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  1. #1
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    Synchronous Flyback is cheapest way?

    Hi,
    The attached is a Flyback with vin = 400V (post PFC bus) and vout = 4.5v and iout = 13A.
    Its power factor corrected because its for lighting. The loads are multiple single LED linear current regulators.
    The synchronous FET is needed due to the high current.
    There is secondary side overcurrent sensing with latch off. A microcontroller is then needed to un-latch the overcurrent trip some 500us after overcurrent trip occurs.
    Do you see any cheaper way of doing this?


    (Ltspice sim and schem attached)

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    Re: Synchronous Flyback is cheapest way?

    What kind of micro is it?

    Some of Microchip's micros include opamps, comparators and programmable logic cells. In that case most of the circuitry in the lower right could be integrated into the micro. (This line of parts is like $2 and has fantastic power supply control potential)

    https://www.microchip.com/wwwproducts/en/PIC16F1778


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    Re: Synchronous Flyback is cheapest way?

    Do you see any cheaper way of doing this?
    of doing what exactly ...?


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    Re: Synchronous Flyback is cheapest way?

    Looks like the latched OCP is all at the board level, though
    there's ideal components which are always suspicious.
    Why not make it a "motorboat" timeout (one-shot)
    instead? If the uC (or whatever) is just going to keep on
    resetting the OCP every time, seems like there is no real
    intelligence and you could get the same action with a
    74AC123, NE555, etc. after the comparator.


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  5. #5
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    Re: Synchronous Flyback is cheapest way?

    of doing what exactly ...?
    Its really the syc rect management...that incurs loads of components here.
    I wonder if the ADP1071 would be better, though it dfoesnt have current sensing and so i suppose it has a feature to hold the sync rect off when it goes into light load...

    ADP1071
    https://www.analog.com/media/en/tech...1-1-1071-2.pdf



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