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• OP – AMP is a high gain voltage amplifier with differential input and single ended output. 
• Working of OP­AMPS: OP­AMP amplifies the difference between the inverting and non inverting input. It works in the open loop mode and closed loop mode. 
• Characteristics of OP­AMP: An ideal op­amp has the following characteristics:

1. Infinite open loop gain 
2. Infinite input impedance 
3. Zero Output impedance 
4. Infinite Bandwidth 

• OP­AMP made of transistors: The diagram shows discrete op amp made of transistors with a gain of 100. This is not widely used.
  
• IC 741: IC 741 is the most common type of op­amp. It consists of differential amplifier, voltage amplifier and output amplifier. 
• IC 741 features : IC 741 has the following features: 

1. Zero common mode gain. 
2. The offset null pins are used to place external resistors. 

• Hybrid: A hybrid op amp consists of three triodes and coupling capacitor at the input. 
• Applications 

1. It is used as low pass or high pass filter. 
2. It is also used in electrocardiogram amplification. 
3. Resistor vs Inductor: Resistor is used to reduce the magnitude of the voltage whereas inductors are used to shift the AC voltage phase.

• Resistor vs Capacitor: A capacitor stores charge whereas resistor uses potential energy to generate power. 
• Capacitor vs inductor: Both capacitor and inductor store energy but capacitor stores it in electric filed whereas inductor stores it in magnetic field. 
• Transistor vs diode: A diode consists of 2 layers whereas transistor consists of 3 layers. A transistor works like diodes placed back to back. 
• Diode vs Zener diode: Diodes can work in both forward and reverse bias but zener diodes are meant to work only in the reverse bias mode. 
• Transformer vs Transistor: A transistor contributes to power gain by taking power from external power supply whereas a transformer is used for impedance matching. 
• Transistor vs op­amp: A transistor needs biasing to turn it on and an op­amp although made up of transistors does not need biasing and can amplify the difference. 
• Simple circuit 

1. A car­ reverse horn. It starts blowing as soon as the car is in the reverse gear. 
2. The circuit of reverse horn consists of resistors, capacitors, transistors and diodes. 
3. A battery of 12 V is supplied to provide power to the circuit. 
4. The power supply passes through the transistor which acts as a switch and provides power to a zener diode. It regulates the current and passes it to the transistors which generate sound waves which are again amplified by another transistor. 

• A Zener diode is like any semiconductor diode which allows current to flow in the forward direction but also in the reverse direction during a certain voltage called breakdown voltage 
• Symbol of Zener diode 
  
• Operation of Zener diode: A normal semiconductor diode usually is damaged due to overheating when reverse voltage is applied for long duration. But in a Zener diode, a large amount of current can be passed through it and only a small change would be observed in the voltage level. It is usually used in reverse bias condition.

Types of Zener diodes :-

• Based on the breakdown voltage, Zener diodes can be classified into 2 types: Surface Zener and Sub Surface Zener .

• Surface Zeners

1. Breakdown Voltage: 6.8 – 10 V 
2. NPN transistor where Collector and Emitter are at cathode and Base at Anode 
3. Charges accumulated in the diode cause Zener walk out

• Sub surface Zeners 

1. This diode is similar to surface zener, the only difference being that the avalanche is deeper inside in the structure. 
2. Thus there is no Zener walk out and the zener voltage is maintained. 

• A diode is an electrical device which allows current to flow easily in the circuit. 
• The most common form of diode is semiconductor diode 
• Symbol of a diode  

Introduction to Semiconductor Diodes:-

These are the following types of diodes: 

• It is an electric device that transfers energy between two circuits using Electromagnetic Induction. 
• Operation of transformer 

1. The operation of a transformer can be explained with the help of these two laws: Electric current produces magnetic field across the conductor and a change in magnetic field induces voltage at the ends of the conductor. 

• Features of Transformer
  

1. There is no copper loss in the windings 
2. There is no inductive loss 
3. Flux is present only within the magnetic core 

• Construction of Transformer

Based on the application, a transformer consists of a core made up of ferromagnetic or ceramic material and a coil made up of some insulating magnetic material or copper wires. Transformer oil is used for cooling transformer

• Losses in a Transformer 

• These are the losses in a transformer: 

1. Winding loss 
2. Hysteresis loss 
3. Eddy current loss 
4. Hum Stray loss 

• Winding losses: Current flowing through windings causes heating and losses due to heating. 
• Hysteresis losses: Each time the magnetic field is reversed, some energy is lost. It is hysteresis loss. 
• Eddy current losses: Eddy currents are present in the ferromagnetic core and cause resistive heating in the core. 
• Hum: Magnetic flux causes the core to physically expand slightly and it results in a humming noise. 
• Stray losses: Inductive leakage and radiation losses are all stray losses in an inductor.

