Figure 91. NPN Transistor Operation.

Electronic Principles
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The current flow in the external circuit is always due to the

movement of free electrons. Therefore, electrons flow from the

negative terminals of the supply batteries to the Ntype

emitter. This combined movement of electrons is known as

emitter current (IE).

Because electrons are the majority carriers in the N material.,

they will move through the N material emitter to the emitter

base junction. With this junction forward biased, electrons

continue on into the base region. Once the electrons are in the

base, which is a Ptype material, they become minority carriers.

Some of the electrons that move into the base recombine with

available holes, For each electron that recombines, another

electron moves out through the base lead as base current IB