INTRODUCTION
If you are new to electronics or starting to build
electronic circuits, then the important thing to do is to get familiar with few
Basic Electronic Components and Equipment. Without understanding these basic
electronic components i.e. their values, ratings, purpose etc. your circuit
design might not function as expected. There are many electronic components
like Resistors, Capacitors, LEDs, Transistors, etc. and there are also many
equipment like a Power Supply, Oscilloscope, Function Generator (or Signal
Generator), Multimeter, etc.
In this tutorial, you can get a brief overview of few of the
most common basic electronic components. You can easily understand the concept
if I divide this tutorial in to Basic Electronic Components and Measurement and
Analysis Equipment. So, first, I’ll start with the basic electronic components.
1.1 Basic Electronic Components
There
are many ways to classify different types of electronic components but the most
common way is to classify them in to three types: Active Electronic Components,
Passive Electronic Components and Electromechanical Components.
1.2 Active Electronic Components
Strictly
speaking in terms of Physics, an Active Component is a device that acts as a
source of energy, like a battery. But the definition of Active Components
according to few electronic engineers is that they are the devices that depend
on a source of energy and can introduce power in to a circuit.
Active
Electronic Components can control the flow of electrons through them. Some of
the commonly used Active Components are Transistors, Diodes, ICs (Integrated
Circuits), Power Sources (Batteries, AC and DC Power Supplies), etc.
1.3 Diodes
Diode is a non-linear semiconductor device that allows flow
of current in one direction. A Diode is a two – terminal device and the two
terminals are Anode and Cathode respectively. The following is the symbol of a
Diode.
There
are again a variety of components that come under the category of Diodes. They
are PN Junction Diode, Light Emitting Diode (LED), Zener Diode, Schottky Diode,
Photodiode and DIAC.
Normal
PN Diodes are often used in AC to DC Converter circuits. You might be familiar
with LED or a Light Emitting Diode. It is a semiconductor device (or a PN
Junction diode, to be more specific) that emits light when activated.
A
Zener Diode allows flow of current in both directions and is often used as a
voltage stabilizer. Schottky Diode is similar to a regular PN Diode but with
less forward current and hence is often used in fast switching circuits.
1.4 Transistors
Transistor,
the invention that changed the future of electronic circuits, is a
semiconductor device that can be used to either switch electrical power or
amplify electronic signals.
A
Transistor is a 3 terminal device that can either act as a current controlled
device or a voltage controlled device. Transistors are further classified in to
Bipolar Junction Transistors (BJT) and Field Effect Transistors (FET).
A
Bipolar Junction Transistor or BJT uses both the charge carriers i.e. electrons
and holes and is often used as a current amplifier. Based on the construction,
BJTs are further divided in to NPN and PNP Transistors.
Field
Effect Transistor or FET uses only a single charge carrier. Junction FET (JFET)
and Metal Oxide Semiconductor FET (MOSFET) are the two types of FETs.
Based
on the construction of the FETs, they are divided in to two types: N – Channel
and P – Channel. MOSFETs are commonly used in power supplies, Audio circuits
and other power electronic applications.
The
combination of N – Channel MOSFET and P – Channel MOSFET, which is called
Complimentary Metal – oxide Semiconductor (CMOS) is a very common digital logic
in the manufacturing of microprocessors, microcontrollers, Memory modules and
other VLSI (Very Large Scale Integration) Integrated Circuits (IC).
1.5 Integrated Circuits (ICs)
An
Integrated Circuit or an IC is an integration or incorporation of several
electronic components (mainly transistors) on a single device (or chip) made up
of a semiconductor material (usually Silicon).
Almost
all electronic devices like TVs, Mobile Phones, Laptops, Audio Players,
Routers, etc. have Integrated Circuit in them.
ICs
are again divided in to Analog ICs and Digital ICs. Analog ICs work on Analog
Signals like Temperature, Audio, etc. which are continuously varying in nature.
Digital ICs on the other hand, work on Discrete Signals i.e. zero volts and a
non-zero volts (like 5V or 3.3V) that are represented as Binary 0 and 1.
The
commonly used IC in basic electronic circuits are Op – Amps (Operational
Amplifiers) like LM741, Timers like NE555, Microcontrollers like AT89S52,
Counters like CD4017 and Motor Drivers like L293D.
1.5 Passive Components
Passive
Components cannot control the flow of current through them i.e. they cannot
introduce energy in to the circuit but can increase or decrease voltage and
current.
Two
terminal components like Resistors, Capacitors, Inductors and transformers are
examples of Passive Components.
1.7 Resistors
The
basic of all electronic components are the Resistors. It is a passive
electronic components that introduces electrical resistance in to the circuit.
Using resistors, we can reduce the current, divide voltages, setup biasing of
transistors (or other active elements), etc.
Resistors
are again divided in to Fixed Resistors and Variable Resistors. Fixed
Resistors, as the name suggests, have a fixed resistance and its resistance
doesn’t change due to external parameters.
WHAT IS RESISTOR?
Resistor
is basic component that is used in all the electronic circuits. It is a passive
element that resists the flow of electrons. Thus it allows only certain amount
of current to pass through it. Remaining current is converted into heat.
The
working principle of bulb is that electricity is passed through the filament
usually tungsten, which is a resistor. The energy is converted to and released
as light and heat.
Resistor Symbols
Generally
there are two standards that are used to denote the symbol of a resistor
viz.Institute of Electrical and Electronics Engineers (IEEE) and International
Electro Technical Commissions (IEC).
The
IEEE symbol of resistor is a zigzag line as shown in the below figure.
Resistor IEEE Symbol
The
IEC symbol
Resistor IEC Symbol
Why is a resistor used in a circuit?
Let
us take an example to answer this question.
