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ANALOG CIRCUITS – I

Apr 07, 2018

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    DEEPAK.P

    ECE

    SNGCE

    ANALOG CIRCUITS I

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    RC circuits

    Diode circuits

    Voltage regulators

    UNIT I

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    Basics of circuit analysis

    Calculate the ID,VR

    Answer-----7.3V,3.32 mA

    0.7V

    8 V

    2.2 K

    VD

    VR

    ID

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    Basics of circuit analysis

    Calculate the ID,VR

    0.7V

    8 V

    2.2 K

    VD

    VR

    ID

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    Basics of circuit analysis

    Calculate the ID,VR,VD

    Assume that RD is Germanium Diode

    8 V

    2.2 K

    RD

    VR

    ID

    Low R

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    Basics of circuit analysis

    Calculate the ID,VR,VD

    Assume that RD is Silicon Diode

    8 V

    2.2 K

    RD

    VR

    ID

    High R

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    Diode

    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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    Diode

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    Diode

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    Diode Biasing

    Forward Voltage DropElectricity uses up a little energy pushing its

    way through the diode, rather like a personpushing through a door with a spring.This means that there is a small voltage

    across a conducting diode, it is called theforward voltage dropand is about 0.7V forall normal diodes which are made from silicon.The forward voltage drop of a diode is almost

    constant whatever the current passingthrough the diode so they have a very steepcharacteristic (current-voltage graph).

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    Diode

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    Diode

    Reverse Voltage

    When a reverse voltage is applied a perfectdiode does not conduct, but all real diodesleak a very tiny current of a few A or less.

    This can be ignored in most circuitsbecause it will be very much smaller thanthe current flowing in the forward direction.

    However, all diodes have a maximum

    reverse voltage (usually 50V or more)and if this is exceeded the diode will failand pass a large current in the reversedirection, this is called breakdown.

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    Diode characteristics

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    IdealDiodeForward bias

    Reverse bias

    R is Low

    R is High

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    RealDiodeForward bias

    Reverse bias

    Cell

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    Different Diode Bias

    Determine the bias condition of the diodein the following cases0V5V

    5V0V

    5V 0V

    3V5V

    5.1V5V

    -3V-5V

    -6V-2V

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    Diode application

    It is useful in non linear wave shaping circuits.

    Commonly used circuits areClippers

    Clampers.

    Rectifiers

    In electronics, a clipper is a device designed to prevent

    the output of a circuit from exceeding a

    predetermined voltage level without distorting theremaining part of the applied waveform.

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    CLIPPING

    A clipping circuit consists of linear elements likeresistors and non-linear elements like junction diodes

    or transistor.

    Clipping circuits are also called asSlicers, amplitude

    selectors or limiters.

    One of the most basic clipping circuit is thehalf-wave rectifier.

    A half-wave rectifier clips either thenegative half cycle or the positive half cycleof an alternating waveform, and allows topass only one half cycle.

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    Application of Clipping Such a circuit has great applications in

    radars, digital computers and otherelectronic systems for removing unwantedportions of the input signal voltages aboveor below a specified level.

    Another application is in radio-receivers forcommunication circuits where noise pulsesthat rise well above the signal amplitudeare clipped down to the desired level.

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    Clipper Circuits

    The basic components required for aclipping circuit are an ideal diode and aresistor.

    In order to fix the clipping level to thedesired amount, a dc battery must also beincluded.

    Different levels of clipping can be obtainedby varying the amount of voltage of the

    battery and also interchanging thepositions of the diode and resistor.

    04/21/12Deepak.P20

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    Classification of CLIPPING

    Classifications Of ClippersAccording to non-linear devices used,

    clippers may be classified asDiode clippers andTransistor clippers.

    According to biasing, the clippers may beclassified as

    Unbiased clippers andBiased clippers.

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    Classification of CLIPPING

    According to configuration used theclippers may be

    Series diode clippersA series combination of diode, resistor and reference supply

    Parallel or shunt diode clippers

    Multi-diode clippers/Combinational clippers

    It consisting of several diodes, resistors and reference voltages.

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    Classification of CLIPPING

    According to level of clipping the clippersmay bePositive clippers

    Negative clippers

    Biased clippers and

    Combination clippers

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    Classification of CLIPPING

    There are two types of clipper circuitsSeries clipping

    Parallel clipping

    Series clipping

    In these types of circuits, the diode is connected

    between the input and output voltage terminals.

    Parallel clipping

    In these types of circuits, the diode is connected inparallel.

