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UCC256403: Bias winding BW pin functionality mis behaviour

ANEESH TS
Prodigy 70 points
Part Number: UCC256403
Other Parts Discussed in Thread: PMP40766

Hi TI Experts,

I designed 60V/10A CC CV power supply using UCC256403. I am using front end PFC with 400V output. My transformer turns ratio is Npri:Nsec:Nbias = 24T:6T:3T. I am using BW pin for output over voltage protection with resistor devider 100K(Rbwupper) and 8.2K(Rbwlower) for 140% of rated voltage over voltage. The problem i was getting is in some of the boards this works and some other boards my output voltage dips with this combination, when i remove Bias winding protection( By removing Rbwupper resistor) my board works.Basically there are lot of variations between different boads. I have seen in PMP40766 the output overvoltage protection is detecting with some comparator not with bias winding. Could someone can explain this?.

Regards

Aneesh

  • 0
    TI__Guru 73475 points

    Hello,

    I have seen issues with primary aux voltage sensing for over voltage protection that are triggered by aux winding noise.  If you are using different transformer manufactures and/or hand wound transformers this behavior can occur.

    You might want to compare the auxiliary winding signal of your working units to your non working units to ensure the signals look the same.  Please note that noise at the BW pin can trip OVP.  If it is noise you should be able to add some filtering at the BW pin to remove it.

    Regards,

  • 0 in reply to Mike O'
    Prodigy 70 points

    Hi Mike,

    Thanks for your feedback. I will probe the bias winding and check the signal quality. 

    Regards

    Aneesh

  • 0 in reply to ANEESH TS
    TI__Guru 73475 points

    Hello,

    Thanks for letting us know.

    Regards,