# Losses in Gate Capacitance

Discussion in 'Homework Help' started by hulk_mehraboon, May 18, 2012.

1. ### hulk_mehraboon Thread Starter New Member

May 18, 2012
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0
how can i get this formula for Mosfet? i need the integration Please help ????
this is the power dissipation in both switches (Mosfet) Due to power conduction in by Rds(on):
P switching = (V  ID/ 2)  (Ton + Toff)  Fsw + (Coss V2 Fsw)
I have found the prove of the first part of this formula but the second part (Coss V2 Fsw) i have no idea how you can get this formula can anyone help me please !!!

2. ### mcgyvr AAC Fanatic!

Oct 15, 2009
5,164
1,130
Well fsw is the switching frequency (determined by you) and Coss is output capacitance.. (also determined by you)

If its just being used an an on/off switch those variables are not needed and its just P=I^2R I believe

http://www.maxim-ic.com/app-notes/index.mvp/id/1832

3. ### crutschow Expert

Mar 14, 2008
17,686
4,883
The energy stored on a capacitor is 1/2 CV$^{2}$. But the same amount of energy is dissipated in the resistor (or transistor) used to charge the capacitor. This can be found by integrating the total energy used (charge x voltage) in charging the cap from a fixed voltage source. Thus the total energy lost in charging and discharging a cap is CV$^{2}$.

And to get the power dissipated in a switching application you simply multiply the energy dissipated per charge and discharge times the switching frequency or CV$^{2}$Fsw.

Last edited: May 18, 2012
4. ### hulk_mehraboon Thread Starter New Member

May 18, 2012
2
0
finally some answers million tnx