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    Positive Clipper

    04/21/12Deepak.P25

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    +VE series CLIPPING

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    Transfer Characteristics

    04/21/12Deepak.P27

    Vm

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    Negative Diode Clipper

    04/21/12Deepak.P28

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    -VE series CLIPPING

    Diodes will act as an "ON/OFF switch.

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    -VE Parallel CLIPPING

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    Clipper circuits

    04/21/12Deepak.P31

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    Negative& Positive Diode Clipper

    04/21/12Deepak.P32

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    Biased Negative Clipper

    A biased clipper comes in handy when asmall portion of positive or negative halfcycles of the signal voltage is to beremoved.

    When a small portion of the negative halfcycle is to be removed, it is called a biasednegative clipper.

    04/21/12Deepak.P33

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    Biased Positive Clipper

    04/21/12Deepak.P34

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    Biased Positive Clipper and Biased Negative Clippers

    04/21/12Deepak.P35

    Biased Positive Clipper and Biased Negative

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    Biased Positive Clipper and Biased Negative

    Clipper

    04/21/12Deepak.P36

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    Combination Clipper

    When a portion of both positive andnegative of each half cycle of the inputvoltage is to be clipped (or removed),combination clipper is employed. The

    circuit for such a clipper is given in thefigure below.

    04/21/12Deepak.P37

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    Transistor Clipper

    Transistor can be used to clip the I/P waveform.

    Positive clipper , negative clipper, Combinational

    clipper can be designed using Transistor circuit.

    The practical circuit for positive and negative clippingis Transistor switching circuit.

    The practical circuit for obtain Double side clipping is

    Transistor amplifier circuit.

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    Function of a Simple Switch

    An OFF type switch

    Lamp does not glows

    No current will flow in the circuit

    Lamp

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    Function of a Simple Switch

    An ON type switch

    Lamp glows

    Some amount of current flows in the circuit according to

    the resistance.

    Lamp

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    Transistor as a Switch

    Bipolar transistors can be made to operate as an"ON/OFF switch.

    Because a transistor's collector current is

    proportionally limited by its base current, it can be

    used as a current-controlled switch.

    If the circuit uses the Transistor as a Switch, then the

    biasing is arranged to operate the transistor in the

    "Saturation" and "Cut-off" regions.

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    Transistor as a Switch

    If we are using PNP transistor, Battery should be reversed.

    Lamp

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    Transistor Act as an OFF type switch

    Transistor is biased in cutoff, lamp OFF , No current flow

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    Cut OFF Region

    Cut-off" region

    Both junctions are reverse-biased.

    Here the operating conditions of the transistor are

    Zero input base current (Ib),

    Zero output collector current (Ic)Maximum collector voltage (Vce)

    Here the transistor is switched fully "OFF".

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    Transistor Act as an ON type switch

    Transistor saturated, lamp ON, Current flows

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    Saturation Region

    Saturation" region

    Both junctions are Forward-biased.

    Here the transistor will be biased so that the maximum

    amount of base current is applied, resulting in

    Maximum collector current flowMinimum collector emitter voltage

    Here the transistor is switched fully "ON".

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    Transistor Switching Circuit

    Transistor switching circuit can be divided in to two

    Normally ON type

    Normally OFF type

    In normally OFF ,transistor will be in cutoff.In normally ON ,transistor will be in saturation.

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    O/P Characteristics of CE configuration

    Load Line

    Soft Saturation Point

    Hard

    SaturationP

    oint

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    Simple Amplifier

    VCC

    O/PI/P

    RB

    RC

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    Amplifier Operation

    LOAD LINE

    VCC

    VCC/

    (RC+RE)

    Q POINT

    VCEQ

    ICQ

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    Normally ON type Switch

    VCC

    O/PI/P

    RBRC

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    Normally ON type SwitchThe Q point of the transistor must fix in the hard

    saturation/Soft Saturation point.For that ,fix VCEQ=0.2and

    ICRC= VCC-VCEQ

    DC Load Line

    VCC

    VCC/RC

    Q POINT

    VCEQ

    ICQ

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    Design of Normally ON type SwitchAssume VCC,IC,

    O/P Loop equationVCC=VCE+ICRC VCE sat=0.2

    RC=VCC VCE sat/ IC ;

    I/P Loop equation

    IC= IB

    VCC=5 IB RB+VBE ;

    RB=VCC -VBE / 5 IB ;

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    O/P wave form when I/P is Square wave

    INPUT

    OUTPUT

    0.2 V

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    O/P when I/P is Sine wave

    VCC

    VCC/(RC)

    Q POINT

    VCEQ

    0.2V

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    Normally OFF type Switch

    VCC

    O/P

    I/P

    RB

    RC

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    Normally OFF type SwitchThe Q point of the transistor must fix in the cut-off

    For that ,fix VCEQ=VCC andICQ=0; To fix ICQ=0 , IB =0, So No Dc bias is applied to the base.

