wires shouldn't contribute to emi and so on. I need to understand this. anyway I will try to get thicker wires tomorrow.

[BrianHG]

hmm ac coupling for measuring ripple\noise?

So long as the bandwidth is withing your voltmeter's frequency range & having a true-rms meter also helps.

I still can't figure out the 'buzz' your getting on inactive inductors...

[VEGETA]

I am doing measurements now:

No load:
V_7805: 5.044v
V_3.3_after_7805: 3.361v
V_supply: 12.3v
V_opamp_supply: 11.98v
V_output5v: 5.146v
V_output3.3v: 3.481v
ac measurement: keeps doing 0v and 2v each half second on 5v rail, and about 1.4v with 0v on 3.3v rail

update: inductors has 12.3v on both sides

update2: buzzing is gone when putting bit load.

update 3: i soldered 4.6v wire to input of inductor and still same result and sound. also, voltage drops to 2.4v when using 1.6 ohm load in 3.3 rail

[BrianHG]

ac measurement: keeps doing 0v and 2v each half second on 5v rail, and about 1.4v with 0v on 3.3v rail

Odd.  Oscillate, then stop, then oscillate.  Are the gate capacitors installed?

update: inductors has 12.3v on both sides

update2: buzzing is gone when putting bit load.

update 3: i soldered 4.6v wire to input of inductor and still same result and sound. also, voltage drops to 2.4v when using 1.6 ohm load in 3.3 rail

What happens to the 12v source with the 1.6ohm load.
Also check the opamp supply and gate and drain voltages.

[VEGETA]

Odd.  Oscillate, then stop, then oscillate.  Are the gate capacitors installed?

yes it is installed.

What happens to the 12v source with the 1.6ohm load.

gets some 10mv drop, same as opamp supply. nothing big.

as for gate voltage after R17 (100ohm), it is 1.1v when no load and gets to 10v when 1.6ohm.

[VEGETA]

I lifted the inductors input pin, buzzing still the same.

edit: i completely took off the inductors... same result

[VEGETA]

I took the 1000uf caps exact same result

EDIT: I soldered the 12v on L1 pin without using the jumper, still same result.

buzzing is not from elec caps or inductors

[VEGETA]

here is the mosfet used: https://www.infineon.com/dgdl/Infineon-IRLIZ44N-DS-v01_02-EN.pdf?fileId=5546d462533600a401535664286325cb

I also have this one: https://www.mouser.com/datasheet/2/149/IRL640A-87605.pdf

[BrianHG]

as for gate voltage after R17 (100ohm), it is 1.1v when no load and gets to 10v when 1.6ohm.

This doesn't sound right.  It should be between 4.3v to 6.3v max depending on load.  Never 1.1v, and only going to 10v if the mosfet cant drive enough current or it is not a logic level mosfet.

[gnuarm]

as for gate voltage after R17 (100ohm), it is 1.1v when no load and gets to 10v when 1.6ohm.

This doesn't sound right.  It should be between 4.3v to 6.3v max depending on load.  Never 1.1v, and only going to 10v if the mosfet cant drive enough current or it is not a logic level mosfet.

The FET has a very low threshold.  It will pass amps of current with just 2V Vgs.  So in regulation the Vg should never be more than 5.8V.  10V certainly has the part turned on fully.  What is the output voltage with the 1.6 ohm load? 

What is V_FB1 with the 1.6 ohm load? 

What is the voltage on both sides of R17? 

You can probably do some debugging without the 1.6 ohm load.  i see you have a 100 ohm resistor on the output, R22, which is enough to not be looking at zero current measurements.  The output voltage is a bit high, 3.48V.  It should be the same as the reference voltage (3.361V) with a very small margin.  When debugging, keep it simple.  Try figuring out why the output voltage is high with no added load for starters.  The output voltage should depend on nothing other than the reference voltage and the operation of the op amp and FET.

V_opamp_supply: 11.98v
V_3.3_after_7805: 3.361v
V_output3.3v: 3.481v

To find out why the output is so high when the reference is good, measure all the points in the control loop and the power input to the FET, pin 2, the drain.  Please present those measurements clearly in a table like you did below.  That is everything involved in setting the output voltage and should be enough to understand where a problem might be.  Essentially, we need the measurements of pins 1, 2 and 3 on both the FET and the op amp, no load and with load.  While you are at it, measure the power and ground pins on the op amp, not the traces, be sure to measure on  the pins directly. 

I don't understand the AC measurement.  Are you saying the voltage outputs are bouncing between half the expected voltage and ground??? 

ac measurement: keeps doing 0v and 2v each half second on 5v rail, and about 1.4v with 0v on 3.3v rail

I have no idea what this is saying.  If it is literally true, how can you present these other measurements???  A problem like this will require opening the feedback loop by removing R19 and taking measurements. 

[VEGETA]

I have provided input voltage of 4.6v only to the 3.3v mosfet while 5v mosfet is without power, yet its drain seems to have 10v or so. I am not sure if it is the drain or gate but both shouldn't be with any voltage right? its output is about 130mV though.

I am at work now, when I return I will jump into re-doing the setup and do required tests.

What is the voltage on both sides of R17?

the measurement I took was showing 1.1v on both sides (nearly) when no load but didn't do it for full load, full load (1.6 ohm) has about 10v for gate pin.

To find out why the output is so high when the reference is good, measure all the points in the control loop and the power input to the FET, pin 2, the drain.  Please present those measurements clearly in a table like you did below.

I will do it when I return for sure.

I don't understand the AC measurement.  Are you saying the voltage outputs are bouncing between half the expected voltage and ground???

I have no idea what this is saying.  If it is literally true, how can you present these other measurements???  A problem like this will require opening the feedback loop by removing R19 and taking measurements.

I put multimeter in AC voltage measurement instead of DC, then measured the points only to find that the reading jumps between 0 and 2v, and 0 to 1.4v as mentioned above... each half a second or something.

All of this aside... why and where is that continuous buzzing sound is?! I mean i took off all elec. caps and the 2 inductors, it is still there without a change. also, when the load is quite high the sound disappears.

[gnuarm]

I have provided input voltage of 4.6v only to the 3.3v mosfet while 5v mosfet is without power, yet its drain seems to have 10v or so. I am not sure if it is the drain or gate but both shouldn't be with any voltage right? its output is about 130mV though.

I am at work now, when I return I will jump into re-doing the setup and do required tests.

Yeah, this is why I asked for the information in a table format.  I don't have any idea what you said above.  I can't understand what you are measuring if you are changing the circuit or describe your measurements in different ways than what I am asking about. 

I'm working on a project right now with about a dozen people and only a couple others are electrical engineers.  I don't have a test setup and when they ask me to help debug I can never get information in a form I can understand.

What is the voltage on both sides of R17?

the measurement I took was showing 1.1v on both sides (nearly) when no load but didn't do it for full load, full load (1.6 ohm) has about 10v for gate pin.

See?  It's not clear what you mean by "didn't do it".  I really don't want to have to exchange multiple messages to get the info.  It has to be complete and in a form I can understand exactly what it going on.  So pick a configuration and lets test that one.  Starting with the 3.3V output is fine.  Let's make sure the 5V circuit is completely disconnected so it is not a factor.  Then write down ALL the readings at every important point with clear labels.  This is why I put names on every net on my designs.  Makes it easier to communicate... much easier.

To find out why the output is so high when the reference is good, measure all the points in the control loop and the power input to the FET, pin 2, the drain.  Please present those measurements clearly in a table like you did below.

I will do it when I return for sure.

I don't understand the AC measurement.  Are you saying the voltage outputs are bouncing between half the expected voltage and ground???

I have no idea what this is saying.  If it is literally true, how can you present these other measurements???  A problem like this will require opening the feedback loop by removing R19 and taking measurements.

I put multimeter in AC voltage measurement instead of DC, then measured the points only to find that the reading jumps between 0 and 2v, and 0 to 1.4v as mentioned above... each half a second or something.

If this is not happening on a DC measurement, let's just ignore it for now.  i have no idea what your meter is doing with this.  Normally an AC reading will be off, but stable when measuring DC.

All of this aside... why and where is that continuous buzzing sound is?! I mean i took off all elec. caps and the 2 inductors, it is still there without a change. also, when the load is quite high the sound disappears.

You need to track that down with your ear.  If not that perhaps a scope.  What is left on the board if all electrolytic caps and inductors are left?  I don't  really know what you have.  The photo I saw only showed caps.  I didn't see any chips.

BTW, first thing you should do is to inspect every solder joint.  Make sure there is a good connection.  When measuring voltages of suspect connections measure the voltage on a pin, then the same signal on another pin.  If either solder joint is bad the bad reading will be only on one pin.  Often putting the probe on a bad solder joint will make it work.

[VEGETA]

I will do exactly that, gonna put labels to all joints that I am gonna measure. All of them will be for no load and specific load (gonna mention it). I will see the soldering too but it shouldn't be the problem.

i have taken the 2 big inductors, the ones left are the small inductors which are inputs to switchers... so they are not used here since I am feeding a direct voltage at mosfet drain. Also, the lm358 op-amp + 7805 regulator + diodes. I tried listening to it but for sure it is not from the mosfets but the board is 50x50mm so very small area to know for sure which component does it. I will try recording a video to show you in details and you can hear the sound. I hope the forum allows uploading videos.

I think you have a pdf for the schematic (not the v1.1, this is not the one used here), if not, I will send it.

___

Data will be like this:

No load:

v_gate =
v_drain =
v_output_3.3v =
v_opamp_supply =
v_opamp_feedback =
7805_5v_voltage_ref =
7805_3.3v_voltage_ref =
v_12v_input =

anything else should be added?

[VEGETA]

No load test  of 3.3v rail:

v_gate = 1.35v
v_drain =4.64v from external buck module using same 12v source.
v_output_3.3v = 3.436v
v_opamp_supply = 12.38 supplied directly from 12v supply.
v_opamp_feedback = 3.446v
7805_5v_voltage_ref = 5.044v
7805_3.3v_voltage_ref = 3.360v, see note below.
v_12v_input = 12.38v.


NOTE: I noticed that before connecting power to mosfet drain, the 3.3v reference voltage which is derived from the resistor divider is only about 1.4v while the 7805 voltage is 5.044v. when connecting the mosfet drain power, it becomes 3.3v.


3.3 ohm load test  of 3.3v rail:

v_gate = 6.77v
v_drain =3.9v from external buck module using same 12v source. maybe it drops due to higher current
v_output_3.3v = 3.28v
v_opamp_supply = 12.11 supplied directly from 12v supply.
v_opamp_feedback = 3.337v
7805_5v_voltage_ref = 5.044v
7805_3.3v_voltage_ref = 3.331v, see note below.
v_12v_input = 12.11v.
buzzing completely gone

[BrianHG]

Without a switcher making your lower voltage to feed the 'drains', the drains should always be 12v wired directly to your 12v supply.

I don't know why you are getting a buzz, are you sure your wiring is correct?  An audible buzz means something is being driven hard, very hard, with low frequency, usually square wave off-on-off pulse oscillation.  Nothing can be properly deternined with those wires of yours and the photographs you provided.  Are you sure your wiring is correct.  Also, is the polarity of the caps you soldered on correct?  Are they getting warm?

The output without the mosfets should be 0v.  With the source & gate wired, the output should be s=3.3v & g=~5-6v.  If not, something is wired wrong.

Is there any ripple on your +12v source?

[VEGETA]

Without a switcher making your lower voltage to feed the 'drains', the drains should always be 12v wired directly to your 12v supply.

I don't know why you are getting a buzz, are you sure your wiring is correct?  An audible buzz means something is being driven hard, very hard, with low frequency, usually square wave off-on-off pulse oscillation.  Nothing can be properly deternined with those wires of yours and the photographs you provided.  Are you sure your wiring is correct.  Also, is the polarity of the caps you soldered on correct?  Are they getting warm?

The output without the mosfets should be 0v.  With the source & gate wired, the output should be s=3.3v & g=~5-6v.  If not, something is wired wrong.

Is there any ripple on your +12v source?

I re-done the wiring and got rid of all thin wires, only few still remain and they are correct.

There are no caps now, all taken off as well as inductors. this is just voltage directly at mosfet input (drain). I increased the voltage so that any drop didn't effect the operation but results above is the same. when I install a 3.5 ohm load, the buzz disappears and the regulation is kinda good with 3.290v at the output and about 3.331 at opamp inputs with margin.

I will try an npn (BD437) on 5v rail to see what is going on. also gonna do more tests with 1.6 ohms load since it is the one driving this to maximum.

if any of this didn't work, then i might try another board.

if you have the schematic, then see the points:

12v input: on input of 7805, on the cap pin.
ground: on J1 gnd pin.
6.5v: on 3.3v mosfet drain directly.

[VEGETA]

few updates:

- I have tried another new board, but same result happens. Also, I noticed that the 3.3v mosfet is really hot even at no load.

- using npn didn't give any good results, keeps being 5v but when putting load it drops and magic smoke happens due to the large voltage gap.

- I tried using 1.6 ohms and the result is 3.26v or so on 3.3v rail and 4.928v on 5v rail with no buzzing\continuous_beeping sound. can't go much because no heatsink installed.

- I have attached a picture of my wiring + pictures of real wiring (no shorting between any pin).


I started suspecting that the switchers + chosen KIA mosfets gonna make some change since that is the full circuit. And at the same time I find it bizarre that the circuit has some issues even with injecting voltages this way. having the full circuit allows us to get enough current on both rails without any drop voltage. do you think this might be the solution?

[BrianHG]

few updates:

- I have tried another new board, but same result happens. Also, I noticed that the 3.3v mosfet is really hot even at no load.

Hun?
Please measure the impedance of the mosfet pads to GND on the PCB.  No mosfet.  You should see 100 ohm, our current default pull-down resistor.  Definitely not enough to make a to220 mosfet get 'hot'.


Again, those 'Gate' voltages sound wrong.  A 1.35v from gate to GND should not output 3.436v, if anything, it should be close to 0v.

[gnuarm]

few updates:

- I have tried another new board, but same result happens. Also, I noticed that the 3.3v mosfet is really hot even at no load.

- using npn didn't give any good results, keeps being 5v but when putting load it drops and magic smoke happens due to the large voltage gap.

- I tried using 1.6 ohms and the result is 3.26v or so on 3.3v rail and 4.928v on 5v rail with no buzzing\continuous_beeping sound. can't go much because no heatsink installed.

- I have attached a picture of my wiring + pictures of real wiring (no shorting between any pin).


I started suspecting that the switchers + chosen KIA mosfets gonna make some change since that is the full circuit. And at the same time I find it bizarre that the circuit has some issues even with injecting voltages this way. having the full circuit allows us to get enough current on both rails without any drop voltage. do you think this might be the solution?

I don't understand your posts.  Here you show 12V directly connected to the drain of the MOSFET and yet you previously said the voltage was around 5V.  Did the previous measurements have a 5V regulator in the path to the drain? 

So what are the measurements in this configuration?   Whichever configuration you wish to trouble shoot let's stick with it and not jump around confusing the matter. 

No load test  of 3.3v rail:

v_gate = 1.35v
v_drain =4.64v from external buck module using same 12v source.
v_output_3.3v = 3.436v
v_opamp_supply = 12.38 supplied directly from 12v supply.
v_opamp_feedback = 3.446v
7805_5v_voltage_ref = 5.044v
7805_3.3v_voltage_ref = 3.360v, see note below.
v_12v_input = 12.38v.

I expect to see the two inputs to the op amp at virtually the same voltage.  The spec on the op amp is for low single digit mV input offset, so a difference of 14 mV should not be seen.  You also have 10 mV across the 3.3K feedback resistor which indicates 3 uA of bias current which is far above the low nA spec of the LM358. 

Any chance your op amp is a counterfeit part?  Did you buy them from a reputable source?

[BrianHG]

few updates:

- I have tried another new board, but same result happens. Also, I noticed that the 3.3v mosfet is really hot even at no load.

- using npn didn't give any good results, keeps being 5v but when putting load it drops and magic smoke happens due to the large voltage gap.

- I tried using 1.6 ohms and the result is 3.26v or so on 3.3v rail and 4.928v on 5v rail with no buzzing\continuous_beeping sound. can't go much because no heatsink installed.

- I have attached a picture of my wiring + pictures of real wiring (no shorting between any pin).


I started suspecting that the switchers + chosen KIA mosfets gonna make some change since that is the full circuit. And at the same time I find it bizarre that the circuit has some issues even with injecting voltages this way. having the full circuit allows us to get enough current on both rails without any drop voltage. do you think this might be the solution?

I don't understand your posts.  Here you show 12V directly connected to the drain of the MOSFET and yet you previously said the voltage was around 5V.  Did the previous measurements have a 5V regulator in the path to the drain? 

So what are the measurements in this configuration?   Whichever configuration you wish to trouble shoot let's stick with it and not jump around confusing the matter. 

No load test  of 3.3v rail:

v_gate = 1.35v
v_drain =4.64v from external buck module using same 12v source.
v_output_3.3v = 3.436v
v_opamp_supply = 12.38 supplied directly from 12v supply.
v_opamp_feedback = 3.446v
7805_5v_voltage_ref = 5.044v
7805_3.3v_voltage_ref = 3.360v, see note below.
v_12v_input = 12.38v.

I expect to see the two inputs to the op amp at virtually the same voltage.  The spec on the op amp is for low single digit mV input offset, so a difference of 14 mV should not be seen.  You also have 10 mV across the 3.3K feedback resistor which indicates 3 uA of bias current which is far above the low nA spec of the LM358. 

Any chance your op amp is a counterfeit part?  Did you buy them from a reputable source?

I was getting that feeling as well.

He needs a scope.  His volt meter readings may be all incorrect if he is measuring some sort of saw-tooth oscillation on those lines, but, not at the 3.3v reference point.

Without load, his 3.3v mosfet's output (source) should only have a 33ma load to GND, should it be getting hot?

If it is a nasty saw waveform, he might need to remove C38 & C39.

[VEGETA]

few updates:

- I have tried another new board, but same result happens. Also, I noticed that the 3.3v mosfet is really hot even at no load.

Hun?
Please measure the impedance of the mosfet pads to GND on the PCB.  No mosfet.  You should see 100 ohm, our current default pull-down resistor.  Definitely not enough to make a to220 mosfet get 'hot'.


Again, those 'Gate' voltages sound wrong.  A 1.35v from gate to GND should not output 3.436v, if anything, it should be close to 0v.

I measured the resistance of mosfet drain pad to ground (with no mosfet installed), result is 50.7k ohm. those gate voltages happen when no load, but when load is put they become reasonable.

I don't understand your posts.  Here you show 12V directly connected to the drain of the MOSFET and yet you previously said the voltage was around 5V.  Did the previous measurements have a 5V regulator in the path to the drain?

So what are the measurements in this configuration?   Whichever configuration you wish to trouble shoot let's stick with it and not jump around confusing the matter.

here is the one configuration I stick with:

No load test  of 3.3v rail:

v_gate = 1.35v
v_drain =4.64v from external buck module using same 12v source.
v_output_3.3v = 3.436v
v_opamp_supply = 12.38 supplied directly from 12v supply.
v_opamp_feedback = 3.446v
7805_5v_voltage_ref = 5.044v
7805_3.3v_voltage_ref = 3.360v, see note below.
v_12v_input = 12.38v.


NOTE: I noticed that before connecting power to mosfet drain, the 3.3v reference voltage which is derived from the resistor divider is only about 1.4v while the 7805 voltage is 5.044v. when connecting the mosfet drain power, it becomes 3.3v.


3.3 ohm load test  of 3.3v rail:

v_gate = 6.77v
v_drain =3.9v from external buck module using same 12v source. maybe it drops due to higher current
v_output_3.3v = 3.28v
v_opamp_supply = 12.11 supplied directly from 12v supply.
v_opamp_feedback = 3.337v
7805_5v_voltage_ref = 5.044v
7805_3.3v_voltage_ref = 3.331v, see note below.
v_12v_input = 12.11v.
buzzing completely gone

however, the post you quoted was another test after that, so let's stick with the ones written here.

I expect to see the two inputs to the op amp at virtually the same voltage.  The spec on the op amp is for low single digit mV input offset, so a difference of 14 mV should not be seen.  You also have 10 mV across the 3.3K feedback resistor which indicates 3 uA of bias current which is far above the low nA spec of the LM358.

Any chance your op amp is a counterfeit part?  Did you buy them from a reputable source?

well, lm358 bought from JLCPCB and LCSC, Chinese parts. I have previously bought ones but also from the same source. no way I can get ones now.

voltages on input pins of the opamp are different only when no load, but when putting load it gets nearly the same as shown in measurements... only few mV of difference.

the problem is that all 125 boards have the exact same parts, i could try to remove one opamp and install one of my older ones to see if it makes a difference.

[VEGETA]

I tried removing the opamp and install another one but failed, destroyed the footprint. so small i couldn't work with it.

[VEGETA]

On a side trial different than the one mentioned above, I removed the opamp by destroying it with heat... then soldered a buck module directly at the gate of the mosfet. now I outputted 4.6v to get 3.3v but it won't regulate properly on high loads.

so can we assume the fault is the opamp? since now no ringing or sound. what is the solution? I don't have the proper tools to remove such very small footprints as I tried now and couldn't remove it without brute forcing it. I paid a lot for the panels only to see it fail for no obvious reason... I am really frustrated now. Don't know what next step to take.

on a side note, a guy promised me to sell me Hanmatek DOS1102 digital oscilloscope for about 115$ after sending it to repair... he disappeared ffs!!

[gnuarm]

Do me one favor... you have tag lines linking to some web sites.  Add a link to someplace where I can see your schematic.  I keep having to dig back through the thread to find it.  As an image file it opens in MS photos which craps out after being open a while. 

[gnuarm]

few updates:

- I have tried another new board, but same result happens. Also, I noticed that the 3.3v mosfet is really hot even at no load.

Hun?
Please measure the impedance of the mosfet pads to GND on the PCB.  No mosfet.  You should see 100 ohm, our current default pull-down resistor.  Definitely not enough to make a to220 mosfet get 'hot'.


Again, those 'Gate' voltages sound wrong.  A 1.35v from gate to GND should not output 3.436v, if anything, it should be close to 0v.

I measured the resistance of mosfet drain pad to ground (with no mosfet installed), result is 50.7k ohm. those gate voltages happen when no load, but when load is put they become reasonable.

I don't understand your posts.  Here you show 12V directly connected to the drain of the MOSFET and yet you previously said the voltage was around 5V.  Did the previous measurements have a 5V regulator in the path to the drain?

So what are the measurements in this configuration?   Whichever configuration you wish to trouble shoot let's stick with it and not jump around confusing the matter.

here is the one configuration I stick with:

No load test  of 3.3v rail:

v_gate = 1.35v
v_drain =4.64v from external buck module using same 12v source.
v_output_3.3v = 3.436v
v_opamp_supply = 12.38 supplied directly from 12v supply.
v_opamp_feedback = 3.446v
7805_5v_voltage_ref = 5.044v
7805_3.3v_voltage_ref = 3.360v, see note below.
v_12v_input = 12.38v.

It would help if you included pin numbers so we know we aren't working around a communication error, but this is ok for now. 

NOTE: I noticed that before connecting power to mosfet drain, the 3.3v reference voltage which is derived from the resistor divider is only about 1.4v while the 7805 voltage is 5.044v. when connecting the mosfet drain power, it becomes 3.3v.

When you have no power on the MOSFET the output is a load on the feedback circuit.  The diode D3 connected that load to the V_3.3 signal which is a resistor divider and so is subject to change in value with loading.  When the FET is powered the circuit keeps the output very near the reference and the diode does not conduct.  I'm not sure the diode is required, but it should not hurt.  This is why V_3.3 is dragged down with no power on the FET drain or you will see the same thing if the op amp doesn't drive the FET. 

I was having a brain cramp.  I was reading gate voltage at 1.35V and thinking it was a bit low, but ok, then I realized that's not with a source at ground but at 3.4V!!!  So this is impossible.  The FET would be fully turned off and the source pulled down to ground by the 100 ohm R22. 

It is hard to think of a way you could have 1.2V between the source and drain when the gate is pulled so low.  if the source and drain were swapped you would see the body diode turn on, but the voltage between them would be well less than 1V with 33 mA of current.  Still, this almost has to be a wiring error with the FET or it is not the right part or a counterfeit part. 

I see you got parts from LCSC.  I don't know if their parts are real or counterfeit.  They sell Xilinx parts at less than a quarter of other distributors.  How can they do that if they are buying them from Xilinx?

3.3 ohm load test  of 3.3v rail:

v_gate = 6.77v
v_drain =3.9v from external buck module using same 12v source. maybe it drops due to higher current
v_output_3.3v = 3.28v
v_opamp_supply = 12.11 supplied directly from 12v supply.
v_opamp_feedback = 3.337v
7805_5v_voltage_ref = 5.044v
7805_3.3v_voltage_ref = 3.331v, see note below.
v_12v_input = 12.11v.
buzzing completely gone

however, the post you quoted was another test after that, so let's stick with the ones written here.

Ok, a drop in Vd of over 0.7V with 1 amp of current from a 2 amp supply is pretty poor performance.  With over 3V Vgs and 0.6V Vds the FET should be passing 15 amps.  Again, something is very wrong with the FET or your load resistor is not what you think it is.

I expect to see the two inputs to the op amp at virtually the same voltage.  The spec on the op amp is for low single digit mV input offset, so a difference of 14 mV should not be seen.  You also have 10 mV across the 3.3K feedback resistor which indicates 3 uA of bias current which is far above the low nA spec of the LM358.

Any chance your op amp is a counterfeit part?  Did you buy them from a reputable source?

well, lm358 bought from JLCPCB and LCSC, Chinese parts. I have previously bought ones but also from the same source. no way I can get ones now.

voltages on input pins of the opamp are different only when no load, but when putting load it gets nearly the same as shown in measurements... only few mV of difference.

the problem is that all 125 boards have the exact same parts, i could try to remove one opamp and install one of my older ones to see if it makes a difference.
[/quote]

You had 125 boards made before you debugged the circuit???  Wow! 

Vfb is about the same as Vref, but 6 mV offset is still outside the op amp spec even if only a little.  However the feedback is 60 mV off from the 3.3V output voltage so 18 uA into the -input on the op amp, well out of spec, about 1000x out of spec.  The diode will pass a tiny current, but much smaller than this when the voltage is only a few mV. 

To be sure of what you are measuring, please make the measurements directly on the pins of the op amps and the FET pins.  I see I was looking at the wrong op amp circuit previously.  This op amp circuit is pins 5, 6, 7.  The FET is still pins 1, 2, 3, or it might be more clear to call them G, D and S respectively.  Go back to your data sheets to make sure there's no mistake in the pin out.

Clearly something is wrong and you need to rule out every assumption possible.  Debugging is like being a detective.  Collect evidence and figure out what info is right and what info is wrong.  Someone in the circuit is lying to you.  Who can it possibly be?  Right now the FET looks to be the guilty party.  Try to verify the wiring and pin numbers. 

[VEGETA]

It would help if you included pin numbers so we know we aren't working around a communication error, but this is ok for now.

I sent the pdf schematic to you via PM.

Still, this almost has to be a wiring error with the FET or it is not the right part or a counterfeit part.

I made sure to check the wiring many times using the datasheet, and it is correct. The part is purchased long time ago from aliexpress but I think it is good since I used it in another electronic load circuit and worked as intended.

so according to schematic and layout diagram, pin 1 is gate on pin 1 of the foot print (left pin), pin 2 is drain which is the pad of footprint, pin 3 is the source which is pin 3 of the footprint (right pin).

I see you got parts from LCSC.  I don't know if their parts are real or counterfeit.  They sell Xilinx parts at less than a quarter of other distributors.  How can they do that if they are buying them from Xilinx?

I don't know about Xilinx parts but general parts like mosfets and npns are manufactured in China and won't be hard for them to make it. we based the design on this mosfet: https://lcsc.com/product-detail/MOSFET_KIA-Semicon-Tech-KND3403A_C382143.html which is a Chinese brand.

as you see, the same pin numbering between this and the one I tried.

