Rectifier Circuits

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EST 130, Rectifier Circuits

• CEC

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Contents

• Regulated Power Supply.
• Rectifier Circuits.
• Half Wave Rectifier.
• Centre Tapped Full Wave Rectifier.
• Bridge Rectifier.
• Rectifier Parameters.
• Filtering and Regulation.

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Regulated Power Supply

• To convert power line ac voltage to the required
  dc value.
• Diodes are unidirectional devices, allows current
  to flow through them in only one direction.
• Rectifier diodes convert bidirectional ac line
  voltage to unidirectional pulsating dc voltage.
• Mostly silicon diodes used.

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Block Diagram of Regulated Power Supply

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Step Down Transformer

Primary
Secondary
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Use of Diodes

• Unidirectional property conducts when forward
  biased, off when reverse biased.
• Silicon diodes used reverse current small of
  the order of nanoamperes.
• Cut in voltage of 0.6 V for silicon diodes.
• Germanium diodes cut in voltage lt 0.3 V, but not
  used for rectification larger reverse currents
  of the order of microamperes.

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Unidirectional Property of Diodes

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Types of Rectifiers

• Half Wave Rectifiers only one diode.
• Centre Tapped Full Wave Rectifiers two diodes.
• Bridge Rectifier four diodes in bridge
  configuration.

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Half Wave Rectifier

D1 Forward Biased during positive half cycle
Only Positive Half Cycle
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Half Wave Rectifier

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Capacitor Filter

Electrolytic Capacitors as filters
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Half Wave Rectifier

Diode Reversed
Only Negative Half Cycle
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Centre Tapped Full Wave Rectifier
Cathodes connected together
Top of the Secondary

IL
Bottom of the Secondary
Centre Tap
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Centre Tapped Full Wave Rectifier

• When the top of the secondary is positive, D1 is
  forward-biased, causing current to flow in the
  load, RL, D2 is off, being reverse-biased.
• When the top of the secondary is negative, D2 is
  forward-biased, causing current to flow in the
  load, RL, D1 is off, being reverse-biased.
• Direction of current through RL the same for both
  half-cycles of secondary voltage.

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Full Wave Rectifier

IL
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IL
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Full Wave Rectifier

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Capacitor Filter

Time Constant RLC increased when C is increased,
C discharges more slowly, ripple reduces.
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Centre Tapped Full Wave Rectifier

Centre Tap
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Full Wave Bridge Rectifier
D2, D3 Forward Biased during positive half cycle.

IL
D1, D4 Forward Biased during negative half cycle.
Current Flow through RL in the same direction.
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Bridge Rectifier

D2, D3 Forward Biased
IL
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Bridge Rectifier
D1, D4 Forward Biased

IL
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Bridge Rectifier
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Bridge Rectifier

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Bridge Rectifier Modules

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Frequency of Output Waveform

• One cycle includes the variations between two
  successive points having the same value and
  varying in the same direction.
• Half Wave Rectifier fout fin
• Full Wave Rectifier fout 2fin
• Bridge Rectifier fout 2fin
• where fin frequency of the input waveform.

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Time Constant RLC increased when C is increased,
C discharges more slowly, ripple reduces.
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Comparison
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Filters and Regulators

• Filters smoothen pulsating DC.
• Can be Capacitive Filter, Inductive Filter and
  CRC Filter.
• Use of Zener diode regulators, Transistor based
  voltage regulators or IC regulators.
• Zener diodes used for voltage regulation.
• IC Regulators positive (IC 78xx) and negative
  (IC 79xx) voltage regulators.

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Zener Diode Regulator

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Transistor Voltage Regulator

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Voltage Regulator ICs

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IC Regulated Power Supply

Step Down Transformer
Voltage Regulator
Output
Rectifier and Filter
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Thank You