Transistor Action or Working of Transistor

A brief description of the three segments of a transistor is given below:

1. Emitter: This is the segment on one side of the transistor. It is of moderate size and heavily doped. It supplies a large number of majority carriers for the current flow through the transistor.
2. Base: This is the central segment. It is very thin and lightly doped.
3. Collector: This segment collects a major portion of the majority carriers supplied by the emitter. The collector side is moderately doped and larger in size as compared to the emitter.

p-n-p Transistor:

From given fig., we can see that, the emitter-base junction is forward biased. Collector-base junction is reverse biased.

The resistance of emitter-base junction is very low so the voltage of V_ee (V_eb) is quite small (i.e., 1.5 V). the current in p-n-p transistor is carried by holes and at the same time their concentration maintained But in external circuit the current is due to flow of electrons.

I_e = emitter current

I_b = base current

I_c = collector current

n-p-n Transistor:

In the base, I_e and I_c flow in opposite direction. In this transistor, the emitter-base junction is forward biased and its resistance is very low. So, the voltage of V_EE is quite small. The collector base junction is reverse biased. The resistance of this junction is very high. So, the voltage of V_CC (V_CB) is quite large (45 V). In n-p-n transistor, the current is carried inside as well as in external circuit by the electrons. Thus, in this case also,

In the base, I_e and I_c flow in opposite direction.