Gate Drive & Supply Requirements

Thread Starter


Joined Feb 14, 2013
I want to drive(PWM) two MOSFET(s) with their source(s) pin tied back to back to switch AC supply (220V,50Hz). PWM Freq. = 50KHz and Load current=5A.

To drive the gate I am using Gate Drive Optocoupler : HCPL-3120
(With Under Voltage Lock Out). I want to drive the MOSFET at 15V.

Based on my reading, I understand that MOSFET gate acts like a capacitor and requires charging to it turn on. Also that it is a trade-off between Switching Frequency and Switching Losses. (i.e Higher the switching freq., higher the gate current required.) But couldn't find an elegant & straightforward resource online for calculations.


Given the switching freq. and load current
1. How to calculate the gate current requirements ?

2. How to select Gate Resistor (Resistance and Power) ?

3. How to select Discharging Resistor between Gate and Source (Resistance and Power) ?

4. Suggest a Power Supply design (220V AC to 15V DC) to supply gate drive voltage.

For sake of simplicity, let us work out the above parameters for one MOSFET first. (Assuming for two of them its twice)

The datasheet for MOSFET and Gate Drive Optocoupler are attached.
Also the Image for MOSFET arrangement is attached.

I hope the above information is enough to answer my questions and my understanding about MOSFET is correct. Still feel free to point out mistakes (if any).

Please illustrate calculation with equations (if any), I really want to learn it.

Thanks and Regards


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