Low ripple low noise small power supply design

[gnuarm]

The linear regulator shown here has unity gain at 1 MHz, so is not usefully attenuating input noise until the same frequencies as most linear regulators.

how did you know its unity gain at 1 MHZ? from op-amp?

Yes, the op amp has a gain BW product of 1 MHz, the common emitter configuration is essentially a gain of 1 and the feedback is direct. 

you asked about design goals, here is what I have: low noise low ripple to never affect analog video and audio by any means. the problem is analog video\audio signals are about 1v p-p so any noise and ripple will affect them. so the lower noise\ripple the better.

Those are not  design goals unless you have numbers for "never affect...".   "Lower is better" is not a spec.  Not trying to rag on you, but concrete goals should be set as it's not really true that lower is always better.  Everything has a price.  You have indicated many times that dollars matter to you.  The cost should be part of the spec.  Specific noise figures should be part of the spec just as the current and voltage are part of the spec.  These are actually requirements, but it's to much work to explain requirements vs. specs and why it's important.  I've been fighting that battle for some time on the ventilator project I'm working on.

[VEGETA]

Those are not  design goals unless you have numbers for "never affect...".   "Lower is better" is not a spec.  Not trying to rag on you, but concrete goals should be set as it's not really true that lower is always better.  Everything has a price.  You have indicated many times that dollars matter to you.  The cost should be part of the spec.  Specific noise figures should be part of the spec just as the current and voltage are part of the spec.  These are actually requirements, but it's to much work to explain requirements vs. specs and why it's important.  I've been fighting that battle for some time on the ventilator project I'm working on.

The problem is that I don't have a scope. why? look at this product: https://www.ebay.com/itm/Sega-Dreamcast-ReDreamPSU-Power-Supply/303170616893?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

my product should be the same as this one, and all these PSUs are clones\replicas\similar to this one: https://github.com/PSUThings/PSU/blob/master/Dreamcast/PCB/DreamPSURev2-0.pdf

The ebay one I linked (I have it) it uses LM2596 buck + 33uH inductors on the output + 100uF for input and output. that is it, very minimal and straightforward. what noise\ripple do you expect from this?

the github one uses TPS54525 with copy-pasting datasheet circuit.

I wanted mine to be lets say 10 times better in terms of noise and ripple. since I don't have a scope to measure their output, then it is very hard for me to put noise figures.

kindly see their ICs datasheets and see what expect noise\ripple from them, and if our design here gives better or not. maybe this is the best approach now.

I could say I want 10uV ripple\noise but maybe this is just too hard to get, but i will be happy with beating these products by a good margin. if they offer 10mv and I can get 1mv, then I consider this a success.

[gnuarm]

well, 400mV seems like a lot is not it? what about normal operation at 2.8A of 3.3v, what ripple and noise is expected?

I plan to get DS1054Z for sure, but right now I cannot do it because it is gonna take a lot of money. Shipping is not cheap and itself is not cheap. thus I saw locally offered items by chance and found this one. Still negotiating with him though.

So I could get this one, then wait and get the rigol one.

we'll see what happens

EDIT:

on AOZ page 6, full load operation continuous load seems to have very little ripple at 50mV\div. the graph is not so clear but that seems like about 5mV maximum, this is without linear stage or filters.

You might see high speed spikes at 400 mV at the time the diode starts to conduct.  But you won't see anything that large with a frequency at the switching rate.  Nothing you might call "ripple".  The ripple is due to the switching between driving the choke from the line and the choke "coasting", driving the current through the diode and ground.  You should see ripple more like a few tens of millivolts, maybe even just 10 mV.  If you are seeing anything like 400 mV of ripple, you need to address the design issue in the switcher.

The high frequency stuff is well filtered by passives.  Most people are happy with what caps can do.  There should be a physically small cap with solid connections to the ground and power planes, short and direct, 100 nF is fine.  Then there should be a large value cap sized to match the load.  It can be a bulk cap such as an electrolytic, but should have as low ESR as possible.  Tantalums are good in this use, but some don't like their failure rate.  They require massive over rating, at least 2:1.  So a 5V regulator would require at least a 10 volt cap, preferably 16V. 

I would like to see the output waveform of the switcher if you do this filtering. 

