Hi Elias,

I believe it is more than one. The main sharp gradient I think is the collapsing magnetic field in the coil.

Hitting a battery directly with that through the diode from the bottom of the coil (collector) may be another sharp gradient...maybe not as sharp as the collapsing field. Or if charging caps, the caps discharging to a battery could be considered a sharp gradient.

Sharp gradients seem to simply produce a much stronger potential difference getting a stronger influx of the virtual photon potential to move towards the different "poles."

Possibly every fast off/on in the transistor could be a sharp gradient...every off/on of a diode may be a sharp gradient...each and every single one probably collectively adds to the potential in the circuit.