Date: _________

3. STUDY OF ACTIVE AND PASSIVE COMPONENTS

INTRODUCTION

An electronic circuit is composed of various types of components. Some of these components

are termed as active components because they take part in the transformation of the energy
while other components, which only dissipate or store energy, are called as passive elements.
The vacuum tubes, rectifier, transistors are some of-the common active while the resistances,
which dissipate the power and energy storing elements such as capacitances and inductances
are known as passive elements. The transformers may be regarded as a matching device.
The success of any electronic circuit depends not only on proper selection of the active
elements but on the passive and matching elements too. The proper function, of an active
device is decided by the proper values of these passive elements. Hence the selection of these
elements such as resistances, inductances, capacitance, and transformers not only require the
proper attention, but also decide the proper function of the active devices as well as the
circuit as a whole.

ELECTRONIC COMPONENTS:

These can be classified into

Passive Components: Components like resistance, capacitance inductance, and fall in this
class.
Active Components: They can be further classified as
 Semiconductor Devices: Semiconductor diode, zener diode, and varactor diode
etc.Uni-junction transistor, Bipolar junction transistor (BJT), FET, Controlled rectifier
etc.
 Vacuum Tube Devices : Vacuum tube diode, triode, Tetrode, Pentode, Hexode,
Heptode etc.
 Gas Tube Devices: Gas diodes, Thyratons etc.
 Photo Sensitivity Devices: Gas photodiodes, photo multiplier tubes, photodiodes,
light emitting diode, photosensitive transistor etc.

PASSIVE DEVICES:
RESISTANCES: Resistors can be made to control the flow of current, to work as Voltage
dividers, to dissipate power and it can shape electrical waves when used in combination of
other components. Basic unit is ohms, ()

RESISTIVE ELEMENTS Metal alloys, carbon and graphite used with binders etc. are the,
usual resistive materials. The alloys used as resistance wire usually have higher specific
resistances than the base metals and have lower temperature coefficient of resistance. The
three most common types of resistance wire used are nickel-copper, nickel. Chromium-
aluminum and nickel-chromium. Carbon and graphite are used as the basic resistance
materials when they are mixed and heated with proper variety of resin binders. These types
of resistances are generally known as composition carbon type’s resistors. The resistive
element may be either in the form of a film or a solid slug, which consists of a number of
conducting particles held together by resin. In the film type the base materials may be glass,
ceramic and plastics.
Resistors can be
(i) Fixed resistors with two ends,
(ii) Variable resistor orpotentiometers.
Resistors are specified by the value of resistance, in ohms maximum power dissipation in
watts, and precision in %.
Types: Resistors can be designed in many ways by usage, shape, physical construction
tolerances, resistances are of the following three types i.e.

(i) Fixed Resistors

(ii) Semivariable Resistors
(iii) Variable Resistors

The fixed resistances are those whose values cannot be changed. In case of semi variable
types of resistances their values can be changed with help of a screwdriver. Semi variable
types resistances are known as preset. In case of the variable resistances their values can be
changed from zero to maximum with the help of a movable arm.

Types include : Metal oxide, non inductive, carbon composition, carbon film, metal film,
deposited film, ceramic, chip fixed, variable, trimmer, carmet, miniature, PC Board SPST
combination, wire wound fixed and variable units, dual potentiometers, power resistors,
precision, conductive plastic, hybrid and surface mount.

Resistances in series R = R1 + R2 + R
Resistances in parallel 1/R = 1/R1 + 1/R2 + 1/R3 + -Voltage drop
V = I.R I is current,
Power dissipation P = I2.R = V2/R

RHEOSTATE:
A wire wound pot that can dissipate 5 and more watts is often referred to as a rheostat. The
resistance wire is wound on an open ring of ceramic which is covered with vitreous enable,
except for the track of the wiper arm. Rheostats are used to control motor speeds, x-ray tube
voltages, ovens and many other high power applications.