Rather than a standard scope, why not consider a digital attached scope.  The 20 MHz band width is not hard to find with a 100 or 200 MHz sample rate.  I have one here somewhere.  A Hantek I ended up getting for free.  I couldn't get the software to work and when I contacted the supplier they found the tracking info said it was lost so I got my money back!  lol  I understand people have hacked them and there is open source software for it that actually works.  I'm not expecting much out of it, but it's something to get going. 

How do you plan to evaluate your supply?  Are there visible symptoms on using the poor supplies on the unit it powers?  Do you have them documented so you can check your unit in a comparison? 

[gnuarm]

I wanted mine to be lets say 10 times better in terms of noise and ripple. since I don't have a scope to measure their output, then it is very hard for me to put noise figures.

kindly see their ICs datasheets and see what expect noise\ripple from them, and if our design here gives better or not. maybe this is the best approach now.

I could say I want 10uV ripple\noise but maybe this is just too hard to get, but i will be happy with beating these products by a good margin. if they offer 10mv and I can get 1mv, then I consider this a success.

The ad you linked claims 30 mV.  Does that board not work?  As the listing says it depends on clean input from the 12V supply.  That's actually a bit specious.  One of the functions of a regulator is called line to load regulation meaning how much the output changes from a change in the input voltage.   It should be very low so the 12V supply should not matter much. 

If you can get 1mV noise from all sources, that will be very good indeed.  But since you have no way to measure it...

[VEGETA]

The one in ebay link (LM2596) is what I use. It outputs good quality picture but I use LCD monitor via VGA and I didn't make a proper comparison and so on to find artifacts. HOWEVER, I had 2 12v PSUs... one is bad and other is less bad. on the bad PSU, this product doesn't output nice picture! actually the picture is full of waves and garbage... like a lot! hence it requires a good power supply. I had to get a better 12v psu than the one I have in order for it to work. I don't know about dreampsu (github) but people in retro gaming industry said it is not good, check here: https://twitter.com/voultar/status/1248271361778253824?lang=en

I want mine to be better than those. if they offer 30mV, then I must do reasonably better... don't you think so?

If you can get 1mV noise from all sources, that will be very good indeed.  But since you have no way to measure it...

I will get that analog scope for sure, I cannot get digital one anytime soon. so analog is all we got.

how much noise\ripple do you expect from this? approximately?

[VEGETA]

Hello,

I have tested the board and the initial results are promising. Kindly see pictures of the setup here: https://imgur.com/a/xCkHsew

The setup is without the switcher ICs + MOSFETS since they didn't arrive yet, still in customs. I have used IRLIZ44 mosfets instead and hook the 12v voltage directly to mosfet drain instead of the lowered voltage which supposed to come from the switchers. This is very hard for the circuit since now it needs to source the entire current from 12v, not from lowered voltage which means the 12v supply should be capable of high amps @ 12v which mine isn't.

Anyway, I have made a big resistor (as in pics) which is about 3.6 ohms and the circuit regulates while using it, on both rails. without load the voltages are 5.1 and 3.5 but when putting load it gets a bit down.



I have 2 PSUs, one is DYI made from buck modules which is 2 amps max, so drop voltage is to be expected and happened. the other is a 12v adjustable wall adapter, good quality and works well with other dream psu products. However, despite being rated at 12v 3 amps, the board outputs 4.5v and 3.1v at 1.6 ohms resistor (put on each rail separately). will this drop voltage be gone when using proper reduced voltages?

as you see, I have soldered 3 of 1000uf where they should but put a jumper instead of 10uH inductor. the board outputs buzzing sound, is it from the inductors despite being bypassed in this setup? why is that? the sound is almost gone when putting big load.

I will try to upgrade the setup tomorrow by having 2 buck modules output the required voltages to mosfet drains instead of the 12v jumper and will update you about the results.

What do you think so far? what about the drop voltage?

regards

[BrianHG]

Hello,

I have tested the board and the initial results are promising. Kindly see pictures of the setup here: https://imgur.com/a/xCkHsew

Eww, long unpredictable thin wires...

The setup is without the switcher ICs + MOSFETS since they didn't arrive yet, still in customs. I have used IRLIZ44 mosfets instead and hook the 12v voltage directly to mosfet drain instead of the lowered voltage which supposed to come from the switchers. This is very hard for the circuit since now it needs to source the entire current from 12v, not from lowered voltage which means the 12v supply should be capable of high amps @ 12v which mine isn't.

OK.

