Clipper
The clipper circuits are basically used to clip the portion of any input signal without changing or distorting the remaining part of the input waveform.
Positive Clipper Circuits
As we see from the above figure the diode is forward biased during the positive half cycle of the input sinusoidal waveform. But the PN junction diode starts conducting after it crosses the cut off voltage. As we already know it should be greater than 0.7volts and 0.3 volts for Si and Ge diodes respectively.
The diode conducts for a complete positive half cycle and maintains the voltage across itself until the sinusoidal waveform falls below the value. As the diode conducts the output here is clipped.
For the negative half cycle the diode becomes reversed biased and a reverse current of very small amount flows across the diode. Hence, we can say that there is no voltage change in this case due to no flow of current. Therefore, the output is unaltered in this and is equal to the input applied voltage.
Negative Clipper Circuits
As we see from the above figure the diode is reverse biased during the positive half cycle of the input sinusoidal waveform. But the PN junction diode acts as an open circuit. The output in this case is equal to the input applied voltage.
For the negative half cycle the diode becomes forward biased and starts to conduct. Hence, we can say that there is no voltage at the output due to no flow of current.
Clipping of Both Half Cycles
Now if we connect two diodes both reverse to each other in parallel then the output is clipped in both the half cycles. The diode D1 clips the positive half cycle the same as it does in the positive clipper. The diode D2 clips the negative half cycle the same as it does in the negative clipper.
They are used as voltage limiter circuits.
Clampers
The clamper circuit shifts the waveform to a different dc level without changing the applied signal level. The circuit consists of a capacitor, a diode and a resistor.
This is also called a level shifter because we can shift the level of the signal by using a clamping circuit.
As the circuit consists of a capacitor connected parallel across the load. The capacitor circuit depends upon the time constant of the capacitor. Then the capacitor charges when the diode is forward biased and starts conducting. The capacitor should not discharge drastically when the diode is reverse biased. There are two types of clamper circuits i.e positive and negative clampers.
Negative Clamper
The diode conducts in the positive half cycle as it is forward biased and the capacitor charges. In the negative half cycle the output is the sum of input voltage and voltage stored across the capacitor.
Positive Clamper
In this the diode is connected in the opposite direction than in the negative clamper. In this case the output voltage is the sum of input voltage and capacitor voltage. The diode conducts in the negative half cycle and charges the capacitor. Hence, the voltage is clamped in a positive direction.
Applications
- In sonar, radar systems and also in test equipment.
- For the protection of the amplifiers from large signals.
- It helps in removing distortions.
- The overdrive recovery time is improved.
- They are used as voltage multipliers.
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