I was always under the impression that when the top switching device turns off, the inductor generates a large negative voltage because it wants to resist the change in flow of current. That's why the reverse biased freewheel diode is there in a asynchronous buck regulator, so the current can keep flowing.
How does the above circuit work then? The bottom PNP transistor, taking the place of the freewheel diode, cannot conduct current in that direction afaik. Current can flow emitter to ground but not from ground to emitter, can it ?
Although I'm not sure what I'm seeing here. There appears to be a dip below ground on the negative cycle. At first I thought this was the inductor's negative voltage spike, somehow being cut off by the transistor. But the same is happening on the positive cycle, with a little 'bulge' above VCC.
Could anyone enlighten me about how this works and what is happening?