this post was submitted on 27 Dec 2023
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MOSFET gate resistor (discuss.tchncs.de)
submitted 10 months ago by Rolive@discuss.tchncs.de to c/askelectronics@discuss.tchncs.de
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Since MOSFETs have a gate capacitance you'd want to limit the inrush of current from the output of a microcontroller to prevent it from getting damaged prematurely. That's what gate resistors are usually good for.

Another thing is that most MOSFETs don't fully activate with a gate voltage below 10V (n type) so usually a microcontroller pin isn't good enough for switching large loads.

I have a 24V system and have made a voltage divider using two 10k resistors to step down 24V to 12V as gate driving voltage which is pulled down with a weaker MOSFET. The power MOSFET essentially ends up with a 10k gate resistor this way meaning it will take a bit longer to fully saturate.

Is too high harmful? In this situation the load is a heater that activates when the room temperature drops below 18C and deactivates when it gets above 22C so fast switching is not an issue.

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[โ€“] cmnybo@discuss.tchncs.de 7 points 10 months ago (1 children)

For something that's not switching at a high frequency, slow rise and fall times are fine as long as you are staying within the safe operating area of your MOSFET. A 10K gate resistor could certainly work, but it will depend on your MOSFET and load.

[โ€“] Rolive@discuss.tchncs.de 4 points 10 months ago

That's good. My switching frequency is a few times per hour.

I am a little bit concerned that the slow rise/fall time make the MOSFET go outside its operating parameters for a fraction of a second. The resistance gradually changes meaning the mosfet will dissipate more power but also less current will flow.

So if you switch many times per second the gate capacitance with the resistor acts as a low pass filter reducing the gate voltage.