This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

PMP20367: PMP20367

Part Number: PMP20367

Dear all, 

For the use of UCC24610D, I notice that there are some extra components connected to the VD pin, i.e. Q501, D501, which don't appear in the datasheet of UCC24610D.

I really appreciate it if someone can tell what are these used for.   

Thanks a lot.

  • Hello Sir,

    myself checked schematics and BoM, I could not figure out part designators #501;
    if you refer to Q2/D8:
    as diode rectifiers could be replaced by synchronous rectifiers those parts ensure,
    that SR controller is only driving the FETs as auxiliary 5V on secondary are stable.
    The FETs itself are driven out of transformer winding via SR controller.

    Here Q5 and Q8 are not populated.

    Best regards, Bernd

  • Thanks, Bernd.

    Firstly, it is my fault to give the wrong component designators. I did refer to Q2/D8.

    But can you be more specific? Why can these devices ensure SR controller is only driving the FETs as auxiliary 5V on secondary are stable? What will happen if it is not stable? 

    I ran a simulation in Tina-TI, and I found that with these two components, the output voltage on C16 is totally changed. So actually, I still don't see the meaning of adding these two. 

    Really appreciate it if you can give a further explanation.

    Best regards, Jimmy

  • Hello Sir,

    please have a look at DIRECT DRIVEN SYNCHRONOUS RECTIFICATION,
    that's a very cheap method for low voltage outputs to drive the SR directly out
    of the transformer windings - please check active clamp forward PMP7094.

    But the gates are directly at the secondary windings, this could cause trouble
    as load is pre biased or secondary voltage exceeds max. Vgs.

    So TI designed a secondary side controller for bullet proof operation.
    To ensure proper function the sequence is:  stable Vdd before Vg output.

    Best regards, Bernd

  • Thanks, Bernd. Now I think I might know why we need these.