MODULE 1

Introduction to “ELECTRONICS”

Electronics – Field of science and engineering which deals with the motion of electrons under the influence of applied electric or magnetic field.

with the electron devices and their utilizations.

“ELECTRONICS DEALS WITH THE MOTION OF ELECTRONS”

ELECTRONS

• Everything is made up of atoms.
• Periodic table contains 118 elements, Each element is made up of atoms.
• An atom consists of neutrons, protons & electrons.
• The negatively charged electrons are attracted towards the positively charged protons, which holds atom together.
• Electrons can move from one atom to another, called as Motion of electrons.
• The controlled flow of charged particle is fundamental to the operation of all electronic devices.

EVOLUTION

EVOLUTION = TRANSFORMATION

Vacuum Tube

Transistor

• Device that controls electric current flow through semi conductor materials.

• Transistor is a 3 layer or 3 terminal device – Emitter , Base, Collector.
• Current flow between two terminal is controlled by the third input terminal.

Transistor is classified based on ,

1. current controlled device-BJT
2. voltage controlled device-FET

USES

• Amplification.
• Switching

Integrated Circuits

• An integrated circuit is a set of electronic circuits on one small plate (“chip”) of semiconductor materials.

• • Micro miniaturization process leads to the invention of Integrated Circuits.

IC’s are classified based on the number of transistors on a Chip

SSI – Less than 100 transistors. MSI – 100 to 1000 transistors.

LSI – 1000 to 10,000 transistors. VLSI – 10,000 to 1 million transistors. ULSI – Over than 1 million transistors.

History of Electronics

Three key components :

Vacuum tubes – Transistors – Integrated circuits

Thomas Alva Edison (1883)

Discovered that electrons will flow from one metal conductor to another through a vacuum- Edison effect

John Fleming (1904)

Applied the Edison effect in inventing a two element electron tube called “ Vacuum Diode”

Lee Dee Forest (1906)

Made a break through in the field of electronics, by invention of “Vacuum Triode”-used in radio Communication, telephone etc.

John Bardeen, William Shockley and Walter Brattain at Bell Labs (1947)

Invention of Transistors (light weight, low cost ,less power etc.) made revolution in the field of electronics.

In 1958, Jack Kilby of Texas Instruments introduced the idea of Iintegrated circuit(IC) – large num. of electronic components fabricated together on a single chip.

Active and Passive Components

Active components : Capable of amplifying or processing an electrical signal with the help of passive components.

Passive Components

• They are not capable of amplifying or processing an electrical signal by themselves.
• But active components can not do anything with out the help of passive components.

RESISTORS

RESISTANCE

• The property of a substance, which opposes the flow of an electric current through it is called the resistance.
• Resistors are electronic components used to oppose the flow of current
• OHM’S LAW

According to ohms law,

Resistance is defined as the ratio of the voltage applied across a resistors terminal to the intensity of current formed in it.

Represented by letter : ‘R’

Measured in OHMS

Symbol :

SPECIFICATIONS OF A RESISTOR

Tolerance :

• Allowed variation of resistance from its normal value.
• Larger the tolerance – More the resistance variation.
• Smaller the tolerance – More stable resistance.
• Common way of specifying the resistor tolerance is in PERCENTAGE – %
• Eg: a 100 ohm resistor with 10% tolerance, means that its value can be fixed between 90 to 110ohm.

Operating Temperature :

• • The temperature that the resistor can continue to operate before being destroyed.

Temperature Co efficient:

• • TC describes the relative change of resistors physical property that is associated with the given change in temperature.

• • Positive TC – Temperature increases , Resistance also increases.
  • Negative TC – Temperature increases , Resistance decreases.

Standard Resistance values :

• • Standard resistance values are derived by assigning sufficient number of zeros or decimal points to these numbers :

10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68 and 82.

