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Understand the Joule Thief Circuit

I quote from Wikipedia (https://en.wikipedia.org/wiki/Joule_thief): ... This self-stroking/positive-feedback process almost instantly turns the transistor on as hard as possible (putting it in the

This self-stroking/positive-feedback process almost instantly turns the transistor on as hard as possible ( putting it in the saturation region), making the collector-emitter path look like essentially a closed switch ( since VCE will be only about 0.1 volts, assuming that the base current is high enough). Due to this positive feedback, the transistor is turned on so hard that its collector voltage can't go any lower, usually about 200 mV. One of two things happen: The current levels off due to the inherent equivalent series resistance of the primary winding, or the the transformer core magnetically saturates.

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