PRESENTATION FOR GROUP 5
FILTERS
WAVE-SHAPING CIRCUITS
REGULATED POWER SUPPLY
FILTERS
 After rectification a constant DC power is expected but there is always
an undesirable ripple content.
 To eliminate this, we use filter circuits.
 There are four main types of these circuits namely
 Shunt capacitor filter
 Series inductor filter
 Chock input (LC) filter
 (∏) section filter / CLC filter
SHUNT CAPACITOR FILTER
 The Shunt capacitor filters comprise of capacitor along with the load
resistor.
 In this, the capacitor is connected in parallel with respect to the output
of rectifier circuit and also in parallel with the load resistor.
 During conduction, the capacitor starts charging and stores energy in
the form of the electrostatic field.
 The capacitor will charge to its peak value because the charging time
constant is almost zero.
DIAGRAMS
 During non-conduction, the capacitor will discharge through the
load resistor.
 Thus, in this way, the capacitor will maintain constant output
voltage and provide the regulated output.
 The shunt capacitor filters use the property of capacitor which
blocks DC and provides low resistance to AC.
 Thus, AC ripples can bypass through the capacitor.
 If the value of capacitance of the capacitor is high, then it will offer
very low impedance to AC and extremely high impedance to DC.
 Thus, the AC ripples in the DC output voltage gets bypassed
through parallel capacitor circuit, and DC voltage is obtained
across the load resistor.
 Let Vr be the ripple component of voltage, and Vdc is the DC
value of Voltage and voltage across the load resistor RL be VL
max.
Let the charging duration be T1, and discharging duration be T2.
Then, total charge lost during non-conduction or discharge will be
given as:-
The value of charge Q = CVr.
SERIES INDUCTOR FILTER
 As an inductor allows dc and blocks ac, a filter called Series Inductor
Filter can be constructed by connecting the inductor in series, between
the rectifier and the load.
 This is so because inductors have a high reactance to AC current and
low impedance to DC current .
 n series inductor filter the inductor is connected in series with the
rectifier output and the load resistor.
 Thus, it is called series inductor filter.
 The property of an inductor to block AC and provides zero resistance to
DC is used in filtering circuit.
 When the value of DC output from the rectifier is more than the average
value then the rectifier store the excess current in the form of magnetic
energy.
DIAGRAMS
 Then the value of DC from the rectifier is less than the average value
then the inductor release the stored magnetic energy in order to balance
the effect of the low value of DC.
 In this way series inductor filter maintains the regulated DC supply.
 Moreover, inductor blocks the AC ripples present in the output voltage
of rectifier; thus, smooth DC signal can be obtained
CHOCK INPUT (LC) filter
 A filter circuit can be constructed using both inductor and capacitor in
order to obtain a better output where the efficiencies of both inductor
and capacitor can be used.
 The figure below shows the circuit diagram of a LC filter.
RIPPLE FACTOR CALCULATION
 et the voltage across load resistor RL be VL. Thus, the value of VL is
given by the below equation.
Where Vdc is the DC output voltage output of full wave rectifier, and Rc
is the resistance of inductor coil.
The value of resistance of inductor coil is much less than the value of
resistance of load resistor.
 Expanding the term of VL with the help of Fourier series we get the
below equation.
 The value of resistance of inductor coil or more precisely the value of
reactance of inductor coil is much less than the resistance of load
resistor RL.
 Thus, the entire DC voltage will appear across the load resistor and the
value of DC voltage across RL will be equal to VLmax.
 The reactance of inductor coil or choke coil increases with the increase
of frequency thus at higher frequencies the voltage will be negligible.
 Thus, the AC voltage is considered significant up to second harmonics
only i.e. VLmax.
 When the value of load resistance is infinite then the output
circuit will behave as an open circuit, in this case, ripple factor can
be given by the below equation.
DIAGRAMS
 The rectified output when given to this circuit, the inductor allows dc
components to pass through it, blocking the ac components in the
signal.
