Download common collector amplifier

EXPERIMENT 2
Common Colector Amplifier
EENG-251-01
Electronics 2 Lap
Instructor: Vraka Maria
Author Name:
Leandrou Vasilis
School of Sciences and Engineering
Department of Engineering
University of Nicosia
Nicosia, Cyprus
Table of Contents
OBJECTIVES ..................................................................................................................... 1
BACKGROUND THEORY ............................................................................................... 1
EQUIPMENT and COMPONENTS USED .........................................................................
EXPERIMENTAL METHOD AND PROCEDURE ......................................................... 3
Part 1 ................................................................................................................................... 3
Part 3....................................................................................................................................5
Part 4....................................................................................................................................6
DATA ................................................................................................................................. 8
Data discussion ............................................................................................................... 9
Error Analysis ................................................................................................................. 9
CONCLUSIONS............................................................................................................... 10
ii
OBJECTIVES
This report aims to:

First purpose is to count the open circuit voltage gain, input and output resistance
of the common collector amplifier.

To consider the common collector amplifier by using the small signal equivalent
model.

Show the use of the common collector as a buffer between a high impedance
source and a law impedance load.
BACKGROUND THEORY
The common collector amplifier is very important to the BJT because it has very high
input resistance, high current gain, very small output resistance and approximately unity
voltage gain that make the emitter follower an ideal buffer between a high impedance
source and a low impedance load.
A small signal ac equivalent circuit can be use to calculate the gain, input and output
resistance of the common collector amplifier. The open circuit voltage gain Av of the
emitter follower amplifier can be calculate by using the equation
The input resistance rin, can be calculate bu using the equation
1
rin= R1// R2// β(re + RE // rs)
The output resistance rout can be calculate by using the equation:
rout= RE// (re+(R1//R2// rs) / β)
EQUIPMENT and COMPONENTS USED

2N2222 silicon transistor

DC power supply

Analog signal generator

Resistors: 1-100kΩ, 2-47kΩ, 1-12kΩ, 1-10kΩ, 1-1kΩ, 1-470MΩ

Capacitors: 2-10μF

Potentiometers: 1-50kΩ, 1-200kΩ

Dual Trace Oscilloscope
2
EXPERIMENTAL METHOD AND PROCEDURE
Part 1
The following circuit was connected in order to determine the β of the transistor.
RB
RC
VRC
VBE
Fig 1 β circuit
The voltage across the collector resistor VRC and the based to emitter voltage VBE was
measured. The β was calculated using the following formula:
VRC = 7.28V
VBE =0.63V
β=
( VRC )( RB )
( RC )( VCC - VBE )
3
β=
7.28x1.51MΩ . =162hfe
4.7KΩx(15-0.63)
The measurement of β was found 157hfe.
For the second transistor:
VRC = 2.96V
VBE =0.61V
β=
2.96x1.51MΩ . =66hfe
4.7KΩx(15-0.61)
The measurement of β was found 60hfe.
Part 2
The following circuit was connected to measure the voltage gain Av, input resistance rin
and the output resistance rout of the common collector amplifier.
.
fiq 2 common collector amplifier
4
The signal generators frequency was set to 10 KHz and then was adjusted until
Vo= 0.1Vp-p. The input voltage vin was measured and the phase relationship vin and
Vo. The open circuit voltage Av is Vo / vin.
vin = 34.7mV
Vo = 35.4mV
Av = 1.02
To measure the output resistance rout, a 200 Ω potentiometer was connected as a
rheostat between the output capacitor and the ground. The potentiometer was adjusted
until the Vo was 0.5m Vp-p. Then the potentiometer was removed and measured.
rout= 7.1 Ω
To measure the input resistance rin, the signal generator was reconnected and 50KΩ
potentiometer was connected as a rheostat between the input capacitor and the signal
generator. The potentiometer was adjusted until vL = 0.5mVp-p. Then the potentiometer
was removed and measured.
rin= 7.31KΩ
5
Part 3
The following circuit was connected to demonstrate the effect of loading on a common
emitter amplifier.
Fiq 3 effects of loading
Vs was set 0.1Vp-p at 10 kHz. VL was measured and VL / Vs were calculated.
vL = 15.5mV
vS= 35.35mV
vL / vS= 0.43
6
Part 4
The following circuit was connected to demonstrate the use of a common collector stage
to a buffer a low impedance load from high output resistance of the common emitter
amplifier.
Fiq 4 common collector stage to buffer
Vs was set 0.1Vp-p at 10 kHz. VL was measured and VL / Vs were calculated.
vL = 0.305V
vS= 35.35mV
vL / vS= 8.62
7
DATA
At part 1
β1= 162hfe
β2= 66hfe
At part 2
vin = 34.7mV
Vo = 35.4mV
Av = 1.02
rout= 7.1 Ω
rin= 7.31KΩ
At part 3
vL = 15.5mV
vS= 35.35mV
vL / vS= 0.43
At part 4
vL = 0.305V
vS= 35.35mV
vL / vS= 8.62
8
Data discussion
The common collector amplifier is very important to the BJT because it has very high
input resistance rin= 7.31KΩ, high current gain, very small output resistance rout= 7.1 Ω
and approximately unity voltage gain Av = 1.02 that make the emitter follower an ideal
buffer between a high impedance source and a low impedance load.
When we demonstrate the effects of loading common emitter amplifier the vL / vS= 0.43
but when we demonstrate the use of a common collector stage to a buffer a low
impedance load from high output resistance of the common emitter amplifier vL / vS=
8.62
Error Analysis
Theoretical
Measured
% Error
Av
1.18
1.02
13.55
VL/VS
0.45
0.43
4.4%
9
CONCLUSIONS
The open circuit voltage gain, input and output resistance of the common collector
amplifier were measured.
The use of the common collector as a buffer between a high impedance source and a law
impedance load was demonstrated.
The common collector amplifier is very important to the BJT because it has very high
input resistance rin= 7.31KΩ, high current gain, very small output resistance rout= 7.1 Ω
and approximately unity voltage gain Av = 1.02 that make the emitter follower an ideal
buffer between a high impedance source and a low impedance load.
When we demonstrate the effects of loading common emitter amplifier the vL / vS= 0.43
but when we demonstrate the use of a common collector stage to a buffer a low
impedance load from high output resistance of the common emitter amplifier vL / vS=
8.62
To measure the input resistance rin, the signal generator was reconnected and 200Ω
potentiometer was connected as a rheostat between the input capacitor and the signal
generator. The potentiometer was adjusted until the voltage is the half of vL.
To measure the output resistance rout, a 10 KΩ potentiometer was connected as a
rheostat between the output capacitor and the ground. The potentiometer was adjusted
until the voltage is the half of Vo.
10