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SESSION 2015-2016
By-Subrat Kumar Singh
School- Father Agnel School
Roll no -32

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CERTIFICATE
This is to certify that Subrat Kumar
Singh of class 12-‘A’ has successfully
completed the physics project ‘Half
Wave Rectifier’, under my supervision
and up to my satisfaction, for
submission to class 12 CBSE Board
project.
Signature of external examiner:

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Signature (subject teacher):
It gives me a great pleasure to
express my gratitude and deepest
respect to my physics teacher Mrs.
Menka Prabhakar for her guidance
and excellent supervision. Her
constant encouragement only drove
me to work, to bring out this work

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successfully. I would also like to
thank our lab assistant Mr. Lalit for
guiding me through this project.
Finally, I wish to pay a glowing
tribute to my parents for their love,
affection and support.

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TOPIC
 OBJECTIVE
 INTRODUCTION
 COMPONENTS
 THEORY
 WORKING
 PROCEDURE
 RESULT
 PRECAUTIONS
 SOURCES OF
ERROR
 BIBLIOGRAPHY

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Rectifier is an electronic device
which converts the alternating
current to unidirectional current, in
other words rectifier converts the
AC voltage to DC voltage. We use
rectifier in almost all the electronic
devices mostly in the power
supply section to convert the main
voltage into DC voltage. Every
electronic device will work on the
DC voltage supply only.

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A PN junction is a device formed by
joining p-type ( doped with B, Al)
with n-type (doped with P, As, Sb)
semiconductors and separated by a
thin junction is called PN Junction
diode or junction diode.

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p-n Junction Formation
Two processes occur during
formation of a p-n junction
1. Diffusion
2. Drift

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- In a n-type semiconductor
(Conc. of electrons) is more than (Conc. of
holes)
- In a p-type semiconductor
(Conc. of holes) is more than (Conc. of
electrons)
- During the formation of p-n junction,
and due to concentration gradient
across p- and n- sides, holes diffuse
from p- side to n- side and electrons

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Diffuse from n- side to p- side. This
motion of charge carriers gives rise to
diffusion current across the junction.
- When an electron diffuses from n→p
due to the concentration gradient, it
leaves behind an ionized donor on n
side (positive charge) which is immobile
as it is bonded to surrounding atoms.
As electrons continue to diffuse from n→p, a
layer of positive charge on n- side of the
junction is developed.
- Similarly, when a hole diffuses from
p→n, it leaves behind an ionized
acceptor which is immobile.

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As holes continue to diffuse from p→n,
a layer of negative charge on p- side of
the junction is developed.
- This space charge region on either side
of the junction together is known as
depletion region as the electrons and
holes taking part in the initial movement
across the junction depleted the region
of its free charges.

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DRIFT
When an electric field is applied across the
semiconductor material, the charge carriers
attain a certain drift velocity Vd , which is
equal to the product of the mobility of the
charge carriers and the applied Electric Field
intensity E ;

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Drift velocity Vd = mobility of the
charge carriers X Applied Electric field
intensity.
→ Holes move towards the negative
terminal of the battery and electrons move
towards the positive terminal of the battery.
This combined effect of movement of the
charge carriers constitutes a current known
as “ the drift current “ .
→ Thus the drift current is defined as the
flow of electric current due to the motion of
the charge carriers under the influence of an
external electric field.

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→ Drift current due to the charge carriers such as
free electrons and holes are the current passing
through a square centimeter perpendicular to the
direction of flow.
When the positive terminal of the battery is
connected to the p-type material and the
negative terminal of the battery is connected
to the n-type material, such a connection is
called forward bias

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Above figure shows the p-n junction diode in
forward bias condition. The p region is
connected to the positive terminal and n region
is connected to the negative terminal of the DC
voltage source. A resistor is also connected in
series with the diode to make sure the current in
the circuit does not rise above the maximum
limit and damage the diode. When the diode is
forward biased, the electric field in the depletion
region and the external electric field due the DC
voltage source are in opposite direction (This is
shown in the above figure). This reduces the
effective/net electric field in the depletion

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region. Recall that in the previous section on p-n
junction diode, we had discussed that the flow
of electrons and holes ceased due to the electric
field. Since the net electric field is now reduced
due to forward bias, electrons and holes now
crosses the junction and constitutes a current.
The direction of current is from p-region to n-
region.
The flow of current can be explained as follows.
The electrons and holes crosses the p-n junction
as a result of reduced electric field in the
depletion region. Electrons from the n-region
crosses the junction and enters the p-
region.Since the positive terminal of the battery
is connected to the p-region, the electrons
experiences an attractive force and moves to the
positive terminal of the battery. Same discussion
can also be applied to holes. Thus we can

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conclude that current flow takes place when the
diode is forward biased.
Now we shall see the effect of applying forward
bias to the diode. The topics we shall discuss are
as follows
 Effect on depletion region due to forward
bias
 Effect of barrier potential during forward bias
 When the diode is connected in forward
bias, the electric field due to external voltage
source and the electric field due to depletion
region are in the opposite direction. This
reduces the net electric field in the junction
and the electrons can now pass from n-
region to the p-region. As more electrons
now flows into the depletion region, the

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number of positive ions is reduced. Same
discussion can also be applied to holes. With
the reduction in net electric field, the holes
can now flow into the n-region. As the holes
pass through the depletion region, the
number of negative ions also decreases.
Hence the the width of depletion region
decreases due to reduction in the number
of positive and negative ions. This is shown
graphically in the figure below.

 n-side diffuse from the junction edge of n-side to the
other end of n-side.

