Both of these statements are illustrated in the figure below. (The clamper has changed the dc average of the input waveform from 0 V to +5 V without altering its shape.)
A clamper with its input and (ideal) output waveforms.
There are two basic types of clampers:
- A positive clamper shifts its input waveform in a positive direction, so that it lies above a dc reference voltage. For example, the positive clamper in the figure above shifts the input waveform so that it lies above 0 V (the dc reference voltage).
- A negative clamper shifts its input waveform in a negative direction, so that it lies below a dc reference voltage.
The direction of the diode determines whether the circuit is a positive or negative clamper.
Clamper operation is based on the concept of switching time constants. The capacitor charges through the diode and discharges through the load. As a result, the circuit has two time constants:
- For the charge cycle,
and 
(where 
is the resistance of the diode) - For the discharge cycle,
and 
(where 
is the resistance of the load)
Since is normally much greater than 
, the capacitor charges much more quickly than it discharges.
is normally much greater than , the capacitor charges much more quickly than it discharges.A biased clamper allows a waveform to be shifted above (or below) a dc reference other than 0 V.
Several biased clampers.
The circuit in the figure (a) uses a dc supply voltage (V) and a potentiometer to set the potential at the cathode of 
. By varying the setting of 
, the dc reference voltage for the circuit can be varied between approximately 0 V and the value of the dc supply voltage.
. By varying the setting of , the dc reference voltage for the circuit can be varied between approximately 0 V and the value of the dc supply voltage.The zener clamper in figure 4(b) uses a zener diode to set the dc reference voltage for the circuit. The dc reference voltage for this circuit is approximately equal to 
.
Summary of Clamping Circuits
(i)Waveform remains the same but its level is shifted either upward or downward,.Summary of Clamping Circuits
(ii)The clamping circuit does not change the peak-to-peak or rms value of the wave form. Thus referring to fig 21.40, the input waveform and output waveform have the same peak-to-peak value that is, 2Vmax. If the input voltage and clamped output are measured by an ac voltmeter, the readings will be the same.
(iii)The clamping circuit, of course alters the peak and average values of the wave form. In figure shown above the input waveform has a peak value of Vmax and average value over a complete cycle is zero. The clamped output varies from 2 Vmax and 0 (or 0 and -2Vmax). Thus ths peak value of the clamped output is 2Vmax and average value is Vmax.
To further understand clipping circuits, here are the solutions to some problems in Electronic Devices and Circuit Theory (10th edition) by Boylestad and Nashelsky:
Problem 37 page 128
Sources:
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