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PMP20058: Reducing Output Ripple of Flyback Boost Regulator

J. A.
Prodigy 170 points

Part Number: PMP20058

The PMP20058 Reference Design is an isolated flyback regulator intended to provide 54V for Power-over-Ethernet (PoE) applications.

IEEE 802.3af (PoE) indicates that the maximum ripple voltage to be:

The following scope shot from the PMP20058 test results document shows an output ripple of approximately 1.0V with positive spikes every 10µs or so.

Has anyone looked at filtering this ripple voltage?  Do you have any suggestions with slight modifications to the existing reference design?  I suspect that this will require adding an inductor and low-ESR capacitor, but I have prototypes with this design already in-house.  Might there be another way?

  • 0
    TI__Expert 6540 points

    HI,

    The output filter on PMP20058 is just capacitive. The best way to dramatically reduce the ripple is to use a pi filter like you suggested.

    Please make sure to use ceramic capacitors at the diode output, then you can use electrolytic or ceramic after the inductor. Care must also be taken so that the resonant frequency of the LC filter does not interfere with the feedback loop.

    Thanks,

    Robert