hello.

Some of my lab lessons, we needed to know how to calculate fet or igbt gate current.

For exmpl;

1)driver circuit is a totem poled optoisolator.

2)100ohm gate resistor connected between gate and opto.

3)12Volt opto output.

4)10kHz switching freq by pwm signal.

5)Total Gate Charge (Qg) is 146 nC

6)Gate-Source Charge (Qgs ) is 35 nC

7)Gate-to-Drain ("Miller") Charge is 54nC

8) There is no snubber circuit.

NOTE: 5-6-7th infos are from irf3205's datasheet

Can someone explain how to calculate that current value will flow from opto through the gate resistor ? Or is there any excel file to make that calculation ?

Many thx. HANS.

Edit:

I know gate current is not constant; it varies exponentially as the capacitance charges. Im asking of the max current will flow through the gate when fet is fully on and gate capacitance is fully discharged. Also for short discharging time, a fast recovery diode paralel connected to gate resistor should be better right ?

Some of my lab lessons, we needed to know how to calculate fet or igbt gate current.

For exmpl;

1)driver circuit is a totem poled optoisolator.

2)100ohm gate resistor connected between gate and opto.

3)12Volt opto output.

4)10kHz switching freq by pwm signal.

5)Total Gate Charge (Qg) is 146 nC

6)Gate-Source Charge (Qgs ) is 35 nC

7)Gate-to-Drain ("Miller") Charge is 54nC

8) There is no snubber circuit.

NOTE: 5-6-7th infos are from irf3205's datasheet

Can someone explain how to calculate that current value will flow from opto through the gate resistor ? Or is there any excel file to make that calculation ?

Many thx. HANS.

Edit:

I know gate current is not constant; it varies exponentially as the capacitance charges. Im asking of the max current will flow through the gate when fet is fully on and gate capacitance is fully discharged. Also for short discharging time, a fast recovery diode paralel connected to gate resistor should be better right ?

Last edited: