Max gate-source voltage of fet?

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grizedale

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Hello,

The gate-source voltage allowable for this SPA04N60C3 FET is stated as "+-30V at >1Hz" (page 1)

Does that mean it'll be ok for me to drive it at 70KHz with +22V in a flyback?


SPA04N60C3
https://www.farnell.com/datasheets/13301.pdf


...or is their an implication here that though it can stand +-30V, it'll be delicate and may well fail?
 

Yes, I think you can drive this by +22V source. If you can control gate voltage and keep that to +15V, that would give you extra margin. In this case even in case of un damped oscillation due to parasitic on gate terminal, max overshoot would not exceed the rated gate voltage.
 
+22V should be okay, but you'll need to damp the gate waveform with some resistance to prevent excessive overshoot internally due to the parasitic gate inductance/capacitance. Putting a ~24V TVS diode on the gate to source would probably help too.
 
I think what the 1Hz remark is telling you, is that there is
some charge-soak or hot carrier or similar reliability effect
under DC bias, and they are rating in a continuous switching
mode. Which you are after, so OK. There might be some
fine print that changes the rating for DC apps.
 
Thankyou

mtwieg:

Putting a ~24V TVS diode on the gate to source would probably help too
Click to expand...

Would it be ok to use a 24V zener instead of a TVS?
 

Well a TVS diode is essentially a zener optimized for high pulse handling. As long as it's a decently fast zener it should be okay.
 
Another viewpoint: TVS diodes are not particularly fast but simply rugged large chip zener diodes. The junction capacitance can be expected respectively high. Thus my suggestion is, you can use TVS diodes if you have no problems to drive the extra capacitance. It's no problem with medium speed multi kW IGBTs, but possibly unwanted with smaller and faster devices.

It's not clear to me by the way, why you are trying to drive the gate voltage up to the limits.
 
It's not clear to me by the way, why you are trying to drive the gate voltage up to the limits.
Click to expand...

......The reason is because i am using UC3842 pwm controller....it takes 17.5V to come on....then the bias winding has to get above this in order to diode-OR out the start-up regulator.

...so the Vcc voltage, which is used to drive the gate, is nearly 20V.
 

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