What is ELECTRONICS


Electronic is electron-mechanics, which refers to the study of behavior of an electron under different conditions. The Institution of Radio Engineers(IRE) have given the definition of electronics as ” the field of science and engineering which deals with the study of electron devices and their utilization.” Electron-device is a device in which conduction occurs due to the flow of electrons.
Electronics is even important even in other branches of engineering-mechanical, electrical etc.
Electronics is dealing with milli- and micro- ranges of voltage, current, etc,, but it can control kilo-and Mega- ranges of volts amperes ,etc.

APPLICATION OF ELECTRONICS :

Most of the blessings offered to the people today is provided by Electronics. It is involved in every sphere of human life.

ELECTRONICS TODAY:

Vacuum tubes or valves were the integral part of electronics until the end of World War II. Vacuum-triode was the heart and soul of everything. Transistor was found out in 1948 by Walter Brattain, William Shockley, John Bardeen, at the Bell Laboratories. They were awarded the Nobel Prize for their discovery of transistor. The first Integrated-Circuit or IC was discovered during the early Sixties. The usage of valves was stopped during that time, transistors and ICs replaced them.

COMPONENTS:

An integrated Circuit or IC contains as many transistors,resistors,capacitors,etc in the range of thousands. Electronic components can be divided into two-Active and Passive.

Active Components:

There are many active components in the field of electronics. Active components are classified into semiconductor-type and tube-type active devices. Tube devices are again classified into vacuum tubes and gas tubes. They evolve before the invention of semiconductor devices.Semiconductor devices replaced them because of their usefulness. Passive Components:
Passive components are resistors, capacitors and inductors. They are by themselves not capable of amplifying electrical signals. But, without these, active components cannot work.

1. Resistor:

Resistance is the property of a substance due to which it opposes the flow of electricity through it. It is measured in Ohms. The device which allows resisting the flow of electricity is called Resistor.

2. Capacitor:

A capacitor is a device which is meant to store electrons and release whenever necessary. Capacitance is a measure of a capacitor’s ability to store charge. The unit is Farad. Capacitor offers low impedance to ac but very high impedance to dc.A capacitor forms a tuned circuit in series or parallel with an inductor.

3. Inductors:

A magnetic field is generated when current flows through a coiled wire. This reaction of magnetic field, trying to keep current flowing at a steady state is known as inductance. The force is called induced emf.The component producing inductance is called inductor. Inductors like capacitors or resistors can be classified into fixed and variable types.

METALS,INSULATORS AND SEMICONDUCTORS

A material is able to conduct electricity if it contains movable charges in it. The free electrons works as charge carriers. metal such as copper or iron contains a large number of free electrons at room temperature. There is no energy gap between valence-band an conduction-band.the two bands overlap each other. An insulating material such as plastic has a very wide energy band. It is impossible for an electrons in the valence band to jump to the gap, to reach the conduction band. Only at a high temperature, an electron jump across the gap.
The energy gap between valence band and conduction band is less than 1 eV for Germanium, and 1.12 eV for Silicon.

SEMICONDUCTORS

Conductors are good conductors of electricity. Some of the examples of good conductors are copper, silver,aluminium ,etc.The materials which arebad conductors of electricity are called insulators. Examples of insulators are plastic, ceramic,bakelite ,etc.An another group of materials such as germanium or silicon, which are neither good conductors nor good insulators are called semiconductors. At room temperature, their conductivity is less than that of a conductor.
At high temperature, semi conductors conducts better,i.e the semiconductors have negative temperature coefficient of resistance. The conductivity of a semiconductor can be controlled by controlling the amount of impurities added to it. This is known as doping.

INTRINSIC SEMICONDUCTORS:

To make a semiconductor device, we need a semiconductor in its purest form. Semiconductors in its purest form is called intrinsic semiconductor. A semiconductor is not truly intrinsic unless its impurity content is less than one part impurity in 100 million parts of semiconductors.

EXTRINSIC SEMICONDUCTORS:

There is a little use for intrinsic or pure semiconductors. Almost all of the semiconductor devices are made from extrinsic semiconductors. The process of adding impurities to a semiconductors is called doping. Doping is done after the semiconductors materials has been refined to a high degree of purity. A doped semiconductors is called an extrinsic semiconductor.


PN JUCTION:

If we join a piece of p-type material to a piece of n-type material, such that the crystal structure remains same, a pn junction is formed. If the boundary of a pn junction is formed, it is called semiconductor diode.


JUNCTION THEORY:

The most important characteristics of a pn junction is its ability to conduct current in one direction only.In the reverse direction,it offers very high resistance.

PN junction with no external voltage:

The p-region has holes(majority carriers) and negativelycharged impurity ions(minority carriers).The n-region has free electrons and positively charged impurity ions.Holes and electrons are mobile charges,but ions are immobile.As soon as the PN-junction is formed,holes from the p-region diffuses into the p-region.They combines with the free electrons in the n-region.Free electrons in the n-region diffuses into the p-region and combines with the holes.The diffusion of holes and free elctrons occurs for a short time.Further diffusion of holes and electrons is stopped by the potential barrie.


PN junction with forward bias:

When a pn-junction is forward biased,the holes are repelled from the positive terminal of the battery and drift towards the junction.Some of the holes and the free electrons penetrate the diffusion region.This reduces the potential barrier.More majority carriers diffuse across the junction.Thus we get a continuous electron current in the external circuit.


PN junction with reverse bias:

The holes in the p-region are attracted towards the negative terminal of the battery.The electrons in the n-region are attracted to the positive termianl of the batter.This action widens the depletion region and makes the majority carriers difficult to diffuse across the junction.This barrier potential is helpful to the minority carriers in crossing the junction.The rate of generation of minority carriers depends upon the temperature.If the temperature is fixed, the rate of generation of minority carriers remains constant.The current due to the flow of minority carriers remains the same,whether the voltage is high or low.For this reason, current in the reverse bias condition is known as reverse saturation current.

Reverse breakdown:

If the reverse bias is made too high,the current through the pn-junction increases abruptly.At this voltage,the crystal structure breaks down and usually this condition is avoided.The crystal structure will be retained when the excess reverse bias is removed,provided that overheating has not permanently damaged the crystal.