The document discusses electronic devices and their characteristics. It covers topics like valence bands, conduction bands, forbidden energy gaps, and the differences between conductors, insulators, and semiconductors. Diodes are described as having applications in rectification, logic gates, signal isolation, power supplies, lighting, and voltage regulation. The V-I characteristics and working of a half-wave rectifier circuit are also summarized.

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Valence Band
The electrons in the outermost shell are known as valence electrons.
These valence electrons contain a series of energy levels and form an energy band known as the valence
band.
The valence band has the highest occupied energy.

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Conduction Band
The free electrons conduct the current in the conductors and are therefore
known as the conduction electrons.
The conduction band is the one that contains the conduction electrons and has
the lowest occupied energy levels.
Forbidden Energy Gap
The forbidden energy gap refers to the gap between the valence band
and the conduction band.

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The Characteristics of Conductors are as Follows:
There is no forbidden energy gap in a conductor.
The valence band and the conduction band overlap in conductors.
There are a high number of free electrons available for the conduction of electricity.
With a slight increase in voltage, there is an increase in the conduction as well.
No concept of hole formation is there because the continuous flow of electrons contributes to the
current produced.

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The Characteristics of Insulators are as Follows:
The forbidden energy gap is large enough in insulators with a value of 10eV.
The electrons in the valence band are tightly bound or firmly attached to atoms.
Some insulators might show conduction with an increase in the temperature.

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The Characteristics of Semiconductors are as Follows:
The forbidden energy gap is small in a semiconductor.
For Germanium (Ge), the value of the forbidden energy gap is 0.7eV, and for Silicon (Si), it is 1.1eV.
The conductivity of semiconductors increases with the rise in temperature.Semiconductors are neither a good
conductor or an insulator.

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Applications and Uses of diodes
There are various types of diodes and these diodes are used in numerous ways.
The most basic function would be changing AC current to DC current by removing some part of the signal. This
functionality would make them rectifiers. They are used in electrical switches and are used in surge protectors
because they can prevent a spike in the voltage.
Diodes help in performing digital logic. Millions of diodes are used similar to logic gates and used in modern
processors.
They are used for isolating signals from a supply. For example, one of the major uses of diodes is to remove
negative signals from AC current. This is known as signal demodulation. This function is basically used in radios
as a filtering system in order to extract radio signals from a carrier wave.
They are also used in creating power supplies and voltage doublers. Using a full wave rectifier will help to deliver
a more stable voltage. Combination of a diode with a capacitor will help to make small AC voltage multiply to
create a very high voltage.
The light emitting diodes or LEDs are used in sensors and also in laser devices any many other light illumination
devices.
Zener diodes are used as voltage regulators and varactors are used in electronic tuning and varistors are used in
suppressing AC lines
Diodes are the basis of op-amps and transistors.

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V - I Characteristics

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Half Wave Rectifier Circuit

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Working of Half Wave Rectifier
In this section, let us understand how a half-wave rectifier transforms AC into DC.
A high AC voltage is applied to the primary side of the step-down transformer. The
obtained secondary low voltage is applied to the diode.
The diode is forward biased during the positive half cycle of the AC voltage and reverse
biased during the negative half cycle.
The final output voltage waveform is as shown in the figure below:

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