Ok, a drop in Vd of over 0.7V with 1 amp of current from a 2 amp supply is pretty poor performance.  With over 3V Vgs and 0.6V Vds the FET should be passing 15 amps.  Again, something is very wrong with the FET or your load resistor is not what you think it is.

I have IRL640A mosfet to try, although I guess it gave me the same result but that was an old trial without high loading. I could try installing it and test if it makes sense but I don't think it is much different than iril44z mosfet.

You had 125 boards made before you debugged the circuit???  Wow!

I admit it is a mistake but we were kinda sure and optimistic about the design since no reason why it would fail or have a problem. I am still waiting for the mosfets and switchers hoping that it would make the circuit work. do you expect it would make a difference?

To be sure of what you are measuring, please make the measurements directly on the pins of the op amps and the FET pins.

I measured on the opamp pins and output connector. today I will try measuring the fet pins.

Clearly something is wrong and you need to rule out every assumption possible.

I am ready to do anything if it would make the boards work as intended. that is why when all parts arrive and get soldered, it will be the best test to do.

[gnuarm]

I don't know what to say.  I don't think adding parts will make it work better and I'm pretty sure it will make it harder to debug.  I think you should get rid of the 12 to 5V switcher you have now.  Run 12V to the FET.  I assume that supply will not droop with 1 amp of current, right?  Or test with a half amp, or a quarter amp if the FET gets too hot. 

Your circuit is not right at idle, so no need to load it really. 

I think you need to test Brian's idea that you might have oscillations.

[VEGETA]

I don't know what to say.  I don't think adding parts will make it work better and I'm pretty sure it will make it harder to debug.  I think you should get rid of the 12 to 5V switcher you have now.  Run 12V to the FET.  I assume that supply will not droop with 1 amp of current, right?  Or test with a half amp, or a quarter amp if the FET gets too hot. 

Your circuit is not right at idle, so no need to load it really. 

I think you need to test Brian's idea that you might have oscillations.

If I have oscillation, what to do to make the current boards work?

I am working hard to get a scope but the guy told its repair is not finished yet or no news from repair technician.

as for buck regulator, I ditched it in the last test as seen in the voltages.

today I couldn't do anything since I was tired but tomorrow I will for sure. my current plan is to use the board which I destroyed the on-board opamp... then use another opamp in its place by wiring it to the points in the board to see if lm358 is the reason.

brian said stuff about removing 1nf caps... will this really work? I mean do it affect oscillation being so little? I think it slows the reaction a little bit but make the entire circuit bad?? also, the sound issue is still not known. removing these caps is very easy and if it will fix the circuit then that would be a happy solution.

[gnuarm]

I don't know what to say.  I don't think adding parts will make it work better and I'm pretty sure it will make it harder to debug.  I think you should get rid of the 12 to 5V switcher you have now.  Run 12V to the FET.  I assume that supply will not droop with 1 amp of current, right?  Or test with a half amp, or a quarter amp if the FET gets too hot. 

Your circuit is not right at idle, so no need to load it really. 

I think you need to test Brian's idea that you might have oscillations.

If I have oscillation, what to do to make the current boards work?

Figure out why it is happening first, that will tell you how to fix it. 

I am working hard to get a scope but the guy told its repair is not finished yet or no news from repair technician.

as for buck regulator, I ditched it in the last test as seen in the voltages.

Sorry, you've lost me.  The last numbers I see show

v_drain =4.64v from external buck module using same 12v source.

How could the drain be 4.64V if it is connected directly to 12V without the switcher?

today I couldn't do anything since I was tired but tomorrow I will for sure. my current plan is to use the board which I destroyed the on-board opamp... then use another opamp in its place by wiring it to the points in the board to see if lm358 is the reason.

I don't know what to say.  There are so many mistakes made because you thought you could get this to work on the first pass without any debug.  Using small pitch surface mount parts when you don't have the means of soldering them is a big mistake.  Making 125 boards as your first run was a huge mistake.  I am floored that you attempted this.  I can easily afford such a mistake but I will always make a prototype before I run a production batch. 

brian said stuff about removing 1nf caps... will this really work? I mean do it affect oscillation being so little? I think it slows the reaction a little bit but make the entire circuit bad?? also, the sound issue is still not known. removing these caps is very easy and if it will fix the circuit then that would be a happy solution.

I don't know why you think 1 nF is "little".  A few pF in the wrong place can cause oscillations with a fast circuit or a high gain circuit.  The 1 nF cap is doing nothing useful in this design anyway.  So remove it.  It was only there as part of a "capacitance multiplier" concept that doesn't apply to this circuit because it is a regulated output.  The added capacitance can only slow the response of the feedback path which causes oscillations.

[VEGETA]

Sorry, you've lost me.  The last numbers I see show

12v directly and buck module gave the same results. i am sorry if i didn't document the 12v directly one, it will be my next thing to do soon.

I don't know what to say.  There are so many mistakes made because you thought you could get this to work on the first pass without any debug.  Using small pitch surface mount parts when you don't have the means of soldering them is a big mistake.  Making 125 boards as your first run was a huge mistake.  I am floored that you attempted this.  I can easily afford such a mistake but I will always make a prototype before I run a production batch. 

well, I told you we were confident that it will work since nothing in the circuit is weird or special circuit. still, it is a mistake to do and I should learn from it.

The 1 nF cap is doing nothing useful in this design anyway.  So remove it.

I will remove it for sure. gonna keep u updated with what happens.

[gnuarm]

Sorry, you've lost me.  The last numbers I see show

12v directly and buck module gave the same results. i am sorry if i didn't document the 12v directly one, it will be my next thing to do soon.

You may think it is the same results, but the Vd will be different.  Every value you measure is important in the context of the others.  Change Vd and Vds changes which presents a very different picture of what is going on.  If Vd doesn't change there is something very, very wrong.

I don't know what to say.  There are so many mistakes made because you thought you could get this to work on the first pass without any debug.  Using small pitch surface mount parts when you don't have the means of soldering them is a big mistake.  Making 125 boards as your first run was a huge mistake.  I am floored that you attempted this.  I can easily afford such a mistake but I will always make a prototype before I run a production batch. 

well, I told you we were confident that it will work since nothing in the circuit is weird or special circuit. still, it is a mistake to do and I should learn from it.

Not trying to beat you up about it.  Yes, a learning experience.

The 1 nF cap is doing nothing useful in this design anyway.  So remove it.

I will remove it for sure. gonna keep u updated with what happens.

Ok

[VEGETA]

1nf caps turned off + no load on both rails:

power:
v_opamp_supply = 12.36
v_12v_input = 12.36v.

3.3v rail:
v_gate = 1.277v
v_drain = 12.36v
v_output_3.3v = 3.432v on connector + 3.432v on pin.
v_opamp_feedback = 3.442v
7805_3.3v_voltage_ref = 3.360v


5v rail:
v_gate = 1.598v
v_drain = 12.36v
v_output_5v = 5.116v
7805_5v_voltage_ref = 5.041v
v_opamp_feedback = 5.126v


same sound exist.

however, both now and before removing caps... i noticed when i press or touch R17  sound gets... faster.

[VEGETA]

1.6 ohm load:

power:
v_opamp_supply = 11.02v
v_12v_input = 11.06v.

3.3v rail:
v_gate = starts at 6.27 and keeps rapidly decaying, could not keep it up due to heat but it went below 5.7 and was still decaying. the solder melted while doing it due to heat and mosfet fell xD
v_drain = 10.65v
v_output_3.3v = 3.204v on connector + 3.255v on pin. it increases slowly but could not keep it up due to heat.
v_opamp_feedback = 3.289v
7805_3.3v_voltage_ref = 3.271v

[gnuarm]

The numbers on your circuit are all wrong and I can't tell you how to fix it without an oscilloscope to see what is going on.  You must have something oscillating. 

One thought.  It is very odd that the gate voltage is below the source voltage.  Try connecting the op amp output to the - input (V_FB1) short term.  The 3.3K R19 will allow the op amp output to control the input.  Then the gate voltage should be 3.3V regardless of load.  I'd like to see what the output is then. 

For the short term if I were you, I would focus on getting the switching regulators working and use this for the 3.3 volt output and a similar part for the 5V output.

https://www.digikey.com/en/products/detail/stmicroelectronics/LD1085D2M33R/669198

This will at least get you a working circuit to start with.  Then you can try some things with the FET circuit. 

[VEGETA]

if I connect pin 7 which is output of opamp to R19 (or the 3.3v output) it gives about 53mv on the 3.3v output while using 1.6 ohms load.

getting such LDO is good if I want to rework the circuit entirely since it won't fit on the current board. I don't think they will fit in the same board and layout.

If I am gonna re-do the circuit, I would probably use a good switcher IC with very little noise such as TPS62913 but this one still not active part, very new. Another part is LM61460, this one can deliver good noise\ripple (<10mV) but can't beat TPS62913 which can get below 1mv despite being a switcher. these ICs are not cheap but if I could get them to replace the linear stage + heatsink + extra components (opamp+7805) then I go for it


actually the original design of this psu uses similar approach to yours. see it in attachment. what do you think? it was very straight forward but I wanted cap multi and then you know what happened.

however, i still want to think there is a way to salvage these boards if we could solve the problem.

[Vovk_Z]

- I have attached a picture of my wiring + pictures of real wiring (no shorting between any pin).

I think you using C38, C38 1nF caps wrong. Remove them from gates, and put them between 1-2 and 67 legs of LM358.
...
And you may try lower R16, R17 a bit (22-47 R). But this is not the main problem.

[BrianHG]

I do not know how you are feeding the drains on the mosfets, but, I would wait until you install the AOZ1284 switcher ICs and power the PCB the way it was designed to be powered.  You cannot Gerry rig in a third party switcher which may be under-powered and inject ground bounce along long thin wires and connection to your uncertain

As for C38 and C39, yes, those should not be installed.

After the 2 AOZ1284 are installed, if there is oscillation because of a cheap op-amp, the easiest way to control it would be to place a cap 1nf, 10nf, 100nf cap between the mosfet gate and source.

I am not sure why your mosfets are conducting/feeding 3.3v out of the source when there is only 1.25v on the gate.  Are you sure your volt meter's GND is connected to the PCBs true GND?

[gnuarm]

if I connect pin 7 which is output of opamp to R19 (or the 3.3v output) it gives about 53mv on the 3.3v output while using 1.6 ohms load.

What is the voltage on pin 7 of the op amp?  Is that still about 3.3V?  Connecting to the +3V3 is a bad idea.  The point is the gate to drain voltage is wrong in all cases.  It is far too low with no load. 

Oh, and try testing at a current level that doesn't melt the solder!!!

getting such LDO is good if I want to rework the circuit entirely since it won't fit on the current board. I don't think they will fit in the same board and layout.

I'm pretty sure you can make it work the way you have things wired up now.  If the regulator doesn't work then maybe there is something wrong with the circuit board.

If I am gonna re-do the circuit, I would probably use a good switcher IC with very little noise such as TPS62913 but this one still not active part, very new. Another part is LM61460, this one can deliver good noise\ripple (<10mV) but can't beat TPS62913 which can get below 1mv despite being a switcher. these ICs are not cheap but if I could get them to replace the linear stage + heatsink + extra components (opamp+7805) then I go for it

This is why I asked what your goals/requirements were.  Do you really need to get ripple down to 1 mV?  You are trying to make it work in an application, what does that application require?

actually the original design of this psu uses similar approach to yours. see it in attachment. what do you think? it was very straight forward but I wanted cap multi and then you know what happened.

however, i still want to think there is a way to salvage these boards if we could solve the problem.

This is why I asked about the fixed gate drive.  You can use an NPN with a bias to V3.3 +  a diode drop to drive the base.  Then the gain of the transistor will smooth out the ripple. 

But why would you think any other circuit won't have a similar problem to this circuit?  Something is going on that you are not aware of.  This is a learning experience.  It's also an opportunity to learn how to use a scope.

What is the speed of the switching on the buck converters?  Certainly not over 1 MHz or not by much anyway.  You can get a 20 MHz digital USB scope to use with your computer for around $100.  That should work with your problem to let you see what is going on.  There are some open threads here for low end units.

[gnuarm]

I do not know how you are feeding the drains on the mosfets, but, I would wait until you install the AOZ1284 switcher ICs and power the PCB the way it was designed to be powered.  You cannot Gerry rig in a third party switcher which may be under-powered and inject ground bounce along long thin wires and connection to your uncertain

As for C38 and C39, yes, those should not be installed.

After the 2 AOZ1284 are installed, if there is oscillation because of a cheap op-amp, the easiest way to control it would be to place a cap 1nf, 10nf, 100nf cap between the mosfet gate and source.

I am not sure why your mosfets are conducting/feeding 3.3v out of the source when there is only 1.25v on the gate.  Are you sure your volt meter's GND is connected to the PCBs true GND?

Perhaps it would be better to measure each important parameter point to point, Vgs, Vds, etc? 

I have no idea what the long wires would be doing to a circuit like this.  The op amp is only about 1 MHz GBW i seem to recall, so a bit of stray capacitance shouldn't be that important, but still! 

[BrianHG]

Perhaps it would be better to measure each important parameter point to point, Vgs, Vds, etc? 

I have no idea what the long wires would be doing to a circuit like this.  The op amp is only about 1 MHz GBW i seem to recall, so a bit of stray capacitance shouldn't be that important, but still!

Yes.
Though, as the mosfet heats up, the voltage on the gate will decay since that figure is temperature dependent.
The opamp seems to have a huge differential offset.  Probably a fake LM358N.  This is not the quality I would like, but they can be still used if they don't oscillate, or worst case, a cap may be need across the mosfet gate and source to feedback/null the high frequency.

Without a scope, we cannot tell where that buzzing is coming from.  It might have something to do with his source switcher having a low power mode which pulses the power out.  Sending 12v to the mosfet drains will heat them up FAST without a heat sink.  They will still heat up without any heatsink even if you feed them 4.3v.  The method of sending 4.3v with an unknown switcher was never foreseen as a design consideration for this PCB.  The power loop and GND on that PCB was designed and is expected to be tight where the AOZ1284 switchers feeding the drains were designed to go from 0 amp load to 4 amp load, in constant frequency mode.