·
Consider
an LED connected to a battery of 9V. Assume the Forward current of the LED is
3mA.
·
If
a resistor is connected between the Led and battery the Led will glow.
·
If
there is no resistor in between LED and battery, Led will glow but after some
time it heats up enormously. This is because of the more current (>30 mA)
Passing through the LED.
·
Thus
Resistor is necessary to control the current flow.
·
Resistor
used in the circuit can be used for many purposes. For example to adjust the
voltage levels, to provide biasing to active components, for dividing the
voltage levels etc.
What is a resistor made out of?
·
Resistors
are made of ceramic rods coated with a metal or metal oxide.
·
This
coating determines the resistance value of the resistor.
·
If
coating is thicker, lower is the resistance value of the resistor.
What is Resistance?
·
Resistance
is the property of the resistor to oppose the current. Let us understand this
clearly.
·
Generally
materials are divided as conductors and insulators.
·
Conductors
allows the current to flow through them as they have free electrons.
·
Insulators
do not have electrons and they oppose the free movement of electrons in them.
This opposing force is resistance.
Thus
resistance can be defined as the opposition force offered by the material to
the current flow.
How do You calculate Resistance?
The
mechanism of energy flow through a conductor can be described as follows
In
the presence of an active source, the passive elements like resistors will
always absorb energy and the currents through them will always flow from higher
potential to lower potential.
If
the same potential difference is applied between the ends of two different but
geometrically similar conductors like rods of copper and of glass, it results
in different currents. This characteristic of the conductor that results in
different currents is its electrical resistance.
The
definition of resistance can be derived from the Ohm’s law in its
Electromagnetic theory form or Continuum form
J
= σ E —-1
Here
σ is the conductivity of the material i.e. conductor.
E
is the electric field developed along the length of conductor due to flow of
electrical energy through the conductor. If ‘V’ is the voltage drop across the
conductor and ‘L’ is the physical length of conductor then
E
= V/L —-2
The
current density J is resulted within the conductor due to the flow of
electrical energy through the conductor. If ‘I’ is the current flowing through
the conductor and ‘A’ is the cross sectional area of conductor, then by the
definition of current density
J
= I/A —-3
Now
combining equations 1, 2 and 3
I/A
= σ V/L
V
= (L/Aσ) I —-4
The
term in parenthesis is constant and let us denotes it by ‘R’.
∴V = R I
This
is the Ohm’s law form in circuit analysis.
By
the definition of Ohm’s law, the current flowing through a conductor is
directly proportional to the potential difference applied.
I
∝ V
The
proportional constant is called Resistance parameter of the conductor R.
∴I = V/R
R
= V/I
The
resistance of a conductor, between its two points is determined, by applying a
potential difference V between those two points and measuring the current I .
The
unit of resistance is Volts per Ampere and is given the name Ohm (Ω).
∴ 1Ω = 1 volt per ampere = 1 V/A.
From
earlier calculations
V
= (L/Aσ) I
∴ R = L/(A σ) I
σ
is the conductivity of the conductor which is the measure of conductor’s
ability to conduct electric current.
1/σ
is the reciprocal of electrical conductivity called electrical resistivity
denoted by the symbol ρ (rho).
Resistivity
is the measure of a conductor’s ability to resist the flow of electric current.
∴ Resistance of a material ∝ resistivity of the material.
R
= ρL/A Ω
Resistance
of a conductor can be defined as the conductor’s opposition to the flow of
current through it.
Resistance
is a property of an object like conductor. Resistivity is a property of a
material from which the object is made.
What is the Power rating of a Resistor?
Power rating of a resistor is the maximum value of power
(combination of voltage and current) a resistor can handle. If the input power
of the resistor is greater than this value, resistor may damage. Power rating
of a resistor is also called wattage.
Resistors
have wide range of power ratings from 1/8th to 1 watt. Resistors with more than
1 watt are called Power resistors.
V-I Characteristics of a Resistor
V-I
Characteristics of a resistor are the relation between the applied voltages and
the current flowing through it.
From
Ohm’s law, we know that when the voltage applied across the resistor increases,
the current flowing through it also increases i.e. the voltage applied is
directly proportional to current.
The
above specifications are valid in case of a pure resistance i.e. ideal resistor
and the temperature is constant. In practical conditions, these values may vary
depending on the operating environment and the characteristics might be
different from the ideal linear values.
Variation of Resistance with Temperature
·
As
the temperature of the surroundings increases the resistance of the material
changes.
·
The
reason for this change is not because of the variations in the dimensions of
the material but rather the change in the resistivity of the material.
·
When
there is a rise in the temperature, the heat will cause an atomic vibration and
these vibrations will cause a collision between the free electrons and the
electrons in the inner layers of the atom.
·
These
collisions will use the energy of free electrons. If more collisions take
place, more energy of free electron is used and increases the resistance to
flow of current. This is the case in conductors.
·
In
case of insulators the resistance decreases with increase in temperature.
·
The
reason is the availability of number of free electrons which are released from
its captive stage.
·
In
mathematical terms, a fractional change in resistance is directly proportional
to the change in the temperature.
In
mathematical terms, a fractional change in resistance is directly proportional
to the change in the temperature.
∆R/R0∝∆T
Where
∆R is the small change in resistance
∆R
= R – R0
R
is resistance at temperature T
R0 is
resistance at temperature T0
∆T
is change in temperature
∆T
= T – T0
If
we denote the proportionality constant in the above equation as alpha (α)
Then
∆R/R0 = α∆T
Where
α is the temperature coefficient of the resistance.
The
temperature coefficient of resistance is used to describe the relative change
in resistance in association with change in temperature.
If
the change in temperature is small then the above equation can be written as
R
= R0 [1+α (T-T0)]
If
the resistance increases with increase in temperature, then the material is
said to be having a positive temperature coefficient. These materials are
conductors.
If
the resistance decreases with increase in temperature, then the material is
said to be having a negative temperature coefficient. These materials are
insulators
Variable
Resistors, on the other hand, have a variable resistance that can either be
changed manually like in case or Trimmers and Potentiometers or which
controlled by external factors like Light Dependent Resistor (LDR) or
Thermistor.
Ohm’s
Law defines the behavior of a resistor which states that the current through a
conductor is directly proportional to the voltage across the conductor. The
proportionality constant is called as Resistance.
The
mathematical representation of Ohm’s Law is I = V/R.
1.8 Capacitors
The
second important passive components is a capacitor, a device that stores energy
in the form of electric field. Most capacitors consists of two conducting
plates that are separated by a dielectric material.
If
Q is the charge on any one of the conductor plates and V is the voltage between
them, then the Capacitance C of the Capacitor is C = Q/V.
In
electronics circuits, a capacitor is mainly used to block DC Current and allow
AC Current. The other applications of capacitors are filters, timing circuits,
power supplies and energy storing elements.
There
are many types of Capacitors like Polarized, Non – Polarized, Ceramic, Film,
Electrolytic, Super Capacitors etc.
What is Capacitor?
Capacitor
is also known as condenser. This is one of the passive components like resistor.
Capacitor is generally used to store the charge. In capacitor the charge is
stored in the form of “electrical field”. Capacitors play a major role in many
electrical and electronic circuits.
Generally,
a capacitor has two parallel metal plates which are not connected to each
other. The two plates in the capacitor are separated by non conducting medium
(insulating medium) this medium is commonly known as Dielectric.
There
are different types and different shapes of capacitors available, from very
small capacitors which are used in resonance circuits to large capacitors for
stabilizing HVDC lines. But all capacitors are doing the same work that is
storing the electrical charge.
The
shape of a capacitor is rectangular, square, circular, cylindrical or spherical
shape. Unlike a resistor, an ideal capacitor does not dissipate energy. As the
different types of capacitors are available different symbols were available to
represent them which are shown below.
Why capacitors are important?
Capacitors
have many properties like
1.
They
can store the energy and it can dissipate this energy to the circuit when ever
required.
2.
They
can block DC and allow AC to flow through it, and this can couple one part of
the circuit with the other.
3.
Circuits
with capacitors depend on the frequency, so can be used to amplify certain
frequencies.
4.
As
the capacitors when applied with AC input, the current leads the voltage and
thus in power applications it increases the pay load power and makes it more
economical.
5.
It
allows high frequencies and so it can be used as a filter either to filter low
frequencies or to collect high frequencies.
6.
As
the reactance and frequency of the capacitor are inversely related, this can be
used to increase or decrease the circuit impedance at certain frequency and can
be used as filter.
Likewise,
capacitors exhibit many properties, when used in AC or DC circuits and hence
they play important role in electrical and electronic circuits.
Construction of a Capacitor
As
said before, there are different types of capacitors. These different types
will have different type of construction. A Parallel plate capacitor is the
simplest capacitor. Let us understand the construction of this capacitor.
It
consists of two metal plate separated by a distance. The space between these
two plates is filled with a dielectric material. The two leads of the capacitor
are taken from these two plates.
The
capacitance of the capacitor depends on the distance between the plates and
area of the plates. Capacitance value can be changed by varying any of these
parameters.
A
variable capacitor can be constructed by making one of these plates fixed and
other moving.
Dielectric of a Capacitor
Dielectric
acts as an insulating material between the plates . Dielectric can be any non
conducting material such as ceramic, waxed paper, mica, plastic or some form of
a liquid gel.
Dielectric
also plays an important in deciding the value of capacitance. As the dielectric
is introduced between the plates of the capacitor, its value increases.
Different
dielectric materials will have different dielectric constants, however this
value is >1.
Below
table gives value of dielectric constant for each dielectric material
Dielectric
can be of two types
1.
Polar
dielectrics: These dielectrics will have permanent dielectric movement
2.
Non
Polar dielectrics: These will have temporary dielectric moment. By placing them
in a electric field they can be induced with dipole moments.
Complex Permittivity
The
product of the relative permittivity (εr) of the dielectric material and
permittivity of free space (εo) is known as “Complex permittivity” or “Actual
permittivity” of the dielectric material. The expression for the complex
permittivity is given as follows,
ε
= ε0 * εr
The
value of complex permittivity will always be equal to the relative
permittivity, because the permittivity of free space is equal to ‘one’. The
value of dielectric constant or complex permittivity varies from one dielectric
material to another.
Some
standard values of complex permittivity (ε) for common dielectric materials are
Air = 1.0005, Pure Vacuum = 1.0000, Mica = 5 to 7, Paper = 2.5 to 3.5, Wood = 3
to 8, Glass = 3 to 10 and Metal Oxide Powders = 6 to 20 and etc.
capacitors
can be classified according to the properties and characteristics of their
insulating or dielectric material, they are given below as
1.
High
Stability & Low Loss Capacitors — Mica, Low-K Ceramic, and Polystyrene
capacitors are examples for this type.
2.
Medium
Stability & Medium Loss Capacitors – Paper, Plastic Film, and High-K
Ceramic capacitors are examples for this type.
3.
Polarized
Capacitors – Example for this type of capacitors are Electrolytic, Tantalum’s.
Working
As
said before capacitor consists of two conductor separated by a dielectric, when
there is any potential difference between the two conductors electric potential
is developed. This causes the capacitor to charge and discharge.
Let
us understand this in a practical way. When the capacitor is connected to a
battery (a DC source) , current starts flowing through the circuit.
