Any recommendations for a PCB or kit to build a +/- 15 volt power supply?
Add two (three) big Caps and you are done. Works perfect in 12V, should be the same in 15V.
@fcd72 Thanks, that could indeed work well.
I should have been more clear though; I’d ideally like to have something that doesn’t take mains but low-voltage AC from a wall wart. Something like the breadboard friends +/- 5V power supply that does go up to 15V.
Maybe that wouldn’t even make sense?
To be honest this only makes sense if you are afraid of connecting 220V Mains to the PSU and isolate everything either by hiding it away in a Box or with tape. Every other attempt to get stable ± 15 V is much more expensive, especially with Wallwarts. Ask Olivier about the pain making a good ± 8V PSI from ansingle AC adaptor and then think about if you want to do this with twice the Voltage (thus much higher thermal problems…).
To make a proper PSU you need symmetrical Power Input to your regulators, sadly there are no symmetric AC Wallwarts out there. At least i know of none.
btw. how exactly does one have to add the caps for the PSU?
+12V > +Side of Cap / - Side Of Cap > GND
+5 V > +Side of Cap / - Side Of Cap > GND
GND > +Side of Cap / - Side Of Cap > -12V
You can start with qp’s revised link (actually I edited it because it didn’t link to the right article!) - this is the same kind of schematic as the Ambika PSU too. If space is a problem, you can try decreasing the total rectification filter capacitance from 10000µF to a lower value. To get the right value, you can do a Spice simulation of your PSU with a load resistor representing the current eaten by your boards, or you can just build it and try removing caps until you see ripples on the regulator outputs.
What suggested qp doesn’t work because you need a center tap, and while you get this out of a transformer, you don’t get this out of an AC wallwart.
The real question is how much current you need! Unless you want less than 150mA, you’re screwed. When using an external AC wall-wart you have to use half-wave rectification, which means that you need big caps to hold the charge in the “wrong” part of the AC cycle. To make things easier you can use a higher input voltage the drawback being that high-voltage AC wallwarts are harder to find, and that bigger heatsinks will be needed for your regulators (like on the doepfer DIY case kit DIY Kit1)
All these solutions really suck. If I had to design a +/- 15V PSU with the constraint that the input is a wallwart to cover my ass from lawsuits :D, I would go with a 18V DC input, a 15V positive regulator with generous heatsink, and a DC-DC converter to get the negative rail.
@pichenettes, I edited the comment and added a PSU that runs on a wall wart. Just need to change the regulators for +/- 15
I’d like to put the four Hexinverter NeinOhNein PCBs in a single plexi desktop case so the power requirement would be pretty modest.
Life could be so easy
This + 2 Caps will do.
Thank you all for this, it’s very helpful.
100mA per rail? Might be a bit too low…
thanks for the fix pichenettes.
pichenettes I was thinking the same even thoughfcd72’s suggestion sure looks easy.
I have no clue hoe much these PCBs draw - im shure there must be some higher rated DC/DCs somewhere - why bother with Saturn 5 Size Caps when you can have such a cool thingie???
Edit: Sometimes COnrad pretends to be your friend:
Hm. I might give that 500mA puppy a try just to see how it goes.
500mA should be enough for 3HE 19" Rack i guess…