MAHENDRA COLLEGE of ENGINEERING

Salem-campus, attur main road, minnampalli, salem

EE25C04 Basic Electronics and Electrical Engineering

Electronic devices are capable of performing the following functions.

1. Rectification: Conversion of AC to DC is known as rectification.
2. Amplification: The process of raising the strength of week signal is known as
amplification.
3. Control: Electronic devices find wide application in automatic control, controlling
the voltage supply to any
equipment.
4. Inverter : Electronic device can convert DC power to AC power.
5. Converter : Electronic device can converter AC to DC power or DC TO DC or AC
to AC
6. Photo electricity: Electronic devices can convert light energy into electrical energy.
Conductors are those which allow the current to pass through it, insulators are those
materials who do not allow the current to pass through it. Semiconductors are those
which are having both properties of conductors and insulators. At absolute
temperature they behave like perfect insulators but with rise in temperature their
conductivity increases. By some special procedure their conducting property
controlled by requirement.

Types of Electronic Components

These are of 2 types: Passive and Active Components. Both these types of
components can be either Through-Hole or SMD.
1. Passive Components
These components are those that do not have gain or directionality. They are also
called Electrical elements or electrical components.
Example: Resistors, Capacitors, Diodes, Inductors.
Uses of resistors:
I. It establishes proper values of voltages due to IR drops
II. It is used to provide load.
The Laws of resistance
I. The resistance of conductor is directly proportional to its length i.e. R α L
II. The resistance of conductor is inversely proportional to its cross-sectional area i.e.
R α 1/A

III. The resistance of a conductor depends upon material.

IV. The resistance of conductor depends upon its temperature.
Where ρ is constant and is known as Specific resistance of the material. If L is equal
to 1 cm and A is 1 cm (cross sectional area of the conductor)
Specific Resistance: The specific resistance of material is resistance offered by 1cm
The reciprocal of specific resistance is called conductivity. It is denoted by 1/ ρ.
Some resistances used in electronic circuits are having their values directly written.
But maximum carbon resistances are color coded.
B-------- Black------------0
B--------Brown---------- 1
R--------Red-------------- 2
O-------Orange---------- 3
Y------- Yellow-----------4
G------- Green----------- 5
B--------Blue-------------- 6
V--------Violet------------7
G------- Grey--------------8
W-------White------------9
A carbon resistor has four colors on it. We should start from the color which is
nearest to the terminal.
1. First color is No. 2. Second color is also No.
4. Tolerance color (Gold-----±5%, Silver
Example
Red
Black orange
1. Fist color RED (2) 2. Second color is BLACK(0)
Silver (tolerance color i.e. ±10%).
The value of resistor is 20 x 10
Silver color indicates that practical value of resistor lies in between 19K
If third color is gold or silver then value of resistor is as follows
1. The first color is No. 2. Second color is No. 3. If third color is Gold then multiplied
by 10
Silver then multiplied by 10-2.
Example:
RαL/A
R =ρ. L / A
R =ρ
Color coding of resistors can be remember by a popular line
Example

2. Active Components
These components are those that have gain or directionality.

Example: Transistors, Integrated Circuits or ICs, Logic Gates.

A Resistor is an electrical device that resists the flow of electrical current. It is a

passive device used to control, or impede the flow of, electric current in an electric
circuit by providing resistance, thereby developing a drop in voltage across the
device.
There are two basic types of resistors:
1. Linear Resistors: Resistors whose value changes with the applied voltage and
temperature. Linear resistors are further classified as Fixed and Variable
resistors.
2. Non Linear Resistors: When resistance do not behave linearly with parameters
such as voltage, current or temperature (Ohm’s Law).

A capacitor is a device used to store and release electricity, usually as the result of a
chemical action. Also referred to as a storage cell, a secondary cell, a condenser or an
accumulator. A Leyden Jar was an early example of a capacitor. Capacitors are
further divided into two mechanical groups: Capacitors with Fixed-capacitance and
variable capacitors.
A Diode is an electronic component that allows electric current to flow in one
direction only. It is a semiconductor device that consists of a p-n junction. It can be
either forward biased or reverse biased.
They are most commonly used to convert AC to DC, because they pass the positive
(+) part of the wave, and block the negative (–) part of the AC signal, or, if they are
reversed, they pass only the negative part and not the positive part.
Types of a diode:
1. Light Emitting Diode: Light is generated when electric current flows through it.
2. Laser diode: Generates coherent light. It is widely utilized in CD drives, DVD
players, laser printers etc.
3. Photodiode: Current flow when exposed to light.
4. Schottky Diode: Diode with low voltage drop.
5. Tunnel Diode: Diode in which electric current decreases with increase in
voltage.
6. Varactor / Varicap Diode: Diode with Variable capacitance.
7. Zener Diode: Current flows in one direction, but also can flow in the reverse
direction when above breakdown voltage.
Farad: One farad is defined as the capacitance of a capacitor which required a charge
of one coulomb to
establish a potential difference of one volt between its plates.
Factors controlling the capacitance of a capacitor
I. Plate area : capacitance of a capacitor is directly proportional to area of plates
CαA
II. Distance between two plates: Capacitance of a capacitor is inversely proportional
to distance between the two plates.
C α 1/d
III. Type of Di-electric material : The capacitance of a capacitor depends upon the di-
electric constant of the insulating material used Hence capacitance of capacitor given
by
C = єrє0A/D
Where єr is relative permittivity of free space and Where є0 is permittivity of free
space which is given by 8.85x10-12.Relative permittivity of some of the material is
given below
Material єr for Air or vacuum 1,Ceramic 50 to 300,Mica 3 to 6,Paper 3 to 5
Capacitor blocks DC and allows AC to pass through it.
Capacitor in Series:- Connecting capacitors in series is equivalent to increase the
thickness of capacitance and distance between the plates increases Hence the
combined capacitance will decrease as C α1/d. As d increases C will decrease. Hence
1/C=1/C1+1/C2+1/C3……..
Capacitors in parallel:- Connecting capacitors in parallel is equivalent to adding their
plate area, and therefore the value of capacitance increases . Hence net value of
capacitance
C=C1+C2+C3+…………
All capacitors commonly used in electronic circuits are generally divided into two
main categories.
1.Fixed Capacitors
Electrolytic Capacitors Non Electrolytic Capacitors
4. Inductor

An inductor is a passive electrical device (typically a conducting coil) that introduces

inductance into a electric circuit. It is basically a coil of wire with many winding,
often wound around a core made of a magnetic material, like iron. Simplest form of
an inductor is made up of a coil of wire.
The inductance measured in henrys, is proportional to the number of turns of wire,
the wire loop diameter and the material or core the wire is wound around.
Inductors are categorized into different types based on their core material and
mechanical construction:
1. Air Cored Inductor
2. Iron Cored Inductor
3. Ferrite Cored Inductor
4. Iron Power Inductor
5. Bobbin Based Inductors
6. Toroidal Inductors
7. Multilayer Ceramic Inductors
8. Film Inductors
9. Variable Inductors
10. Coupled Inductors
11. Molded Inductors

Basic Active Electronic Components

1. Transistor

A transistor is a semiconductor device that acts as an amplifier, a switch, or a signal

