transistor investigatory project

1. Hrithik Singla
Roll No. 2130797
XII-B
PHYSICS INVESTIGATORY
PROJECT

2. CERTIFICATE
This is to certify that Hrithik Singla, a
student of class XII-B has successfully
completed the research on the below
mentioned project under the guidance
of Mr. Anil Sir (Subject Teacher) during
the year 2018-19 in partial fulfillment of
physics practical examination.

3. ACKNOLEDGEMENT
In the accomplishment of this project
successfully, many people have best
owned upon me their blessings and
the heart pledged support, this time I
am utilizing to thank all the people
who have been concerned with
project.
Primarily I would thank god for being
able to complete this project with
success. Then 'would like to thank my
Physics teacher Mr. Anil sir, whose
value able guidance has been the ones
that helped me patch this project and
make it full proof success his
suggestions and his instructions has
served as the major contributor
towards the completion of the project.

4. INDEX
1.INTRODUCTION
2.EXPERIMENT
3.MATERIALS REQUIRED
4.PHOTO OF THE CIRCUIT
5.THEORY
6.CIRCUIT DIAGRAM
7. CIRCUIT EXPLANATION
8.PROCEDURE
9.OBSERVATION
10.CALCULATION
11.CONCLUSION
12.RESULT
13.PRECAUION
14. SOURCES OF ERROR
15.BIBLIOGRAPHY

5. INTRODUCTION
The invention of the bipolar transistor in
1948 ushered in a revolution at
electronics. Technical feats previously
requiring relatively large, mechanically
fragile, power-hungry vacuum tubes were
suddenly achievable with tiny .
mechanically rugged, power-thrifty specks
of crystalline silicon. This revolution made
possible the design and manufacture of
lightweight, inexpensive electronic devices
that we now take for granted.
Understanding how transistors function is
of paramount importance to anyone
interested in understanding modern
electronics. A bipolar transistor consists of

6. a three-layer -sandwich" of doped
(extrinsic)
semiconductor materials, either P-N-P
Each layer forming the transistor has a
specific name, and each layer is provided
with a wire contact for connection to a
circuit.
The functional difference between a PNP
transistor and an NPN transistor is the
proper biasing (polarity) of the junctions
when operating. For any given state of
operation, the current directions and
voltage polarities for each kind of
transistor are exactly opposite each other.
Bipolar transistors work as current-
controlled current regulators. In other
words, transistors restrict the amount of

7. current passed according to a smaller,
controlling current. The main current that
is controlled
goes from collector to emitter, or from
emitter to collector, depending on the
type of transistor it is (PNP or NPN,
respectively). The small current that
controls the main current goes from base
to emitter, or from emitter to base, once
again depending on the kind of transistor
it is (PNP or NPN, respectively). According
to the standards of semiconductor
symbolically, the arrow always points
against the direction of electron flow.
Bipolar transistors are called bipolar
because the main flow of electrons
through them takes place in two types of
semiconductor material: P and N, as the

8. main current goes from emitter to
collector (a vice versa). In other words,
twotypes of charge carriers—electron and
holes—comprise this main current
through the transistor. As you can see, the
controlling current and the controlled
current always mesh together through the
emitter wire, and theft electrons always
flow against the direction of the
transistor's arrow. This is the first and
foremost rule in the use of transistors: all
currents must be going in the proper
directions for the device to work as a
current regulator. The small, controlling
current is usually referred to simply as the
base current because it is the only current
that goes through the base wire of the

9. transistor. Conversely, the large,
controlled current is referred to as the
collector con-eat because it is the only
current that goes through the collector
wire. The emitter current is the sum of the
base and collector currents, in compliance
with Kirchhoff's
Current Law. No current through the base
of the transistor, shuts it off like an open
switch and prevents current through the
collector. A base current, turns the
transistor on like a closed switch and
allows a proportional amount of cancel
through the collector. Collector current is
primarily limited by the base current.
regardless of the amount of voltage
available to push it. The next section will
explore in more detail the use of bipolar
transistors as switching elements.

10. EXPERIMENT
Material Required
i. Breadboard —1
ii. Transistor: BC547 (NPN) —1
iii. Preset: 10 k0 — 1
iv. LED — 2
iv. Resistor: 330 0 - 2
v. Color Code: 330 0 — Orange
Orange Brown Gold
vi. 9V Battery —1
vii. Connecting Wire Pieces
viii. Multimeter — 1
Theory:

11. In common emitter circuit of a
transistor, emitter base makes input
section and is forward biased and
emitter collector junction make output
section and is reverse biased. The
variation in the output voltage w.r.t. the
variation in input voltage for a
transistor are shown in figure.
The amount of amplification is decided
by the p (beta) of the transistor.
Β =hfe = Ic/IB
Where
• lc is the collector current.
• IB is the base current.
β an intrinsic property of the transistor.
Different transistors have different betas.

