DIODE (Semiconductor Devices)

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    Schematic Diagram and Physical

    Structure of Diode

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    Schematic Diagram and Physical

    Structure of Diode

    The lead connected to the P-types is called

    anode.

    The lead connected to the N-types is called

    Cathode.

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    Physics of a diode When a diode is absent of a voltage source, the

    protons and electrons are aligned in their proper

    layers (as shown ) by default.

    A region exists between the P-Type and N-Type

    layers called the depletion zone

    The size of the depletion zone in a diode changesas voltage or the configuration of a circuit is

    changed.

    The depletion zone has some very interesting

    characteristics. Because it is made of a material

    similar to the P-Type and N-Type material, it has"holes" that electrons fill in to prevent positive

    charges from going through, thus preventing

    current from flowing. There is only one way the

    holes can be opened for positive charges to flow

    through and current to be produced.The electron/proton activity in active state

    and the electron/proton alignment inits insulating state.

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    Forward-Biased

    On the other hand, if the battery's polarity is

    reversed and the positive end is connected to

    the diode's positive end, the electrons in thediode will repel from the negative end and

    free electrons will open the "holes" to allow

    protons to enter the N-type region and

    interact with the electrons.

    This interaction gives aforward-biased

    behavior of the diode.

    The interaction creates current and in the

    case of light emitting diodes, photons whichcreate light.

    In this "active" state, the depletion zone is at

    its minimum size.

    Positive end of the battery meets the

    positive end (the anode) of the diode,

    causing current flow..

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    Reverse-Biased

    As know, like charges repel and opposite

    charges attract.

    Whenever a battery is connected to a diode in

    a way such that the negative end is connected

    to the P-Type (or anode) end of the diode,

    charges will be driven to the edges of the

    diode and the depletion zone is at its largest

    size (above left).

    This configuration gives the diode a

    behavior of what is called reverse-biased.

    Because no protons are able to flow through

    the depletion zone, current does not flow in

    this state.

    Negative end of the battery meets

    the negative end (the cathode) of

    the diode, no current flow occurs.

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    Physics of a diode The graph on the right shows represents

    relationship of current over voltage in a zener

    diode.

    This graph is similar to the basic junction diode

    except the junction diode does not have the

    current drop shown on the left side of the graph

    (it remains zero).

    In most diodes the holes in the depletion layer

    won't open until a specific amount of voltage has

    been surpassed.

    Since silicon is the material most diodes are madeof, the voltage in most diodes at which the holes

    can be opened and current be produced is

    approximately 0.7V.

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    The anode (positive end) isconnected to the negative end of

    the battery.

    Charges in the diode layers areattracted to the outermost edges,

    so the depletion zone is at itslargest, no current is flowing,and the diode is off.

    A voltage VD still exists in thediode even when a currentdoesn't. Because the orientationof the diode is opposite to thebattery, the voltage going

    through the diode is the negativevalue of the battery, or -5V.

    Application of a diode in a circuit

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    Anode is now connected to thepositive end of the battery,

    charges are interacting in thediode and current is flowingthrough.

    Since the voltage across a diodewhen current is going through it is0.7

    Since the current through thecircuit is uniform, the currentthrough the resistor, diode, andthe wires is:

    I = V/R = (5V-0.7V)/(1000)

    = 4.3mA

    Application of a diode in a circuit

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    Knee Voltage In the forward region of the graph, the voltage

    at which the current starts to increase quicklyis called the knee voltage of the diode.

    If the knee voltage is higher, the diodeconducts easily

    If the knee voltage is lower, the diodeconducts poorly

    (The knee voltage for a silicon diode isapproximately 0.7 volt and for a germaniumdiode 0.3 volt)

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    Forward Current

    If the value for forward-bias voltage increased,

    the value of current will increase and theresistant of the joint will decrease

    The more the voltage, the less the resistant of

    the joint, and the more of the current.

    The current is known as forward current(ID)(in miliAmpere scale).

    The decrease resistance is known as forwardresistance (RD).

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    Reverse Current Electrons in N type material is attracted to the

    +ve terminal of voltage supply (VS). This willcause the depletion region become larger(widen).

    The resistant become higher and known as

    reverse resistant, RS.

    The current is known as reverse current (Is)(inmiliAmpere scale).

    Due to that, there is no electrons current flowacross the joint region.

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    Breakdown Voltage

    This limit is known as insulation

    breakdown voltage.

    It can cause the P-N joint burn.

    To overcome this situation, the

    maximum reverse-bias voltage

    supplied to the P-N joint must not

    exceed the insulation breakdown limit.

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    Considered has no barrier [email protected] voltage, no leakagecurrent, no resistance in front ( rd )and no breakdown voltage.

    Figures show characteristic arc diode have been distinguishedwhen several matter deserted.

    IDEAL DIODE

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    A Zener Diode is a special kind of diode which permits current to flow in the

    forward direction as normal, but will also allow it to flow in the reverse

    direction when the voltage is above a certain value - the breakdown voltage

    known as the Zener voltage.

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    A zener diode can be used to make a simple voltage regulation circuit

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    The illustration above shows this phenomenon in a Current vs. Voltage

    graph. With a zener diode connected in the forward direction, it behaves

    exactly the same as a standard diode - i.e. a small voltage drop of 0.3 to

    0.7V with current flowing through pretty much unrestricted. In the reversedirection however there is a very small leakage currentbetween 0V and

    the Zener voltage - i.e. just a tiny amount of current is able to flow. Then,

    when the voltage reaches the breakdown voltage (Vz), suddenly current

    can flow freely through it.

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    It made to afford issue reverse current that high value

    without damaging diode.

    In breakdown zener and after that voltage acrossdiode will still and equivalent with a zener voltage.

    Zener diode may be made so that voltage zener

    determine at value that selected (2.4V - 200V).

    Advantages

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    Light emitting diodes, commonly called LEDs, are real

    unsung heroes in the electronics world.

    Among other things, they form the numbers on digital clocks,

    transmit information from remote controls, light up watches

    and tell you when your appliances are turned on.

    Basically, LEDs are just tiny light bulbs that fit easily into an

    electrical circuit.

    In the case of LEDs, the conductor material is typically

    aluminum-gallium-arsenide (AlGaAs).

    LED

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    How Can a Diode Produce Light?

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    How Can a Diode Produce Light?

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    Ab t Ph t di d

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    Photodiodes are similar to regular semiconductor diodes except that they

    may be either exposed (to detect vacuum UV or X-rays) or packaged with a

    window or optical fiber connection to allow light to reach the sensitive part

    of the device.

    Many diodes designed for use specifically as a photodiode will also use a

    PIN junction rather than the typical junction.

    Photo diodes are semi conductor devices responsive to high energy

    particles and photons.

    Photodiodes operate by absorption of charged particles and generate a flow

    of current in an external circuit, proportional to the incident power.

    Photodiodes can be used to detect the presence or absence of minute

    quantities of light and can be calibrated for extremely accurate

    measurements from intensities below 1pW/cm2.

    About Photodiode

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    Laser Diode

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    Laser Diode

    Laser Diode

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    Laser Diode

    GND: Negative return for LDs and PD cathodes (-ve).

    VLD: Violet (~405 nm) diode anode (+ve).

    RLD: Red (~650 nm) diode anode (+ve).IRLD: IR (~780 nm) laser diode anode (+ve).

    PD: Photodiode anode.

    This is a close-up of the connections on my

    unit. (Note the remaining section of polymer-

    PCB).Black: LD and PD cathodes (GND, -ve).

    Blue: VLD anode (+ve).

    Red: RLD anode (+ve).

    Laser Diode

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    Laser Diode

    Laser diode emitting red, with small

    collimating lens.

    Laser Diode

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    Laser Diode

    This is the Laser diode mounted on a

    heatsink with the red emitter

    powered.And now, this is what you have all

    been waiting for.....

    Output

    Laser Diode

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    Laser Diode'laser diode', this generally refers to the combination of the semiconductor chip

    that does the actual lasing along with a monitor photodiode chip (for used for

    feedback control of power output) housed in a package (usually with 3 leads) that

    looks like a metal can transistor with a window in the top. These are thenmounted and may be combined with drivercircuitry and optics in a 'diode lasermodule' or the common (red) laser pointer.

    Diode lasers use nearly microscopic chips of Gallium-Arsenide or other exotic

    semiconductors to generate coherent light in a very small package.

    The energy level differences between the conduction and valence band electrons

    in these semiconductors are what provide the mechanism for laser action.

    Fortunately, laser diodes are now quite inexpensive (with prices dropping as you

    read this) and widely available.

    The active element is a solid state device not all that different from an LED.

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    Applications of Laser Diodes

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    Applications of Laser Diodes

    Typically found in CD players, CDROM drives,

    laser printers, and bar code scanners.

    These were scanned at 150 dpi.

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    1. Average Current2. Average Voltage

    3. RMS (Root Means SquareVoltage)

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    The strength or power of

    a wave signal. The

    "height" of a wave when

    viewed as a graph.

    Higher amplitudes are

    interpreted as a higher

    volume, hence the name

    "amplifier" for a devicewhich increases

    amplitude.

    Amplitude

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    The distance between

    any point on a wave and

    the equivalent point on

    the next phase. Literally,

    the length of the wave.

    Amplitude

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    The frequency of a wave is the number of

    waves produced by a source each second. It isalso the number of waves that pass a certainpoint each second. The unit of frequency is

    the hertz (Hz).

