20 January 2009

PC Power Supply for the Lab Bench

Seems like everyone has converted an old PC Power Supply for use in the lab. I've been using old wall warts for most of what I need so I haven't really paid much attention to the weekly instructable or hack that gives the step-by-steps. I admit, it sounds great. Plug in the supply and you have instant regulated +3.3VDC, +5VDC, +12VDC, -12VDC, -5VDC, and +5VSB. Yup, sounds great.

Wait. +5VSB, what's that? It's the 5 Volt Standby voltage. It's the voltage that remains running when the power supply suspends and is used to power the "wake on" devices such as network cards and modems used to bring the computers out of suspend mode. It's been around on PSUs for quite some time, I guess just haven't noticed it.

Since the wall warts are ok for me, why am I writing about a PSU? Because Spoofee told me about a dirt cheap one. Buy it, rebate, and it's almost free! I love almost free 'cause it's really cheap. Okay, I did the buy and rebate thing and now have a PSU sitting on the bench. I guess the instructables are needed.

But first a warning. All I'm doing here is simply putting the PSU into a test mode so I can vampire the juice from a connector. Although the volts are regulated, the current can zap the crap out of your circuit if you short something. Check out the instructable above to see how you can do this better. Read the comments to that instructable to see the many cons on using a PSU for your project. I'm lazy and just want quick power to run a VFD that I'll blog about soon. You, are not lazy and will do this better. If you do this to a PSU, be careful.

Here's a real decent pin-out that I found at Help With PCs. I especially like the color coding 'cause it helps my old eye find the right volt pin quickly.

The Ultra X-Connect PSU that I have has a ATX 2-pin, 6-pin Xeon, 4-pin Pentium 4, and five 4-pin Molex connectors.

A problem with ATX PSUs, they won't power up without the Main Power connector being hooked up. To power up an ATX or ATX-2 PSU for testing, short pin 14 (PS_ON) with one of the grounds.

I just stuck a wire in the 20-pin main power connector and shorted pin 14 (PS_ON) to pin 15 (GND). Just like that pic over on the right.

The PSU rumbled to a start and viola, free power. VFD, here I come.

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