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    high voltage induction from high voltage switching mosfet

    Would a TO-247 aluminum heatsink uninsulated to the to247 tab which is switching 0-1100v induce major voltage spikes to any nearby components pads or traces on the board?
    Last edited by Zak28; 14th April 2019 at 00:45.

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    Re: high voltage induction from high voltage switching mosfet

    is the tab connected to the the drain, or the source, or is it isolated?

    what is the switching frequency and desired rises/fall time?

    without any other information, i'm going with yes it will cause spikes


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    Re: high voltage induction from high voltage switching mosfet

    Quote Originally Posted by wwfeldman View Post
    is the tab connected to the the drain, or the source, or is it isolated?

    what is the switching frequency and desired rises/fall time?

    without any other information, i'm going with yes it will cause spikes
    Would be 100-250hz @ 3-5amps heatsink goes to same voltage as MOSFET tab.

    How far away then does a gate-source TVS diode need to be from the gate pin since the high voltage noise would cause it to constantly clamp?



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    Re: high voltage induction from high voltage switching mosfet

    How far away then does a gate-source TVS diode need to be from the gate pin since the high voltage noise would cause it to constantly clamp?
    Sounds like you have no realistic idea of switching noise propagation. The said electrically "hot" heat sink must be expected to couple capacitively into high impedance circuit nodes and possibly also radiate EMI. But it hardly affects low impedance nodes like the gate circuit dierctly. The strongest coupling between switching drain and gate node is inside the FET, by the way.

    Another effect to be considered is that capacitive loading of the switching node causes ground return currents which may affect the control lines to the gate driver and the control circuit in general.


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    Re: high voltage induction from high voltage switching mosfet

    Quote Originally Posted by FvM View Post
    Sounds like you have no realistic idea of switching noise propagation. The said electrically "hot" heat sink must be expected to couple capacitively into high impedance circuit nodes and possibly also radiate EMI. But it hardly affects low impedance nodes like the gate circuit dierctly. The strongest coupling between switching drain and gate node is inside the FET, by the way.

    Another effect to be considered is that capacitive loading of the switching node causes ground return currents which may affect the control lines to the gate driver and the control circuit in general.
    Other than keeping traces short and wide are there specialty components and layout techniques to eliminate ground currents?

    Gate driver and has 100nF MLCC at its Vcc and MOSFET has 100nF MLCC in parallel with 2000uF drain-source electrolytic.



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