For example : 1.0 Ώ, 10 Ώ, 100 Ώ, 1.0K Ώ, 10K Ώ, 100K

Ώ, 1.0M Ώ, 10M Ώ

Types of Resistors

FIXED RESISTORS

A fixed resistor is one for which the value of its resistance is specified and cannot be varied. Major types of fixed resistors are

1. Carbon composition Resistors.
2. Wire wound Resistors.
3. Metal film Resistors.
4. Carbon film Resistors.   

Carbon composition Resistors

• • Resistive material used is composition of powdered carbon(graphite) and an insulating material.
  • Leads are made of tinned copper wires.
  • Resistor is enclosed in a plastic case to prevent the entry of moisture & other harmful contents.

Characteristics

Available resistance value – 1Ώ to 22 MΏ Tolerance Range – ± 5% to ± 20%

Power rating – 0.1W to 2W

• The size of the carbon composition resistors increases for high wattage ratings in order to withstand the higher current & heat dissipation.

Wire wound Resistors

• The wire is wound around a ceramic, plastic or porcelain insulating cylindrical core.
• Metal resistance wires such as Nichrome & Manganin can be used.
• The ends of the wire are soldered to the two caps attached to the end cores.
• The completed wire wound resistor is coated with a insulating material such as ‘Baked enamel’

Characteristics

• Available resistance range – 1Ώ to 100KΏ
• Tolerance Range – ± 5%
• Power rating – 3W to 200W
• They are stable & reliable – withstand up to 450°C.
• Disadvantage – large size, high cost & poor high frequency performance

Carbon film Resistors

• Are formed by depositing a carbon film over an insulating core.
• A helical groove is cut in it to create a long narrow resistive path
• Thickness of helical groove decides the required resistance.
• Contact caps are fitted on both ends with tinned copper wire.

Characteristics

Available range – 10Ώ to 100 MΏ Tolerance Range – ± 5%

Power rating – 0.1W to 0.5W

• Also known as precision type resistor

Advantages – better stability against temperature and humidity

Metal film Resistors

• It is constructed by using Film deposition techniques
• depositing a thin or thick film of resistive material (nichrome) on an insulating substrate (ceramic core).
• Desired resistance values are obtained by either trimming the layer of thickness or by cutting the helical grooves of suitable pitch along its length.

• • Used when more accurate value is needed
  • Protective coating is used to safeguard the device from moisture and mechanical stress

Characteristics

Available range – 0.1Ώ to 10^4 MΏ Tolerance – ±0.05%

Power rating – 1W

VARIABLE RESISTORS

• The resistance value of a variable resistor can be changed
• Used in electronic circuits to adjust the values of currents and voltages
• Applications: changing the volume of sound, brightness of a television

• This gives three connections to the component: two connected to the fixed element, and the third is the slider.

1. Rheostat.
2. Potentiometer.
3. Preset.

VARIABLE RESISTORS

Potentiometers

• Also called as ‘POT’ – is a special form of variable resistor with 3 terminals.
• 2 terminals connected to the two ends of the resistive elements & third one connects to a sliding contact.
• Potentiometers are manufactured as carbon composition, metallic film and wire wound resistors

• can be constructed as linear or non linear.
• Linear-wire is wound of uniform width, resistance varies linearly with the movement of contact
• –used in voltage divider circuits
• Nonlinear- width is not uniform
• –used in radio & TV receivers for volume control, brightness control, contrast control etc.

II Rheostat

• It is used to control the current flow in circuit branches.
• Construction – A resistive wire is wound over an insulating ceramic core and a wiper slides over the winding.

• Used in high power applications such as controlling the speed of motors, intensity of light etc.

III Presets

• Presets are used in applications where the variation of resistance is not done frequently
• Preset is a kind of potentiometer having a metallic wiper that can be moved with a screw driver
• Track on which wiper moves is carbonized or metallized ceramic
• Application: Presetting the line and frame frequency in a TV receiver.

 Preset Resistor

MODULE 1

• Capacitance is defined as the ratio of the electric charge Q on each conductor to the potential difference V between them C=(Q/V).
• When there is a potential difference across the conductors, capacitor gets charged
• An electric field develops across the dielectric, causing positive charge +Q to collect on one plate and negative charge −Q to collect on the other plate.
• The SI unit of capacitance is the farad (F).

A capacitor offers low impedance to AC but very high impedance to DC – BYPASS Capacitor.

Symbol of a capacitor

SPECIFICATIONS OF A CAPACITOR

Nominal capacitance

• The nominal value of the capacitor is the value measured in pico-Farads (pF), nano-Farads (nF) or micro-Farads (µF)
• It is marked onto the body of the capacitor as numbers, letters or coloured bands.

Voltage Rating

• The maximum voltage that a capacitor can safely be exposed to and store.

Leakage Current

• The dielectric used inside the capacitor to separate the conductive plates is not a perfect insulator
• It results in a very small current flowing or “leaking” through the dielectric due to the influence of the powerful electric fields built up by the charge on the plates when applied to a constant supply voltage.

Working Temperature( T )

• Changes in temperature around the capacitor affect the value of the capacitance because of changes in the dielectric properties.

Breakdown voltage of a capacitor

Temperature Coefficient, ( TC )

• It is the maximum change in its capacitance over a specified temperature range.
• It is generally expressed as parts per million per degree centigrade (PPM/°C)

Tolerance

• Tolerance rating expressed as a plus-or-minus value either in picofarad’s (±pF) or in microfarads(±uF)
• A 100µF capacitor with a ±20% tolerance could legitimately vary from 80µF to 120µF and still remain within tolerance.

FIXED CAPACITORS

I Electrolytic Capacitor

• They are polarised capacitors
• anode electrode (+) are made of a special metal & insulating oxide layer acts as the dielectric of the electrolytic capacitor.

• A non-solid or solid electrolyte which covers the surface of the oxide layer serves as the second electrode (cathode) (-) of the capacitor. The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again.
• Depending on the nature of the anode metal used and the electrolyte used, there are two kind of electrolytic capacitors.
• 1. Aluminum electrolytic capacitor
• 2.Tantalum electrolytic capacitor

Aluminum electrolytic capacitor

• Use a high-purity etched aluminum foil as electrode and aluminium oxide (Al2O3) as dielectric.
• The electrolyte forms the second plate of capacitor.
• Another layer of aluminium without oxide coating is also provided for making electrical contact between one of the terminals and electrolyte.

Characteristic:

• Capacitance Value ranges from 1uF to thousands of uF.
• Voltage ranges from 1V to 500V
• Filtering of ripples in power supply

INDUCTOR – CAPACITOR FILTER

Rectifier output

Tantalum electrolytic capacitors

• Use a high-purity tantalum powder with tantalum pentoxide as dielectric.
• They are used in circuits which demands high stability in capacitance value.
• They are lighter and smaller than aluminium electrolytic capacitor
• Characteristics:
• Working voltage- up to 50V
• Capacitence values- 47nF to 470uF

II Mica Capacitors

• Mica is a transparent, high dielectric strength mineral, having high breakdown voltage & is chemically inert, which produce high stable capacitors.
• Mica capacitors are constructed by sandwiching layers of metal foil separated by mica strips.

Capacitance value – 5 to 10,000pF Tolerance – ± 1 to ± 20

Voltage ranges –up to 500V

• Advantages: Good insulation, hence they can utilized in high voltage circuits.
• Disadvantage: Expensive and do not have high value of capacitence.

• Application: Used in resonance circuits & high frequency filters

III Ceramic capacitors

• This type of capacitor consists of ceramic disc with copper or silver plating deposited on opposite faces of ceramic.
• Leads are attached to these plates.
• They can be used in high frequency applications.
• Have no polarity can be used in ac and dc circuits

• The two most common types are multi-layer ceramic capacitors and ceramic disc capacitors.

ceramic disc capacitors

Multilayer Ceramic Chip Capacitor :

Layers of ceramic and metal are alternated to make a multilayer chip capacitor.

