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7/29/2019 Lab 9 transistor.docx
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DEPARTMENT OF BIOMEDICAL ENGINEERING
FACULTY OF ENGINEERING
UNIVERSITY MALAYA
Lab 9 : Transistor
Objective
1. To learn about the parameters of the transistor.2. To determine the characteristics of the transistor.
Introduction
Transistor is a semiconductor which has abilities to amplify, control and generate
signals. It is a device with three terminals/legs, which are base(B), collector(C), and
emitter(E). There are two types of transistors, which are bipolar junction
transistors(BJTs) and field-effect transistors(FETs). The bipolar junction transistors are
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divides into NPN and PNP type. The letters are referred to the type of the
semiconductor used to make each layer. N are the element from Group 15 in the
Periodic Table which are electrons rich group while the P are the element from Group
13 in the Periodic element which are electrons deficient group. The most common
materials used for making the layers of transistors are silicon, gallium-arsenide, and
germanium, into which the impurities had been introduced by a process called
doping process. The N-type transistor are the device which having excess of
electrons while for P-type transistor, it is having excess of holes of deficiency of
electrons.
There is a fundamental fact within the transistor. For a proper operational
transistor, its input is normally forward biased while its output is reversed biased. The
transistors are usually found embedded in the Integrated Circuit (IC) as it can carry
out various functions.
The figure shows the symbol of the transistor.
Equipments
1. 2 Power supplies2. 2 Digital Multimeter (DMM)
Materials
1. 1 BC141(T039) Transistor2. 1 47k resistor3. 1 1.2k resistor4. Connecting wires/Jumpers
Procedure
1.2k
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Figure 9.1 Transistor Test Circuit
1. The circuit is connected as shown in the Figure 9.1. The power supplies VCC andVBB should be at zero before turning on the power supply.
2. The power supply VCC is turned on but the VBB remains off. The VCC are graduallybeing increased its output until VCE reads 3V. The values of IC are being taken are
recorded. The voltage being measured is VCE and not VCC.
3. The values of VCC are continually being increased until VCE reads values of 5V, 10V,15V and 20V. In every case, the values of the IC are being taken and recorded.
4. The power supply of VCC is turned to zero while VBB are being turned on. Its valuesare increased until the values of IB read 10A.
5. The values of VCC are being adjusted so the VCE reads 3V, 5V, 10V, 15V, and 20V. Inevery case, the values of IC are measured in the same time the IB should be kept
constant at 10A.
6. Before repeat step 5, the IB is increased to 20A.7. The values of IB are now increased to 30A, 40A, 50A, 60A, and 70A. For
every values of IB, the step 5 is repeated as to measure the values of IB.
8. The results obtained are recorded into Table 1. A graph of IC versus VCE is plottedon a graph paper.
9. By referring the graph that had been drawn, a load line are drawn in the graphby select an appropriate point at the center of the graph and then draw a straight
line from VCC=20v, pass through the selected center point and the line are
extended to the x-axis. The transistor parameter defining this condition are:a) IBQfor the quiescent base currentb) ICQfor the quiescent collector currentc) VCEQfor the quiescent collector-emitter voltageThese values are read and recorded in the Table 2. These parameters are
important as it enable the calculation and set the transistor biasing necessary for
linear operation.
10.Alpha() and Beta() are two parameters that used to defining the DC currentgain of the transistor for the common-emitter configurations. From the collector
characteristics curves, Beta can be determined at the operating point by :
=IC/IB
47k
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11.To calculate the amplifier performance of the transistor, the transistorh-performance is arbitrarily defined values. They are derived from the collector
and base characteristics curve. The parameters are :
a) hie - transistor input impedance()b) h
oe transistor output impedance()
c) hfe dynamic current gaind) hre reverse voltage ratio
12.For design purpose, the transistor manufacture normally will provideapproximately values. For example,
a) hie800 to 1200()b) hoe2.5X10-4c) hfe50 to 100d) hre25 to 40 A/V
13.From the graph, the differences in values of IC, IC and IB, IB. The value of the hfecan be calculated. The calculation will be shown and the date will be recordedinto the Table 3. The following formula can be used to calculate h fe.
hfe=IC/IB
Results
Table 1
IB VCE Transistor(mA) IB VCE Transistor(mA)
0 3 0.00 40A 3 5.88
5 0.00 5 5.9810 0.00 10 6.24
15 0.00 15 6.49
20 0.00 20 6.75
10A 3 1.13 50A 3 7.56
5 1.14 5 7.70
10 1.17 10 8.05
15 1.19 15 8.43
20 1.22 20 8.83
20A 3 2.75 60A 3 9.04
5 2.79 5 9.23
10 2.87 10 9.71
15 2.94 15 10.20
20 3.03 20 10.74
30A 3 4.41 70A 3 10.53
5 4.46 5 10.75
10 4.61 10 11.30
15 4.77 15 11.93
20 4.94 20 12.30
Table 2
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IBQ(A) ICQ(mA) VCEQ(V)
40 6.2 10 155
The values of IBQ, ICQ, and VCEQcan be obtained from the graph.
