Basic Electronics Engineering Lecture Notes (58 Pages), Lecture notes of Basic Electronics

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BASIC ELECTRONICS ENGINEERING

MODULE- 1

1. ELECTRONIC DEVICE

1.1 Basic Concept of Electronics and its application.

Definition: The branch of engineering which deals with current conduction through a vacuum or gas or semiconductor is known as electronics. An electronic device is that in which current flows through a vacuum or gas or semiconductor. (Or) Electronics is the branch of science that deals with the study of the flow of electrons and their effects in a vacuum, gases, and semiconductor materials. Applications: Electronics has gained much importance due to its numerous applications in our daily life starting from home to any industry. For simplification we categorise them in some area such as  Consumer Electronics. Electronics devices which make our life easy and better such as air conditioner, cooking appliances, dryer, personal computer, mobile phones, etc.  Commercial applications. Electronic devices and gadgets are widely used for the commercial purpose such as Telephone, Air conditioning, heating, Digital Advertising, power supplies, Personal computer, MP3s, office equipment, light dimmer, uninterruptible power supplies (UPS), etc.  Medical applications. With the advancement of the electronics field, and particularly that of computer technology has made possible many of the application which made possible for nurses and doctors to examine his patient. Many machines like NMR, ECE, x-ray, etc use electronics. There is noticeable advancement of electronics in the field of medical sciences. There are a

are electronics devices. Even in commercial airlines, there are numerous electronic devices which are used to measure different physical parameters like humidity, temperature, pressure, elevation, etc.

1.2 Basic Concept of Electron

Emission & its types.

Electron emission is defined as the liberation of electrons from any surface of a substance. Any metal consists of plenty of free electrons. Even at room temperature, these free electrons moves randomly inside the metal from one atom to another but can not leave the surface of the metal to provide electron emission. This is because the free electrons reach the extreme boundary of the metal are pulled back by the positive nuclei behind them & their kinetic energy decreases. Thus at the surface of a metal, a free electron encounters forces that prevent it to leave the metal. In other words, the metallic surface offers a barrier to free electrons and is known as surface barrier. However, if sufficient external energy is given to the free electron, its kinetic energy is increased and thus electron will cross over the surface barrier to leave the metal. This additional energy required by an electron to overcome the surface barrier of the metal is called work function of the metal. The amount of additional energy required to emit an electron from a metallic surface is known as work function of that metal. Types of Electron Emission. The process of emission happens by supplying Energy equal to or greater than the work function to the metal & the electron absorbs the energy, thus able to overcome the surface barrier and leaves the metal surface. Depending on the process of supplying external energy to the metal surface, the emission is of different types. (i) Thermionic Emission.

The process of electron emission from a metal surface by supplying thermal energy to it is known as thermionic emission. In this method, the metal is heated to sufficient temperature (about2500ºC) to enable the free electrons to leave the metal surface. The number of electrons emitted depends upon the temperature. The higher the temperature, the greater is the emission of electrons. This type of emission is employed in vacuum tubes. (ii) Field emission. The process of electron emission by the application of strong electric field at the surface of a metal is known as field emission. In this method, when a sufficiently high positive charge is placed in front of the emitter surface, due to the strong electrostatic force of the created electric field, the free electron can get sufficient energy to overcome the surface barrier and can get emitted from the surface of the emitter body. As this type of electron emission is caused by the electric field present in the space, it is called field emission. The stronger the electric field, the greater is the electron emission. (iii) Secondary emission. Electron emission from a metallic surface by the bombardment of high-speed electrons or other particles is known as secondary emission. In this method, When a beam of high-velocity electrons stricks on the metal surface, the kinetic energy of high

(i) Insulators. Insulators ( e.g. wood, glass etc.) are those substances which do not allow the passage of electric current through them. In terms of energy band, the valence band is full while the conduction band is empty. Further, the energy gap between valence and conduction bands is very large (15 eV). Therefore, a very high electric field is required to push the valence electrons to the conduction band. However, when the temperature is raised, some of the valence electrons may acquire enough energy to cross over to the conduction band. Hence, the resistance of an insulator decreases with the increase in temperature i.e. an insulator has negative temperature coefficient of resistance. (ii) Conductors. Conductors ( e.g. copper, aluminium) are those substances which easily allow the passage of electric current through them. It is because there are a large number of free electrons available in a conductor. In terms of energy band, the valence and conduction bands overlap each other. Due to this overlapping, a slight potential difference across a conductor causes the free electrons to constitute electric current. (iii) Semicondutors. Semiconductors ( e.g. germanium, silicon etc.) are those substances whose electrical conductivity lies in between conductors and insulators. In terms of energy band, the valence band is almost filled and conduction band is almost empty. Further, the energy gap between valence and conduction bands is very small. Therefore, comparatively smaller electric field (smaller than insulators but much greater than conductors) is required to push the electrons from the valence band to the conduction band. In short, a semiconductor has : (a) almost full valence band (b) almost empty conduction band

(c) small energy gap (1 eV) between valence and conduction bands. At low temperature, the valence band is completely full and conduction band is completely empty. Therefore, a semiconductor virtually behaves as an insulator at low temperatures. However, even at room temperature, some electrons (about one electron for 1010 atoms) cross over to the conduction band, imparting little conductivity to the semiconductor.

1.4 Difference between Intrinsic & Extrinsic Semiconductor.

Intrinsic Semiconductor: A semiconductor in an extremely pure form is known as an intrinsic semiconductor. In an intrinsic semiconductor, even at room temperature, hole-electron pairs are created. When electric field is applied across an intrinsic semiconductor, the current conduction takes place by two processes, namely; by free electrons and holes. The free electrons are produced due to the breaking up of some covalent bonds by thermal energy. At the same time, holes are created in the covalent bonds. Under the influence of electric field, conduction through the semiconductor is by both free electrons and holes. Therefore, the total current inside the semiconductor is the sum of currents due to free electrons and holes. Extrinsic Semiconductor: When a small amount of impurity is added to a pure semiconductor it becomes extrinsic semiconductor. The intrinsic semiconductor has little current conductivity at room temperature, to make it suitable for electronic applications we must change its conducting properties. This is achieved

The addition of trivalent impurity provides a large number of holes in the semiconductor. Typical examples of trivalent impurities are gallium, indium, boron etc. Such impurities which produce p-type semiconductor are known as acceptor impurities because the holes created can accept the electrons. In p-type semiconductor holes are the majority carriers whereas electrons are said to be the minority carriers. Difference between Intrinsic & Extrinsic Semiconductor.

1.5 Difference between vacuum tube & semiconductor.

Vacuum tube Semiconductor  Power consumption is high and heat wastage is comparatively high  Lower power consumption, less wastage of heat  Large size than transistor  Size is so small as compared to vacuum tubes.  High cost.  Low cost.  Less suitable for portable products.  Suitable for portable device.  It requires the high voltage power supply, not suitable for smaller voltage devices.  It requires a lower power supply, suitable for smaller voltage devices  Low voltage gain  High voltage gain  There is glass tube in a vacuum tube so not that much physical strength.  Physical strength is high  Not that much depend upon temperature  Depend upon Temperature  High input impedance  Low input impedance  Made up of wires.  Made up of PN junction.  Vacuum tubes can easily be replaced by a user  Relatively maintenance more difficult, cannot easily be replaced by a user.

This pn junction does not allow flow of current. To make it suitable for electronics circuits we need to biasing (applying external voltage) pn-diode. There are two ways of biasing pn-diode (i) Forward biasing (ii) Reverse biasing (i) Forward biasing When a diode is connected in a Forward Bias condition, a negative voltage is applied to the N-type material and a positive voltage is applied to the P-type material. Like charges repel, so the free electrons are pushed toward the PN junction. Similarly, the holes are repelled by the positive terminal of the battery toward the PN junction. If the voltage pushing the electrons and holes has sufficient strength to overcome the depletion zone (approximately 0.7 V for typical silicon diode) the electrons and holes combine at the junction and current passes through the diode. The forward voltage at which the deplation region vanishes and the current in diode raises rapidly is called „ Knee voltage ‟.

(ii) Reverse biasing When a diode is connected in a Reverse Bias condition, a positive voltage is applied to the N-type material and a negative voltage is applied to the P-type material. The negative terminal attracts the positive holes in the P-type silicon and the positive terminal of the battery attracts the free electrons in the N-type silicon. All the charge carriers are pulled away from the PN junction which essentially creates a larger depletion region. In reverse bias condition there is a small reverse leakage current because of minority carriers which is independent of reverse supply voltage called „ Reverse saturation current’. The minimum reverse voltage at which pn junction breaks down with sudden rise in reverse current is called „ Breakdown voltage’.

