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UCC28064A: PFC current issue

Wenhsiang Lin
Intellectual 520 points
Part Number: UCC28064A

Hi Team:

Please help below question and Schematic & waveform as below, thanks.

1.What kind of condition , may cause PFC current noise as below waveform ?

2.What's problem cause PF drop on max load of 1.84

A ? 

Ch1:Vbulk , Ch2:Vds_Q2 , Ch4:L6_PFC current

EP1720 SCH for PFC 190626.pdf


  • 0
    TI__Guru* 86236 points

    Hello,

    When I look at the misbehaved waveform it looks like the inductor current is doubling in magnitude.  From the switch node it looks like the gate drive turns off briefly and then turns on again.  This results in the inductor current doubling because the inductor is not zero current switched.

    This could be cause by noise coupling into the ZCD_A/B pin causing gate drive misfires.  This could be resolved by filtering the ZCD_A/B pins.  I see on the schematic there are place holders for these capacitors.  You might try adding 22 to 33 pf to these pins to see if it helps remove the disturbance.

    The other issue that I have seen that can cause this behavior is if the input of the boost is higher than the output of the boost.  However, 560uF should be enough capacitance but you might want to check this out anyway.

    Regards,

    Mike

  • 0 in reply to Mike O'
    Intellectual 520 points

    Hi Mike:

    Please help below question , thanks a lot.

    1.After change to 33pF & 47pF , still have the same issue , need your help to provide other solution to improve issue of PFC current noise.

    2.If ZCD1 & ZCD2 trace work In parallel of layout , will it cause interference with each other ?

    3.Please help to share what 's kind of status need to connect to PGND or AGND ?