SLUA159 Datasheet, PDF (13/28 Pages) Texas Instruments – Zero Voltage Switching Resonant Power Conversion

APPLICATION NOTE
ZVS Clamped Configurations -- Half and
Full Bridge Topologies: Zero voltage switching
can be extended to multiple switch topologies
for higher power levels, specifically the half and
full bridge configurations. While the basic
operation of each time interval remains similar,
there is a difference in the resonant tlZ interval.
While single switch converters have high off-
state voltage, the bridge circuits clamp the
switch peak voltages to the DC input rails,
reducing the switch voltage stress. This alters
the duration of the off segment of the resonant
interval, since the opposite switch(es) must be
activated long before the resonant cycle is com-
pleted. In fact, the opposite switch(es) should
be turned on immediately after their voltage is
clamped to the rails, where their drain to
source voltage equals zero. If not, the resonant
tank will continue to ring and return the switch
voltage to its starting point, the opposite rail.
Additionally, this off period varies with line and
load changes.
Examples of this are demonstrated in Figs.
14 and 15. To guarantee true zero voltage
switching, it is recommended that the necessary
sense circuitry be incorporated.
U-138
Fig. 14 -- Clamped ZVS Configuration
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