gate resistance values

[mukeshp11]

Dear All,

I want to calculate the exact values of teh on and off gate resistance for MOSFET irf840.

I see from data sheet for my vgs 15V i have 55nc of charge.
So i will get ig=Qc(charge)/Time to rise.

If i take rise time say 1us or something like that.
The i can find Rg as Vgs/Ig.

Similarly i have to go for ig during off and find out Roff resistor.

Am i correct in this case by following above equation.
or can somebody suggest some method better for selecting exact on and off values of gate resistors.


Regards
Mukeshh

 

[tonybg]

The Gate behaves as a capacitor. If the frequency is higher you will need bigger current to charge and discharge the gate.Here is a good article on the subject.