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WEBENCH® Tools/UCC28C43: flyback design circuit evaluation

leela prasad gullipalli
Prodigy 175 points
Part Number: UCC28C43

Tool/software: WEBENCH® Design Tools

Dear sir,

i designed this circuit for 70W 

primary inductance is 500uH

primary turns 80 turns

core gapped ee30 core

output_ 15V/0.7A(6turns)

output_ 5V/1.3A(3turns)

output_ -9V/0.3A(4turns)

output_ 24V/0.7A(10turns)

output_ 15V/0.7A(6turns)

this circuit is not operating  with  constant duty ratio with loading also.  frequency skipping is happening please suggest some solution sir

  • 0
    TI__Expert 4015 points
    I would look at what is happening on the COMP pin if you are not getting the duty cycle and frequency you expect. You have a circuit pulling down on the COMP pin, you could try removing that initially to see if that is the problem.

    Also for debug purposes you could try disconnecting the drive and connecting the COMP pin to Vref to see if you get 100% duty cycle pulses at the expected frequency.

    Hope this helps.
    Thanks
    Billy
  • 0 in reply to Billy Long
    Prodigy 175 points
    YES I AM GETTING 100% DUTY RATIO. IT IS OPERATING WITH SWITCHING FREQUENCY BUT SOME PULSES ARE WITH ZERO PERCENT DUTY RATIO AND SOME ARE MORE PERCENT DUTY RATIO
  • 0 in reply to leela prasad gullipalli
    TI__Expert 4015 points
    Can you post some waveforms which show the issue you are encountering.
    Also plots of the OUT, COMP, CS, FB and RT/CT pins when the issue is occurring may allow us to understand what is happening.
    Please set the time/div on the scope so that a few switching cycles can be seen at the time the issue occurs.

    Thanks
    Billy