The Electronic system Electric system : any technical system is
an assembly of components that are connected together to form a
functioning machine or an operational procedure. An electronic
system includes some common used electrical devices such as
resistors, capacitors, transformers, inductors, and few classes of
semiconductors ( diodes, transistors )
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The current in conductor and insulator
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Voltage, current, and resistance Voltage : v and sometimes E
Its equal to the work done to move the electric charge from the
negative point to the positive point and its measured in volt. The
electron charge is equal to 6*10 18 Current : I, the rate of flow
of electric charge past from the negative to the positive point and
measured in ampere or amp
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The same current into point in a circuit equals to the sum of
the currents out from the circuit ( kirchhoff current law) A node
is any point in the circuit
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The sum of voltage drops around any closed circuit is zero (
kirchhoff voltage law)
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Risistors
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Resistance 1-It has 2 kinds,constant resistance and variable
resistance that I control it by changing its value. 2-we can
measure it using avometers. 3- It's job to decrease the current as
a lot of application if dont use resistance the system failure or
corrupt.The law wish depend on it is ohms low V=I*R.V is constant
but when R increase the current will decrease so as to the volt
must be const
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Calculate the value of the next resistors
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Semiconductors
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semiconductors A semiconductor is a material which has
electrical conductivity between that of a conductor such as copper
and an insulator such as glass. The conductivity of a semiconductor
increases with increasing temperature, behavior opposite to that of
a metal. Semiconductors can display a range of useful properties
such as passing current more easily in one direction than the
other. Because the conductive properties of a semiconductor can be
modified by controlled addition of impurities or by the application
of electrical fields or light, semiconductors are very useful
devices for amplification of signals, switching, and energy
conversion. Understanding the properties of semiconductors relies
on quantum physics to explain the motions of electrons through a
lattice of atoms.
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Semiconductors A semiconductor is a material which has
electrical conductivity between that of a conductor such as copper
and an insulator such as glass. The conductivity of a semiconductor
increases with increasing temperature, behavior opposite to that of
a metal. Semiconductors can display a range of useful properties
such as passing current more easily in one direction than the
other. Because the conductive properties of a semiconductor can be
modified by controlled addition of impurities or by the application
of electrical fields or light, semiconductors are very useful
devices for amplification of signals, switching, and energy
conversion. Understanding the properties of semiconductors relies
on quantum physics to explain the motions of electrons through a
lattice of atoms. Current conduction in a semiconductor occurs via
free electrons and "holes", collectively known as charge carriers.
Adding impurity atoms to a semiconducting material, known as
"doping", greatly increases the number of charge carriers within
it. When a doped semiconductor contains excess holes it is called
"p-type", and when it contains excess free electrons it is known as
"n-type". The semiconductor material used in devices is doped under
highly controlled conditions to precisely control the location and
concentration of p- and n-type dopants. A single semiconductor
crystal can have multiple p- and n-type regions; the p-n junctions
between these regions have many useful electronic properties.
Semiconductors are the foundation of modern electronics, including
radio, computers, and telephones. Semiconductor-based electronic
components include transistors, solar cells, many kinds of diodes
including the light-emitting diode (LED), the silicon controlled
rectifier, photo-diodes, and digital and analog integrated
circuits. Increasing understanding of semiconductor materials and
fabrication processes has made possible continuing increases in the
complexity and speed of semiconductor devices, an effect known as
Moore's Law.
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The Semiconductor Industry Semiconductor devices such as
diodes, transistors and integrated circuits can be found everywhere
in our daily lives, in Walkman, televisions, automobiles, washing
machines and computers. We have come to rely on them and
increasingly have come to expect higher performance at lower cost.
Personal computers clearly illustrate this trend. Anyone who wants
to replace a three to five year old computer finds that the
trade-in value of his or her computer is surprising low. On the
bright side, one finds that the complexity and performance of the
todays personal computers vastly exceeds that of their old computer
and that for about the same purchase price, adjusted for
inflation.
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intrinsic semiconductor As a result of the thermal energy
present in the material, electrons can break loose from covalent
bonds and become free electrons able to move through the solid and
contribute to the electrical conductivity. The covalent bonds left
behind have an electron vacancy called a hole. Electrons from
neighboring covalent bonds can easily move into an adjacent bond
with an electron vacancy, or hole, and thus the hold can move from
one covalent bond to an adjacent bond. As this process continues,
we can say that the hole is moving through the material
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Doped semiconductor A semiconductor that has had impurity atoms
added to modify the electrical conduction characteristics.
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Extrinsic semiconductor A semiconductor that has been doped
with impurities to modify the electrical conduction
characteristics.
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Hole An electron vacancy in a covalent bond between two atoms
in a semiconductor. Holes are mobile charge carriers with an
effective charge that is opposite to the charge on an
electron.
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P-N N-type semiconductor: A semiconductor that has been doped
with donor impurities to produce the condition that the population
of free electrons is greater than the population of holes. P-type
semiconductor: A semiconductor that has been doped with acceptor
impurities to produce the condition that the population of holes is
greater than the population of free electrons.
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p-n Junctions P-n junctions consist of two semiconductor
regions of opposite type. Such junctions show a pronounced
rectifying behavior. They are also called p-n diodes in analogy
with vacuum diodes. The p-n junction is a versatile element, which
can be used as a rectifier, as an isolation structure and as a
voltage- dependent capacitor. In addition, they can be used as
solar cells, photodiodes, light emitting diodes and even laser
diodes. They are also an essential part of Metal-Oxide-Silicon
Field-Effects-Transistors (MOSFETs) and Bipolar Junction
Transistors (BJTs).
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Diodes allow electricity to flow in only one direction. The
arrow of the circuit symbol shows the direction in which the
current can flow. Diodes are the electrical version of a valve and
early diodes were actually called valves.
