power connectors for mainboards

Bari Ari bari at onelabs.com
Fri Jun 20 11:33:00 CEST 2003

ron minnich wrote:

>I have four K7SEMs which I would like to run from one PC power supply. 
>Does anyone know if there are off-the-shelf cables available to do this 
>type of thing? Essentially a "Y" connector for the mainboard power 
I've never seen any for ATX power supplies since you'd have to deal with 
a couple control signals.

ATX supply has a PWR_OK ouput and also PS_ON# input.

"PWR_OK is a “power good” signal. It should be asserted high by the 
power supply to
indicate that the +12 VDC, +5VDC, and +3.3VDC outputs are above the 
thresholds. Conversely, PWR_OK should be de-asserted
to a low state when any of the +12 VDC, +5 VDC, or +3.3 VDC output voltages
falls below its undervoltage threshold, or when mains power has been 
removed for a time
sufficiently long such that power supply operation cannot be guaranteed 
beyond the power-down
warning time."

"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 five main DC output rails: +12VDC, +5VDC, +3.3VDC, -5VDC, 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 
The power supply shall provide an internal pull-up to TTL high. The 
power supply shall
also provide debounce 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."

PS_ON# could just be pulled low with a jumper or switch to ground if you 
didn't care about power control by the motherboard since the ATX supply 
would be always on.


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