Clipper Circuits

A clipper is a device which limits, remove or prevents some portion of the wave form (input signal voltage) above or below a certain level In other words the circuit which limits positive or negative amplitude ,or both is called chipping circuit. The clipper circuits are of the following types.

1. Series positive clipper
2. Series negative clipper
3. Shunt or parallel clipper
4. Shunt or parallel positive negative
5. Clipper Dual (combination)Diode clipper

SERIES POSITIVE CLIPPER

In a series positive clipper, a diode is connected in series with the output, as shown in Fig 1(a). During the positive half of the input voltage, the terminal A is positive with respect to B. This reverse biases the diode and it acts as an open switch Therefore all the applied voltage drops across the diode and none across the resistor As a result of this there is no output voltage during the positive half cycle of the input voltage.

During the negative half cycle of the input voltage the terminal B is positive with respect to A. Therefore it forward biases the diode and it acts as a closed switch. Thus there is on voltage drop across diode during the negative half cycle of the input voltage. All the input voltage is dropped across the resistor as shown in the output wave form.

Clippers prevent either or both polarities of a wave form exceeding a specific amplitude level. However a positive Clipper is that which removes or clips the positive half completely. Hence the circuit of the Fig 2.1 is called a positive Clipper Here it may he noted the diode acts a series switch between the source and load. Due to this reason the circuit is called series positive clipper.

SERIES-POSITIVE CLIPPER WITH BIAS

Sometimes it is desired to remove a Small portion of positive or apposite halt cycle of the signal voltage (input signal). For this purpose a biased clipper is used Fig 2 shows the circuit of a biased series positive clipper.

It may be observed that the clipping takes place during the positive cycle only when the input voltage is greater thence battery voltage (i.e. V_i > V_B). The chipping level can be shifted up or down by varying the bias voltage (V_B)

SERIES NEGATIVE CLIPPER

In a series negative clipper a diode is connected in a direction appositive to that of a positive clipper Fig 3 shows the circuit of a negative clipper.

During the positive half cycle pf the voltage, the terminal A is positive with respect to the terminal B There for the diode is forward biased and it acts it as a closed switch As a result ,all the input voltage appears across the resistor as shown in Fig 3(b). During the negative half cycle of the input voltage, the terminal B is positive with respect to the terminal A. Therefore the diode is reverse biased and it acts as an open switch, Thus there is no voltage drop across the resistor during the negative half cycle as shown in the output waveform.

It may be observed that if it is desired to remove or clip the negative half -cycle of the input , the only thing is to be done is to reverse the polarities of the diode in the circuit shown in Fig 1 such a clipper is then called a series negative clipper

SERIES-NEGATIVE CLIPPER WITH BIAS

Fig 4 shows the circuit of a biased series negative diver. In this circuit clipping take place during the negative half cycle only when the input voltage V_i > V_B she clipping level can be shifted up or down by varying the bias voltage ( -V_B)

SHUNT OR PARALLEL POSITIVE CLIPPER

A parallel clipper circuit uses the same diode theory and circuit operation a resistor and diode are connected in series with the input signal and the output signal is developed across the diode. The output is in parallel with the diode hence the circuit name parallel clipper the parallel clipper can limit either the positive or negative alternation of the input signal Fig 5 shows the circuit of a shunt positive clipper In this circuit. The diode acts as a closed switch when the input voltage is positive (i.e. V_i > 0 and as an open switch when the input voltage is negative (i.e. V_i< 0) the output waveform is the same as that of a series positive clipper in the parallel clippers the alp will develop when the diode is cut off.

SHUNT OR PARALLEL POSITIVE CLIPPER WITH BIAS

As is in Fig 6 (a), positive terminal of the battery is connected to the cathode of the diode. This causes the diode to be reversed biased at all times except when the input signal is more positive the bias voltage(i e V_i > V_B). it will be interesting to know that if the polarity of the bias voltage is reversed , the resulting circuits will be as shown in Fig 6(b) Here the input signal lying above the voltage —V_B is clipped the waveforms of the of the output voltage are also shown with figures

SHUNT OR PARALLEL NEGATIVE CLIPPER

The negative clipper has allowed to pass the positive half cycle of the input voltage and clipped the negative half cycle completely Fig 7 shows the shunt (parallel) negative clipper.

In such a circuit the diode acts as a closed switch for a negative input voltage (i.e. V_i < O) and as an open switch for a positive input voltage (i.e. V_i O) the output waveform of the Circuit is the same as that of series negative clipper.

SHUNT OR PARALLEL NEGATIVE CLIPPER WITH BIAS

In such a circuit clipping take place during the negative half cycle only when the input voltage (V_i < V_B) the clipping level can be shifted up or down by varying the bias voltage (—V_B). It will be interesting to know that if the polarity of the bias voltage is reversed, then the resulting circuits will be as shown in Fig 8 (b) Here the entire signal below the voltage level VII has been clipped off .

DUAL (COMBINATION) DIODE CLIPPER

The type of clipper combines a parallel negative clipper with negative bias (D₁ and B₂) and a parallel positive bias (D₁ and B₁). Hence the combination of a biased positive clipper and a biased negative clipper is called combination or dual diode clipper. Such a clipper circuit can clip at both two in dependent levels depending upon the bias voltages. Fig 9(a) show the circuit of a dual (combination) clipper.

Let us suppose a sinusoidal ac voltage is applied at the input terminals of the circuit. Then during the positive half cycle, the diode D₁ is forward biased, while diode D₂ is reverse. biased. Therefore the diode D₁ will conduct and will acts as a short circuit. On the other hand, diode D₂ will acts as an open circuit. However, the value of output voltage cannot exceed the voltage level of V_B1 as Shown in Fig 9.

Similarly during the negative input half cycle the diode D₂ acts as a short circuit while the diode D₁ as an open circuit However the value of output voltage cannot exceed the voltage level of V_B2 It may be noted that the clipping levels of the circuit be varied by changing the values of V_B1 and V_B2 If the values of V_B1 and V_B2 are equal, the circuit will clip both the positive and negative half cycles at the same voltage level. Such a circuit is known as a symmetrical clipper