26 December 2022

 

CHAPTER -13 :APPLY THE PRINCIPAL OF SEMICONDUTOR

 

A substance that can conduct electricity is called

the conductor and a substance that cannot conduct electricity is known as the insulator. Semiconductors have properties that sit between the conductor and insulator. A diode, integrated circuit (IC) and transistor are all made from semiconductors.

 

Computer chips, both for CPU and memory, are composed of semiconductor materials

 

A semiconductor is a substance that has specific electrical properties that enable it to serve as a foundation for computers and other electronic devices. It is typically a solid chemical element or compound that conducts electricity under certain conditions but not others. This makes it an ideal medium to control electrical current and everyday electrical appliances.

 

 

 

 

Uses of Semiconductors in Everyday life

·         Temperature sensors are made with semiconductor devices.

·         They are used in 3D printing machines

·         Used in microchips and self-driving cars

·         Used in calculators, solar plates, computers and other electronic devices.




 

TYPES OF SEMICONDUCTOR

 

1)   Intrinsic semiconductor:

An intrinsic type of semiconductor material is made to be very pure chemically. It is made up of only a single type of element.

Germanium (Ge) and Silicon (Si) are the most common type of intrinsic semiconductor elements. They have four valence electrons (tetravalent). They are bound to the atom by covalent bond at absolute zero temperature.

When the temperature rises, due to collisions, few electrons are unbounded and become free to move through the lattice, thus creating an absence in its original position (hole). These free electrons and holes contribute to the conduction of electricity in the semiconductor. The negative and positive charge carriers are equal in number.


2)  Extrinsic Semiconductor

The conductivity of semiconductors can be greatly improved by introducing a small number of suitable replacement atoms called IMPURITIES. The process of adding impurity atoms to the pure semiconductor is called DOPING. Usually, only 1 atom in 107 is replaced by a dopant atom in the doped semiconductor.

An extrinsic semiconductor can be further classified into:

 

·         N-type Semiconductor

·         P-type Semiconductor

 

 

 

 

N-Type Semiconductor

·         Mainly due to electrons

·         Entirely neutral

·         I = Ih and nh >> ne

·         Majority Electrons and Minority – Holes

When a pure semiconductor (Silicon or Germanium) is doped by pentavalent impurity (P, As, Sb, Bi) then, four electrons out of five valence electrons bonds with the four electrons of Ge or Si.

The fifth electron of the dopant is set free. Thus, the impurity atom donates a free electron for conduction in the lattice and is called Donar“.

Since the number of free electron increases by the addition of an impurity, the negative charge carriers increase. Hence, it is called n-type semiconductor.

 

P-Type Semiconductor

·         Mainly due to holes

·         Entirely neutral

·         I = Ih and nh >> ne

·         Majority Holes and Minority Electrons

When a pure semiconductor is doped with a trivalent impurity (B, Al, In, Ga ) then, the three valence electrons of the impurity bonds with three of the four valence electrons of the semiconductor.


This leaves an absence of electron (hole) in the impurity. These impurity atoms which are ready to accept bonded electrons are called Acceptors“.

With the increase in the number of impurities, holes (the positive charge carriers) are increased. Hence, it is called p-type semiconductor.

 

 

 

DIODE SEMICONDUTOR

A diode is a two-terminal electronic component that conducts current primarily in one direction (asymmetric conductance); it has low (ideally zero) resistance in one direction, and high (ideally infinite) resistance in the other.

The diode have two points, one anode and anathoer cathode.

DIODE ARE ONE DIRECTIONAL(Positive to Negative ).

Diode are used in turning AC to DC , Inverters, Powe r supply etc

 

 




 

 

Working principle of semiconductor diode

N-type have a significant number of free electrons and very few holes. But in P-type, It has a high concentration of holes and very few free electrons. For this reason, the free electron from n side will diffuse into the p side and recombine with holes present there, leaving position is not movable ions in n side and creating negative immobile ions in the p-type side of the diode.




Hence, revealed positive giver particles present in the n-type side close to the junction edge. Correspondingly, revealed negative acceptor particles present in the p-type side close to the junction edge.

For this reason, the number of positive ions and negative ions will accumulate on n-side and p side too. This region is formed in the depletion region due to the free carrier in the region.

 




 

Because of the nearness of these positive and negative ions, a static electric field called as barrier potential is made over the PN junction of the diode. It is classified “barrier potential” since it goes about as an obstruction and opposes the further migration of gaps and free electrons over the junction.

