That's what I thought. The max rating of amps is on the +5 line, at 40 amps, but its shared with the 3.3 . Not a worry.
The zener is something that Yo_Duh and I discussed extensively.
As it is, if you turn off one of the supplies, the other PSU will actually drive the MOSFET of the other PSU, right through the zener. (Is it a problem? I dunno :shrug: )
So my solution was to wire the zener to ground, instead of having it wired to the Source.
Since Vgs needs to be at least 2.0 and max 4.0 for the MOSFET to turn on, with a max supply voltage of 12v, I'd need to change that zener to at least a 16v. With the minimum supply voltage of 3.3 the gate voltage cannot be more than 23.3v, otherwise it'll blow the gate. So a zener that's between 16 and 23.3 should work.
But otherwise, you're still right: the zener is designed to protect the MOSFET from transients: I will certainly review how my mod affects that protection.
I'll post more thoughts later.
