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Damping out mains input LC filter ringing in a 500W Boost PFC?


Well-Known Member
We are designing a 500W Boost PFC LED driver to operate in average current mode.

Our contractor wants to add a small 15W Constant off time flyback to always pull current from the post bridge DC bus and also dump its energy into the leds. He says that this is necessary because otherwise there will be severe ringing in the mains input LC filter at the zero crossings which will adversely affect the THD of the mains input current. He says that this Flyback will act so as to damp out this ringing.

Please can you confirm that his desire for this additional 15W flyback SMPS is bogus?

I mean, yes, in very light load, (say <10W) there would be some ringing in the mains input current due to the mains LC input filter, and this will happen at the mains voltage zero crossings, but this is nothing to worry about and there’s no need to damp it with an additional Flyback SMPS as described. Would you agree?

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