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Original question:

UCC28730: Startup Operation

UCC28730: won't start switching and regulating the output

David Smedberg
Prodigy 40 points
Part Number: UCC28730
Other Parts Discussed in Thread: UCC24650

Hello,

I'm currently trying to implement the UCC28730 circuit in to the a TI reference design 40V-1000Vin 15 Vout but modified to 24 V output instead. I have changed resistor values to match the datasheet of UCC28730 but it won't start switching when I connect 300 V to HV. I saw that VDD needs to be 21 V to keep the switching going after startup. But it seems like the controller don't start switching at all so it won't give a VDD voltage from the AUX on the transformer.

I was reading on a troubleshoot document (http://www.ti.com/lit/an/slua783/slua783.pdfAlso, do I have to use the wakeup circuit UCC24650 to be able to use UCC28730? 

Because I am working with a company on my bachelor thesis on this I don't know if I can share the circuit here on an open forum. Any help would mean very much! 

Best regards

David

  • 0
    TI__Guru 74095 points

    You do not have to use UCC24650 together with UCC28730.

    When VDD reaches its on voltage, you should see three pulses on DRV. If you do not see the three pulses on DRV, your circuit has connection problem so you need to find out.

    You can follow the trouble shooting notes. 

    It is better you get an EVM to help you learn and understand how the IC works.