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To find mosfets gate to source voltage (Gds)

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Nihaludeen

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To find mosfets gate to source voltage (Vgs)

IMG_20180715_133709.jpg

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

datesheet of irf3205
http://www.irf.com/product-info/datasheets/data/irf3205.pdf

Pgate= 146nC * 40v * 1Khz
= 146*40*1* 10^-9 * 10^3
= 5840 * 10^-6
= 0.0058Watts


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.
 

Re: To find mosfets gate to sourse voltage (Gds)

Hi,

One point is that VGS max is 20V. Your calculations are correct for 40V.
 
Re: To find mosfets gate to sourse voltage (Gds)

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.
 
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    d123

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