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PMP23287: Snubber Circuit Recommendation

Shinichi Inoue
Guru 21686 points
Part Number: PMP23287
Other Parts Discussed in Thread: TPS23730, PMP22477

Dear Specialists,

My customer is considering TPS23730 and confirming PMP23287.

They have a question.

I would be grateful if you could advise.

---

I'm considering to realize a POE class 6 24V2.5A circuit using the TPS23730.

I'm referring to the PMP23287 circuit, but the snubber circuit is not connected.

I think the snubber circuit should be added, so please tell me the reference circuit and constants.

Can I use the same circuit (diode + capacitor + resistor) in PMP22477?

If possible could you please provide application note for the snubber calculation method.

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I appreciate your great help in advance.

Best regards,

Shinichi

  • +1
    TI__Intellectual 2530 points

    Shinichi,

    PMP22477 is a flyback converter.  It has the RCD clamp on the drain of the primary FET to clamp the voltage, but often an R/C snubber in parallel with the primary FET is required for sufficient clamping of the voltage overshoot and ringing at turn-off.

    PMP23287 is an active clamp forward converter.  The drain of the main primary FET Q11 is clamped at turn-off by clamp FET Q10, so there should not be any voltage overshoot at turn-off.  Also, this topology uses a resonant transition during switching, resulting in zero voltage transitions (or at least partial ZVT).  This should significantly reduce voltage ringing during switching.  If there is voltage overshoot and ringing at turn-off there is probably a layout issue.

    I would not add a snubber to the primary FET Q11 with this topology.  It will alter the resonant transition time, requiring more delay between Q11 and Q10 switching.  This will result in the synchronous FETS Q6 and Q8 operating on their body diodes for a longer period of time, reducing efficiency.

    Thanks,

    David

  • 0 in reply to David Strasser
    Guru 21686 points

    Hi David,

    Thank you for your reply.

    I understand that for flyback converters it is recommended to have a snubber in parallel with the main FET.

    I also found an example of using an RCD snubber with a flyback converter in the reference design PMP22477.

    https://www.ti.com/lit/pdf/tidma48

    We'll offer two options to our customers.

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi