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UC3875: U-136A appnote schematic

Vasiliy Aleksandrovich
Intellectual 290 points
Part Number: UC3875

Hello TI!

Recently I read application note for UC3875 PS controller and I've got a question about its implementation schematics. Why are DC-blocking capacitors not indicated in the circuit? Without them, the transformer will have a constant voltage and it will work with bias. Is this a mistake or is it intentional? Please let me know.

Best regards, Vasily.

  • 0
    TI__Expert 6080 points

    Hello Vasiliy,

    The DC blocking capacitors are not required because the OUTA and OUTB are the same duty cycle and out of phase with each other. This means when the OutA is high the end of the transformer with the polarity dot is positive and the negative end of the transformer is zero from OUTB. During the next cycle the OUTA will be low and OUTB would be high. Hence the transformer will be balanced.

    The same applies to OUTC and OUTD.

    Regards,

    Sonal

  • 0 in reply to Sonal Singh
    Intellectual 290 points

    Hi, Sonal!

    Thanks a lot, shure, I got it! My bad, I did not immediately notice this fact. My apologies for dumb question.

    Regards,

    Vasiliy