Download Voltage_current characteristics of BJT

Electronic I (DMT 121)
Laboratory Module
Exp. 5
EXPERIMENT 5
Current and Voltage Characteristics of BJT
1.
OBJECTIVE:
1.1
1.2
1.3
2.
To practice how to test NPN and PNP transistors using a multimeter.
To demonstrate the relationship between collector current (IC) and base
current (IB).
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 6.1 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
(6.1)
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Electronic I (DMT 121)
Laboratory Module
Exp. 5
The voltage across R1 can be calculated by Ohm’s Law
V1 = IBR1
(6.2)
Where IB is dc base current.
3.
COMPONENT AND EQUIPMENT:
PART A : Testing Transistor Diode Junction
3.1
3.2
3.3
3.4
2N3904 NPN transistor
2N3906 PNP transistor
Multimeter
Breadboard
PART B : Current and Voltage Characteristics of BJT
3.1
3.2
3.3
3.4
3.5
4.
100 kΩ resistor
2N3904 NPN transistor
Two dc power supply
Two multimeter
Breadboard, wires
PROCEDURE:
PART A : Testing Transistor Diode Junction
4.1 Measuring Voltage across 2N3904 NPN transistor junction:
4.1.1 The schematic diagram and diode junction represented are shown in
Figure 6.2.
Figure 6.2
4.1.2
4.1.3
Pin configuration of 2N3904 transistors
Take your multimeter and select a low-resistance meter range.
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.
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Electronic I (DMT 121)
Laboratory Module
Exp. 5
(NOTE: You have forward biased the transistor’s base-emitter diodes junction.)
4.1.4
4.1.5
4.1.6
4.1.7
4.1.8
4.1.9
4.1.10
4.1.11
4.1.12
4.1.13
4.1.14
Record the display reading in Table 6.1.
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 in Table 6.1.
Then, connect the meter’s positive lead to the base and the negative
lead to the transistor’s collector lead.
Record your result in Table 6.1.
After that, 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 result in Table 6.1.
Now connect the meter’s positive lead to the collector the negative lead
to the transistor’s emitter lead.
Note and record this value in Table 6.1.
Then, 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 this value inTable 6.1.
(NOTE: If transistor diode junction was forward biased, you should have
obtained a value between 0.5 and 0.8 and if the transistor diode junction was
reverse biased, the transistor would be in an “open-circuit” condition).
4.2
Measuring Voltage across 2N3906 PNP transistor junction:
4.2.1 The schematic diagram and diode junction represented are shown in
Figure 6.3.
Figure 6.3
4.2.3
4.2.5
4.2.6
4.2.7
4.2.8
4.2.9
Pin configuration of 2N3906 transistors
Take your multimeter and select a low-resistance meter range.
Now, connect the meter’s positive lead to the transistor’s base lead and
the negative lead to the transistor’s emitter lead.
Record your result in Table 6.2.
Then, reverse the meter’s leads so that the positive lead is connected to
the emitter and negative lead is connected to the base.
Note the meter reading, and record the result in Table 6.2.
Then connect the meter’s positive lead to the base and the negative
lead to the transistor’s collector lead.
Record your result in Table 6.2.
After that, reverse the meter’s leads so that the positive lead is
connected to the collector and the negative lead is connected to the
base.
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Electronic I (DMT 121)
Laboratory Module
Exp. 5
4.2.10 Record the result in Table 6.2.
4.2.11 Now, connect the meter’s positive lead to the collector and the negative
lead to the transistor’s emitter lead.
4.2.12 Note the meter reading, and record this result in Table 6.2.
4.2.13 After that, reverse the meter’s leads so that the positive lead is
connected to the emitter and the negative lead is connected to the
collector.
4.2.14 Note the meter reading, and record this result in Table 6.2.
4.3
Compare the result of Table 6.1 and Table 6.2.Write your observations.
PART B : Current and Voltage Characteristics of BJT
4.1 Measure and record the actual resistance of your 100 kΩ resistor.
Figure 6.4
4.2
4.3
4.4
4.5
4.6
4.7
4.8
4.9
4.10
4.11
4.12
Construct the circuit shown in Figure 6.4. Both supply voltages should initially
be set to 0 VDC.
