1. Lab Session-02
1
Unit No : 01
Unit Title :
Semiconductor diode
characteristics and its
Applications
BE LAB (09EE2103)
Department of
Electrical Engineering
Faculty of Diploma Studies
Basic Electronics
2. Disclaimer
It is hereby declared that the production of the said content is meant for non-
commercial, scholastic and research purposes only.
We admit that some of the content or the images provided in this channel's videos
may be obtained through the routine Google image searches and few of them may be
under copyright protection. Such usage is completely inadvertent.
It is quite possible that we overlooked to give full scholarly credit to the Copyright
Owners. We believe that the non-commercial, only-for-educational use of the
material may allow the video in question fall under fair use of such content.
However we honour the copyright holder's rights and the video shall be deleted from
our channel in case of any such claim received by us or reported to us.
2
Basic Electronics
3. Content
3
Chapter:01: Diode characteristics and its applications
Types of semiconductors.
P-N junction diode formation and characteristics.
Applications - Diode as rectifier, half wave, full wave and bridge rectifier, clipping and
clamping circuit.
Need of filters.
C, L, LC, π filters.
Zener diode & it's application,
Photo diode
LDR
Photovoltaic Cell
Light Emitting Diode
Varactor Diode
Basic Electronics
4. Outline of Lecture
Introduction to Electronics
Electronic component
Passive component – R,L, C
Active component
Voltage source
Current source
Conductor , Insulator and semiconductor
Symbol of Semiconductor Devices
4
Basic Electronics
5. Introduction to Electronics
Electronics comprises the physics, engineering, technology and applications
that deal with the emission, flow and control of electrons in vacuum and matter.
It uses active devices to control electron flow by amplification and
rectification, which distinguishes it from classical electrical engineering which
uses passive effects such as resistance, capacitance and inductance to
control current flow.
Type of Electronics:
1) Analog Electronics
2) Digital Electronics
5
Basic Electronics
6. Electronic component
1) Passive component
2) Active component
6
The circuit element may be active type or
passive type.
An active element is that which is capable of
delivering power to some external device. For
example a voltage source or current source.
Whereas a passive element cannot deliver
power on the contrary absorbs power from the
active element. Examples of passive elements
are resistor, inductor, capacitor.
Fig: Active and passive element
Basic Electronics
7. Passive component
1) Resistance:
Property of a material to oppose the flow of electric current through it is called
resistance.
We studied that when a conductor is given emf, electric current flows due to the
flow of free electrons.
When these electrons move, they collide with the atoms.
So flow of electric current is opposed.
Due to this collision, some kinetic energy is converted in to heat energy.
Crystalline structures of different materials are different.
So all materials do not oppose the flow of electric current equally.
That means resistance of different material is different.
7
Basic Electronics
8. Passive component
8
Factors affecting resistance
Resistance of a conductor depends upon the following
factors.
1. Length of conductor (l)
2. Cross sectional area of conductor (a).
3. Material of conductor.
4. Temperature of conductor.
Basic Electronics
9. Passive component
9
2) Inductor:
An inductor, also called a coil, choke, or reactor, is a passive two-terminal
electrical component that stores energy in a magnetic field when electric current
flows through it.
An inductor typically consists of an insulated wire wound into a coil.
Air core and Iron core types
Energy stored : ½ LI2
Basic Electronics
10. Passive component
10
3) Capacitor
When an insulating material is placed between two conducting plates a capacitor
is formed.
The ability of capacitor to store electric charge is called the capacitance.
Paper, oil, mica, electrolyte, ceramic etc. are types
Equation: C= Q/V
Energy stored : ½ CV2
Basic Electronics
11. Active component
11
1) Voltage Source :
A voltage source may be of d.c. type or a.c. type.
The voltage source supplies voltage.
Ideal voltage source:
The voltage source which can supply constant voltage for any value of load
current is called the ideal voltage source.
The internal resistance (impedance) of ideal
voltage source is zero.
In practice, ideal voltage source does not exist.
But it is useful to understand the practical
voltage source.
Basic Electronics
12. Active component
12
2) Current Source :
Current source supplies current.
Current source is also of d.c. type or a.c. type.
Ideal current source :
An ideal current source supplies constant current to any value of the load
resistance (impedance).
An ideal current source had infinite internal resistance (impedance).
Basic Electronics
14. Atom and its Structure
Protons and neutrons are heavy particles.
This is because the number of protons, neutrons and electrons and their arrangement in
different elements are different.
However all the atoms of a particular element are identical.
The number of protons and electrons are equal.
This number is called atomic number and is denoted by letter Z.
14
Basic Electronics
15. Conductor Insulator and Semiconductor
Materials which allow the current to flow easily through them are called the
conductors.
Metals are good conductors of current.
In this also, silver, copper and aluminium are good conductors. Metal, salt solutions,
acids also are good conductors.
In atom of conductors there are less than four electrons in the outermost orbit.
Resistivity of conductor is low.
Material which do not allow the current to flow through them are called insulator.
Dry wood, rubber, porcelain, mica, PVC are all insulating materials.
In insulators, the outermost orbit of atom is completely filled.
Resistivity of insulating material is very high.