Anyway, I have made a big resistor (as in pics) which is about 3.6 ohms and the circuit regulates while using it, on both rails. without load the voltages are 5.1 and 3.5 but when putting load it gets a bit down.

This shouldn't be unless there is some oscillation going on.
What voltage do you read on the opamp VCC?
What voltage do you read on the output of the 78L05?
Where is you voltmeter GND connected to?
Where are you reading the output voltage from?

I have 2 PSUs, one is DYI made from buck modules which is 2 amps max, so drop voltage is to be expected and happened. the other is a 12v adjustable wall adapter, good quality and works well with other dream psu products. However, despite being rated at 12v 3 amps, the board outputs 4.5v and 3.1v at 1.6 ohms resistor (put on each rail separately). will this drop voltage be gone when using proper reduced voltages?

as you see, I have soldered 3 of 1000uf where they should but put a jumper instead of 10uH inductor. the board outputs buzzing sound, is it from the inductors despite being bypassed in this setup? why is that? the sound is almost gone when putting big load.

So long as the opamp VCC is high enough, the mosfet VGS is low enough and the mosfet drain has enough supply voltage, there shouldn't be a drop in the first place.  Your wires look too thin for even 1 amp let alone 3.  Also, if you are measuring the voltage anywhere else than the output connector on your PCB, because of those thin long wires, do not expect to see the right voltages.  Also, try AC measurements with your voltmeter.  Thise thing long wires in the op-amp feedback circuit will cause oscillation.

I will try to upgrade the setup tomorrow by having 2 buck modules output the required voltages to mosfet drains instead of the 12v jumper and will update you about the results.

What do you think so far? what about the drop voltage?

regards

Right now it's hard to tell.  Those long thin wires in the circuit and unknown points where you have been probing your voltages, I cannot tell.

[VEGETA]

Eww, long unpredictable thin wires...

these are all I have right now, unfortunately. Maybe I could get thicker wires tomorrow from my company (1mm sq wires).

This shouldn't be unless there is some oscillation going on.
What voltage do you read on the opamp VCC?
What voltage do you read on the output of the 78L05?
Where is you voltmeter GND connected to?
Where are you reading the output voltage from?

voltage on op-amp.. I don't remember correctly but it was like 0.3-0.5v less than supply voltage. I guess 12.3v was the supply, and the op-amp was about 12v or so. I am not so sure but it is high enough.

7805 voltage is 5v as expected, not 5.0000v but few mV more.

Voltmeter and reading is on the final connector itself.

So long as the opamp VCC is high enough, the mosfet VGS is low enough and the mosfet drain has enough supply voltage, there shouldn't be a drop in the first place.

drop doesn't happen on low loads, but only on high loads. I suspected this because of the input supply itself but the 2nd input supply was capable of 12v @ 3 amps...

Your wires look too thin for even 1 amp let alone 3. 

well, will it cause problems other than high heat in the wire itself? do you think this contributes to the drop voltage? how?

Also, if you are measuring the voltage anywhere else than the output connector on your PCB, because of those thin long wires, do not expect to see the right voltages.

I measure on output connector. again, what is the cause of thin wires?

Also, try AC measurements with your voltmeter

hmm ac coupling for measuring ripple\noise?

Thise thing long wires in the op-amp feedback circuit will cause oscillation.

but thin wires shouldn't contribute to emi and so on. I need to understand this. anyway I will try to get thicker wires tomorrow.

[BrianHG]

hmm ac coupling for measuring ripple\noise?

So long as the bandwidth is withing your voltmeter's frequency range & having a true-rms meter also helps.

I still can't figure out the 'buzz' your getting on inactive inductors...

[VEGETA]

I am doing measurements now:

No load:
V_7805: 5.044v
V_3.3_after_7805: 3.361v
V_supply: 12.3v
V_opamp_supply: 11.98v
V_output5v: 5.146v
V_output3.3v: 3.481v
ac measurement: keeps doing 0v and 2v each half second on 5v rail, and about 1.4v with 0v on 3.3v rail

update: inductors has 12.3v on both sides

update2: buzzing is gone when putting bit load.

update 3: i soldered 4.6v wire to input of inductor and still same result and sound. also, voltage drops to 2.4v when using 1.6 ohm load in 3.3 rail

[BrianHG]

ac measurement: keeps doing 0v and 2v each half second on 5v rail, and about 1.4v with 0v on 3.3v rail

Odd.  Oscillate, then stop, then oscillate.  Are the gate capacitors installed?

update: inductors has 12.3v on both sides

update2: buzzing is gone when putting bit load.

update 3: i soldered 4.6v wire to input of inductor and still same result and sound. also, voltage drops to 2.4v when using 1.6 ohm load in 3.3 rail

What happens to the 12v source with the 1.6ohm load.
Also check the opamp supply and gate and drain voltages.

