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Flyback clamp snubbers design differences

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Jun 28, 2008
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Flyback snubbers


which is the difference (advantages/disadvantages) between these two clamp snubber?

Which is the best for noise? Why?


Flyback snubbers

The one on the left is probably going to be quieter and more
efficient because it soaks up high dV/dt (in the cap) but
never hard-clips the voltage (at full current?). The one on
the right will hard conduct at any DC / pulse voltage greater
than the stack.

Question is, are you trying to kill ringing / EMI, or are
you really wanting to clip overvoltage?

Flyback snubbers

Left circuit has softer reset waveform, RC resonates with the leakage inductance of the transformer. Right clamps the voltage spike and has more EMI (why the Zener diode is necessary I don't know)

Re: Flyback snubbers

why the Zener diode is necessary I don't know
It's flyback topology, wthout the zener, you would cut the output voltage.

As a problem, the leakage inductance energy depends on converter output current, the RCD snubber creates permanent
losses even with no output load. Some designs are also combining RCD and zener snubber, the latter only taking effect under
full load conditions. A tricky variant of the RCD snubber is using a slow recovery diode to recover part of the capacitor stored energy.

Re: Flyback snubbers

dick_freebird said:
Question is, are you trying to kill ringing / EMI, or are
you really wanting to clip overvoltage?


hey friends
i too have the same doubt how zener and diode combination works as snubber...
if u find material on this please send to me
i think RCD combination gives better solution. for flyback dc converters is snubber for transformer is enough or do we need across switching device/?
clarify my doubts......
i got confused with this snubber circuit design...
if any body good in designing snubber circuits, please mail me
thank u

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