15
Basic Electronics
16. Cont…
Some materials do not allow the current to flow easily through them like conductors
and do not oppose the flow of current like insulators.
These materials are known as semiconductors.
Germanium, silicon etc. are semiconductors.
There are four electrons in the outermost orbit of atom of this material.
Resistivity of semiconductor is between that of conductor and insulator.
16
Basic Electronics
17. Band theory of conduction
The atomic bond:
The ionic bond:
17
Basic Electronics
22. Applications of Semiconductors
22
Basic Electronics
Semiconductors are used in power devices, light emitters (including solid-state
lasers), optical sensors.
As they have voltage and current handling capabilities, and they are considered as
future elements in manufacturing electronic devices like industrial-control
equipment, communication with data-processing, etc.
25. Question
1. Define DC voltage, current, power and energy
2. How to measure Voltage and current?
3. What is difference between conductor, semiconductor and
insulator?
4. Which are the insulator material?
5. Which are semiconductor material?
25
Basic Electronics
26. Summary of Lecture
26
Introduction to Electronics
Electronic component
Passive component – R,L, C
Active component
Voltage source
Current source
Conductor , Insulator and semiconductor
Symbol of Semiconductor Devices
Basic Electronics
28. Lab Session-03
28
Prof. Dhiraj Shrimali
Unit No : 01
Unit Title :
Semiconductor diode
characteristics and its
Applications
BE LAB (09EE2103)
Department of
Electrical Engineering
Faculty of Diploma Studies
Basic Electronics
29. Disclaimer
It is hereby declared that the production of the said content is meant for non-
commercial, scholastic and research purposes only.
We admit that some of the content or the images provided in this channel's videos
may be obtained through the routine Google image searches and few of them may be
under copyright protection. Such usage is completely inadvertent.
It is quite possible that we overlooked to give full scholarly credit to the Copyright
Owners. We believe that the non-commercial, only-for-educational use of the
material may allow the video in question fall under fair use of such content.
However we honour the copyright holder's rights and the video shall be deleted from
our channel in case of any such claim received by us or reported to us.
29
Basic Electronics
30. Summary of previous session
30
Atomic structure
AC Waveform
Sinusoidal terminology
Semiconductor
Energy band diagram
Types of semiconductor
Basic Electronics
32. PN Junction Diode :
When at one end of the rod of intrinsic semiconductor the acceptor
type impurity is added P-type semiconductor is formed at that end.
At the other end the acceptor type impurity is added, N-type
semiconductor is formed.
Thus in a semiconductor when there is P-type semiconductor at one
end and N-type semiconductor near to it at the other end, is called
the PN junction diode.
One terminal is brought out of the P-type and is called the anode.
Similarly one terminal is brought out of the N-type and is called the
cathode.
Construction and symbol are shown in figure.
The arrow shows the easy flow of current when it is forward biased.
32
Basic Electronics
33. VI characteristic :
33
The VI characteristic looks like that shown in figure.
Forward characteristic :
Looking to the forward characteristic it is seen that
initially when the voltage across the diode is less than the
knee voltage, the current is very small because the barrier
potential which is 0.7 V in silicon diode opposes the
applied voltage.
When the forward voltage reaches 0.7 V, the potential
barrier is overcome and the junction offers very low
resistance.
Then if the forward voltage is increased the current rises
rapidly.
The increase in current is more compared to the increase in
the voltage i.e. it does not obay the Ohm's law.
Basic Electronics
Fig: VI characteristic of junction diode
34. Cont…
Knee voltage
The forward voltage at which the current
through the forward biased diode starts to
increase rapidly is known as the knee
voltage.
This value is 0.7 V for the silicon diode and
0.3 V for the germanium diode.
34
Basic Electronics
Fig: VI characteristic of junction diode
35. Cont…
Reverse characteristic :
The reverse characteristic is also shown in figure.
It is drawn in the fourth quadrant as the voltage is
negative and current flow is also in the negative direction.
Reverse voltage is in volts where-as the current is in
microampere.
The reverse current very small and independent of the
applied reverse voltage, if the temperature is constant (the
reverse current is temperature dependent).
Current rises rapidly when breakdown voltage is reached.
Reverse current is limited by current limiting resistor R.
35
Basic Electronics
Fig: VI characteristic of junction
diode
36. Cont…
Breakdown voltage:
The reverse voltage at which the junction breaks down and results in sudden increase
in reverse current is known as the breakdown voltage.
Applications of PN junction diode :
There are many applications of PN junction diode. Some applications are listed here.
1. As low power and high power rectifier.
2. As a switch.
3. In clipping circuit.
4. In clamping circuit.
5. For protection of transistor, SCR and OP-Amp.
6. As detector in AM radio receiver (here point contact diode is used.)
36
Basic Electronics
37. Rectifier:
37
Rectifier is a device with the help of which the alternating current is
converted in to the direct current and the rectification is the process in which
the alternating current is converted in to the direct current.
Basic Electronics
Fig: Block diagram of rectifier
38. PN Junction Diode as Rectifier :
38
When junction diode is forward
biased, it offers very low resistance
and allows the current to flow
easily (Fig. (a)).
