Study of diode as a Clipper & clamper Circuit

 Objective:-  Study of the diode as a clipper & clamper. Draw and measure the input and output waveform.

 Required Components: - Resistor 1K -1 No, Diode (1N4007 ) -1No, A.C Voltage, DC Voltage, DSO, Coupling wires, Multi meter

Theory:-

For a clipping circuit at least two components—an ideal diode and resistor are required and sometimes a dc battery is also employed for fixing the clipping level. The diode acts as a closed switch when forward biased and an open switch when reverse biased. Depending on the orientation of the diode, the positive or negative region of the input signal is “clipped” off and accordingly the diode clippers may be positive or negative clippers. Half wave rectifier circuits can also be called the basic clippers. 

Biased Clipper – The level to which an ac voltage is limited can be adjusted by adding a bias voltage v2, in series with the diode. Biased clippers are employed for this purpose. The circuit diagram for a biased positive clipper (that is for removing a small portion of positive  half cycle) is illustrated in figure.When the input signal volt­age is positive but does not exceed DC voltage V2, the di­ode D remains reverse biased and most of the input voltage ap­pears across the output. When during the positive half cycle of input signal, the signal voltage exceeds the DC voltage V2, the diode D is forward biased,i.e conducts heavily.

Procedure: - 1) Connect the components according to the circuit diagram  given. Take V_IN=5V rms , V_BIAS=2.5v  2) Connect DSO across the load R and input source. 3) Simultaneously measure both the input and output waveform in DSO ch-1 and ch-2 respectively.     
     

Positive Bias Diode Clipping

Likewise, by reversing the diode and the battery bias voltage, when a diode conducts the negative half cycle of the output waveform is held to a level –V_BIAS – 0.7V as shown.

Negative Bias Diode Clipping

 

A variable diode clipping or diode limiting level can be achieved by varying the bias voltage of the diodes. If both the positive and the negative half cycles are to be clipped, then two biased clipping diodes are used. But for both positive and negative diode clipping, the bias voltage need not be the same. The positive bias voltage could be at one level, for example 4 volts, and the negative bias voltage at another, for example 6 volts as shown.

Diode Clipping at Different Bias levels *take Vin = 7v Rms *

When the voltage of the positive half cycle reaches +4.7 V, diode D₁ conducts and limits the waveform at +4.7 V. Diode D₂ does not conduct until the voltage reaches –6.7 V. Therefore, all positive voltages above +4.7 V and negative voltages below –6.7 V are automatically clipped.

The advantage of biased diode clipping circuits is that it prevents the output signal from exceeding preset voltage limits for both half cycles of the input waveform, which could be an input from a noisy sensor or the positive and negative supply rails of a power supply.

If the diode clipping levels are set too low or the input waveform is too great then the elimination of both waveform peaks could end up with a square-wave shaped waveform.

Diode as a clamper

Object :- Study of diode as a  positive clamper

Required Components: -Capacitor-1uF 1No, Resistor-680K-1 No, Diode ( IN4007 )-1No, A.C Voltage Source,  DC Voltage,  DSO

Theory: -A Clamper Circuit is a circuit that adds a DC level to an AC signal.A Clamper circuit can be defined as the circuit that consists of a diode, a resistor and a capacitor that shifts the waveform to a desired DC level without changing the actual appearance of the applied signal.  The different types of clampers are positive  and negative clampers.

 The magnitude of R and C must be chosen such that the time constant RC is large enough to ensure that the voltage across the capacitor does not discharge significantly during the interval the diode is non- conducting. 

A Clamping circuit restores the DC level. When a negative peak of the signal is raised above to the zero level, then the signal is said to be positively clamped.

A Positive Clamper circuit is one that consists of a diode, a resistor and a capacitor and that shifts the output signal to the positive portion of the input signal. The figure below explains the construction of a positive clamper circuit.

Initially when the input is given, the capacitor is not yet charged and the diode is reverse biased. The output is not considered at this point of time. During the negative half cycle, at the peak value, the capacitor gets charged with negative on one plate and positive on the other. The capacitor is now charged to its peak value Vm

. The diode is forward biased and conducts heavily.

During the next positive half cycle, the capacitor is charged to positive Vm while the diode gets reverse biased and gets open circuited. The output of the circuit at this moment will be

V0=Vi+Vm

Hence the signal is positively clamped as shown in the above figure. The output signal changes according to the changes in the input, but shifts the level according to the charge on the capacitor, as it adds the input voltage.

 

Positive Clamper

The circuit for a positive clamper is shown in the figure. During the negative half cycle of the input signal, the diode conducts and acts like a short circuit. The output voltage  V₀ =0V.The capacitor is charged to the peak value of input voltage V_m. and it behaves like a battery. During the positive half of the input signal, the diode does not conduct and

acts as an open circuit. Hence the output voltage  V0 =Vm+Vm. This gives a positively clamped voltage.

To see the output in DSO keep it in DC coupling mode.