modulator. It consists of three layers – the emitter, base, and collector – each doped
with different materials to create either a positive (P-type) or negative (N-type)
charge. This ingenious design enables transistors to control the flow of current and
amplify weak signals with remarkable precision.
There are two primary types of transistors:
1. Bipolar junction transistors (BJTs); and
 2. Field-effect transistors (FETs).
2. IC or Integrated Circuit
It is made up of combination of several transistors, diode, resistor, capacitors in a
tiny semiconductor chip. Integrated Circuit Electronic Components or IC are of
small size and very light weight. They produce excellent results at low power.
Types of IC on the basis of technology:
1. Linear IC: This type of IC works on analog signal.
2. Digital IC: This type of IC works on digital signal.
Types of IC on the basis of external structure:
1. Single in-line pin package (SIPP).
2. Dual in-line pin package (DIPP).
3. Quard pin package (QPP).
4. Pin Grid Array Package (PGA).
5. Ball Grid Array Package (BGA).
6. Leadless Chip Carrier (LCC) Package.
3. Logic Gates
Logic gates are fundamental building blocks of digital circuits, used in computers
and electronic devices to perform logical operations. They manipulate binary values,
representing true (1) or false (0) states, through Boolean algebra.Common types of
logic include: AND, OR, NOT, NAND, NOR, XOR, and XNOR gates, each executing
specific logical functions. Logic gates are fundamental building blocks of digital
circuits, used in computers and electronic devices to perform logical operations.
They manipulate binary values, representing true (1) or false (0) states, through
Boolean algebra.Common types of logic include: AND, OR, NOT, NAND, NOR,
XOR, and XNOR gates, each executing specific logical functions.
Energy band diagram of conductors, semiconductor, insulator
In terms of their electrical properties, materials can be classified into three groups:
Conductors Semiconductors Insulators.
Insulators:
An insulator is a material that does not conduct electrical current under normal
conditions. Most good insulators are compounds rather than single-element
materials and have very high resistivity. Valence electrons are tightly bound to the
atoms; therefore, there are very few free electrons in an insulator. Examples of
insulators are rubber, plastics, glass, and quartz.
Conductors:
A conductor is a material that easily conducts electrical current. Most metals are
good conductors. The best conductors are single-element materials, such as copper
(Cu), silver (Ag), gold (Au), and aluminum (Al), which are characterized by atoms
with only one valence electron very loosely bound to the atom. These loosely bound
valence electrons become free electrons. Therefore, in a conductive material the
free electrons are valence electrons.
 Semiconductors:
A semiconductor is a material that is between conductors and insulators in its
ability to conduct electrical current. A semiconductor in its pure (intrinsic) state is
neither a good conductor nor a good insulator. Single element semiconductors are
antimony (Sb), arsenic (As), boron (B), silicon (Si), and germanium (Ge). Compound
semiconductors such as gallium arsenide, are also commonly used. The single-
element semiconductors are characterized by atoms with four valence electrons.
Silicon is the most commonly used semiconductor.
Energy Bands:
The energy bands in a solid correspond to the energy levels in an atom. An electron
in a solid can have only those discrete energies that lie within these energy bands.
These bands are, therefore, called allowed energy bands. These (allowed) energy
bands are, in general, separated by some gaps which have no allowed energy levels.
These gap (regions) are known as forbidden energy bands.
Band corresponding to valence electrons is called valence band and the band
beyond forbidden band is called conduction band, into which, the electrons pass,
and move freely. The electrons in the outermost shell are called valence electrons.
The band formed by a series of energy level containing the valence electrons is
known as Valence Band. Valence band is also defined as a band which is occupied
by the valence electrons. The valence band may be partially or completely filled up
depending on the nature of the material. The next higher permitted band is the
conduction band. The energy levels occupying this band is defined as the lowest
unfilled energy band. This band may be empty or partially filled. In conduction
band, the electrons can move freely. Both conduction band and valence bands are
separated by a region or gap known as forbidden band. This band is collectively
formed by a series of energy levels above top of the valence band and below the
bottom of the conduction band. The energy gap between the valence band and
conduction band is called the forbidden energy gap or forbidden band. It should be
noted that no electron can exist in this band. When an electron in the valence band
absorbs enough energy, it crosses the forbidden gap and enters into the conduction
band.
Classification of Metals, Semiconductors and Insulators
On the basis
of width of
forbidden
gap valence
and

conduction band the solids are classified into insulators, semiconductors and
conductors ,Insulators. The band structure of insulators is as shown in fig. The
energy gap between conduction band and valence band is very high and is about
10eV. The forbidden energy band is very wide. Due to this, electrons cannot jump
from valence band to conduction band. In insulator, the valence electrons are bound
very tightly to their parent atoms.

Energy Bands
For insulators, the gap can be crossed only when breakdown conditions occur as
when a very high voltage is applied across the material. The band gap is illustrated
in Figure for insulators. In semiconductors the band gap is smaller, allowing an
electron in the valence band to jump into the conduction band if it absorbs a photon.
The band gap depends on the semiconductor material.
Types of Semiconductors Semiconductors can be classified as: Intrinsic
Semiconductor
 Extrinsic Semiconductor
 Intrinsic Semiconductor An intrinsic type of semiconductor material is made to be
very pure chemically. It is made up of only a single type of element. Germanium
(Ge) and Silicon (Si) are the most common type of intrinsic semiconductor elements.
They have four valence electrons (tetravalent). They are bound to the atom by
covalent bond at absolute zero temperature. When the temperature rises, due to
 collisions, few electrons are unbounded and become free to move through the lattice,
thus creating an absence in its original position (hole). These free electrons and holes
contribute to the conduction of electricity in the semiconductor. The negative and
positive charge carriers are equal in number

