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  1. #1
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    Putting a 1Meg resistor across offline Flyback SMPS transformer....voltage rating

    Hello,
    We wish to put a 1Meg resistor between primary and secondary of our 60W offline Flyback LED driver transformer. (to stop secondary from floating up to mains peak potential).
    However, we cannot find a cheap one with a voltage rating up to 3000VAC, -The isolation voltage requirement. Do you know of any? We could use six of these MMB0207s in series, but we dont have the board space..
    www.vishay.com/docs/28713/melfprof.pdf

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  2. #2
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    Re: Putting a 1Meg resistor across offline Flyback SMPS transformer....voltage rating

    so a 1Meg res to phase? you cannot guarantee phase and neutral connections in a psu - that is a requirement of design safety

    If you have an earth you can connect to that from 0 ohm to 10Meg ...



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  3. #3
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    Re: Putting a 1Meg resistor across offline Flyback SMPS transformer....voltage rating

    Thanks, I mean connecting a 1Meg resistor between primary 0V to secondary 0V…….ie across the isolation barrier. This should stop the secondary from floating up to mains peak (or negative mains peak).
    As you know, primary 0V alternately connects to Neutral, and then negative-going-live…as the rectifier bridge diodes switch over…..as such, this is on average, less than mains peak in terms of its potential.



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  4. #4
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    Re: Putting a 1Meg resistor across offline Flyback SMPS transformer....voltage rating

    an average current to a person of 114uA ( rms) while this might meet medical psu specs - time for a better idea methinks



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