 Now, from that signal, few more ac components if any present are
grounded so that we get a pure dc output.
 This filter is also called as a Choke Input Filter as the input signal first
enters the inductor.
 The output of this filter is a better one than the previous ones.
(∏) SECTION FILTER
 This is another type of filter circuit which is very commonly used.
 It has capacitor at its input and hence it is also called as a Capacitor Input Filter.
 Here, two capacitors and one inductor are connected in the form of π shaped
network.
 A capacitor in parallel, then an inductor in series, followed by another capacitor in
parallel makes this circuit.
 If needed, several identical sections can also be added to this, according to the
requirement. The figure below shows a circuit for π filter Pi−filter.
DIAGRAMS
Working of a Pi filter
 In this circuit, we have a capacitor in parallel, then an inductor in series, followed by
another capacitor in parallel.
 Capacitor C1 − This filter capacitor offers high reactance to dc and low reactance to ac
signal. After grounding the ac components present in the signal, the signal passes to the
inductor for further filtration.
 Inductor L − This inductor offers low reactance to dc components, while blocking the ac
components if any got managed to pass, through the capacitor C1.
 Capacitor C2 − Now the signal is further smoothened using this capacitor so that it allows
any ac component present in the signal, which the inductor has failed to block.
 Thus we, get the desired pure dc output at the load.
WAVE SHAPPING CIRCUITS
TYPES OF WAVESHAPPING CCTS
1. CLIPPING CIRCUITS
2. CLAMPING CIRCUITS
CLIPPING CIRCUITS
A circuit which clips or cuts off a certain potion of the supplied voltage
and produce a defined output as shown in the waveform
 These are also known as clippers, limiters, slicers or amplitude selector
circuits
Series positive clipper
OPERATION FOR POSITIVE SERIES CLIPPER
 During the positive half cycle, terminal A is positive and terminal B is
negative. Therefore, the diode D is reverse biased during the positive half
cycle. During reverse biased condition, no current flows through the diode.
So the positive half cycle is blocked or removed at the output.
 During the negative half cycle, terminal A is negative and terminal B is
positive. Therefore, the diode D is forward biased during the negative half
cycle. During forward biased condition, current flows through the diode. So
the negative half cycle is allowed at the output.
Series positive clipper with positive bias
OPERATION OF SERIES POSITIVE CLIPPER WITH POSITIVE
BIAS
 During the positive half cycle, terminal A is positive and terminal B is negative. That means the
diode is reverse biased by the input supply voltage (Vi) and forward biased by the battery voltage
(VB). Initially, the input supply voltage Vi is less than the battery voltage VB (Vi < VB). So the
battery voltage dominates the input supply voltage. Hence, the diode is forward biased by the
battery voltage and allows electric current through it. As a result, the signal appears at the output.
 When the input supply voltage Vi becomes greater than the battery voltage VB, the diode D is
reverse biased. So no current flows through the diode. As a result, input signal does not appear at
the output.
 During the negative half cycle, terminal A is negative and terminal B is
positive. That means the diode D is forward biased by both battery voltage
VB and input supply voltage Vi. It implies, during the negative half cycle, it
doesn’t matter whether the input supply voltage is greater or less than the
battery voltage, the diode always remains forward biased. So the complete
negative half cycle appears at the output.
Series positive clipper with negative bias
Operation of Series positive clipper with negative bias
 During the positive half cycle, the diode D is reverse biased by both input supply voltage Vi and battery
voltage VB. So no signal appears at the output during the positive half cycle. Therefore, the complete
positive half cycle is removed.
 During the negative half cycle, the diode is forward biased by the input supply voltage Vi and reverse
biased by the battery voltage VB. However, initially, the battery voltage VB dominates the input supply
voltage Vi. So the diode remains to be reverse biased until the Vi becomes greater than VB. When the input
supply voltage Vi becomes greater than the battery voltage VB, the diode is forward biased by the input
supply voltage Vi. So the signal appears at the output. e half cycle is removed.