Thus
negative charge is accumulated on one plate and positive charge is accumulated
on the other plate. This process continuous until the capacitor voltage reaches
supply voltage.
When
the charging voltage is equal to the supply voltage capacitor stops charging
further even though the battery is connected. When the battery is removed two
plates will be accumulated with positive and negative charges. Thus the charge
is stored in the capacitor.
But
when the supply voltage is from an AC source it charges and discharges
continuously The rate of charging and discharging depends on the frequency of
the source.
Example
Working
can be understood using simple example here. Below circuit shows two switches A
and B. When switch 1 is closed, current starts flowing from the battery to the
capacitor. When the capacitor voltage reaches the supply voltage, it stops
charging further.
Now
connect the switch to position B. Now you can observe the LED starts glowing
and this slowly fades out as the capacitor is discharging.
Capacitance
of the capacitor is given by
C=KεA/d
or
C=
εA/4πd
or
C
= εo * εr (A/d)
Where,
C
– Capacitance of the capacitor
A
– Area between the plates
D
– Distance between the two Plates
εo
– Permittivity of free space
εr
– Relative permittivity.
K-
Dielectric Constant
Capacitance of a Capacitor
Capacitance
is the property of the capacitor that defines the maximum amount of electrical charge
stored in it. It exists in nature everywhere.
Capacitance
may vary depending on the shape of the capacitor. Capacitance can be calculated
by using the geometry of the conductors and dielectric material properties. Let
us see the capacitance of a parallel plate capacitor.
Capacitance
is defined as the ratio of charge (Q) on the either plates to the potential
difference(V) between them ,
C
=Q/V,
Thus
current can be obtained as
I(t)=C[d(v)/d(t)]
This
can be expressed Farads (F) which is named after English physicist Michael
Faraday.
From
the above definition we can observe that capacitance is directly proportional
to the charge (Q) and is inversely proportional to the voltage (V).
Capacitance
of the capacitor can be increased by increasing the number of plates, which
helps to maintain the same size of the capacitor. Here, area of the plates is
increased.
Standard units of capacitance
Generally
Farads is a high value so, capacitance is expressed as sub units of capacitor
real time such as micro farads(uF) , nano farads(nF) and pico farads(PF).
Most
of the electrical and electronic applications are covered by the following
standard unit (SI) prefixes for easy calculations,
·
1
mF (milli farad) = 10−3 F = 1000 μF = 1000000 nF
·
1
μF (microfarad) =10−6 F = 1000 nF = 1000000 pF
·
1
nF (nano farad) = 10−9 F = 1000 pF
·
1
pF (picofarad) = 10−12 F
To
convert µF to nF or pF or to a wide range of other units and vice versa, we
need to use the Electric Capacitance Unit Converter.
Voltage Rating of a Capacitor
This
is not voltage until which the capacitor charges but the maximum voltage until
which the capacitor can operate safely. This voltage is called as working
voltage (WV) or DC working voltage (DC-WV).Below figure shows the
voltage rating of the capacitor.
If
the capacitor is applied with voltage greater than this voltage, it may be
damaged by producing an arc between the plates due to dielectric break down.
While
designing the circuits with capacitors, care should be taken such that the
voltage rating of the capacitor is greater than the voltage used in the
circuit. For example if the circuit operating voltage is 12V then it is
necessary to choose a capacitor with voltage rating of 12V or above.
This
working voltage of a capacitor depends on the factors like dielectric material
used between the capacitor plates, dielectric thickness and also on the type of
circuit which is used.
1.9 Inductors
If
capacitors store energy in the form of electric field, then inductors are
devices that store energy in the form of Magnetic Field. Inductor is nothing
but a wire that is wound in the form of a coil.
Inductor
is also a passive component and is widely used in AC equipment like filters,
chokes, tuned circuits etc.
The
core around which the coil is wound i.e. air, iron, ferrite etc. will determine
the strength of the magnetic field. Inductors oppose the change in electric
current through them and the changes in current will result in induction of
voltage.
INTRODUCTION
Inductor
consists of wire wound around a core of ferrite material that includes an air
gap. Inductor stores the energy in the form of the magnetic field. Inductor has
many electrical properties when subjected to a magnetic field. One of the
important property of this inductor is whenever the current flows through the
wire it creates the magnetic field around it. If we coil the wire, the magnetic
field is stronger. When the electric current flows through the coil the
magnetic flux will increase exponentially and stabilize at particular point,
then stores the electric energy in the form of magnetic energy. When electric
supply stops then the magnetic energy will decreases exponentially and turns
back into electrical energy. By this we can say that it will temporally store
the energy. The faster the change in the magnetic field the induced emf or
voltage will be greater. To know about current and magnetic flux relation let
us know Lenz’s Law.
Before
going to Lenz’s Law first we have to know about Faraday’s Law of induction. It
states that the magnitude of emf induced in the coil is equal to the rate of
change of flux that links with the coil. This is equated as below
ᶓ
α dΦ/dt
Whereas
the product of number of turns in the coil and flux related with the coil gives
us the flux linkage.
Lenz’s
Law states that an emf is generated by change in magnetic flux as stated in
faraday’s law. The polarity of this induced emf is such that it produces a
current such that magnetic field opposes the change which produces it.
ԑ
= -N (∂ΦB / ∂t)
Where
∂ΦB = change in the magnetic flux
ԑ
= induced emf
N
= no. of turns
A
= Area of the coil
u
= permeability of the core.
L
= Length of the coil
di/dt
= Rate of change of current in the coil.
When
the electric current is flowing in the coil, the coil will build up the
magnetic field around it. At the time of building the field , coil inhabits the
flow of current and once if the field is build, current can flow normally
through the wire. Due to this reason there will be exponential increase in the
magnetic flow before reaching the steady state. When the electric current is
turned off then the magnetic field around the coil will keep the current flow
in the coil until the field collapses. This makes the electric current to
decrease exponentially before it reaches its actual state.