ii. Zener Breakdown. When the high electric field is applied across the junction, the charge carrier starts jumping across the junction. These electrons constitute the heavy current in the reversed direction. In Zener breakdown, the temporary breakdown of junction occurs. The junction regains its original position when the reverse voltage removes. It occurs in the heavily doped pn junction having thin deplation region. Difference between avalanche breakdown and zener breakdown Avalanche Breakdown Zener Breakdown The process of applying high voltage and increasing the free electrons or electric current in semiconductors and insulating materials is called an avalanche breakdown. The process in which the electrons move across the barrier from the valence band of p-type material to the conduction band of n- type material is known as Zener breakdown. It occurs in diodes that are lightly doped. It occurs in diodes that are highly doped. The valence electrons are pushed to conduction due to the energy imparted by accelerated electrons, which gain their velocity due to their collision with other atoms. The valence electrons are pulled into conduction due to the high electric field in the narrow depletion region. The increase in temperature increases the breakdown voltage. The increase in temperature decreases the breakdown voltage. The VI characteristic curve of the avalanche breakdown is not as sharp as the Zener breakdown. The VI characteristics of a Zener breakdown has a sharp curve. This is observed in Zener diode having a Zener breakdown voltage greater than 8 volts. This is observed in Zener diodes having a Zener breakdown voltage of 5 to 8 volts.

Zener Diode Zener diode is an ordinary diode which is properly doped so that it has a sharp breakdown voltage. Unlike normal pn junction diode it allows current in forward bias as well as reverse bias condition. It starts conducting in reverse direction when reverse voltage reaches a predetermined value. Zener diode is mostly used in reverse bias condition only. The circuit symbol is shown in figure. Working principle When zener diode connected in the reverse mode, which is usual in most of its applications, a small leakage current may flow. As the reverse voltage increases to the predetermined breakdown voltage (Vz), a current starts flowing through the diode. The current increases to a maximum, which is determined by the series resistor, after which it stabilizes and remains constant over a wide range of applied voltage. VI charecterstic of Zener diode The graph between voltage and current of zener diode in forward bias is same as normal pn diode but in reverse bias it has sharp breakdown region at zener voltage Vz. Applications Zener diodes are mostly used in voltage regulator, overvoltage protection & clipper circuits. Light Emitting diode (LED) A light-emitting diode (LED) is a special purpose diode that gives off fairly narrow bandwidth

Advantages of IC Integrated Circuits has many advantages over discrete circuits such as: (i) Extremely small in size, (ii) Low power consumption, (iii) Reliability, (iv) Reduced cost, (v) Very small weight (vi) Easy replacement. Chapter Based Questions:

1. Define Electronics & its application.
2. Define work function.
3. Define Electronic Emission & different types of Emission.
4. Explain Conductor, Semiconductor & Insulator with respect to energy band diagram only.
5. Define doping.
6. Define energy gap & valence electrons.
7. Discuss Intrinsic Semiconductor.
8. Discuss Extrinsic Semiconductor.
9. Define accepter & donor atom.
10. List different types of Impurity.
11. Explain the difference between vacuum tube & semiconductor.
12. State basic concept of integrated circuits (I.C) & its use.
13. Explain P-type and N-type semiconductor junction.
14. Define PN junction Barrier voltage, depletion region, Junction Capacitance.
15. Draw Forward biased & reversed biased junction Diode.
16. Draw symbol, circuit diagram for characteristics (Forward & reversed) Characteristics PN junction diode.
17. Explain Construction (reference to doping level), Symbol ,circuit diagram for characteristics(forwarded & reversed) of Zener Diode.
18. Explain Avalanche &Zener breakdown and its comparison.
19. Explain Construction ,Symbol ,circuit diagram for characteristics of LED.

MODULE- 2

2. ELECTRONIC CIRCUITS

2.1 Rectifier & its uses.

Rectifier A rectifier is an electrical device that converts an Alternating Current (AC) into a Direct Current (DC) by using one or more P-N junction diodes. When AC voltage or AC current is applied across the P-N junction diode, during the positive half cycle the diode is forward biased and allows electric current through it. However, when the AC current reverses its direction to negative half cycle, the diode is reverse biased and does not allow electric current through it. Thus, electric current flows through the diode only during the positive half cycle of the AC current. This current which flows across the diode is nothing but a DC current. Thus, the P-N junction diode acts like a rectifier by converting the AC current into DC current. Rectifiers are mostly used to provide continuous voltage (DC Voltage) required to run almost all electronic devices & circuits.

2.2 Principles of working of different types of Rectifiers with their merits

anddemerits

Types of Rectifier: The rectifiers are mainly classified into two types: (i) Half wave rectifier (ii) Full wave rectifier Half Wave Rectifier As the name suggests, the half wave rectifier is a type of rectifier which converts half of the AC input signal (positive half cycle) into pulsating DC output signal and the remaining half signal (negative half cycle) is blocked or lost. A half-wave rectifier is the simplest of them all as it is composed of only a single diode.