• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 315 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

Original question:

UCC28950: PMP8740 design chages

UCC28950: Secondary Side Mosfet replacement

Nidheesh BR
Expert 1295 points
Part Number: UCC28950
Other Parts Discussed in Thread: PMP8740

Hi,

If I am repacing secondary MOSFETs with diodes(disconnecting secondary gets also), will it affect my ZVS achievement?

Secondary MOSFET switching is mandatory for ZVS?

Thanks.

  • 0
    Expert 1295 points

    Forgot to mention.. in PMP8740 board.

  • 0 in reply to Nidheesh BR
    TI__Mastermind 25570 points

    Hello Nidheesh

    The short answer to your question is, no, it won't affect the primary size ZVS behaviour.

    Regards

    Colin

  • 0 in reply to Colin Gillmor
    Expert 1295 points

    Hi Collin,

    Thank you for the information.

    One more doubt, In synchronous rectification mode, As the MOSFET is reverse biased when the gate is being supplied then it is not going to conduct current in the drain-source direction right?

    Am I right? if not please correct me.

    Thanks.

  • 0 in reply to Nidheesh BR
    TI__Mastermind 25570 points

    Hello Nidheesh

    Apologies for the delay in responding. Anyhow ....

    The SR is connected so that it conducts current from the source to drain and does not conduct from drain to source. The gate drive signal is such that when the current is flowing from source to drain the MOSFET is turned on and the current flows in the device channel instead of the body diode. The MOSFET is turned off to prevent current flowing from drain to source. The MOSFET behaves as an ideal diode and this is the easiest way to think about it. If the SR drives are disconnected from the MOSFETs (and their gates connected to their sources) the power stage will still operate, but with higher losses because the Vf of the body diode is higher than the voltage drop due to the channel resistance (Rds_on*Iout). 

    Regards

    Colin

  • 0 in reply to Colin Gillmor
    Expert 1295 points

    Hi Colin,

    Perfect. Thank you for clearing my confusion and for a nice explanation.

    Regards

    Nidheesh