Answer 8—The basic voltage rating of the transistors must be greater than two times the input voltage, because when one end of the primary is pulled to ground, the other end swings up from the supply voltage by the same amount through basic autotransformer action.

Furthermore, any “leakage” inductance—less than 100% mutual coupling between the two halves of the primary—will cause inductive spikes above that nominal peak value when each transistor switches off. There needs to be a way of clamping or snubbing these spikes.

Contributor: David Tweed