snubber design

Discussion in 'General Electronics Chat' started by renju, Dec 18, 2009.

  1. renju

    Thread Starter New Member

    Feb 2, 2009
    any help there with snubber design? i wnt a snubber cct for MOSFET 2N 6766 for a 8A constant current source. input s 70V . i am getting ringing in the waveform across MOSFET. this MOSFET is used in push pull configuration with a transformer primary.
  2. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    It depends on the operating frequency.

    A typical 50Hz contact snubber uses 0.1uF + 100 Ohm.

    The capacitor should be of a suitable value so fast edges are passed to the resistor, but not too much of the base AC waveform.
  3. Duane P Wetick

    Senior Member

    Apr 23, 2009
    I think the 2N6766 N chan Mosfet has a free wheeling diode across D-S, so that will protect the semiconductor, so a suitable capacitor across the transformer winding will stop the ringing. The 0.1/100 RC may do the job, as Jenkins suggests. I would observe the damping with a scope, however, and add a MOV if any HV spikes are left over.

    Cheers, DPW [ Spent years making heaters out of op-amps.]
  4. lmartinez

    Active Member

    Mar 8, 2009
  5. S_lannan

    Active Member

    Jun 20, 2007
    for a push pull circuit an rc snubber across each switching fet works alright for me.

    as a rule of thumb i think usually the capacitor should be a 4 times larger than the output capacitance of the switching mosfet so try 2nf or so and start with a 100 ohm resistor and try smaller resistors too.