Fig: Conduction Mechanism in Case of Intrinsic Semiconductors (a) In absence of

electric field (b) In presence of electric Field
Extrinsic Semiconductor The conductivity of semiconductors can be greatly
improved by introducing a small number of suitable replacement atoms called
IMPURITIES. The process of adding impurity atoms to the pure semiconductor is
called DOPING. Usually, only 1 atom in 107 is replaced by a dopant atom in the
doped semiconductor. An extrinsic semiconductor can be further classified into:
 N-type Semiconductor
 P-type Semiconductor

The important specifications

of resistors are as given below,
 Range of resistance value: The resistors
are manufactured with specified values.
 Tolerance: A manufactured resistor has a certain tolerance to which the resistance
may differ from the nominal value.
 Power rating: Power rating is the maximum power supported by the resistor. This
rating is measured in watts (W) to explain how much heat energy a resistor can
dissipate without overheating and sustaining damage.
 Operating temperature: The operating temperature is the temperature that the
resistor can continue to operate before being damaged.
 Operating voltage: The operating voltage of a resistor specifies the maximum
voltage above which the resistor may damage.
 Thermal stability: The thermal stability of a resistor is indicated by temperature
coefficient which is usually expressed in parts per million per degree centigrade. The
smaller value of temperature coefficient will have less variation in the resistance
value.
Types of Resistors
Resistors are classified on the basis of the material composition, adjustability and
application. Below are some different types of resistors:
1.Fixed Resistors
This type of resistors have predefined resistance values which cannot be changed.
They are commonly used in building electronic circuits. Fixed resistors are further
classified in following types.
Metal Film Resistors
This type of resistors has high accuracy, offers low noise and has high temperature
stability which makes them ideal for precision applications.
Carbon Film Resistors
This type of resistors provide better stability than carbon composition resistors
because they use a thin carbon layer on a ceramic substrate.
Carbon Composition Resistors
These resistors are cost effective but have high noise levels. They are made from a
mixture of carbon particles and a binder.
Wire Wound Resistors
They are made by winding the metal wire around an insulating core. These resistors
handle high power applications with low noise.
Thick and Thin Film Resistors<h5>
These resistors provide high reliability and miniaturization. They are mostly used in
SMD (Surface Mount Device) applications.
2. Variable Resistors
These types of resistors allow manual adjustment of resistance values and are used
for tuning and calibration.
Potentiometers
This is a three terminal resistor used for voltage division in volume controls and
sensor adjustment.
Rheostats
These are two terminal variable resistors mainly used for current control in high
power applications.
Trimmers
These are small preset resistors designed for fine tuning circuits.
3. Special Purpose Resistors
These resistors are used for specific functions.
Thermistors
These are temperature sensitive resistors. They are classified as NTC (Negative
Temperature Coefficient) in which resistance decreases with rising temperature
which are mostly used in temperature sensors and PTC (Positive Temperature
Coefficient) in which resistance increases with rising temperature.
LDR (Light Dependent Resistor)
These resistors change resistance based on light intensity used in automatic lighting
systems.
Varistors (VDR- Voltage Dependent Resistor)
These resistors change resistance based on voltage levels.
Fusible Resistors
These resistors work as a fuse under excessive current flow and protects the circuit
from damage.
4. Power Resistors
These resistors are designed to dissipate large amounts of power while maintaining
stability.
Cement Resistors
These resistors are encased in ceramic material to withstand high power loads.
Metal Oxide Resistors
These types of resistors handle high voltage and temperature conditions very
effectively.
Shunt Resistors
These resistors are used in current sensing applications to measure high currents
with low resistance.
Functions of Resistors
1. Current Limiting
Limiting the flow of electric current is one of the most important functions of a
resistor. To prevent the excessive current in the circuit, the resistors are placed in
series with active components like LED/LCD display modules or microcontrollers.
2. Voltage Division
To generate specific voltage levels from higher voltage source resistors are used in
voltage divider circuits. This phenomena is very useful in analog circuits, sensor
applications and microcontroller interfacing. In this we use two resistors in series
and derive lower voltage output based on the ratio of their resistance values.
3. Signal Conditioning
To ensure signals are suitable for processing by other components resistors help in
shaping and refining signals. They are used in pull-up and pull-down resistors
which ensures stable logic levels in digital circuits by preventing floating inputs.
They are used in Biasing resistors to establish proper operating conditions and are
also used in RC filters to help signal smoothing and noise reduction.
4. Power Dissipation and Heat Generation
 For preventing sensitive components resistors convert excess electrical energy into
heat. This function is important in power supply circuits and high power
applications.
Properties of Resistors
Below are some properties of resistors which determine their performance in
different applications.
1. Resistance
Resistance is the main property of resistors which determines how much it opposes
the flow of electric current. Resistance varies based on material composition, length
and cross-sectional area.
2. Tolerance
This tells us how much actual resistance can vary from the stated value. It is crucial
for precision circuits. +- 5% is the standard resistor.
3. Temperature Coefficient
It measures how much a resistor’s resistance changes with temperature fluctuations.
Low TCR resistors are used in precision applications and high TCR resistors may
cause performance issues in extreme environments.
4. Noise Characteristics
Resistors like carbon composition resistors generate electrical noise due to
irregularities in their structure. Metal film and wire wound resistors offer lower
noise levels and are preferred in high precision audio and RF circuits.
Working Principle of Resistors
The working principle of the resistor is based on Ohm’s law which states that the
voltage across a resistor is directly proportional to the current passing through it.
V=IXR
Free electrons in the conductor collide with atoms when voltage is applied across a
resistor’s terminals which causes resistance to flow the current. The level of
opposition depends on the material, length, cross-sectional area and temperature of
the resistor.

