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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    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
    4,770
    970
    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

    This might help you..

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

    Expert

    Mar 14, 2008
    13,016
    3,235
    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
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    0
    finally some answers million tnx
     
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