Shunt positive clipper
Operation of Shunt positive clipper
 In shunt clipper, the diode is connected in parallel with the output load resistance. The
operating principles of the shunt clipper are nearly opposite to the series clipper.
 The series clipper passes the input signal to the output load when the diode is forward
biased and blocks the input signal when the diode is reverse biased.
 The shunt clipper on the other hand passes the input signal to the output load when
the diode is reverse biased and blocks the input signal when the diode is forward
biased.
 In shunt positive clipper, during the positive half cycle the diode is forward biased
and hence no output is generated. On the other hand, during the negative half cycle
the diode is reverse biased and hence the entire negative half cycle appears at the
output.
Shunt positive clipper with positive bias
Operation of Shunt positive clipper with positive bias
 During the positive half cycle, the diode is forward biased by the input supply voltage
Vi and reverse biased by the battery voltage VB. However, initially, the input supply
voltage Vi is less than the battery voltage VB. Hence, the battery voltage VB makes the
diode to be reverse biased. Therefore, the signal appears at the output. However, when
the input supply voltage Vi becomes greater than the battery voltage VB, the diode D is
forward biased by the input supply voltage Vi. As a result, no signal appears at the
output.
 During the negative half cycle, the diode is reverse biased by both input supply voltage
and battery voltage. So it doesn’t matter whether the input supply voltage is greater or
lesser than the battery voltage, the diode always remains reverse biased. As a result, a
complete negative half cycle appears at the output.
Shunt positive clipper with negative bias
Operation of Shunt positive clipper with negative bias
 During the positive half cycle, the diode is forward biased by both input supply
voltage Vi and battery voltage VB. Therefore, no signal appears at the output during
the positive half cycle.
 During the negative half cycle, the diode is reverse biased by the input supply
voltage and forward biased by the battery voltage. However, initially, the input supply
voltage Vi is less than the battery voltage VB. So the battery voltage makes the diode
to be forward biased. As a result, no signal appears at the output. However, when the
input supply voltage Vi becomes greater than the battery voltage VB, the diode is
reverse biased by the input supply voltage Vi. As a result, the signal appears at the
output
Applications of clippers
 Clippers are commonly used in power supplies.
 Used in TV transmitters and Receivers
 They are employed for different wave generation such as square,
rectangular, or trapezoidal waves.
 Series clippers are used as noise limiters in FM transmitters
Clamping circuits
 clamping refers to shifting of the position of a wave along the vertical
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axis(y-axis) i.e. fixes the amplitude of the waveform at a desired level
The shape of the output waveform is not affected by the clamping circuit.
Generally a diode, capacitor and resistor are used for clamping.
A capacitor is used to provide a dc offset (dc level) from the stored charge.
The clamper is also referred to as a DC restorer, clamped capacitors, or AC
signal level shifter.
Positive clamper
Operation of Positive clamper
 During the negative half cycle of the input AC signal, the diode is forward
biased and hence no signal appears at the output. In forward biased
condition, the diode allows current through it. This current will flows to the
capacitor and charges it to the peak value of input voltage Vm. The capacitor
charged in inverse polarity (positive) with the input voltage. As input
current or voltage decreases after attaining its maximum value -Vm, the
capacitor holds the charge until the diode remains forward biased.
 During the positive half cycle of the input AC signal, the diode is
reverse biased and hence the signal appears at the output. In reverse
biased condition, the diode does not allow current through it. So the input
current directly flows towards the load.
 When the positive half cycle begins, the diode is in the non-conducting
state and the charge stored in the capacitor is discharged (released).
Therefore, the voltage appearing at the output is equal to the sum of the
voltage stored in the capacitor (Vm) and the input voltage (Vm) { I.e. Vo =
Vm+ Vm = 2Vm} which have the same polarity with each other. As a
result, the signal shifted upwards. The peak to peak amplitude of the
input signal is 2Vm, similarly the peak to peak amplitude of the output
signal is also 2Vm. Therefore, the total swing of the output is same as the
total swing of the input.
 Applying KVL: The algebraic sum of the voltage rises and drops in a
closed loop is equal to zero
Vi +Vo – Vc = 0
Vo = Vc – Vi
0 = Vc – Vi
Vc = Vi (the capacitor charges upto a maximum Vi)
Diode reverse biased Applying KVL: (taking note that C has a full charge =
Vi)
Vi + Vc – Vo =0
Vo = Vi + Vc
But Vc = Vi from the diode conducting phase above
Hence: Vo = 2Vi
The average voltage or the DC level has been shifted from 0 to Vm
Biased clampers
Sometimes an additional shift of DC level is needed. In such cases,
biased clampers are used. The working principle of the biased clampers is
almost similar to the unbiased clampers. The only difference is an extra
element called DC battery is introduced in biased clampers.
Positive clamper with positive bias
 If positive biasing is applied to the clamper then it is said to be a
positive clamper with positive bias. The positive clamper with
positive bias is made up of an AC voltage source, capacitor, diode,
resistor, and dc battery.
Positive clamper with positive bias
Operation of Positive clamper with positive bias
 During the positive half cycle, the battery voltage forward biases the diode
when the input supply voltage is less than the battery voltage. This current
or voltage will flows to the capacitor and charges it.
 When the input supply voltage becomes greater than the battery voltage
then the diode stops allowing electric current through it because the diode
becomes reverse biased.
 During the negative half cycle, the diode is forward biased by both
input supply voltage and battery voltage. So the diode allows electric
current. This current will flows to the capacitor and charges it.
Positive clamper with negative bias
Operation of Positive clamper with negative bias
 During the negative half cycle, the battery voltage reverse biases
the diode when the input supply voltage is less than the battery
voltage. As a result, the signal appears at the output.
 When the input supply voltage becomes greater than the battery
voltage, the diode is forward biased by the input supply voltage and
hence allows electric current through it. This current will flows to
the capacitor and charges it.
 During the positive half cycle, the diode is reverse biased by both
input supply voltage and the battery voltage. As a result, the signal
appears at the output. The signal appeared at the output is equal to
the sum of the input voltage and capacitor voltage.
Regulated power supply
This is an embedded circuit which converts unregulated AC to a
constant DC even if the input changes.
A Regulated Power Supply Rectifier is made up of 4 blocks
Step-down transformer
Rectifier
DC filter
Regulator
Principle of operation
Step-down transformer
 The transformer steps down the voltage to a favorable AC voltage
value .
 For this to happen the turns on the secondary coil have to be
considerably less than those in the primary side of transformer
Rectification
 Here a Full wave bridge rectifier is employed to convert the stepped-
down AC voltage into a DC voltage
 The voltage at this point becomes unidirectional.
 A Half wave rectifier could be used but its efficiency is half that of the
full wave rectifier , so for optimum output the full wave bridge
rectifier becomes the first choice.
Dc filtration
 Though the voltage appearing in the prior stage is unidirectional, it has got
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a high ripple content.
So to solve this, a DC filter is needed.
In our illustration above , a capacitor filter is used .
Capacitor charges as instantaneous voltage rises but discharges
exponentially through the load as soon as the voltage value starts to
reduce .
The result would be an almost constant DC value.
However there are various methods of executing the same task for
example the use of LC filter or a Choke input filter.
This process significantly reduces the ripple content of the wave.
Regulation
 Variation of the output voltage after filtration may originate from change
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of input , temperature changes, change of load current .
This is solved by employing a regulator.
In our illustration an IC 7805 is used but again there are other options
depending on the application for example Zener diode operated in the
Zener region or a Transistor series regulator.
The regulator maintains a constant output by dissipating heat when the
regulator input voltage surges.
Meaning the difference in input and output power of the regulator is lost
as thermal energy to be absorbed by the heatsink.
Regulator keeps the output voltage constant even if the input voltage
changes.