[gnuarm]

Testing does not need to be done at 2 amps.  The 100 ohm built in load is good enough.  Add a 10 ohm load to see how it does with a bit more current.  Measurements can be taken before the solder melts.  Provide power from a bench supply.  Add a resistor between the 12V rail and the drain to dissipate power.  There are a million ways to manage that. 

I don't know what to do here.  The op amp does not behave 100% correctly, the FET is really anomalous passing current with the gate at negative voltages wrt the source. 

If I were debugging the board I would be looking for something mechanically wrong like bad soldering or wrong connections.  I guess the board is being used because the small parts are on it.  I take it the FET is not the part designed in and so the wires to connect it?  I don't even see a part number on the schematic. 

If the switchers are to be mounted and tested, then the FET needs to be left off until the switcher is properly tested. 

He tried driving the gate from a fixed 3.3V, maybe drive it from a fixed 5V, but not a 2 amp load!  There is something wrong with the FET and it needs to be figured out. 

Heck attach a pot to the 12V supply with the wiper tied to the FET gate.  Take output measurements at every setting between 0 and say 4.5V, but with a 10 ohm load maybe. 

[VEGETA]

I will try putting a potentiometer at the gate of the mosfet to give its gate voltage from 0-12v. I hope connected opamp won't affect it. output load will be 47R for both rail.

also, I will try putting ceramic caps on mosfet source to gate.

switchers and original mosfets will need more time to arrive.

[gnuarm]

I will try putting a potentiometer at the gate of the mosfet to give its gate voltage from 0-12v. I hope connected opamp won't affect it. output load will be 47R for both rail.

also, I will try putting ceramic caps on mosfet source to gate.

switchers and original mosfets will need more time to arrive.

Don't do all these things at one time.  The op amp needs to be disconnected when you attach the pot wiper to the gate.  You can lift R17.  What FET are you using?  I've been looking at a data sheet for IRLIZ44NPbF.  Still, no FET should be on with a negative Vgs unless it is enhancement mode and I don't think they make those in power versions.

When you do soldering on the PCB you need to do it quickly.  Holding the iron on the board for extended times is not good for the tracks. 

[VEGETA]

I am using IRLIZ44N mosfets.

right now I have 2 boards, one with op-amp and 2 mosfets installed which is used on tests mentioned previously. and another one without opamp which I removed.

I will use the no opamp board for wiper test and the board with opamp for testing caps on source and gate.


as for your previous question on requirements, i wanted low noise low ripple psu for Sega Dreamcast. I would be happy with less than 10mV total ripple+noise. much happier with lower than 1mV but I guess it is kinda hard with my current skills.... until I found about TPS62913 but this IC still in pre-production.

So I am trying my best to make current circuit and boards work. worst situation is that I would redesign the board from scratch. then I would be using different and more straightforward and easy approach, like using those TI switchers I mentioned in previous post here.

[VEGETA]

I have tested putting 100nf then 1nf on source to gate... didn't work. sound increased and output voltage increased to 5.8v and 4.3 volts.

HOWEVER, I put 1000uF caps directly on 3.3v and 5v rails on the output connector... and it worked. sound disappeared and putting the massive load of 1.6 regulated well -> 3.3v on 3.3v rail and about 4.950v on 5v rail. It was increasing but I took it off due to heat.

same test on 3.6 ohms load resulted in 3.340v and 5.004v. on both trials... 0 sound happened. I could hear my air conditioner out of the sudden silence that happened.

any explanation of this?

EDIT:

I tried up to 100uF and it works, however 3.3 and 6.8uf didn't work.


no load test:

3.3v: 3.360v
5v: 5.042v
both 3.3v opamp inputs are 3.360 and 3.361.


1.6 ohm:
3.3v: 3.263 (increasing slowly, disconnected due to heat)
5v:4.925 (decreasing slowly, disconnected due to heat)
3.3v opamp ref: 3.325
3.3v opamp fb: 3.325
5v opamp ref: 5.020 or 5.019
5v opamp fb: 5.020

[gnuarm]

I think this indicates the previous readings were disrupted by a large AC component.  The circuit has been working all along, but the oscillations corrupted the measurements.  The gate voltage was probably messed up because of the rectification by the input diode.  Once you get your oscilloscope you will probably be able to see large excursions on the output of the op amp when you remove the cap.

Reminds me of one of the early researchers in liquefying gasses had been running the device for some time but could not see anything in the collection flask.  Finally he tried shining a light into the flask and found it was half full.  The optical density of the liquid was so close to the gas that the meniscus was hard to see! 

[gnuarm]

I'm actually very surprised you don't have a large cap on the output anyway.  Caps are the first and easiest way to clean up ripple after all.  The schematic shows 22 uF on the output.  Is that ceramic?  I would add a 470 uF electrolytic cap. 

[VEGETA]

I'm actually very surprised you don't have a large cap on the output anyway.  Caps are the first and easiest way to clean up ripple after all.  The schematic shows 22 uF on the output.  Is that ceramic?  I would add a 470 uF electrolytic cap.

well, you are correct. I assumed it would be enough to have 22uf ceramic despite knowing the elec. cap is easy to add and good to circuit.

maybe now I can buy elec. caps and solder them in a neat way on bottom side to make the circuit work and the product as intended. next version, I will try adding it in schematic and PCB layout near the pin. 100uf was enough but 470uf is better while having the same smt footprint.

so, can you figure out the oscillations source? I am annoying the scope guys with phone calls daily now...!

[BrianHG]

so, can you figure out the oscillations source? I am annoying the scope guys with phone calls daily now...!

It must be the opamp feeding the mosfet with it's hard turn-on 'knee', overshooting the output voltage, then relaxing down below the set output voltage.  The buzz was probably the 22uf ceramic output caps as that hard turn-on knee will make an audible sound do to the microphonic effect ceramic caps have.  The 1000uf cap prevents that turn-on & turn-off effect allowing the opamp to settle on a fixed voltage.  Without the cap, increasing the output load also has a similar effect as the output wont shoot past the set voltage as easily as a 33ma load being driven by a 50amp mosfet.

Though the gate voltage will change with mosfet temperature, the output should stay stable unless the opamp & 78L05 are also warming up.  However, this voltage change should only be a few 10s of mv, maybe 0.05v with a cheap opamp.  This output voltage drift can be removed with a high quality, or even temperature compensated opamp.

[gnuarm]

Continuing oscillations (as opposed to a temporary ringing) happen for one reason, the Barkhausen criteria is met.  That criteria is the loop gain is 1 and the phase change is 0.  Your circuit has an inversion at the op amp input (180 degrees), so another 180 degrees is being shifted in the RC of the capacitance.  Each RC circuit can shift up to 90 degrees.  Then a bit of delay in the amp adds the rest. 

Is C39 removed?  That part has lots of potential for causing oscillations.

I'm not sure how adding capacitance to the output fixes this, but regulators often have requirements for minimum and maximum output capacitance.  They also indicate a minimum ESR.  I'm no expert on control loop stability, so I can't explain the details of why your circuit gets so emotional.  That's also why I use off the shelf regulators. 

You might try a small cap across R19.  I often see this in regulator circuits for stability purposes.  Try your 1 nF cap there or even smaller, 100 pF is not too small.  This capacitor shifts the phase in the other direction and also improves the response time of the feedback loop.

[VEGETA]

Continuing oscillations (as opposed to a temporary ringing) happen for one reason, the Barkhausen criteria is met.  That criteria is the loop gain is 1 and the phase change is 0.  Your circuit has an inversion at the op amp input (180 degrees), so another 180 degrees is being shifted in the RC of the capacitance.  Each RC circuit can shift up to 90 degrees.  Then a bit of delay in the amp adds the rest. 

Is C39 removed?  That part has lots of potential for causing oscillations.

I'm not sure how adding capacitance to the output fixes this, but regulators often have requirements for minimum and maximum output capacitance.  They also indicate a minimum ESR.  I'm no expert on control loop stability, so I can't explain the details of why your circuit gets so emotional.  That's also why I use off the shelf regulators. 

You might try a small cap across R19.  I often see this in regulator circuits for stability purposes.  Try your 1 nF cap there or even smaller, 100 pF is not too small.  This capacitor shifts the phase in the other direction and also improves the response time of the feedback loop.

C39 and C38 are removed. even when removed, without elec. caps, the circuit still have the same behavior. adding the elec. caps was the answer.

now I need to figure how to add them to the boards in a neat way. 

also, to modify the PCB and add them as smt parts on bottom side. I guess there is some room near the mosfets and along the way to output connector. putting small elec caps can be done there... 100uF is guaranteed but gonna search lcsc for bigger value caps with small sizes.


I will try adding a small 1nf cap around r19 to see if i can get away with it and without elec caps.

[VEGETA]

I was searching for high quality switchers do to another version, as a side project and found these:

https://www.ti.com/product/TPS62913 -> promises noise\ripple in the uV range. still pre-production, TI told me release date is still not confirmed and fat. approx price is 1.8-2.5$ @ 100 quantity. ~1.65$ @ 250 quantity.

https://www.ti.com/product/LM61460 -> active part. output noise\ripple is <5 mV for FPWM mode, and about 10 mV for auto (if I read the graphs properly). Price is 3.3$ @ 100 quantity, <3$ @ 250 quantity.

https://www.analog.com/en/products/LT8652S.html -> active and new part with Silent Switcher 2 technology. Promises 10 mV ripple\noise at full load without putting extra caps\inductors. It has 2 outputs so it can be used as one chip solution for 3.3v and 5v. Price is 5.8-6.5$ @ 100 quantity. So maybe 6$ for one device plus passives and output connectors... probably cheaper than multi part solution? I kinda like this solution if I could enhance its output to lower than 5mV as a side project for now (no 125 boards hhhh).

what do you think of these picks if you were to design it again?

Note: for now, I am sticking with current design and will enhance it by adding the required caps to the boards. this is for not-so-seen future xD

[VEGETA]

I realized I made a stupid choice of getting 3.96mm pitch 2-position connectors instead of the standard for fans of 2.54mm.

I guess this won't be fixable on current boards... damn. more to fix on next boards version...

[gnuarm]

So I spent a little time simulating an idea and here is what I came up with.  This circuit uses transistors in place of the op amp since that is limiting the performance.  Even then, the limitation seems to be in driving the capacitance of the FET gate.  The FET in this simulation is fairly low, 9 nC.  They measure the charge required rather than the actual capacitance since that is the more useful way to view it.  By adding 8 - 0603, 1 uF, low ESR, ceramic caps I got the output ripple down to 7 mVpp with a 100 mVpp ripple at the input (from the switcher).  I think that is pretty good.

To utilize the caps to their best advantage will require good layout.  I also added a 100 uF electrolytic cap, but it does little for the ripple really.  The ESR on that type of cap is large.  0603 is a good size for ceramic caps.  Smaller is better for high frequency, but this is not so high as to require 0402 or smaller caps.  You can find 0805 size with lower ESR which might let you use fewer of them.  Since they are larger it may be a wash in terms of board space. 

The resistors are sized to use 26 mA in the control circuit.  Using less current slows it down for more ripple.  The resistors can be smaller (higher current) for lower ripple, but a point of diminishing returns will be eventually reached. 

I just read about the fan connector.  That can be fixed with an adapter cable easily enough.

[VEGETA]

putting a ceramic 22nf cap around r19 didn't help. also around d3 and d4 (opamp inputs) didn't help. the only way it could be stable is just on the output.

I tested that 100uf is the minimum it works with, I will be  buying lots of them to hand solder them. However, making them fit neatly is tricky.

looks like you didn't check the 3 switchers I posted above.

if I ever get a scope I will test your circuit.


EDIT: I found that 220uF 16v elec. caps are the perfect physical size. they are shorter than 100uF 16v but a bit wider which is not important. I guess 220uF gonna be ok.

[gnuarm]

No, I didn't read the data sheets on the three candidates.  I think you said you had to wait for two of them as they are not in production.  All three would require a board spin.  What would you like me to look at exactly? 

If 100 uF is the minimum that makes the circuit stable then you definitely want to use the 220 uF part.  But you need to test with the parts you will use and get a data sheet to see what the ESR is.  The ESR is likely more important than the value of capacitance. 

There are many form factors for capacitors.  I'm sure you can get both parts in the same height.  What is important to a capacitor is volume.  More capacitance or more voltage means more volume if all else is the same.  There is no reason to let the form factor dictate the electrical value of the capacitor.  What height are you using?  Our project is using some large value caps that are pretty compact, 8.3 mmsq x 10 mm tall, 1,000 uF, 25V.  Since you can use a smaller value and voltage you should be able to find a much smaller package.  Have you used Digikey's search facility?

What is the frequency of the switchers you have designed in?

[gnuarm]

Did you look into the many USB attached digital oscopes available and reviewed on this site?  I think many of them will do the job you need with a price around $100.

[VEGETA]

No, I didn't read the data sheets on the three candidates.  I think you said you had to wait for two of them as they are not in production.  All three would require a board spin.  What would you like me to look at exactly? 

yes that would require board respin as an updated version, let's call it version 2. which is not top priority right now. I wanted your opinion about using these as the main part in v2 of the board which is gonna be without linear stage. will they be good enough to reach <10mV ripple\noise? perhaps even lower than that?

TPS62913 is the only one which is still in pre-production, the others are active. LM61460 seems good but only 1 output at relatively high price, while LT8652S has 2 outputs in one package with price of 6.5$ @ 100 quantity, very pricey but gonna be enough to do everything by itself plus passives. do you know better switchers in terms of output ripple?

If 100 uF is the minimum that makes the circuit stable then you definitely want to use the 220 uF part.  But you need to test with the parts you will use and get a data sheet to see what the ESR is.  The ESR is likely more important than the value of capacitance.

There are many form factors for capacitors.  I'm sure you can get both parts in the same height.  What is important to a capacitor is volume.  More capacitance or more voltage means more volume if all else is the same.  There is no reason to let the form factor dictate the electrical value of the capacitor.  What height are you using?  Our project is using some large value caps that are pretty compact, 8.3 mmsq x 10 mm tall, 1,000 uF, 25V.  Since you can use a smaller value and voltage you should be able to find a much smaller package.  Have you used Digikey's search facility?   

the ones I will get are 220uF 16v elec. caps which are leaded not smt, and from local suppliers. will never get them from outside. I have small quantity here and they are tiny, like 7mm in length which is suitable to the board since I am gonna hand solder them and situate them where it fits.

