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Electrical Engineering Department
EENG351- Electronics I – LAB
Instructor: Eng. Nahida Abdullah
Experiment: Input & Output characteristics of Transistors
Written by: Mohammad Wehbi
Partners: Zeinab Zbib – Mohammad Osseily
Password: secCG7MZ
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Objectives:
 Check the conductivity & non-conductivity of npn and pnp
transistors.
 Determine the Input characteristics of a transistor.
 Determine the differential input resistance.
 Determine the output characteristics of a transistor.
 Determine the differential output resistance.
Instruments Used:
 Leybold Didactic COM3LAB master unit.
 PC’s Window XP Professional.
 Experiment board cat-No: 70015.
 Virtual lab on COM3LAB master unit:
∙ Digital multimeters
∙ 1 digital storage oscilloscope.
∙ 1 function generator.
 Set of wires.
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Introduction:
The transistor is a 3-layer semi-conductor device consisting of
either 2n & 1p, or 2p & 1n type layers of material, known as npn
and pnp transistors, respectively.
Experiment I
Each transistor is composed of 3 terminals: Base, Collector and
Emitter.
To check the conductivity of the transistor in npn or pnp, we
connect the terminals of these transistors to the terminals of the
voltage source.
The results are given in the table for both cases:
Symbols: - x → Conductive
- - → Non-conductive.
npn transistor
-↓
com
B
C
E
+→
B
///////
x
x
C
///////
-
pnp transistor
E
///////
3
-↓
com
B
C
E
+→
B
///////
-
C
x
///////
-
E
x
///////
According to the results obtained, we
can notice the shape of the diodes in npn or pnp transistors, and we
can, therefore, represent each configuration as:
npn
pnp
Now, in order to determine the input characteristics of a
transistor, connect the Base to the negative terminal of a voltage
source (MM1), keeping the collector free (open), and connect the
Emitter to the negative terminal of a second source (MM2).
Starting this experiment with a full-turned Potentiometer to the
right. We start to turn it to the left, slowly, in order to get and
notice the change of the voltage UBE and the current through the
base terminal IB.
The results are shown down:
MM1
0.455
0.451
0.419
0.400
0.390
0.369
0.300
0.264
0.238
MM2
0.639
0.639
0.639
0.635
0.634
0.633
0.625
0.620
0.615
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These results give us a set of points
showing the aspect of the graph,
representing the variation of the
Base-Emitter voltage with respect to
Base current, which represent the
Dynamic resistance re given by:
0.208
0.186
0.131
0.076
0.044
0.014
0.010
0.008
0.007
0.005
0.612
0.608
0.597
0.578
0.560
0.516
0.507
0.488
0.474
0.454
the
re = ∆UBE/ ∆IB ( UCE constant)
Calculating the dynamic resistance:
re =
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The second measurement of the dynamic resistance is done same
as previous circuit, but we close the collector terminal, and here
are the new results:
MM1
0.122
0.114
0.105
0.099
0.090
0.080
0.070
0.060
0.040
0.030
0.024
MM2
0.646
0.643
0.640
0.638
0.635
0.633
0.629
0.625
0.615
0.608
0.602
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The aspect of the graph of the
variation of the VBE with respect
is given by:
0.018
0.013
0.009
0.005
0.004
0.004
0.004
0.004
0.004
0.004
0.004
0.004
0.592
0.577
0.567
0.535
0.491
0.485
0.410
0.345
0.314
0.245
0.199
0.118
to IB
Calculating the dynamic resistance will give:
re =
Experiment II
The output characteristic indicates the dependence of the Emitter
current on the Collector-Emitter voltage.
These characteristics are influenced by the Base current IB.
First, we connect the Collector to the negative terminal of the
oscilloscope, the Emitter to Y1, and the Base to a variable voltage
source.
Set the generator G1 to Triangular signal, VPP to 10, F=50 Hz, and
V= 5v.
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Set the oscilloscope on Y1 mode, 2v/div, -1volts;
Horizontally, set time/div =1ms, and Y1 to trigger.
Having these settings, we, therefore, obtain a set of graphs
showing the variation of VCE with respect to IC, including the
graphs of IB.
These variations give us the differential output resistance occurred
between the Collector voltage and current by:
ra= ∆UCE/∆IC ( IB = constant)
This resistance can be calculated by determining the tangent at the
operating point (Qpoint) and calculating the ratio of the Collector
voltage to its current.
The obtained graph is as follow
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Conclusions:
1. The conductivity between the plates of a transistor changes
according to their connections.
2. A npn transistor is almost considered as a diode
characteristics.
3. The Base-Emitter represents in a npn transistor a diode in a
Forward-Bias state.
4. The input characteristics with an open or closed Collector are
almost the same.
5. The dynamic input resistance is the ratio between the
variation of the Base-Emitter voltage and the Base current.
6. When the voltage across the Collector is low, its current rises
sharply, while a high Collector voltage gives rise to a
constant Collector current, depending on the value of the
Base current, given by: IC = β IB .
7. The dynamic output resistance is the ratio between the
variation of the Collector voltage and the Collector current.
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