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UCC28710: VDD UVLO observed during load transients. Can we use this with UCC24650 wake up monitor to improve load transient response?

Akshatha Pai
Prodigy 20 points
Part Number: UCC28710
Other Parts Discussed in Thread: UCC28712, UCC24650

Hi,

We are developing a flyback converter with 85-265Vrms 50Hz input to 12V, 1.5A output using the PSR IC UCC27812D. But during our tests we observed that the output is oscillating when a speaker load is used(varying load requirement). Sometimes the VDD drops below UVLO and leads to shut down of the converter.  Please find the attached circuit and waveforms for your reference.

  1. What do you recommend to troubleshoot/resolve this?
  2. Can we use the wake up monitor UCC24650 with this PSR IC UCC28710/UCC28712 to improve the load transient response? 
  3. Any other improvements in the circuit to be done?

Regards,

Akshatha

Input Cap used = 56uF at the rectified input

  • 0
    TI__Mastermind 24075 points

    Hi Akshatha,

    Thank you for the query on UCC28712.

    I will review the schematic and get back by tomorrow.

    Regards,

    Harish

  • 0 in reply to Harish Ramakrishnan5
    TI__Mastermind 24075 points

    Hi Akshatha,

    I reviewed the schematic briefly the following are my initial comments:

    1/ The Vdd capacitor seems low at 1uF. Try increasing this to 10uF

    2. The ouput capacitor at 150uF seems low. Try increasing this to 500-680uF.

    3. You could use a CLC type configuration filter at the output. Try putting the heavier capacitors at the output first, then the 10uH inductor and then lower value capacitance like the 22uF whic you have in the schematic.

    Please try the above and let us know your feedback. 

    Regards,

    Harish