PWM drive via mosfet - what does a series gate resistor do?

Thread Starter

peskywinnets

Joined Jan 19, 2009
47

Jony130

Joined Feb 17, 2009
5,186
A gate resistor separates a driver circuit (microcontroller) from MOSFET's parasitic capacitance and inductance. These parasitic capacitances and inductances for a resonant tank circuit, which causes oscillation or ringing.
 

cabraham

Joined Oct 29, 2011
82
I always use gate resistors, but typically 1.0 to 10 ohms for high speed PWM, 10 to 100 ohms for low speed applications. The 150 ohm value is rather high for a PWM gate drive. How fast is the PWM in Hz? A 150 ohm resistor will result in a slow FET transition from on to off and vice-versa. If it is a very small FET w/ low gate charge, I suppose 150 ohms could work. Just curious.

Claude
 

Thread Starter

peskywinnets

Joined Jan 19, 2009
47
Their PWM is running at 1khz ....but I've a circuit in mind that will be using 20khz (I need to run it above audio hearing range), hence the curiousity (also my PIC VCC will only be 2.5V, so I'm figuring I can get away with quite a low value series gate resistor?)
 
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Thread Starter

peskywinnets

Joined Jan 19, 2009
47
this is for leds in an audio cct, not motors....and even these jaded 50 yr old ears can still hear up to 13khz (younger ears upto 18khz)
 
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