Question

Explain the function of base region of a transistor. Why is this region made thin and lightly doped?
Draw a circuit diagram to study the input and output characteristics of n-p-n transistor in a common emitter (CE) configuration. Show these characteristics graphically. Explain how current amplification factor of the transistor is calculated using output characteristics.

Solution

The base provides proper interaction between the charge carriers of emitter and collector. The flow of majority charge carriers from emitter to the collector is controlled by the base of a transistor.
When the emitter is forward biased, electrons and holes recombination process occurs in the base region.
If the base is thin and lightly doped, it will have a small number density of majority charge carriers. This reduces the rate of electron hole recombination, which is necessary for a transistor action.

A circuit for drawing the input and output characteristics of an n-p-n transistor is shown in figure below:

The corresponding input and output characteristics are also shown graphically:

The variation of current on the input side with input voltage (I_B versus V_BE) is known as input characteristics, while the variation in the output current with output voltage (I_cversus V_CE) is known as output characteristics.

Current amplification factor of the transistor ( $β_{ac}$ ) - The ratio of change in collector current to the change in base current when, the collector-emitter voltage (V_CE) is constant. The transistor is in active state.

Therefore,
$β_{ac} = \frac{∆ I_{c}}{∆ I_{B}}$

As seen in the graph, we can say that, I_c is increasing almost linearly with I_B.

For Daily Free Study Material Join wiredfaculty

Wave Optics

Some More Questions From Wave Optics Chapter

Mock Test Series

NCERT Sample Papers

Entrance Exams Preparation

Phone Number

Email Address

Location