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UCC28740: Design issue for UCC28740

Zhang Liang
Genius 5755 points

Part Number: UCC28740

Tool/software:

Hi,

Please help to check our schematic and there are no 12V output voltage for our design:

We have below issue:

1. The VDD waveform(Yellow line) and DRV waveform(Blue line), is it right?

2. We want the input voltage is 90-260VAC and output voltage is 12VDC, and the Npa is 5.5, the RS1 is less than Vin(run)=90, Is it right?

3. The schematic diagram refer to below:

AC-TO-DC12V-POWER-T-V1.2-原理图.pdf

  • 0
    TI__Guru* 86286 points

    Hello,

     

    Your inquiry has been received and will be answered in the order that it was received.

     

    Regards,

  • 0 in reply to Mike O'
    TI__Guru* 86286 points

    Hello,

     

    The following link will bring you to the UCC28740 excel design tool that you can use to check/modify your design.

    https://www.ti.com/tool/download/SLUC487

     

    From your waveform during startup it looks like the design is shutting down due to a fault.  It is giving three sample pulses and then shutting down.  The faults that could cause this behavior are over current, over voltage or input under voltage.  You can figure out which fault is being triggered by probing Vout, VDD, CS and the aux winding voltage.  Look at the last three switching cycles to determine which fault.

    The UCC28740 uses primary fault sensing.  The following link will bring you to an application note that discusses how primary fault sensing works, the issues with it, and how to remove the issue with filtering and snubbing.  These issues will show up as startup and regulation issues similar to what you are observing.

    https://www.ti.com/lit/pdf/sluaac5

    Thank you for your interested in power control devices from Texas Instruments.  If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

     

    Regards,