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UCC28700: Schematic Check

Brian Antheunisse
Expert 5305 points
Part Number: UCC28700

Hi guys,

My customer has designed the following AC/DC converter using the UCC28700. They are seeing nothing on the output (either one). 

Do you guys see anything wrong? 

Thanks,

Brian

  • 0
    TI__Mastermind 40090 points
    Hello Brian,

    I see almost immediately that your transformer output is shorted. If the board wire connected as the schematic shows, you will get no output.
    But the output voltage imply that there are 2 windings on the output. The schematic shows only one with dual terminals.

    I conjecture that if the xfmr has 2 windings on the output, then the drawing mislead the proper connection for a center-tapped arrangement.
    If there is actually only one winding with 2 terminals at each end, then you will be unable to get 2 different voltages from it.

    Given that this major issue needs to be resolved first, I did not review the rest of the design.

    Best Regards,
    Ulrich
  • 0 in reply to Ulrich Goerke
    TI__Mastermind 40090 points
    Hi again Brian,

    One other thing. The drawing is a bit fuzzy, but it seems that the polarity marks for the windings are also incorrect for a flyback topology.
    IF we assume the secondary and auxiliary polarities are correct, then the primary dot is at the wrong end of the winding. Or rather, the primary is hooked up backwards and the transformer is being energized in a forward-mode fashion (in addition to the apparent short on the secondary). Please double check the polarity of the connections.

    Bes Regards,
    Ulrich