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Correct zener voltage for a mosfet gate

Discussion in 'General Electronics Discussion' started by bonedoc, Mar 2, 2012.

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  1. bonedoc


    Dec 21, 2011
    I would like to protect the gate of of mosfet. It has a +-15V GS rating. I am driving it at 12V max with a driver. What voltage of a zener diode should I place reverse biased at the gate?

    I have heard the a zener will usually start conducting before its zenner voltage. So, I dont want this to be a problem. On the other hand, I dont want to get to close to the 15V rating, as to avoid damage.

    What is a good value?
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    I would go with something greater than 12 and less than 15 :)

    Unless your driver is unable to supply a small continuous current, or the gate impedance is highly important, the small leakage prior to the knee voltage should not be a concern.

    Technically you can place 2 back to back zeners in series, but as common usage is to bring the gate voltage tot he source to turn it off, the additional zener is not (again commonly) required.

    I would tend to make sure my driver couldn't exceed the Vgs(max) of the device rather than providing protection. If your gate resistor is low and your gate driver is capable of high currents then you are setting yourself up for high power dissipation in the zener.
  3. alfa88


    Dec 1, 2010
    I'm not much of an expert in this area but on a power supply for my TV they're using a 15V zener.
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