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Hi,

for a PFC you usually have some kind of rectifier ... thus there can be no preference of the one or the other half wave.

But for sure if the PFC output power rises/falls ... you will always see some short term DC component.

But this also may be a measurement artefact.

Example:

Let´s say the output power continously rises. Obviously the input current also needs to rise.

If you now just focus on the average of the half wave let´s imagine it rises with a constant rate of 50mA

P: 100mA

N: 150mA

P: 200mA

N: 250mA

P: 300mA

N: 350mA

P: 400mA

N: 450mA

P: 500mA

N: 550mA

P: 600mA

N: 650mA

and so on

Take the first full wave: positive 100mA, but negative 150mA ... makes some "offset" and a resulting negative average of -25mA over this full wave

next full wave: +200mA and -250mA --> again -25mA

next full wave: +300mA and -350mA --> again -25mA

you see "measure" a negative DC offset of continously -25mA

clearly "-25mA" is fact! .. you woud say.

But is it really?

Take the same numbers ... but now start your measurement with the negative halfwave.

First full wave: N 150mA and P 200mA --> now you get a positive offset of +25mA in average!

next full wave: +250mA and -300mA --> again +25mA

next full wave: +350mA and -400mA --> again +25mA

you see "measure" a positive DC offset of continously +25mA

"+25mA" is fact! ..

WAIT! we used the same input signal ... just a different window of time!

--> But one time we see negative offset and the other time we see positive offset. A clear measurement artefact!

Klaus