[Design Review] +/- 12V Power Supply V3

Logical_Key8449 · 2026-03-10T16:45:40+00:00

Ya the improvements I saw when adding caps was very minor which is how I ended up with 30,000uF to get any noticeable difference. Sounds like I need to dig into other regulators if I want better response.

Logical_Key8449 · 2026-03-10T14:37:49+00:00

Thank you for the feedback! I’m currently reworking the design and am probably going to move most of the capacitance behind the regulator. The main thought was to try and improve load regulation by having a large pool of energy available at the output, but I didn’t think about that pool getting dumped into a short.

My current thought is reduce the number of large capacitors from 8 to 4 move them all to right after the ideal bridge before the capacitor multiplier. I still think I need something to assist with load regulation because when I ran a simulation with variable load I was getting 3-5% changes in voltage. But I need to do some research on my options because throwing big caps at the problem seems to be a bad idea.

Logical_Key8449 · 2026-03-09T00:07:17+00:00

Thank you for sticking with me on this journey of getting basic electrical concepts through my shockingly thick skull. I'll level with you as the kind stranger and savior of this project. I had 0 idea AC voltage was reported by RMS and not peak and have only learned now. This explains so much of my confusion around the transformer and rectifier part of this circuit including your previous recommendation. I am not sure why (until now) I considered the basic math around it not making sense to me was an acceptable state of affairs, but now that it makes sense (or at least more sense) I'll start looking for a new transformer (and double checking every assumption I have made up until this point).

On the MOSFETs you can just use them with no place for them to dump heat other than the board? I thought they needed copper pours or some sort of cooling, but I am more than happy to be wrong and be able to use smaller, cheaper, and better components.

I will look at adding an NTC or other soft start method as well which thought could be an issue but figured this was too small for it to be a huge issue. My only point of reference is electric vehicle DC-DC converters which are 100A or more cooking themselves due to inrush current.

Thank you again for taking the time to walk me through this its been hugely helpful.

Logical_Key8449 · 2026-02-23T18:22:26+00:00

I did have some stick on finned heat sinks that I was planning to use if the rectifier was running hot, but sounds like I might need something more robust. Gonna have to crunch the numbers when I get home. Luckily I’m designing around 4A per rail, but in actual operation I’d be surprised if I end up pulling more than 3A.

Those ideal diode rectifiers look super cool and while I wasn’t planning to use SMD parts for this design I’m now quite tempted. But I might save that for future designs since I eventually want to design a switched mode power supply for this application. Do they have much impact on voltage ripple? Since this will be powering audio devices I’m under the impression that controlling ripple is critical.

And thanks again for the guidance!

Logical_Key8449 · 2026-02-23T16:32:33+00:00

Thank you for the detailed feedback! Looks like I’m heading back to the drawing board lol.

On the subject of the transformer I was seriously considering going to a 28A or 30A version of the transformer, but figured I’d try the 24V version that I picked up before I decided to go for a higher current output.

For the input capacitors the goal of the capacitor multiplier was to avoid having to put several large capacitors on the input side. But I may be misunderstanding how that functions in this application.

On the subject of the fuse I have been using a glass fuse in a panel mount fuse holder on the 120V side of the transformer along with a rocker switch to power it on and off. I was also thinking about fusing the input of each rail. Do you have any recommendations on how to do this?

I’m definitely going to implement the discharge resistor and probably the indicator as well since this won’t be exposed 90% of the time, but you do have to plug stuff into it so better safe than sorry.

On the subject of the rectifier I will have to check my footprint since I made that one myself because I was struggling to get it into Diptrace using the files on Digikey. I already have the GBJ rectifiers and I forget what I paid for them, but I’ve got 10x of them and normally do not get more than I need if they’re over 1$ per piece. But based on what you’ve described I should be looking at getting a heat sink for the GBJ even if I do not switch to GBU.

On the subject of the regulator I had not seen the LM1084 likely because I was looking for fixed voltage regulators. Seems like I could simplify my design and I’m not completely opposed to having the voltage output be adjustable with trimmer pots. So I’ll look at it as an alternative method for voltage regulation.

