1. Clippers and Clampers-3
Thought of the Day
To be conscious that
you are ignorant
is a great step to
Knowledge.
-- Benjamin Disraeli.
बुधवार, 21 नवम्बर 2018
Clippers and Clampers-3

2. Clippers and Clampers - 3
D.C. Kulshreshtha
बुधवार, 21 नवम्बर 2018
Clippers and Clampers-3

3. Clippers and Clampers-3
An Exercise
The ac supply in your home has one live wire (red coloured) and the other neutral wire (black coloured).
The voltage of the live wire with respect to neutral wire swings between the lower and upper voltage-levels, 50 times in a second.
What are these two levels ?
Ans V and V.
Can you suggest some simple scheme to make the ac voltage (of live wire) swing between +511 V and -111 V ? ( Hint : You can use a battery and a transformer.)
बुधवार, 21 नवम्बर 2018
Clippers and Clampers-3

4. Clippers and Clampers-3
The circuit
Now, draw the output voltage waveshape.
बुधवार, 21 नवम्बर 2018
Clippers and Clampers-3

5. Clampers (Electronic Circuits)
Also called DC Restorers.
It clamps (or holds, or ties) either the positive or the negative peak of a signal to a definite level.
The circuit has a capacitor, a diode, and a resistor.
In addition, it may have a dc supply to introduce additional shift.
Time constant τ = RC is made much larger than T (time period) of the signal.
The capacitor does not discharge when diode is not conducting.
बुधवार, 21 नवम्बर 2018
Clippers and Clampers-3

6. Clippers and Clampers-3
Positive Clamper
(a) The input.
(b) The circuit.
On first negative cycle, the diode turns ON. The capacitor starts charging. At negative peak, the circuit is as shown in (c). The capacitor charges to Vm.
बुधवार, 21 नवम्बर 2018
Clippers and Clampers-3

7. Clippers and Clampers-3
Slightly beyond negative peak, the diode turns OFF. Capacitor does not discharge much because of high RC. At positive peak, the circuit is as shown in (d). The net output is shown in (e).
बुधवार, 21 नवम्बर 2018
Clippers and Clampers-3

8. Clippers and Clampers-3
(e) The output.
The charged capacitor acts like a battery of Vm. This is the dc voltage that is added to the signal, as seen in (e). The output sits on 0 V level. The output is shifted in positive direction.
बुधवार, 21 नवम्बर 2018
Clippers and Clampers-3

9. Clippers and Clampers-3
Negative Clamper
(a) The circuit.
(b) The output.
The diode is turned around. The capacitor voltage reverses, and the circuit becomes negative clamper. It is clamped to zero-volt level, but always remaining below 0 V.
Memory Aid : The diode points in the direction of shift.
बुधवार, 21 नवम्बर 2018
Clippers and Clampers-3

10. Clippers and Clampers-3
Note :
The total swing of the output is the same as that of the input.
A clamper can also have an added dc voltage. It is then called biased clamper.
Start the analysis of the circuit for that part of input, for which diode is ON.
Assume that the capacitor charges to voltage level decided by the circuit.
Assume that when diode is OFF, the capacitor does not discharge.
बुधवार, 21 नवम्बर 2018
Clippers and Clampers-3

11. Clippers and Clampers-3
Example 1
Determine the output for the input of 1 kHz shown.
(b) The circuit.
(a) The input.
Is it a positive or negative clamper ?
Ans. : Biased positive clamper.
बुधवार, 21 नवम्बर 2018
Clippers and Clampers-3

12. Clippers and Clampers-3
Solution :
The time constant of the circuit,
The time period of the input signal,
Thus, the capacitor holds the charge when the diode is OFF.
We begin analysis with the period from T/2 to T; the diode is ON.
The circuit is as shown in (a)
बुधवार, 21 नवम्बर 2018
Clippers and Clampers-3

13. Clippers and Clampers-3
The output is across R, but it is also across 3-V battery.
Hence, vo = 3 V, during this period.
Applying KVL, VC -3 = 0; VC = 18 V.
For the period from T to 3T/2, the circuit is as shown in (b).
बुधवार, 21 नवम्बर 2018
Clippers and Clampers-3

14. Clippers and Clampers-3
(b)
(c)
Applying KVL, vo = = 23 V.
Thus, the output is as shown in (c).
Note that the output swing is also 20 V.
बुधवार, 21 नवम्बर 2018
Clippers and Clampers-3