Clamping Diode

Introduction to Clamping Diode:

Clamper diodes ads dc level to an ac voltage.  Campers are sometime known as dc restores.

There are two main types of Clamping Diodes:
  • Positive Clamping Diode
  • Negative Clamping Diode

Explanation and Operation of Clamping Diode:

we can see in below diagram (a)  clamping circuit is given, where a positive dc level in the output waveform.  The operation of this circuit can be seen by considering the first negative half-cycle of the input voltage.  When the input voltage initially goes negative, the diode is forward biased, allowing the capacitor to charge to near the peak of the input (Vp (in) -0.7 V ), just after the negative peak, the diode is reverse biased.  This is because the cathode is held near Vp(in) – 0.7 V by the charge on the capacitor.  The capacitor can only discharge through the high resistance of RL.  So, from the peak of one negative half cycle to the next, the capacitor discharges very  little.  The amount that is discharged, of course, depends on the value of RL.  For good clamping action, the RC time constant should be at least ten times the period of the input frequency.

Positive Clamper:

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(a) Positive Clamper Operation

The net effect of the clamping action is that the capacitor retains a charge approximately equal to the peak value of the input less the diode drop.  The capacitor voltage acts essentially as a battery in series with the input voltage.  The dc voltage of the capacitor adds to the input voltage by superposition.

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(b) Clamping Circuit

Negative Clamper:

If the diode is turned around , negative dc voltage is added to the input voltage to produce the output voltage as shown in diagram (c)

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(c) Negative Clamping Circuit

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