How are modern PSU's protected against overvoltage?

[OwenBurnett]

How are modern PSU's protected against over voltage?
I mean against the case that due to a circuit failure it may decide to put out more voltage than it was supposed to.
Like for example when the Switching transistor in the DC-DC converter decides to stay open permanently (than you'd have 12 V on the +3 or +5V rail )

I'm especial interested in the new Seasonic X-650

Is there a Z-Diode that would short out the rail rather than letting the over voltage fry the rest of the PC?
Or is it only some IC that monitors the voltage and well may also fail without turning of the PSU. With a Z-Diode you at least know that when it fails it shorts the PSU and the rest is fine....

[Stefan Payne]

I believe that there is no protection, the CPU would burn.
But the PSU should have such protections.

PS: CPUs are usually powered by the +12V Rail except for the new Intel Core ix CPUs wich are also powered by the 3,3V rail (the integrated Northbridge)

[OwenBurnett]

PSU <-> CPU 2 out of 3 letters are the same 1 even in the same place and it sounds so damn simmilar...
I ment PSU f***ing spelling

[370forlife]

Usually there is a IC with protection circuitry that monitors the voltage of the rails and shuts down the psu if one or more of the rails gets too high.

[Stefan Payne]

At least when its not totally crap it has such protection...

[370forlife]

Ehh, usually just the worst of the worst have no OVP. Most leadman's even have it. It's common however to see no UVP and also the dreaded two transistor 5vsb circuit with no OVP.

Though I have seen some cheap, cheap, cheap units with imitation IC's that claim to have OVP, but really don't.

[Hondacity]

Originally Posted by Stefan Payne

PS: CPUs are usually powered by the +12V Rail except for the new Intel Core ix CPUs wich are also powered by the 3,3V rail (the integrated Northbridge)

which motherboard manufacturer utilize 3.3v rail for their imc voltage supply?

i asked one designer..and they don't do this...

[Stefan Payne]

Every LGA1366 and most to all LGA1156 boards.
That's how it is in the Intel VRM11 Spec...

Originally Posted by the russians

The thing is that the isolated 12 V power line is only used for processor cores. As for the Uncore part of the CPU, it is powered from the mainboard via a 24-pin connector.

(beware there's a link)

[Hondacity]

vrm11.1
http://www.intel.com/assets/PDF/designguide/321736.pdf

input voltage should be 12v...

as per shamino(evga)

12v - comes from 24pin mobo connector...