Write an experiment on Diode Clipper PDF

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Write an experiment on Diode Clipper...

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Experiment # 13 Objective: Write an experiment on Diode Clipper.

Apparatus:      

AC Voltage Source Zener Diode Resistance (Load) Oscilloscope DC Voltage Source Variable Resister

Schematic Diagram:

DC source

Oscilloscope

Theory: OscilloScope: An oscilloscope is a type of electronic test instrument that allows observation of constantly varying signal voltages, usually as a two-dimensional plot of one or more signals as a function of time. It can also convert the other signals such as sound or vibration to voltages and displayed. The oscilloscope can be adjusted so that repetitive signals can be observed as a continuous shape on the screen. There are many types of oscilloscope such as:  CRO (cathode-ray oscilloscope)  DSO (digital storage oscilloscope), A storage oscilloscope allows single events to be captured by the instrument and displayed for a relatively long time, allowing observation of events too fast to be directly perceptible.

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Variable resistor: A variable resistor is a potentiometer with only two connecting wires instead of three. However, although the actual component is the same, it does a very different job. The pot allows us to control the potential passed through a circuit. The symbol used for variable resister is shown below.

Diode Clipper: The Diode Clipper, also known as a Diode Limiter, is a wave shaping circuit that takes an input waveform and clips or cuts off its top half, bottom half or both halves together.

Types Of Clipper Diode Circuit:  Positive Diode Clipping Circuit  Negative Diode Clipping Circuit  Clipping of both cycle

Positive Diode Clipping Circuits: In this diode clipping circuit, the diode is forward biased (anode more positive than cathode) during the positive half cycle of the sinusoidal input waveform. For the diode to become forward biased, it must have the input voltage magnitude greater than +0.7 volts (0.3 volts for a germanium diode).

When this happens the diodes begins to conduct and holds the voltage across itself constant at 0.7V until the sinusoidal waveform falls below this value. Thus the output voltage which is taken across the diode can never exceed 0.7 volts during the positive half cycle. During the negative half cycle, the diode is reverse biased (cathode more positive than anode) blocking current flow through itself and as a result has no effect on the negative half of the sinusoidal voltage which passes to the load unaltered. Then the diode limits the positive half of the input waveform and is known as a positive clipper circuit.

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Negative Diode Clipping Circuits: Here the diode is forward biased during the negative half cycle of the sinusoidal waveform and limits or clips it to -0.7 volts while allowing the positive half cycle to pass unaltered when reverse biased. As the diode limits the negative half cycle of the input voltage it is therefore called a negative clipper circuit.

Clipping of Both Half Cycles: If we connected two diodes in inverse parallel as shown, then both the positive and negative half cycles would be clipped as diode D1 clips the positive half cycle of the sinusoidal input waveform while diode D2 clips the negative half cycle. Then diode clipping circuits can be used to clip the positive half cycle, the negative half cycle or both.

Zener Diode: A zener diode is a silicon PN junction device that is designed for operation in the Reverse breakdown region. The symbol for a zener diode is shown below. The zener diode has a bent line Instead of a straight line representing the cathode terminal that reminds you of the letter Z (for Zener diode).

A Zener diode allows current to flow from its anode to its cathode like a normal semiconductor diode, but it also permits current to flow in the reverse direction when its "Zener voltage" is reached. Zener diodes have a highly doped p-n junction.

Zener Diode Clipping: The zener diode is acting like a biased diode clipping circuit with the bias ed voltage being equal to the zener breakdown voltage. In this circuit during the positive half of the

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waveform zener diode is reverse biased so the waveform is clipped at the zener voltage, VZD1. During the negative half cycle the zener acts like a normal diode with its usual 0.7V junction value. We can develop this idea further by using the zener diodes reverse-voltage characteristics to clip both halves of a waveform using series connected back-to-back zener diodes as shown.

Full-wave Zener Diode Clipping: The output waveform from full wave zener diode clipping circuits resembles that of the previous voltage biased diode clipping circuit. The output waveform will be clipped at the zener voltage plus the 0.7V forward volt drop of the other diode. So for example, the positive half cycle will be clipped at the sum of zener diode, ZD1 plus 0.7V from ZD2 and vice versa for the negative half cycle.

Uses of clipper Diode:  Diode clippers are used for clipping the excessive noise peaks in FM transmission.  These are used for the protection of different circuits.  These are used as regulator in stabilizer.

Procedure: Diode as a clipper:  First of all make the circuit as shown in the figure.

 The zener diode connected is of the value 9.2V.  Zener diode is used to give a specific value at output  An oscilloscope is used to check the output voltage. As clear that in output wave diagram, the voltage is 9.2V (as same to zener diode voltage).  The two zener diodes are used to get same output voltage at both forward and reverse biasing.

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Diode as a Regulator:  Make the circuit diagram as shown in figure with a DC voltage V in.

 Here RL is variable load resistance which is used to change the load.  An oscilloscope is also connected with output loading.  When I apply the voltage, I saw that waveform at output is same while I changing the input voltage.  It proves that in case of DC voltage the zener diode is used like a regulator

Conclusion: From the above experiment I have concluded that zener diode is a device from which we can get the desired output voltage whether input is variable or not. In industries it is helpful to operate the machinery which is operated at various voltages.

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