Question

In the following common emitter circuit, if β = 100, VCE = 7V, VBE = Negligible and RC = 2 kΩ, then IB is equal to

• (A) 0.01 mA
• (B) 0.04 mA
• (C) 0.02 mA
• (D) 0.03 mA

Answer 1

The Correct Option is B

Explanation:
Considering the output circuit, we have${\mathrm{V}}_{\mathrm{CC}}={\mathrm{i}}_{\mathrm{C}}{\mathrm{R}}_{\mathrm{C}}+{\mathrm{V}}_{\mathrm{CE}}$$i_C{R}_C=15-7=8V$Hence, $i_C=\frac{8}{R_C}=\frac{8}{2\times {10}^3}=4\mathrm{mA}$$i_B=\frac{I_C}{\beta }=\frac{4\times {10}^{-3}}{100}=0.04\mathrm{m}.\mathrm{A}$

Answer 2

A transistor is a three-terminal semiconductor device, also known as a bipolar junction transistor (BJT) because of two types of charge carrier electrons and holes.

There are three types of junction transistors

• n-p-n transistors: When a thin layer of p-type semiconductor is sandwiched between two thick layers of n-type semiconductor, we get a transistor known as an n-p-n transistor.
• p-n-p transistors: When a thin layer of n-type semiconductor is sandwiched between two thick layers of p-type semiconductor, we get a transistor known as a p-n-p transistor.

Since the transistor is a three-terminal device, it can be connected in a circuit in three different ways

• Common-emitter (CE) configuration
• Common-base (CB) configuration
• Common-collector (CC) configuration

Common-emitter (CE) Configuration

In this configuration, the emitter terminal of the transistor is common between the input and output circuit.

• The variation of base current I_B with the variation of base-emitter voltage V_BE at constant collector-emitter voltage V_CE is called the input characteristic of a transistor in a common-emitter configuration.
• The input characteristics in the common-emitter configuration are the same as that of the forward-biased junction diode.
• The variation of collector current I_C with the variation of collector-emitter voltage V_CE at constant base current I_B is called output characteristics of a transistor in common-emitter configuration

The relation between base current I_B, collector current I_C, and emitter current I_E of a transistor in a common emitter configuration is given by

I_E = I_B + I_C

The output voltage or collector voltage is given by

V_CE = V_CC + I_CR_C

Current gain of a common-emitter transistor is given by the ratio of collector current I_C to base current I_B i.e.

ꞵ = I_C / I_B