However, for the enhanced version of this current design (call it v1.1), I will include smt elec. caps on board for sure while removing 1nf opamp to mosfet gate caps. footprint won't be a problem since we need 6.3v rated caps which are generally small. I guess we can even get 470uf with low footprint, gonna get down to do it sometime in near future.

Also, I have included a pi filter (1uH inductor with ceramic caps before and after it) for both switchers output just before linear stage. its placement in layout is not perfect but probably better than before.

What is the frequency of the switchers you have designed in?

we went for 2 MHz.

Did you look into the many USB attached digital oscopes available and reviewed on this site?  I think many of them will do the job you need with a price around $100.

I know some Hantek and Owon ones. getting them to me in Jordan will have shipping costs and customs.

I saw this one on Amazon for quite good price. gonna take 41$ shipping and customs fee. However it doesn't support AC coupling!

this one seems better but it will cost 150$ to get here.

I will wait to see what happens with that DOS1102 used scope for now.

[BrianHG]

yes that would require board respin as an updated version, let's call it version 2. which is not top priority right now. I wanted your opinion about using these as the main part in v2 of the board which is gonna be without linear stage. will they be good enough to reach <10mV ripple\noise? perhaps even lower than that?

TPS62913 is the only one which is still in pre-production, the others are active. LM61460 seems good but only 1 output at relatively high price, while LT8652S has 2 outputs in one package with price of 6.5$ @ 100 quantity, very pricey but gonna be enough to do everything by itself plus passives. do you know better switchers in terms of output ripple?

Take a careful look at the TPS62913 datasheet's example PCB.  The example PCB, figure 10-2 on page 29 with the second LC filter was needed to achieve the super low < 10uV ripple noise.  That PCB is 44mm wide.  If you want to replicate that low noise, you will need to make a PCB at least 44mm plus your final output connectors, say 55mm wide.  Now I am not saying you need a perfect replication, but, if you want what's shown to you in the datasheet, you need that 'void/space' between the switcher and second inductor L, at least 3/4 the width I said.  To prevent power dips during transient current loads, especially on the 3.3v rail, you will want some heavy-duty uF caps on the output as well as the source 12v supplying the system.

Noting that it is a TI part, I believe you can achieve a good clean 3 amps with the part if you use the same primary L1 inductor.

Following the rules, you should expect that the 12v to 3.3v 7mv ripple on figure 6.11 should vanish like what's seen on figure 6.13, though the switcher performs with half the noise when going from 5v to 3.3v.

Going back on this thread, I posted another low EMI switcher from TI like the LM61460, but it was a 4 amp version.  Just another part you might look into.  Make sure you configure either switcher in FPWM mode so that the output stays perfectly regulated even at currents below 500ma at the cost of some efficiency when drawing low current outputs.  Since you aren't making a battery powered device, the FPWM mode is fine.

[BrianHG]

this one seems better but it will cost 150$ to get here.

I will wait to see what happens with that DOS1102 used scope for now.

The USB isolation is a good protective measure, all round, not just for your PC, but the device you are testing.

[VEGETA]

Take a careful look at the TPS62913 datasheet's example PCB.  The example PCB, figure 10-2 on page 29 with the second LC filter was needed to achieve the super low < 10uV ripple noise.  That PCB is 44mm wide.  If you want to replicate that low noise, you will need to make a PCB at least 44mm plus your final output connectors, say 55mm wide.  Now I am not saying you need a perfect replication, but, if you want what's shown to you in the datasheet, you need that 'void/space' between the switcher and second inductor L, at least 3/4 the width I said.  To prevent power dips during transient current loads, especially on the 3.3v rail, you will want some heavy-duty uF caps on the output as well as the source 12v supplying the system.

The 2nd filter is necessary for the performance, it is just a ferrite bead with some caps and they take the feedback after the ferrite bead.

I didn't find where they mention I need that space, but rather the layout shape has to be followed. I would need 2 of that switcher, one for 3.3v and another for 5v, all will be in 50x50mm board since now a lot of components (mosfets + 7805 + opamp) won't be there which makes room.

Following the rules, you should expect that the 12v to 3.3v 7mv ripple on figure 6.11 should vanish like what's seen on figure 6.13, though the switcher performs with half the noise when going from 5v to 3.3v.

yes, the performance is all about the 2nd filter. it achieves <500 uV total ripple and noise which is marvelous. the only hard part about it is the layout which in of it self not so hard given time. remember this is gonna be the only critical component in the board.

Going back on this thread, I posted another low EMI switcher from TI like the LM61460, but it was a 4 amp version.  Just another part you might look into.  Make sure you configure either switcher in FPWM mode so that the output stays perfectly regulated even at currents below 500ma at the cost of some efficiency when drawing low current outputs.  Since you aren't making a battery powered device, the FPWM mode is fine.

you mean LM61440? about 2.27$ @ 250 quantity, so 4.6$ for 2 of them, assuming removing linear stage and other stuff, this is not so expensive. it shows 20mv p-p for 100mA auto mode which is not good but the 4A load is about 3.5 mV auto mode. they don't show the output ripple\noise for fpwm mode though. I assume if we used fpwm mode and added other stages of L-C filters plus big bulk caps we would achieve < 1mV??

[Vovk_Z]

I'm actually very surprised you don't have a large cap on the output anyway.  Caps are the first and easiest way to clean up ripple after all.  The schematic shows 22 uF on the output.  Is that ceramic?  I would add a 470 uF electrolytic cap.

Using quite a large (470 uF) cap at the output to maintain stability - is not a smart way. It is rather the opposite. (I'm sory).

[VEGETA]

I'm actually very surprised you don't have a large cap on the output anyway.  Caps are the first and easiest way to clean up ripple after all.  The schematic shows 22 uF on the output.  Is that ceramic?  I would add a 470 uF electrolytic cap.

Using quite a large (470 uF) cap at the output to maintain stability - is not a smart way. It is rather the opposite. (I'm sory).

well, putting a large cap 100uf or more was the solution to the problem and made the circuit stable. I will use 220uF.

what is you suggestion then?

[VEGETA]

I've been playing around and got some modification to the board:

- 1nF caps of opamp output removed.
- R19 is now 6.8K.
- added elect. caps (220uF) to linear output + 2 more ceramics (100nF + 1nF).
- added LC filter after switchers which are 2.2uF with 100nF + 1nF caps before and after it. I've put them in the layout as good as I could, maybe not perfect.
- adjusted the footprint of J1, J4 and J5 to be 2.54mm since this is the standard which made a lot of room.

here are some pics: https://slow.pics/c/9loK3z3G

[BrianHG]

I've been playing around and got some modification to the board:

- 1nF caps of opamp output removed.
- R19 is now 6.8K.
- added elect. caps (220uF) to linear output + 2 more ceramics (100nF + 1nF).
- added LC filter after switchers which are 2.2uF with 100nF + 1nF caps before and after it. I've put them in the layout as good as I could, maybe not perfect.
- adjusted the footprint of J1, J4 and J5 to be 2.54mm since this is the standard which made a lot of room.

here are some pics: https://slow.pics/c/9loK3z3G

Yes the 220uf are needed, however, the way you had to wire the LC filter due to location and space may make things worse or have no effect.  Notice on the example TI PCB how straight and fat the GND and filter cap traces are for their LC filter and how deliberately separated from the switcher it is positioned.  It is laid out that way on purpose.  I would wait until you can scope the current board to see if the extra LC filter is needed.

As for R19 and R18, I cannot say what the best value should be without scoping the PCB.  They were put in to prevent the input of the opamp from receiving the 'grunt' of a high current power signal trace, not as some sort of gain value.  I would make those 2 resistors as small as possible yet not be too heavy current if the opamp input happens to be diode clamped during power-up or power-down.  I would have used 1k for those 2, but, you were 'part consolidating'...

[VEGETA]

the way you had to wire the LC filter due to location and space may make things worse or have no effect.

i am open to suggestions as i told you they placing is not perfect. however, only the one on top is kinda bad as it is above Vcc trace, the other one is good. for the one on top, i can let the power trace go down a bit to make room for making ground trace as thick.. gonna eat a bit of the mosfets pour but still ok.

I can even relocate all of them to be directly above L5 which makes power and gnd signals short and thick.

moving the other LC filter to the right will make it above 5v and 3.3v rails... not good.

As for R19 and R18,

changing resistor values is easy. I can choose any other value used in the design if it suites, or at worst case, get a new value. no big deal.

[VEGETA]

oscilloscope wise.. getting my dream DS1054Z will cost me 461$ from amazon but without customs which may get 100$ more... while from a proxy service ubuy will cost me totals including customs 421 JOD which is 594$ not so huge but not so little. Isolated Owon will cost 150$. the DOS1102 guy still didn't respond and I am getting frustrated.

The only think available locally is this: https://mikroelectron.com/Product/PICOSCOPE-2204A-MADE-IN-UK/ which is 100 JD (145$ or so) for just 10 Mhz with 10mv per div.

[gnuarm]

I've been playing around and got some modification to the board:

- 1nF caps of opamp output removed.
- R19 is now 6.8K.
- added elect. caps (220uF) to linear output + 2 more ceramics (100nF + 1nF).
- added LC filter after switchers which are 2.2uF with 100nF + 1nF caps before and after it. I've put them in the layout as good as I could, maybe not perfect.
- adjusted the footprint of J1, J4 and J5 to be 2.54mm since this is the standard which made a lot of room.

here are some pics: https://slow.pics/c/9loK3z3G

Yes the 220uf are needed, however, the way you had to wire the LC filter due to location and space may make things worse or have no effect.  Notice on the example TI PCB how straight and fat the GND and filter cap traces are for their LC filter and how deliberately separated from the switcher it is positioned.  It is laid out that way on purpose.  I would wait until you can scope the current board to see if the extra LC filter is needed.

As for R19 and R18, I cannot say what the best value should be without scoping the PCB.  They were put in to prevent the input of the opamp from receiving the 'grunt' of a high current power signal trace, not as some sort of gain value.  I would make those 2 resistors as small as possible yet not be too heavy current if the opamp input happens to be diode clamped during power-up or power-down.  I would have used 1k for those 2, but, you were 'part consolidating'...

The only reason to use R18 and R19 at all is because of the bias current of the op amp inputs.  Ideally this resistance is as low as possible, but it should match between the + and - inputs.  This creates a balanced drop for both inputs minimizing offset.  V5 runs through a 3.3K resistor to the + input of U4A so R18 is 3.3K.  V3.3 is from a divider that produces a 6.7K Thevenin equivalent so R19 should be 6.7K.  Of course these values can be adjusted up or down as long as the + and - input resistances match.  The schematic is an image rather than a PDF so I can't search it to see where V_5 goes and how much current is drawn, but I expect the total load is light and the resistor chain for creating V_3.3 can draw a lot more current without problem.  Or a proper voltage reference could be used and resistor dividers used for feedback, but I think it has been said that the DC accuracy is not at all important.

[gnuarm]

oscilloscope wise.. getting my dream DS1054Z will cost me 461$ from amazon but without customs which may get 100$ more... while from a proxy service ubuy will cost me totals including customs 421 JOD which is 594$ not so huge but not so little. Isolated Owon will cost 150$. the DOS1102 guy still didn't respond and I am getting frustrated.

The only think available locally is this: https://mikroelectron.com/Product/PICOSCOPE-2204A-MADE-IN-UK/ which is 100 JD (145$ or so) for just 10 Mhz with 10mv per div.

For what you are doing now that is just fine.  You say you want the noise and ripple as low as possible and so need a good scope to measure it.  But to sell a product you only need the noise and ripple low enough to work in the application.  i think that is going to allow noise and ripple at levels easily seen by the 10 MHz Picoscope.  The idea of getting the levels below 1 mV are not useful really unless you had sensitive analog circuitry which does not include standard video signals. 

[Vovk_Z]

what is you suggestion then?

It was at post #318.

[VEGETA]

what is you suggestion then?

It was at post #318.

you said:

I think you using C38, C38 1nF caps wrong. Remove them from gates, and put them between 1-2 and 67 legs of LM358.
...
And you may try lower R16, R17 a bit (22-47 R). But this is not the main problem.

1nF caps removed from v1.1 and gonna physically remove them from current boards. putting it at opamp 1-2 and 6-7 legs didn't do much without 220uF at final output rail. I tried putting 22nF instead of 1nf at opamp 1-2 and 6-7 but didn't work too.

lowering R16 and R17 is not that important as you said, not the problem.

so now we need a solution other that bulk elec. caps at output, if you have one.

[Vovk_Z]

Is there a last schematics?

[VEGETA]

Is there a last schematics?

i have sent it to you via PM.

i didn't lower 100 ohm resistors though.

[BrianHG]

The only think available locally is this: https://mikroelectron.com/Product/PICOSCOPE-2204A-MADE-IN-UK/ which is 100 JD (145$ or so) for just 10 Mhz with 10mv per div.

I don't know... Never heard of picoscope.  I would start a thread here on EEVblog and ask around first.  There exist many true lemons when it comes to these tiny devices.

[Vovk_Z]

as for your previous question on requirements, i wanted low noise low ripple psu for Sega Dreamcast. I would be happy with less than 10mV total ripple+noise.

If less than 10 mV noise is ok then you don't need any linear post filtering at all. Just a small LC output filter could be fine.

[gnuarm]

as for your previous question on requirements, i wanted low noise low ripple psu for Sega Dreamcast. I would be happy with less than 10mV total ripple+noise.

If less than 10 mV noise is ok then you don't need any linear post filtering at all. Just a small LC output filter could be fine.

I agree.  This project is what happens when you don't have proper requirements.  Better is the enemy of good enough. 

I believe the progression was,

• I need a cleaner PSU output.
• I need a capacitance multiplier
• Add op amp feedback to that capacitance multiplier
• Change the NPN to an nFET because it's lower impedance

Nowhere in this process was the imagined result compared to what was needed.  If some is good, then more is better and too much is just enough.