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Properties of a pn junction The pn junction possesses some
interesting properties that have useful applications in modern
electronics. A p-doped semiconductor is relatively conductive. The
same is true of an n- doped semiconductor, but the junction between
them can become depleted of charge carriers, and hence
non-conductive, depending on the relative voltages of the two
semiconductor regions. By manipulating this non- conductive layer,
pn junctions are commonly used as diodes: circuit elements that
allow a flow of electricity in one direction but not in the other
(opposite) direction. This property is explained in terms of
forward bias and reverse bias, where the term bias refers to an
application of electric voltage to the pn junction.
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Forward bias In forward bias, the p-type is connected with the
positive terminal and the n-type is connected with the negative
terminal.
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Forward bias With a battery connected this way, the holes in
the P-type region and the electrons in the N-type region are pushed
toward the junction. This reduces the width of the depletion zone.
The positive charge applied to the P-type material repels the
holes, while the negative charge applied to the N-type material
repels the electrons. As electrons and holes are pushed toward the
junction, the distance between them decreases. This lowers the
barrier in potential. With increasing forward-bias voltage, the
depletion zone eventually becomes thin enough that the zone's
electric field cannot counteract charge carrier motion across the
pn junction, as a consequence reducing electrical resistance. The
electrons that cross the pn junction into the P-type material (or
holes that cross into the N-type material) will diffuse in the
near-neutral region. Therefore, the amount of minority diffusion in
the near-neutral zones determines the amount of current that may
flow through the diode.
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Reverse bias Reverse-bias usually refers to how a diode is used
in a circuit. Therefore, no current will flow until the diode
breaks down. Connecting the P-type region to the negative terminal
of the battery and the N-type region to the positive terminal
corresponds to reverse bias.
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Reverse bias Because the p-type material is now connected to
the negative terminal of the power supply, the 'holes' in the
P-type material are pulled away from the junction, causing the
width of the depletion zone to increase. Likewise, because the
N-type region is connected to the positive terminal, the electrons
will also be pulled away from the junction. Therefore, the
depletion region widens, and does so increasingly with increasing
reverse-bias voltage. This increases the voltage barrier causing a
high resistance to the flow of charge carriers, thus allowing
minimal electric current to cross the pn junction. The increase in
resistance of the pn junction results in the junction behaving as
an insulator.
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Types Of Diodes
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How are the Diode Work
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Zener diode A Zener diode is a diode which allows current to
flow in the forward direction in the same manner as an ideal diode,
but will also permit it to flow in the reverse direction when the
voltage is above a certain value known as the breakdown
voltagediodebreakdown voltage
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Zener diode Zener diode is a special purpose P-N junction
diode. It was invented by Clarence Zener. A zener diode works as a
normal P-N junction diode in the forward biased condition. The
specialty is that, it is designed to operate in the reverse biased
condition! The normal diode will not allow current flow in the
reverse biased condition, and if the reverse voltage exceeds the
breakdown voltage, the diode may get permanently damaged. But the
zener diode will not damage, even if the reverse voltage exceeds
the breakdown value. The voltage across the zener diode will stay
stable, irrespective of the input voltage. So the zener diode is
ideal for applications requiring stabilized voltages.
Avalanche Effect (breakdown) Zener diodes are used with reverse
bias, making use of the breakdown that occurs across a silicon
junction when the reverse voltage causes a large electrostatic
field to develop across the junction. This breakdown limit occurs
at low voltages (below 6 V) when the silicon is very strongly
doped, and such breakdown is termed Zener breakdown, from Clarence
Zener who discovered the effect. For such a true Zener diode
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Summary The forward-bias and the reverse-bias properties of the
pn junction imply that it can be used as a diode. A pn junction
diode allows electric charges to flow in one direction, but not in
the opposite direction; negative charges (electrons) can easily
flow through the junction from n to p but not from p to n, and the
reverse is true for holes. When the pn junction is forward-biased,
electric charge flows freely due to reduced resistance of the pn
junction. When the pn junction is reverse-biased, however, the
junction barrier (and therefore resistance) becomes greater and
charge flow is minimal.
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Review Questions State the difference between the forward bias
and the reverse bias? What are the main types of Diodes ? Briefly
describe? What is meant by : Crystal Recombination Intrinsic
Semiconductors Extrinsic semiconductor Avalanche Effect Zener
Diode
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Review Questions What is meant by P-N Junction? Explain the
difference between the P-type and the N-type? What is meant by
Hole? What is meant by breakdown voltage? State the difference
between the donor and the accepter Junctions?
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Review Questions Define the Semiconductors and doped
semiconductors? Define the depletion layer ? State the major usage
of semiconductors in industry? Illustrate the covalent bond, with
figures?
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Transistors The transistor is our most important example of an
"active" component, a device that can amplify, producing an output
signal with more power in it than the input signal.
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Transistors
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Transistor usage The transistors used in all the electronic
circuit because its ability to control the current flow in the
circuit. This circuits such as: 1) electronic switch 2) digital
electronic circuits 3) Registers 4) flip-flops 5) Amplifiers
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Types of Transistors
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Bipolar Junction Transistor
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Bipolar junction transistor A bipolar junction transistor (BJT
or bipolar transistor) is a type of transistor that relies on the
contact of two types of semiconductor for its operation. BJTs can
be used as amplifiers, switches, or in oscillators. BJTs can be
found either as individual discrete components, or in large numbers
as parts of integrated circuits. Bipolar transistors are so named
because their operation involves both electrons and holes. These
two kinds of charge carriers are characteristic of the two kinds of
doped semiconductor material. In contrast, unipolar transistors
such as the field- effect transistors have only one kind of charge
carrier.