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UCC29950 PFC Audible Noise

mark prosser
Prodigy 165 points
Other Parts Discussed in Thread: UCC29950

Hi Peter

Many Thanks for looking , I will obtain more plots asap - fyi I have added attached  ( same condition just expanded) plots with Rectified AC and current observation along with switching.

I now have the PFC running in standalone condition and the same point still exists.

Best Regards

Mark003.TIF000.TIF

001.TIF

Apart from this noise issue everything is functioning as desired.

Best regards

Mark Prosser

  • 0
    TI__Mastermind 31580 points

    Hi Mark,

    I will ask the applications engineer for this controller to look at this issue. In meantime can you send more plots of the PFC stage gate drive so we can see if there is any instability between the switching cycles and please include the CS pin waveform as well.

    Thanks

    Peter

  • 0 in reply to Peter Meaney
    TI__Mastermind 25570 points

    Hello Mark

    Unfortunately it's impossible to tell what is going on from the plot you show. However - the input current should definitely be better behaved than what you are seeing. I took the plot below from our UCC29950 EVM at 300Wout and 90Vin (max load).

    The plots Peter asked for would be very helpful

    We designed the UCC29950 it to make it easy to us and one consequence of this is that the design procedure is quite prescriptive. Given that you followed it closely then you are likely correct in thinking that this is a layout issue.

    It is possible to run the PFC power stage on its own. Simply disconnect the gate drives to the LLC stage and connect the LLC MOSFET gates to their sources. Then use a high voltage load to load the PFC stage output directly. This would eliminate most sources of noise associated with the LLC stage - except any noise associated with the LLC gate drive outputs from the controller itself.

    If you wish, please feel free to send me a schematic and pcb layout to me - my email address is colingillmor@ti.com

    Please let me know how you get on.

    regards

    Colin