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  1. #1
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    CCM boost PFC with reverse recovery management

    There is a small inductor in the drain of the fet of this boost converter (attached). It massively reduces the reverse recovery spike that goes through the fet at switch on.
    Why donít CCM PFC boost converters use this?
    It means you donít have to be stuck with high peak current BCM boost PFCs....and the extra coil needed to mark out the BCM points.
    LTspice sim also attached

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  2. #2
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    Re: CCM boost PFC with reverse recovery management

    That's fine for mouse power - but it doesn't scale ...


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    Re: CCM boost PFC with reverse recovery management

    Thanks, at one of the worlds major TV design/manufacturers, they were using a ferrite bead in the place where i show a drain_inductor....(they werent using the freewheeling diode with it).

    (..that was in a Boost PFC supplying a LED TV)

    But why should it not scale?
    Admittedly if you run the sim it shows quite a high "shard" of current in the drain_inductor, but this seems harmless enough.
    There is a dramatic reduction in the reverse recovery spike current through the fet at fet turn on.

    Another point, is that the other alternative to this, BCM Boost, does not scale well either...its peak current gets too high as the power gets up.

    And using a SiC diode in CCM boost also doesnt scale well...since SiC Vf loss is high



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    Re: CCM boost PFC with reverse recovery management

    Hi
    I attended an interview and they briefly showed a schem of a 650W Boost PFC. Just downstream of the Diode, there was a gate controlled device, with a symbol something like a SCR……its gate was driven from a bias winding on the main Boost PFC inductor. It appeared to be for preventing reverse recovery currents…..ie, when the boost inductor was in the “discharging cycle”, then the device would be off and it simply wouldn’t be possible for reverse recovery current to flow back through the main Boost diode.
    I tried googling for it but cant find such a circuit. Do you know of one?



  5. #5
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    Re: CCM boost PFC with reverse recovery management

    inrush startup SCR most likely ... turn off time of common scr = 10uS


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