I am looking for some advice on driving the gate of my mosfet.
I am currently using a voltage divider with a capacitor to help hold the dc level and sinking this to ground with an optocoupler to effect PWM of the gate for variable power delivery.
(the v divider carries 5mA and the gate charge of my particular fet is 210nC)
With my PWM frequency set to 2khz, i can see the square waveform and notice the smoothed rise (showing the charging of the gate capacitance). However the shape is still a square wave aside from the visible charging of the gate and slight knee indicating the miller capacitance.
This switches clean throughout the duty cycle and allows the fet to dip in and out of conduction without spending too much time in the linear region. The result is a nice cool mosfet.
Now the issue... when i crank the PWM frequency up to 20khz (to eliminate audible buzzing) i get alot of dissipation in the mosfet and device failure after a minute or so.
When i observe the PWMed gate waveform i can see what looks like shark fin with the miller capacitance knee and a relatively vertical drop to zero V - far from the square wave seen at 2Khz.
The gate needs to be driven more adequately to avoid the linear region.
I could try increase the current available to the gate to enable faster charging by getting higher rated resistors and altering the values of the v divider.
I know mosfet driver IC's are also an option.
Can anybody provide some guidance?
Thanks!
I am currently using a voltage divider with a capacitor to help hold the dc level and sinking this to ground with an optocoupler to effect PWM of the gate for variable power delivery.
(the v divider carries 5mA and the gate charge of my particular fet is 210nC)
With my PWM frequency set to 2khz, i can see the square waveform and notice the smoothed rise (showing the charging of the gate capacitance). However the shape is still a square wave aside from the visible charging of the gate and slight knee indicating the miller capacitance.
This switches clean throughout the duty cycle and allows the fet to dip in and out of conduction without spending too much time in the linear region. The result is a nice cool mosfet.
Now the issue... when i crank the PWM frequency up to 20khz (to eliminate audible buzzing) i get alot of dissipation in the mosfet and device failure after a minute or so.
When i observe the PWMed gate waveform i can see what looks like shark fin with the miller capacitance knee and a relatively vertical drop to zero V - far from the square wave seen at 2Khz.
The gate needs to be driven more adequately to avoid the linear region.
I could try increase the current available to the gate to enable faster charging by getting higher rated resistors and altering the values of the v divider.
I know mosfet driver IC's are also an option.
Can anybody provide some guidance?
Thanks!