[VEGETA]

Odd.  Oscillate, then stop, then oscillate.  Are the gate capacitors installed?

yes it is installed.

What happens to the 12v source with the 1.6ohm load.

gets some 10mv drop, same as opamp supply. nothing big.

as for gate voltage after R17 (100ohm), it is 1.1v when no load and gets to 10v when 1.6ohm.

[VEGETA]

I lifted the inductors input pin, buzzing still the same.

edit: i completely took off the inductors... same result

[VEGETA]

I took the 1000uf caps exact same result

EDIT: I soldered the 12v on L1 pin without using the jumper, still same result.

buzzing is not from elec caps or inductors

[VEGETA]

here is the mosfet used: https://www.infineon.com/dgdl/Infineon-IRLIZ44N-DS-v01_02-EN.pdf?fileId=5546d462533600a401535664286325cb

I also have this one: https://www.mouser.com/datasheet/2/149/IRL640A-87605.pdf

[BrianHG]

as for gate voltage after R17 (100ohm), it is 1.1v when no load and gets to 10v when 1.6ohm.

This doesn't sound right.  It should be between 4.3v to 6.3v max depending on load.  Never 1.1v, and only going to 10v if the mosfet cant drive enough current or it is not a logic level mosfet.

[gnuarm]

as for gate voltage after R17 (100ohm), it is 1.1v when no load and gets to 10v when 1.6ohm.

This doesn't sound right.  It should be between 4.3v to 6.3v max depending on load.  Never 1.1v, and only going to 10v if the mosfet cant drive enough current or it is not a logic level mosfet.

The FET has a very low threshold.  It will pass amps of current with just 2V Vgs.  So in regulation the Vg should never be more than 5.8V.  10V certainly has the part turned on fully.  What is the output voltage with the 1.6 ohm load? 

What is V_FB1 with the 1.6 ohm load? 

What is the voltage on both sides of R17? 

You can probably do some debugging without the 1.6 ohm load.  i see you have a 100 ohm resistor on the output, R22, which is enough to not be looking at zero current measurements.  The output voltage is a bit high, 3.48V.  It should be the same as the reference voltage (3.361V) with a very small margin.  When debugging, keep it simple.  Try figuring out why the output voltage is high with no added load for starters.  The output voltage should depend on nothing other than the reference voltage and the operation of the op amp and FET.

V_opamp_supply: 11.98v
V_3.3_after_7805: 3.361v
V_output3.3v: 3.481v

To find out why the output is so high when the reference is good, measure all the points in the control loop and the power input to the FET, pin 2, the drain.  Please present those measurements clearly in a table like you did below.  That is everything involved in setting the output voltage and should be enough to understand where a problem might be.  Essentially, we need the measurements of pins 1, 2 and 3 on both the FET and the op amp, no load and with load.  While you are at it, measure the power and ground pins on the op amp, not the traces, be sure to measure on  the pins directly. 

I don't understand the AC measurement.  Are you saying the voltage outputs are bouncing between half the expected voltage and ground??? 

ac measurement: keeps doing 0v and 2v each half second on 5v rail, and about 1.4v with 0v on 3.3v rail

I have no idea what this is saying.  If it is literally true, how can you present these other measurements???  A problem like this will require opening the feedback loop by removing R19 and taking measurements. 

[VEGETA]

I have provided input voltage of 4.6v only to the 3.3v mosfet while 5v mosfet is without power, yet its drain seems to have 10v or so. I am not sure if it is the drain or gate but both shouldn't be with any voltage right? its output is about 130mV though.

I am at work now, when I return I will jump into re-doing the setup and do required tests.

What is the voltage on both sides of R17?

the measurement I took was showing 1.1v on both sides (nearly) when no load but didn't do it for full load, full load (1.6 ohm) has about 10v for gate pin.

To find out why the output is so high when the reference is good, measure all the points in the control loop and the power input to the FET, pin 2, the drain.  Please present those measurements clearly in a table like you did below.

I will do it when I return for sure.

I don't understand the AC measurement.  Are you saying the voltage outputs are bouncing between half the expected voltage and ground???

