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PMP40379: Feedback Design

Neethu Joy
Prodigy 65 points
Part Number: PMP40379
Other Parts Discussed in Thread: TL431

Hi,

I was designing  a circuit using the reference design of PMP40379. I want to know how the feedback resistors R627, R621 (https://www.ti.com/lit/pdf/tidrxp7) to the opto-coupler is designed. The design Vout is 230V DC. Will be more useful if you could provide any design equations.

  • 0
    TI__Mastermind 26645 points

    Hi Neethu,

    R627 controls the gain of the fast lane of the feedback circuit. This is normally expressed as a gain term of Rpullup/Rled. In PMP40379, this expression would be 100k/20k where the 100k is the internal RFB resistor. R621 is to allow for providing bias to the TL431 to keep its reference voltage stable in the event no current is driven through the opto-coupler.

    I think you can refer to this app note regarding compensation design with TL431: https://www.ti.com/lit/an/slua671/slua671.pdf

    Best Regards,

    Ben Lough