Datasheet

LTC1922-1
10
OPERATIO
U
.
and must be considered when specifying the power trans-
former. If ZVS is required over the entire range of loads, a
small commutating inductor is added in series with the
primary to aid with the passive leg transition, since the
leakage inductance alone is usually not sufficient and
predictable enough to guarantee ZVS over the full load
range.
Figure 1. ZVS Operation
State 4 (Power Pulse 2)
During power pulse 2, current builds up in the primary
winding in the opposite direction as power pulse 1. The
primary current consists of reflected output inductor
current and current due to the primary magnetizing induc-
tance. At the end of State 4, MOSFET MC turns off and an
active transition, essentially similar to State 2, but oppo-
site in direction (high to low) takes place.
State 1.
POWER PULSE 1
V
IN
MA
MB
MF
MC
MD
ME
MF
ME
MF
ME
FREEWHEEL
INTERVAL
MA
MB
MC
MD
State 2.
ACTIVE
TRANSITION
MA
MB
MC
MD
State 3.
PASSIVE
TRANSITION
MA
MB
MC
MD
State 4.
POWER PULSE 2
MA
MB
MC
MD
LOAD
LOAD
LOAD
V
OUT
V
OUT
L1
L2
N:1
PRIMARY AND
SECONDARY SHORTED
V
OUT
1922 F01
I
P
≈ I
L01
/N + (V
IN
• T
OVL
)/L
MAG
+
+