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UCC28064A: UCC28064

Stuart Linzer
Intellectual 260 points
Part Number: UCC28064A


Hello, 

Data sheet for UCC28064A equation 24 for turns-ratio of each auxiliary winding.  My design:

Vin-max = 134 VAC

Vout = 420 VDC

Equation gives turns ratio of 115.  

This appears to be a high number as PFC inductor I would like to use has turns ration of about 10.  Is it ok to use actual turns ratio of 10?

Is external clamping required?

Regards, 

Stuart

  • 0
    TI__Genius 11350 points

    Hi Stuart,

    The formula is written to ensure a minimum of 2V at peak high line to reset the ZCD comparator.  Using your Vin/Vout with a 10-turn ratio: ((420-(134*2^0.5)))/10 turns = 23V, so you'll have plenty of margin to reset the comparator.

    The controller has 3V internal clamps on ZCDx. Just make sure you chose your Rzcdx value to limit Izcdx to 2mA or less to protect those clamps.

    Regards,

    Ray