I saw this practice in China several years ago. Evidently the long recovery time keeps the snubber connected to the input and a lossless charge recovery takes place.
Good analysis. Powertint seems to have copied the method for their LinkSwitch-II application - without explaining the operation principle. In older applications notes, they used a classical RCD snubber (a fast recovery diode without a series resistor).
You should consider, that the snubber purpose isn't effective energy transfer to a load but reduction of overvoltage from transformer leak inductance. If you can recover some of the energy temporarily stored in the snubber capacitor, you improve the efficiency.
A super fast diode doesn't turn on considerably faster than a standard diode. The difference is in reverse-recovery respectively turn-off. And there is no need for extra fast turn-on with a snubber.
thankyou FvM, though considering a flyback, , when the mosfet is switched off, an inductive current has been immediately broken.....and therefore the voltage on the drain will start building masively high.....
......surely one needs the snubber diode to come on absolutely as fast as possible...?.....otherwise, how do we stop this massively building drain voltage ?
I saw this practice in China several years ago. Evidently the long recovery time keeps the snubber connected to the input and a lossless charge recovery takes place.