SMPS Over Voltage Protection

Question

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?

Answer 1

If any of it's protections are tripped, a quality ATX power supply will turn itself off, overriding the PS_ON signal. (Even all the crappy cheap ones I've worked with did, but one can't vow for everything that's out there). So yes, the protections still work, even if you use the power supply to power a diffirent load.

You should however take note that switching power supplies with multiple output windings on their transformer can only regulate based on one output voltage, often +12V for example. This can cause poor regulation if the bulk of the load is not on this output.

Answer 2

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.