forward_rr_splane_solution

forward_rr_splane_solution - t = t 1 , transistor Q 1 is...

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1 Reverse recovery of freewheeling diode in the forward converter. The key elements of the power stage in a conventional hard-switched forward converter are illustrated in the Fgure below. The transformer reset circuit is not shown. The transformer leakage inductance is L ± , and is modeled as an inductor in series with the secondary winding. Diode D 2 has linear output capacitance C d , as illustrated. All components are otherwise ideal, and the output Flter inductor L F operates in continuous conduction mode with small current ripple. The object of this problem is to apply the state-plane analysis discussed in class to under- stand what happens during the reverse-recovery transition of diode D 2 . ±igure 2 illustrates typical waveforms for the turn-off transition of diode D 2 ; these waveforms are similar to diode switching waveforms discussed in the textbook on pp. 101 to 103. At t = 0, diode D 2 conducts the load current I F , and elements Q 1 and D 1 are off. At time
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Unformatted text preview: t = t 1 , transistor Q 1 is turned on; this causes i d ( t ) to decrease with slope – nV g / L ± . Diode D 2 continues conducting when i d ( t ) passes through 0 at t = t 2 . At time t = t 3 , the diode D 2 stored charge has been removed, and this diode becomes reverse-biased. Since i ± ( t 3 ) is not equal to I F , the tank circuit formed by the leakage inductance L ± and diode output capacitance C d rings sinusoidally for t > t 3 . This ringing can impose a peak inverse voltage + – Q 1 D 2 D 1 V g 1 : n C d L ± i ± ( t ) – v d ( t ) + I F i d ( t ) L F Fig. 1 Problem 1: voltage ringing is induced at the turn-off transition of diode D 2 in the conventional PWM forward converter. t Area – Q r t t 3 t 1 t 2 v d ( t ) i d ( t ) – nV g I F PIV Fig. 2 Diode D 2 voltage and current waveforms during the diode turn-off transition, for the forward converter of Problem 1....
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forward_rr_splane_solution - t = t 1 , transistor Q 1 is...

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