see also

• Diode Commutation Experiments
• "kickback is your friend. It is the thing that produces your output voltage. ... The correct way to reduce the kickback voltage of the coil ... is with a C across the primary, just like on an old 'points' ignition system. This will store the excess energy and release it to the secondary if there is a spark."
  • however, "capacitors turn voltage glitches into current glitches".
  • "There is a diode in series with the capacitor, so that it could never discharge back through the IGBT when it turns ON. The problem then becomes: what to do with the energy in this capacitor? A typical snubber places a resistor in parallel with this capacitor to drain off the charge. In this case, we are basically shifting the IGBT losses to power dissipated in this resistor. The nice thing is that we can locate said resistor remotely, but still, we have to get rid of that heat. My approach is to, instead, make use of this energy stored in the snubber capacitor. Basically, this capacitor becomes the "power supply" for another small boost converter."
  • "While the values can be optimised for the application, a 100 ohm resistor in series with a 100 nanofarad capacitor of appropriate voltage rating is usually effective. This type of snubber is often manufactured as a single component."
  • What is the effect of too large of a capacitor?
    It lowers the secondary voltage.
    What is the effect of too small of a capacitor?
    It results in destructive arcing at the points.
• you don't always need the freewheeling diode though?