Not trying to harp on things, but I'm working on a volunteer ventilator project with virtually no requirements and no understanding of requirements analysis.  A revision 1 of the pcb was completed in a couple of months.  Revision 2 is at the 9 month mark.  I think I'm suffering from PTSD.

[gnuarm]

The only think available locally is this: https://mikroelectron.com/Product/PICOSCOPE-2204A-MADE-IN-UK/ which is 100 JD (145$ or so) for just 10 Mhz with 10mv per div.

I don't know... Never heard of picoscope.  I would start a thread here on EEVblog and ask around first.  There exist many true lemons when it comes to these tiny devices.

For USB attached scopes Picoscope is top notch.  That's why a 10 MHz unit is $145 rather than well under $100 like the crap devices.

I remember back in the day of analog scopes the real separation between the good scopes and the so-so scopes was their triggering.  I think that is still true.  Unfortunately it is harder to specify the triggering specs, not that it would matter much.  Makers lie about all the other specs, triggering would just be another one to lie about.

There's a thread here somewhere for a new scope company that might actually be producing a decent, low cost product.  Over a year ago the guy was posting about a new lower end product like this one.  I think now he is selling a better spec devices for a price like this one.  Here is a price sheet the guy posted.
https://drive.google.com/drive/folders/178z_YfgW_qpdFXZxuJiwVYOVIO74Y6BA

Here is one of the threads where Loto is mentioned. https://www.eevblog.com/forum/testgear/how-to-promote-an-usb-oscilloscope-to-individual-engineers-i-am-the-loto-instru/?all]
[url]https://www.eevblog.com/forum/testgear/how-to-promote-an-usb-oscilloscope-to-individual-engineers-i-am-the-loto-instru/?all[/url]

[VEGETA]

update: I managed to have an offer for Hantek 6022BE very lightly used for 100 JOD (140$). this is the only thing available to me now. it is the same as that 10Mhz picoscope.

the hantek doesn't support ac coupling, i guess it is important to have ac coupling for our use.

which one should I get? since they are the same price.

[gnuarm]

I don't know what you mean the Hantek is the same as the Picoscope.  I have a 6022 Hantek that I never got to work because the software would not run.  They have no support and their products are universally deprecated.  I have the version with the logic analyzer built in and paid only $80 for it. 

If I knew where it was I would send it to you. 

My recommendation is to get pretty much anything other than the Hantek.

[VEGETA]

I don't know what you mean the Hantek is the same as the Picoscope.  I have a 6022 Hantek that I never got to work because the software would not run.  They have no support and their products are universally deprecated.  I have the version with the logic analyzer built in and paid only $80 for it. 

If I knew where it was I would send it to you. 

My recommendation is to get pretty much anything other than the Hantek.

I meant they both have 2 channels and same price. actually the picoscope was 180JD (254$) and now on offer to be 100 JD (140$). it supports ac and dc coupling 10mv\div sensitivity @ 10mhz but the hantek is 20mhz with dc coupling only.

so you suggest i go with picoscope?

[BrianHG]

but the hantek is 20mhz with dc coupling only.

Get a .1uf cap and place it at the end of the probe.
But I get the drift, why the difficulty in avoiding a single relay which would be needed to switch between AC&DC input.

[gnuarm]

update: I managed to have an offer for Hantek 6022BE very lightly used for 100 JOD (140$). this is the only thing available to me now. it is the same as that 10Mhz picoscope.

the hantek doesn't support ac coupling, i guess it is important to have ac coupling for our use.

which one should I get? since they are the same price.

"Bandwidth" is often the subject of lies. 

The Hantek samples at 48 MSPS, the Picoscope at 100 MSPS.  Which do you think will work better?  What happens when using two channels? 

Read a few reviews.  This is your money.  Spend it wisely based on facts, not other people's opinions.  I have my own biases. 

[VEGETA]

Looks like I will be getting the picoscope. 10mhz will be good enough for now, and it has ac coupling too unlike the hantek. hantek price is too much too.

on a side note, we decided 220uF to be the go-to value since it was shown to be stable with 100uF. However, I ran another test and the circuit got to be stable with about 17uF elec caps only (6.8u + 6.8u + 3.3u) on 5v rail and (6.8u + 6.8u + 6.8u) on 3.3v rail for the 1.6 ohms load. meaning, I could use smaller value like 22uf or 47uf. I still want to get 220uF if I got small enough formfactor though. won't make a final decision until I see the FULL circuit with all components since I am still hoping it will work better.

Then I can test various caps values.

[VEGETA]

I finally got all parts.

Unfortunately, I couldn't solder the switchers properly. I have an air dryer, not a heat gun... despite being very hot, it wasn't enough to melt the solder paste that I got locally (liquid and gel type).

I managed to solder one switcher IC somehow using soldering gun and the result is 7.1v on the 5v output for some reason. I later on lost this IC in solder mania. even though it outputted 7.1v, it still produced that annoying sound which needed an electrolytic cap to disappear.

Maybe tomorrow I could remove the solder mask from switcher pin 9 (thermal pad) to be able to solder it using soldering iron.

the weird thing on this board which had the soldered switcher, is that the 5v regulator outputted 7.1v exactly as the feedback pin on the opamp but when removing the switcher it outputted 5v normally.

I started to get really frustrated on this project after all that time and many hardships + my big fatal mistake on making many boards at once without testing it.

I made another version using the same switching circuit + LC filters but with very simple off-the-shelf linear regulators as seen in attachments. I also layed out the board (same switching parts). but if the switching part is the problem, then maybe I should consider something else??

I will keep you updated on tomorrow's trials but also I would like to hear your opinion on making another version of this project which is simpler and gonna 100% work.

required specs are:

1- straight forward design that is guranteed to work, no homebrew linear stuff. off-the-shelf parts.
2- < 10mV P-P total noise and ripple. Preferably less than that if possible without significantly more costs.
3- can be assembled using cheap PCB assembly services or manually.
4- 50x50mm board size exactly as this one.
5- preferably without heatsink or linear parts if possible.

^ these were clear specs to work with now, and I am fueled by my anger this time to make a better one. one that is clearly better than any other solution on the market.

I am sorry to tire you all with me all that time, but I really learned the very hard lesson from this.

[VEGETA]

I started also a separate one using TPS62913 which is going to be in production soon as TI confirmed, pre-production parts are available and identical as they confirmed. this one delivers in the uV range total noise and ripple as in their datasheet.

I layed the board exactly as their app note and datasheet says, but only one rail for now as seen in picture below.

JLCPCB won't be able to assemble this as they don't have the TI one in their library but PCBWay for sure can, dunno about price for just 5 assembled boards will be.

so now we have this one here to go with or your suggestion.

always thanks for your support and sorry again for dragging you with me this far to get frustration.

[gnuarm]

Hi, good to see you back.  I have to say one thing I learned from the exercise with you previously was that while I'm still not impressed with a capacitor multiplier, it did one thing well.  That is handle higher frequency ripple which an IC based linear regulator can't do because of the limited bandwidth of the amp inside.  That would have been the same problem with your op amp based design since the op amp has limited bandwidth. 

So a linear following the switcher can be effective if it just uses the transistor and not the op amp.  That circuit would remove the ripple very well, but not maintain a stable output from load variations so well.  I don't see that in your requirements, so I don't know if this is an option. 

But it sounds like you want nothing to do with linear stages.  So...

Does TI say how their chip works to reduce the ripple so much?  When did they say they would have samples and when would they have production?  Actually, it looks like they have samples now.  You can buy up to 50.  Why not get a hand full and see how the prototypes work?   The data sheet looks pretty wild.

[VEGETA]

Hi, good to see you back.  I have to say one thing I learned from the exercise with you previously was that while I'm still not impressed with a capacitor multiplier, it did one thing well.  That is handle higher frequency ripple which an IC based linear regulator can't do because of the limited bandwidth of the amp inside.  That would have been the same problem with your op amp based design since the op amp has limited bandwidth. 

So a linear following the switcher can be effective if it just uses the transistor and not the op amp.  That circuit would remove the ripple very well, but not maintain a stable output from load variations so well.  I don't see that in your requirements, so I don't know if this is an option. 

But it sounds like you want nothing to do with linear stages.  So...

Does TI say how their chip works to reduce the ripple so much?  When did they say they would have samples and when would they have production?  Actually, it looks like they have samples now.  You can buy up to 50.  Why not get a hand full and see how the prototypes work?   The data sheet looks pretty wild.

hello and thanks for your follow.

I have a low ripple low noise requirement, a total of <10mv p-p.

What do you think about my 1084-based design? also the TI one?

I messaged TI and they said this IC will be available in late march, which is maximum of 2 weeks. the pre-production ones are usable though, same package and same footprint. so I could use the pre-production one in prototype PCBs for now using PCBway right?

check TI datasheet and app note, here is what is in datasheet:

Low output 1/f noise < 20 μVRMS (100 Hz to 100kHz)
•  Low output voltage ripple < 10 μVRMS after ferritebead
•  High PSRR of > 65 dB (up to 100 kHz)
•  2.2-MHz or 1-MHz fixed frequency peak currentmode control

and see figures of 2nd stage ripple and noise, it is well below 0.5mv total!

here is an evaluation unit: https://www.ti.com/lit/ug/slvubx2a/slvubx2a.pdf?ts=1615930746111&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FTPS62913

it is a new design of this chip which uses ferrite bead inside compensation loop itself to achieve this. the IC is tiny though but can deliver 3 amps. i guess 3 amps is enough for 3.3v rail and more than enough for 5v rail.

[gnuarm]

I don't know anything about the 1084 design.  The TI device is interesting.  I haven't read enough of it to understand how it works.  If you use any of these I recommend you read the data sheet thoroughly and make your design as close as possible to the reference design they provide.

Also be aware that their testing is done under perfect conditions of constant load, etc.  Load regulation is often as important as removing ripple.  Does the TI data sheet show anything regarding load transient regulation?

[VEGETA]

I put a link for a design of mine using 1084 regulator, check it above.

anyway, the TI part uses 2nd pole\stage internal compensation to achieve such low values of noise and ripple. datasheet says < 25uV of total RMS noise and ripple which is insanely good. assume my layout wasn't perfect and caused this to double, it will be 50uV or let's say it was a bit more worse, 100uV... this is still extremely nice.

I didn't find enough data on load regulation in their datasheet but they mentioned that I should do good layout to prevent bad load regulation which I will anyway.

I am gonna continue with this TI part if you don't have a better alternative. Last night I kept doing the layout of the board but didn't finish it. Once I finish it, I will review the layout with you here.

[VEGETA]

I managed to solder the 5v switcher properly and when mosfet is there it works (+ filter cap to remove sound). However, when I put 1.6 ohms load it drops to 4.750v instead of 5.050v when no load.

I also soldered a 3.3v switcher on another board somehow and it outputted the required 4.6v, but this board got ruined again.

[gnuarm]

What is the input voltage to the 5V switcher when it is under load?  Did you get your scope yet?  You can view the waveforms across the high current components and see what is happening.  A switcher should regulate normally until the transistor is saturated. 

Is this a no name switchers from eBay or Aliexpress?  They are often not nearly up to the specs they claim.

[VEGETA]

What is the input voltage to the 5V switcher when it is under load?  Did you get your scope yet?  You can view the waveforms across the high current components and see what is happening.  A switcher should regulate normally until the transistor is saturated. 

Is this a no name switchers from eBay or Aliexpress?  They are often not nearly up to the specs they claim.

No scope yet.

I tried for hours and hours last night but no use, soldering it is difficult. I succeeded twice but somehow it got ruined again. I will try next week when I return.

I got this AOZ1284 switcher from LCSC.

input voltage to switchers are the 12v source, dunno if it changes with load but it shouldn't.

[gnuarm]

I don't think you realize how little information you provide when you answer a question.  Of course the input to the switcher is a "source".  Is it another power supply? a battery?  Can't you measure the voltage with a meter when the switcher is drooping?

I'm asking the question to try to diagnose what is wrong.  That means details are needed.  Your 1.6 ohm load will draw over 3 amps on a 5V source.  Is the circuit rated for that?  I'm not asking about the data sheet for the chip.  I asking about the design.

It's going to be very hard to diagnose a problem that makes a switcher droop.  First thing to try is other loads.  Find out if it is drooping at lower currents like 2 amps, 2.5 amps, 1 amp...  If it is only drooping above some current the current limit must be kicking in.  If the droop depends on the current over a wide range, then something is wrong that is interfering with the regulation. 

[VEGETA]

Ok I will try soldering the switchers next Monday and do more detailed tests.

Is it another power supply? a battery?

it is an adjustable wall power supply which can deliver 12v @ 3amps, not bad quality.

Your 1.6 ohm load will draw over 3 amps on a 5V source.

the switchers are supposed to have 4 amps of maximum current, so 3.2 amps should be fine. of course the final output needed for 5v is less than 2 amps. the dreamcast won't take more than 1 amps actually. However, we wanted to have 2 amps for the 5v rail just in case mods are installed. in summery, the circuit should output 2-3 amps and more. However, the mosfets will get hot without heatsink so a heatsink is required. I didn't install one yet since I don't have one but as you said, more tests will be done.

It's going to be very hard to diagnose a problem that makes a switcher droop.  First thing to try is other loads.  Find out if it is drooping at lower currents like 2 amps, 2.5 amps, 1 amp...  If it is only drooping above some current the current limit must be kicking in.  If the droop depends on the current over a wide range, then something is wrong that is interfering with the regulation.

yes I will have other loads once I make a complete board with 2 switchers. it is very hard to solder them! last night I barely could solder one switcher using the "scrap the solder mask and tin it with solder then put ic and heat using iron technique".

If I get one board complete and did all these tests, I will send it to you via EMS if you accept.



On a side note, the TI design is about to be complete. I am just figuring out the inductor choice now.

[VEGETA]

I have managed to solder the 3.3v switcher and mosfet, and it works.

It outputs the following:

without elec. cap: 3.4v (+some 10s of mV, didn't remember).
with elec. cap: 3.360v

with elec. cap + 1.3R load: 3.294v (starts at about 3.3v but slowly decreases as it gets hot, no heatsink).

However I noticed something very weird, that is the switcher doesn't start at all until I momentarily short the pin #1 which is the output with pin #9 which is the input of 12.6v. I noticed this very clearly.

