UCC28063A: PF optimization for UCC28063A

Hi Leo,
thanks for your interest on UCC28063A.
Can I know what is the input voltage when you find the PF is low?
Do you have the input current waveform or the input current waveform? Can you share with us?
for the UCC28063A PF, I have two suggestions:
1, Decrease the X cap before the inductor. This is to decrease the bypass current from x cap to decrease the zero crossing distortion.
2, Add the high voltage ratio cap (for example 10pF/630V) between the positive point of rectified bridge and the Vinac pin of the UCC28063A. This is to decrease the over compensation Ton time of zero crossing.

Hi ,
Thank you for your advice. When the input voltage below 240V, there will be noise,and the capacitance of X cap has a little effect on pf value.
I will try your suggestion later .

Hi Leo,
I think under 240Vac input, the PF should be no bad if you follow the Excel calculator in TI website.
once the input line voltage is high, for example 264Vac input, please make sure the ZCD pin voltage is still higher than the ZCD pin threshold. If at this condition, the IC miss the ZCD detecting, there should be some noise on PFC inductor and you can see the current inductor that there will have some current distortions at the peak period.

David sorry, I made a mistake.
The only question PF is low , 1kW load PF is about 0.98, 500W load PF is 0.92, there is no noise, just PF value is low.
I had test a cap of 33pf/1KV between positive point and Vinac，it can not work , i will find a 10 pf cap

Hi David,
It's solved, thank you!