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UCC28711D - freuency issue

Raja Saha94
Intellectual 575 points

Hi all,

 I am using UC28711D for my flyback SMPS. Input voltage is 400-800V and output is 110V,1.5A.

It is observed at no load, the freqq is near about 10 KHZ  and at full load  it is increased to 33 KHz.

But my concern is I have designed the SMPS with 100 KHZ switching frequency , but at full load also it never goes to 100KHZ, it goes only upto 33 KHZ. 

How to solve this issue?

please help..

Regards

Raja Saha

  • 0
    TI__Expert 5900 points
    Hi Raja,
    would you like to share the schemtic and your transformer design parameters?
    And also please share the waveform of CS at full load.
    The initial suspect is based on Pin=0.5*Lp*Ipk^2*Fs*eff
    The problem could be the real Lp or Ipk dosen't follow your calculations.

    Br
    Kening