    Practically a small negative voltage is applied to the Base.

    VCC

    VCC/RC

    Q POINT

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    Design of Normally OFF type SwitchAssume VCC,IC,

    O/P Loop equationVCC=VCE+ICRC VCE sat=0.2

    RC=VCC VCE sat/ IC ;

    I/P Loop equation

    IC= IB

    VCC=5 IB RB+VBE ;

    RB=VCC -VBE / 5 IB ;

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    O/P wave form when I/P is Square wave

    INPUT

    OUTPUT

    0.2V

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    O/P when I/P is Sine wave

    ICQ

    VCC

    VCC/(RC)

    Q POINT

    VCEQ

    ICQ=0 VCEQ=VCC

    CAPACITOR

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    CAPACITOR

    A capacitor is a device that can store electrical charge.The simplest type is a "parallel plate " Capacitor that

    consists of two metal plates that are separated by an

    insulating material.

    Capacitor is a two-terminal device.

    Capacitor has two active electrodes.Anode

    Cathode

    CAPACITOR

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    CAPACITOR

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    Charging of a Capacitor from a DC source

    If we connect the two plates to each other with abattery, the free electrons is accumulated in one plate

    of a capacitor. Similarly positive charges is

    accumulated to the another plate.

    Ch i f C it

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    Charging of a Capacitor

    If we quickly remove the wires without touching the

    plates, the charge remains on the plates.Because the two plates have different charge, there is a

    net electric field between the two plates.

    The "capacitance" of a capacitor is stated in terms of

    the amount of charge (Q) stored at a given voltage

    drop (across the capacitor).

    C = Q / V

    C = A / d= 0 r

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    Charging of a Capacitor from a AC source

    Assume that, we connect the capacitor to an ACsource.

    In the positive half cycle + ve charges were

    accumulated in one plate.

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    Charging of a Capacitor from a AC source

    In the negative half cycle +ve charges wereaccumulated in the other plate.

    It is similar to coupling of an AC signal.

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    Charging wave form of a Capacitor

    Clamping

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    Clamping

    The clamping circuit can shift the waveform to a

    specified voltage level.

    Clamping circuit actually introduces a dc level to an

    AC signal.

    It is also known as DC restorercircuit.

    It is used in the television receiver to restore the

    original dc reference voltage to the video signal.

    In television system ,the dc reference levelcorresponding to thebrightness level of the picture is

    not transmitted with video signal.

    Clamping

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    Clamping

    A capacitorand a diode can be used to design

    clamping circuits.

    Clamping can be classified in to

    +ve clamping-ve clamping

    Biased clamping circuits can be designed to clamp a

    waveform at a desired level

    Problem

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    Problem

    Vi=Vm Sint

    VO

    Draw the O/P/ wave form when the I/P is 20 Vpp

    Answer

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    Answer

    -10 V

    10 V

    Problem

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    Problem

    Vi=Vm Sint

    VO

    Draw the O/P/ wave form when the I/P is 20 Vpp and it

    contains a DC voltage of 2V

    Answer

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    Answer

    2V

    10 V

    -10 V

    Simple Clamping

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    SimpleClamping

    V

    +-Vi=Vm Sint

    VO

    Battery

    Answer

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    Answer

    V

    Vm+V

    Vm-V

    Simple Clamping

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    SimpleClamping

    Vm

    Vi=Vm Sint

    VO

    +-

    Answer

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    Answer

    -V

    Vm-V

    -Vm-V

    Simple Diode Clamping

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    SimpleDiodeClamping

    Vm

    In negative half cycle ;Vo=vi+Vm=Vm Sint+Vm

    + -Vi=Vm Sint

    VO

    Capacitor

    Simple Diode Clamping

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    SimpleDiodeClamping

    Vm

    Simple Diode Clamping

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    SimpleDiodeClamping

    VmVm

    O/P when I/P is square wave

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    O/P when I/P is square wave

    Vm+Vm

    Simple Diode Clamping

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    SimpleDiode Clamping

    Vm

    +-

    In the 2nd

    positive half cycle;Vo=Vi-Vm=Vm Sint-Vm

    Vi=Vm Sint

    VO

    Capacitor

    O/P when I/P is square wave

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    O/P when I/P is square wave

    Vm+Vm

    O/P when I/P is square wave

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    O/P when I/P is square wave