Calculate the value of V1 that is required to generate a current of 5 µA through
R1.
Adjust VBB to obtain the value of V1 calculated in Step 4.3.
Adjust VCC so that VCE is 0.5 VDC.
Measure and record the value of IC in appropriate space in Table 6.3.
Increase VCC to provide a VCE of 1 VDC. Measure and record the corresponding
value of IC in Table 6.3.
Repeat step 4.7 for each of the values of VCE listed in Table 6.3.
After completing the measurements in step 4.8 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.
Repeat steps 4.5 through 8 for IB = 10 µA.
Repeat steps 4.5 through 4.10 until Table 6.3 is complete.
Using the data recorded in Table 6.3, plot the characteristic collector curves for
the 2N3904 in the space provided in Figure 6.5
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Electronic I (DMT 121)
Laboratory Module
Exp. 5
Name
: ______________________________
Date : ______________
Matric No.:______________________________
5.
Course : ______________
RESULTS:
PART A : Testing Transistor Diode Junction
Table 6.1
Step Number
2N3904 NPN Transistor
Meter Leads
+
-
4.1.4
Base
Emitter
4.1.5
Emitter
Base
4.1.7
Base
Collector
4.1.9
Collector
Base
4.1.11
Collector
Emitter
4.1.13
Emitter
Collector
Table 6.2
Step Number
2N3906 PNP Transistor
Meter Leads
+
-
4.2.3
Base
Emitter
4.2.5
Emitter
Base
4.2.7
Base
Collector
4.2.9
Collector
Base
4.2.11
Collector
Emitter
4.2.13
Emitter
Collector
Instructor Approval :
Result
____________________
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Result
Date :
_____________
Electronic I (DMT 121)
Laboratory Module
Exp. 5
Name
: ______________________________
Date : ______________
Matric No.:______________________________
Course : ______________
PART B : Current and Voltage Characteristics of BJT
(1)
For Step 4.1 :
The value of R1 : ________________ Ω
(2)
For Step 4.3 :
The value of V1 : _______________ V
Table 6.3
VCE (Vdc)
IB (µA)
+0.5
+1
+5
+10
+15
+20
5
10
20
30
40
50
Instructor Approval :
____________________
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Date
:
_____________
Electronic I (DMT 121)
Laboratory Module
Exp. 5
Name
: ______________________________
Matric No.:______________________________
Date : ______________
Course : ______________
Figure 6.5
Instructor Approval :
____________________
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Date
:
_____________
Electronic I (DMT 121)
Laboratory Module
Exp. 5
Name
: ______________________________
Matric No.:______________________________
6.
CALCULATIONS:
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Date : ______________
Course : ______________
Electronic I (DMT 121)
Laboratory Module
Exp. 5
Name
: ______________________________
Date : ______________
Matric No.:______________________________
7.
Course : ______________
DISCUSSION
PART A : Testing Transistor Diode Junction
2.6V
0.7V
(a)
(b)
2.6V
(c)
0.7V
(d)
Figure 6.6
Again, a student used Digital Multimeter (DMM) to test the transistor as shown in Figure
6.6. From the testing, what type of the BJT transistor?
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Electronic I (DMT 121)
Laboratory Module
Exp. 5
Name
: ______________________________
Matric No.:______________________________
Date : ______________
Course : ______________
PART B : Current and Voltage Characteristics of BJT
1.
Troubleshooting problem
Figure 6.7
Again, a student wires the circuit as shown in Figure 6.7 and measures zero
volts for VCE . List up three possible problem?
2. Using the characteristic curves, predict the values of IC for each of the IB and
VCE combinations listed below.
IC =
_________________ when IB = 25 µA and VCE = 10 Vdc
IC =
_________________ when IB = 35 µA and VCE = 8 Vdc
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Electronic I (DMT 121)
Laboratory Module
Exp. 5
Name
: ______________________________
Matric No.:______________________________
8.
Date : ______________
Course : ______________
CONCLUSION:
Name the two variables that are plotted on a collector characteristic curve.
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