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by LeifCarrotson 33 days ago
The capacitors in your PSU's rectifier have to float through 8.333ms interruptions every. single. cycle.

20 milliseconds is barely distinguishable from a single 60 Hz sine wave period. 10 milliseconds just over half a cycle.
3 comments
Aurornis 33 days ago
> The capacitors in your PSU's rectifier have to float through 8.333ms interruptions every. single. cycle.

They do not. You must be thinking of very old power supply technology with a simple bridge rectifier in front of some capacitors.

Switch mode power supplies with power factor correction spread the current draw across the cycle to keep the power factor high. They are drawing power from the line for most of the cycle. There is not a 8.3ms interruption.

> 20 milliseconds is barely distinguishable from a single 60 Hz sine wave period. 10 milliseconds just over half a cycle

The ATX 3.1 power supply standard only requires 12ms of hold up time.

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Dylan16807 33 days ago
> The capacitors in your PSU's rectifier have to float through 8.333ms interruptions every. single. cycle.

It's not an 8ms interruption, it's 8ms between peaks. The part you could call an interruption is more like 2.5ms and even then it's not zero power draw. You need an order of magnitude more buffering to handle a 20ms dropout.

> 20 milliseconds is barely distinguishable from a single 60 Hz sine wave period.

Right, so think about that harder. A 60Hz sine wave has two wide periods of power and two narrow gaps. And 20 milliseconds is longer than that entire process combined.

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scottlamb 33 days ago
> 20 milliseconds is barely distinguishable from a single 60 Hz sine wave period.

I've read that the newest PSUs are only guaranteed to last 12ms. Of course they may last much longer, especially if running near idle, but I'd prefer something that works well with any compliant device.

Here's one source: "Measured in milliseconds, hold-up time indicates how long a PSU can sustain its output within specified voltage limits after a loss or drop in input power. ATX 3.1 features a shorter hold-up time of 12ms, compared to ATX 3.0's 17ms hold-up time. This results in a small improvement in the PSU's efficiency." https://www.corsair.com/us/en/explorer/diy-builder/power-sup...

I haven't dug through the spec itself.

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Dylan16807 33 days ago
How is that supposed to improve efficiency? Also that change sucks, it's cutting the margins way too tight.

At least I can be comforted that for my current power supply, the most recent version of it made for ATX 3.1 actually increased the hold-up time. So not all manufacturers are cutting that corner.

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