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RCD reset
Dissipative type Clamp/Reset technical
Very low cost design of reset circuit with discrete components R, C and D
Max. operating duty could be slightly higher than 50% (up to 55~65%),
depending the magnetizing current reset by RC constant
Critical point:
• Higher consumption because the energy storage on “C” should dissipates by
passive component “R”
• The transformer volt/second balance should tradeoff by adjust the value of “C”
and “R” for Clamp/Reset
• In case VDS ≤ 2Vin but very possible higher than 2VIN in worst case at open
loop operating and max duty exceed 50%
• To avoid transformer saturation need to evaluate the Dset max of PWM in
case of short circuit
Forward Converter
The maximum voltage stress
the nominal snubber capacitor voltage
The snubber capacitor voltage is fixed and
almost independent of the input voltage, the
MOSFET voltage stress can be reduced
compared to the reset winding approach when
the converter is operated with a wide input
voltage range.
Another advantage of RCD reset method is
that it is possible to set the maximum duty
ratio larger than 50% with relatively low
voltage stress on MOSFET compared to
auxiliary winding reset method, which results
in reduced voltage stress on the secondary