SLUA159 Datasheet, PDF (18/28 Pages) Texas Instruments – Zero Voltage Switching Resonant Power Conversion

APPLICATION NOTE
ZVS Forward Converter -- Design
Example
1. List circuit specifications:
&N = ^{18 to 26 V}
vo = 5.0 V ; I, = 2.5 to 10 A
2. Estimate the maximum voltage across the
switch:
U-138
Table VI - Interval Durations vs. Line & Load
=26•(1+(10/2.5)) = 26•5 = 130 V
3. Select a resonant tank frequency, oR’
A resonant tank period frequency of 500KHz
will be used. It was selected as a compro-
mise between high frequency operation and
low parasitic effects of the components and
layout.
4. Calculate the resonant tank impedance and
component values.
Resonant tank impedance, ZR > VIN,,,Joti,,
To accommodate the voltage drop across the
MOSFET, calculate VDs(on~min, which equals
Fig. 23 - Switch Times vs. Line & Load
5. Calculate each of the interval durations @,,
thru f& and ranges as they vary with line
and load changes.
The zero voltage switched buck converter
“gain” in kiloHertz per volt of V,N and kHz
per amp of IO can be evaluated over the
specified ranges. A summary of these fol-
lows:
It may be necessary to use the highest gain
values to design the control loop compensation
for stability over all operating conditions. While
this may not optimize the loop transient re-
sponse for all operating loads, it will guarantee
stability over the extremes of line and load.
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