After this moment of touch, it starts working as described.


On a side note, I finished the design using the TI part TPS62913 and sent it to PCBway and AllPCB. Got a final offer from PCBway for 5 completely assembled boards of 181$ including shipping and still waiting for AllPCB offer. 181$ is so expensive since the TI part from PCBway is about 3.5$ each = 35$ total for 5 boards. Not gonna be economical for production with this price but it gets decreased with quantity + it is still pre-production unit. If you can help, I can send you the schematic + layout to check. I followed it as best as I can according to datasheet and app note.

[gnuarm]

Not sure why the cap would impact the output voltage.  A 6 mV droop with temperature is good.  Very few applications are actually concerned with the exact voltage.  Noise on the rail is more important if you are running analog circuitry from it. 

I forget, what problems are caused by the ripple in the supply?  Does it mess up the video sync?  It seems like that could be resolved with some filtering capacitors on the supply into the impacted circuitry.  I can't remember why you need to get sub millivolt ripple levels.

Why not post your schematics here?  It is helpful if you can print them to a PDF with the text intact so part numbers can be selected and copied and ref des can be searched. 

[VEGETA]

the cap at the final output pin is 220v elec. cap which is necessary for linear circuit stability, this was our conclusion.

I want low ripple since I really like the idea of designing a quality PSU, plus ripple and noise affects output video signal in analog video game consoles. so why not make a very good psu once and for all.

I attached the schematic of this design and also "low_noise_PSU" which is the new one.

[gnuarm]

Is this schematic "as built"?  I see C38 and C39 which need to be removed. 

I see three separate filtering circuits.  I don't understand why you need them to feed the on board switchers.  Filtering the input to U1 is useful, but not going to the switchers.  Does Vcc go on to feed other sensitive circuits?  If so, then the filters prevent noise from the switcher inputs from feeding to the other circuits.  You do need the larger cap and the smaller cap to smooth the current pulses. 

It is important to route the paths around the input, through the input caps back to ground very short.  This path is an important source of noise.  The current through the output inductor and cap are not.  The current through the inductor is pretty constant... that's what inductors do.  The diodes D1 and D2 need to be as direct as possible between LX and ground. 

I don't see a reason to not increase R1 from 100 ohms to 1K.  Worse case draw on the output of that regulator is 2 mA, so dropping 2 volts won't harm a thing.  Higher resistance gives higher attenuation of noise.

Who said the output cap needs to be 220V???  That is an absurdly high voltage.

This is your original design from weeks ago, right?

[VEGETA]

Is this schematic "as built"?  I see C38 and C39 which need to be removed. 

yes as built. I tried removing these 2 caps previously and it didn't affect the circuit. adding an elect. cap made it stable even with these 2 caps.

I see three separate filtering circuits.  I don't understand why you need them to feed the on board switchers.  Filtering the input to U1 is useful, but not going to the switchers.  Does Vcc go on to feed other sensitive circuits?  If so, then the filters prevent noise from the switcher inputs from feeding to the other circuits.  You do need the larger cap and the smaller cap to smooth the current pulses. 

one for each switcher, that makes it 2 filtering circuits. and another one to deliver 12v input to output connector which goes to dreamcast and it is used to drive gd-rom drive motor... no need for it to be low noise at all, but also it shouldn't add the noise to the system as it uses the same ground. filtering it this way was the solution. this rail also is the input to the 5v reg and linear stage op-amp as you see, which need to have low noise.

filtering switchers input is not really necessary but it would be a problem if the 12v input itself is very bad noise and ripple, I thought it might affect the switchers so i added a small inductor with caps.

It is important to route the paths around the input, through the input caps back to ground very short.  This path is an important source of noise.  The current through the output inductor and cap are not.  The current through the inductor is pretty constant... that's what inductors do.  The diodes D1 and D2 need to be as direct as possible between LX and ground. 

the layout is done properly and took a lot of time. very good layout as datasheet and better.

I don't see a reason to not increase R1 from 100 ohms to 1K.  Worse case draw on the output of that regulator is 2 mA, so dropping 2 volts won't harm a thing.  Higher resistance gives higher attenuation of noise.

this may aid in making it more low noise, but the problem was that the circuit wasn't functioning to begin with.

Who said the output cap needs to be 220V???  That is an absurdly high voltage.

actually it is 220uF 16v, that was a typo.

This is your original design from weeks ago, right?

this is the design that was produced, yes.

and the "low_noise_psu.pdf" is a totally new design based on new TI switcher which promises <1mV of total ripple and noise. I spent some time with this to make it very good layout. please check it and see if you have a comment. the boards are not manufactured yet, only quotation.

[gnuarm]

Is this schematic "as built"?  I see C38 and C39 which need to be removed. 

yes as built. I tried removing these 2 caps previously and it didn't affect the circuit. adding an elect. cap made it stable even with these 2 caps.

Zero reason to add them back.  They do nothing but slow the feedback which can increase the noise.  Feedback is what reduces noise.  Slow it and the noise is not properly mitigated.  Get rid of them permanently.

I see three separate filtering circuits.  I don't understand why you need them to feed the on board switchers.  Filtering the input to U1 is useful, but not going to the switchers.  Does Vcc go on to feed other sensitive circuits?  If so, then the filters prevent noise from the switcher inputs from feeding to the other circuits.  You do need the larger cap and the smaller cap to smooth the current pulses. 

one for each switcher, that makes it 2 filtering circuits. and another one to deliver 12v input to output connector which goes to dreamcast and it is used to drive gd-rom drive motor... no need for it to be low noise at all, but also it shouldn't add the noise to the system as it uses the same ground. filtering it this way was the solution. this rail also is the input to the 5v reg and linear stage op-amp as you see, which need to have low noise.

You seem to want to add things without understanding how they work.  I assume the dreamcast circuitry is fed through the output connector on the pin labeled "12V"?  That pin also feeds the 5V regulator, so any noise coming back from that is fed into your voltage reference.  Why not feed that from the Vcc input before the filter? 

Remove the two filters feeding the two switchers leaving a 22uF cap and a 100nF cap.  With a 3 amp load, you might want to increase the capacitance from 22 uF to 100 uF. 

C * dV = I * dT, dV and dT are deltas

I don't know the frequency your switcher is running, but assuming 1 MHz, that gives...

dV = I * dT / C = 3 A * 1 us / 100 uF = 0.030V

So 100 uF will give 30 mV ripple going into the switcher which should be fine.  22 uF will be 136 mV ripple. 

Also, the ground circulation paths should be isolated from the rest of the design if you can.  A very short path between the high current/high frequency loops on a separate area of copper, like an island.  Connect that area to the rest of the ground plane via a single connection.  Remember the thermal breaks I was complaining about in one of your layouts?  One connection like your thermal break.  This prevents voltage differentials from interfering with the rest of the circuit. 

filtering switchers input is not really necessary but it would be a problem if the 12v input itself is very bad noise and ripple, I thought it might affect the switchers so i added a small inductor with caps.

That is not of use.  The place to add filtering is between the switcher and the linear.

It is important to route the paths around the input, through the input caps back to ground very short.  This path is an important source of noise.  The current through the output inductor and cap are not.  The current through the inductor is pretty constant... that's what inductors do.  The diodes D1 and D2 need to be as direct as possible between LX and ground. 

the layout is done properly and took a lot of time. very good layout as datasheet and better.

I don't see a reason to not increase R1 from 100 ohms to 1K.  Worse case draw on the output of that regulator is 2 mA, so dropping 2 volts won't harm a thing.  Higher resistance gives higher attenuation of noise.

this may aid in making it more low noise, but the problem was that the circuit wasn't functioning to begin with.

You asked for advice.  This is my advice.  If you want to have noise in your circuit, the reference will cause it more than anything else. 

Much of your original design was either adding ineffective components like the filtering before the switchers or even counter productive like the cap on the FET gate.  The reference is the gold standard for the entire rest of the design.  Keep that clean or the output will be hard to clean up.

Who said the output cap needs to be 220V???  That is an absurdly high voltage.

actually it is 220uF 16v, that was a typo.

This is your original design from weeks ago, right?

this is the design that was produced, yes.

and the "low_noise_psu.pdf" is a totally new design based on new TI switcher which promises <1mV of total ripple and noise. I spent some time with this to make it very good layout. please check it and see if you have a comment. the boards are not manufactured yet, only quotation.

I don't see a layout, only schematics.

[VEGETA]

Zero reason to add them back.  They do nothing but slow the feedback which can increase the noise.  Feedback is what reduces noise.  Slow it and the noise is not properly mitigated.  Get rid of them permanently.

I didn't add them, the boards are already manufactured (125 boards, was my mistake to make many boards as mentioned).

You seem to want to add things without understanding how they work.  I assume the dreamcast circuitry is fed through the output connector on the pin labeled "12V"?  That pin also feeds the 5V regulator, so any noise coming back from that is fed into your voltage reference.  Why not feed that from the Vcc input before the filter?

yes the output to dreamcast is fed through that 6 pin connector, it has ground, 12v, 3.3v, and 5v.

That is not of use.  The place to add filtering is between the switcher and the linear.

Noted.

I actually made another iteration doing just that but as I mentioned, I went for a completely new design using TI part. So all new design is going to be the TI part, not this circuit.

I may use this circuit as side project for the future, just to get it working properly.

You asked for advice.  This is my advice.  If you want to have noise in your circuit, the reference will cause it more than anything else.

Much of your original design was either adding ineffective components like the filtering before the switchers or even counter productive like the cap on the FET gate.  The reference is the gold standard for the entire rest of the design.  Keep that clean or the output will be hard to clean up.

So you mean I feed 12v output pin directly from 12v input without filtering from the 1000uF of reference? I could just put caps on the output pin instead and keep the reference alone.

I don't see a layout, only schematics.

I provided the layout as images in previous posts, kindly refer to them now since I am away from my laptop for now. when I return, I will upload them again.

________

for now I will focus on the TI part, kindly refer to the attached design "low_noise_psu.pdf" and see it if you have any note.

[VEGETA]

Hello, if anyone still here.

I have got the design I done with TPS62913, and it worked perfectly fine first go, no problem what so ever. I still didn't measure total output ripple due to no scope, but I noticed something indicative.

I have a 12v brick which is very bad and noisy, when i connect it to the power supply I have (called re-dream, which promises 30mv ripple, best in market) it results in a lot and a lot of noise and garbage in picture. When I use this bad source with my design, it produces noticeably less noise and garbage.

Anyway, I adjusted the design slightly to move some components for better arrangement, and added 2 more 22uF input caps per TPS62913 which now has 4 caps instead of 2, datasheet doesn't put a limit on input capacitance but just output capacitance. I also added 5 22uF caps to 12v rail itself (which also feeds the 2 rails). Plus, I added another ground pour on bottom layer and connected it to top layer ground, separated nicely from 12v one.

I noticed 5v rail goes to 5.13v on load, so I don't know if this is dangerous or not.

[gnuarm]

I seem to recall the TPS62913 is a low noise switcher.  Did you follow that with a linear?  Not that I am encouraging that, just asking the question since that was your original concept. 

I don't recall the details, but I think you are outputting 5V and 3.3V at maybe 3 amps.  That should leave you lots of headroom, 5V perhaps.  Add up your max load on the 12V input (after the voltage conversion which will reduce the input current) and consider adding a resistor between the input and the caps.  The caps can only filter input noise as part of an RC filter (or LC).  If you don't add an R or L to the input filter design the cap is working with the low impedance of the 12V supply.  By adding a resistor you likely get a much better filter with the same size input cap.  It does dissipate power, which can make an L a lot more attractive. 

[VEGETA]

I seem to recall the TPS62913 is a low noise switcher.  Did you follow that with a linear?  Not that I am encouraging that, just asking the question since that was your original concept. 

I don't recall the details, but I think you are outputting 5V and 3.3V at maybe 3 amps.  That should leave you lots of headroom, 5V perhaps.  Add up your max load on the 12V input (after the voltage conversion which will reduce the input current) and consider adding a resistor between the input and the caps.  The caps can only filter input noise as part of an RC filter (or LC).  If you don't add an R or L to the input filter design the cap is working with the low impedance of the 12V supply.  By adding a resistor you likely get a much better filter with the same size input cap.  It does dissipate power, which can make an L a lot more attractive.

Yes I got TPS62913, 2 of it. One for 3.3v and one for 5v, from 12v input, no LDO after it.

I have an L in input plus many caps... but no R since it will get really hot... about 25W is delivered from 12v source to the design + 12v rail. Do you mean a 0R resistor?

[VEGETA]

Kindly see the schematic.

these are the bulk caps added on 12v rail + input of each dc-dc regulator.

I assume you mean I add 0.05R series resistor before the 1000uF cap? or multiple 0.05R resistors between the caps to act as multistage?

[gnuarm]

You have inductors, so forget the resistor.  I don't understand all the same value caps.  You have six 22 uF caps at the 1000 uF cap, then four more at he regulator input.  The image is clipped, so I can't tell about the output, but you have three before the ferrite bead (which is not really an inductor, it's a high frequency resistor) and at least three more after. 

You need to read the data sheet carefully.  While total capacitance can be an issue for some regulators, the ESR of the capacitors can also be an issue, too much or too little.  Be sure to read all the details on this in the data sheet.  Double check the value of C23 as well.  That is specifically for compensation and needs to be adjusted when R7 and R8 are changed.  It doesn't need a high degree of accuracy, but might be different for the 5V and 3.3V circuits or adjust the R's to work with the same value of C23.

[VEGETA]

You have inductors, so forget the resistor.  I don't understand all the same value caps.  You have six 22 uF caps at the 1000 uF cap, then four more at he regulator input.  The image is clipped, so I can't tell about the output, but you have three before the ferrite bead (which is not really an inductor, it's a high frequency resistor) and at least three more after. 

You need to read the data sheet carefully.  While total capacitance can be an issue for some regulators, the ESR of the capacitors can also be an issue, too much or too little.  Be sure to read all the details on this in the data sheet.  Double check the value of C23 as well.  That is specifically for compensation and needs to be adjusted when R7 and R8 are changed.  It doesn't need a high degree of accuracy, but might be different for the 5V and 3.3V circuits or adjust the R's to work with the same value of C23.

