CLAMPERS
Clampers are those circuits those allow us to transfer the dc level up or down based on the
requirement of the user.
They are also called as DC voltage restorers. For this circuit we need a simple resistor, capacitor
and load (resistor). It simply works on the fact that the diode conducts current only in one
direction.
There two types of clampers:
1. +ve unbiased clamper
2. –ve unbiased clamper
+ve unbiased clamper: consider the circuit given below
Vin
Vout (load)
In the above circuit, Vin is the input voltage and Vout is the voltage obtained at the load.
During the first +ve cycle, the diode is in reverse bias and it acts like an open circuit. Thus it
doesn’t charge the capacitor. During the first –ve cycle, the diode is in forward bias and the circuit
is complete. Thus charging the capacitor to Vin with a polarity such that –ve side is near the source
and +ve side near the diode.
-
+
Vout
Vin
So during the next +ve cycle, a total of 2Vin falls on the load mainly due to capacitor which was
charged to Vin in the previous –ve cycle and the source which supplies Vin to the load. Thus we
have shifted the dc level. During the next negative cycle, the diode is forward biased hence the
capacitor is charged again to Vin and since the diode acts like a short, the voltage across the load
will fall to zero. The waveform would be something of this sort
2Vin
Vin
T
-ve unbiased clamper: Consider the circuit given below
Vin
Vout (load)
During the first +ve cycle, the diode is forward biased and hence it acts like a short. The
potential across the load is zero. Here is when the capacitor charges to the Vin. The polarity of
the capacitor is shown in the given diagram.
Vout
Vin
During the first –ve cycle, the diode is in reverse bias and it acts like an open circuit. Hence a total
of -2Vin will fall on the load due to the capacitor and the source.
After the completion of the first –ve cycle, the capacitor is completely discharged. With the
beginning of the second +ve cycle, the diode is again in forward bias (it acts like a short). Thus the
potential across the load falls to zero. The capacitor charges again to Vin with the same polarity as
shown above. The cycle continues as long the source is switched on.
The waveform will be something like this.
T
2Vin