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Original question:

UCC28070: how to use UCC28070 only in voltage mode and disable current mode

UCC28063A: ZCD lost (delayed) in bridgeless boost pfc in negtive half line cycle

Siliang Zhang
Prodigy 110 points
Part Number: UCC28063A

I have used UCC28063A  in bridgeless boost PFC, but there are some problems. Pls see the figures below. 

Two auxiliary windings are used to acheve ZCD in positive and negative linecycle,respectively (see fig. 1), but the ZCD signal seems lost (or delayed) in the negative half line cycle (see Fig. 2).

  • 0
    TI__Guru* 75615 points

    Hello Siliang,

    The waveform you have shown seems to be controlling a FET reference below ground with the ZCD- aux signal.  This can be observed by the drain voltage going from ground to roughly -30V below ground.  The inductor ripple is tracking and it appears the boost FET is turning on when the inductor current at 0 A.

    Could you take wave forms of where you are having the issue.  It will also be helpful if you included the schematic.

    Regards,

    Mike 

  • 0 in reply to Mike O'
    Prodigy 110 points

    Thank you Mike, I finally found that  ZCD signal was interfered by common mode noise, it's much better after adding CM chokes.