January 7, 2019

Using an ATX power supply on the workbench

These are cheap (often available in the right dumpster at certain times) and can be useful. Once you know the pinout, provide a stabilizing load, and manipulate the "power on" signal, you are in business.

There seem to be dozens of articles where people have build these.
Here are a few:

What about really old "AT" power supplies?

These are the ones with two connectors (P8 and P9) with pins all in a line. Each connector has 6 pins, so there are 12 total. These predate ATX supplies, and many of you reading this may never have encountered them. These were once the standard with 386 and 486 machines. 
P8 - 1  Orange - power good
P8 - 2  Red  -- +5 or n/c
P8 - 3  Yellow -- +12
P8 - 4  Blue -- -12
P8 - 5  Black -- Gnd
P8 - 6  Black -- Gnd

P9 - 1  Black -- Gnd
P9 - 2  Black -- Gnd
P9 - 3  White (or yellow) -5
P9 - 4  Red -- +5
P9 - 5  Red -- +5
P9 - 6  Red -- +5
Note that there is no "power on" signal as for ATX supplies. No 3.3 volts either.

The one I am currently working with has a cable that is intended to be connected to an AC switch, and when I connect it, it fires right up, even without a load. Pretty nice actually.

Have any comments? Questions? Drop me a line!

Tom's Electronics pages / tom@mmto.org