Capacitance value : 100pF to 0.1uF Voltage ranges – 100v to 100 kV

IV Paper capacitor

• Paper capacitor consists of metal foils separated by strips of paper
• This paper is coated with a dielectric material such as wax, plastic or oil.

• They have no polarity and can be used in both DC & AC circuits.

• Disadvantage- Large size

Capacitance value : 500pF to 50uF

Tolerance : ±10% to ±20% Voltage ranges : 100V to 100kV

V Plastic Film Capacitor

• Plastic film capacitors are constructed in basically the same way as paper capacitors, expect that a thin sheet of plastic ( such as Mylar, Teflon or polyethylene) is employed as dielectric.
• This dielectric improves the properties of the capacitor by minimizing leakage currents, even at temperatures of up to 150-200°C.

Capacitance value : 5000 pF to 10uF Tolerance : ±20%

Voltage range : 100V to 600V

VARIABLE CAPACITORS

I Gang Capacitor

• Gang capacitors is a group of capacitors ganged together.
• It is a rotor-stator type variable capacitor which consists of two sets of metal plates.
• The fixed plates are connected together to form the stator & movable plates are connected together to form the rotor.

• Capacitance is varied by rotating the shaft.
• Gang capacitors are used in radio receivers to tune the radio frequencies.

II Trimmer

• • Trimmer capacitors are used in electronic circuits, where the frequent capacitance variation is not needed.
  • The dielectric may be mica or ceramic.

• • A screw mounted on the trimmer helps to vary the capacitance.
  • It produce low value capacitance in the order of pF and find applications in TV, radio and other broad cast receivers.

III Padder

• • It is a trimmer with comparatively high value capacitance with air as dielectric.
  • It consists of two concentrically mounted tiny aluminium cups.

• • By turning the screws, the air gap between the two aluminum cups can be varied to vary the capacitance.
  • Capacitance value : 5pF to 600pF.

NUMBERING OF CAPACITORS

Step 1:

• If the number written on the capacitor is greater than 1 = value is in pF
• If the number written on the capacitor is less than 1= value is in uF.

Example : 10 = 10pF, 0.1 = 0.1uF

Step 2:

• If there are 3 digits in the number, the third number indicates the number of zeros to be put after the 2 digits & the value will be in pF.

Example : 104 = 10,0000 pF or 0.1 uF

Step 3:

• If the letter K follows the digits, the value will be in kilo picofarads.
• If the letter is ‘n’ or ‘ M’ then it will be nano farads or micro farads.

Example : 10k = 10kpF, 47n = 47nF, 47M = 47uF

Step 4:

• If the letter n , M or k is between 2 numerals, the value of the capacitor can be obtained by putting the decimal in place of that letter and multiplying by the respective factors nF, uF or kpF.

Example : 4k7 = 4.7kpF , 2M2 = 2.2uF

Step 5 :

• If the letters k or M follows the 3 digit number, it implies the tolerance value

K = 10%

M = 20%

COLOUR CODING OF A CAPACITOR

• The inductance of a circuit is one Henry
  • if the rate of change of current in a circuit is one ampere per second and this results in an electromotive force of one volt.
• Inductor offers high impedance to AC and low impedance to DC.
  • Inductance offered by an inductor = SL , s=jω
• Inductane of a inductor depends on :

I Number of turns of the coil.

1. area of the coil.
2. Nature of the core.

Specifications

• Nominal Inductance – Inductor specifications normally include the value of inductance (expressed in H, μH, or nH)
• Current Rating – The maximum current which can be continuously applied to the inductor under a given set of conditions.
• Tolerance – as the maximum permissible percentage deviation from the marked value.
• Temperature coefficient –
  • It is the maximum change in its inductance over a specified temperature range.
  • usually expressed in parts per million, ppm, per unit temperature change.

• DC Resistance – the amount of resistance that an inductor can for passing DC signals.

Based on the type of core used, inductors have been classified I Air core Inductor

• Made of thin copper wire wound over a former made of thick card board.
• 
• Have low inductance value & suitable for radio (high) frequency applications.

