Making a Bench Supply From a Computer Power Supply

General PC Power Supply Color Code (verify these are right on your power supply!)


RED +5 Volts
WHITE -5 Volts
YELLOW +12 Volts
ORANGE "Power Good"

Since Personal Computer power supplies are abundant, you can usually find one that is cheap or free.

A switched power supply must be preloaded to regulate correctly - the specific load required may differ among power supplies but 10% seems to be the recommended starting point.   The above example is a 200 watt version that provides 5 volts at 20 amps.   To start with a power supply like this, get a couple of 10 watt, 1 ohm resistors from Radio Shack, tie them in series between the 5 volt and ground leads on the power supply (I put mine inside the case to keep them cool since they do heat up a tad), bring some of the other leads out to a barrier strip and you have a nice bench supply. I used P8, P9 and one of the four wire connectors as the feed for the barrier strip.  "Power Good" and one ground was used for the "Power On" LED.

Normal warnings #1: PC power supplies have lethal voltages inside. Don't do this if you haven't played with these things before. You can kill yourself.

Normal warnings #2: This may not work with your power supply. Specifically, you should test the voltages and try different loads (use SMALLER resistors for a start!) if the 5 volt regulation is not working properly.