Flyback clamp snubbers design differences

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berni80

Joined: 28 Jun 2008
Posts: 46

01 Nov 2009 10:50 Flyback snubbers

Hi,

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

Which is the best for noise? Why?

Thanks!!

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dick_freebird

Joined: 04 Mar 2008
Posts: 312
Helped: 45
Location: USA

02 Nov 2009 1:53 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?

snafflekid

Joined: 09 May 2007
Posts: 120
Helped: 16
Location: USA

02 Nov 2009 7:41 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)

FvM

Joined: 22 Jan 2008
Posts: 5161
Helped: 767
Location: Bochum, Germany

02 Nov 2009 8:27 Re: Flyback snubbers

Quote:

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.