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    Offline LED drive SMPS >50W must have open feedback loop protection via aux coil?

    Hello,
    We are doing a 100W led lamp, it is powered by a 100w offline smps.
    If the led load goes open, we have an opto which crosses the isolation barrier and shuts down the pwm controller on the primary side.
    ..but is this enough?...do we also need to have a auxiliary coil in the isolation transformer which gets used for overvoltage protection by relaying an "image" of the output voltage back to a shut down cct on the primary side.?

    Or is a simple opto, on its own, enough?

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    Re: Offline LED drive SMPS >50W must have open feedback loop protection via aux coil?

    Depends, how high does the output go in the event of a fault, and how much energy is potentially available?

    Maybe you can use the turns ratio on the magnetics to limit the worst case output voltage to something SELV?
    Maybe you can just have the magnetics saturate before the voltage becomes dangerous and take out a fuse?

    I am assuming that at the 100W level the topology is something a bit smarter then a flyback?

    Regards, Dan.


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    Re: Offline LED drive SMPS >50W must have open feedback loop protection via aux coil?

    Smart Drivers have OVP and UVP with latching hysteresis
    A best design is easily achieved with good test specs™
    A better question deserves a better answer. ™
    ... so include all your acceptance criteria ( values, % tolerance) and assumptions in your question or any design.

    ... Tony Stewart EE since 1975
    - slightly north of Toronto


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  4. #4
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    Re: Offline LED drive SMPS >50W must have open feedback loop protection via aux coil?

    Thanks, this is a qr flyback running off 400v pfc output.



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