Author Topic: Low ripple low noise small power supply design  (Read 24753 times)

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Offline VEGETA

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Low ripple low noise small power supply design
« on: September 04, 2020, 01:57:42 pm »
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!
« Last Edit: January 28, 2021, 07:24:07 am by VEGETA »
 

Offline Vovk_Z

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #1 on: September 05, 2020, 07:42:55 am »
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.
 

Offline VEGETA

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #2 on: September 05, 2020, 09:24:07 am »
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.


Offline Vovk_Z

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #3 on: September 05, 2020, 01:58:12 pm »
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.
 
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Offline BrianHG

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #4 on: September 05, 2020, 03:26:22 pm »
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 (Ptot 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'?

« Last Edit: September 05, 2020, 04:00:51 pm by BrianHG »
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Offline BrianHG

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #5 on: September 05, 2020, 04:10:59 pm »
The minimum transistor I would use is an MJE200.
Very good hFE 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.
« Last Edit: September 05, 2020, 04:13:15 pm by BrianHG »
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Offline BrianHG

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #6 on: September 06, 2020, 02:01:38 am »
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.
« Last Edit: September 06, 2020, 02:21:49 am by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #7 on: September 06, 2020, 02:44:31 am »
why would a Dreamcast need "low ripple low noise" ?
 

Offline VEGETA

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #8 on: September 06, 2020, 11:27:40 am »
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?



Quote
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

Offline BrianHG

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #9 on: September 06, 2020, 07:04:10 pm »

Quote
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.
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Offline BrianHG

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #10 on: September 07, 2020, 12:47:41 am »
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).)
« Last Edit: September 07, 2020, 01:49:55 am by BrianHG »
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Offline VEGETA

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #11 on: September 07, 2020, 08:08:22 am »
Quote
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.

Quote
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.

Quote
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!

Quote
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.


Offline BrianHG

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #12 on: September 07, 2020, 12:16:33 pm »
Quote
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.

Quote
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.

Quote
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!

Quote
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.
« Last Edit: September 07, 2020, 02:06:13 pm by BrianHG »
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Offline VEGETA

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #13 on: September 07, 2020, 07:50:06 pm »
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?

Offline BrianHG

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #14 on: September 07, 2020, 09:28:51 pm »
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.
« Last Edit: September 07, 2020, 10:09:59 pm by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #15 on: September 07, 2020, 11:34:33 pm »
seems like a discussion of whether an anti aircraft gun or an surface to air missile is the most appropriate for  killing a fly :)
 
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Offline BrianHG

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #16 on: September 08, 2020, 01:05:28 am »
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #17 on: September 08, 2020, 03:53:56 am »
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.
 

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #18 on: September 08, 2020, 08:26:16 am »
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.
 

Offline VEGETA

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #19 on: September 08, 2020, 09:05:30 am »
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.

Quote

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.

« Last Edit: September 08, 2020, 09:28:49 am by VEGETA »
 

Offline BrianHG

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #20 on: September 08, 2020, 05:54:03 pm »
Quote

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.
« Last Edit: September 08, 2020, 06:00:17 pm by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #21 on: September 08, 2020, 06:09:54 pm »
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.
« Last Edit: September 08, 2020, 06:13:27 pm by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #22 on: September 09, 2020, 11:48:36 am »
Quote
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.

Quote
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?

Quote
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.

Quote
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?

Offline VEGETA

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #23 on: September 09, 2020, 01:10:17 pm »
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?



Offline BrianHG

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #24 on: September 09, 2020, 06:06:40 pm »
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.
« Last Edit: September 09, 2020, 06:55:09 pm by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #25 on: September 09, 2020, 06:44:48 pm »
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #26 on: September 09, 2020, 06:53:48 pm »
Quote
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.

Quote
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.

Quote
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?

Quote
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.

Quote
     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.

Quote
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.

Quote
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?

Quote
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.

Quote
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.



Offline BrianHG

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #27 on: September 09, 2020, 07:51:16 pm »
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.
Quote
Quote
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.
Quote

Quote
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.
« Last Edit: September 09, 2020, 07:58:27 pm by BrianHG »
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Offline BrianHG

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #28 on: September 09, 2020, 08:49:11 pm »
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.
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Offline VEGETA

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #29 on: September 09, 2020, 09:43:04 pm »
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!