I have no idea what this is saying.  If it is literally true, how can you present these other measurements???  A problem like this will require opening the feedback loop by removing R19 and taking measurements.

I put multimeter in AC voltage measurement instead of DC, then measured the points only to find that the reading jumps between 0 and 2v, and 0 to 1.4v as mentioned above... each half a second or something.

All of this aside... why and where is that continuous buzzing sound is?! I mean i took off all elec. caps and the 2 inductors, it is still there without a change. also, when the load is quite high the sound disappears.

[gnuarm]

I have provided input voltage of 4.6v only to the 3.3v mosfet while 5v mosfet is without power, yet its drain seems to have 10v or so. I am not sure if it is the drain or gate but both shouldn't be with any voltage right? its output is about 130mV though.

I am at work now, when I return I will jump into re-doing the setup and do required tests.

Yeah, this is why I asked for the information in a table format.  I don't have any idea what you said above.  I can't understand what you are measuring if you are changing the circuit or describe your measurements in different ways than what I am asking about. 

I'm working on a project right now with about a dozen people and only a couple others are electrical engineers.  I don't have a test setup and when they ask me to help debug I can never get information in a form I can understand.

What is the voltage on both sides of R17?

the measurement I took was showing 1.1v on both sides (nearly) when no load but didn't do it for full load, full load (1.6 ohm) has about 10v for gate pin.

See?  It's not clear what you mean by "didn't do it".  I really don't want to have to exchange multiple messages to get the info.  It has to be complete and in a form I can understand exactly what it going on.  So pick a configuration and lets test that one.  Starting with the 3.3V output is fine.  Let's make sure the 5V circuit is completely disconnected so it is not a factor.  Then write down ALL the readings at every important point with clear labels.  This is why I put names on every net on my designs.  Makes it easier to communicate... much easier.

To find out why the output is so high when the reference is good, measure all the points in the control loop and the power input to the FET, pin 2, the drain.  Please present those measurements clearly in a table like you did below.

I will do it when I return for sure.

I don't understand the AC measurement.  Are you saying the voltage outputs are bouncing between half the expected voltage and ground???

I have no idea what this is saying.  If it is literally true, how can you present these other measurements???  A problem like this will require opening the feedback loop by removing R19 and taking measurements.

I put multimeter in AC voltage measurement instead of DC, then measured the points only to find that the reading jumps between 0 and 2v, and 0 to 1.4v as mentioned above... each half a second or something.

If this is not happening on a DC measurement, let's just ignore it for now.  i have no idea what your meter is doing with this.  Normally an AC reading will be off, but stable when measuring DC.

All of this aside... why and where is that continuous buzzing sound is?! I mean i took off all elec. caps and the 2 inductors, it is still there without a change. also, when the load is quite high the sound disappears.

You need to track that down with your ear.  If not that perhaps a scope.  What is left on the board if all electrolytic caps and inductors are left?  I don't  really know what you have.  The photo I saw only showed caps.  I didn't see any chips.

BTW, first thing you should do is to inspect every solder joint.  Make sure there is a good connection.  When measuring voltages of suspect connections measure the voltage on a pin, then the same signal on another pin.  If either solder joint is bad the bad reading will be only on one pin.  Often putting the probe on a bad solder joint will make it work.

[VEGETA]

I will do exactly that, gonna put labels to all joints that I am gonna measure. All of them will be for no load and specific load (gonna mention it). I will see the soldering too but it shouldn't be the problem.

i have taken the 2 big inductors, the ones left are the small inductors which are inputs to switchers... so they are not used here since I am feeding a direct voltage at mosfet drain. Also, the lm358 op-amp + 7805 regulator + diodes. I tried listening to it but for sure it is not from the mosfets but the board is 50x50mm so very small area to know for sure which component does it. I will try recording a video to show you in details and you can hear the sound. I hope the forum allows uploading videos.

I think you have a pdf for the schematic (not the v1.1, this is not the one used here), if not, I will send it.

___

Data will be like this:

No load:

v_gate =
v_drain =
v_output_3.3v =
v_opamp_supply =
v_opamp_feedback =
7805_5v_voltage_ref =
7805_3.3v_voltage_ref =
v_12v_input =

anything else should be added?

