Clampers

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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.
• Clamping networks have a capacitor connected
  directly from input to output with a resistive
  element in parallel with the output signal. The
  diode is also in parallel with the output signal
  but may or may not have a series dc supply as an
  added element.

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• There is a sequence of steps that can be applied
• Examine the response of the portion of the input
  signal that will forward bias the diode. If the
  diode is reverse bias, skip the analysis for that
  interval time, and start analysis for the next
  interval time.
• During the period that the diode is in the on
  state, assume that the capacitor will charge up
  instantaneously to a voltage level determined by
  the surrounding network.
• Assume that during the period when the diode is
  in the off state the capacitor holds on to its
  established voltage level.
• Maintain awareness of the location and defined
  polarity for vo to ensure that the proper levels
  are obtained.
• Check that the total swing of the output matches
  that of the input.

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Analysis of the previous network

• Diode on and
• vo 0
• Diode off and vo-2V

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• Magnitude of R and C must be appropriate to
  ensure ?RC where the time constant is large
  enough and capacitor may not discharge during the
  time interval while diode is not conducting
• We will assume for practical purposes the
  capacitor will fully charge or discharge in 5
  time constant.

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Example

• Determine Vo for the below network.

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Solution

• f1000Hz, so a period of 1ms or interval 0.5ms
  between each level.
• the diode will start to conduct (t1 till t2), and
  then V05V.
• from the Kirchoffs Law
• VC20V5V25V
• in the next positive half cycle, we will find
  V035V(outside loop)
• Time constant, ? RC 10ms, total discharge time
  50ms where is large enough before the capacitor
  is discharged during interval t2 till t3

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Output waveform
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Example

• Repeat previous example using a silicon diode
  with V? 0.7 V. Solution

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Solution

• Diode is on, then vo4.3 V and Vc 24.3 V
• Diode is off, then vo34.3 V

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• The input signal can be any type of waveform
• - sine, square, triangle wave, etc.
• .

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VOLTAGE-MULTIPLIER CIRCUITS

• Voltage-multiplier circuits are employed to
  maintain a relatively low transformer peak
  voltage while stepping up the peak output voltage
  to two, three, four, or many times the peak
  rectified voltage.

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Voltage-Doubler
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• ve half cycle -ve half cycle

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How does a Voltage-Doubler work

• During the positive voltage half-cycle diode D1
  conducts (and diode D2 is cut off), charging
  capacitor C1 up to the peak rectified voltage
  (Vm) with the polarity shown in figure.
• During the negative half-cycle D1 is cut off and
  diode D2 conducts charging capacitor to 2 Vm

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Voltage Doubler
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ve half cycle -ve half cycle
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Voltage Tripler and Quadrupler