Prototype power supply

A project log for Digital Transistor Matcher/Tester

An automated transistor tester, as well as matched pair finder, for DIY synthesizer projects.

Kuri P. YonKuri P. Yon 01/05/2019 at 07:530 Comments

For the prototyping of this project (and presumably many others), I had actually planned to use the benchtop DC supply that I had ordered, the Rigol DP832, but it isn't going to be delivered on time, and I really wanted to get going on this project. The usual solution for needing a bipolar power supply, two 9-volt batteries in series, wouldn't work here because I need at least 12V supply rails. So I put together a circuit that splits a +24VDC supply into ±12VDC supply rails, using a TL431 voltage reference and LM317/337 adjustable positive/negative linear voltage regulators:

(Sorry for the ugly hand-drawn schematic, but I didn't feel like drawing it into a CAD program.)

Anyway, after a bit of messing around with things, I finally got it to where at least it looks stable on my meter:

Not a perfect split, but it was never going to be. I'm going to check the supplies for noise before I go ahead with using it, but at least I now have a way of moving forward on this project.

Oh, and just for giggles, this is how the circuit ended up looking:

It sure is ugly! And it sure does work! Function over form, people...