Author Topic: Active PFC and true sinewave UPS?  (Read 2032 times)

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Offline fubar.grTopic starter

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Active PFC and true sinewave UPS?
« on: August 17, 2015, 10:34:52 am »
People say that computers with Active PFC PSUs require true sinewave UPS, else bad things can happen.

Is this true and why? I can't find anything conclusive on the subject

Offline TheElectricChicken

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Re: Active PFC and true sinewave UPS?
« Reply #1 on: August 17, 2015, 10:57:01 am »
Power Factor Correction (PFC)

I suspect they are looking for a sine wave to compare current to, and get stuck with a modified square wave which makes them go nuts.
 

Offline TheElectricChicken

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Re: Active PFC and true sinewave UPS?
« Reply #2 on: August 17, 2015, 11:05:34 am »
eeeeeh, what a complicated subject, or at least they want it so....
 

Offline TheElectricChicken

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Offline T3sl4co1l

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Re: Active PFC and true sinewave UPS?
« Reply #4 on: August 17, 2015, 11:23:06 am »
Depends on the controller IC.  Some are just fine with any waveform, given the response time of the control loop (don't expect 400Hz or harmonic-rich waveforms to have high PFC).  Including DC.  Others are rather special purpose and require that the input always dip to zero (internal offset compensation?) or oscillate smoothly at a mains-esque frequency (low voltage harmonics).

As a generality, true sinewave is the only thing you can be assured will work with any load (given that it can deliver startup current as needed), anything else is either-or.

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Offline MagicSmoker

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Re: Active PFC and true sinewave UPS?
« Reply #5 on: August 17, 2015, 11:34:28 am »
Theoretically, a true power factor correction circuit won't care what the input voltage waveform looks like; it will shape the current drawn by the downstream load to match it.

That said, some PFC controller ICs seem to choke if presented with anything but a sinusoidal voltage waveform (e.g. - UCC28070, which, let's just say, has not been one of the more glorious ICs to come out of Unitrode/TI).

If you want to go to the trouble of figuring out whether a particular PFC device can deal with a MSW inverter, check the datasheet for the PFC IC to see if it can handle a DC input (e.g. - UC3854, which *is* one of the more glorious ICs from Unitrode/TI).

All that said, an MSW inverter may damage any kind of load that isn't mostly/purely resistive and you don't have to pay too much of a premium anymore for a pure sine wave output so why take the chance?


NB - Seems T3sl4co1l beat me to it.

 


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