But when it is reverse biased, it
offers very high resistance so
negligible current flows (b).
This property of PN junction diode
is used in rectifier.
Basic Electronics
Fig. Junction diode (a) Forward bias (b) Reverse bias
39. Cont…
39
Classification of Single-phase Rectifier :
There are two main types of electronic
rectifier.
1. Single-phase rectifier and
2. Poly phase rectifier.
There are two types of single-phase rectifier.
Half wave rectifier and full wave rectifier
There are two types of single-phase full wave
rectifier
(a) Full wave rectifier with two diodes and
(b) Bridge rectifier
Basic Electronics
40. Half wave Rectifier
40
In half wave rectifier conduction of current takes place only during the positive or
negative half cycles.
Circuit of half wave rectifier is shown in figure-a and the waveforms of the input and
output are shown in figure -b.
Diode D and load R, are connected with the secondary winding of the transformer.
Basic Electronics
41. Cont…
41
Function of transformer :
Voltage can be stepped up or stepped down with the help of transformer.
To get certain d. c. voltage from the rectifier, certain a. c. voltage has to be given
to the rectifier.
Now normal voltage available is 230 V. So the required a. c. Voltage can be
given to the rectifier with the help of transformer.
Moreover using transformer the circuit is isolated from the supply mains.
Basic Electronics
42. Cont…
42
Working :
During the positive half cycle of a. c. when terminal a becomes positive with respect to
terminal b, anode A of diode D becomes positive with respect to its cathode K So diode
becomes forward biased and offers very low resistance.
Current flows in the direction a A KXYba i. e. the current through the load flows in the
direction X to Y.
So terminal X becomes the positive and terminal Y becomes the negative of the d. c. supply.
Basic Electronics
43. Cont…
43
But during the negative half cycle of a. c., when terminal a becomes negative with
respect to terminal b the diode becomes reverse biased and current cannot flow.
Waveforms of the input and output are shown in figure-b.
From the waveforms it is seen that the conduction of current takes place only in one
direction i.e. it occurs only during the half wave.
So this type of rectifier circuit is called the half wave rectifier.
Basic Electronics
44. Cont…
44
Disadvantages :
1. Output voltage is pulsating d. c. and it is available only during the positive half
cycle. So there are many a. c. components in the output along with d. c. so
costly filter circuit is required to obtain smooth d. c.
2. Power is delivered only during the half cycles so the output power is less.
3. Output voltage is half of that of the full wave type rectifier.
4. Current flows only during the half cycle so choke input filter cannot be used.
Basic Electronics
45. Question
1. What is diode?
2. What is application of diode?
3. What is function of rectifier?
4. What is function of inverter?
5. What is ripple frequency?
6. Which are types of transformer? what is use of its?
7. What is knee voltage and breakdown voltage?
8. What is value of knee voltage of diode?
45
Basic Electronics
48. Lab Session-05
48
Unit No : 01
Unit Title :
Semiconductor diode
characteristics and its
Applications
BE LAB (09EE2103)
Department of
Electrical Engineering
Faculty of Diploma Studies
Basic Electronics
49. Disclaimer
It is hereby declared that the production of the said content is meant for non-
commercial, scholastic and research purposes only.
We admit that some of the content or the images provided in this channel's videos
may be obtained through the routine Google image searches and few of them may be
under copyright protection. Such usage is completely inadvertent.
It is quite possible that we overlooked to give full scholarly credit to the Copyright
Owners. We believe that the non-commercial, only-for-educational use of the
material may allow the video in question fall under fair use of such content.
However we honour the copyright holder's rights and the video shall be deleted from
our channel in case of any such claim received by us or reported to us.
49
Basic Electronics
51. Outline of Lecture
51
Basic Electronics
Rectifier
Half wave rectifier
Full wave rectifier
Filter in Rectifier circuit
52. Rectifier
52
Rectifier is a device which convert AC to DC .
Classification of Single-phase Rectifier :
There are two main types of electronic rectifier.
1. Single-phase rectifier and
2. Poly phase rectifier.
There are two types of single-phase rectifier.
Half wave rectifier and full wave rectifier
There are two types of single-phase full wave rectifier
(a) Full wave rectifier with two diodes and
(b) Bridge rectifier
Basic Electronics
53. Half wave Rectifier
53
In half wave rectifier conduction of current takes place only during the positive or
negative half cycles.
Circuit of half wave rectifier is shown in figure-a and the waveforms of the input and
output are shown in figure -b.
Diode D and load R, are connected with the secondary winding of the transformer.
Basic Electronics
54. Cont…
54
Function of transformer :
Voltage can be stepped up or stepped down with the help of transformer.
To get certain d. c. voltage from the rectifier, certain a. c. voltage has to be given
to the rectifier.
Now normal voltage available is 230 V. So the required a. c. Voltage can be
given to the rectifier with the help of transformer.
Moreover using transformer the circuit is isolated from the supply mains.
Basic Electronics
55. Cont…
55
Working :
During the positive half cycle of a. c. when terminal a becomes positive with respect to
terminal b, anode A of diode D becomes positive with respect to its cathode K So diode
becomes forward biased and offers very low resistance.
Current flows in the direction a A KXYba i. e. the current through the load flows in the
direction X to Y.
So terminal X becomes the positive and terminal Y becomes the negative of the d. c. supply.
Basic Electronics
56. Cont…
56
But during the negative half cycle of a. c., when terminal a becomes negative with
respect to terminal b the diode becomes reverse biased and current cannot flow.
Waveforms of the input and output are shown in figure-b.
From the waveforms it is seen that the conduction of current takes place only in one
direction i.e. it occurs only during the half wave.
So this type of rectifier circuit is called the half wave rectifier.
Basic Electronics
57. Cont…
57
Disadvantages :
1. Output voltage is pulsating d. c. and it is available only during the positive half
cycle. So there are many a. c. components in the output along with d. c. so
costly filter circuit is required to obtain smooth d. c.
2. Power is delivered only during the half cycles so the output power is less.
3. Output voltage is half of that of the full wave type rectifier.
4. Current flows only during the half cycle so choke input filter cannot be used.
Basic Electronics
58. Full wave rectifier with two diodes :
58
In this type of rectifier circuit the current through the load flows in the same
direction during both the positive and negative half cycles, so this type of
rectifier is known as the full wave rectifier.
Two diodes are required and there should be center taping in the secondary of
the transformer.
Basic Electronics
59. Cont…
59
Circuit :
Circuit is shown in figure(a) and the
waveforms of the input and output are
shown in figure(b).
There is centre tap c in the secondary
winding of the transformer. D1 and D2are
two diodes whose cathodes are joined
together and connected to the one lead of
the load.
It becomes the positive of the d. c. supply.
Negative terminal of the load is connected
to the centre tap..
Basic Electronics
60. Cont…
60
During the positive half cycle of a. c., when terminal a becomes positive with respect to
centre tap c, terminal b becomes negative with respect to c at the same time.
So diode D1 becomes forward biased and diode D2 becomes reverse biased.
Diode D1 allows the current to flow but diode D2 cannot conduct.
Current flows in the direction a A1 K1 X Y c a.
During the negative half cycle when terminal a becomes negative with respect to centre
tap c, terminal b becomes positive with respect to c.
Diode D1 becomes reverse biased and diode D2 becomes forward biased.
So diode D1 cannot conduct and diode D2 conducts and current flows in the direction b
A2 K2 X Y c b.
Terminal X becomes the positive and terminal Y becomes the negative of the d. c
supply.
Basic Electronics
61. Cont…
61
Waveforms of the input and output are shown in figure (b).
It is seen that the output waves do not enter in the negative direction and direct current
is available only during the positive half cycles.
In this way two diodes are used in this type of rectifier and transformer with centre
taping in the secondary winding is required.
Value of the d. c. voltage is double than that of the half wave rectifier.
Basic Electronics
62. Cont…
62
Advantages :
1. Value of the output voltage is double than the half wave rectifier.
2. Output power is double than the half wave rectifier.
3. Only two diodes are required whereas the bridge rectifier requires four diodes.
Disadvantages :
1. It is necessary to have center taping in the secondary winding of the transformer.
2. Peak inverse voltage across the diodes is double than that in bridge rectifier so diodes
with higher PIV ratings are required to be used.
3. At any time only half of the transformer winding is in use and during that period the
other half of the winding is inactive. Due to this, the secondary utilization factor of the
transformer is less.
Basic Electronics
63. Full wave Bridge Rectifier :
63
In this type of rectifier circuit, it is not necessary to have centre taping in the
secondary winding of the transformer but four diodes are required.
Figure shows the circuit and the waveforms.
As the circuit resembles to the Wheatstone bridge, this rectifier circuit is called the
bridge rectifier.
Basic Electronics
64. Cont…
64
Circuit :
T is a transformer.
Cathodes of diodes D1 and D2 are joined together
which becomes the positive of the d. c. supply.
Anodes of diodes D3 and D4 are joined together
which becomes the negative of the d. c. supply.
Anode of diode D1 and cathode of diode D4 are joined
together to which one lead of the secondary winding
of the transformer is connected.
Similarly, anode of diode D2 and cathode of diode D3
are joined together to which another lead of
transformer secondary is connected.
Basic Electronics
65. Cont…
65
Working:
During the positive half cycle when terminal a becomes positive with respect to terminal b,
diodes D1 and D3 are forward biased and conduct the current.
Diodes D2 and D4 do not conduct as they are reverse biased.
Current flows in the direction a D1 X Y D3 b a.
Basic Electronics
During the negative half cycle when terminal b becomes
positive with respect to terminal a, diodes D2 and D4
become forward biased and diodes D1 and D3 become
reverse biased so diodes D2 and D4 conduct the current and
diodes D1 and D3 cannot conduct the current.
Current flows in the direction b D2 X Y D4 a b.
Thus four diodes are required and it is not necessary to have
centre taping in the secondary winding of the transformer.
66. Cont…
66
Advantages :
1. Transformer without center taping in the secondary winding is used.
2. PIV across diodes is half than that full wave rectifier with two diodes.
3. Output voltage is double than the full wave rectifier with two diodes for the same
secondary voltage.
