Experiment 1, Plotting CommonEmitter Characteristic Curves
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To show the basic method for
plotting characteristic curves of a
typical NPN transistor
2. To give you experience working with
the Common-Emitter (CE) amplifier
configuration
1.
 Common-emitter characteristic curves
show how a particular transistor type
will react to variations in collectoremitter voltage, collector current and
base current.
 Once these variations are known, it is
possible to develop a complete picture of
how well a transistor will operate in a
given amplifier design.
 In this experiment, we will first look at
the basic procedure followed to obtain a
family of such curves, and then see what
our data actually tells us
 A typical set of characteristic curves is
shown on the next slide.
 Such a group of lines is usually referred
to as a family of curves, because more
than one line is drawn on the graph
 Each line shows how the collector
current (IC) varies as the collectoremitter voltage (VCE) is changed, while
the base current (IB) is held constant
 The horizontal axis, of the graph, is
divided into various values of VCE, while
the vertical axis includes various values
of IC
 Each line represents all possible
combinations of VCE and IC for a
particular value of base current
 Note that each curved line is marked
with the base-current value. The values
shown in the previous figure are for an
NPN transistor.
 (Voltages and currents used with PNP
transistors will have the same shape, but
will have the opposite polarity)
 CE characteristic curves are plotted by
setting the base current (IB) to some
specific value, and then measuring the
change in IC as VCE changes
 The circuit in the following slide show
how this can be accomplished: R1 is used
to set the base current IB to various
specific values, while R4 sets VCE as
desired.
 (R2 and R4 protect the transistor from
excessive base and collector currents,
respectively)
 The following steps are to be used for
gathering curve data
1. Use R1 to set IB to the desired value s
between 10 mA and 30 mA
indicated on the ammeter in base circuit
2. Set VCE to the lowest desired value
3. Measure IC with the ammeter in the
collector circuit (Ckt)
4. Set VCE to the next higher voltage
5. Repeat steps 3 and 4 until IC has been
measured at all desired values of VCE
(at the specific base current)
6. Set the base current to the next desired
value
7. Repeat steps 1 through 6 until all data
has been measured
 You will gather data about the
characteristic curves of a typical NPN
transistor, in this experiment.
 Once all data has been collected, you will
plot the data points on a graph, to assemble
a family of curves.
 It is important that you take your time to
make accurate measurements and
accurately plot the data points.
You will be using this graph for the
other experiments in this lesson.
1 330 W, ½ Watt Resistor (orange, orange, brown)
1 100 kW, ½ Watt Resistor (brown, black, yellow)
1 1 kW potentiometer (on trainer)
1 100 kW potentiometer (on trainer)
1 MPSA20 NPN transistor (or similar)
Note: Your results may be considerably
different than those found by CIE. This is
because the current gain for each transistor
may be quite different . Do not be surprised if
your results are not close to ours.
Turn on the trainer power and adjust
the positive power supply to +15 V.
and then turn off the trainers’ power.
1.
a)
2.
Be sure not to disturb this setting
for the rest of the experiment.
With the power off, construct, on the
breadboard, the following circuit.
a) The transistor Pin out (Lead
configuration) is shown at the bottom
of the schematic diagram.
1. Make sure to wire the transistor
correctly so it is not damaged
b) Note the two places in the circuit where
the ammeter will be inserted.
1. Remember to remove the jumper when
inserting the ammeter in the circuit
2. Remember to place the jumper back in
the circuit when removing the ammeter
Removing the jumpers only applies to
the current measurements
3.
a)
4.
c)
The jumpers are not to be removed
when the voltmeter is connected to
measure VCE.
Remove the base Ckt jumper and
place the ammeter to measure IB.
Note: The meters “A and V” are
illustrated by the schematic symbols
on the pictorial diagram. A
V
3. Switch the meter to the 0.05 mA (50
mA) range and turn on the trainer s’
power
1. Set R4 to the middle of its rotation and
adjust R1 for a base current of 10 mA
4. Remove the ammeter and reconnect
the jumper
a) Set the meter to the 10V DC range and
connect it to measure VCE.
b) Adjust R4 to measure O V
Connect the meter to measure the
collector current (IC) and switch the
meter to the 25 mA current range
5.
Remove the jumper across the meter
and observe the reading
1.
a)
6.
If necessary, switch to a lower current
range to get a more accurate reading
Record the present current value in
the first row of the data table under
the column headed “IB = 10 mA”.
Remove the meter, and reinstall the
jumper in the collector circuit
7.
Switch the meter to the 10 V DC
range, and connect it to measure VCE.
Set the voltage to exactly 1 V, and
repeat the current measurement
procedure in step 5.
1.
2.
1.
3.
Remember to remove the jumper
when making the IC measurement
Repeat the IC measurement for each
VCE value in the data table
Repeat steps 3 through 7 with each
base current value listed in the data
table
8.
1.
2.
Make sure the jumper wires are
installed when the meter is
removed, and disconnected when
current readings are taken.
Record the value, in the appropriate
space, as you take each collector
current reading
When you have completed all the
measurements, turn off the power
supply power and refer to the
following Characteristics Curve
Graph for Exp 1.
9.
Plot the data points, on the
Characteristic curve graph for Exp 1,
you have stored in the data table
a)
1.
Plot each set of points for a given base
current at one time
2. Connect each set of points into a smooth
line and mark each line with the
appropriate base current
10. Before dismantling the circuit, mark
the transistor you used in some way
for identification purposes.
a)
In later experiments, you will be using
several transistors of the same type
and you will have to identify the
transistor used to make the curves in
this experiment
Our results for this experiment are
shown in the following two slides.

Your results should show the same
general trend, but don’t be concerned
if there are considerable discrepancies
between our results and yours.



The transistor you used can have a
current gain of between 40 and 400.
Such a wide variation in current gains
will affect the shape of the curves
considerably
 In this experiment, you measured the
characteristics of a typical NPN
Transistor-an MPSA20. You compiled
your data and plotted the points on a
graph to form a “family” of characteristic
curves
 To get your data, you first set the base
current on a specific value, and then
varied VCE between 0 and 10 V in 1 V
increments
 You then measured the collector current
at each VCE setting.
 When all the readings for a particular
base current were made, you changed
the base current and repeated the
procedure
 Next you plotted your data on a graph
and connected the points to form a
“family” of curves
 The lines in the graph should have been
nearly parallel, but non-linearities in the
transistor may have caused some
variations.
 Your family of curves could be farther up
or down the graph than the curves
shown the plotted characteristic curve
graph, because of the wide variations in
current gain between different
transistors of the same type
 Rosenow, K. (2001). Lesson 1432:
Common-Emitter Amplifier
Characteristics. Cleveland: Cleveland
Institute of Electronics.
Developed and Produced by the
Instructors in the CIE Instruction
Department.
© Copyright 11/2012
All Rights Reserved / Nov. 2012