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #30 on: September 09, 2020, 10:22:04 pm »
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.
« Last Edit: September 09, 2020, 10:31:10 pm by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #31 on: September 10, 2020, 01:58:09 am »
I will try to re-design the thing from scratch and give you the update... at least the main circuit for one rail.



Quote
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?

Quote
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?

Quote
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.

Quote
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.

Quote
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?

Quote
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?

Offline VEGETA

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #32 on: September 10, 2020, 02:38:42 am »
I have made a very quick kicad schematic. kindly check it

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #33 on: September 10, 2020, 03:54:39 am »


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.
« Last Edit: September 10, 2020, 04:01:19 am by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #34 on: September 10, 2020, 05:14:44 am »
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.
« Last Edit: September 10, 2020, 07:37:43 am by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #35 on: September 10, 2020, 05:19:09 am »
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
« Last Edit: September 10, 2020, 08:45:05 am by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #36 on: September 10, 2020, 05:16:33 pm »
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...
« Last Edit: September 10, 2020, 06:30:30 pm by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #37 on: September 10, 2020, 06:42:08 pm »
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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #38 on: September 10, 2020, 07:29:00 pm »
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.
« Last Edit: September 10, 2020, 07:39:56 pm by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #39 on: September 10, 2020, 08:21:25 pm »

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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #40 on: September 11, 2020, 12:08:34 am »

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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #41 on: September 11, 2020, 01:30:24 am »

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.
« Last Edit: September 11, 2020, 02:42:25 am by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #42 on: September 11, 2020, 01:59:04 am »
Hmmm this changes things, Quote: https://bitbuilt.net/forums/index.php?threads/dreamcast-r-d-and-documenting.1368/
Quote
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.
« Last Edit: September 11, 2020, 02:30:12 am by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #43 on: September 11, 2020, 02:41:57 am »
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?

Quote
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.


___________

Quote
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.


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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #44 on: September 11, 2020, 03:06:08 am »
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.
« Last Edit: September 11, 2020, 03:16:47 am by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #45 on: September 11, 2020, 03:13:49 am »
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
« Last Edit: September 11, 2020, 03:20:33 am by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #46 on: September 11, 2020, 03:44:50 am »
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
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #47 on: September 11, 2020, 04:56:03 am »
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #48 on: September 11, 2020, 05:06:14 am »
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.
« Last Edit: September 11, 2020, 05:16:05 am by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #49 on: September 12, 2020, 04:27:46 pm »
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.

« Last Edit: September 12, 2020, 05:57:30 pm by VEGETA »
 

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #50 on: September 13, 2020, 05:48:47 am »
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
« Last Edit: September 13, 2020, 07:21:11 am by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #51 on: September 13, 2020, 07:24:53 am »
Quote
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.

Quote
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

Quote
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.

Quote
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?

Quote
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).

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #52 on: September 13, 2020, 07:59:29 am »
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #53 on: September 13, 2020, 04:52:09 pm »

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.

« Last Edit: September 13, 2020, 06:03:24 pm by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #54 on: September 13, 2020, 06:02:20 pm »
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?

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #55 on: September 13, 2020, 06:52:51 pm »
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.
« Last Edit: September 13, 2020, 07:01:15 pm by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #56 on: September 13, 2020, 07:23:35 pm »
For the ferrite beads, you might be better off just using the same 10uh inductors.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #57 on: September 13, 2020, 07:40:22 pm »
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #58 on: September 13, 2020, 08:38:44 pm »
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.

Quote
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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #59 on: September 13, 2020, 09:06:38 pm »
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:
Quote
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #60 on: September 13, 2020, 09:42:01 pm »
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...
« Last Edit: September 13, 2020, 11:43:14 pm by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #61 on: September 13, 2020, 11:40:50 pm »
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.
« Last Edit: September 14, 2020, 01:29:12 am by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #62 on: September 14, 2020, 12:09:21 am »
Another mistake...
Your 'FSW' resistors are set to 20k.
This is not 2MHz....


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

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.
« Last Edit: September 14, 2020, 12:21:54 am by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #63 on: September 14, 2020, 06:40:02 am »
Quote
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.

Quote
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.



« Last Edit: September 14, 2020, 06:46:52 am by VEGETA »
 

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #64 on: September 14, 2020, 07:26:37 am »

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
« Last Edit: September 14, 2020, 07:34:52 am by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #65 on: September 14, 2020, 08:37:31 am »
Quote
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.

Quote
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.