ZENER DIODE REGULATOR
 A Zener diode is used for regulating output the voltage
 The Zener diode is a specifically designed diode which
has the ability to maintain constant voltage across the
load
 Therefore it can be used to provide constant voltage
across the load.
 For the Zener diode to do the regulation, the input
voltage must be equal or greater than the reverse
breakdown voltage of the diode.
 Zener diode characteristic curve is shown in the next
slide
ZENER DIODE CHARACTERISTICS
 The Zener diode regulator is arranged as shown below
 Zener diode regulator can operate when Vin is changed or when RL
is changed.
WHEN Vin changes
 When Vin increases;
 Is increases, Iz decreases and IL remains constant
 Increase of Is cause voltage drop across Rs to increase thereby Vo is
kept constant.
 When Vin decreases;
 Is decreases, Iz decreases, IL remains constant.
 Vs will decrease and Vo is kept constant
When RL changes
 When RL increases;
 IL decreases, Iz increases but Is and Rs remains constant, Vs is kept
constant.
 Vo will be kept constant.
 When RL decreases;
 IL increases, Iz decreases but Is and Rs remains constant .
 Vo is kept constant.
TRANSISTOR SERIES REGULATOR
 As shown in the figure, a transistor series voltage regulator
consists of the following components. Transistor is connected in
series with RL.
 The transistor behaves like a variable resistor.
 Its value is determined by the input base current, Ib.
 Transistor (Q1) – It helps to modify the resistance of the circuit to maintain
voltage constant. Its terminals are Base, emitter and collector. The Zener
diode is connected to the base of the transistor, and input is given at the
collector side. The load is connected to the emitter. Let VBE be the baseemitter voltage.
 Zener Diode – The Zener diode as shown in the circuit diagram, is connected
to the base of the transistor. The Zener diode is used to set the fixed reference
voltage to the transistor base. The voltage across Zener diode Vz always
remains constant irrespective of change in input voltage.
 Series Resistance Rs – Series resistance RS is used to limit the current
through Zener diode.
 Load Resistance RL – It is the resistance of the load connected at the output
terminals.
 Transistor series regulator can operate when Vin is changed or when RL is
changed.
 Assume that the input voltage given at the terminals is 12 V. Which is the
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unregulated DC supply voltage given at the input terminals. Assume that the
breakdown voltage of the Zener diode is 9 V. This means that, Zener diode starts
conducting at 9V. Since the Zener diode is connected to the base of the transistor,
9 V becomes the reference voltage to the transistor base, which is a fixed value.
The voltage across the load, i.e. the output voltage is the voltage difference between
Zener diode voltage and the voltage across base-emitter. That is it can be given as
V0 = VZ – VBE
The voltage across base-emitter is conducting voltage of the transistor whose value
is 0.7V. As the input voltage is 12 V, hence the output voltage becomes 9 – 0.7 =
8.3 V as per the above equation.
Now if there is an increase in input voltage, let us say 12.5 V, then the voltage
across the load also increases initially. It increases to 8.7 V. But the Zener diode
maintains the voltage constant at 9 V.
Therefore the voltage of the transistor becomes less than 0.7 V. For this to happen
the resistance across collector-emitter increases. (This is the property of transistor,
transfer resistance). Hence now the output voltage maintains constant at 8.3 V.
 Now let us consider the case for a decrease in input voltage. A
decrease in input voltage will decrease the load voltage initially. But
again the load voltage has to be maintained constant. This time, the
resistance across collector-emitter decreases, which increases the
base-emitter voltage. It can be noted that the transistor collectoremitter
 Resistance changes as per the change in input voltage. This happens
due to the transistor principle and fixed voltage provided by the
Zener diode.
 In both the cases with a change in input voltage, the load voltage
remains constant. Hence it can be seen that with a change in input
voltage, the output voltage remains constant. That is how a transistor
series voltage regulator acts as a regulating element
OP AMP SERIES REGULATOR
 The arrangement of the regulator is shown below
 The amplifier is connected in a closed loop configuration with negative
feedback.
