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LM5026: self synchrounous rectification with 24V Output

Yazhu Liu
Intellectual 1410 points
Part Number: LM5026
Other Parts Discussed in Thread: PMP20878

Hi Team,

 

Our customer is evaluating LM5026 in their design, the spec is as below.

Vin=50~134V, Vout=+/-24V, Iout=5.2A, transformer turns ratio=5:4

They'd like to implement self synchrounous rectification at secondary side, I promote the self driven synchronous rectification solution in PMP20878(http://www.ti.com/tool/PMP20878) But customer still have some question related to that.

1. The maximum secondary side voltage will be up to 110V, which may cause high power loss on the resistor R100, will that cause any problem?

2. What is the function of the following circuit?

3. When self driven synchronous rectifier is used, there will be overlapping part of continuous and rectifier MOS conduction. Do we have some design tips which can help to decrease this overlapping time?

Could you please give some comments on that?

Thanks.

Best Regards,

Livia

  • 0
    TI__Genius 13660 points

    Hi Yazhu, an expert will get back to you tomorrow. thank you. —— Teng

  • 0 in reply to Teng Feng
    TI__Intellectual 1410 points

    Hi Teng,

    Thanks.

    Do we have any update on this question?

    Best Regards,

    Yazhu

  • 0 in reply to Yazhu Liu
    TI__Genius 13660 points

    Hi Yazhu,

    Sorry for the long time delay.

    1./ R100 is used to provide the bias current for Zener D101, from Zener MMSZ5240B-7-F datasheet, the minimum Zener Breakdown Current should be smaller than 2mV, if you worry about over power of R100, I think you can increase R100 and parallel multi resisters. 

    2./  The cycled part circuit is the snubber circuit for MOSFET Q15, in which, C102 and R102 path is used to eliminate the short and small spike. D34, C47 and R45 path is used to eliminate the larger and longer-lasting spike.

    3./ This is a current fed application, I don’t think there is a overlap issue. Does customer has any issue in the application?

    Regards,

    Teng