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UCC28634: Power supply doesn't output any voltage

Anthony Williams
Prodigy 10 points

Part Number: UCC28634

Hi , I am using UCC28634DR on a PCB Design for a fly back converter, designed by WEBENCH Power designer. After the fabrication and assemble of the pcb, when power was applied to the input of the circuit, the circuit did not output any voltage at all. The transformer was built using base WEBENCH specifications. What we found was the VDD pin pulsing from 5.2 to 10.1 volts over and over as well as HV pin pulsing as well. The SD pin is LOW at .145mv, it seems the circuit is in fault mode but what causing it? 

  • 0
    TI__Guru* 86286 points

    Hello,

    The Webench tool will give you a working schematic and instructions no how to build the transformer.  However, these primary side regulated flyback converters are susceptible to aux winding noise. 

    I would study VDD, CS, VSENSE and Vout to see what these signals look like.  If VDD is cycling between VDD(start) and VDD(stop) the design is shutting down to either an OCP fault or OVP fault.  By studying these waveforms you will figure out which fault it is.

    The following draft of an application note was written for PSR control fault sensing and the common issues with false fault shutdown and how to resolve them. These controllers operate similar to the UCC28634 and the recommendations should help here as well.

    8424.SLUAAC5 8 4 21.pdf 

    Regards,