I have a quibble regarding the simulation model and some of the graphical responses depicted
here. Two of the graphs depict a
sharp change in the transfer function, somewhere in the vicinity of 0.8 volts at the emitter-base junction. This
sharp transition point on the graph does not occur with real devices. I suspect this
sharp change is caused by something changing abruptly in the software model, because in the REAL world the only thing that exhibits such a
sharp change are devices with internal mechanisms like positive feedback and quantum-mechanical tunneling. The BJT has neither of those "baked in" to its design.
To his credit,
@danadak did provide a close-up view, in his post #56, of the collector current as a function of the base-emitter voltage from about 0.1V forward bias to about -0.3V reverse bias. Nary a sharp corner in sight, which agrees with theory (Ebers-Moll) and experimental measurements. From 0.0V to -0.3V reverse bias, only reverse saturation current occurs, right up until the reverse bias "punches through" the thin depletion layer.
Punch-through isn't shown on that graph, and of course you never want to deliberately reverse-bias the base-emitter junction, lest you destroy that junction and the transistor... well, maybe you could salvage the base-collector terminals for use as a small-signal diode... Nah. That's an old "trick" from the 1950s when transistors were veeery expensive, too expensive to discard just because someone hooked up the voltage with the wrong polarity. <sigh> Don't even ask how I know this.
Well, I should say "almost never" because someone will no-doubt find a working example where large reverse-bias, and signal excursions leading to a reverse-biased base-emitter junctions, occur deliberately... maybe while trying to emulate an over-driven vacuum tube guitar amplifier stage. There are folks on this forum (who haven't spoken yet) who make amplifiers (usually guitar amps) that deliberately distort their audio frequency inputs. And of course commercial foot-operated "stomp boxes" are used by virtually ALL real rock-and-roll ensembles (bands to most follks, but sometimes accompanied by full orchestras with music sheets and such) to modify the sound of their musical instruments.
