The Novice Writer: CLAMPERS

Before starting with clampers, we must know the basic working of the diode:
(Refer this link http://wp.me/p6vMKz-4)

Clampers : –

Clamping circuits, also known as dc restorers or clamped capacitors, shift an input signal by an amount defined by an independent voltage source.
The entire input reaches the output in a clamping circuit – it just shifts the waveform so that the maximum (or minimum) value of the input is “clamped” to the independent source.
Additional shifts can also be obtained by introducing a DC supply to the basic clamper circuit.
In this circuits we need to take care of the time constant as the rate of charging and discharging of the capacitor will change the output waveform.
So, we need to choose the values of resistor and capacitor according to the equation ” T=RC “. – where T-time constant, R-value of resistor and C-value of the capacitor. We must keep this value sufficiently large to ensure that the voltage across capacitor does not discharge significantly during the interval diode is not conducting.

∗*We will always start our analysis from the point the diode is forward biased because, if we start our analysis from the time interval the diode is reversed biased we can not predict the voltage across the capacitor for that time interval and hence we can not do further analysis. And capacitor might not always be charge up to input voltage.

Negative Clamper : –

1.)Unbiased :

In this case, we do not have any DC supply connected to the circuit.
When the input waveform is a positive half cycle the diode in this case ( negative clamper) becomes forward biased and thus acts as a short circuit.
This leads to the charging of the capacitor to a value Vm volts(which can be calculated using KVL equation).
We get Vm=Vi(input voltage) and Vo(output voltage)=0.(as diode acts as a short circuit).
For the half-cycle, the diode is reversed biased and hence acts as an open circuit.(polarities of capacitor does not change)
Now we again apply KVL to the present state of the circuit and get the value of Vo. Which comes out to be Vo=-(Vm+Vi)=-2Vi.
Hence, the whole input waveform is shifted down by Vi volts.

2.)Biased :

Considering the first circuit in the above image.
1. When Ei > 0; i.e. diode is forward biased;
  - We get Eo=E;
  - And applying KVL to the mesh we get,
  - Em =Ei – E.
2. When Ei<0; i.e. diode is reversed biased;
  - We Apply KVL to the present state of the circuit and get ,
  - Eo = – Ei – Em = – Ei – Ei + E = -2Ei + E.
Similarly, we can deduce the waveform for the second circuit in the above image.

Positive Clamper : –

1.)Unbiased :

In this case, we will start our analysis by keeping the input waveform in the negative half cycle. As our diode should be forward biased when we start our analysis.
Just like negative clamper circuit this circuit also does the same thing but the only difference being it shifts the waveform upwards.

2.)Biased :

Considering the first circuit in the above image.
1. When Ei < 0; i.e. the diode is forward biased;
  - We get Eo = E
  - And on applying KVL to the circuit; We get,
  - Em = Ei + E
2. When Ei >0; i.e the diode is reversed biased;
  - on applying KVL we get,
  - Eo = Ei + Em = Ei + Ei + E = 2Ei + E;
3. Hence, the circuit will move the input waveform upward by E volts.
Similarly, we can deduce the waveform for the second circuit.