Input Output Waveform of H.W rectifier

JUNCTION DIODE AS RECTIFIER:

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An electronic device which converts A.C. power into DC. power is called a rectifier.

The junction diode offers a low resistance path, when forward biased and a high resistance path when reverse biased. This feature of the junction diode enables it to be used as a rectifier.

The two half cycles of alternating input e.m.f. provide opposite kinds of bias to the junction diode.

If the junction diode gets forward biased during first half cycle, it will get reverse biased during the second half cycle and vice-versa.

 

In other words, when an alternating e.m.f. signal is applied across a junction diode, it will conduct only during those alternate half cycles, which bias it in forward direction.

7.1. HALF WAVE RECTIFIER:

  • A rectifier, which rectifies only one half of each A.C. input supply cycle, is called a half wave rectifier.
  • Principle: It is based on the principle that junction diode offers low resistancepath, when forward biased and high resistance when reverse biased. When A.C. input is applied to a junction diode it gets forward biased during one half cycle and reverse biased during the next opposite half cycle. Thus output is obtained during alternate half cycles of the A.C. input.
  • Arrangement:  The A.C. supply is fed across the primary coil P of a step-down

Transformer. The secondary coil S of the transformer is connected to the junction diode and a load resistance RL shown in Fig. 1.11. The output D.C. voltage is obtained across the load resistance RL.

  • Theory:
  • Suppose that during the first half of the input cycle, the junction diode gets forward biased. The conventional current will flow in the direction of the arrow heads.
  • The upper end of RL will be at positive potential w.r.t. the lower end. The magnitude of output across RL during first half cycle at any time will be proportional to the magnitude of current through it.
  • Hence, during the first half of the input cycle, when junction diode conducts, output across RL vary in accordance with A.C. input

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Half wave Rectifier                                       Input Output Waveform of H.rectifier

Fig 1.10 HW Rectifier with its waveform

  • During the second half cycle, junction diode will get reverse biased and hence no output will be obtained across RL·
  • Critically, a small current will flow due to minority carriers and a negligible output will be obtained during this half cycle also.
  • During the next half cycle, output is again obtained as the junction diode gets forward biased.
  • Thus a half wave rectifier gives discontinuous and pulsating output across the load resistance as shown in Fig. Hence half wave rectification involves a lot of wastage of energy and hence it is not preferred.

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