connecting ps_on to common on 24 pin atx

S

Seraphim974

Gawd
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Nov 7, 2003
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I was wondering if you have a psu installed in a pc, is it ok to short ps_on to ground and leave it shorted to keep Computer on or is that ok but it could be momentary or has to be maintained short? Anyone know? Was wanting to have a N.O. contact from a 120 volt relay to keep maintained short. Thanks!
 
From the ATX12V Power Supply Design Guide (link goes to .pdf), section 3.3.2:

"PS_ON# is an active-low, TTL-compatible signal that allows a motherboard to remotely control the power supply in conjunction with features such as soft on/off, Wake on LAN*, or wake-on-modem. When PS_ON# is pulled to TTL low, the power supply should turn on the four main DC output rails: +12VDC, +5VDC, +3.3VDC and -12VDC. When PS_ON# is pulled to TTL high or open-circuited, the DC output rails should not deliver current and should be held at zero potential with respect to ground. PS_ON# has no effect on the +5VSB output, which is always enabled whenever the AC power is present. Table 14 lists PS_ON# signal characteristics. The power supply shall provide an internal pull-up to TTL high. The power supply shall also provide de-bounce circuitry on PS_ON# to prevent it from oscillating on/off at startup when activated by a mechanical switch. The DC output enable circuitry must be SELV-compliant. The power supply shall not latch into a shutdown state when PS_ON# is driven active by pulses between 10ms to 100ms during the decay of the power rails."

I know so little about electricity that I have a hard time wiring a light switch, but this document seems to talk about the sort of thing you want to do, so perhaps you have an answer there that I don't understand.
 
well, I certainly welcome anyone to wade in here and tell me I have my head up my ass

I have left that pin shorted to ground for extended periods with no ill effects
 
Nice. This will work for this school project.
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well it should stay on anyway, what is the issue with using a momentary switch?

CNC rig?
 
The pc is a host computer for a robotic arm that is on same power bus as the monitor and arms controller that are all 3 powered with 120v. I just wanted the same spst industrial switch that supplies power to the pc to energize a relay to start the pc as Well. Its kind of a minor thing j just thought it would be neat to do

Just brownie points because it is a program that only lightly touches on computer hardware
 
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