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 This motion of charge carriers on either side gives rise
to current.
 The total diode forward current is sum of hole diffusion
current and conventional current due to electron
diffusion. The magnitude of this current is usually mA.
With the diode is forward biased, the
electrons get enough energy from the
voltage source to overcome the potential
barrier and cross the junction. Similarly the
holes get sufficient energy to overcome the
barrier and cross the junction. The amount
of energy required by the electrons to
cross the junction is equal to the barrier
potential (0.3 V for Ge and 0.7 V for Si).
This simply means that when the diode is

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forward biased, the voltage drop across the
diode is approximately 0.7 V (for Si).
Actually, the amount of voltage drop is little
above 0.7 V due to internal resistance of the
material and contact resistance of the
conducting material used to form the legs
of diode.

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When the positive terminal of the battery is
connected to n-type material and the negative
terminal of the battery is connected to p-type
material, such a connection is called reverse
bias.
Above figure shows the diode connected in
reverse bias. You can clearly see that the

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negative terminal of the battery is connected to
p-type material and the positive terminal of the
battery is connected to n-type material. A
resistor is also connected in series with the
diode, although resistor is not required when the
diode is reverse biased. When the diode is
reverse biased, the electric field due to the
battery and the electric field of the depletion
region are in the same direction. This makes the
electric field even stronger than that before
reverse bias was applied. The electrons from the
n-type material (majority carriers) now faces a
stronger electric field and it becomes even more
difficult for them to move towards the p-type
material. Same discussion also applies to holes.
The holes from the p-type material (majority
carriers) now faces a stronger electric field and it
becomes even more difficult to move from p-
type to n-type material.Hence we conclude that

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there is no flow of current due to majority
carriers when the diode is reverse biased.
 p-n Junction diode
 Step down transformer
 Resistor
 L.E.D.
 Connecting wires
 Capacitor

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The half wave rectifier is a type of rectifier that
rectifies only half cycle of the waveform. This
article describes the half wave rectifier circuit
working. The half rectifier consist a step down
transformer, a diode connected to the
transformer and a load resistance connected to
the cathode end of the diode. The circuit
diagram of half wave transformer is shown

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below:
The main supply voltage is given to the
transformer which will increase or decrease the
voltage and give to the diode. In most of the
cases we will decrease the supply voltage by
using the step down transformer here also the
output of the step down transformer will be in
AC. This decreased AC voltage is given to the
diode which is connected serial to the secondary

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winding of the transformer, diode is electronic
component which will allow only the forward
bias current and will not allow the reverse bias
current. From the diode we will get the pulsating
DC and give to the load resistance RL.
The input given to the rectifier will have both positive
and negative cycles. The half rectifier will allow only
the positive half cycles and omit the negative half
cycles. So first we will see how half wave rectifier
works in the positive half cycles.

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Positive Half Cycle:
 In the positive half cycles when the input AC power
is given to the primary winding of the step down
transformer, we will get the decreased voltage at
the secondary winding which is given to the diode.
 The diode will allow current flowing in clock wise
direction from anode to cathode in the forward
bias (diode conduction will take place in forward
bias) which will generate only the positive half cycle
of the AC.
 The diode will eliminate the variations in the supply
and give the pulsating DC voltage to the load
resistance RL. We can get the pulsating DC at the
Load resistance.
Negative Half Cycle:
 In the negative half cycle the current will flow in
the anti-clockwise direction and the diode will go in
to the reverse bias. In the reverse bias the diode
will not conduct so, no current in flown from anode
to cathode, and we cannot get any power at the
load resistance.
 Only small amount of reverse current is flown from
the diode but this current is almost negligible. And
voltage across the load resistance is also zero.

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1. Take a cardboard piece, cover it and make
a diagram of your half wave rectifier.
2. Now punch holes wherever required.
3. Then insert the components in their
respective holes.
4. Now connect one end of the diode to one
end of transformer (which reduces net
peak value from 220V to 9V) and other
end to resistor.
5. The other end of resistor is connected to
L.E.D. which in turn is connected to the
other end of transformer.

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6. A filter capacitor is connected in parallel to
resistor and L.E.D.
The half wave rectifier is made and L.E.D. glows
without fluctuation.

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1.Connections should be neat, clean and
tight.
2.Do not touch the wires while current flows
through them
1.The capacitance of the capacitor may not be
large enough.
2.The main frequency may not be stable.
 Pradeep’s fundamental physics vol 2 (class 12)
 NCERT Physics Class 12 Part 2
 http://dei.vlab.co.in

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 http://www.physicsforums.com
 Comprehensive practical physics for class 12