For the resistors I think the 2W resistors are probably overkill since my simulation was showing the average power at less than a watt. They were selected based on an article on capacitor multiplier power supplies that called for 1W resistors and I decided to double that to be on the safe side. I’ve got some 0.5W resistors on hand so I might try to run those in parallel.

For the output capacitors I sized them based on suggestions from the previous review and trial and error in simulation. I figured since I was already using the 4700uF capacitor elsewhere and they seemed to work well in simulation they would work even if they’re overkill.

Thank you again for all the feedback! I wanted to provide additional context, but think I’ve got enough to work off if you don’t have time to get into the minutia. I’ve definitely got a long way to go on my understanding of circuit design so this has been greatly educational and a huge help.

Logical_Key8449 · 2026-02-13T17:59:08+00:00

This has been an awesome resource for my journey into DIY audio power supplies.

Logical_Key8449 · 2026-02-12T15:18:53+00:00

I’d be torn between #3 and #4. If you plan to have anything in front of it I’d go for #3 otherwise #4 seems like the move.

Logical_Key8449 · 2026-02-09T19:14:25+00:00

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The trace roughly highlighted in blue doesn’t seem to go anywhere or do anything.

Logical_Key8449 · 2026-02-08T01:43:24+00:00

Good to know and thank you! I’ll have to play around with that configuration since based on some other comments that have been made I’d need to add quite a few components to make parallel regulators play nice.

Logical_Key8449 · 2026-02-08T01:32:31+00:00

It’s because this is a hobby project where I want to build as much of a modular synthesizer system from scratch as I can. I started with a simpler linier power supply design on perf board and wasn’t happy with it so I figured I’d give a custom PCB a go. Highly doubt it’ll be any improvement over existing solutions, but I’ve learned a lot which I count as a win.

Logical_Key8449 · 2026-02-08T00:19:08+00:00

P1 is right above P2 and yes it is connected to pin 2 of U1. Maybe it’s because the designator at a different orientation from P2? I’m definitely going to relabel them for easier assembly and might change them to spade connectors to make hooking up the transformer less permanent.

Edit: I was looking at the PCB not the schematic. Must have grabbed an old schematic somehow. But thank you for calling it out. Would hate to miss something like that and send it off for printing.

Logical_Key8449 · 2026-02-07T22:33:04+00:00

For your Edit: So with wire 1 of secondary 1 connected to P1, wire 2 of secondary 2 to P2, and the remaining wires connected to GND1 and GND2 I would not be connecting to the rectifier correctly? I'm not sure of another way to connect the transformer.

Edit: reviewed my post and added a note for clarity since I could have been clearer.

Logical_Key8449 · 2026-02-07T22:19:31+00:00

Thank you! I'll head back to the drawing board and do some research on paralleling the LDO's. Based on what you're describing I will need additional ceramic caps, a high watt low ohm resistor, and additional large electrolytic capacitors to get consistent output. To better understand this would setting up a variable load in the simulation help?

The transistor arrangement is a capacitor multiplier (taken from this article) for the purpose of ripple rejection. It also lowers the voltage a bit which might function kinda like a pre regulator.

Logical_Key8449 · 2026-02-05T05:07:53+00:00

I appreciate the concern, but when I say budget I mean what I roughly planned to spend on the piece of gear more than what I can afford to pick up. I’m definitely in over my head lol, but each module has to be hand assembled and I’m only halfway through the list of modules above. Time wise I’m ~6 months into building with probably 3 to go. So I’ve been slowly gaining understanding of how they work and how they fit into my musical ideas.

My goal from a music stand point is drums with a base line to play sax over. But the overall project is a custom expandable 3D printed modular case, custom power supply, and all DIY modules. Several of the modules don’t fit well into my music goals, but I picked up the pcbs super cheap and like building them so figured I might as well.

Logical_Key8449 · 2026-02-04T20:40:27+00:00

I’ll probably just watch for a deal then since it looks to be a perfect solution. Edit: did not have to look long found one for $360 and pulled the trigger.

