SLUA159 Datasheet, PDF (14/28 Pages) Texas Instruments – Zero Voltage Switching Resonant Power Conversion

APPLICATION NOTE
ZVS Half Bridge: The same
turns ratio, N, relationship
applies to the half bridge to-
pology when & in the previ-
ous equations is considered to
be one-half of the bulk rail-to-
rail voltage. V’& is the voltage
across the transformer primary
when either switch is on.
Refer to the circuit and
waveforms of Figs. 14 and 15.
CR, the resonant capacitor
becomes the parallel combina-
tion of the two resonant capac-
itors, the ones across each
switch. Although the resonant
inductor value is unaffected, all
series leakage and wiring in-
ductance must be taken into
account.
The off state voltages of the
switches will try to exceed the
input bulk voltage during the
resonant stages. Automatic
clamping to the input bulk
rails occurs by the MOSFET
body diode, which can be
externally shunted with a high-
er performance variety. Unlike
the forward converter which
requires a core reset equal to
the applied volt second prod-
uct, the bidirectional switching
of the half (and full) bridge
topology facilitate automatic
core reset during consecutive
switching cycles [ll,l2].
U-138
Fig. 16 -- ZVS Half Bridge Circuit
Fig. 17 -- ZVS Half Bridge Wavefoms
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