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UCC2897A: Contact flyback circuit

KIM Andy
Expert 2530 points
Part Number: UCC2897A
Other Parts Discussed in Thread: TPS2373, TPS2373-4EVM-758, , PMP20541

Hi

Currently, my client is trying to develop POE by applying TPS2373 and UCC2897A based on TPS2373-4EVM-758.

I was very satisfied with the EVM.

But it is too expensive to apply UCC2897A as active clamp circuit.

So we want to apply UCC2897A as flyback.

There are some questions about the application.

1. I would like to know about the setting of the AUX stage if the 2nd SR IC is not applied.

    


2. The datasheet only shows the ovp for the input. Can I make OVP settings for the output?

3. It has been confirmed that there is very little inrush current when it is active clamp. Can Flyback get the same results?

please answer about my question.

  • 0
    TI__Mastermind 34465 points
    Hello Andy,
    The pdf you attached shows the PMP20541 reference design. This uses the UCC2897A in a flyback application with the AUX output driving a synchronous FET on the secondary. This synchronous FET is also the main flyback rectifier. So the answers to your questions are:
    (1) If SR is not required then you can disconnect the AUX pin and remove the SR FET. Replace the FET with a rectifier diode.
    (2) You can have OVP on the output by measuring the voltage on pin 6 of the transformer and shutting down the system when this exceeds your OVP threshold.
    (3) The inrush current is mostly determined by the input capacitance. So if you were satisfied with the inrush from the EVM I suggest you use the same input capacitance with the flyback application. Also check the soft start time and the peak current setting on the CS pin.
    The flyback can be designed to have the same inrush as the forward application

    Regards
    John