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Blackened

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Joined: 11/08/2012
Location: Australia
Posts: 66

Posted: 01:34am 24 Aug 2013

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Hello all,

This would seem a bit of a no-brainer, but thought I'd ask just in case I've read the specs wrong.

I'm planning to use an old ATX power supply in my project. Looks like the standby current will be sufficient for just about all my needs, but I will need 12V for the case fan when the temperature starts to climb, and I plan to use the 12V to drive a pump once the bits n bobs turn up from China.

Am I correct in assuming I can switch the ATX on by connecting the power-on lead to a pin configured for open collector, to pull it low? The specs say the power-on lead is pulled high (5V) by the ATX, and will switch on once pulled low.

Thanks everyone!! Just want to make sure I'm not going to fry anything

Gordz
Regular Member

Joined: 10/08/2013
Location: Australia
Posts: 55

Posted: 07:44pm 24 Aug 2013

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I have used ATX power supplies for stuff before and a standard TTL type signal is fine for switching it on and off. I found that I needed a 100mA load on the +5 to keep it alive though so I connected a 5v fan permanently. Later I found a brand that had an integrated fan and did not need the minimum load.

Downwind

Guru

Joined: 09/09/2009
Location: Australia
Posts: 2333

Posted: 08:28pm 24 Aug 2013

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Shorting the green wire to ground will activate the PSU, but as has been said a load is normally required to get a stable output on both 5v and 12v rails, the easiest method i find is to leave an old 3.5 floppy drive connected to the PSU and you will get good stable voltages out.

Good pinout information here......

http://pinouts.ru/Power/atxpower_pinout.shtml

Pete.

Sometimes it just works

Blackened

Regular Member

Joined: 11/08/2012
Location: Australia
Posts: 66

Posted: 02:00am 25 Aug 2013

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Thanks Gordz and Pete,

I forgot that I'd need the 12V for a 7inch composite LCD monitor too, so that's the 12V load taken care of. Will I still need a dummy load for either the PSUs 5V or 3.3V? I'll be drawing power from the 5V standby, and 12V standard lines unless advised otherwise. Could I just bridge the 5V standby and the normal 5V?

Man I need new glasses!! You don't know how bad your eyes have become until you start trying to read resistor bands, even having trouble soldering the finer wires together.

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