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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #66 on: September 14, 2020, 08:10:10 pm »
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.
« Last Edit: September 14, 2020, 09:57:50 pm by BrianHG »
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« Last Edit: September 14, 2020, 10:11:46 pm by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #68 on: September 15, 2020, 03:43:26 am »
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #69 on: September 15, 2020, 10:53:16 pm »
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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #70 on: September 15, 2020, 10:59:39 pm »
Back in a few hours....
Yes, some overkill there in the wrong places.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #71 on: September 15, 2020, 11:33:58 pm »
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
 
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #72 on: September 16, 2020, 02:18:06 am »
Here you go.  I think you are ready for the PCB part placement.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #73 on: September 16, 2020, 02:41:39 am »
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #74 on: September 16, 2020, 06:02:59 am »
Quote
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.

_____

Quote
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.

Quote
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.  :horse:


____

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?

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #75 on: September 16, 2020, 07:14:42 am »
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #76 on: September 16, 2020, 08:22:09 am »
Quote
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?

Quote
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.

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

from the datasheet or where?

Quote
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.

Quote
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.

Quote
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.
« Last Edit: September 16, 2020, 08:41:42 am by VEGETA »
 

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #77 on: September 16, 2020, 09:05:15 am »

Quote
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.
« Last Edit: September 16, 2020, 09:11:52 am by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #78 on: September 16, 2020, 09:35:19 am »
LM358 datasheet PSRR: Worst case 65db, normally 100db (between 0.00056 and 0.00001) :


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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #79 on: September 16, 2020, 06:06:42 pm »
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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #80 on: September 16, 2020, 08:02:30 pm »
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #81 on: September 16, 2020, 08:04:43 pm »
Have you looked at 47uf 16v X5R 1206/1210 caps?
You could use half the number of 10uf caps.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #82 on: September 16, 2020, 10:33:39 pm »
Quote
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.

Quote
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!

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #83 on: September 16, 2020, 10:58:39 pm »
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  :-DD :-DD :-DD

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #84 on: September 17, 2020, 01:01:23 am »
 :scared: That's MAD!  :scared:

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

Maybe cut the 10uf in half.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #85 on: September 17, 2020, 01:10:15 am »
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #86 on: September 17, 2020, 07:45:44 pm »
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #87 on: September 18, 2020, 12:08:08 pm »
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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #88 on: September 18, 2020, 05:39:32 pm »
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #89 on: September 18, 2020, 06:08:05 pm »
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #90 on: September 18, 2020, 06:23:10 pm »
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


Quote
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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #91 on: September 18, 2020, 07:17:06 pm »

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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #92 on: September 18, 2020, 07:19:26 pm »
I hope you are testing a 1 or 2 PCBs before building 250pcs...
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #93 on: September 18, 2020, 09:22:36 pm »

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
 
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #94 on: September 18, 2020, 09:38:25 pm »

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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #95 on: September 18, 2020, 10:41:51 pm »
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?
Former username: NANDBlog
 
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #96 on: September 19, 2020, 12:47:11 am »
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #97 on: September 19, 2020, 07:18:32 am »
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

:)
 
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #98 on: September 19, 2020, 07:31:47 am »
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...
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #99 on: September 19, 2020, 10:07:03 am »
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!


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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #100 on: September 19, 2020, 06:52:11 pm »
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...
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #101 on: September 19, 2020, 07:40:15 pm »
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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #102 on: September 19, 2020, 09:52:48 pm »
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #103 on: September 20, 2020, 12:17:03 am »
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #104 on: September 20, 2020, 02:39:42 am »
Actually, if you keep this layout, rotating the mosfets 90 degrees may also work.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #105 on: September 20, 2020, 05:20:26 am »
Quote
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).

Quote
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.

Quote
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.

Quote
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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #106 on: September 20, 2020, 02:54:15 pm »
Quote
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #107 on: September 21, 2020, 02:31:17 pm »
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?
« Last Edit: September 21, 2020, 02:32:57 pm by VEGETA »
 

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #108 on: September 21, 2020, 06:29:30 pm »
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.
« Last Edit: September 21, 2020, 06:37:59 pm by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #109 on: September 22, 2020, 11:34:29 am »
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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #110 on: September 22, 2020, 06:19:03 pm »
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #111 on: September 23, 2020, 05:41:35 am »
Quote
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.

Quote
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?

Quote
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.

