The University Of Asia PacificDepartment of Computer Science & Engineering

ECE 202

Experiment No: 05

Name of the Experiment : Study of N-P-N Common Emitter Transistor.

Objective: To determine the input and the output characteristics of an N-P-N transistor in Common Emitter (CE) configuration. Theory:Transistor has two p-n junctions, one is called the emitter junction an other is called the collector junction. When transistor is used as an amplifier, it is operated in active mode. In active mode, emitter junction is forward biased and collector junction is reverse biased.

Figure: 1

Emitter current is given by, IE = IB + IC = [(1+)/] IC

Where, = IC / IB is called common emitter gain.In good transistor IC>>IB i.e, >>1. IC can also be expressed as IC = IB

where, = /(1+). is called common base current gain. For good transistor, is close to unity.

Proper dc biasing of a transistor is a prerequisite for proper operation as an amplifier. The purpose of the biasing is to fix the IC (dc) and VCE (dc). But IC is a function of temperature, VBE and . It is desirable to design a biasing circuit where IC is insensitive to change in .

When E-B junction is forward biased and C-B junction is reverse biased, the transistor operates in active mode. For saturation mode of operation, both junction are forward-biased. Cut-off region operation requires that both E-B and C-B junctions be reverse biased. The inverted active operation occurs when E-B is reverse biased and C-B is forward biased.

Equipments: n-p-n transistor (c829) one piece Reesistor (2K, 1K, 500 , 100 ) Multimeter Bread board

1K 100K + VRB - +VBE- +VCE-+VRC-

Circuit Diagrams:

Figure: 2 Common Emitter Configuration

Procedure:1. Connect the circuit as shown in fig.2.2. First set Vcc = 10V. Apply voltage to B-E junction. Adjust the value of VCC so that

VCE is zero. Vary VBB and measure VBE for different values of IB.

3. Repeat the above experiment for VCE = 1 Volt.4. Vary VBB so that IB is about 10 A. Vary VCE in steps of 2.5 volts and measure VCE

and IC.

5. Repeat the experiment for IB = 20 A and 30 A. Simultion:

Simulate the input and output characteristics curve of circuit shown in fig. 2 using Pspice Text Editor.

(Submit the report part at the Lab)

Course No: ECE 202 Expt. No: 05Registration No: Semester: Roll No: Date:

Report:

Data:

1 Plot output and input characteristics of the n-p-n CE transistors in the graph paper and a) Mark active, saturation and cut-off regions of the characteristics.b) Calculate the early voltage from the output characteristics.

c) Discuss the effect of changing VCE on the input characteristics.

d) Discuss the effect of changing on the output characteristics.

2. What are the role of the 2K and 1K fixed resistors in the circuits ?.

3. Write the Pspice Text Editor program used to simulate the input and output characteristics curve of circuit shown in fig. 2.

4. Discussion: