Saturday , November 17 2018

# Diode Clampers

A diode clampers adds a DC level to an AC voltage. Sometimes we call clampers as  DC restorers.

“A clamper is a digital circuit that changes DC level signal to the desired DC level.”

In other words, the diode clampers circuit moves the whole signal up or down to set either the positive peak or negative peak of the signal at the desired level. The DC component actually adds or subtracts from the input signal.

# Types Of Clamping Circuits

Diode clampers circuit’s are of three types

• Positive Clamping Circuit
• Negative Clamping Circuit
• Biased Clamping Circuit

## Positive Clamping Circuit

If the circuit pushes the signal upwards then the circuit is a positive clamper. While the signal moves upwards, the negative peak of the signal meets the zero level.

The positive clamper comprises a voltage source Vin, capacitor, diode and load resistor. The diode is connected in parallel with the output load. So the positive clamper passes the input signal to the output load when the diode is reverse biased and blocks the input signal when the diode is forward biased.

### Explanation

During negative half cycle of input AC signal, the diode clampers are forward biased and no signal appears on the output. In forward biased situation, the diode allows electric current through it. This current will flows to the capacitor and charges it to the peak value of input voltage Vin. The capacitor charged in inverse polarity (positive) with the input voltage. As input current or voltage decreases after reaching its maximum value -Vin, the capacitor holds the charge until the diode remains forward biased.

During positive half cycle of input AC signal, the diode clampers are reverse biased and subsequently signal appears on output. In reverse biased condition, the diode does no longer allow electric current through it. So the input current directly flows towards the output.

When the positive half cycle begins, the diode is in non-conducting state and the capacitor is starts discharging. Therefore, the voltage appeared at the output is equal to the sum of the voltage stored in the capacitor (Vc) and the input voltage (Vin) ( Vo = Vin+ V= 2Vin} which have the same polarity with each other. As a result, the signal shifted upwards.

The peak to peak amplitude of the input signal is 2Vin, similarly the peak to peak amplitude of the output signal is also 2Vin. Therefore, the total swing of the output is same as the total swing of the input.

“The basic difference between the clipper and clamper is that the clipper removes the unwanted portion of the input signal whereas the clamper moves the input signal upwards or downwards.”

## Negative Clamping Circuit

If the circuit pushes the signal downwards then the circuit is a negative clamper. While the signal moves downwards, the positive peak of the signal meets the zero level.

### Explanation

During positive half cycle of input AC signal, the diode clampers are forward biased and hence no signal appears at output. In forward biased condition, the diode allows electric current through it. This current will flows to the capacitor and charges it to the peak value of input voltage in inverse polarity -Vin. As input current or voltage decreases after attaining its maximum value Vin, the capacitor holds the charge until the diode remains forward biased.

During the negative half cycle of the input AC signal, the diode clampers are reverse biased and hence the signal appears at the output. In reverse biased condition, the diode does not allow electric current through it. So the input current directly flows towards the output.

When the negative half cycle begins, the clamper is in the non-conducting state and the capacitor starts discharging. Therefore, the voltage appeared at the output is equal to the sum of the voltage stored in the capacitor (-Vc) and the input voltage (-Vin) {I.e. Vo = -Vin– V= -2Vin} which have the same polarity with each other. As a result, the signal shifted downwards.

## Biased Clamping Circuit

Sometimes an additional shift of DC level is needed. In such cases, biased clampers are used.

These biased clamping circuit are further classified in to four classes.

• Positive clamper with positive bias
• Positive clamper with negative bias
• Negative clamper with positive bias
• Negative clamper with negative bias

### Positive Clamper With Positive Bias

If positive biasing is applied to the clamper then it is said to be a positive clamper with positive bias.

During the positive half cycle, the battery voltage forward biases the diode while the input supply voltage is less than the battery voltage. This current or voltage will flows to the capacitor and charges it.
when the input supply voltage becomes more than the battery voltage then the diode stops permitting electric current through it as it becomes reverse biased.

During the negative half cycle, the diode is forward biased by both input supply voltage and battery voltage. So the diode allows electric current. This current will flows to the capacitor and charges it.

### Positive Clamper With Negative Bias

If negative biasing is applied to the positive clamper then it is said to be a positive clamper with negative bias.

During the negative half cycle, the battery voltage reverse biases the diode when the input supply voltage is less than the battery voltage. As a result, the signal appears at the output.

When the input supply voltage becomes greater than the battery voltage. The diode is forward biased by the input supply voltage and subsequently allows electric current through it. This current will flows to the capacitor and charges it.

During the positive half cycle, the diode is reverse biased by both input supply voltage and the battery voltage. As a result, the signal appears at the output. The signal appeared at the output is equal to the sum of the input voltage and capacitor voltage.

### Negative Clamper With Positive Bias

If positive biasing is applied to the negative clamper then it is said to be a negative clamper with positive bias.

During the positive half cycle, the battery voltage reverse biases the diode when the input supply voltage is less than the battery voltage. When the input supply voltage becomes greater than the battery voltage. The diode is forward biased by the input supply voltage and hence allows electric current through it. This current will flows to the capacitor and charges it.

During the negative half cycle, the diode is reverse biased by both input supply voltage and battery voltage. As a result, the signal appears on the output.

### Negative Clamper With Negative Bias

If negative biasing is applied to the negative clamper then it is a negative clamper with negative bias.

During the positive half cycle, the diode is forward biased by both input supply voltage and battery voltage. As a result, current flows through the capacitor and charges it.

During the negative half cycle, the battery voltage forward biases the diode when the input supply voltage is less than the battery voltage. When the input supply voltage becomes greater than the battery voltage. The diode is reverse bias by the input supply voltage and hence signal appears at the output.

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