    Frequency

    Diff b RMS l d P k l

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    The value of an AC voltage is continually changing from zero

    up to the positive peak, through zero to the negative peak and

    back to zero again. Clearly for most of the time it is less than

    the peak voltage, so this is not a good measure of its real effect.

    Instead we use the root mean square voltage (VRMS) which

    is 0.7 of the peak voltage (Vpeak):

    Difference between RMS value and Peak value

    VRMS = 0.707 Vpeakand

    Vpeak = 1.4 14 VRMS

    These equations also apply to current.

    The RMS value is the effective value of a varying voltage or current. It is the

    equivalent steady DC (constant) value which gives the same effect.

    A V l

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    Average Value = = 0.637 values peak

    Average Value

    Average value one sine wave for half cycles positive is peak-to

    peak value segmented with :

    E l 1

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    Example -1

    Calculate and get Vp, Vp-p, Vrms, Vaverage and frequency.

    A

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    Answer

    E ample 2

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    Example - 2

    Equation to a current AC is I = 70.71 sin 520t

    Determine :

    i) Current peak value.

    ii) RMS current value.

    iii) Current average value.

    iv) Wave frequency.

    v) Current after 0.0015 seconds through 0 in positive hike.

    Answer

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    Answer

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    RECTIFIERS

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    REGULATED POWER SUPPLY

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    RECTIFIER

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    RECTIFIER

    1. Half-wave rectifier

    2. Full wave rectifier

    3. Bridge rectifier

    HALF WAVE RECTIFIER

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    HALF WAVE RECTIFIER

    In half wave rectification, either the positive or negative half ofthe AC wave is passed, while the other half is blocked.

    Because only one half of the input waveform reaches the output,

    it is very inefficient if used for power transfer.

    Half-wave rectification can be achieved with a single diode in a

    one phase supply, or with three diodes in a three-phase supply.

    Vin Vout

    OPERATION

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    OPERATION

    During positive cycle entry signal, diode D in forward biased.

    D act as closed switch so current can go through it.

    Voltage fall in RL is equal positive cycle magnitude entry signal if we neglect

    voltage fall in diode.

    During negative cycle entry signal, D diode in reverse biased.

    D act as open switch so current cant go through it.

    Voltage fall in RL is zero.

    Output voltage in positive cycle is Vout = Vin 0.7V(Si)

    Signal output frequency is equal with input frequency

    FULL WAVE RECTIFIER

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    FULL WAVE RECTIFIER

    A full-wave rectifierconverts the whole of the input waveform to one of constant

    polarity (positive or negative) at its output.

    Full-wave rectification converts both polarities of the input waveform to DC (direct

    current), and is more efficient.

    However, in a circuit with a non-center tapped transformer, four diodes are required

    instead of the one needed for half-wave rectification. This has some disadvantages that

    we will see later on. Four rectifiers arranged this way are called a diode bridge or bridge

    rectifier:

    OPERATION

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    OPERATION

    When voltage AC will given in circuit, M and N at transformer secondary will be positive

    and negative in rotation. When input voltage positive cycle were given, terminal M will be

    positive and N will be negative. Diode D1be forward biased therefore diode D2 be reversebiased. Current will through from M, E, A, B, C, F N. 1 positive cycle were be appeare at

    load RL.

    Output voltage in positive cycle is Vout = VM-N 1.4V(Si)

    Signal output frequency is 2x with signal input frequency

    :

    RECTIFIER

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    RECTIFIER

    There are several ways of connecting diodes to make a rectifier to

    convert AC to DC. Thebridge rectifieris the most important and itproduces full-wave varying DC.

    A full-wave rectifier can also be made from just two diodes if a

    centre-tap transformer is used, but this method is rarely used nowthat diodes are cheaper. A single diode can be used as a rectifier

    but it only uses the positive (+) parts of the AC wave to produce

    half-wave varying DC.

    Bridge rectifier

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    Bridge rectifier

    A bridge rectifier can be made using four individual diodes, but it is also

    available in special packages containing the four diodes required. It is called a

    full-wave rectifier because it uses all the AC wave (both positive and negative

    sections). 1.4V is used up in the bridge rectifier because each diode uses 0.7V

    when conducting and there are always two diodes conducting, as shown in the

    diagram below. Bridge rectifiers are rated by the maximum current they can

    pass and the maximum reverse voltage.

    Alternate pairs of diodes conduct, changing over

    the connections so the alternating directions of

    AC are converted to the one direction of DC.

    Single diode rectifier

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    Single diode rectifier

    A single diode can be used as a rectifier but this produces half-wave varying

    DC which has gaps when the AC is negative. It is hard to smooth this

    sufficiently well to supply electronic circuits unless they require a very small

    current so the smoothing capacitor does not significantly discharge during the

    gaps.

    Output: half-wave varying DC

    (using only half the AC wave)

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