ATX Power Supply Question

[designgeek]

I have a weird question.

I'm modifying an ATX power supply to use as a bench power supply for my various projects (it's amazing how often one needs 3, 5, or 12 volts) and I was wondering about one of the rails, specifically the -12v. What is it for? It can't handle much current, all the other rails can handle 15 or so amps but -12v on every power supply I've seen can't handle more than a few hundred milliamps. I would imagine it would be coupled with the +12v rail for a total of 24v in a few rare instances but even those I can't find. All the fans I've seen run 12v.

I'm asking you because you are all brilliant plus it's damn near ungoogleable. Even advanced search options seem to disregard -12. 🙄

 

[localoid]

I have a weird question.

I'm modifying an ATX power supply... (stuff snipped) ...

I'm asking you because you are all brilliant plus it's damn near ungoogleable. Even advanced search options seem to disregard -12. 🙄

The book, PC Hardware in a Nutshell, published by O'Reilly, might give some insight. (The first link shown goes to the Google Book preview of said book.)

 

[chown33]

It's usually for the negative supply of an RS-232 interface.

It could also be used to produce -5VDC with an onboard regulator. That's sometimes useful in analog, as is -12VDC.