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About the control IC UCC28070's input current zero crossing problem.

Lai Han-Ying
Prodigy 50 points
Other Parts Discussed in Thread: UCC28070

I design a 4kW PFC with the control IC UCC28070.

I refer  TI's application note,then design the circuit.

The problem is that the input current have zero crossing, that makes THD is higher than 5.5%.

I have tried to improve the compensation components and the capacitor after the full-bridge. But it is no used.

Another problem is when voltage is small, duty cycle can not full open .Duty cycle of near zero  voltage's is like the high voltage's duty cycle.

I do not know whether two problems have relationship.And how to solve this problem.

The picture is the input current and voltage waveform.

Thanks for your helping!!

  • 0
    TI__Genius 9790 points

    hi, Han-ying

    The two issues you mentioned have relationship.

    What is the maximum duty during zero-cross with heavy load? It should be close to 100%.

    what is the resistor on the pin #19 and #20, the resistor on #20 affects the maximum duty.

    here is my comments:

    1. make maximum duty close to above 95%.

    2. tune current compensator, to get more low frequency gain.

    regards,

    yunsheng

  • 0 in reply to Yunsheng Qu
    Prodigy 50 points

    Thanks for your reply!

    I change the maximum Duty-Cycle resistor.Setting the duty-cycle to 98% and tune current compensator.

    But while input current at zero crossing, Vgs still can not close to 100%.

    I do not know why Vgs can not full open when zero crossing.

    Thanks foe your helping! 

  • 0 in reply to Lai Han-Ying
    TI__Genius 9790 points

    hi,

    why the VDS of MOSFET in 4th picture is so low when pwm is narrow?

    you can try to increase current loop bandwidth and decrase x-cap of input filter.

    regards,

  • 0 in reply to Yunsheng Qu
    Prodigy 50 points

    Thanks for your reply!

    I have tried to increase current loop bandwidth from fs/10 to fs/5, but it is no use.

    About the x-cap of input filter,I have changed from 2.2 uF to 1 uF,but it seems no use.

    I think about the duty cycle problem and zero crossing problem whether having relationship with figure's spike?

    Thanks for your helping!