nFet surge protection

Thread Starter

cmartinez

Joined Jan 17, 2007
7,243
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?
 

crutschow

Joined Mar 14, 2008
26,388
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.
 

Thread Starter

cmartinez

Joined Jan 17, 2007
7,243
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.
Good point, I'll look into that when I select the Fets... thanks
 
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