THERMISTOR:
A Thermistor is non-linear resistance made of semiconductor material that is extremely
sensitive to change in temperature. For a small change in body temperature of a Thermistor,
there is an appreciable change in its resistance, where as most conductors have a positive
temperature coefficient, the thermistor can exhibits a positive or negative temperature
coefficient, (NTC). The thermistor is mostly negative temperature coefficient resistances.
The resistances of thermistor decreases rapidly for increased temperature.
The thermistor are used in wide variety of applications. They can be used in measurement
and control of temperatures, time delay, temperature compensation and liquid level
indicators. The thermistor is available in the form of a disk, bead, or bolted assembly
packages.

Temperature-Resistance Characteristics of Thermistor.

VARISTORS:
These are voltage dependent resistances. They also fall under the category of non- linear
resistors. According to the Ohm's Law the current is directly proportional to the impressed
voltage but in case of varistors the current is proportional to the nth power of the impressed
voltage i.e.
I α Vn
where I is the current in Amperes and V is the impressed voltage on the Varistors. Figure-2
shows the V-I characteristics of the Varistors.

V-I characteristic of Varistors

Application of the varistor includes voltage surge and protective circuits and the generation
of non-sinusoidal waveform. The varistors are made out of silicon carbide and is available
in the form of disk, rod or washers. They can withstand and d.c.voltage upto 10 kV or so.

CAPACITORS :
It stores the charge across its two plates. Capacitor opposes the change of voltage across its
plates; the electric field developed across the plate opposes the rapid change in voltages. It
produces phase difference between voltage applied to it and the current, which passes
through it. The current leads the voltage by 90º in the ideal capacitance with infinite
resistance across the plates.
Design of capacitor is connected with relation of the proper electric material for particular
type of application. The dielectric material used for capacitors may begrouped in the various
classes. The dielectric coverage for different value of capacitor is shown below

The value of capacitor never remains constant except under certain fixed conditions. It
changes with temperature, frequency and ageing. The capacitance value marked on the
capacitor strictly applies only at specified room temperature and at low frequencies. The
behavior of capacitor at various frequencies may be grouped into the following seven classes.

Mica, glass, air, and low loss ceramic capacitors are used from few kHz to few hundreds
MHz.

Paper and metalized paper capacitor cover the frequency range from few Hz to few hundred
kHz.

High dielectric constant ceramic capacitor can only be used between the frequency ranges
from few kHz to few hundred of kHz however, they can find use from very low frequency
to 1000 kHz. Aluminum electrolytic capacitor can find use at power frequency from 10Hz
to 1000Hz but can be used up to 10 kHz.
Tantalum electrolytic capacitor may be used from dc to few hundred Hz. Polyethylene, tere-
phthalate (Mylar), cellulose acetate capacitor may find use from few hundred Hz to few
MHz.
Polystyrene, polyethylene, poly-tetra-fluoro-ethylene (Teflon) capacitors are used from dc
to 1000 MHz range. They are reported to give satisfactory performance even at higher
frequencies.

The capacitance units in farads µF,pF,nF

Value of the capacitance is given by Its value and the max specify. Voltage whichcan be
safely applied to its

When capacitor is put in parallel the over all capacitance C in series

C = C1+C2+C3 + ------
Parellel is

C=

VARIABLE: Air variable capacitors are supplied as single or multi gauge type, and
trimmers.

VARACTORS :( voltage variable capacitors) When a p-n diode is reversed biased the
depletion, region becomes devoid of free electrons and holes. Thus in such a situation the
depletion layer may be considered to be layer while the p and n regions as the plates of
capacitors.
When the reversed biased increased the width of the depletion layer will increase, hence the
capacitance will decrease. While with reduction of reverse bias the capacitance will increase
as shown

Such types of diodes are also known as voltage variable capacitors or varactors. The
symbol of the varactors diodes in shown

symbol of the varactors

Capacitors are named in a number of ways: after the dielectric they use, or their
application or some physical attribute.

TRANSFORMERS:
The transformers used in electronic circuits may be classified into three classes depending on
their application.
 Power transformers used with power supplies.

S. Type Symbol
N
o.

1 Transformer with magnetic core

2 Shielded, transformer with

magneticcore

3 Magnetic core with a shield

betweenwindows

4 Air corded transformer

One winding transformer with

adjustable inductance

6 Transformer with tapings

 7 Autotransformer

8 Single phase three winding

transformer

9 Three phase with 1-phase two

winding transformer

Table shows various types of symbols of transformers.