The value of B are calculated by the following formula,
= IC/IB
=6.2
=6.2
0.04
= 155
Table 3
hfe 160
To calculate the value of hfe, the following formula are used,
hfe=IC/IB
IC = 6.20 4.60
= 1.60
IB = 40 30
= 10
hfe =1.60
= 160
Graph 1 IC versus VCE
Discussion
IC versus VCE
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For a NPN transistor, the most common circuit configuration is the Common Emitter
Amplifier. To understanding the basic operation of a bipolar transistor, we can take a
look into VCE-IC curves. This curve is derived from a common-emitter transistor and
the characteristics of the common-emitter output of the transistor can be
determined. A common-emitter transistor is when the emitter is the common
terminal for the input and output. In order to analysis the transistor circuits, the
input current, IB and the output voltage, VCE of the transistor are considered as the
independent variables. Biasing is very important in amplifier process as it able to
establish the correct operating point of a transistor amplifier ready to receive signals.
Therefore, it can reduce the distortion of the output signal.
A DC load line can be drawn in the curve to show all possible operating points
of the transistor from fully ON to fully OFF. The quiescent operating point and
the Q-point(Quiescent point) can be found from the curve. The most important
factor to be taken into consideration is the effect of VCE to the IC when VCE is larger
than 1.0V. From the curve, we can see that I C is mainly unaffected by changes in VCE.
For the common-emitter configuration, we can use this equation, I E=IB + IC.
Based on the graph, we can see that IC is increase rapidly to a saturation level for a
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constant value of IB and in the same time, the VCE increase from zero. There is a small
amount of collector current flows although IB is equal to zero.
The output characteristics curve of the transistor can be divided into 3 regions.
Which are the active region, cut-off region and the saturation region.
The active region is the region where the collector is reverse biased and the
emitter is forward biased. The collector current, IC is very sensitive due to the
changes of the IB. only a slight change is able to produces a very large change in
and the collector current are changed substantially.
The Cut-off region is the region when IE=0 and IC=ICO. The emitter junction has to
be in a slightly reverse biased condition. For example, 0.1V for germanium and 0V for
silicon
.
The last region will be the saturation region. Saturation region is the bottom part
of the curve. The voltage is fallen almost to zero. In this configuration, the collector is
still in reverse biased as the saturation entered.
Below showing the formula of IC and VCC when VCE and IC are zero respectively.
The value of is obtained by dividing the IC with IB. is defined as the parameter
of the transistor common-emitter configuration. The value of can be determined by
getting the values from the curves. is also known as hfe. They have no unit as there
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are the ratio of the IC and IB.
As we compare the curve with the theoretical graph, we can see that there are
deviations. This might because of some errors such as random errors, zero errors and
also parallax error. Besides errors, the deviation might be caused by the leakage of
the current in the circuit. Therefore, precaution must be taken in order to obtaine
accurate data in the experiment. One of it is the electrical elements that used during
the experiment had to be double checked as to determine whether the elements are
in good conditions to be used in the experiment. Besides that, the digital multimeter
plays a very important role in this experiment. We must use the digital multimeter in
the correct ways as it is very sensitive and easily fused. To prevent leakage of current,
jumpers or connection wires should be avoid using too much as it will create more
resistance in the circuit. By the way, the elements should be connect to the
breadboard correctly as if connect wrongly then the circuit might will burned. The
power supply should be turned off if not in used, and the V CC should be turn to zero
before increase the VBB. This is to ensure that data obtained is more accurate.
Conclusion
The parameters of the transistors are learned and the characteristics are determined.
Thus, the objectives of the experiment are achieved. From the parameters and the
data obtained, we can conclude that transistor is a device that can used for
amplification or act as a switch in the electric circuit.
References1. C.K. Alexander, Matthew N. O. Sadiku, (2007). Fundamental of Electric Circuits 3rd
Edition. The McGrow Hill Companies.
2. BC141(T039) Transistor Data Sheet. 1997. SGS-Thomson Microelectronics.3. http://mediatoget.blogspot.com/2011/09/common-emitter-configuration-of.htm
l
4. http://ecelab.com/vce-ic-curves.htm5. http://www.electronics-tutorials.ws/transistor/tran_2.html
http://mediatoget.blogspot.com/2011/09/common-emitter-configuration-of.htmlhttp://mediatoget.blogspot.com/2011/09/common-emitter-configuration-of.htmlhttp://mediatoget.blogspot.com/2011/09/common-emitter-configuration-of.htmlhttp://mediatoget.blogspot.com/2011/09/common-emitter-configuration-of.htmlhttp://mediatoget.blogspot.com/2011/09/common-emitter-configuration-of.htmlhttp://ecelab.com/vce-ic-curves.htmhttp://ecelab.com/vce-ic-curves.htmhttp://www.electronics-tutorials.ws/transistor/tran_2.htmlhttp://www.electronics-tutorials.ws/transistor/tran_2.htmlhttp://www.electronics-tutorials.ws/transistor/tran_2.htmlhttp://ecelab.com/vce-ic-curves.htmhttp://mediatoget.blogspot.com/2011/09/common-emitter-configuration-of.htmlhttp://mediatoget.blogspot.com/2011/09/common-emitter-configuration-of.html