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WEBENCH® Tools/UCC29950: Procedure for shutting down ucc29950

JooHee Yu
Prodigy 30 points
Part Number: UCC29950
Other Parts Discussed in Thread: UCC2895

Tool/software: WEBENCH® Design Tools

Hello, I am designing a rectifier using UCC29950.

To protect the output overvoltage, I want to implement the shutdown function of the primary control when the power overvoltage is exceeded.

In the case of UCC2895 you can stop PWM by dragging the SS pin down to GND.

Like this, how can the UCC29950 turn off PWM in self-bias mode?

Please allow me to shutdown OVP while operating in self-bias mode.

I'll wait for a quick reply.

regards.

  • 0
    TI__Mastermind 25570 points

    Hello Joo Hee

    There is no shutdown function on the UCC29950 when it is operating in Self Bias mode. The reason for this is that in self bias mode the controller relies on the LLC stage to supply its VCC rail and if the LLC / PFC stages were stopped then the VCC rail would collapse and the controller stop operating.

    You could stop the switching in Self Bia mode by pulling AC1 and AC2 low (one FET for each) but the problem is how to keep the FETs operating when the Self Bias VCC rail collapses.

    The best solution to this is to add a small bias supply for VCC and to operate the UCC29950 in Aux Bias mode where PFC and LLC switching can be stopped by pulling the MD_SEL/PS_ON pin low.

    Please review the VBULK(OVP) Over voltage protection built into the UCC29950 - it was designed to protect against and overvoltage condition on Vbulk and may provide the protection you need

    Regards

    Colin

  • 0 in reply to Colin Gillmor
    Prodigy 30 points

    Hi, Colin.

    Thank you very much for your reply.

    Regards

    Joo Hee.