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PMP10215: What is the function of the output section of the schematics

Jonas Jalling
Prodigy 20 points
Part Number: PMP10215

Hello,

I'm trying to analyze the schematics of this PSU, but a section of it puzzles me. I have highlighted the section in the attached image. Can someone explain to me what is happening here, and what the function is?

Thanks in advance

BR Jonas

  • 0
    TI__Expert 5185 points

    Hello Jonas,

    This circuit clamps the spike on D6/D3 actively, so it recovers the energy coming from leakage inductance of the transformer and recovers it to the output.

    In fact, if V(C12) > V(D26)+V(D26), we have a drop on R69 and if this drop is > of U13 threshold, the output of U13 delivers a logic "1" level as long as V(C12) keeps its value (which is the spike value). As a consequence, Q13, D27 and L10 form a Buck converter with P-Channel FET and delivers the energy coming from C12 into Vout (36V). R73 is needed because, in case of short circuit on output, this Buck converter will not be able to recover the energy from the spike (because on a short circuit, regardless of the current, the power is zero), therefore R73 burns this energy.

    Finally, D23 is a further protection, set slightly higher than V(D26)+V(D26), to clamp V(D6) voltage during heavy transients on output current.

    Best regards,

    Roberto

  • 0 in reply to Roberto S.
    Prodigy 20 points

    Hello Roberto,

    thank you for the fast response. Reading your description, it now makes sense - thats a clever design!

    My plan was to make the PSU myself, but unfortunately some of the inductors/transformers aren't available for purchase.

    BR Jonas