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5
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Filter Circuits
5
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C
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But the output of a rectifier
circuit contains ripple components in addition to a D
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term
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Ripple components are high
frequency A
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Signals in the D
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These are not desirable, so they must be
filtered
...

Many types of passive filters are in use such as
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5
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1
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c
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c
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c
...

Here Xc (=1/2πfC, the impedance of capacitor) should be smaller than RL
...
If C value is very small, Xc will be large and hence current
flows through RL only and no filtering action takes place
...
When the input voltage 𝑣 = 𝑉𝑚 𝑠𝑖𝑛 𝜔𝑡 is greater than
the capacitor voltage, C gets charged
...
The stored energy in the capacitor maintains the load voltage at a high value for
a long period
...
The waveforms are as shown
in figure 5
...
Capacitor opposes sudden fluctuations in voltage across it
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Fig 5
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3 Rectifier with shunt Capacitor filter

vo

Vm

0

𝜃1 𝜃2

π

2π

3π

ωt

Fig 5
...
, Lecturer, MEA Engineering College>

www
...
org

5
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Filter Circuits

EC04 403 Electronic Circuits

The discharging of the capacitor depends upon the time constant C
...
Hence the smoothness and the
magnitude of output voltage depend upon the value of capacitor C and RL
...
But the maximum value of the capacitor is limited by the current
rating of the diode
...
These types of filters are used in circuits with small load current like transistor radio
receivers, calculators, etc
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Advantages
Disadvantages
 Low cost
 Capacitor draws more current
 Small size and weight
 Good characteristics
 Can be connected for both HW and FW rectifiers
 Improved d
...
output
5
...
Fig 5
...
Here the reactance of the inductor is more for ac components and it offers more opposition to
them
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c
...
Therefore the inductor blocks
a
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components in the output of the rectifier and allows only d
...
component to flow through R L
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5 Filter output waveform

Fig 5
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Therefore filter circuits consisting inductors can only be used together with full wave rectifiers
...
Series inductor filters are used in equipments of high load currents
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 Bulky and large in size
 Note suite for HWR

...
edutalks
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2

5
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4 LC filter
It is a combination of inductor and capacitor filter
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6
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But in case of a capacitor filter it is
reverse that when increasing current the ripple also increases
...
The ripple factor of a chock input filter is given by
𝜸 = 𝟏
...
6 Rectifier with filter
5
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7 output waveform of Rectifier with LC filter

Since the d
...
resistance of the inductor is very low it allows d
...
current to flow easily through it
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c
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c
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The capacitor appears open
for d
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and so all d
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5
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1 Bleeder resistor
For optimum functioning, the inductor requires a minimum current to flow through, at all time
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To keep up the circuit current above this minimum value, a resistor is permanently connected across the
filtering capacitor and is called bleeder resistor
...
It also provides a path for the capacitor to discharge when power supply is
turned off
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5
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8
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It is also called capacitor input filter because the rectifier feeds
directly into the capacitor C1
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c
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c components
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c
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c
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The chock offers very high
reactance to the a
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component
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c
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c
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c
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c
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The ripple factor in a π-section filter is given by 𝛾 = 2 𝑋 𝐶1 𝑋 𝐶2 𝑋 𝐿 𝑅 𝐿
...
edutalks
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3

5
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8 Rectifier with CLC filter

Fig 5
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, Lecturer, MEA Engineering College>

www
...
org

5

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Title: XTECH
Description: Best notes for an Electronic and Telecommunication Engg.

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