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EKT 102 / Basic Electronic Engineering
EXPERIMENT 5
CURRENT AND VOLTAGE
CHARACTERISTICS OF BJT
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EKT 102 / Basic Electronic Engineering
EXPERIMENT 5
Current and Voltage Characteristics of BJT
1.
2.
OBJECTIVES:
1.
To practice how to test NPN and PNP transistors using a multimeter.
2.
To demonstrate the relationship between collector current (IC) and base
current (IB).
3.
To provide the opportunity for plotting the output characteristic curves for a
transistor using measured component values.
INTRODUCTION:
PART A: Testing Transistor Diode Junction
Basically, a bipolar (BJT) transistor can be represented internally by two diode or p-n
junctions. Consequently, a multimeter can be used to check each diode junction, as was
done in Experiment 2. If we know the three terminals, then it is possible to determine if a
given transistor is NPN or PNP bipolar transistor.
Figure 1 Schematic diagram of circuit
PART B : Current and Voltage Characteristics of BJT
The ratio of the dc collector current ( IC) to the dc base current (IB) is the dc beta () which is
the dc current gain of transistor is
β=
IC
IB
(5.1)
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EKT 102 / Basic Electronic Engineering
The voltage across R1 can be calculated by Ohm’s Law
V1 = IBR1
Where IB is dc base current.
3.
COMPONENT AND EQUIPMENT:
PART A: Testing Transistor Diode Junction
1
2
3
4
2N3904 NPN transistor
2N3906 PNP transistor
Multimeter
Breadboard
PART B: Current and Voltage Characteristics of BJT
1
2
3
4
5
100 kΩ resistor
2N3904 NPN transistor
DC power supply
Multimeter
Breadboard, wires
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(5.2)
EKT 102 / Basic Electronic Engineering
4.
PROCEDURE:
PART A: Testing Transistor Diode Junction
1. Testing 2N3904 NPN junction with an ohm-meter:
i.
The schematic diagram and diode junction represented are shown in
Figure
Figure 2
ii.
iii.
iv.
Pin configurations of 2N3904 transistors
Take your multimeter and select a low-resistance meter range (x10)
Connect the meter’s positive lead to the transistor’s base lead, with the
meter’s negative lead connected to the transistor’s emitter lead.
Record the display reading.
(NOTE: You have forward biased the transistor’s base-emitter diodes junction.)
v.
vi.
vii.
viii.
ix.
x.
xi.
xii.
xiii.
xiv.
Now, reverse the meter’s leads so that the positive lead is connected to
the emitter and the negative lead is connected to the base.
Record the display reading.
Connect the meter’s positive lead to the base and the negative lead to the
transistor’s collector lead.
Record the display reading.
Reverse the meter’s leads so that the positive lead is connected to the
collector and the negative lead is connected to the base.
Record the display reading.
Connect the meter’s positive lead to the collector the negative lead to the
transistor’s emitter lead.
Record the display reading.
Reverse the meter’s leads so that the positive lead is connected to the
emitter and the negative lead is connected to the collector.
Record the display reading.
(NOTE: If transistor diode junction was forward biased, you should have
obtained a value between 0.5Ω and 0.8Ω and if the transistor diode junction
was reverse biased, the transistor would be in an “open-circuit” condition).
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EKT 102 / Basic Electronic Engineering
2. Testing 2N3906 PNP junction with an ohm-meter:
xv.
The schematic diagram and diode junction represented are shown in
Figure 3.
Figure 3
Pin configuration of 2N3906 transistors
xvi.
Take your multimeter and select a low-resistance meter range (x10).
Connect the meter’s positive lead to the transistor’s base lead and the
negative lead to the transistor’s emitter lead.
Record the display reading.
xvii.
Reverse the meter’s leads so that the positive lead is connected to the
emitter and negative lead is connected to the base.
Record the display reading.
xviii.
Connect the meter’s positive lead to the base and the negative lead to the
transistor’s collector lead.
Record the display reading.
xix.
Reverse the meter’s leads so that the positive lead is connected to the
collector and the negative lead is connected to the base.
Record the display reading.
xx.
Connect the meter’s positive lead to the collector and the negative lead to
the transistor’s emitter lead.
Record the display reading.
xxi.
Reverse the meter’s leads so that the positive lead is connected to the
emitter and the negative lead is connected to the collector.
Record the display reading.
xxii.
Compare the result of both transistors. Write your observations.
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EKT 102 / Basic Electronic Engineering
PART B : Current and Voltage Characteristics of BJT
1. Measure and record the actual resistance of your 100 kΩ resistor.
Figure 4
2. Construct the circuit shown in Figure 4 using 2N3904 transistor.
3. Both supply
voltages should initially be set to 0 V.
4. Calculate the value of V1 that is required to generate a current of 5 µA through R1.
5. Adjust VBB to obtain the value of V1 calculated in procedure 4.
6. Adjust VCC so that VCE is 0.5V.
7. Measure and record the value of IC.
8. Repeat step 5 for each of the values of VCE listed in Table 1. Using data, plot the
characteristic collector curves for the 2N3904.
9 . After completing the measurements in step 6 for IB = 5 µA, return VCE to 0 VDC.
Calculate the value of V1 that is required to generate a current of 10 µA through R1.
Adjust VBB to provide this value of V1.
10. Using the data recorded in Table 4 plot the characteristic collector curves for the
2N3904.
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EKT 102 / Basic Electronic Engineering
Lab Assignment 4
CURRENT AND VOLTAGE CHARACTERISTICS OF BJT
Name
:___________________________________
Matrix Number
:___________________________________
Programme
:___________________________________
Date
:___________________________________
Total marks:
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EKT 102 / Basic Electronic Engineering
PART A: Testing Transistor Diode Junction
1. Testing 2N3904 NPN junction with an ohm-meter
Step Number
Meter Lead (+)
Meter Lead (-)
Result
2. Testing 2N3906 NPN junction with an ohm-meter
Step Number
Meter Lead (+)
Meter Lead (-)
Result
PART B : Current and Voltage Characteristics of BJT
VCE (Vdc)
IB (µA)
+0.5
+1
+5
+10
5
10
20
30
40
50
Table 1 : Value of IC
**Note : Plot on GRAPH paper
8
+15
+20
EKT 102 / Basic Electronic Engineering
From the graph, make some discussion regarding the current and voltage characteristic of
BJT.
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