A DRSSTC plus a supply that ramps the bus voltage up over the burst. The topload voltage is low early, so a small coil does not flash over. Later the arcs are long and straight, usually more than ten times the winding. Everything on the records wall descends from this idea. The branches below are the ways of making the ramp.
Sources
This is the card from the driver tree, written from what the builder published. Send corrections through the forum.