12. CIRCUIT DIAGRAM
For this, experiment we will use the
transistors in the common-emitter
configuration. The input signal is
applied between the base and emitter,
and the output is taken from the
collector and emitter. Circuit diagram:
transistor as amplifier and switch

13. CIRCUIT EXPLANATION
1. In this circuit two same-colored LEDs
are used so that the effect of
amplification can be clearly seen.
2. A preset (10 kΩ) is used in the circuit.
It is used as a voltage divider to apply
different voltages at the base. To use
preset as a voltage divider, either of the
side terminals is given Vcc and the other
ground.
3. The middle terminal the preset is
connected in series with the positive
terminal of LED, the negative terminal
of LED, is connected in series with a
resistor R, (330 Ω). The other end of the
resistor is connected to the base of the
transistor.

14. 5. One end of resistor, R5 (330 Ω) is
connected to the collector. The other
end of the corresponding resistor is
connected to the negative terminal of
LED
6. The positive terminal of LED is
connected to Vcc.
PROCEDURE
1. Make the circuit diagram (on
breadboard, if possible).
2. Make All connections neat, clean and
tight.
3. Now, set a particular input voltage (V')
using the preset, and measure it. Also,
measure the voltages At the base (Vb)
and collector (Vc) and compare them.
4. Measure the base current (10 and the

15. collector current (IC) and verify the
amplification factor.
5. Now, rotate the preset to a position,
where both the LEDs glow brightly. At
this position, measure the input voltage
(V') at the middle terminal of the preset.
Also, measure the voltages A the base
(VB) and collector (VC) and compare
them.
6. Again, measure the base current (VB)
and the collector (Vc) current and verify
the amplification factor.

16. OBSERVATION
For the first reading: -
• VI = 3.02 V
• VB 0.63 V
• Vc = 6.36 V
• IB = 9µA
• lc = 3.22 mA = 3220 RA
For the second reading: -
• VI = 8.29 V
• VB 0.89 V
• VC 0.03 V
• IB = 12.27 mA • lc = 15.98 mA

17. CALCULATIONS
For the first reading: -
• Current Gain, β = hfe = Ic / IB = 3220 /
9 = 358
• Voltage Gain, A = Vo /VI = 6.36/ 3.02 =
2.1
• Power Gain, P = 13*A = 358 * 2 = 716
. For the second reading: -
• Current Gain, 13 = hfe = lc /IB = 15.98 /
12.27 = 1.3
• Voltage Gain, A = Vo /VI = 0.03 / 8.29 =
3.6 *1o^-3
• Power Gain, P = β*A = 1.3 * 3.6

18. CONCLUSION
• For the first readings, VB is less than the
collector voltage VC. Since the base
voltage is less than the collector voltage,
we can say that the base - collector
junction is reverse biased. This is a
necessary condition for the transistor to
be in the active region. The value of p
(hFE) for this transistor should be
between 100 - 400. The calculated value,
358, lies in this range. This means that
the transistor is in the active region.
• So, in the active region, the transistor
acts as an amplifier as long as the base -
emitter junction is forward biased and

19. the base - collector junction is reverse
biased.
• Now, for the second reading, on
comparing the base and the collector
voltages, we can see that the base voltage
VB is more than the collector voltage VB.
Since the base voltage is more than the
collector voltage, we can say that the
base - collector junction is forward
biased. This is a necessary condition for
the transistor to be in the saturation
region. Also, the collector voltage is close
to zero volt (ground).
• The value of β (hFE), 1.3, is less than the
ideal gain (100) of a transistor. This
means, the transistor does not act as an
amplifier in this case, it acts like aswitch.

20. In the saturation region, the collector -
emitter voltage VcE is reduced to almost
0 V. We can see that the value of the
collector voltage with respect to the
emitter (ground) is 0.03 V. The collector
and emitter act as two terminals of the
switch, which get nearly shorted.
RESULT
• In the active region, the transistor acts as
an amplifier as long as the base – emitter
junction is forward biased and the base -
collector junction is reverse biased.
• A transistor gets saturated when its
base - emitter junction and base -
collector junction is forward biased. In
saturation, the potential difference

21. between the emitter and the collector is
approximately equal to zero volt. This
voltage across the collector - emitter
junction is called the collector - emitter
saturation voltage. The value of the
saturation region for the NPN transistor
in my project is around 0.25 - 0.6 V.
PRECAUTIONS
1. All connections should be neat, clean
and tight. 2. The input voltage should be
increases gradually.
3. Don't connect the terminals of the
battery to each other.
• The transistor may be faulty.

22. BIBLIOGRAPHY
• Guidance from Teacher
• NCERT Class 12 Physics Book
• Comprehensive Physics Practical Book
• www.cooljunk.in/physics-project-kit
• www.google.com