When
the wire is coiled as a series of continuous loops , it is called as solenoid.
In this type , the magnetic field strength will increase or decrease with the
increasing and decreasing currents respectively. It is similar to effect of bar
magnet but with the variable field strength.
Inductor Symbols
The
symbol of Air core
The
symbol for Iron core
The
symbol for Ferrite core
The
symbol for Variable core
Inductance
is the property of an Inductor .The current generated in the inductor due to
magnetic field is proportional to the rate of change of magnetic field is
called as inductance. Higher the inductance value, more the inductor will
resists from the sudden changes in the current.
Inductance
is given by L = µN2A / l
Where
L
– Inductance of the coil.
µ
– Permeability of the core.
N-Number
of turns in the coil
A-Area
of the coil.
l
-Length of the inductor.
Self-inductance
A
change in the current causes change in the voltage in that circuit due to the
magnetic flux generated by the current flow. Simply inductance within the coil
gives us self-inductance. Chokes are best example for self-inductance effect.
Mutual-inductance
A
change in the current in one circuit causes the change in voltage of next
circuit .The linkage of magnetic field between both circuits leads to mutual
inductance. Transformers are best example for mutual inductance effect.
When
‘n’ number of inductors are connected in series the total inductance value is
the sum of all the individual inductances.
L
total = L1+L2+… +Ln
Inductors in parallel
When
‘n’ numbers of inductors are connected in parallel the total inductance value
is the low and is equated as follows
L
total = 1/ ((1/L1) + (1/L2) +..+ (1/Ln))
If
we observe these two equations these are very similar to the resistors
connected in series and parallel.
The
SI unit of inductance is Henry. It is named after the American physicist Joseph
Henry. This is denoted by ‘H’.
One
Henry is nothing but the rate of change of current in a circuit is one ampere
per second , then the resultant emf is one volt. This is equated as
H=
(V.s)/A = Wb/A.
Where
V = Volts, s = second, Wb = Weber, and A = Ampere.
INDUCTANCE PREFIXES
1mH
= 1 milli-Henry = 10-3 H
1μH
= 1 micro-Henry = 10-6 H
1nH
= 1 nano-Henry = 10-9 H
1. Material of the core
One
of the important factors that affect the inductance value is permeability. If
the magnetic permeability of the core is more the inductance is more and if
this permeability of the core is less, the inductance is also less. Because a
core with higher permeability will generate greater amount of magnetic flux for
any given amount of field force.
2. Number of turns of the inductor
If
the number of turns of the inductor increases, inductance also increases.
Because for any given amount of current , the amount of generated magnetic flux
is always greater , if the inductor consists of more number of turns.
3. Length of the coil
If
the coil length increases the inductance decreases. If the length is decreased,
inductance is increased. For any amount of given current, for longer length of
coil the generated magnetic flux results in more opposition to the generation
of that flux.
4. Area of the coil
By
taking the cross-sectional area of the coil, if the area increases the
inductance increases and if the area decreases, value of the inductance will
comparatively decreases. As the area increases more flux is induced and
inductance is more.
The
inductance value can also be affected by the external effects caused by the
other wires and components which are near by the inductor, once it is assembled
in the circuit. For accurate inductance value the approximated inductance value
has to be calculated.
Let
us consider a solenoid wound with a single layer of turns with some diameter of
the wire and the turns are placed evenly then the typical formula for approximating
the inductance value is given as follows.
L
= (d2n2)/(l + 0.45d)
Where
d
= diameter of the coil in meters.
n
= no. of turns in the coil.
L
= inductance in henry.
Current,
Voltage and power calculation
The
voltage in an inductor will depends on the rate of change of current through
the inductor. Whenever the change is created that initial change is opposed by
the induced emf. The emf induced in the coil will be same but the voltage will
acts like a source with increasing current and voltage will acts like a load
with decreasing current.
The
work done by the source in order to remain the current flowing through the coil
against the induce emf is power. It is given as
P
= d/dt (½ (L x I2)).
The
magnetic field density B (t) which is measured in tesla is equal to the
magnetic field strength H (t), multiplied by the magnetic core permeability
‘μ’ .
This
is given as
B
(t) = μ x H (t).
The
magnetic flux which is measured in webers, equal to magnetic flux density B (t),
multiplied by the cross-sectional area of the core ‘Ac’.
This
is given as
Φ(t)
= Ac x B (t).
The
energy stored in an inductor is equal to the amount of work done to establish
the current flow through the inductor and to generate magnetic flux.
This
given as
E
= ½ (L x I2)
Where:
L = Inductance,
I = current flow through the inductor and
E = Energy stored.
Example
Let
us consider the following circuit with current flowing through the coil is 5 A.
If
the switch is opened for 15 milli-sec then the emf induced in the coil is given
as
VL =
L di/dt = 0.5 (5/0.015) = 166 volts
Since
the inductors are formed by the electrically conductive metal wire , they will
have a series resistance. This series resistance will generate heat by
converting the electric current flowing through the coil. Due to this heat the
sensitivity of the inductor decreases. Thus the quality factor is nothing but
the ratio of the inductance to the resistance. This is given as
Q
= ω L/R
Where
Q
= quality factor
ω
= angular frequency (Hz)
L
= inductance (H)
R
= resistance (Ω)
Back
EMF generated in an inductor: The EMF produced in the inductor will depend on
the source currents that are either the current is AC or DC.
The
self-induced emf VL = – L di/dt is applicable only for the AC current because
there will be rate of change of current that is di/dt is not equal to zero. If
the flow of the inductor current is constant, that is at DC current the di/dt
is zero. At this stage the inductor acts like a piece of wire.
