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LM5157: design check

Will Wang47
Expert 6560 points
Part Number: LM5157

Tool/software:

Hi team,

Customer would like to design a flyback circuit using LM5157, input is 20V, output is 6V/2A.

Based on their existing transformer, their excel design file as follow, could you help check if this is OK?

Customer now use primary side feedback design, they also would like to know the difference between primary feedback and secondary side feedback.

Could you also help comment on this?

LM5157_58_Quickstart_Calculator_for_Flyback_Regulator_Design_V1_0_0——U09-11-04.xlsx 

Thanks and Best regards,

Will

  • 0
    TI__Genius 10995 points

    Hi Will,

    Thanks for eaching out.

    The quickstart calculator seems to be good to me.

    With a PSR flyback, you can have isolation without needing an optocoupler. However, the regulation is not that accurate. Depending on the leakage inductance of the transformer, you will get around +-5% accuracy. Using SSR feedback, the accuracy will be much better, but an additional optocoupler or opto emulator will be needed, or you cannot have isolation.

    Best regards

    Moritz

  • 0 in reply to Moritz
    TI__Expert 6560 points

    Hi Moritz,

    Thanks for your comments.

    One more question, for PSR application, does it OK for the primary side for feedback function only? While very limited load at the primary side.

    Customer would like to get PSR design, but no load to the PSR, could would like to confirm with you for this point.

    Best regards,

    Will 

  • 0 in reply to Will Wang47
    TI__Genius 10995 points

    Hi Will,

    The regulation will be better, if there is a small dummy load (some mA).

    Best regards

    Moritz