• State TI Thinks Resolved
  • Locked Locked
  • Replies 2 replies
  • Answers 2 answers
  • Subscribers 63 subscribers
  • Views 142 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

UCC28742: UCC28742 frequency question

UCC28742: Line frequency ripple in output

Naizeng Wang
Expert 5480 points
Part Number: UCC28742

Hi team.

When the bulk capacitor is small, there are line frequency(60Hz) ripple in output, which is caused by limited duty cycle. I think it should be 120Hz. Is there any wrong? 

Br,

Nison

  • 0
    TI__Expert 7080 points

    Hi Nison,

    Based on your description, I agree with you this output voltage drop might caused by maximum duty cycle limitation. since UCC28742 has a CC mode function when the max. duty reaches to ~0.475 at low bulk voltage , It will start entry CC mode . then output voltage will drop.  if the bulk capacitance can't be increased , you can try to decrease turns ratio of transformer Nps.

    Thanks.

  • 0 in reply to Jaden Ning
    TI__Expert 7080 points

    It's a little odd in your waveform is looks like the voltage drop are the same with different load condition 0.3A and 1A. can you share the design specification : input voltage range , output voltage , rated output current , transformer turns ratio , Lm , Bulk capacitance . and the test condition when you capture the waveform . if you can share the schematic , it will be more better.

    Thanks.