I have to find out the gate loss of the mosfet (irf3205) in my circuit, for high side fet.
The formula to calculate the gate charge loss of a mosfet is, Pgate = Qg * Vgs * Fsw
Pgate= Power loss at gate
Qg= gate charge
Vgs= gate to source voltage (voltage require to drive the mosfets gate)
Fsw= Switching frequency
Is the about gate power loss is right?, Because i have a doubt in "Vgs".
I have to switch 40v supply, so the high side mosfet require 40v gate voltage to switch the vcc(40v) supply.
I'd say you have to check the upper side MOSFET gate-to-source voltage swing, instead of the power supply voltage, as d123 hinted.
Keep also in mind that this loss you're calculating is dissipated in the gate driver, not in the MOS itself.
What are you using as a gate driver? The gate driver datasheet usually is very helpful in explaining how to calculate its own losses.