                   Types of Transformers

• Based on the purpose of transformers, they are classified into Power transformers, Instrument transformers, RF transformers, Audio Transformers.

1. Power Transformer: Used for high voltage transmission purposes. 
2. Instrument Transformer: They are used to operate instruments at high voltage, high current cicuits and safely isolate the control circuit. 
3. RF Transformer: Transformers used in Radio Frequency applications. 
4. Audio Transformer: They block radio frequency signals, split and combine audio signals.

• The following are the types of inductors: 

1. Air core inductor, 
2. Ferromagnetic core inductor, 
3. variable inductor

• Air core inductor: It is an inductor which has its coil wound on non­magnetic material like plastic or ceramic and there is only air present in between the windings. 
• Ferromagnetic inductor: It is an inductor which has its coil wound on a magnetic core made up of ferromagnetic or ferromagnetic material.

 Laminated core: It is a type of ferromagnetic inductor whose core is made up of thin steel sheets or laminations. 

Ferrite core: It is a type of ferromagnetic inductor whose core is made up of ferrite. 

Torroidal core: It is a type of ferromagnetic inductor where the coil is wound on a straight rod shaped core. 

Choke: It consist of a coil of insulating material wound on a magnetic material.

• Variable inductor: It is made up of ferrite magnetic core which can be slid or screwed to change inductance. 

Features of inductor:-

• Inductors are used in

1. Signal Processing 
2. Filtering out some frequencies 
3. Removing hums from DC output

• All materials have inherent magnetic characters formed due to the movement of electrons. 
• Transition metals, lanthanides and their compounds are used as magnetic materials. 
• The properties of magnetic materials are: 

1. Paramagnetism, 
2. Ferromagnetism, 
3. Antiferromagnetism, 
4. Ferrimagnetism. 

                  Introduction to inductor

• *An inductor is a two terminal electric component which resists changes in electric current. 
• *It is a conductor wire wound into coil. 
• *Construction of Inductor 

1. >Inductors are made up of insulating wire like copper wire wound on a plastic or ferromagnetic material. 
2. >The inductor symbol is shown. 
   

• Working :-

1. When current flows through the coil, a magnetic field is set. 
2. This field restricts the flow of current. 
3. Once the field is created then current passed normally through it thus resisting any change in the flow of current. 

• Characteristics:-

1. The resistance of the wire used in winding the coil is assumed negligible. 
2. The amount of induced voltage in a coil is directly proportional to the rate of change of magnetic field of coil. 
3. The induced voltage of the coil is proportional to the number of turns. 

• Based on the type of materials used in the capacitor plates, the following types are the most common types of capacitors: Ceramic Capacitors, Film Power Capacitors, Super Capacitors and Variable Capacitors. 

1. Ceramic Capacitors: Ceramic capacitors are made up of ceramic and metal where metal acts as the electrode and ceramic is the dielectric. This type of capacitor is used in applications of high frequency and high current pulse loads. 
2. Film Power Capacitors: In film power capacitors, the dielectric films are drawn to a thin layer surrounded by metallic electrodes on a cylindrical wiring. Polypropylene is used as the dielectric. 
3. Super Capacitors: Super capacitors are electrochemical capacitors with no specific dielectric in it. The storage of charge is obtained by either separation of charge or redox reactions. 
4. Variable Capacitors: All the above mentioned capacitors are fixed capacitors which cannot vary their capacitance. A variable capacitor can vary its capacitance by mechanical motion. 

The 2 methods used to vary capacitance are tuning and trimming

Applications of capacitor:-

• Capacitors are used in designing filters. They are used to reduce the impact of electric noise in digital circuits. Also to separate the AC components of a signal from DC components. Large capacitors are used to store energy. 
• Safety with capacitors: Capacitors retain charge for a long time even after the power is removed. So before touching the circuit, ensure that the capacitor is fully discharged. 

• A capacitor is a passive electronic component used to store electric charge. 
• The unit for measuring capacitance is Farads. 
• The standard capacitor values are 1, 10,100,510,910pF 
• Capacitors are also marked with color bands to denote value. 
• The first 2 bands are the first and second digit whereas the third band denotes the multiplier. 
• Symbol for capacitor is shown.
  