[VEGETA]

No load test  of 3.3v rail:

v_gate = 1.35v
v_drain =4.64v from external buck module using same 12v source.
v_output_3.3v = 3.436v
v_opamp_supply = 12.38 supplied directly from 12v supply.
v_opamp_feedback = 3.446v
7805_5v_voltage_ref = 5.044v
7805_3.3v_voltage_ref = 3.360v, see note below.
v_12v_input = 12.38v.


NOTE: I noticed that before connecting power to mosfet drain, the 3.3v reference voltage which is derived from the resistor divider is only about 1.4v while the 7805 voltage is 5.044v. when connecting the mosfet drain power, it becomes 3.3v.


3.3 ohm load test  of 3.3v rail:

v_gate = 6.77v
v_drain =3.9v from external buck module using same 12v source. maybe it drops due to higher current
v_output_3.3v = 3.28v
v_opamp_supply = 12.11 supplied directly from 12v supply.
v_opamp_feedback = 3.337v
7805_5v_voltage_ref = 5.044v
7805_3.3v_voltage_ref = 3.331v, see note below.
v_12v_input = 12.11v.
buzzing completely gone

[BrianHG]

Without a switcher making your lower voltage to feed the 'drains', the drains should always be 12v wired directly to your 12v supply.

I don't know why you are getting a buzz, are you sure your wiring is correct?  An audible buzz means something is being driven hard, very hard, with low frequency, usually square wave off-on-off pulse oscillation.  Nothing can be properly deternined with those wires of yours and the photographs you provided.  Are you sure your wiring is correct.  Also, is the polarity of the caps you soldered on correct?  Are they getting warm?

The output without the mosfets should be 0v.  With the source & gate wired, the output should be s=3.3v & g=~5-6v.  If not, something is wired wrong.

Is there any ripple on your +12v source?

[VEGETA]

Without a switcher making your lower voltage to feed the 'drains', the drains should always be 12v wired directly to your 12v supply.

I don't know why you are getting a buzz, are you sure your wiring is correct?  An audible buzz means something is being driven hard, very hard, with low frequency, usually square wave off-on-off pulse oscillation.  Nothing can be properly deternined with those wires of yours and the photographs you provided.  Are you sure your wiring is correct.  Also, is the polarity of the caps you soldered on correct?  Are they getting warm?

The output without the mosfets should be 0v.  With the source & gate wired, the output should be s=3.3v & g=~5-6v.  If not, something is wired wrong.

Is there any ripple on your +12v source?

I re-done the wiring and got rid of all thin wires, only few still remain and they are correct.

There are no caps now, all taken off as well as inductors. this is just voltage directly at mosfet input (drain). I increased the voltage so that any drop didn't effect the operation but results above is the same. when I install a 3.5 ohm load, the buzz disappears and the regulation is kinda good with 3.290v at the output and about 3.331 at opamp inputs with margin.

I will try an npn (BD437) on 5v rail to see what is going on. also gonna do more tests with 1.6 ohms load since it is the one driving this to maximum.

if any of this didn't work, then i might try another board.

if you have the schematic, then see the points:

12v input: on input of 7805, on the cap pin.
ground: on J1 gnd pin.
6.5v: on 3.3v mosfet drain directly.

[VEGETA]

few updates:

- I have tried another new board, but same result happens. Also, I noticed that the 3.3v mosfet is really hot even at no load.

- using npn didn't give any good results, keeps being 5v but when putting load it drops and magic smoke happens due to the large voltage gap.

- I tried using 1.6 ohms and the result is 3.26v or so on 3.3v rail and 4.928v on 5v rail with no buzzing\continuous_beeping sound. can't go much because no heatsink installed.

- I have attached a picture of my wiring + pictures of real wiring (no shorting between any pin).


I started suspecting that the switchers + chosen KIA mosfets gonna make some change since that is the full circuit. And at the same time I find it bizarre that the circuit has some issues even with injecting voltages this way. having the full circuit allows us to get enough current on both rails without any drop voltage. do you think this might be the solution?

[BrianHG]

few updates:

- I have tried another new board, but same result happens. Also, I noticed that the 3.3v mosfet is really hot even at no load.

Hun?
Please measure the impedance of the mosfet pads to GND on the PCB.  No mosfet.  You should see 100 ohm, our current default pull-down resistor.  Definitely not enough to make a to220 mosfet get 'hot'.


Again, those 'Gate' voltages sound wrong.  A 1.35v from gate to GND should not output 3.436v, if anything, it should be close to 0v.