You cannot have Boost PFC running off square wave mains of a UPS

[opampsmoker]

Do you agree You cannot have a Boost PFC running off square wave mains of a UPS?
When the mains fails, and the UPS kicks in...if it is kicking out square wave mains, then the Boost PFC stage must be totally switched out, and an SMPS thats designed to run off square wave mains must be switched in...do you agree?

 

[Diver300]

It entirely depends on the implementation of the PFC.

A PFC power supply is a complicated device, and it could have been designed with a square wave in mind, or it could have been designed to only work with a sine wave. As there are so many ways that it could be made, it's not really possible to have a blanket statement that it won't work.

It's quite possible that a PFC power supply will be quite happy with a square wave. With zero voltage input, the power supply can't do anything. When the voltage is steady, for a few ms each half cycle, the PFC power supply may well behave exactly as it would near the peak of a sinewave, so it could work fine.

On the other hand, there may be some input sensing circuit that will not regard a square wave as a valid input, so it'll do nothing and not work at all. I've seen that with a laptop power supply running from an inverter. I don't think the power supply contained PFC. On some inverters it just would not turn on, and would behave as though there was no power at all. I think that the power supply would be detecting the periods of no power, and they were too long. I bypassed the problem by running the power supply from the DC link voltage of the inverter.