 Audio transformers cover the input and output transformers and isolation
transformers.
 Pulse transformers used in various types of pulse circuits.

INDUCTORS: Like capacitors, inductors also store energy in one part of AC cycle and
return it during the next part of the cycle.

Inductance is that property of a device that reacts against a change in current through the
device. Inductors are components designed for use in circuits to resist changes in current and
thus serve important control functions.

Inductor designed is based on the principle that a varying magnetic field induces a voltage in
any conductor in that field. Thus, a practical inductor may simply be a coil wire. The current
in each loop of the coil produces a magnetic field that passes through neighboring loops. If
the current through the coil is constant the magnetic field is constant and no action takes
place. A change in the current, however,produces a change in the magnetic field. The energy
absorbed or released from the changing magnetic field reacts against the change in current,
and this is exhibited as in induced voltage (electromotive force, emf), which is counter to the
change inapplied voltage. The inductor thus behaves as impedance to ac current.

The counter emf is directly proportional to the rate of change of current through the coil
(VL=L[di/dt]). The proportionality constant is the inductance L, which has the unit of henrys
(H) In an ac circuit, as shown in, the inductor offers reactance to alternating current. The
inductive reactance XL has the units of ohms and is given by
XL = wL = 2fL
Total inductance L = L1 + L2 + L3 -----------
Inductances in parallel: 1/L = 1/L1 + 1/L2 + 1/L3

SEMICONDUCTORS DEVICES:

It is not easy to define a semiconductor if we want to take into account all its physical
characteristics. However, a semiconductor is defined on the basis of electrical conductivity as
under A semiconductor is a substance which has resistivity ( 10-4 to 0.5' m) in between
conductors and insulators e.g. germanium, silicon, carbon etc. When a semiconductor is
neither a good conductor nor an insulator, then why not to classify it as a resistance material?
The answer shall be readily available if we study the following table :

Sr. Substance Nature Resistivity

No
.
1 Copper Good conductor 1.7 × 10-8 m
2 Germanium Semiconductor 0.6 ‘ m
3 Glass Insulator 9 × 1011 '  m
4 Nichrome resistance material 10-4  m

Comparing the resistivity of above materials, it is apparent that the resistivity of germanium
(semiconductor) is quite high as compared to copper (conductor) but it is quite low when
compared with glass (insulator). This shows that resistivity of a semiconductor lies in
between conductor and insulators. However, it will be wrong to consider the semiconductor
as a resistance material. For example, nichrome, which is one of the highest resistance
material, has resistivity much lower than germanium. This shows that electrically germanium
cannot be regarded as conductor or insulator or a resistance material. This gave a such
substances like germanium the name of semiconductors.

It is interesting to note that it not the resistivity alone that decide whether a substances
semiconductor or not. For example it is just possible to prepare an alloy whose resistivity
falls within the range of semiconductors but the alloy cannot be regarded as a semiconductor.
In fact, semiconductors have a number of peculiar properties which distinguish them from
conductors, insulators and resistance materials.

PROPERTIES OF SEMICONDUCTORS:

The resistivity of semiconductor is less than an insulator but more than a conductor. The
semiconductors have negative temperature coefficient of resistance i.e. the resistance of
semiconductor decreases with the increase in temperature and vice- versa. For example
germanium is actually an insulator at low temperatures but it becomes a good conductor
at high temperatures.
When a suitable metallic impurity (e.g. arsenic, gallium etc.) is added to a semiconductor, its
current conducting properties change appreciably. This propertyis most important.

Two type of semiconductor material known as P - type and N - type such as silicon and
germanium.

p-type : Impurity of lower group, it contain excess of holes or deficiency of electrons.

n-type : Impurity of higher group, contains excess of electrons or deficiency of holes.

DIODES :
By forming a junction of n & p type material. Barrier potential is formed across the
junction due to crossing of holes to n side and crossing of electron to p side.

This property of current flow in only one direction i.e. when the diode is forward biased is
used in rectification. Though, theoretically the forward resistance of the diode is zero but
practically it is not. The voltage drop in forward direction is v = i rd.

CHARACTERISTICS :

Where Rd is dynamic forward resistance. The junction drop is 0.3V in Germanium. And
0.7V in silicon diode.

