Thursday, January 14, 2010
Trying to understand the zero loss in M1 during turn-off transition.
From lectures 1 & 2, during the M1 turn-off transition, the energy loss in M1 was said to be zero. However the plot of v_s(t) was shown as a sloping line as it drops from Vdc towards 0. But inductor current must continue flowing with +ve polarity. That means it flows through C1 during the period marked X? I wasnt; sure I understood this very well.
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Assumption was made that M1 turn-off transition is done in no time (instantaneously). M1 current I(M1) goes down from i_L to zero amps instantaneously (looking at the Vs graph presented in the lectures 1 and 2 this happens at time t=0) and voltage across the M1 Vds(M1)=0V at time t=0 (since Vs(t=0)=Vdc).
Power loss(M1 turn off)=I(M1)*Vds(M1)=0 W.
Even before the period marked X started, the lossless M1 turn-off transition has ended. Mosfet current I(M1)=0A during periods marked X, D2 and M2.
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