nFet surge protection

Discussion in 'General Electronics Chat' started by cmartinez, Jan 30, 2015.

  1. cmartinez

    Thread Starter AAC Fanatic!

    Jan 17, 2007
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    I'm making a bi-directional back-to-back nFet switch to drive an AC motor, as shown in the following circuit.

    Capture.JPG

    I'm not worried about the driver since I've already built one based on a design posted by @JDT (btw, thanks man!) and it works wonderfully on a resistive load.
    Anyway, I've placed a TVS diode across the mosfets to protect them a bit.
    My question is this, I'm very much aware that motors demand up to 10 times more amps at startup (perhaps even more) than their normal rating. Is there any way to protect the fets from this surge, other than having to buy enormously oversized fets for this application?
     
  2. ronv

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    Nov 12, 2008
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    cmartinez likes this.
  3. cmartinez

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  4. crutschow

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    Mar 14, 2008
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    The MOSFETS will limit the current due to their normal ON resistance value. If the surge doesn't exceed the pulse current rating of the MOSFET then you may not need any additional surge protection.
     
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  5. cmartinez

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    Jan 17, 2007
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    Good point, I'll look into that when I select the Fets... thanks
     
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