I have some related questions here and I hope I get better understanding thru this forum.

ATX SMPS has Over Voltage Protection. Does it mean that it will shut itself down in over voltage situation or will it attempt to regulate the output voltage within limits and still remain on?

Motherboards interact with SMPS thru PWR_ON line Pin#16 on 24 Pin ATX Power Connector. It’s pulled to active low to start the SMPS and open circuited to put it in standby mode. So there’s a circuit on motherboard that controls this.

So if the SMPS has capacity to shut itself down, does it practically override this motherboard circuit, if the need be?

Can OVP kick in if I attach a different load to SMPS instead of a motherboard e.g. a Car Audio system?


The switching supply is designed to always regulate a voltage using pwm control. Ovp was designed to protect an expensive motherboard or memory board in case the pwm circuit fails, and Leaves the output Fets in a 100% on state. This would raise +5vdc to around +8vdc or higher.

Most switchers above 25 watts have this on usually just the +5 or +3.3v logic supplies.

  • \$\begingroup\$ Don't know in detail about ATX power supplies. But all the ones we design & build shut themselves down in the event of an over current or over voltage condition. At that point, depending on the design, the PS will remain off until input power or some other control is cycled, or it will, after some delay, try to turn itself back on. \$\endgroup\$
    – SteveSh
    Dec 8 '19 at 1:00

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