II Iron core Inductor

• Made of copper wire wound on a laminated iron core.
• Laminated iron core consists of thin iron sheets pressed together & insulated from each other-avoid eddy cureent loss
• Suitable for Audio (Low) frequency applications.

Eddy current create flux which oppose the flux lines that original created them

III Ferrite core Inductor

• Made of copper wire wound on a ferromagnetic material called ferrite.
• In variable type ferrite core inductor, the ferrite core is made to move in & out of the coil, there by the inductance value can be changed.
• Variable inductors are used in frequency tuning application.
• Choke is an inductor that is used to block high frequency alternating current(AC) in an electrical circuit, while passing low-frequency or direct current(DC)

I Filter Chokes :

• It has many turns of fine wire wound on an iron core made of laminated sheets
• It is used in smoothing the pulsating currents produced by rectifying AC into DC.

II Audio Frequency Chokes :

• AFCs are used to provide high impedance to audio frequencies (about 20Hz to 20kHz).
• Smaller in size & have lower inductance in comparison to filter chokes.

III Radio Frequency Chokes :

• RFCs are used to provide high impedance to radio frequencies ( above 10kHz).
• They are often wound in complex patterns to reduce self- capacitance and proximity effect losses.
• Radio frequency chokes (RFC) often have iron powder or ferrite cores.
• Proximity effect

In parallel wires the distribution of AC current is not uniform. The presence of magnetic fields generated by nearby wire affect the current in other and increases the resistance of the conductors. This effect is known as proximity effect.

MODULE 1

• Transformer is an electrical device which is designed to transfer electrical energy from one circuit to another at different voltages without changing frequency
• It works on the principle of mutual induction.

• A varying current in the transformer’s primary winding creates a varying magnetic flux in the core.
• Since the core is common for secondary winding, this varying magnetic field induces a varying electromotive force (EMF) or voltage in the secondary winding.
• The primary and secondary windings are wrapped around a core of infinitely high magnetic permeability.
• Thus all of the magnetic flux passes through both the primary and secondary windings

• • With a voltage source connected to the primary winding and load impedance connected to the secondary winding, the transformer currents flow in the indicated directions.

According to Faraday’s law of induction, an emf induced in any circuit is due to the rate of change of magnetic flux linkage through the circuit.

• Back EMF – Self induced EMF in primary winding opposes the applied voltage.
• If DC is applied to a Transformer, flux produced in primary will not vary & remain constant in magnitude

• Voltage Rating : It is the maximum voltage that the transformer winding can produce.
• Current Rating : It is the maximum current that the transformer winding can carry.
• Power Rating : It is the maximum power which can be continuously delivered by the transformers.
• Frequency Range : It is the range of frequencies in which the transformer operates without failure.
  • Regulation : It is the measure of the ability of a transformer to maintain its rated output voltage under load.
  • It is expressed in percentage.

I. Power Transformers

Power transformers are of two types – Step up & Step down transformers.

Step up Transformer :

• • • The number of turns in the primary winding is less than that in secondary winding.
    • The AC voltage fed across the primary gets boosted up & available across the secondary winding.

Step down Transformer :

• • Number of turns in the secondary winding is less than that of primary winding.
  • It converts the high voltage signals to low voltage.

II Audio Frequency Transformer

• • These transformers are used in Audio frequency (low frequency) applications in the range of 20 – 20,000Hz.
  • AF transformers are used for voltage, current and Impedance transformation.
  • AF transformers are also called as Input – Output Transformers.
  • Input transformers are used to couple low impedance source such as microphone, transmission line etc with high impedance circuit like amplifiers.
  • Output transformers are used in public addressing system to match the high output impedance of an amplifier with loud speaker having low impedance.

III Auto Transformers

• • In ideal transformers, the primary & secondary windings are completely insulated from each other and magnetically linked by a common core.
  • But in auto transformer, both windings are inter related electrically as well as magnetically. ie Single continuous winding for both the primary & secondary.
  • According to the desired secondary voltage, taps are brought out at convenient points on the winding.

