3 _ Transistor Operation

Transistor Operation Tutorial

The forward biased base/emitter junction causes electrons to be attracted from the emitter area towards the base.
Arriving in the base area, most of the negative electrons come under the influence of the more positive collector and are attracted by it.
This is shown in the left hand drawing, where the base current plus collector current equals the emitter current.

Alpha gain is collector current divided by emitter current, and is always less than 1.
Beta gain is collector current divided by base current and can be a fairly high number.

Therefore, causing a small base current to flow makes a much larger collector current flow.
A small base current controls a large collector current.

There is 0.6 volts across the base/emitter junction, when it is forward biased. (0.3 volts for germanium).