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slow diode in SMPS snubber

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snubber design for smps

heres and smps RCD snubber for flyback offline but the diode is a slow IN4007

isn't that against the rules of smps...ie this diode is too slow?

dexmc5.jpg
 


smps snubber application note

a lossless charge recovery takes place
Click to expand...
It seems to improve efficiency by a percent or 2 and best of all uses inexpensive parts.
Click to expand...
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.
 

diode snubber

FvM:- I see what you mean..but i thought this diode had to turn on super fast before the turn off spike builds up real high ?

...hence a 1N4007 would be inadequate ?
 

flyback snubber diode reverse recovery time

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.
 

smps slow

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 ?

...we need to nip it in the bud extreme quickly ?
 

snubber circuit for smps

larrymeares said:
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.

see https://ieeexplore.ieee.org/Xplore/login.jsp?url=/iel5/4448710/4448711/04448797.pdf?arnumber=4448797

for technical details.

It seems to improve efficiency by a percent or 2 and best of all uses inexpensive parts. The technique also works for MOSFET gate drives.
Click to expand...

Nice info, do you have such paper on your hand?

Thanks in advance
Pow
 

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