Time
constant of an inductor: Let us consider the circuit as shown below with an
inductor and an open switch.
Since
the switch is open there will be no flow of current in the circuit. Thus the
rate of change of current di/dt is zero at this condition. We know that when
di/dt is zero there is no self-induced emf in the circuit.
When
we close the switch the current will flow through the circuit and slowly rise
to its maximum value at the rate determined by the inductance of the inductor.
The rate of current which flows through the inductor multiplied by the
inductance gives us VL. Thus there will be self-induced emf (VL) in the circuit
and this value depends on the inductance value of the inductor in the circuit
VL= L di/dt .This VL will fights against the applied voltage until the current
reaches its maximum value and reaches the steady state. At this stage only the
coils D.C resistance will exists to oppose the current flow. Because in DC
inductor the variation of current take place only during the transition state
that is from zero to maximum and maximum to zero. Since DC is zero frequency
component there is no reactance offered by the circuit in steady state
condition.
Again
when the switch is opened the current flowing through the circuit will fall ,
but the inductor again will fight against this change and try to keep the
current flowing at its previous value by inducing the voltage in the other
direction.
1.
Inductor
with inductances in the nano-henry range , will only filter out very high
frequencies i.e., above 100 MHz so these are mainly used in radio frequency
circuits like old boom box in 1980s.
2.
Inductors
in micro-henry range will filter out the frequencies about 50 KHz to few MHz
These are typically used in D.C. power supplies to smooth out the voltage.
3.
Inductors
in milli-Henry range are very effective and these are used in audio crossover
circuits to separate low and high frequency sounds.
4.
Inductor
ideally acts like a low pass filter since the impedance of an inductor
increases as the frequency of a signal increases.
5.
Since
inductor will sense the magnetic fields from a distance these are used in
inductive sensors. These inductive sensors are used in traffic signalling to
detect the amount of traffic.
6.
By
combining two inductors which have a shared magnetic field will acts like the
transformer. These inductive based transformers are applicable only at lower
frequencies.
7.
In
fixed speed applications inductive motors are used.
1.10 Power Sources
DC
Power Supply
Bench
Power Supply is an important piece of equipment when it comes to working around
electronic circuits. Electronic components majorly work on DC Power Supply and
hence having a reliable source of DC Power Supply is very important.
There
are many types of Power Supplies like AC – to – DC Power Supplies, Linear
Regulators, Switching Mode Power Supply, etc.
An
alternative to bench power supply is to use a wall adapter as per the project
requirement like 5V or 12V.
1.11 Batteries
Battery
is a device that converts chemical energy in to electrical energy and provides
power to devices like mobile phones, laptops, flashlights, etc. In electronics,
we often use batteries to power our circuits, either to make the circuit
portable or just to test the functionality of the circuit.
Batteries
come in different sizes and voltage. Batteries are also classified as Primary
and Secondary. You can use Primary Batteries until they are drained out and
discard them later. In case of Secondary Batteries, you can use them even after
they are drained out by recharging them.
In
electronic circuits, we often use 1.5V AA Batteries or 9V PP3 Batteries.
1.12 Display Devices
16
x 2 LCD
The
most commonly used display module in electronic circuits is an LCD Display and
in particular, a 16 x 2 LCD Display. It is an alpha – numeric display with two
rows and 16 columns and can display a maximum of 32 characters.
1.13 7 – segment display
Another
common display module is the Seven Segment Display. It can be used to display
decimal numerals in different electronic devices like clocks, meters,
calculators, public information systems, etc.
Introduction
Seven
segment display is the most common device used for displaying digits and
alphabet. One can see a device in TV shows counting down to ‘0’, these are
nothing but seven segments. Use of LEDs in seven segment displays made it more
popular.
The
binary information can be displayed in the form of decimal using this seven
segment display. Its wide range of applications is in microwave ovens,
calculators, washing machines, radios, digital clocks etc.
The
seven segment displays are made up of either LEDs (Light emitting diode) or LCDs
(Liquid crystal display). LED or light emitting diode is P-N junction diode
which emits the energy in the form of light, differing from normal P-N junction
diode which emits in the form of heat.
Liquid
crystal displays (LCD) use the properties of liquid crystal for displaying. LCD
will not emit the light directly .These LED’s or LCD are used to display the
required numeral or alphabet. Single seven segment or number of segments
arranged in an order meets our requirements.
The
seven segment display dates back to century old. In the year 1908 F.W. Wood
invented eight segment displays which displays the digit ‘4’ by using diagonal
bar. After that in 1910 seven segment display is invented and is illuminated
using incandescent bulbs .They are used in electric power plants but has gained
no much reputation.
Later
in 1970’s, with the advent of LEDs usage of seven segment displays increased to
a large extent.
Generally
seven segment displays are available in 10 pin package. The pin diagram of
seven segment display is shown in the above figure. Seven segment display is an
electronic circuit consisting of 10 pins.
Out
of 10 pins 8 are LED pins and these are left freely. 2 pins in middle are
common pins and these are internally shorted. Depending on either the common
pin is cathode or anode seven segment displays can be either named as common
cathode or common anode display respectively.
These
are available from different vendors .They have shape of rectangular box
similar to that of IC but in large size.
From
top view 8 segments can be seen (7 display segments and one decimal point) in
the form of numeral ‘8’.
Here,
the 7 LED’s called segments are assigned with an alphabet from A to G.
Forward biasing the particular segment or LED will emit the light energy thus
illuminating a part of numeral. There is another segment assigned as H, used
for displaying dot.
The
decimal or dot point is used for representing the decimal point in a numeral.
For example to display 2.5, dot is used to represent the decimal point in this
numeral.
