I'm working on designing and building a Eurorack compatible (audio synthesizer) bipolar power supply for my own use, to use with both commercially available synth modules and modules that I will build myself.
My target specifications are:
Clean +12v DC rail, delivering up to 1 amp.
Clean -12v DC rail, delivering up to 1 amp.
Ground output
All reasonable safety features to protect the connected devices, and to protect against fire, etc.
I'm new to electronics, and I'm looking for advice on suitability of parts and for any general feedback/improvements on the design.
I did a first draft, and ordered some parts, and I have a basic version working on a breadboard.
Schematic for first design:
It works, but there's a lot of room for improvement. I've been doing research and here's the things I'd like to improve:
1. Add an inrush current limiter because of the large caps.
2. Add fuses on input and output
3. Improve the design to make the output more stable.
4. Revisit the transformer. I'm currently using a wallwart AC to AC adapter and have questions.
5. Revisit the rectifier.
6. Over/under voltage protection? And what stops connected devices from receiving under voltage power while the capacitors are warming up after first being plugged in?
Here's an oscilloscope reading under load:

The blue is the +12v rail at the output. The yellow is the 12VAC input. There's very little draw on the -12v rail (purple).
I'm not sure why the AC is clipping. But the +12v DC rail is definitely noisy when loaded with ~400mA.
This is a sketch of the improvements I'd like to make:
And I'd like to ask a few questions and get some feedback.
1. For the ICL, I think these are what I want:
https://www.digikey.com/en/products/detail/B59213J0130A020/495-76085-ND/7364726?itemSeq=360994674
It looks like the right thing from the data sheet. Is this a good choice?
2. For D7 and D8, which is intended to prevent voltage from going backwards through the regulators, is this what I want?
https://www.digikey.com/en/products...1N5817-E3/73GICT-ND/9600242?itemSeq=361142543
I was told I needed a SCHOTTKY diode instead of the 1N4007's used elsewhere.
This one (linked) is rated for 20v and 1 amp. I think it would be running at it's limit, since the circuit is designed to produce 1 amp per rail, and even though the power supply and the output are 12 volts, I measure 20volts on a meter where the caps are, before the voltage regulator, which I assume to be a side effect of the capacitor smoothing. Do I need a diode with a higher voltage /current rating?
What about:
https://www.digikey.com/en/products...conductor-diodes-division/SB560-E3-54/1023528
Which is 60v, 5A. Is it better to have a higher voltage and amperage rating so there is overhead?
3. To smooth the output, I've found something called a "capacitance multiplier". I've drawn one in, but need to research this more. Specifically how you can make a negative version of one, and how to size the parts. But, is this a good design pattern for stabilizing audio power supplies?
4a. Transformers. There are two main options: A wallwart going into a "DC" power jack (which is actually AC) or a transformer mounted on the board with a mains connection.
I found this:
https://www.digikey.com/en/products/detail/70062K/1295-1021-ND/3881320?itemSeq=361143964
Is it suitable?
The reason I'm not happy with the current walwart solution is that it gets very hot. It's the only part that seems to be generating heat. There is also a very limited selection of AC to AC wallwarts and they are hard to find (most are DC output). I really don't like how hot my current wallwart gets.
The one I'm using now is this:
https://www.digikey.com/en/products...4915292?s=N4IgTCBcDa4MwHYC0BGAHAtSByAREAugL5A
Now I also have a really dumb question. Since the goal is to have 1 amp of +12vDC and 1 amp of -12vDC, do I still only want a 1 amp input transformer, since it's two amps going out (one per rail)?
Will oversizing the transformer help with heat? ie. can I use a wallwart rated for 2.5 amps or something, and fuse it to 1 amp on the input and will it run much cooler since it's running at 30% capacity instead of 100%?
A bigger one:
https://www.digikey.com/en/products/detail/BPE2E/HM1577-ND/454399?itemSeq=361697495
The goal is to reduce the temperature on the wallwart casing.
4b. Or use a toroidal transformer on the board. What are the advantages to that? Do they run cooler?
5. The rectifier. What I have now, I believe is called a half-wave rectifier, and there's two of them. I found another pattern for a bridge rectifier (four diodes in a diamond pattern) and tried it, but what I get from that is +12 and +6 volts, depending on where it is tapped. Getting +6 volts might be useful, but the bridge rectifier doesn't seem to output the -12 volts which I need. I don't suppose I can have two bridge rectifiers, where one of them is installed with every diode backwards from what it's "supposed" to be , to get a negative bridge rectifier?
The only other pattern I saw like this required a special transformer with a center tap. Which comes back to the transformer thing.
Is the dual half-wave the best bipolar pattern that can be used with a wallwart ?
6. Fuses:
I was going to use these on the outputs:
https://www.digikey.com/product-detail/en/0287001.PXCN/F4191-ND/3102551/?itemSeq=361144269
https://www.digikey.com/product-detail/en/3557-2/36-3557-2-ND/2137305/?itemSeq=361274344
Do we also need to fuse the ground since it's actually at a higher potential than the "negative" rail?
Is there anything wrong with automotive fuses? (The idea is that I can buy one locally at an auto store to replace).
For the input:
https://www.digikey.com/en/products/detail/bel-fuse-inc/5ET-1-R/1009785
https://www.digikey.com/en/products/detail/würth-elektronik/696106003002/7244558
That should work with both a wallwart and before a toroidal transformer (if we did it that way), since it is rated for 250 volts.
7. Caps. Do we need less smoothing capacitors (the 4700uf, labeled C1-C6) if you use a capacitance multiplier? Or do they serve a different function?
Thanks,
Nick
My target specifications are:
Clean +12v DC rail, delivering up to 1 amp.
Clean -12v DC rail, delivering up to 1 amp.
Ground output
All reasonable safety features to protect the connected devices, and to protect against fire, etc.
I'm new to electronics, and I'm looking for advice on suitability of parts and for any general feedback/improvements on the design.
I did a first draft, and ordered some parts, and I have a basic version working on a breadboard.
Schematic for first design:

It works, but there's a lot of room for improvement. I've been doing research and here's the things I'd like to improve:
1. Add an inrush current limiter because of the large caps.
2. Add fuses on input and output
3. Improve the design to make the output more stable.
4. Revisit the transformer. I'm currently using a wallwart AC to AC adapter and have questions.
5. Revisit the rectifier.
6. Over/under voltage protection? And what stops connected devices from receiving under voltage power while the capacitors are warming up after first being plugged in?
Here's an oscilloscope reading under load:

The blue is the +12v rail at the output. The yellow is the 12VAC input. There's very little draw on the -12v rail (purple).
I'm not sure why the AC is clipping. But the +12v DC rail is definitely noisy when loaded with ~400mA.
This is a sketch of the improvements I'd like to make:

And I'd like to ask a few questions and get some feedback.
1. For the ICL, I think these are what I want:
https://www.digikey.com/en/products/detail/B59213J0130A020/495-76085-ND/7364726?itemSeq=360994674
It looks like the right thing from the data sheet. Is this a good choice?
2. For D7 and D8, which is intended to prevent voltage from going backwards through the regulators, is this what I want?
https://www.digikey.com/en/products...1N5817-E3/73GICT-ND/9600242?itemSeq=361142543
I was told I needed a SCHOTTKY diode instead of the 1N4007's used elsewhere.
This one (linked) is rated for 20v and 1 amp. I think it would be running at it's limit, since the circuit is designed to produce 1 amp per rail, and even though the power supply and the output are 12 volts, I measure 20volts on a meter where the caps are, before the voltage regulator, which I assume to be a side effect of the capacitor smoothing. Do I need a diode with a higher voltage /current rating?
What about:
https://www.digikey.com/en/products...conductor-diodes-division/SB560-E3-54/1023528
Which is 60v, 5A. Is it better to have a higher voltage and amperage rating so there is overhead?
3. To smooth the output, I've found something called a "capacitance multiplier". I've drawn one in, but need to research this more. Specifically how you can make a negative version of one, and how to size the parts. But, is this a good design pattern for stabilizing audio power supplies?
4a. Transformers. There are two main options: A wallwart going into a "DC" power jack (which is actually AC) or a transformer mounted on the board with a mains connection.
I found this:
https://www.digikey.com/en/products/detail/70062K/1295-1021-ND/3881320?itemSeq=361143964
Is it suitable?
The reason I'm not happy with the current walwart solution is that it gets very hot. It's the only part that seems to be generating heat. There is also a very limited selection of AC to AC wallwarts and they are hard to find (most are DC output). I really don't like how hot my current wallwart gets.
The one I'm using now is this:
https://www.digikey.com/en/products...4915292?s=N4IgTCBcDa4MwHYC0BGAHAtSByAREAugL5A
Now I also have a really dumb question. Since the goal is to have 1 amp of +12vDC and 1 amp of -12vDC, do I still only want a 1 amp input transformer, since it's two amps going out (one per rail)?
Will oversizing the transformer help with heat? ie. can I use a wallwart rated for 2.5 amps or something, and fuse it to 1 amp on the input and will it run much cooler since it's running at 30% capacity instead of 100%?
A bigger one:
https://www.digikey.com/en/products/detail/BPE2E/HM1577-ND/454399?itemSeq=361697495
The goal is to reduce the temperature on the wallwart casing.
4b. Or use a toroidal transformer on the board. What are the advantages to that? Do they run cooler?
5. The rectifier. What I have now, I believe is called a half-wave rectifier, and there's two of them. I found another pattern for a bridge rectifier (four diodes in a diamond pattern) and tried it, but what I get from that is +12 and +6 volts, depending on where it is tapped. Getting +6 volts might be useful, but the bridge rectifier doesn't seem to output the -12 volts which I need. I don't suppose I can have two bridge rectifiers, where one of them is installed with every diode backwards from what it's "supposed" to be , to get a negative bridge rectifier?
The only other pattern I saw like this required a special transformer with a center tap. Which comes back to the transformer thing.
Is the dual half-wave the best bipolar pattern that can be used with a wallwart ?
6. Fuses:
I was going to use these on the outputs:
https://www.digikey.com/product-detail/en/0287001.PXCN/F4191-ND/3102551/?itemSeq=361144269
https://www.digikey.com/product-detail/en/3557-2/36-3557-2-ND/2137305/?itemSeq=361274344
Do we also need to fuse the ground since it's actually at a higher potential than the "negative" rail?
Is there anything wrong with automotive fuses? (The idea is that I can buy one locally at an auto store to replace).
For the input:
https://www.digikey.com/en/products/detail/bel-fuse-inc/5ET-1-R/1009785
https://www.digikey.com/en/products/detail/würth-elektronik/696106003002/7244558
That should work with both a wallwart and before a toroidal transformer (if we did it that way), since it is rated for 250 volts.
7. Caps. Do we need less smoothing capacitors (the 4700uf, labeled C1-C6) if you use a capacitance multiplier? Or do they serve a different function?
Thanks,
Nick