    Vm+Vm

    Problem

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    Problem

    Vm

    Vi=Vm Sint

    VO

    +

    -

    The I/p signal with 24 Vpp is applied to a clamper circuit. Sketch the O/P wave

    form

    Problem

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    Problem

    Vm

    VO

    +

    -

    The I/p signal with 24 Vpp is applied to a clamper circuit. Sketch the O/P wave

    form

    Positive Clamping

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    Positive Clamping

    Vm

    +

    -

    Draw the o/p wave form

    VO

    O/P when I/P is square wave

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    O/P when I/P is square wave

    Vm+Vm

    Negative Clamping

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    Negative Clamping

    Vm

    +

    -

    Draw the o/p wave form

    VO

    Biased Clamper

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    Biased Clamper

    Vm

    Vi=Vm Sint

    VO

    +

    -

    The I/p signal with 24 Vpp is applied to a clamper circuit. Sketch the O/P wave

    form

    -

    +5V

    Biased Clamper

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    Biased Clamper

    Biased Clamper

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    Biased Clamper

    Biased Clamper

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    Biased Clamper

    Biased Clamper

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    Biased Clamper

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    RC Circuits

    An RC circuit is simply a circuit with avoltage source (battery) connected inseries with a resistor and a capacitor.

    A resistor-capacitor circuit (RC circuit), or

    RC filter or RC network, is an electric circuitcomposed of resistors and capacitorsdriven by a voltage or current source. The1st order RC circuit, composed of one

    resistor and one capacitor, is the simplestexample of an RC circuit.

    04/21/12Deepak.P95

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    RC Circuits

    04/21/12Deepak.P96

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    RC Circuits

    04/21/12Deepak.P97

    As with circuits made up simply ofresistors, electrical currents can flow in thisRC circuit, with one modification. A batteryconnected in series with a resistor will

    produce a constant current. The samebattery in series with a capacitor willproduce a time varying current, whichdecays gradually to zero. If the battery is

    removed and the circuit reconnectedwithout the battery, a current will flow (fora short time) in the opposite direction asthe capacitor "discharges". A measure of

    how long these transient currents last in a"

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    RC Circuits

    04/21/12Deepak.P98

    Time ConstantThe time constant of an RC circuit is the

    product of its resistance and capacitance.For R in ohms and C in farads, the time

    constant tis in seconds.T = RC

    The range of frequencies that the filterpasses is called its bandwidth. The point at

    which the filter attenuates the signal to halfits unfiltered power is termed its cutofffrequency. This requires that the gain ofthe circuit be reduced to

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    RC Circuits

    04/21/12Deepak.P99

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    RC Circuits

    04/21/12Deepak.P100

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    RC Circuits

    High Pass FilterA High Pass Filter or HPF, is the exact opposite to that

    of Low Pass filter circuit, as now the two components

    have been interchanged with the output signal (Vout)

    being taken from across the resistor.Where the low pass filter only allowed signals to pass

    below its cut-off frequency point, c, the passive high

    pass filter circuit as its name implies, only passes

    signals above the selected cut-off point, c eliminatingany low frequency signals from the waveform.

    04/21/12Deepak.P101

    High Pass Filter

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    04/21/12Deepak.P102

    In this circuit arrangement, the reactance of the capacitor is very high at

    low frequencies so the capacitor acts like an open circuit and blocks any

    input signals at Vin until the cut-off frequency point (c) is reached. Above

    this cut-off frequency point the reactance of the capacitor has reduced

    sufficiently as to now act more like a short circuit allowing all of the input

    signal to pass directly to the output as shown below in the High PassFrequency Response Curve.

    High Pass Filter

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    04/21/12Deepak.P103

    High Pass Filter

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    04/21/12Deepak.P104

    The circuit gain, Av which is given as Vout/Vin (magnitude) and is

    calculated as:

    Cut-off Frequency and Phase Shift

    High Pass Filter

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    High pass filter stages can be cascadedtogether to form a second-order (two-pole)filter as shown.

    04/21/12Deepak.P105

    High Pass Filter

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    A very common application of a passivehigh pass filter, is in audio amplifiers as acoupling capacitor between two audioamplifier stages and in speaker systems todirect the higher frequency signals to thesmaller "tweeter" type speakers whileblocking the lower bass signals or are alsoused as filters to reduce any low frequencynoise or "rumble" type distortion. Whenused like this in audio applications the highpass filter is sometimes called a "low-cut",or "bass cut" filter.

    04/21/12Deepak.P106

    High Pass Filter

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    RC Differentiator

    04/21/12Deepak.P107

    RC Differentiator

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    Each cycle of the square wave input waveformproduces two spikes at the output, one positive and one

    negative and whose amplitude is equal to that of the

    input. The rate of decay of the spikes depends upon the

    time constant, (RC) value of both components, (t = R xC) and the value of the input frequency. The output

    pulses resemble more and more the shape of the input

    signal as the frequency increases.

