Chapter 2: Diode Applications

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Chapter 2 Diode Applications

• -Power supply filters regulators

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Sub-Topic Objectives

• Explain and analyze the operation and
  characteristics of power supply filters and
  regulators
• Explain the purpose of a filter
• Describe the capacitor-input filter
• Define ripple voltage calculate the ripple
  factor
• Discuss surge current voltage regulation

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Power supply filtering

• Filter is a capacitor in a power supply used to
  reduce the variation of the output voltage
  rectifier

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Capacitor-Input Filter
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Ripple Voltage

• Ripple Voltage the small variation (undesirable)
  in
• the capacitor voltage due to the charging
• discharging of the filter capacitor

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Comparison of ripple voltage
Full rectifier easier to filter because of the
shorter time between peaks (smaller ripple)
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Ripple Factor
Ripple Factor (r) indication of filter
effectiveness (the lower
the ripple factor the better filter)
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Example 7
Determine the ripple factor for the filtered
bridge rectifier with a load as indicated in
figure below

Answer 0.079 _at_ 7.9
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Surge Current

• At the instant the switch is closed,
• voltage is connected to the bridge
• and the uncharged capacitor
• appears as a short.
• Produce ISurge through D1 D2
• ISurge could destroy the diodes

• RSurge used to prevent the diodes
• from destroy.
• RSurge lt RL

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IC Regulators

• Combination of capacitor-input filter with
  integrated circuit voltage regulator
• Operation
• the input to the regulator is first filtered
  with a capacitor to reduce the ripple tolt10
• The regulator reduce the ripple to a negligible
  amount (acceptable level)
• 3 terminals input, output and reference

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Percent Regulation

• Line regulation specify how much change occurs in
  the output voltage for a given change in input
  voltage
• Line regulation
• Load regulation specify how much change occurs in
  the output voltage over a certain range of load
  current values.
• Load regulation

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Chapter 2 Diode Applications

• -Clippers Clampers

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Sub-Topic Objectives

• Explain and analyze the operation of diode
  limiting clamping circuits
• Explain the operation of diode limiters
• Determine the output voltage of a biased limiter
• Explain the operation of diodes clampers

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Diode Limiters (Clippers)

• A diode network that have the ability to clip
  (cut short/crop) off a portion on the input
  signal without distorting the remaining part of
  the alternating waveform.
• Used to eliminate amplitude noise or to fabricate
  new waveforms from an existing signal.
• 2 general of clippers
• a) Series clippers
• b) Parallel clippers
• Series Clippers
• Diode is in series with the load.
• Parallel Clippers
• Diode in a branch parallel to the load.

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Simple Series Clipper

• Diodes clip a portion of the AC wave.
• The diode clips any voltage that does not put
  it in forward bias.
• Any type of signals can be applied to a clipper

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Analysis steps for series clipper

• Define the input and output port
• Determine the current flow of the circuit
• Determine the applied voltage (transition
  voltage) that will result in a change of state
  for the diode from the off to on state
• Draw the output waveform directly below the
  applied voltage using the same scales

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Series clipper with dc supply
By adding a DC source to the circuit, the voltage
required to forward bias the diode can be changed.
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Example 8
Determine the output waveform for the network
below
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Simple Parallel Clipper

• By taking the output across the diode, the output
  is now the voltage when the diode is not
  conducting.
• A DC source can also be added to change the
  diodes required forward bias voltage

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Example 9
Determine the Vo and sketch the output waveform
for the below network
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Summary of Series Clippers
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Summary of Parallel Clippers
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Diode Clampers

• A clamper is a network constructed of a diode,
  resistor, and a capacitor that shifts a waveform
  to a different dc level without changing the
  appearance of the applied signal

Positive clamper
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Diode Clampers
Negative clamper
Application The clamping circuit is often used
in TV receivers as a dc
restorer
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Example 10
Determine the output voltage waveform.
Assume that RC is large enough to prevent
significant capacitor discharge
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Summary of Clampers