Step down auto transformer

Step up auto transformer

• Electromechanical components use electromagnetic force to produce mechanical effects.
• They are widely used in electronic applications for controlling purpose.
• Electromechanical components include RELAYS and

CONTACTORS.

• A relay is an electromagnetic switch used to provide an electrical connection between two or more points in a circuit in response to the application of a control signal.
• Relays allow a low power signal to control a large amount of power.
• Relays mainly include Electromechanical relays and Solid state relays.

CONSTRUCTION & WORKING PRINCIPLE OF ELECTROMECHANICAL RELAY

• Electromechanical relay consists of
• a coil wound on a iron core.
• Iron Yoke – provides a path for magnetic flux.
• Armature – movable part of iron which is hinged to the yoke & held by a spring.
• Three contacts –
• NC(normally closed)
• NO(normally open)

Movable contact.

• When a voltage is applied at the coil input, it magnetizes the yoke.
• This causes the armature to move towards the yoke.
• Then the armature opens the NC & closes the NO contacts.
• when the voltage is removed from the coil input, the spring returns the armature to its original position.

Working of a Relay

Parameters of relays

• Coil voltage – The voltage applied to the coil to open or close the contacts.
• Coil current – The current that must be passed through the coil to open or close the contacts.
• Contact rating – The amount of current that can pass through the contact leads.
• Default state – The contact can be either open (NO) or closed (NC) by default .
• Number of poles -The number of separate circuits that can be switched by energizing the coil.

1. SP : Single Pole : one circuit is switched.
2. DP : Double Pole : two circuits are switched.

Throws: describes what happens to the contacts when the coil is energized.

• • Single Throw(ST) – Energizing the coil of a ST relay closes the contacts if it is a NO relay & opens the contacts if it is a NC relay.
  • Double Throw (DT)– Energizing the coil of a DT relay can either open or close the contacts, depending on how it is wired.

Different type of relays

CONTACTORS

• Contactors are relays that switch high current loads .
• it is a control device which use a small current level to energize or de-energize the loads connected to it.
• Large electric motors can be protected from over current damage through the use of overload heaters and overload contacts.
• Contactor also consists of

1. Contact – includes the power contacts as well as auxiliary contacts
2. Spring
3. Electromagnet

• • Power contacts gain the power for the contactor
  • Auxiliary contacts are used to bring a loop with the rest if the devices are attached to it.
  • Contacts are connected to the springs and controlled by the electromagnet.
  • These electromagnets give the initial force to the contacts and make them closed.

• Contacts and electromagnet are enclosed in a frame made of insulating materials.
• Contactors typically have multiple contacts which are normally- open, so that the power to the load is shut off when the coil is de-energized.

Fig. Shows an electric circuit connecting 3-phase ac power to a motor using a contactor and overload heaters.

Power contacts

• The top three contacts switch the respective phases of the incoming 3-phase ac power(410 volts)
• The lower contact is an auxiliary contact which has current rating much lower than that of power contact.
• Overload heater is a low resistance bimetallic strip of metal intended to heat up as the motor draws current.

• • If the temperature of any of these heater elements reaches a critical point, a normally closed switch contact will get opened.
• This normally closed contact is usually connected in series with the relay coil, so that when it opens, the relay will automatically de-enegize thereby shutting off power to the motor.

Solid State Relays

• These active semiconductor devices use light instead of magnetism to actuate a switch.
• When control signal is applied, the light comes from an LED falls on a light sensor.
• This light triggers a solid state switch like MOSFET that either opens or closes the circuit under control.

Solid State Relays

• Application: It is used where the circuit under control is protected from the introduction of electrical noises.
• Advantages: no moving parts, fast response, no contact bounce, low electromagnetic interference
• Drawback: it can accomplish only single pole switching

IMPACT OF ELECTRONICS

• Electronics in industry.
• Electronics in communication & entertainment.
• Electronics in medical field.
• Electronics in Instrumentation.
• Electronics in defense.