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PC Power Supply Discussion Troubleshooting and discussion of computer power supplies

 
 
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Old 05-05-2016
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Default Hold-up time explained

Yeah another topic about the hold-up time. Why? Because I got the feeling some really don't understand what it is, what it does and what the problem is.

What is the hold-up time?
It's the time in milliseconds that the PSU can work without without getting any power, measured at full load.

How does it work?
The primary capacitor of the PSU can store enough energy for the PSU to work some milliseconds after the power is cut.

How long should it last?
According to the ATX specification the PSU should deliver at least 17ms full power with voltages still inside the ATX spec.

But at least 1ms before the output voltages of the PSU go out of spec the PSU should drop the Power OK signal.

Power OK signal?
Yes Power OK signal, that's a wire in the 24 pins ATX connector that tells the motherboard that the power of the PSU is stable and that the PC can start or should shutdown.

What's the problem then?
Some PSU don't drop the Power OK before the output voltages of the PSU go out of spec. This isn't good because it puts a lot of stress on the components of the PC that are powered by the PSU and now getting voltages that are outside of spec.

Is it really a problem?
Well that depends if you experience a lot of problems with power outage where you life, it could be a problem. But if that is the case a UPS is maybe something that you should buy.

But there is something else you should know!
Hold-up time is measured at full load! Almost no one loads his of her PSU till full load. And even if someone does, the chance that PSU is working at full load if the power fails, is almost zero.

So that means that hold-up time actually should last a lot longer in real life conditions. It even could mean that the power OK signal drops before the output voltages go out of spec.

So it actually isn't a problem?
For most people not no.

So please don't make this a huge problem, because it isn't one. It simply isn't done right according to the ATX specification.

For more information and tests see the reviews from Aris on TechPowerUp and TomsHardware:
http://www.techpowerup.com/reviews/?...=25&order=date
http://www.tomshardware.com/articles...power-supplies

Last edited by -The_Mask-; 05-05-2016 at 06:17 AM.
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