Page 292 - Rashid, Power Electronics Handbook

282 S. Hui and H. Chung

Cs1 junction capacitance of the diodes). However, all switches are
L under high-current and voltage stresses, resulting in an
increase in the conduction loss.
S1
Cs2 S2
15.7 Zero-Voltage-Transition (ZVT)
Converters
FIGURE 15.18 Constant frequency multiresonant switch.

By introducing a resonant circuit in parallel with the switches,
S oscillates to zero. When I Lr becomes negative, S will be the converter can achieve ZVS for both power switch and
1
1
turned on with ZVS. Then L resonates with C . When diode without signi®cantly increasing their voltage and
r
S2
current ¯ows through D S2 S will be turned on. As the current stresses [23]. Figure 15.20a shows a buck-type ZVT-
2
output voltage is the average voltage across S , output voltage
2
regulation is achieved by controlling the conduction time of S :
2
All switches in MRCs operate with ZVS, which reduces Cd
Lf
switching losses and switching noise and eliminates oscillation
due to the parasitic effects of the components (such as the
Lr
S S1
Cs1 Vi D C Co R
i D
L
Lf
L D1 Cr
Vi Cs2 Cf R
L
S1 S2 (a)
(a) on
off
S
on
T off
S
S1
V i
T S1 DRIVE
OFF
WAVEFORM V D
T
D S
I
T S2 DRIVE O
ON
WAVEFORM
I
S
t t t t t t
0 1 2 3 4
(b)
I
Lr
Cs1 L L
2V
i
Cs2 I Cs2 I
O O
V
[t0,t1] [t1,t2] C V
r i
L L
V
I Cs2 I D I
O O O
I
[t2,t3] [t3,t4] D t t t t t t t t t
0 1 2 3 4 5 6 7 0
(c) (b)
FIGURE 15.19 Constant frequency buck MRC: (a) Circuit schematics; FIGURE 15.20 Buck ZVT-PWM converter: (a) Circuit schematics; and
(b) gate drive waveforms; and (c) operating stages. (b) circuit waveforms.