Quote
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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #112 on: September 23, 2020, 06:23:59 pm »

Quote
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.
« Last Edit: September 23, 2020, 06:47:53 pm by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #113 on: September 23, 2020, 06:50:54 pm »
Quote
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #114 on: September 28, 2020, 11:35:14 pm »
I have finished routing it, I hope it doesn't need much modifications.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #115 on: September 29, 2020, 02:18:48 am »
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...
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #116 on: September 29, 2020, 08:19:57 am »
Quote
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.

Quote
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.

Quote
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.

Quote
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.


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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #117 on: September 30, 2020, 04:17:57 am »

Quote
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.
Quote

Quote
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #118 on: September 30, 2020, 11:45:11 am »
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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #119 on: September 30, 2020, 11:30:33 pm »
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.


« Last Edit: September 30, 2020, 11:40:07 pm by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #120 on: October 04, 2020, 08:08:24 am »
I will dig into it tonight.

Quote
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.

Quote
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.
« Last Edit: October 04, 2020, 08:14:24 am by VEGETA »
 

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #121 on: October 04, 2020, 12:05:43 pm »
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #122 on: October 05, 2020, 09:02:23 am »
Quote
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?

Quote
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?

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #123 on: October 05, 2020, 07:37:35 pm »
Quote
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.
Quote

Quote
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #124 on: October 08, 2020, 08:23:03 pm »
Well, how is it going?
I hope my instructions were simple and clear enough...
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #125 on: October 08, 2020, 10:13:10 pm »
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  :-DD :-DD :-DD

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  :-// :-// :-//

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #126 on: October 14, 2020, 04:44:08 pm »
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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #127 on: October 14, 2020, 09:04:10 pm »
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.
« Last Edit: October 14, 2020, 09:16:05 pm by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #128 on: October 25, 2020, 10:47:50 am »
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?
« Last Edit: October 25, 2020, 10:55:37 am by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #129 on: October 26, 2020, 05:56:19 am »
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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #130 on: November 17, 2020, 08:58:10 pm »
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!!

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #131 on: November 18, 2020, 04:39:00 am »
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #132 on: November 18, 2020, 08:31:05 am »
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?

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #133 on: November 18, 2020, 04:20:17 pm »
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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #134 on: November 18, 2020, 10:53:23 pm »
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #135 on: November 19, 2020, 07:35:26 am »
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

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #136 on: November 21, 2020, 10:02:45 pm »
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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #137 on: November 21, 2020, 11:04:21 pm »
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.
« Last Edit: November 21, 2020, 11:07:48 pm by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #138 on: November 22, 2020, 08:44:22 am »
Quote
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?

Quote
Your linear regulator mess also needs some cleaning up.

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

Quote
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.

Quote
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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #139 on: November 22, 2020, 05:24:16 pm »
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #140 on: November 22, 2020, 06:06:59 pm »
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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #141 on: November 22, 2020, 07:20:46 pm »
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.
« Last Edit: November 22, 2020, 07:30:18 pm by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #142 on: November 22, 2020, 08:11:15 pm »
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

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #143 on: November 22, 2020, 10:43:37 pm »
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #144 on: November 22, 2020, 11:36:12 pm »
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!

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #145 on: November 23, 2020, 06:16:48 pm »
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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #146 on: November 23, 2020, 07:17:29 pm »
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.


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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #147 on: November 23, 2020, 07:36:27 pm »
Quote
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.

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

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

Quote
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.

Quote
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.

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

I didn't understand this.

Quote
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.

Quote
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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #148 on: November 23, 2020, 08:44:13 pm »
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.


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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #149 on: November 23, 2020, 10:40:36 pm »
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...
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #150 on: November 25, 2020, 04:14:19 am »
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.


« Last Edit: November 25, 2020, 04:17:20 am by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #151 on: November 25, 2020, 08:10:03 am »
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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #152 on: November 25, 2020, 11:14:34 am »
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #153 on: November 30, 2020, 06:52:04 pm »
I enhanced the design further more.

Now I think all are ok.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #154 on: December 01, 2020, 12:13:45 am »
Almost perfect.  I'll upload a few minor patches before I go to sleep tonight.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #155 on: December 01, 2020, 04:52:34 am »
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #156 on: December 01, 2020, 04:59:10 pm »
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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #157 on: December 01, 2020, 05:34:52 pm »
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #158 on: December 01, 2020, 07:11:01 pm »
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.