Disadvantages :
1. Four diodes are required.
2. At any time two diodes conduct the current in series so the voltage drop across the diodes
is double than the full wave rectifier. This becomes important when the output voltage is
less.
Basic Electronics
67. Application of rectifier
67
There are various application of small and medium power rectifiers. Some applications
are as follows:
1. Circuit of radio receiver operates on d.c. supply.
2. D.C. supply is needed for variouus stages of T.V. recciver.
3. Electronic equipments like audio generator, amplifier, CRO require d.c. supply ofor their
operation.
4. It required for battery charging.
5. D.C. supply is required for electroplating process.
Basic Electronics
68. Question
1. What is function of rectifier?
2. What is function of centre tap transformer?
3. What is ripple frequency?
4. How many number of diode required in bridge rectifier?
5. What is use of filter in rectifier?
6. What is PIV ?
68
Basic Electronics
71. Lab Session-06
71
Unit No : 01
Unit Title :
Semiconductor diode
characteristics and its
Applications
BE LAB (09EE2103)
Department of
Electrical Engineering
Faculty of Diploma Studies
Basic Electronics
72. Disclaimer
It is hereby declared that the production of the said content is meant for non-
commercial, scholastic and research purposes only.
We admit that some of the content or the images provided in this channel's videos
may be obtained through the routine Google image searches and few of them may be
under copyright protection. Such usage is completely inadvertent.
It is quite possible that we overlooked to give full scholarly credit to the Copyright
Owners. We believe that the non-commercial, only-for-educational use of the
material may allow the video in question fall under fair use of such content.
However we honour the copyright holder's rights and the video shall be deleted from
our channel in case of any such claim received by us or reported to us.
72
Basic Electronics
75. Necessity Of Filter In RectifierAnd Types :
75
D. C. output from the rectifier is pulsating.
There are a.c. component it in addition to the d.c. components.
Filter circuits are used to remove the a.c. components from the output of the rectifier.
Thus by using the filter circuits the a. c. components are removed and smooth d. c. is
available.
Capacitor, inductor and their combinations are used as filter.
Types of filter circuits :
Different filter circuits are as follows.
1. Shunt capacitor filter
2. Series inductor filter
3. Choke input LC filter
4. Capacitor input LC filter
5. π filter.
Basic Electronics
76. 1.) Shunt capacitor filter
76
A capacitor of comparatively large value is
connected across output terminals of the rectifier as
shown in figure.
Capacitive reactance of capacitor (Xc = 1/2πfc).
So it offers low reactance to the a. c. components.
So the a. c. components will easily be grounded
and will not pass through the load.
Moreover the frequency of d. c. components is zero
so the capacitive reactance for these components
will be infinite hence the d. c. components will not
be able to pass through the capacitor and they will
pass through the load.
Basic Electronics
77. Cont…
77
Looking the effect of the capacitor in the other way, the capacitor charges to the
peak value Em of the d. c. output.
When the value of the d. c. input decreases, at that time the capacitor discharges
slightly through the load and maintains the load current.
However some voltage is reduced.
But if the value of capacitor is sufficient, the reduction in voltage is not much.
Basic Electronics
79. 2) Series inductor filter :
79
Current passing through the inductor does not
change instantaneously.
This is because, when the current through the
inductor tries to increase, e. m. f. is induced in the
inductor which opposes the rise in current.
Similarly when the current tries to decrease, the
e.m.f. induced opposes the decrease in current.
Series inductor filter works on this principle.
Inductive reactance of the inductor is XL =2πfL.
Now as the frequency of d. c. is zero, the d. c.
components pass easily through the inductor.
Basic Electronics
80. Cont…
80
While the inductor offers more reactance to the a. c. components so the a. c.
components cannot pass through the inductor so only d. c. is available to the load.
Due to some voltage drop across the inductor, there is some decrease in the output
voltage.
Some ripple is found in the output.
As this type of filter works on the principle of current, it cannot be used with the half
wave rectifier as there is no current flow during the negative half cycles.
Basic Electronics
82. 3) Choke input LC filter :
82
In this type of filter, an Inductor and a capacitor are used.
Connections are shown in figure .
Inductor is connected in series while capacitor is connected in parallel.
In this type of LC filter, the inductor is connected first so this type of filter is
known as the choke input filter.
Basic Electronics
83. Cont…
83
Inductor allows the d. c. components to pass easily through it but the a. c.
components cannot pass through.
Some a. c. components which manage to pass are bypassed to ground through
the capacitor.
Thus only d. c. components pass through the load.
There is some voltage drop in the inductor so the output voltage is reduced.
Basic Electronics
85. 4) Capacitor input LC filter :
85
In this type of filter also one inductor and one capacitor are used.
But first the capacitor is connected after the rectifier and then the inductor is
connected so it is known as the capacitor input type filter.
In this a. c. components are prevented by the inductor to pass through. A. C.
components are bypassed to ground. Only d. c. components pass through the inductor
and load.
Basic Electronics
86. Cont…
86
As the capacitor is immediately connected after the rectifier, the capacitor is
charged to the peak value of the output voltage.
There is some voltage drop in the inductor.
So there is small voltage reduction in the output.
Basic Electronics
88. 5)π Filter
88
In this type of filter circuit two capacitors and one inductor are used.
First shunt capacitor C1 is connected then series inductor and then capacitor C2 is
connected in parallel.
Most of the a. c. components are bypassed to ground by the shunt capacitor C1and
d. c. components cannot pass through it.
A. C. components cannot pass through the inductor.
Basic Electronics
89. Cont…
89
Those low frequency components which pass through the inductor are bypassed to
ground by capacitor C2.
This type of filter is known as the π type filter because the shape formed by the two
capacitors and one inductor resembles to the Greek letter π.
Sometimes a resistor is connected in place of the inductor.
This reduces the cost but there is voltage drop and power loss in the resistor.
Basic Electronics
91. Question
1. What is filter?
2. What is resonant frequency?
3. What is ripple frequency for full bridge rectifier?
4. How to select value of L and C in filter?
5. What is use of resistor in filter circuit?
6. What is use of inductor and capacitor in filter circuit?
91
Basic Electronics
94. Lab Session-06
94
Unit No : 01
Unit Title :
Semiconductor diode
characteristics and its
Applications
BE LAB (09EE2103)
Department of
Electrical Engineering
Faculty of Diploma Studies
Basic Electronics
97. Zener Diode :
97
We saw that an electric field is produced when PN junction is reverse biased.
The intensity of the field increases with the increase in the reverse voltage.
The covalent bonds are broken. At some reverse voltage there is sharp increase in the reverse
current and it is called the zener break down.
It is seen from the characteristic that even though the current through the diode changes, the
voltage across the diode remains constant. This is called the zener effect. If this reverse
current is limited, the diode does not heat up. The voltage at which the zener break down
occurs can accurately be decided by adding the impurity in certain definite proportion while
manufacturing. This type of diode is called the zener diode.
Zener diode is always operated in reverse bias condition i.e. its anode is connected to the
negative terminal and cathode is connected to the positive terminal of the battery.
Zener diodes are manufactured in the voltage ratings from 2.4 V to 200 V and more and the
power ratings of 150 mW to 50 W.
Basic Electronics
98. Cont…
98
Characteristic :
Characteristic of zener diode is shown in figure (b). It is seen from the reverse characteristic
that the voltage drop across the zener diode is not dependent on current flowing through it.
It means that even though the current through all changes, the voltage drop across it remains
almost constant.
Basic Electronics
Vz is known as the zener voltage
and it is specified for certain test
current IZT.
IZT is known as the zener knee
current.
Minimum of knee current IZT
should be passed through the
zener diode to bring it into action.
Fig: Zener Diode (a) Symbol, (b) Characteristics
99. Cont…
99
Applications of Zener diode:
Various applications of zener diode are as shown below :
1. As voltage regulator
2. As reference voltage device
3. In constant current source with the transistor
4. In over voltage protection and
5. In clipping and clamping circuits
Basic Electronics
Fig: Zener Diode as Voltage regulator
100. Photo diode
100
When conventional PN junction diode is reverse biased, reverse saturation
current flows due to the minority charge carriers (electrons in P-type and holes
in N-type).
More covalent bonds are broken and minority charge carries increase with the
increase in temperature, so the reverse current increases.
When light is thrown on the exposed PN junction then also the reverse current
flows due to the increase in the minority charge carriers as a result of the light
energy.
Photo diode works on this principle.
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101. Cont…
101
Construction :
In photo diode silicon or germanium PN junction is packed in a plastic capsule.
On one end a lens system is formed such that light is focused on the junction.
Other portion is made opaque.
Leads are taken out from P and N materials.
Construction is shown in figure (a) and symbols are shown in figures (b) and (c).
Basic Electronics
Fig.: Photo diode : (a)Construction (b)symbol (c) Alternate symbol
102. Cont…
102
Working :
Photo diode is given reverse bias.
When no light falls on the junction, very small reverse current flows.
This small reverse current flows as a result of breaking of covalent bonds due to the
temperature.
When light falls on the junction, minority charge carriers increase and reverse current
increases. Value of the reverse current increases with the light.
Magnitude of the reverse voltage does not affect the value of the reverse current.
Reverse current remains the same even if the reverse voltage is made zero because barrier
potential works as reverse bias and the reverse cu continues to flow.
When the diode is given some forward voltage, forward current flows, which in opposite
direction to the reverse current so that reverse current decreases.
And when the value of the forward current becomes equal to the reverse current, the net
current becomes zero.
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103. Cont…
103
Characteristics :
Characteristics of photo diode are shown in figure, It is seen that most part of the
characteristic is in the third quadrant, where-as some part is in the fourth quadrant.
Basic Electronics
Fig:- Characteristic of photo diode
Graphs of reverse voltage v/s reverse current are
drawn for different constant values of illumination.
There is small reverse current even when no light is
thrown. This curve is known as the dark
characteristic. This current flows as a result of charge
carriers produced due to breaking of covalent bonds
at room temperature.
When the light is thrown on the junction, value of
reverse current increases.
Curves A, B, C, D are obtained for different levels of
illumination.