Applications of Resistors
 Resistors are used in Automotive electronics where ECU (Electronic Control Unit)
circuits for accurate signal processing.
 They are used in medical devices like ECG and EEG machines where precision
resistors ensure accurate bio-signal measurements.
 Resistors, along with capacitors, create time delay effects in various applications like
oscillators and clock circuits for microcontroller timing.
 Resistors, when combined with capacitors, form RC filters to eliminate noise and
smooth signals in audio, RF, and communication systems.
Types, features and specification of Capacitors
 Capacitors are categorized based on their electrical characteristics and
construction. Understanding these classifications helps in selecting the
right capacitor for specific applications.
o Polarity
  Polarized Capacitors: These must be connected with the correct polarity
(positive and negative terminals). Examples include electrolytic and
tantalum
 Non-Polarized Capacitors: These can be connected in any direction and
are commonly used in AC circuits. Examples include ceramic, film, and
mica
o Adjustability
 Fixed Capacitors: Have a set capacitance value that cannot be changed.
They are the most widely used type in circuits.
 Variable Capacitors: Allow manual or electronic adjustment of
capacitance. Used in tuning circuits, such as radios and RF applications.
Includes trimmer and tuning capacitors.
o Dielectric Material
 The dielectric is the insulating layer between the plates and determines
the capacitor’s performance:
 Ceramic – Compact, used for high-frequency applications
 Film – Stable and reliable, used in precision and audio circuits
 Electrolytic – High capacitance for power supply smoothing
 Tantalum – Compact and stable, ideal for mobile and medical devices
 Mica, Paper, Polymer, Glass – Used in specialized or high-performance
applications
 Capacitor Specifications
 A capacitor’s main job is to store electric charge, and its capacitance value tells
us how much charge it can hold per volt. But there are several other
important things to look at when choosing a capacitor:
 Working Voltage: This is the highest voltage a capacitor can handle safely. If
you go over this limit, it might stop working or get damaged.
 Tolerance: This tells you how close the actual capacitance is to what’s printed
on the label. For example, a 100 µF capacitor with ±10% tolerance can be
anywhere between 90 µF and 110 µF.
 Polarity: Some capacitors (like electrolytic ones) have a positive and negative
side. Connecting them the wrong way can damage them.
 Leakage Current: Even when not in use, a small amount of charge can slowly
escape through the material inside the capacitor. This is called leakage.
 ESR (Equivalent Series Resistance): This is a small resistance inside the
capacitor that affects how it works at higher frequencies. Lower ESR is
usually better.
 Working Temperature: Every capacitor has a temperature range where it
works best. Going outside this range can affect its performance.
 Temperature Coefficient: This tells how much the capacitance changes when
the temperature changes.
 Volumetric Efficiency: This refers to how much charge a capacitor can store
in a small size. Smaller capacitors with high capacitance are considered more
efficient

Types, features and specification of Inductors

The Core of the Inductor is its heart. There are many types of Inductors according to
the core material used. Let us have a look at a few of them.
Air Core Inductor
The commonly seen inductor, with a simple winding, is this Air-Core Inductor. This
has nothing but air as the core material. Air core inductor uses any non-magnetic
material like plastic and ceramic as core to reduce the core losses i.e. eddy current
and stray losses, especially when the operating frequency is very high. However, the
use of a non-magnetic core also decreases its inductance.

