I wanted to calculate the gate resistance value of MOSFET.Do you want to calculate the RB resistor value? And this resistor is in series with the gate terminal ?
The datasheet for FQ%2FFQAF5N90 mosfet shows 100 na leakage at 30 volts. That would mean the gate resistance IN the mosfet is 30V/100na = 300 million ohms.
Thank you so much for your kind reply !!!If you are referring to the MOSFET internal gate resistance, I believe this application note gives the information you are seeking. See Section A4.
It appears in series with (and thus adds to) any external resistance connected to the gate.I still do not understand the importance of internal gate resistance .
You are making it extremely difficult to figure out just what you're asking: first, you want to know about the Rg parameter (the MOSFET intrinsic gate resistance); then you say you're not talking about that, but rather about resistance connected externally in series with the gate. Which is it-- internal, external, or both?I was not talking about Mosfet internal gate resistance .
I an externally connected series resistor "Rgate" connected to MOSFET Gate.
I'm not sure if there is a calculation for it although it seems like it could be calculated.Attachment thread #11
I'm not sure if there is a calculation for it although it seems like it could be calculated.
I usually just use a value at least as large as what is usually posted in the data sheet. To try to actually calculate it you would need to know about all the parasitic inductance and capacitance associated with the pcba and lead lengths.
View attachment 118578
Edit: If you run at a high frequency you need to make sure you don't overheat your driver.
Found this on line. Seems like a good write up.As per my understanding -
Input Capacitance Ciss of MOSFET which is given in datasheet and External resistance gate value Rg(to be Calculated).
T= RgC time constant,
Should be less than(10 times) to the rise time of MOSFET given in datasheet .
10*RgC<tr
That is how we can calculate Rg value .
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