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MHT-CET : Physics Entrance Exam

MHT - CET : Physics - Thermionic Emission Page 2

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4

Uses of Diode as Half Wave and Full Wave Rectifiers:

 



A rectifier is a device which converts a.c. voltage into
d.c. voltage.

Diode as a half wave rectifier:

Circuit diagram

Circuit of a half-wave rectifier using a vacuum diode


Working

  • During positive half cycle, the plate is at positive potential with respect to the cathode. Hence, the diode becomes conducting element and current flows through resistance RL.
  • During negative half cycle, the plate is at negative potential with respect to the cathode. Hence, the diode becomes non-conducting element and no current flows through RL.

The Output Voltage

The output voltage is obtained only during positive half cycle of the input voltage. It is unidirectional and pulsating. The variation of input and output voltage with respect to time is shown below:

The input and output voltage waveforms
for a half wave rectifier



Diodes used as Full Wave Rectifier

Circuit diagram: The circuit of a full-wave rectifier consists of a centre-tapped transformer and two diodes connected as shown in the following diagram:

Circuit of a full wave rectifier using a Vacuum diode



Working:

  • During the positive half cycle of the input voltage, diode D1 is conducting and diode D2 is off. Current flows through RL along the path AD1ORLC.
  • During the negative half cycle of the input voltage D1 is off and D2 is conducting. Current flows through RL along the path AD2ORLC.

Note: During both half cycles of the input voltage, the direction of current flow through RL is same.

The Output Voltage

The output voltage is available across RL during both half cycles of the input voltage. It is unidirectional and pulsating.

The input and output voltage waveforms
in a full wave rectifier


The input and output voltage waveforms in a full wave rectifier.

 

 

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