Air Core Inductors are used for constructing RF tuning coils. They are also used in
filter circuits, snubber circuits, and high-frequency applications including TV and
radio receivers.
Iron Core Inductor
These Inductors have Ferromagnetic materials, such as ferrite or iron, as the core
material. The usage of such core materials helps in the increase of inductance, due to
their high magnetic permeability. These inductors have high power value but are
limited in high-frequency capacity.

The inductors that have ferromagnetic core materials just like these suffer from core
losses and energy losses at high frequencies.
Ferrite Core Inductor
These types of inductors use ferrite cores. Ferrite is a material with high magnetic
permeability made from the mixture of iron oxide (ferric oxide, Fe2O3) and a small
percentage of other metals such as nickel, zinc, barium, etc.
The ferrite core has very low electrical conductivity which reduces the eddy current
in the core, resulting in very low eddy current loss at high frequency. Hence they can
be used in high-frequency applications. They also offer advantages of decreased cost.
There are two types of ferrites i.e. Hard Ferrites and Soft Ferrites.
The Hard ferrites are also called permanent magnets. These will keep the polarity of
the magnetization even after removing the magnetic field. They are not used in
inductors because of their high hysteresis loss.
The Soft ferrites can reverse the polarity of their magnetization without any
particular amount of energy needed to reverse the magnetic polarity. Their
magnetization changes easily and are good conductors of the magnetic field. Thus
they are used in transformers and inductors.
Laminated Steel Core Inductor

In such types of inductors, the core is laminated which means that it is made up of a
bunch of thin sheets placed on top of each other in a tight form. The sheets are
coated with insulation to increase their electrical resistance and prevent eddy current
flow between them. Therefore the eddy current loss in laminated core inductors
decreases significantly. They are used in high-power applications.
Iron Powder Core Inductor
These are formed from very fine particles with insulated particles of highly pure iron
powder. This type of inductor contains nearly 100% iron only. It gives us a solid-
looking core when this iron power is compressed under very high pressure and
mixed with a binder such as epoxy or phenolic. By this action iron powder forms
like a magnetic solid structure which consists of a distributed air gap.
Due to this air gap, it is capable of storing high magnetic flux when compared with
the ferrite core. This characteristic allows a higher DC level to flow through
the inductor before the inductor saturates. This leads to the reduced permeability of
the core.
Mostly the initial permeability is below 100 only. Thus these inductors possess high-
temperature coefficient stability. These are mainly applicable in switching power
supplies.
Ceramic Core Inductor

Ceramic is a non-magnetic material just like air. Ceramic cores are used to provide a
shape for the coil and a structure for its terminals to sit upon. As it is a non-magnetic
material, it has low magnetic permeability and low inductance. But it provides a
reduction in the core losses. It is mostly available in SMD packaging and is used in
applications where low core losses, High Q, and low inductance are required.

PN Junction Diode
A diode is a device which only allows unidirectional flow of current if operated
within a rated specified voltage level. A diode only blocks current in the reverse
direction while the reverse voltage is within a limited range otherwise reverse
barrier breaks and the voltage at which this breakdown occurs is called reverse
breakdown voltage. The diode acts as a valve in the electronic and electrical circuit.
A P-N junction is the simplest form of the diode which behaves as ideally short
circuit when it is in forward biased and behaves as ideally open circuit when it is in
the reverse biased.

The name diode is derived from "di-ode" which means a device having two
electrodes. A simple PN junction diode by doping donor impurity in one portion
and acceptor impurity in other portion of silicon or germanium crystal block. These
make a p n junction at the middle part of the block beside which one portion is p-
type (doped with trivalent or acceptor impurity), and another portion is n-type
(doped with pentavalent or donor impurity). It can also be formed by joining a p-
type (semiconductor doped with a trivalent impurity) and n-type semiconductor
(intrinsic semiconductor doped with a pentavalent impurity) together with a special
fabrication technique such that a p-n junction is formed. It can also be formed by
joining a p-type (semiconductor doped with a trivalent impurity) and n-type
semiconductor (intrinsic semiconductor doped with a pentavalent impurity)
together with a special fabrication technique such that a p-n junction is formed.