Characteristic of Diode
Diodes are specified by max reverse voltage, and forward voltage and maximum current
capacity maximum frequency of operation. Diodes are used in power supplies, for
rectification, and in pulse shaping applications.

Characteristic of Zener Diode

ZENER DIODE:These diodes are operated in reverse bias mode, as the reverse bias is
increased the resistance remains constant until a certain value known as avalanche point is
reached due to avalanche effect the current suddenly increases and the voltage across it
becomes almost constant. \\

Zener voltage may vary from as little as 3 volt to 150 volts depending on the way the Zener is
manufactured used as the voltage regulator.

TRANSISTORS :

Bipolar junction Transistors (BJT) :

It is a three-layer device having two junctions npn and pnp transistors are possible.

Base of emitter junction is forward biased.

Therefore having low resistance. Base to collector junction is reverse biased offering
very high resistance. The order of collector current and emitter current is same but the
collector circuit resistance is very high therefore resulting in voltage or power amplification.
It works in three configurations
INTEGRATED CIRCUITS (I.C’S)
Transistors may be used as discrete units or as components of a microelectronic circuit. The
advent of microelectronics has not affected the functions of the basic components-namely,
transistors, resistors, and so on.

The major difference is that all these components are available as an electrical functional unit
fabricated on a single small IC chip. Many problems of circuit design are solved with the
IC, thus simplifying the design, operation, and maintenance of instrumentation.
ICs may function in a linear or nonlinear manner. The output of a linear IC is directly
proportional to the input. Linear IC applications include many types of amplification,
modulation, and voltage regulation. The operational amplifier is the most important type of
linear IC. Nonlinear ICs include all digital ICs and other circuits where there is not a linear
relationship between the input and output signals. Digital ICs, the most important type of a
nonlinear ICs, usually use some form of bi- stable (on/off) operation. These ICs are common
in computer circuits and in other digital applications such as counters, calculators, and digital
data communication equipment.

ICs must be placed in a protective housing and have connections to the outside world.
There are three methods of packaging ICs in containers (figure-11); the TO-5 glass metal
can, the ceramic flat pack, and the dual-in-line ceramic or plastic flat packs known as
dual-in-line packages (DIPs).

The popular, less expensive plastic (DIP packages can have 14,16,18,24 or 40 connecting
pins. A minimum of two pins is required for connecting the IC to the power supply. The
remaining connections are available for use as terminals for input and output signals.

Full Wave Bridge Rectifier

ELECTRONICS COMPONENTS AND SYMBOLS
COLOUR CODE FOR RESISTANCES
PRELAB QUESTIONS:
1. What is inductive reactance and how is it calculated? Explain its role in AC circuits.
2. Define a semiconductor and provide examples of semiconductor materials. Describe the
conductivity range of semiconductors.
3. Explain the function of resistors in electronic circuits and discuss the types of resistive
materials commonly used.
4. Discuss the concept of resistance in electrical circuits. Explain how resistors are used to control
current and voltage in electronic applications.
5. Describe the function of a rheostat in a circuit. Explain how the resistance wire and wiper arm
contribute to its operation.
6. Define capacitance and its relationship with dielectric materials. Explain the factors that affect
the capacitance value, such as temperature, frequency, and aging.
7. Demonstrate the calculation of resistance values using the color code for resistances. Use the
color bands provided to determine the resistance value.
POSTLAB QUESTIONS:
1. Differentiate active and passive components in electronic circuits. Give examples of each and
explain their purposes.
2. Explain the importance of packaging ICs and discuss the advantages and disadvantages of TO-
5 glass metal can, ceramic flat pack, and dual in line packages (DIPs).
3. Discuss the role of resistors in controlling current, shaping electrical waves, and dissipating
power in electronic circuits. Highlight the significance of choosing the right type of resistor for
specific applications.
4. Evaluate the significance of color code resistance calculation in identifying the resistance value
of resistors. Illustrate the process of determining resistance values using the provided color
code bands.
5. Reflect on the significance of selecting proper inductive and capacitive components in
electronic circuit design. How do these components influence the function of the active devices
and the overall circuit performance?
6. Discuss the classification of semiconductor devices and their respective applications in
electronic circuits. Provide examples of semiconductor devices and explain their roles in
electronic systems.