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UCC28051: Transformer ratio for ZCD pin of UCC28051

Part Number: UCC28051

We are designing project with UCC28051.  We would like to know,  how to calculate transformer ratio for ZCD pin ? Does it have any tool to calculate ? anybody can advise ? Thank you.

  • Hi

    I have asked one of application engineers to respond to this question, you should see a response soon.

    Regards

    Peter
  • When the boost diode is conducting, the ZCD pin has a positive voltage and is internally clamped at about 5V.

    At this time the resistor on ZCD limits the input current to about 2mA or 3mA.

    Normally you would design for about 15V so N_main /N_aux = Vout/15

    where N_main is the turns of the main winding and N_aux is the turns of the auxiliary winding.

    Vout is the high voltage output

    When the boost diode is biased off,  ZCD is negative and the auxiliary voltage is Vac_pk (N_aux/N_main).

    At this time the ZCD voltage is clamped to about -0.65V and once again the resistor limits the input current on ZCD

    That is how you select the turns ratio and the value of the ZCD resistor.

    Regards

    John Griffin