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TYPES OF DIODES

 

 

 

Light Emitting Diode (LED)

When an electric current between the electrodes passes through this diode, light is produced. In other words, light is generated when a sufficient amount of forwarding current passes through it. In many diodes, this light generated is not visible as there are frequency levels that do not allow visibility. LEDs are available in different colours. There are tricolour LEDs that can emit three colours at a time. Light colour depends on the energy gap of the semiconductor used.

Laser Diode

It is a different type of diode as it produces coherent light. It is highly used in CD drives, DVDs and laser devices. These are costly when compared to LEDs and are cheaper when compared to other laser generators. Limited life is the only drawback of these diodes.

Avalanche Diode

This diode belongs to a reverse bias type and operates using the avalanche effect. When voltage drop is constant and is independent of current,

the breakdown of avalanche takes place. They exhibit high levels of sensitivity and hence are used for photo detection.

Zener Diode

It is the most useful type of diode as it can provide a stable reference voltage. These are operated in reverse bias and break down on the arrival of a certain voltage. If current passing through the resistor is limited, a stable voltage is generated. Zener diodes are widely used in power supplies to provide a reference voltage.

Zener diodes are used for voltage regulation, as reference elements, surge suppressors, and in switching applications and clipper circuits

 

 

 

Prepared By :Mausham Aryal (GSS 2079)


 

note of Transformer

 

      Chapter 12 : Transformer

Dear, CTEVT STUDENTS….

IF WE WANT TO TRAVEL THE CURRENT FOR LONG DISTANCE , THEN WE HAVE TO USE TRANSFORMERS BETWEEN SOURCE OF ELECTRICITY(SUCH A KALIGANDAKI HYDROPOWER) AND DESTINATION OF ELECTRICITY(SUCH AS FAN, BULB OF YOUR HOME)

 

 

 




 

 

 

 

 

A transformer is a device that transfers electric energy from one alternating-current circuit to one or more other circuits, either increasing (stepping up) or reducing (stepping down) the voltage.


THE TRANSFORMERS ARE USED TO INCRESE OR DECRESE THE ELECTRIC VOLTAGE

 

In brief, a transformer is a device that

 

1.       transfers electric power from one circuit to another

2.       does so without changing the frequency

3.       It does this using electromagnetic induction and

4.       when the two electric circuits are mutually inductively influenced


Working principle of transformer:

 

 




 

-       If the primary coil have less turn and secondary coil

have more turn, the voltage will increase.

-       If the primary coil have more turn and secondary coil have less turn, the voltage will decrease.

-       The laminated core is the metal which is used to attract the magnetic field

 

Electricity is one of the biggest discoveries in human history, reshaping the planet dramatically. Today, we enjoy a variety of advantages brought about by harnessing this basic force of nature and transporting it to remote places. Faraday and Henry advanced electrical study in 1830 by connecting it to magnetism, which led to the discovery of electromagnetic induction. This discovery changed the world by paving the way for the development of alternating current generators.


The working principle of transformer is based on Faraday’s Law of Mutual Induction or Electromagnetic Induction, which happens between two circuits connected by a mutual magnetic flux. Let’s first investigate the mechanism of electromagnetic induction before moving on to the operation of transformer

 

TYPES OF TRANSFORMER

1.     Step Down Transformer:

A Step-down Transformer is a transformer that converts a high voltage at the primary windings to a low voltage at the secondary windings. In terms of the coil windings, a step- down transformer’s primary winding has more turns than the secondary winding.

 

2.   Step Up Transformer:

A step-up transformer is a transformer that increases the voltage from the primary coil to the secondary coil while managing the same power at the rated frequency in both coils. It converts low voltage & high current from the primary side to the high voltage & low current on the secondary side of the transformer.

 

3.   Isolation Transformer:

An isolation transformer is a transformer used to transfer electrical power from a source of alternating current power to some equipment or device while isolating the powered device from the power source, usually for safety reasons or to reduce transients and harmonics.

 

4 .Air-core transformers

 

Air-core transformers are designed to transfer radio-frequency currents—i.e., the currents used for radio transmission; they consist of two or more coils wound around a solid insulating substance or on an insulating coil form. Iron-core transformers serve analogous functions in the audio-frequency range.

 

 

 

 

Note prepared by : Mausham aryal

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