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

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#### 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 »

#### 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.

#### 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.

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#### 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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#### 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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#### 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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#### 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" ?

#### 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

#### 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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#### 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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#### 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.

#### 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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#### 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?

#### 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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#### 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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#### Doctorandus_P

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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.

#### Zero999

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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.

#### 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 » #### BrianHG • Super Contributor • Posts: 5413 • Country: ##### 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 » __________ BrianHG. #### BrianHG • Super Contributor • Posts: 5413 • Country: ##### 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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#### VEGETA

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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
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?

#### 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?

#### 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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#### 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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#### VEGETA

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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.

#### 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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#### 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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#### 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!

#### BrianHG

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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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#### VEGETA

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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?

#### 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 »

#### BrianHG

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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.
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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#### 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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#### 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:

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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#### 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$chassis mount unit is nowhere near as good as the TDK or Triad Magnetics supplies I listed above. The TDK and Triad units have proper input power chokes, well isolated from the mains and they are well certified and have fully documented datasheets. You get what you pay for... « Last Edit: September 10, 2020, 06:30:30 pm by BrianHG » __________ BrianHG. #### VEGETA • Super Contributor • Posts: 1475 • Country: • I am the cult of personality ##### Re: Small MOSFET for capacitance multiplier in a small PSU « Reply #37 on: September 10, 2020, 06:42:08 pm » If you really want to save on the PSU, use a cheap switcher 3$ 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. #### BrianHG • Super Contributor • Posts: 5413 • Country: ##### 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 » __________ BrianHG. #### BrianHG • Super Contributor • Posts: 5413 • Country: ##### 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. __________ BrianHG. #### VEGETA • Super Contributor • Posts: 1475 • Country: • I am the cult of personality ##### 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. #### BrianHG • Super Contributor • Posts: 5413 • Country: ##### 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 » __________ BrianHG. #### BrianHG • Super Contributor • Posts: 5413 • Country: ##### 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 » __________ BrianHG. #### VEGETA • Super Contributor • Posts: 1475 • Country: • I am the cult of personality ##### 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. #### BrianHG • Super Contributor • Posts: 5413 • Country: ##### 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 » __________ BrianHG. #### BrianHG • Super Contributor • Posts: 5413 • Country: ##### 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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#### 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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#### BrianHG

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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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#### BrianHG

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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.

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#### BrianHG

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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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#### VEGETA

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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?

#### BrianHG

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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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#### VEGETA

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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.

#### VEGETA

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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.

#### BrianHG

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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 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 » __________ BrianHG. #### VEGETA • Super Contributor • Posts: 1475 • Country: • I am the cult of personality ##### 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. #### BrianHG • Super Contributor • Posts: 5413 • Country: ##### 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... __________ BrianHG. #### VEGETA • Super Contributor • Posts: 1475 • Country: • I am the cult of personality ##### 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. #### BrianHG • Super Contributor • Posts: 5413 • Country: ##### 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. __________ BrianHG. #### VEGETA • Super Contributor • Posts: 1475 • Country: • I am the cult of personality ##### 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? #### BrianHG • Super Contributor • Posts: 5413 • Country: ##### 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 » __________ BrianHG. #### VEGETA • Super Contributor • Posts: 1475 • Country: • I am the cult of personality ##### 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$. #### BrianHG • Super Contributor • Posts: 5413 • Country: ##### Re: Small MOSFET for capacitance multiplier in a small PSU « Reply #182 on: December 06, 2020, 08:41:33 pm » So according to this, I think about doing a future enhancement in BOM by using smaller and noticeably cheaper power inductors instead of that big one to reduce total cost. However this is in the future. getting 2 of that small 2.2uH inductor instead of the big 10uH switching one seems ok in terms of current since each one tolerates 3 amps which makes it 6 amps total. However, 2.2+2.2 = 4.4uH instead of 10uH. I am afraid this won't remove ripple as much. getting 5 of it will be more than 10uH and still maybe less or similar footprint but more expensive. I won't bother with this now though. Right now I am contacting JLCPCB for the panels. the damn 22uF 1206 caps costs about 182$ (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. __________ BrianHG. #### VEGETA • Super Contributor • Posts: 1475 • Country: • I am the cult of personality ##### 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. #### BrianHG • Super Contributor • Posts: 5413 • Country: ##### 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. __________ BrianHG. #### BrianHG • Super Contributor • Posts: 5413 • Country: ##### 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? __________ BrianHG. #### VEGETA • Super Contributor • Posts: 1475 • Country: • I am the cult of personality ##### 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. #### BrianHG • Super Contributor • Posts: 5413 • Country: ##### 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. __________ BrianHG. #### VEGETA • Super Contributor • Posts: 1475 • Country: • I am the cult of personality ##### 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.

#### VEGETA

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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.

#### VEGETA

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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.

#### BrianHG

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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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#### VEGETA

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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!

#### BrianHG

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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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#### VEGETA

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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.

____

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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#### VEGETA

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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

#### VEGETA

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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.

#### BrianHG

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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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#### BrianHG

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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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#### VEGETA

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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

I like the 2nd one due to huge availability and very low price. I think I will go for it unless a cheaper suitable one is available.

#### BrianHG

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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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#### BrianHG

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

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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#### VEGETA

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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.

#### BrianHG

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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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#### BrianHG

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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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#### 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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#### VEGETA

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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?

___

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 »

#### 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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#### VEGETA

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