MOSFET gate protection

I have an AC 230V relay built of discrete MOSFETs. Would a 12V 0.3W Zener diode in SOD323 coupled directly to the gates/sources be an appropriate protection against spurious turn-ons/oxide puncture due to high dV/dt on DS or do I need a TVS?

c.

Reply to
circuitmaker
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I think it's best if you post a schematic. You'll have some series R too, I trust.

George H.

Reply to
George Herold

Good practice indicates a use of back-to-back zener; protecting gate from over-voltage either polarity. 12V gives some safety margin as most MOSFETS seem to be rated at 15V.

Reply to
Robert Baer

Two points: First, for n-channel MOSFETs, generally we don't drive them negative, so a single ordinary zener works well. Second, most mosfets are rated at 20V, and 12V drive is often specified, so a 15 or 16V zener would be better as a rule than 12V.

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 Thanks, 
    - Win
Reply to
Winfield Hill

Or a 20 volt zener, to minimize the likelihood of blowing out the zener. Most mosfets stand a lot more than the rated gate voltage.

A series resistor is a good idea too, if speed allows.

Of course, "good practice" is a waste unless you actually expect gate transients.

--
John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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Reply to
John Larkin

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