Construction
The p-type forms anode and the n-type forms the cathode. These terminals are
brought out to make the external connections. N-side will have a significant number
of electrons, and very few holes (due to thermal excitation) whereas the p side will
have a high concentration of holes and very few electrons. Due to this, a process
called diffusion takes place. In this process free electrons from n side will diffuse
(spread) into the p side and recombine with holes present there, leaving positive
immobile (not moveable) ions in n side and creating negative immobile ions in p
side of the diode. Hence, there will be uncovered positive donor ions in n-type side
near the junction edge.

Similarly, there will be uncovered negative acceptor ions in p-type side near the
junction edge. Due to this, numbers of positive ions and negative ions will
accumulate on n-side and p-side respectively. This region so formed is called as
depletion region due to the “depletion” of free carriers in the region. Due to the
presence of these positive and negative ions a static electric field called as barrier
potential is created across the pn junction of the diode. It is called as "barrier
potential" because it acts as a barrier and opposes the further migration of holes and
electrons across the junction.

Forward Bias
In a PN junction diode when the forward voltage is applied i.e. positive terminal of
a source is connected to the p-type side, and the negative terminal of the source is
connected to the n-type side, the diode is said to be in forward biased condition.
There is a barrier potential across the junction. This barrier potential is directed in
the opposite of the forward applied voltage. So a diode can only allow current to
flow in the forward direction when forward applied voltage is more than barrier
potential of the junction. This voltage is called forward biased voltage. For silicon
diode, it is 0.7 volts. For germanium diode, it is 0.3 volts.

When forward applied voltage is more than this forward biased voltage, there will
be forward current in the diode, and the diode will become short circuited. Hence,
there will be no more voltage drop across the diode beyond this forward biased
voltage, and forward current is only limited by the external resistance connected in
series with the diode. Thus, if forward applied voltage increases from zero, the diode
will start conducting only after this voltage reaches just above the barrier potential
or forward biased voltage of the junction. The time, taken by this input voltage to
reach that value or in other words, the time, taken by this input voltage to overcome
the forward biased voltage is called recovery time.

Reverse Bias
The diode is reverse biased i.e. positive terminal of the source is connected to the n-
type end, and the negative terminal of the source is connected to the p-type end of
the diode, there will be no current through the diode except reverse saturation
current. This is because at the reverse biased condition the depilation layer of the
junction becomes wider with increasing reverse biased voltage. Although there is a
tiny current flowing from n-type end to p-type end in the diode due to minority
carriers. This tiny current is called reverse saturation current. Minority carriers are
semiconductor respectively
.
Now if reverse applied voltage across the diode is continually increased, then after
certain applied voltage the depletion layer will destroy which will cause a huge
reverse current to flow through the diode. If this current is not externally limited and
it reaches beyond the safe value, the diode may be permanently destroyed. This is
because, as the magnitude of the reverse voltage increases, the kinetic energy of the
minority charge carriers also increases. These fast moving electrons collide with the
other atoms in the device to knock-off some more electrons from them. The electrons
so released further release much more electrons from the atoms by breaking the
covalent bonds. This process is termed as carrier multiplication and leads to a
considerable increase in the flow of current through the p-n junction. The associated
phenomenon is called Avalanche Breakdown.

V- I Characteristics
Forward Bias When, P terminal is more positive as compared to N-terminal i.e. P-
terminal connected to positive terminal of battery and N-terminal connected to
negative terminal of battery, it is said to be forward biased. Positive terminal of the
battery repels majority carriers, holes, in P-region and negative terminal repels
electrons in the N-region and push them towards the junction. This result in increase
in concentration of carriers near junction, recombination takes place and width of
depletion region decreases. As forward bias voltage is raised depletion region
continues to reduce in width, and more and more carriers recombine. This results in
exponential rise of current.

