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TL431 and PNP for SMPS feedback.

Discussion in 'General Electronics Discussion' started by eem2am, May 7, 2011.

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  1. eem2am


    Aug 3, 2009

    I am doing an isolated, offline flyback SMPS.

    I must have low standby power, and also, very little current (less than 30uA) in the opto-diode during heavy load.

    so i must use this circuit

    .....but do you know of problems with this?....will the feedback loop gain be too high due to the PNP amplfier?

    The PWM controller IC on the primary side has a feedback pin which is connected to the opto collector...........just 90uA COMPLETELY stops switching.

    i cannot use this circuit, as the parallel resistor invokes current in the opto-diode

    ...due to the volt drop across the opto diode
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