 This means that V+ and V- will be approximately equal.
 When Vin increases, initially Vo will also increase, V- will also increase.
 But this increase in V- will cause a decrease in Vo’ and Vo will eventually
decrease.
 When Vin decrease, initially Vo will also decrease , V- will also decrease.
 But this decrease in V- will cause an increase in Vo’ and Vo will eventually
increase.
IC VOLTAGE REGULATORS
 A voltage regulator is an integrated circuit (IC) that provides a constant
fixed output voltage regardless of a change in the load or input voltage.
 It can do this many ways depending on the topology of the circuit
within, but for the purpose of keeping this project basic, we will mainly
focus on the linear regulator.
 A linear voltage regulator works by automatically adjusting the
resistance via a feedback loop, accounting for changes in both load and
input, all while keeping the output voltage constant.
TYPES OF IC REGULATORS
78xx SERIES
II. 79xx SERIES
III. LM 317
IV. LM 377
I.
78xx SERIES
 For many years the 7800 series linear voltage regulators, including the
more popular versions of this series like the 7805, 7812, etc, were the
most popular voltage regulator chips available and they were used in
many electronic circuits, large and small.
 The 7800 series voltage regulators were very easy to use, they were cheap
to buy, and they provided excellent performance.
 There are common configurations for 78xx ICs, including 7805 (5 V),
7806 (6 V), 7808 (8 V), 7809 (9 V), 7810 (10 V), 7812 (12 V), 7815 (15 V),
7818 (18 V), and 7824 (24 V) versions.
79xx series
 IC 79xx is a three-pin negative voltage controller IC.
 It is a small integrated circuit used in a circuit to supply a constant
negative input voltage.
LM 317
 The LM317 device is an adjustable three-terminal positive-voltage
regulator capable of supplying more than 1.5 A over an output-voltage
range of 1.25 V to 37 V.
 It requires only two external resistors to set the output voltage
LM 377
 is an adjustable 3−terminal negative voltage regulator capable of
supplying in excess of 1.5 A over an output voltage range of −1.2 V to −
37 V.
VARIABLE OUTPUT VOLTAGES POWER SUPPLIES
 Variable output voltage power supply is one which includes some
means for the user to easily adjust the output voltage.
 The power supply output voltage can be changed by either changing the
scaling factor of the feedback voltage, injecting a trimming signal into
the feedback node, or changing the reference voltage.
NB: We are using the LM317T in our diagram and for illustrations but
there are other devices that can used.
 The voltage across the feedback resistor R1 is a constant 1.25V
reference voltage, Vref produced between the “output” and
“adjustment” terminal.
SWITCHED MODE POWER SUPPLIES
 Is an electronic power supply that integrates a switching regulator for efficient
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electrical power conversion.
Unlike a linear power supply, the pass transistor of a switching-mode supply
continually switches between low-dissipation, full-on and full-off states, and
spends very little time in the high dissipation transitions, which minimizes wasted
energy.
A hypothetical ideal switched-mode power supply dissipates no power.
Voltage regulation is achieved by varying the ratio of on-to-off time (also known as
duty cycles).
The switched-mode power supply's higher electrical efficiency is an important
advantage.
Switched-mode power supplies can also be substantially smaller and lighter than a
linear supply because the transformer can be much smaller.
This is because it operates at a high switching frequency which ranges from several
hundred kHz to several MHz in contrast to the 50 or 60 Hz mains frequency.
 Despite the reduced transformer size, the power supply topology and
the requirement for electromagnetic interference (EMI) suppression in
commercial designs result in a usually much greater component count
and corresponding circuit complexity.
 Switching regulators are used as replacements for linear regulators
when higher efficiency, smaller size or lighter weight is required.
 They are, however, more complicated; switching currents can cause
electrical noise problems if not carefully suppressed, and simple
designs may have a poor power factor.