Reverse Bias
In reverse biasing P- terminal is connected to negative terminal of the battery and N-
terminal to positive terminal of battery. Thus applied voltage makes N-side more positive
than P-side. Negative terminal of the battery attracts majority carriers, holes, in P-region and
positive terminal attracts electrons in the N-region and pull them away from the junction.
This result in decrease in concentration of charge carriers near junction and width of
depletion region increases. A small amount of current flow due to minority carriers, called as
reverse bias current or leakage current. As reverse bias voltage is raised depletion region
continues to increase in width and no current flows. It can be concluded that diode acts only
when forward biased. Operation of diode can be summarized in form of I-V diode
characteristics graph. For reverse bias diode,
 Where, V = supply voltage ID = diode current IS = reverse saturation current For
forward bias,

Where, VT = volt’s equivalent of temperature = KT/Q = T/11600 Q = electronic

charge K = Boltzmann’s constant N = 1, for Ge = 2, for Si.

Applications of PN Junction Diode

PN junction diode can be used as a photodiode as the diode is

 sensitive to the light when the configuration of the diode is reversebiased. It can be
used as a solar cell.
 When the diode is forward-biased, it can be used in LED lighting
applications.
 It is used as rectifiers in many electric circuits and as a voltagecontrolled
oscillator in varactors.
ZENER DIODE
Zener diode allows electric current in forward direction like a normal diode but it is
heavily doped than the normal p-n junction diode. Hence, it has very thin depletion
region. Therefore, zener diodes allow more electric current than the normal p-n
junction diodes. However, when connected in reverse biased mode, a small leakage
current flows through the diode. As the reverse voltage increases to the
predetermined breakdown voltage (Vz), current starts flowing through the diode.
The current increases to a maximum, which is determined by the series resistor, after
which it stabilizes and remains constant over a wide range of applied voltage.
There are two types of reverse breakdown regions in a zener diode:
Avalanche Breakdown Zener Breakdown. Avalanche Breakdown As the applied reverse
voltage tends to increase that result in the increment of the width of the depletion region.
Even there exist some minority carriers which gain some energy because of increment of
reverse voltage. Due to the gain in kinetic energy of the minority carriers, these free electrons
in movement collide with the stationary ions. This results in the formation of more free
electrons. Further, these again collide with remaining stationary ions and this process
continues it is referred to as carrier multiplication. Because of carrier multiplication, a huge
multiple of free electrons are created and the complete region of the diode becomes
conductive resulting in the breakdown known
as avalanche breakdown.

Zener Breakdown The zener breakdown occurs in heavily doped p-n junction diodes because
of their narrow depletion region. When reverse biased voltage applied to the diode is
increased, the narrow depletion region generates strong electric field.

When reverse biased voltage applied to the diode reaches close to zener voltage, the electric
field in the depletion region is strong enough to pull electrons from their valence band. The
valence electrons which gains sufficient energy from the strong electric field of depletion
region will breaks bonding with the parent atom. The valance electrons which break bonding
with parent atom will become free electrons. These free electrons carry electric current from
one place to another place. At zener breakdown region, a small increase in voltage will
rapidly increases the electric current.
V-I Characteristics of Zener Diode The first quadrant is the forward biased region. Here the
Zener diode acts like an ordinary diode. When a forward voltage is applied, current flows
through it. But due to higher doping concentration, higher current flows through the Zener
diode. In the third quadrant, When a reverse voltage is applied to a Zener voltage, initially a
small reverse saturation current Io flows across the diode. This current is due to thermally
generated minority carriers. As the reverse voltage is increased, at a certain value of reverse
voltage, and current increases drastically and sharply. This is an indication that the
breakdown has occurred. Known as breakdown voltage or Zener voltage, it is denoted by Vz

The zener breakdown voltage of the zener diode is depends on the amount of doping applied.
If the diode is heavily doped, zener breakdown occurs at low reverse voltages. On the other
hand, if the diode is lightly doped, the zener breakdown occurs at high reverse voltages.
Zener diodes are available with zener voltages in the range of 1.8V to 400V.

Voltage Regulator A voltage regulator is a device that regulates the voltage level. It
essentially steps down the input voltage to the desired level and keeps it at that same level
during the supply. This ensures that even when a load is applied the voltage doesn’t drop. The
voltage regulator is mainly used for two main reasons, and they are: To vary or regulate the
output voltage To keep the output voltage constant at the desired value in spite of
variations in the supply voltage. Voltage regulators are used in computers, power generators,
alternators to control the output of the plant