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DEEPAK.P
ECE
SNGCE
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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.
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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
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+VE series CLIPPING
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Transfer Characteristics
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Vm
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Negative Diode Clipper
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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
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Negative& Positive Diode Clipper
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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.
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Biased Positive Clipper
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Biased Positive Clipper and Biased Negative Clippers
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Biased Positive Clipper and Biased Negative
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Biased Positive Clipper and Biased Negative
Clipper
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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.
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RC Circuits
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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
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RC Circuits
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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.
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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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High Pass Filter
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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.
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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.
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High Pass Filter
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RC Differentiator
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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.
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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
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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
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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
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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.
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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.
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Zener characteristic
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Zener characteristic
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Zener Regulator
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Zener Regulator
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Zener Regulator
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Zener Regulator
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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
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