104. Cont…
104
When the reverse voltage is made zero, there is no appreciable decrease in the reverse
current.
When some forward voltage is applied, forward current flows, which is in opposite
direction to the flow of reverse current.
So net reverse current decreases. And when the value of the forward current becomes
equal to the reverse current, net current becomes zero. .
Value of dark current is 25 μA for the reverse voltage of -1.5 V, where-as for the value
of this reverse voltage, the value of the reverse current is 350 μ A for the illumination
of 25 000 lm/m2
.
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105. Cont…
105
Advantages :
1. Response time is fast.
2. Size is small.
Disadvantages :
1. Its active area is small.
2. When the temperature is increased, increase in dark current is more.
3. It requires bias voltage for its operation.
4. It requires amplifier as the current is small in magnitude.
Applications :
1. It is used in high speed switching and counting up to 1 MHz frequency.
2. It finds use in optical communication.
3. It is used in radar tracking system and numerical controlled machines as a shaft encoder.
4. It is used in punched card reader and punched tape reader in computer.
5. It is found useful in brushless d.c. motor.
Basic Electronics
106. LDR
106
LDR or photoconductive cell works on the principle of photoconductive effect. is when light
falls on it, its conductivity increases that means its resistivity decreases..
Construction :
In this, photo conductive material is deposited in zig zag form on an insulated round disc.
A transparent plastic cover is provided to protect it.
Two leads are taken out. Cadmium sulphide (CdS), lead sulphide (PbS), and cadmium
selenide (CdSe) are used as the photo conductive materials.
Basic Electronics
Impurity of silver, antimony or indium is
added in small proportion.
Cadmium sulphide is widely used.
In figure (a) the construction and in (b)
and (c) are shown the symbols.
107. Cont…
107
Working :
When photon of sufficient energy collides with the
photoconductive material, and if this energy is more than the
forbidden gap, covalent bonds are broken in the valence band
and electrons go to the conduction band from the valence
band and holes are produced in the valence band.
Thus electron hole pairs are generated.
Now conductivity of material depends on the concentration of
the charge carries.
So there is increase in the conductivity or decrease in the
resistivity.
The conductivity increases further when more light energy is
supplied.
In Figure, the energy level diagram is shown.
Basic Electronics
Fig.: the energy level diagram of LDR
108. Cont…
108
Characteristics :
To draw the characteristic of the LDR, illumination level is
plotted on the X-axis and resistance is plotted on the Y-axis.
Such characteristic is shown in figure.
Both the illumination level and resistance are plotted on the
logarithmic scale.
It is seen from the characteristic there is decrease in the
resistance with the increase in the illumination level.
Value of the dark resistance is more than 100 kΩ.
Dark resistance means the resistance of the LDR when no
light falls on it
Basic Electronics
Fig.: Characteristics of LDR
109. Cont…
109
Advantages:
1. Power dissipation is more.
2. Voltage rating is more.
Disadvantages:
Response time is more.
Application:
1. CdS type LDR can be used directly to operate the relay
2. It is used for on-off or speed control of d.c.motor
3. It is used in low speed switching and counting
4. It used in exposure control of camera
5. It is used in light metes.
Basic Electronics
110. Photovoltaic Cell
110
In photo voltaic cell emf is generated when light falls over it.
Construction :
Construction of photo voltaic cell is shown in fig-(a), its symbols are shown in fig.(b) and (c).
In this a layer of P-type silicon is formed on a metal plate. Over this a layer of N type
cadmium oxide is formed. So a PN junction is made.
Very thin transparent layer of gold or silver is kept over this N-type material so that light can
fall on PN junction after passing through this.
Basic Electronics
Fig.: Photo Voltaic cell : (a)Construction (b)symbol (c) Alternate symbol
111. Cont…
111
Working :
When light is allowed to fall over the photocell, electron hole pairs are
generated.
Minority charge carriers of N-type material (holes) cross the junction, reach to
P-type material and go to N-type material after passing through the load.
Similarly minority charge carriers of P-region (electrons) cross the junction and
reach to N-region, then go to P-region after passing through the load.
Thus N-lead works as negative terminal and P-lead works as the positive
terminal.
Basic Electronics
112. Cont…
112
Characteristics:
Characteristic of photo voltaic cell is shown in figure.
Output voltage is plotted on X-axis and output current
is plotted on Y-axis. Curves are drawn for different
illumination levels.
When there is no light falling on the photo cell (dark),
voltage output from photocell is zero.
When illumination level is increased, there is no
much change in the output voltage but current
increases.
The photocell should be operated near knee of the
characteristic to get maximum power from it.
Basic Electronics
Fig.: Characteristics of Photo Voltaic cell
113. Cont…
113
Application:
Applications of photocell are as below :
1. In illumination meter.
2. In automatic exposure control of camera.
3. To sense weak light levels
4. In burglar alarm.
5. In shaft encoder. .
6. In batch counting.
7. In film sound recording.
Basic Electronics
114. Light Emitting Diode
114
When PN junction is forward biased, electrons in N-region combine with the
holes in P-region.
Free electrons are in the conduction band and holes are in the valence band.
Thus electrons go to the valence band from the conduction band that is electrons
go to the lower energy level from the higher energy level.