• Capacitor tolerance is the value which determines the extent to which capacitance can vary from actual capacitance. 
• It ranges from ­20% to +80% 

• Temperature Co­efficient 

1. The temperature co efficient is the maximum change in a capacitance with change in temperature. 
2. It is measured in ppm/◦C (Parts per million by degree Celsius)

• The factors affecting capacitor behavior are as follows:

Breakdown voltage, Equivalent circuit, Q factor, Ripple current, Instability, Dielectric absorption, Leakage, Current and Voltage Reversal

 

• Variable Resistors are the resistors in which the resistance can be continually altered and is not definite.
•  A variable resistor has 3 terminals out of which 2 are connected to the ends of the track and a third terminal is connected to the wiper. 
• The motion of the wiper allows in increasing and decreasing resistance. 
• Potentiometer, Rheostat and Trim Pot. 
• A potentiometer is used to divide the voltage. 
• It consists of resistive element. 
• Two terminals connected to electric contacts at the ends and a wiper in between. 
• The wiper slides on the resistive element making electric contact. 
• Rheostat is the most common way of varying resistance. 
• A semicircular insulator is wound by a resistance wire and the wiper slides from one turn of the wire to the next. 
• Trimming potentiometers also known as Trim Pots are similar to potentiometers. 
• But instead of having a knob for adjusting voltage, they are mounted with a screw. 
• They are turned with a screw driver and used for few adjustments.

Applications of Variable Resistors: 

1. Rheostat is used in power control devices like Light Bulb. 
2. Potentiometer is used in audio volume in A/V circuits, measurement of angles and tuning of circuits. 
3. Trim Pot is used in calibrating instruments, A/V circuits. 

Comparison between Fixed and Variable Resistors 

1. Fixed Resistors are resistors with a definite resistance value whereas Variable resistors vary in resistance either manually or automatic. 
2. Fixed resistors are either made up of carbon film, metal foil or wound wire whereas Variable resistors are made up of carbon composition, cermet(ceramic and metal), conductive plastic, wire wound. 
3. Fixed Resistors are used to prevent excessive current in the circuit whereas variable resistors are used to adjust volume and gain controls in the circuit.

• The resistors made up of ceramic body and are cylindrical in shape with definite resistance values are fixed resistors. 

• The resistive element could be either carbon film, thick film or a wound wire element. 

• The properties of fixed resistors depend upon the type of fixed resistor used. 

• A carbon film resistor has 5% tolerance, power rating of 0.125 W­ 2 W, Temperature co­efficient of 250­450ppm/k. 

• A metal film resistor has 1% tolerance, power rating of 0.1­5W and Temperature co­efficient of 10­250ppm/K. 

• A wire wound resistor has 1% tolerance, power rating of 1­200W and Temperature co­efficient of 20­400ppm/K. 

 Types of Fixed Resistor

Based on the type of material used in constructing a resistor it is classified into:  Carbon composition, carbon pile, carbon film, metal film and metal oxide film. 

Carbon Composition is made up of carbon clay composition with plastic coating around it. 

Carbon Pile is made up of a stack of carbon disks compressed between two metal contact. 

Carbon film is deposited on an insulating substrate and cut into thin resistive path. 

Metal Film is cylindrically shaped and coated with Nickel Chromium. 

Metal Oxide Film is made up of tin oxide. 

• Application of Fixed Resistors: The applications of Fixed Resistors are:

1. Protecting other components from damage due to excess current. 
2. Dividing voltage to different parts of the circuit. 
3. Timing applications where a fixed resistor is used along with a capacitor to control time delay. 

• An electronic circuit is composed of various components which are known as electronic components. 
• Electronic components usually have 2 or more leads which can be fitted into the PCB to form a working electronic circuit. 

                  Classification of Electronic components 

• Electronic Components can be broadly classified into two types: 

1. Passive Components 
2. Active Components

• Passive Components: ­ Passive Components are the ones which do not require external energy to operate. They depend on the power provided from the AC circuit. Also, they cannot generate energy of their own. 
• Types of Passive Components:  Some of the Passive Components are: 

1. Resistors 
2. Capacitors 
3. Inductors 
4. Sensors 
5. Transducers 

• Active Components: ­ An active component is a device that has an analog electronic filter with the ability to amplify a signal or produce a power gain.