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TPS23734: Overheating of resistor in auxiliary circuit POE PSR flyback

Lauco de Kleijn
Prodigy 10 points
Part Number: TPS23734

We implemented a POE circuit using TPS23734 controller with primary side regulation, we used Coilcraft POE36PR-12ED flyback transformer

During testing of the circuit we saw that the series resistor in the auxiliary supply (component with refdes R606 in schematic, 3E3 resistor in 0805 package) reaches temperature over 100C even with low loads.

TPS23734 POE circuit.pdf

  • +1
    TI__Mastermind 20521 points

    Hi Lauco de Kleijn,

    Thanks for reaching out to us!

    You need to connect PSRS to PGND when your secondary side is a diode.

    Difference of PSR + SYNC MOSFET and PSR + DIODE is at the discontinuous mode (DCM). The coupled inductance’s current can be reversed with PSR + SYNC MOSFET. PSR SYNC + MOSFET does not have DCM, the CP’s MOSFET can be turned on anytime when PRI’s MOSFET is off. But PSR + DIODE has DCM, the CP’s MOSFET cannot be turned on during discontinues period when PRI’s MOSFET is off since that will discharge the feedback capacitor (C_fb).

    Best regards,

    Diang