Generally,
in LED package either all the cathodes or all anodes of the segments are
combined to form a common pin. Thus each seven segment display will have seven
pins used for displaying the digits, one common pin and another pin for
decimal/dot point
Bottom
view of the seven segment display is shown below. The bottom view of the
segment shows 10 pins of the segment. These are cathode or anode pins of the
LEDs present in the seven segment. Seven segment is illuminated using these
pins.
The
internal structure of display is very hard. Internally, the device will have
SMD LEDs. This can be divided into two parts i.e. internal circuit and the
display. The internal circuit will have LEDs arranged in the rectangular form.
These two parts are surrounded by glass, ceramics and plastic in order to
protect them.
Seven
segment display works, by glowing the required respective LEDS in the numeral.
The display is controlled using pins that are left freely. Forward biasing of
these pins in a sequence will display the particular numeral or alphabet.
Depending on the type of seven segment the segment pins are applied with logic
high or logic zero and in the similar way to the common pins also.
For
example to display numeral ‘1’ segments b and c are to be switched on and the
remaining segments are required to be switched off. In order to display two
digits two seven segments are used.
Depending
on either the common pin is anode or cathode, seven segments are divided into
following types.
The
following are the types of seven segments.
·
Common
Anode (CA)
·
Common
Cathode (CC)
In
common anode type, all the anodes of 8 LED’s are connected to the common
terminal and cathodes are left free. Thus, in order to glow the LED, these
cathodes have to be connected to the logic ‘0’ and anode to the logic ‘1’.
Below
truth table gives the information required for driving the common anode seven
segments.
In
order to display zero on this segment one should enable logic high on a, b, c,
d, e and f segments and logic low on segment ‘g’. Thus, the above table
provides data on seven segments for displaying numerals from 0-9.
As
the name indicates cathode is the common pin for this type of seven segments
and remaining 8 pins are left free. Here, logic low is applied to the common
pin and logic high to the remaining pins.
Truth Table: The truth table of seven segment display is shown below.
Above
truth table shows the data to be applied to the seven segments to display the
digits. In order to display digit‘0’ on seven segment , segments a , b , c , d
, e and f are applied with logic high and segment g is applied with logic low.
A
seven segment display can be driven using resistors, transistors and IC’s. But
mostly the driving is done by the integrated circuits because of their ease
co-operation.
Seven
segment devices are generally made up of LEDs. These LEDs will glow when they
are forward biased. Intensity of the LEDs depends on forward current. So,
sufficient forward current has to be provided to these LEDs to glow with full
intensity. This is provided by the driver and is applied to the seven segments.
The following methods are practiced to drive the seven segments.
Driving
a seven segment using resistor is the most common method. In this, generally we
use the resistor as the driving element. Generally, LED requires 20 milli Amps
of current. Current more than this value may damage the LED. To limit this
current a resistor is used .This is called current limiting resistor. Circuit
is as shown below.
Segment
pins of the seven segment are connected using a resistor and a switch. The 8
switches are connected to the 8 current limiting resistors and they are
connected to a to g segments of display. Let us see how this circuit drives the
digital display.
To
glow the segment ‘a’, close the switch ‘a’. The current passes through resistor
and some drop occurs at current limiting resistor. Thus, the sufficient current
passes to the LED. Suppose to display digit 7 switches a, b, c are closed. But
the disadvantage here is, illuminating all the LEDs at a time reduces the
current.
Driving a Seven Segment Display with Transistor
Another
way of driving the seven segments is through transistor. In this, transistor is
used for amplifying the input current. The collector of the transistor is
connected to the common pin of the seven segment, emitter is connected to the
ground and base is connected Vcc. The transistor connected to the common pin
amplifies the current in the seven segment.
Another
way of driving the seven segments is through integrated circuits. This is
generally called as seven segment driver or decoder. The most frequently used
decoder is 4511. This is a CMOS chip which converts 4 bit binary coded decimal
to 8 bit seven segment data. CMOS seven segment decoder connected to the seven
segments is shown below.
The
above figure shows driving of a seven segment display using BCD to seven
segment decoder. Here we have to give BCD data as input to display digits 0 to
9. For example, to display the digit 7 the input to be applied is 0111.
The
decoder decodes the applied BCD input and sends the appropriate output to the
segments. The decoder outputs are connected to the seven segment inputs through
the resistors. These resistors are used to limit the current.
·
The
applications of seven segments are mostly in digital calculators, electronic
meters, digital clocks, odometers, digital clocks, clock radios, etc.
·
Today
most of the 7 segment applications are using LCDs, because of low current
consumption.
CHAPTER TWO
Basic
Test and Measurement Equipment
When
it comes to designing electronic circuits, testing and measuring various
parameters like current, voltage, frequency, resistance, capacitance, etc. is
very important. Hence, the Test and Measurement Equipment like Oscilloscopes, Multimeters,
Logic Analyzers, Function Generators (or Signal Generators) are often used
regularly.
2.0 Oscilloscope
The
most reliable Test Equipment for observing continuously varying signals is an
Oscilloscope. With the help of an Oscilloscope, we can observe the changes in
an electrical signal like voltage, over time.
Oscilloscopes
are used in a wide range of field like Medical, Electronic, Automobile,
Industrial and Telecommunication Applications.
Originally,
Oscilloscopes are made up of Cathode Ray Tube (CRT) displays but nowadays,
almost all Oscilloscopes are Digital Oscilloscopes with advanced features like
storage and memory.
2.1 Multimeter
A
multimeter is a combination of Voltmeter, Ammeter and Ohmmeter. They provide an
easy way to measure different parameters of an electronic circuit like current,
voltage etc.
Multimeters
can measure values in both AC and DC. Earliest Multimeters are Analog and
consists of a pointing needle. Modern Multimeters are Digital and are often
called as Digital Multimeters or DMMs.
