1. Semiconductors like silicon and germanium can be classified as conductors, insulators, or semiconductors based on their atomic structure and energy bands. Their conductivity can be increased through doping with impurities. 2. A diode is a basic semiconductor device made of doped silicon with a pn junction. It allows current to flow easily in one direction but blocks it in the other. Diodes are used as rectifiers to convert alternating current into direct current. 3. Rectifiers use diodes in various circuit configurations like half-wave, full-wave, and bridge circuits to extract the positive portions of the input waveform and produce a pulsing direct current output. Three-

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Industrial Electronics
Atom
Valance electron
Due to
Shell An energy band in which electrons orbit the nucleus of an atom
Classification of matter based on semiconductor theory.
Conductor
Insulator

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Semiconductor
and germanium
Energy Band.
The band formed by the energy levels. There are main two types.
1. Valance band.
2. Conduction band.
Valance Band.
The band formed by energy level with valance electrons is known as valance band.
Conduction Band.
When an electron acquires enough additional
Energy Gap.
energy gap.
Conduction band is empty in case of insulators.

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Atomic Structure Of Silicon And Germanium.
Covalentbond.
Each silicon atom position itself with four adjacent silicon atoms
tron produce the covalent bond.
Silicon Crystal.

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becoming a free electron. When an electron jump to conduction band vacancy is left in
the valance bond with in the crystal. This vacancy is known as hole.

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Doping
Since semiconductors are generally poor conductors, their conductivity can be increased
by the controlled addition of impurities to the intrinsic (pure) semi conductive material.
This process, called doping, increases the number of current carriers (electrons or holes).
The two categories of impurities are n-type and p-type.
N-Type Semiconductor
To increase the number of conduction-band electrons in intrinsic silicon, pentavalent im-
purity atoms are added. These are atoms with five valence electrons such as arsenic (As),
phosphorus (P), bismuth (Bi), and antimony (Sb).
P-Type Semiconductor
To increase the number of holes in intrinsic silicon, trivalent impurity atoms are added.
These are atoms with three valence electrons such as boron (B), indium (In), and gallium
(Ga).

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Diode
A diode is made from a small piece of semiconductor material, usually silicon, in which
half is doped as a p region and half is doped as an n region with a pn junction and
depletion region in between. The p region is called the anode and is connected to a
conductive terminal. The n region is called the cathode and is connected to a second
conductive terminal.
Forward Bias
If the +ve terminal of the battry is connected to the p region of the diode and the -ve
terminal is connected to the n region.
Reversed Bias
If the +ve terminal of the battry is connected to the n region of the diode and the -ve
terminal is connected to the p region.

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Rectifier
It is an electrical device that converts AC supply into DC and process is called
rectification. Because of their ability to conduct current in one direction and block current
in the other direction, diodes are used in circuits called rectifiers that convert ac voltage
into dc voltage.
Rectifiers are found in all dc power supplies that operate from an ac voltage source.
Rectifier circuit
Rectifier circuit may be single phase or multiphase. Most low power rectifiers for
domestic equipment are single phase and 3-phase rectifier is very important for industrial
application and for power transmission.
Types
1. Single phase rectifier
I. Half wave rectifier.
II. Full wave rectifier
2. Three phase half wave circuit rectifier.
3. Three phase full wave circuit rectifier using center tapped transformer.
4. Three phase bridge circuit rectifier.
1. Single-phase rectifier
Half wave rectifier.
A diode is connected to an AC source and to a load resistor, RL, forming a half-wave
rectifier. When the sinusoidal input voltage goes positive, the diode is forward-biased and
conducts current through the load resistor. The current produces an output voltage across
the load RL, which has the same shape as the positive half-cycle of the input voltage.
 During the negative alternation of the input voltage, the current is 0, so the output voltage
is also 0.
The net result is that only the positive half-cycles of the ac input voltage appear across
the load. Since the output does not change polarity.

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Full Wave Rectifier.
A full-wave rectifier allows unidirectional (one-way) current through the load during the
entire of the input cycle, whereas a half-wave rectifier allows current through the load
only during one-half of the cycle.
The number of positive alternations that make up the full-wave rectified voltage is twice
that of the half-wave voltage for the same time interval.
2. Three Phase Bridge Rectifier
The bridge rectifier uses four diodes connected as shown in Figure. When the inputcycle
is positive as in part (a), diodes D1 and D2 are forward-biased and conduct current in the
direction shown. A voltage is developed across RL that looks like the positive half of the
input cycle. During this time, diodes D3 and D4 are reverse-biased.
When the input cycle is negative diodes D 3 and D 4 are forward-biased and conduct
current in the same direction through RL as during the positive half-cycle.
During the negative half-cycle, D1 and D2 are reverse-biased. A full-wave rectified
outputvoltage appears across RL as a result of this action

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