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Resonant on Vds of mosfet on flyback converter using ucc28630?

user3773259
Prodigy 10 points
Other Parts Discussed in Thread: UCC28630

I've just built a power suply with UCC28630. Everything seem to be ok; but when i saw on VDS voltage, I saw the resonant by Lm-Coss in't orginal as my picture. why?

  • TI__Genius 9130 points

    It's hard to comment on this in too much detail, I would need to see your sch and get some BOM details.

    But we have seen similar waveforms in the past, they were caused by using a primary-side snubber diode that had very slow reverse-recovery. This has the effect of damping the resonant ring very heavily and distorting the waveform as you saw. What diode do you use in the snubber? Check the datasheet reverse-recovery spec, trr < 100 ns is recommended. If there is no trr spec, then it's too slow

     

    I hope this helps fix the issue in your case.

     

    Thanks,

    Bernard