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Introduction to Electronics Electronics

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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.

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http://www.wainet.ne.jp/~yuasa/flash/EngPnJunction.swf http://www- g.eng.cam.ac.uk/mmg/teaching/linearcircuits/diode.html

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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.

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Bipolar junction transistor

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How bipolar transistors are used

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Transport Factor

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The Current gain (transistor gain)

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Darlington transistor

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Power bipolar junction transistor

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Field Effect Transistors (FET)

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