I used 22uF in the design as it was recommended in the datasheet, now I just increased the number of them to get more filtering.

TPS62913 requires a certain amount of output capacitance, not more. Therefore I chose a suitable number of output caps. All other values are verified from datasheet such as C23 and R7\R8. the boards I have now works perfectly fine using them... I just slightly modified the feedback resistors value to get exact 3.3 and 5v since the current one is a bit more.

Ferrite beads are a part of feedback resistor for the switchers since this is what the switcher's design is, to achieve low noise and low ripple performance.

So the new modification is just better and more precise feedback resistors + more input caps.

[gnuarm]

You have inductors, so forget the resistor.  I don't understand all the same value caps.  You have six 22 uF caps at the 1000 uF cap, then four more at he regulator input.  The image is clipped, so I can't tell about the output, but you have three before the ferrite bead (which is not really an inductor, it's a high frequency resistor) and at least three more after. 

You need to read the data sheet carefully.  While total capacitance can be an issue for some regulators, the ESR of the capacitors can also be an issue, too much or too little.  Be sure to read all the details on this in the data sheet.  Double check the value of C23 as well.  That is specifically for compensation and needs to be adjusted when R7 and R8 are changed.  It doesn't need a high degree of accuracy, but might be different for the 5V and 3.3V circuits or adjust the R's to work with the same value of C23.

I used 22uF in the design as it was recommended in the datasheet, now I just increased the number of them to get more filtering.

I hope you realize the data sheet is referring to the total capacitance, not the value of any components.  Using multiple caps means you need to add up the total to compare to the data sheet values.  I can see in your drawing 132 uF of capacitance on the output.  Is that what the device is specified for?

TPS62913 requires a certain amount of output capacitance, not more. Therefore I chose a suitable number of output caps. All other values are verified from datasheet such as C23 and R7\R8. the boards I have now works perfectly fine using them... I just slightly modified the feedback resistors value to get exact 3.3 and 5v since the current one is a bit more.

If the data sheet is specifying a total capacitance maximum, then that is what you design to with the sum of all output capacitance including what is on the load boards.

Ferrite beads are a part of feedback resistor for the switchers since this is what the switcher's design is, to achieve low noise and low ripple performance.

So the new modification is just better and more precise feedback resistors + more input caps.

Not sure what your point is.  I mentioned to you about the feedback capacitor.  If you are using the exact same values as recommended in the data sheet in both the 3.3V and 5V circuits fine.  But the resistor values can't be the same between the two. 

[VEGETA]

I hope you realize the data sheet is referring to the total capacitance, not the value of any components.  Using multiple caps means you need to add up the total to compare to the data sheet values.  I can see in your drawing 132 uF of capacitance on the output.  Is that what the device is specified for?

If the data sheet is specifying a total capacitance maximum, then that is what you design to with the sum of all output capacitance including what is on the load boards.

this IC is new and unique since it uses 2 stages, the 2nd stage being a ferrite bead. the unique thing is that it requires that ferrite bead to enter the feedback loop itself as part of its low noise features. So you have 2 options, either do single stage like any other dc-dc converter or use 2 stages like explained. achieving that very low noise and ripple requires 2 stages.

Datasheet specifies total effective output capacitance including both stages to be 200uF, which I didn't exceed for sure, one of them is a 47u elec. cap as final bulk capacitor preceded with 22uf ceramic ones. 22uf based on datasheet but i can get anything else.

why you asked about 22u? I used them in the design output stage and therefore thought about using them in input filtering to avoid using another part number for no use. space is very tight so I can't use big elec. caps as input bulk filtering caps... therefore using more 22uF seems like the best idea.

You mentioned the target board capacitance but it is very hard to know, the voltage will go to several paths for sure like LDOs, ICs, etc... which I guess won't add capacitance, at least not in bulk

Not sure what your point is.  I mentioned to you about the feedback capacitor.

you mean the one across one of feedback resistors? that one is based upon datasheet recommendation to eliminate as much noise as possible but still very much within range. I tested this design on practical use and it works perfectly fine. this "mod" is just adding more input filtering, that is it. so it won't change the functionality of the device.

If you are using the exact same values as recommended in the data sheet in both the 3.3V and 5V circuits fine.  But the resistor values can't be the same between the two.

Feedback resistors are chosen as needed, and yes they are not the same. in the new mod I changed them to have a more precise value + used 0.5% resistors for extra precision since the 5v rail was outputting 5.15v which is not as I wanted. Now they should be spot on... we'll see.

I will do a final check and order 10 of it.

[gnuarm]

I hope you realize the data sheet is referring to the total capacitance, not the value of any components.  Using multiple caps means you need to add up the total to compare to the data sheet values.  I can see in your drawing 132 uF of capacitance on the output.  Is that what the device is specified for?

If the data sheet is specifying a total capacitance maximum, then that is what you design to with the sum of all output capacitance including what is on the load boards.

this IC is new and unique since it uses 2 stages, the 2nd stage being a ferrite bead. the unique thing is that it requires that ferrite bead to enter the feedback loop itself as part of its low noise features. So you have 2 options, either do single stage like any other dc-dc converter or use 2 stages like explained. achieving that very low noise and ripple requires 2 stages.

Datasheet specifies total effective output capacitance including both stages to be 200uF, which I didn't exceed for sure, one of them is a 47u elec. cap as final bulk capacitor preceded with 22uf ceramic ones. 22uf based on datasheet but i can get anything else.

why you asked about 22u? I used them in the design output stage and therefore thought about using them in input filtering to avoid using another part number for no use. space is very tight so I can't use big elec. caps as input bulk filtering caps... therefore using more 22uF seems like the best idea.

You need to count all capacitance when meeting the spec for the data sheet.  Too much capacitance can cause oscillation, too little capacitance can cause oscillation.  You need to match the requirements in the data sheet whatever they are.

You mentioned the target board capacitance but it is very hard to know, the voltage will go to several paths for sure like LDOs, ICs, etc... which I guess won't add capacitance, at least not in bulk

Not sure what your point is.  I mentioned to you about the feedback capacitor.

you mean the one across one of feedback resistors? that one is based upon datasheet recommendation to eliminate as much noise as possible but still very much within range. I tested this design on practical use and it works perfectly fine. this "mod" is just adding more input filtering, that is it. so it won't change the functionality of the device.

This capacitor does NOT eliminate noise.  It is a high pass filter.  It passes high frequency noise past the feedback resistor so the active regulator can cancel it out.  The resistors have to match the capacitor to get the right characteristics.  Both regulators can't have the same resistors, so the capacitor has to be tuned to the resistors.  Read the data sheet.

If you are using the exact same values as recommended in the data sheet in both the 3.3V and 5V circuits fine.  But the resistor values can't be the same between the two.

Feedback resistors are chosen as needed, and yes they are not the same. in the new mod I changed them to have a more precise value + used 0.5% resistors for extra precision since the 5v rail was outputting 5.15v which is not as I wanted. Now they should be spot on... we'll see.

The point is the capacitor needs to match the different resistor values.

I will do a final check and order 10 of it.

[VEGETA]

You need to count all capacitance when meeting the spec for the data sheet.  Too much capacitance can cause oscillation, too little capacitance can cause oscillation.  You need to match the requirements in the data sheet whatever they are.

well, I can't measure Dreamcast capacitance very accurately but as I told you, I actually tried the design on Dreamcast and it works perfectly fine. therefore, capacitance is ok. I may just use a multimeter to measure capacitance across 5v and 3.3v rails... but will this be accurate?

This capacitor does NOT eliminate noise.  It is a high pass filter.  It passes high frequency noise past the feedback resistor so the active regulator can cancel it out.

the datasheet specifies that this capacitor helps eliminate more noise, yes it is not a traditional low pass filter but the final functionality is this.

The datasheet doesn't specify this cap value to be dependent on feedback resistor but rather a range of its own. I picked the proper value so that it is not too high or low.

here is what datasheet says:

A feedforward capacitor (CFF) is not required for proper operation, but can further improve output noise.
However, care must be taken in choosing the CFF, since the power good (PG) function may not be valid with
a large CFF during start-up, and can cause spurious triggering of the PG pin during a large load transient. The
noise performance with various CFF is shown in Figure 6-31.

and since I practically tested it and it works, then no startup issue is there. Plus, there is no load transient since load is fairly constant. No cons mentioned in the app note (mentioned in datasheet after quoted paragraph) applicable here.
_______


On the other side of the ocean, I added 2 small 1uH inductors on 12v line between the many 22uF capacitors to further enhance noise reduction just before the switchers.

Also, I sent the gerbers and bom to allpcb to manufacture 10 boards.

[gnuarm]

You need to count all capacitance when meeting the spec for the data sheet.  Too much capacitance can cause oscillation, too little capacitance can cause oscillation.  You need to match the requirements in the data sheet whatever they are.

well, I can't measure Dreamcast capacitance very accurately but as I told you, I actually tried the design on Dreamcast and it works perfectly fine. therefore, capacitance is ok. I may just use a multimeter to measure capacitance across 5v and 3.3v rails... but will this be accurate?

Can't say, depends on the meter.  The issue is that the actual values of capacitance vary widely.  +80/-20% from rated value is not unusual for electrolytic caps.  So you may be testing with a unit in the -20% range and will have a problem with a unit in the +80% range... or the other way around.   
 

This capacitor does NOT eliminate noise.  It is a high pass filter.  It passes high frequency noise past the feedback resistor so the active regulator can cancel it out.

the datasheet specifies that this capacitor helps eliminate more noise, yes it is not a traditional low pass filter but the final functionality is this.

The datasheet doesn't specify this cap value to be dependent on feedback resistor but rather a range of its own. I picked the proper value so that it is not too high or low.

here is what datasheet says:

A feedforward capacitor (CFF) is not required for proper operation, but can further improve output noise.
However, care must be taken in choosing the CFF, since the power good (PG) function may not be valid with
a large CFF during start-up, and can cause spurious triggering of the PG pin during a large load transient. The
noise performance with various CFF is shown in Figure 6-31.

and since I practically tested it and it works, then no startup issue is there. Plus, there is no load transient since load is fairly constant. No cons mentioned in the app note (mentioned in datasheet after quoted paragraph) applicable here.

Uh, the load is anything but constant.  That's why regulators are needed. 

If you are happy with the value chosen, fine.  But the capacitor is a filter when combined with the resistors and its operation depends on the corner frequency of the combination even if they don't explain this in the data sheet.  They make some assumptions about the knowledge and experience of the designer. 

We always perform testing to find problems, but you need to understand that testing does not show the absence of problems, only that they have not been uncovered.  That's why there can be field recalls of nearly any equipment.  You can't test quality into a product.  It has to be designed in by understanding what is being designed.

_______


On the other side of the ocean, I added 2 small 1uH inductors on 12v line between the many 22uF capacitors to further enhance noise reduction just before the switchers.

Also, I sent the gerbers and bom to allpcb to manufacture 10 boards.

Good luck.

[VEGETA]

Can't say, depends on the meter.

Mine is aneng 8009, it displayed open circuit for 5v rail and 2.3mF for 3.3v rail. I guess it is not reliable since the design worked perfectly well and for a long duration without problems. if this reading was correct then it wouldn't even start.

Uh, the load is anything but constant.  That's why regulators are needed.

I meant it is a retro gaming console with 22w rated PSU, it does nothing but one task. therefore its load is fairly constant. it doesn't swing or so..

If you are happy with the value chosen, fine.  But the capacitor is a filter when combined with the resistors and its operation depends on the corner frequency of the combination even if they don't explain this in the data sheet.  They make some assumptions about the knowledge and experience of the designer.

they gave a limited range you choose from but they relied on you not going to top range since it will affect stability, or you can ditch it all together and still work. I added a reasonable amount which shouldn't make any problem.

I suggest you go through the datasheet to see what it is all about. this IC uses new technology such as including ferrite bead inside the loop itself and so on.... I hope the result is as good as they claim.

[gnuarm]

If you are happy with the value chosen, fine.  But the capacitor is a filter when combined with the resistors and its operation depends on the corner frequency of the combination even if they don't explain this in the data sheet.  They make some assumptions about the knowledge and experience of the designer.

they gave a limited range you choose from but they relied on you not going to top range since it will affect stability, or you can ditch it all together and still work. I added a reasonable amount which shouldn't make any problem.

I suggest you go through the datasheet to see what it is all about. this IC uses new technology such as including ferrite bead inside the loop itself and so on.... I hope the result is as good as they claim.

If it were my design I'd be all over the data sheet.  But it's not, so I won't.  Far too many activities demanding my time.

BTW, adding the ferrite bead in the control loop is not "new technology".  It is just part of the frequency response of the control loop.  At very high frequencies the ferrite material becomes lossy and the characteristic changes from inductor to resistor.  At those frequencies the control loop has zero gain so the output circuit is just passive.  At the frequencies the control loop is effective the ferrite bead has so little inductance it is just a small addition to the larger inductor.  I'm not sure adding it to the control loop has much effect compared to adding it to the output after the control loop.

[danielcozak]

i AM NEW AT THIS.
Ups...! Just blew my new Hantek 6022be (on its first trial run). Its also my first diode (LR206) blow-up, ;-) by shorting one of the probes. Hence, no more scope. I looked inside the unit and it looks like there is hope. I found and cleaned the only area that seems to have given up. It seems to be an evaporated inductor labeled L3 near the USB cable junction on the left side of the PCB, no JP1. My problem is that I do not know what its Henry value is? Can any body hellllllPPPP me. Mile merci du Québec.
Or Where can I go on the net to find a solution to my question?

[Kleinstein]

The inductgor should not be too critical. It looks like the ground side of the USB. Some filtering is nice there as there can be a ground look to the computer there.  For a first start any small inductor that can stand the current would be OK.  I would guess some 10 - 100 µH, depending on how mich DC current is flowing there. 

It looks like a case of how not to blow the scope:  Remember that USB is usually grounded and the BNC inputs on the scope usually too. So keep an eye on ground loops, that may carry a lot of current (e.g. ground lead of the scope connected to +12 V at the PC).

[Jwillis]

I popped my Hantek 6022be open and measured an inductance of 1uH on L3. Hope that helps .