Question Details

A BJT biasing circuit is shown in the figure, where VBE = 0.7 V and β = 100. The Quiescent Point values of VCE and IC are respectively

Options

A

4.6V and 2.46mA

B

3.5V and 2.46mA

C

2.61V and 3.13mA

D

4.6V and 3.13mA

Show Answer

Correct Answer :

Option A

4.6V and 2.46mA

Solution :

The correct option is 4.6V and 2.46mA.

Based on the provided BJT biasing circuit diagram, the parameters are:
Supply voltage, VCC=12 V
Base voltage-divider resistor, R1=100 kΩ
Base voltage-divider resistor, R2=50 kΩ
Collector resistor, RC=2 kΩ
Emitter resistor, RE=1 kΩ
Base-emitter voltage, VBE=0.7 V
Common-emitter current gain, ��=100

Step 1: Calculate the Thevenin equivalent voltage (Vth) and resistance (Rth) at the base:
The Thevenin voltage is determined by the voltage divider network at the base node:
Vth=VCC·R2R1+R2
Substituting the circuit values:
Vth=12·50100+50=12·50< 150=< 4\text{ V}
The Thevenin resistance is the parallel combination of the base resistors:
Rth=R1·R2R1+R2
Substituting the circuit values:
Rth=100·50100+50=500015033.33 kΩ

Step 2: Determine the base current (IB):
Applying Kirchhoff's Voltage Law (KVL) to the base-emitter loop:
Vth-IBRth-VBE-IERE=0
Since IE=(β+1)IB, we rewrite the relation to solve for IB:
IB=Vth-VBERth+(β+1)RE
Substituting the numerical parameters:
IB=4-0.733.33 kΩ+(100+1)·1 kΩ=3.3134.33 kΩ24.57 μA

Step 3: Calculate the collector current (IC):
Using the relationship between collector current and base current in the active region:
IC=β·IB
IC=100·24.57 μA=2.457 mA2.46 mA

Step 4: Calculate the collector-emitter voltage (VCE):
First, find the emitter current (IE):
IE=(β+1)IB=101·24.57 μA2.48 mA
Applying KVL around the collector-emitter output loop:
VCC-ICRC-VCE-IERE=0
Rearranging to solve for VCE:
VCE=VCC-ICRC-IERE
Substituting the parameters and calculated current values:
VCE=12-(2.46 mA·2 kΩ)-(2.48 mA·1 kΩ)
VCE=12-4.92-2.48=4.6 V

Therefore, the Quiescent Point values are VCE=4.6 V and IC=2.46 mA.

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