Clamper circuits
A clamper circuit is so named because it clamps the ac voltage to a dc reference level.
More specifically, it establishes a dc voltage reference level from which one extremity or peak of an ac signal swings. This circuit is also called a dc restorer or a dc inserter circuit.
A clamping circuit may be thought of as an RC coupling circuit in which the time constant is switched between a high and low value.
The ac signal may be a sine wave or any pulse voltage waveshape. Ideally, the circuit should change only the dc reference level and not the ac voltage waveshape.
Figure 5-1 (a) illustrates a negative-voltage clamper circuit.
Figure 5-1 Negative-Voltage Clamper Using Ideal Diode
The output voltage is negative with reference to zero, from which voltage the positive peaks originate.
This output-voltage waveform is illustrated in Fig. 5-1 (d).
In a clamper circuit the voltage source is in series with a charged capacitor (acting as a voltage source).
The output voltage is the algebraic sum of these two voltages at any instant in time.
5.1 NEGATIVE-VOLTAGE CLAMPER CIRCUIT—IDEAL
Figure 5-1 (a) is a schematic of a negative-voltage clamper circuit. The resultant output voltage is illustrated in Fig. 5-1 (d).
The analysis of this clamping action presupposes that no current is drawn from the output and that the diode employed is ideal.
At h time, the input is +5 V with reference to ground. Diode D, acting as an ideal switch, is forward biased by this input.
Hence, capacitor C charges to 5 V, the polarity of which is indicated in Fig. 5-1 (b).
At t2 time the input is +3 V. The bias of the diode at t2 time is the algebraic sum of the input voltage and the voltage across the capacitor.
Hence, diode D (acting as an open switch)