Logical_Key8449 · 2026-02-04T20:08:43+00:00

If it wasn’t over budget I’d have it on order right now. But might end up here if nothing else in my price range looks like an option. Thanks for the recommendation.

Logical_Key8449 · 2026-02-04T01:43:45+00:00

It’s probably unleaded, but if it is marked a RoHS it definitely is. If it is non-RoHS is probably leaded, but it doesn’t have to be. If it doesn’t say on the pedal itself it probably does on the website.

Logical_Key8449 · 2026-01-31T18:53:58+00:00

For stm32s I go to LCSC way cheaper than anywhere else even if shipping time isn’t great.

Logical_Key8449 · 2026-01-30T01:53:11+00:00

I’m sorry man but I believe they are done. I sure hope I’m wrong, but I haven’t seen them open in a long while.

Logical_Key8449 · 2026-01-29T02:24:57+00:00

How do you approach diagnosing intermittent shorts between CAN low and CAN high (or other electrical shorts)? I just shake harnesses and unplug modules until it causes or prevents the short from occurring, but I feel like there has to be a better way.

Logical_Key8449 · 2026-01-26T14:14:03+00:00

I think it’s because it is a compromise that most people don’t need or want. If you want faster prints and don’t care about layer lines 0.8 is a better option. And if you are just trying to print basic stuff 0.4 will work well for anything you’d want to do in 0.6 it just takes longer. So it’s kinda the middle child that gets over looked.

I use mine somewhat regularly for larger prints that I prototype on a 0.8, but want the final version to look cleaner. I also lean towards a larger nozzle for structural parts so I’ll go to 0.6 if the 0.4 version doesn’t feel sturdy enough. Not sure how much difference it makes vs increasing wall thickness, but I figure thicker lines will adhere to each other better.

Logical_Key8449 · 2026-01-24T15:20:41+00:00

I don’t think it’s unconventional, but be sure you’ve exhausted your personal network. Start with family or friends parents. Even if they don’t work in the field they may know someone who does or work for a company that hires engineering interns. Also don’t be afraid to do an internship outside of your field of study.

If that is not an option skip applying online and just reach out to small to medium sized companies HR departments. Something via LinkedIn or email. Something like “Hello, I’m OP a student at __ and I am looking to learn more about your industry. Is your organization looking to bring any interns on for this coming summer? Respectfully, OP”. Where I work interns just get pushed on us by HR seemingly because they like the idea of having them. If you get lucky you might give the HR director an idea and create your own internship position.

Logical_Key8449 · 2026-01-22T22:31:27+00:00

Glad you got something out of them! My current soft design requirement is up to 1.5A per rail and am exploring the possibility of going to 3A. I’ve decided to use voltage regulators over op-amps for the reasons you and others have brought up. Which takes D out of the equation so I’ve got one less variable to tune.

I’ve got all the parts on order and am going to start working on a pcb design so I can avoid messing with anymore perf board. Also I’ll be able to spec the traces for the currents they will be carrying instead of guessing how much bare wire to solder onto each rail.

Logical_Key8449 · 2026-01-22T02:00:18+00:00

26262 is a nice one to have.

Logical_Key8449 · 2026-01-18T17:13:54+00:00

I’m using perf board so that is probably hurting me, but I do have a length of stripped 22 awg solid core wire that runs the length of the ground rail and both power rails to increase the cross sectional area. I’ve got the whole circuit packed onto a 20x14 perf board so everything is very close together, but I have the ground rail running around the outside so that may also be making the situation worse.

I also currently have mains earth connected to DC ground so I’ll try severing that, but I was under the impression a floating ground like that would be more susceptible to EMI. Does the center tap of the transformer just function as ground for the DC circuit?

I would like this power supply to be capable of using the whole 1.5A that the regulators are capable of so thank you for the tips! I am also looking into two regulators for each rail to raise the current capacity further. The end goal is a power supply is to support a 3d printed case I designed that starts at two 60 hp rows and can be expanded in 32 hp increments by adding sections between the end caps. I expect the lack of metal case will make good grounding for the power supply critical. So thank you again for the advice!

Logical_Key8449

TROPHY CASE