ZVS CIRCUIT DIAGRAM

Zero voltage switching circuit diagram

It consists of a diode D1 and capacitor C connected across switch S.  L,C are the resonant circuit components and  L1, C1 are the filter circuit components. The function of resonant capacitor C is to produce zero voltage across the switch S. Diode D2 provides freewheeling path to load current Io.The working of this converter is divided into five modes with equivalent circuits shown in fig   .The time origin t=0 is redefined as the beginning of each mode. Load current Io is assumed constant and filter inductance i0 is also taken to remain level at Io. Initially switch S is on and conducting I0.Therefore inductor current iL=Io and initial voltage across capacitor is zero.

MODE 1(0<=t<=t1)

Initially switch S is off. Therefore the current flows through Vs-C-L.As a result voltage across S or C  builds up linearly from 0 to Vs at t=t1.Diode D is off . Capacitor gets charged from 0 to Vs. At t=0, Vc=0 therefore switch is turned off at zero voltage as required.

MODE 2 (0<=t<=t2)

At. t=t1 capacitor gets overcharged Vc>Vs. Therefore diode D2 becomes forward biased. Now a resonant current iL is setup in series circuit Vs-C-L and D2.  The capacitor voltage Vc is given by Vc=Vs+VmSinWot.

Fig 4.11(a) Modes of operation  for ZVS resonant converter

MODE3 (0<=t<=t3)

Initially at t=0,Vc=Vs and iL=i0.With time t reckoned zero from the beginning of this mode, capacitor voltage is given by Vc=Vs-Vm SinWot and iL= -Io CosWot. At the end of this mode, at t=t3, Vc=0: as a result reverse bias across D1 vanishes and iL begins to flow through D1.

Waveforms for ZVS converter

MODE4 (0<=t<=t4):

During this mode, capacitor voltage is clamped to zero by diode D1 conducting negative current IL. As soon as ant parallel diode D1 begins to conduct at t=0, gate drive is applied to switch S. The inductor current I_L rises linearly from –I_L3 to zero. At this instant reverse bias of D1 vanishes and already gated switch S turns on. This shows that switch S turns on at zero voltage and zero current. After this current rises linearly to Io in the circuit formed by Vs, C, L and D2.

MODE5 (0<=t<=t5):

At the end of mode 4 or in the beginning of mode5 at t=0, I_L reaches Io. And therefore diode D2 turns off. Switch S continues conducting Io. Mode 5 ends at t=t5 when switch is turned off again at zero voltage. The cycle repeats as before.