Feeding PWM signal trough capacitor to mosfet gate ?

[Externet]

Hi.
For a motor speed control, the output mosfet usually has its gate with a pull-down resistor to source to keep it off; and the PWM square wave source is fed into the gate with usually a small value resistor in series.

If the PWM signal source has a capacitor at its output, would that ensure the Mosfet would never stay on if the PWM source fails and stays 'high' ?

Is it a common practice to feed signal into a mosfet gate trough a capacitor ? Why ?

Say pin 5 with a series capacitor in this random example borrowed from the web:
----> https://www.circuitstoday.com/wp-content/uploads/2010/01/speed-control-for-PCB-drill.png

 

[barry]

I wouldn't advise it. You would basically be creating a high-pass filter and introducing an undesirable decay on the gate voltage. If you are that concerned with the signal staying high too long, I'd add some kind of timer/one-shot circuit that would drive the gate to zero after a given time. Or you could put some protection on your output in the event that the MOSFET stays on too long.

 

[Mr.Cool]

there are better ways to protect against an always ON PWM signal. run PWM digital signal through external logic gates being the most simple. on gate driver side, easiest way is to employ desat protection, even with mosfet switch. no problem.