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ESD protection for mosfets?

Discussion in 'General Electronics Discussion' started by eem2am, Dec 14, 2010.

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  1. eem2am


    Aug 3, 2009

    We have a H Bridge Solenoid driver for a latching solenoid which we pulse with around 400mA.

    The H Bridge is made of mosfets.

    The problem is that our PCB comes with bare metal spade terminals (which are electrically connected to the switching nodes of the H Bridge).

    There is a danger that these bare metal spade terminals could be handled by people.

    I have been told to add components to prevent ESD damage.

    But do you know what components i can add to protect against ESD damage?
    (i mean ESD damage to the FETs)
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Most damage occurs when the Vgs(max) is exceeded. Placing back to back zener diodes between the gate and the source can clamp any voltage (they should be rated below Vgs(max) but above any gate voltage you apply). If your circuit allows it, a resistor between gate and source will allow any charge to leak away, so that the mosfet won't stay turned on for long without being actively powered.
  3. shrtrnd


    Jan 15, 2010
    It seems unreasonable to just tell you to add some miraculous components to 'prevent
    ESD damage'. Pack the board in a static shield bag, and tell whoever removes it, to do
    so at a ESD safe workbench. (While they're grounded). If this is something a tech is just
    going to install in the field, and they don't know anything about handling ESD sensitive
    boards, train them.
    There is no cure-all components or circuits to 'prevent ESD damage' to the board, it's
    HANDLING the board properly, that prevents ESD damage.
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    What shrtrnd says is true.

    However if your board has the gates of mosfets connected directly to external connections, you should have some form of protection if you can.

    This may be simply a resistor to leak away charge, or it may be a complex circuit designed to protect the board from large transients. It all depends on what you need.
    Last edited: Dec 16, 2010
  5. davenn

    davenn Moderator

    Sep 5, 2009
    what ..Who me ? I didnt do anything ;)
    at no time did my hands leave my wrists haha :)
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