Week01 Diode Revision

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    ENGN2218 Electronic Systems and Design1

    Reading for LECTURE 02

    Revision of Diode

    Dr. Salman Durrani

    School of Engineering,

    The Australian National University.http://people.cecs.anu.edu.au/asp/academics/bio

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    ENGN2218 Electronic Systems and Design2

    Revision Slides

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    ENGN2218 Electronic Systems and Design3

    The convention used in this course is

    Commonly used symbols in this course are

    Terminology

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    ENGN2218 Electronic Systems and Design4

    An electric circuit consists of circuit elements (such asvoltage sources, resistors, capacitors and inductors)connected in closed paths by conductors.

    A node in an electrical circuit is a point at which two ormore circuit elements are joined together (an essential

    node is where three or more circuit elements join).

    A loop in an electrical circuit is a closed path whose last

    node is the same as the starting node.

    A mesh is a special case of a loop. A mesh is a loop that

    does not contain any other loops.

    Electric Circuit Vocabulary

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    Kirchhoffs Current Law (KCL):

    Kirchhoffs Voltage Law (KVL):

    Kirchhoffs Laws

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    Conventional current flows from +ve terminal of batteryto ve terminal. Flow of electrons is in opposite directionto conventional current direction.

    The terminal where conventional current enters anelement is assigned +ve polarity and the terminalwhere conventional current leaves an element is

    assigned -ve polarity.

    Following conventional current in a circuit, if we move

    from +ve polarity towards ve polarity (voltage drop),the element absorbs energy that appears as heat orstored chemical energy. If we move from ve polaritytowards +ve polarity (voltage rise), the element supplies

    energy.

    Current and Voltage Conventions

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    The extreme value of R =infinity is given special nameof open circuit. Using analogy of a switch, it corresponds to the case when

    switch is open (i.e. OFF)

    The extreme value of R =0 is given special name ofshort circuit. Using analogy of a switch, it corresponds to the case whenswitch is closed (i.e. ON)

    Open and Short Circuit Concepts

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    Summary of Open and Short Circuit

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    A semiconductor is neither a good conductor nor agood insulator.

    Semiconductors

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    Electronic devices such as diodes and transistors aremade of a semiconductor material.

    A basic knowledge of semiconductor physics helps us tounderstand diode and bipolar junction transistor

    behaviour.

    Common semiconductor materials are

    Silicon (Si) [single-element semiconductor] Germanium (Ge) [single-element semiconductor] Carbon (C) [single-element semiconductor] Gallium Arsenide (GaAs) [compound semiconductor]

    Basic Semiconductor Concepts

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    Silicon is the most widely used material in diodes,transistors other semiconductor devices.

    Intrinsic (pure) Silicon is a crystalline material with Si

    atoms held together by covalent bonds.

    Intrinsic Silicon

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    Extrinsic (impure) semiconductors are formed byadding small amounts of suitable impurities to intrinsicsemiconductors in order to improve conductivity.

    The process of adding controlled impurities to intrinsic(pure) semiconductor materials is called doping.

    Two types of extrinsic semiconductor materials are:

    An n-type semiconductor material consists of Si

    atoms and pentavalent impurity atoms.A p-type semiconductor material consists of Si atoms

    and trivalent impurity atoms.

    Extrinsic Semiconductors

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    An n-type semiconductor material consists of Si atomsand pentavalent impurity atoms such as Arsenic (As),Phosphorus (P), Bismuth (Bi) and Antimony (Sb).

    N-Type Semiconductors

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    A p-type semiconductor material consists of Si atomsand trivalent impurity atoms such as Boron (B), Indium(I) and Gallium (Ga).

    P-Type Semiconductors

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    A pnjunction consists of a single crystal ofsemiconductor material that is doped to produce n-typematerial on one side and p-type on the other side.

    The pn junction is fundamental to the operation ofdevices such as diodes and transistors.

    Barrier Potential is the

    amount of voltage required

    to move electrons throughthe pn junction.

    (0.7V for Si and 0.3V for Ge)

    PNJunction

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    Diode is a device that allows current to flow in onedirection but blocks current in reverse direction.

    An diode is a two terminal device (the anode or p andthe cathode or n) commonly made from Silicon.

    The arrow in the symbol points in the direction ofconventional current flow.

    Diode

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    Bias is the use of a dc voltage to establish certainoperating conditions for an electronic device.

    A diode is said to be forward biased if the p-side of thediode is more +ve with respect to the n-side of the diode.

    A diode is said to be reverse biased if the n-side of thediode is more +ve with respect to the p-side of the diode.

    Basic Definitions

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    Diode is a non-linear device.

    Diode is usually operated in the forward bias and reverse

    bias regions, without entering the breakdown region.

    Volt-ampere Characteristics

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    V-I characteristics for a typical Si diode.

    Volt-ampere Characteristics (contd.)

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    The ideal diode acts as a short circuit for forwardcurrents and as an open circuit with reverse voltageapplied.

    Ideal Diode Model

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    The practical diode model adds a 0.7V voltage source inseries with an ideal diode model.

    Practical Diode Model

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    A mechanical switch in ON state allows current toflow in either direction.

    A diode in ON state allows current to flow in onedirection only (uni-directional switch). The arrow in thesymbol points in the direction of conventional current

    flow.

    Practically, we assume a 0V drop across a mechanicalswitch in ON state while we assume a 0.7V drop

    across a diode in ON state.

    Comparison with Mechanical Switch

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    Comparison of Diode Models