The primary function of a clamper circuit is

• A Clamper Circuit is a circuit that adds a DC level to an AC signal.
• The shape of the output waveform does not change in Clamper circuits. 
• Since the clamper circuit adjusts the DC level of the waveform as shown in the following figure, it is called DC restorer.

Clamping circuit:

• For proper working of a clamper, the time constant of the circuit should be large because the voltage across the capacitor C does not change significantly during the time interval the diode is non-conducting
• The circuit time constant (t = RC) should be at least ten times the time period of the input signal voltage