    04/21/12Deepak.P108

    RC Differentiator

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    From theory we know that the voltageacross the resistor in an RC circuit is givenby:

    Charging: vR = Vp e- tRC

    Discharging: vR = - Vp e- tRC

    04/21/12Deepak.P109

    RC Integrator

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    From theory we know that the voltageacross the capacitor in an RC circuit isgiven by:

    Charging: vc = Vp (1 e-t/RC)Discharging: vc = Vp e- tRC

    04/21/12Deepak.P110

    RC Integrator

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    04/21/12Deepak.P111

    RECTIFIERS

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    RECTIFIERS

    A rectifier is an electrical device that convertsalternating current (AC) to direct current (DC).

    Rectifiers have many uses including as components of

    power supplies and as detectors of radio signals.

    Rectifiers may be made of solid state diodes, vacuumtube diodes, mercury arc valves, and other

    components.

    RECTIFIERS(C td )

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    RECTIFIERS(Contd..)

    Rectifiers can be divided in to twoHalf wave Rectifiers

    Full wave Rectifiers

    In half wave rectification, either the positive or

    negative half of the AC wave is passed, while the otherhalf is blocked.

    Half-wave rectification can be achieved with a single

    diode in a one phase supply, or with three diodes in a

    three-phase supply.

    HALF WAVE

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    RECTIFIERS(Contd..)

    Full WAVE RECTIFIERS

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    Full WAVE RECTIFIERS

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    Full WAVE RECTIFIERS

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    A full-wave rectifier converts the whole ofthe input waveform to one of constantpolarity (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-centertapped transformer, four diodes are

    required instead of the one needed for half-wave rectification. Four rectifiers arrangedthis way are called a diode bridge or bridgerectifier.

    Bridge RECTIFIERS

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    g

    Regulated Power Supply

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    g pp y

    There are many types of power supply.Most are designed to convert high voltageAC mains electricity to a suitable lowvoltage supply for electronics circuits and

    other devices. A power supply can bybroken down into a series of blocks, each ofwhich performs a particular function.

    Regulated Power Supply

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    g pp y

    Each of the blocks is described in more detail below:

    Transformer - steps down high voltage AC mains to low voltage AC.

    Rectifier - converts AC to DC, but the DC output is varying.

    Smoothing - smoothes the DC from varying greatly to a small ripple.

    Regulator - eliminates ripple by setting DC output to a fixed voltage.

    Transformer only

    Transformer + Rectifier

    Transformer + Rectifier + Smoothing

    Transformer + Rectifier + Smoothing + Regulator

    Zener Diode

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    Zener Diode

    04/21/12Deepak.P121

    A Zener diode is a type of diode that permits current not only in

    the forward direction like a normal diode, but also in the reverse

    direction if the voltage is larger than the breakdown voltage

    known as "Zener knee voltage" or "Zener voltage". The device

    was named after Clarence Zener, who discovered this electricalproperty.

    Zener Regulator

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    Zener Regulator

    Zener diodes are widely used as voltagereferences and as shunt regulators toregulate the voltage across small circuits.When connected in parallel with a variable

    voltage source so that it is reverse biased,a Zener diode conducts when the voltagereaches the diode's reverse breakdownvoltage. From that point on, the relatively

    low impedance of the diode keeps thevoltage across the diode at that value.

    04/21/12Deepak.P122

    Zener Regulator

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    Zener Regulator

    A Zener diode is a PN junction that hasbeen specially made to have a reversevoltage

    breakdown at a specific voltage. Its

    characteristics are otherwise very similar tocommon

    diodes. In breakdown the voltage acrossthe Zener diode is close to constant over a

    widerange of currents thus making it useful as a

    shunt voltage regulator.

    04/21/12Deepak.P123

    Zener characteristic

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    Zener characteristic

    04/21/12Deepak.P124

    Zener Regulator

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    Zener Regulator

    04/21/12Deepak.P125

    Zener Regulator

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    Zener Regulator

    04/21/12Deepak.P126

    Fixed IC voltage Regulators

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    Fixed IC voltage Regulators

    Voltage Regulator (regulator), usuallyhaving three legs, converts varying inputvoltage and produces a constant regulatedoutput voltage. They are available in a

    variety of outputs.The most common part numbers start with

    the numbers 78 or 79 and finish with twodigits indicating the output voltage. The

    number 78 represents positive voltage and79 negative one. The 78XX series ofvoltage regulators are designed for positive