 :-+

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #159 on: December 01, 2020, 10:42:48 pm »
This should do it:
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #160 on: December 01, 2020, 11:02:05 pm »
I will do it tomorrow,

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

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #161 on: December 01, 2020, 11:30:14 pm »
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #162 on: December 02, 2020, 10:23:50 pm »
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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #163 on: December 02, 2020, 10:35:09 pm »
I think you got it.
It looks as simple, direct and clean as it will get.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #164 on: December 02, 2020, 10:38:31 pm »
Tomorrow I will make a panel of it, suitable for JLCPCB SMT service.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #165 on: December 02, 2020, 10:58:32 pm »
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #166 on: December 02, 2020, 11:51:43 pm »
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.
« Last Edit: December 02, 2020, 11:53:56 pm by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #167 on: December 03, 2020, 01:24:29 am »
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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #168 on: December 03, 2020, 03:33:10 am »
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #169 on: December 03, 2020, 05:11:20 am »
Q: Isn't the vertical portion of that 3.3v and 5v trace a little close to each other?
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #170 on: December 03, 2020, 08:55:46 am »
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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #171 on: December 04, 2020, 05:31:12 am »
Don't forget to test with dummy loads of varying current...
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #172 on: December 04, 2020, 09:12:35 am »
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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #173 on: December 04, 2020, 08:19:23 pm »
I have made a panel our of it.

25 single boards with 280x280 panel.

next is dealing with BOM and with JLCPCB format.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #174 on: December 05, 2020, 01:43:01 am »
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$?
« Last Edit: December 05, 2020, 01:48:46 am by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #175 on: December 05, 2020, 10:43:49 am »
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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #176 on: December 05, 2020, 12:08:02 pm »
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...
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #177 on: December 05, 2020, 05:31:24 pm »
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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #178 on: December 05, 2020, 07:10:49 pm »
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #179 on: December 05, 2020, 08:58:16 pm »
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?

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #180 on: December 06, 2020, 12:10:02 am »
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.
« Last Edit: December 06, 2020, 12:12:05 am by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #181 on: December 06, 2020, 07:45:03 pm »
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$.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #182 on: December 06, 2020, 08:41:33 pm »
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #183 on: December 06, 2020, 09:13:15 pm »
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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #184 on: December 08, 2020, 12:28:48 am »
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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #185 on: December 08, 2020, 12:36:04 am »
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?
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #186 on: December 08, 2020, 06:54:38 am »
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.


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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #187 on: December 08, 2020, 08:28:24 am »
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #188 on: December 08, 2020, 09:12:31 am »
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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #189 on: December 08, 2020, 04:32:52 pm »
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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #190 on: December 08, 2020, 09:11:54 pm »
I've done the modification.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #191 on: December 08, 2020, 10:22:24 pm »
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.
« Last Edit: December 08, 2020, 10:23:59 pm by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #192 on: December 08, 2020, 11:31:32 pm »
Done.

finally the last ever change!

waiting JLCPCB to know how can I proceed. Also, the switcher is still out of stock!

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #193 on: December 08, 2020, 11:51:36 pm »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #194 on: December 09, 2020, 09:33:26 am »
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.

 :-DD :-DD :-DD

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I will keep you posted on what happens further on.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #195 on: December 10, 2020, 12:30:54 am »
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 )
« Last Edit: December 10, 2020, 01:00:26 am by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #196 on: December 10, 2020, 12:57:25 am »
done

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #197 on: December 10, 2020, 01:36:17 am »
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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #198 on: December 10, 2020, 01:37:25 am »
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #199 on: December 10, 2020, 01:43:22 am »
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!!!!)
« Last Edit: December 10, 2020, 01:49:41 am by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #200 on: December 10, 2020, 02:23:57 am »
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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #201 on: December 10, 2020, 03:48:38 am »
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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #202 on: December 10, 2020, 04:07:06 am »
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #203 on: December 10, 2020, 07:07:05 am »
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.

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #204 on: December 10, 2020, 07:41:29 am »
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #205 on: December 10, 2020, 08:02:37 am »
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.
« Last Edit: December 10, 2020, 08:15:31 am by BrianHG »
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #206 on: December 10, 2020, 08:19:58 am »
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.
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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #207 on: December 10, 2020, 08:39:37 am »
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.

Quote
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?

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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.
« Last Edit: December 10, 2020, 08:45:53 am by VEGETA »
 

Offline BrianHG

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Re: Small MOSFET for capacitance multiplier in a small PSU
« Reply #208 on: December 10, 2020, 08:57:07 am »

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.
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Offline VEGETA

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