shows that a small RC snubber connected across the mosfet switching device can
eliminate the turn off ringing. The oscilloscope trace for an unsuppressed clamped
coil B is shown in fig 2.
2. Unsuppressed turn off transient.
the ringing is very pronounced and could interfere with circuitry. The effect
of the addition of a RC snubber can be seen in fig 3.
3. Turn off ringing almost eliminated.
the size of the resistor and increasing the value of the capacitor completely
removes the ringing as shown in fig 4.
4. Ringing eliminated by snubber.
this small snubber can remove the ringing we are still left with the large overshoot.
In fact the snubber appears to have no significant effect on the shape of the
overshoot. In order to reduce the overshoot we would require a much larger snubber
and this could impact the switching time for the mosfet. The overshoot is most
likely a consequence of the slow recovery of the rectifier type commutating diode.
Using a 'fast' diode may improve the situation.
overshoot is very short and is well within the avalanche capability of the mosfet
module, however, the waveform still contains sharp voltage transitions which could
be capacitively coupled into sensitive circuitry.