So when recombination of electrons and holes occurs, energy is radiated in the
form of heat and light.
In light emitting diode arrangement is made such that the energy radiated is in
the form of light.
Colour of the light radiated depends upon the material of the LED.
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115. Cont…
115
Construction:
N-type epitaxial layer is grown on the substrate.
P-region is formed over it by diffusion process.
Recombination of the charge carries take place in P-region.
So P region is kept on the upper side. Lead is taken out from the P-type material such the light
is not obstructed.
A layer of gold film is kept below N-layer so that the emitted is reflected.
In figure (a) is shown the construction and in (b) and general appearance and in (d) is shown
the symbol.
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116. Cont…
116
In the symbol, the arrows point to the outward side which indicate that the light is emitted (in
photodiode the arrow heads are toward inside).
Semiconductor material used is semi-transparent.
It is gallium arsenide (GaAs) of gallium arsenide phosphide (GaAsP) or gallium
phosphide(GaP).
Red or amber (yellow) light is radiated when GaAsP is used.
Green light is radiated with GaP and invisible infra red radiation comes out when GaAs is
used.
Round LEDs are available with 3 mm or 5 mm or more in diameter.
Rectangular type LEDs are also available which are used in bar graph indicators.
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117. Cont…
117
Working:
LED is forward biased to bring it into action.
Minimum of 10 mA current should be passed through it.
Value of current can be kept between 10 mA to 25 mA.
Due to the forward bias, electrons from N-type material go from the conduction band and
recombine with the holes in the valence band of P-type material.
So energy in the form of light is radiated.
Advantages :
1. Long life.
2. Can be operated at low voltage.
3. Switching is fast.
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118. Cont…
118
Disadvantages :
1. Power consumption is more compared to LCD type display.
2. Display becomes dim in the ambient light.
Applications :
1. As pilot indicator.
2. In opto-isolators.
3. In optical communication.
4. In large numerical displays (in this clusters of LEDs are used.)
5. Rectangular LEDs are used in bar graphs.
Basic Electronics
119. Varactor Diode
119
A Varactor Diode (also known with the names Varicap Diode, Varactor Diode, Tuning Diode)
is a p-n junction diode which acts as a variable capacitor under varying reverse bias voltage
across its terminals.
it is a specially designed semiconductor diode whose capacitance at the p-n semiconductor
junction changes with the change in voltage applied across its terminals.
And because it is a diode that can behave as a variable capacitor, it is named as a Varactor
Diode in short.
Basic Electronics
121. Question
1. What is LED?
2. What is difference between photo voltaic and photo conductive cell?
3. What is LDR?
4. List different types of display.
5. Why LED having different colour?.
121
Basic Electronics
123. Lab Session-07
123
Unit No : 01
Unit Title :
Semiconductor diode
characteristics and its
Applications
BE LAB (09EE2103)
Department of
Electrical Engineering
Faculty of Diploma Studies
Basic Electronics
126. CLIPPERS
There are a variety of diode networks called clippers that have the ability to
“clip” off a portion of the input signal without distorting the remaining part of
the alternating waveform.
Depending on the orientation of the diode, the positive or negative region of
the input signal is “clipped” off.
126
Basic Electronics
127. There are two general categories of clippers:
Series Clipper : The series configuration is defined as one where the
diode is in series with the load.
Parallel Clipper : The diode in a branch parallel to the load.
CLIPPERS
Basic Electronics
128. Series Clippers (Un-biased)
The diode in a series clipper “clips”
any voltage that does not forward bias
it:
A reverse-biasing polarity
A forward-biasing polarity less than
0.7 V (for a silicon diode)
128
Basic Electronics
129. Biased Diode Series Clippers
As in fig the direction of the diode suggests that the signal vi must be
positive to turn it on.
The dc supply further requires that the voltage vi be greater than V volts to
turn the diode on.
129
Basic Electronics
130. Series Clippers
When the diode is in the short-circuit state, such as shown in Fig., the
output voltage vo can be determined by applying Kirchhoff’s voltage
law in the clockwise direction:
130
Basic Electronics
132. Biased Series Clippers
The negative region of the input signal is “pressuring” the diode into the “off” state, supported further by
the dc supply.
In general, therefore, we can be quite sure that the diode is an open circuit (“off” state) for the negative
region of the input signal
132
Basic Electronics
140. Clamper
The clamping network is one that will “clamp” a signal to a
different dc level.
The network must have a capacitor, a diode, and a resistive
element, but it can also employ an independent dc supply to
introduce an additional shift.
140
Basic Electronics
141. Biased Clamper Circuits
The input signal can be any type of
waveform such as sine, square, and triangle
waves.
The DC source lets you adjust the DC
camping level.
141
Basic Electronics
146. Next Session
146
Basic Electronics
Chapter:02: Content
Transistor characteristics and applications
PNP and NPN transistors, conduction through transistor leakage current, relationship
between α and β.
Transistor configuration & characteristics for CB, CE, CC.
Load line and biasing methods of transistor.
Common emitter amplifier.
Common collector amplifier.
Multistage amplifier
Construction of JFET
Characteristics of JFET