DMMs
are available as handheld devices as well as bench devices. A Multimeter can be
very handy in finding basic faults in a circuit.
2.2 Function Generator or Signal Generator
A
Signal Generator, as the name suggests, generates a variety of signals for
testing and troubleshooting electronic circuits. The most common types of
signals are Triangular Wave, Sine Wave, Square Wave and Sawtooth Wave.
Along
with a bench power supply and oscilloscope, a function generator is also an
important piece of equipment when designing electronic circuits.
In this article, we have seen few Basic Electronic
Components and Test Equipment that we come across very frequently when
designing or testing electronic circuits.
There
are a lot more components like Transformers, Buttons, Switches, Connectors,
etc. which we can explore as we move forward with a project.
Transformers.
A transformer uses the principles of
electromagnetism to change one A.C. voltage level to another. Faraday's work in
the 19th century showed that a changing current in a conductor (e.g. a
transformer primary winding) sets up a changing magnetic field around the
conductor. If another conductor (secondary winding) is placed within this
changing magnetic field a voltage will be induced into that winding.
Turns Ratio.
Faraday also calculated that the
voltage induced into the secondary winding would have a magnitude that depends
on the TURNS RATIO of the transformer. i.e. If the secondary winding has half
the number of turns of the primary winding, then the secondary voltage will be
half the voltage across the primary winding. Likewise, if the secondary winding
has twice the number of turns of the primary winding, the secondary voltage
will be double the primary voltage.
Power ratio.
Because the transformer is a passive
component, (it has no external power supply) it cannot produce more power out
from its secondary than is applied to its primary. Therefore if the secondary
voltage is greater than the primary voltage by a particular amount, the secondary
current will be smaller than the primary current by a similar amount, i.e. If
the voltage is doubled the current will be halved.
Fig 11.1.1 Basic Transformer Operation.
Transformation Ratio.
Basic Transformer operation can be
described by two formulae relating the transformation ratio to the turns ratio
of the transformer windings.
·
VP = the primary voltage.
·
IP = the primary current.
·
VS = the secondary voltage.
·
IS = the secondary current.
·
NP = the number of turns in
the primary winding.
·
NS = the number of turns in
the secondary winding.
Transformer Losses.
The formulae in Fig. 11.1.1 relate to
an ideal transformer, i.e. a transformer with no power losses, in which,
Primary volt amperes = Secondary volt amperes. While practical transformers can
be extremely efficient, some losses will occur because not all of the magnetic
flux produced by the primary winding will link with the secondary winding. The
power losses that occur in a transformer are of three types;
Copper Losses.
These losses can also be called
winding losses or I2R losses, because they can occur in windings made from
metals other than copper. The losses become evident as heat, generated in the
(copper) wire windings as they dissipate power due to the resistance of the
wire. The power loss in a transformer winding can be calculated by using the
current in the winding and its resistance, in formula for power, P = I2R.
This formula is the reason copper losses are sometimes called I2R
losses. To minimize the losses the resistance of the winding must be kept low,
using wire of suitable cross sectional area and low resistivity.
Hysteresis losses.
Each time the alternating current
reverses (once each cycle), tiny "magnetic domains" within the core
material are reversed. These are physical changes within the core material and
take up some energy. The amount of energy used depends on the
"reluctance" of the core material; in large cores of power transformers
where hysteresis loss maybe a problem it is largely overcome by using special
low reluctance "grain oriented" steel as the core material.
Eddy Current losses.
Because the iron or steel core is an
electrical conductor as well as a magnetic circuit, the changing current in the
primary will tend to set up an EMF within the core as well as in the secondary
winding. The currents induced into the core will oppose the changes of magnetic
field taking place in the core. For this reason these eddy currents must be
kept as small as possible. This is achieved by dividing the metal core into
thin sheets or "laminations" each one insulated from the others by an
insulating coat of lacquer or oxide. Laminated cores greatly reduce the
formation of eddy currents without affecting the magnetic properties of the
core.
Ferrite Cores.
In high frequency transformers eddy
current losses are reduced by using a core made of a ceramic material
containing a large proportion of tiny metal particles, iron dust or manganese
zinc. The ceramic insulates the metal particles from each other, giving a
similar effect to laminations, and performing better at high frequencies. Due
to the ways of reducing losses described above, practical transformers closely
approach the ideal in performance. In large power transformers, efficiencies of
about 98% can be achieved. Therefore for most practical calculations, it can be
assumed that a transformer is "Ideal" unless its losses are
specified. The actual secondary voltages in a practical transformer will be
only slightly less than those calculated using the theoretical transformation
ratio.
Off Load Current.
Because the action of a transformer
is nearly perfect, the power in both primary and secondary windings is the
same, so when no load is put on the secondary, no secondary current flows and
the power in the secondary is zero (V x I = 0). Therefore, although a voltage
is applied to the primary no current will flow, as the power in the primary
must also be zero. In practical transformers the "Off Load Current"
in the primary is actually very low.
Volts per Turn.
A transformer with a primary winding
of 1000 turns and a secondary winding of 100 turns has a turn’s ratio of
1000:100 or 10:1. Therefore 100 volts applied to the primary will produce a
secondary voltage of 10 volts. Another way to consider transformer voltages is
by volts/turn; if the 100 volts applied to the 1000 turn primary produces
100/1000 = 0.1 volts per turn, then each single turn on the 100 turn secondary
winding will produce 0.1V so the total secondary voltage will be 100 × 0.1V =
10V. The same method can be used to find the values of voltage appearing across
individual tapping’s of an autotransformer when the number of turns per tapping
is known. Simply divide the total voltage across the whole winding by the total
number of turns, and multiply this result by the number of turns in the
particular tapping.
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