I've kinda split some info between two threads, so
here is where I've posted a few notes.
Here's Yo_Duh's circuit.
In my circuit, I've replaced the gate driver with an LTC1163, and the MOSFET with an IRF1404.
The driver will be powered by the "PWR_OK" line, so that the outputs become active once the PSU's outputs are stable.
There will be three MOSFETs per PSU, one for each of the +12, +5 and +3.3 power lines.
I'm also adding a logic circuit, to route a "PWR_OK" signal to the mobo, only when at least 2 PSUs are ON.
Now...
As Since87 pointed out, there may be a flaw in the circuit, where if one of the PSUs is turned off, it may be fed by the other supplies. Otherwise, as long as the PSU outputs are pretty close to each other, everything should be fine.
I proposed reversing the Source and Drain pins of the MOSFET, as a cure.
Also, on the zener diode (15v zener in the article), it would allow a voltage to reach the MOSFET gate, but too low to activate it. So I've modded the circuit to have the zener wired to ground, instead of the Source.
Now all I have to resolve, is how to make sure that the driver is going to output enough voltage to drive the MOSFET for the +12 line.
I'll also be reviewing some added circuit protection, from the IRF website. I have to assume that the load (PC) is capacitive/resistive, and not inductive.
QUESTION:
Incidentally, I have a stupid question: since the zener has to be at least 16v, to activate the +12 line, and no more than 23.3 to activate the +3.3 line, can I use a combination of two zener diodes in series, one rated at 16v and another rated at 3.9 (for example), to achieve what I need?