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PMP10215: Q12 exploded when applying input voltage (240V AC)

Mark Thompson2
Intellectual 610 points
Part Number: PMP10215

Hi there,

I just finished assembling one of these reference designs.  As soon as I turned on the 240V input there was a loud "bang" and upon inspection it appears that Q12 has been destroyed.  What will have caused this?  How can I prevent it happening again after I replace Q12 (and C51 and R66 that looked slightly cooked too).

Finally, what are the implications of not having Q12 in the circuit?

Thank you for your support.

  • +1
    TI__Expert 5495 points

    Hello Mark,

    As you can see from the schematic, the small signal FET Q12 does not have any load, and it works simply as inverter; its load is 1 KOhm (resistor R66), so it cannot be damaged normally. Is it possible that, maybe there was a mistake during assembly, and R66 was 1 Ohm instead of 1 KOhm? It happened also to me once, and Q12 has been damaged.

    If, instead, R66 has the correct value, I suggest to check out if Q11 is damaged. If this FET is shorted, then also D21 will be damaged, and if Q11 has a short between drain and gate, it will damage as consequence also Q12. Can you please double check Q11 if there is a short here?

    Best regards,

    Roberto

  • 0 in reply to Roberto S.
    Intellectual 610 points

    Thanks Roberto.  R66 is the correct value.  I'll test Q11 and get back to you.

  • 0 in reply to Mark Thompson2
    Intellectual 610 points

    Hi Roberto, I think you were correct.  I built our second PMP10215 PCB and it works fine.  It's a relief to know it wasn't any of the parts that we were using (which were the same as the BoM for the PMP10215, except where something wasn't available).  I'll get a replacement Q12 and complete our first board again, hopefully it too works!

    Kind regards,

    Mark