Lab
04
Bipolar Junction Transistor
Prepared By:
Fakulti Kejuruteraan Mekanikal, UMP
Lab Instructor
Lab Location
MAKMAL FKM MF12L12
Lab Objectives
By the end of this lab, students should be able to:
1. Analyze NPN BJT circuit
20
10
Student names
Student ID
Section
1.0
Bipolar Junction Transistor
In this lab, we are going to study the principle of transistor. Specifically, we are going to investigate
the operation of NPN bipolar junction transistor (BJT).
BJT is a current controlling device. By controlling the amount of small
input current, BJT controls the amount of high current flowing through
load. It has three terminals: base terminal, collector terminal and
emitter terminal as shown in Figure 1.
The small current (called based current) enters through the based
terminal. This causes the gate to be opened. Once the gate is
opened, current can flow from collector to emitter. The amount of
current flow (called collector current) is depending on the BJT
operation modes. The collector current can be cut-offed, amplified or
maintained at constant value.
We are going to experiment on BJT and observe the above principles.
2.0
Figure 1
Experiment – NPN BJT
In our experiment, we are going to analyze a BJT circuit for three different operating modes: cutoff
mode, amplifying mode and saturation mode. Our experimental circuit is shown below.
C
B
Figure 2
Notice the base, collector and emitter terminals of the BJT as shown in Figures 2 and 3. You must
ensure that the correct terminal is connected to the correct component. The physical diagram of
MPS 2222A BJT is shown at the right.
C
B
E
Figure 3
Equipment and Components
1.
2.
3.
4.
5.
6.
DC power supply with two voltage channel
Multi-meter
One BJT
One 1.5 K-Ohm resistor (quarter watt)
One 10 K-Ohm resistor (quarter watt)
One 100 K-Ohm resistor (half watt)
Experiment Steps
1.
Vin
(volts
)
0.00
1.00
2.00
4.00
8.00
Build the circuit according to the circuit diagram in Figure 2. Using a multi-meter, measure the
currents and voltages by filling-up the table below.
VRb
(volts)
VBE
(volts)
ib
(mA)
ic
(mA)
VRL
(volts)
VCE
(volts)
h fe 
iC
iB
VRb  VBE VRL  VCE
(volts)
(volts)
Vout
(volts)
10.00
2.
Vin
(volts
)
Build the circuit according to the circuit diagram in Figure 3. Using a multi-meter, measure the
currents and voltages by filling-up the table below.
VRb
(volts)
VBE
(volts)
ib
(mA)
ic
(mA)
VRL
(volts)
VCE
(volts)
h fe 
iC
iB
VRb  VBE VRL  VCE
(volts)
(volts)
Vout
(volts)
0.00
1.00
2.00
4.00
8.00
10.00
3.
Plot the graph of base current ( ib ) versus collector current ( ic ) in Table 1 and table 2. Identify
on the graph the region of the three operation modes. Note: when you plot the data use
based current as x-axis and collector current as y-axis. However, you should rotate you plot 90
degree so that you can have x-axis scale longer than the y-axis.
What is the range of Vb that causes the BJT to operate at cut-off mode? What is the range of ib
that causes the BJT to operate at cut-off mode? What is the minimum voltage that breaks the cutoff mode?
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References
1.
Giorgio Rizzoni, 2004. Principles and Applications of Electrical Engineering, Revised Fourth
Edition, McGraw Hill Inc.