Lab # 004 - Best lab report PDF

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15/10/2019

Lab Title :Design the clipper circuits to obtain the waveforms on oscilloscope.

Objective :To study the diode applications in a clipping circuits. Understand the working of positive and negative clipper circuit Design positive and negative clipper circuits Use a digital oscilloscope to capture and analyse output waveforms.

  

Introduction Of Theory:Diode Clipping Circuits: 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. Clippers or limiters are sometimes used to clip off portions of signal voltages above or below certain levels.

Types Of Clipper Diode Circuit:    

Positive Diode Clipping Circuit Negative Diode Clipping Circuit Clipping of both cycle Biased Diode Clipping Circuits

Positive Diode Clipping Circuit:

FIG # 01 In this diode clipping circuit, the diode is forward biased 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.

Negative Diode Clipping Circuits :

FIG # 02 1|Pa ge

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Here the reverse is true. 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:

FIG # 03 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.

Biased Diode Clipping Circuits To produce diode clipping circuits for voltage waveforms at different levels, a bias voltage, VBIAS is added in series with the diode to produce a combination clipper as shown. The voltage across the series combination must be greater than VBIAS + 0.7V before the diode becomes sufficiently forward biased to conduct. For example, if the VBIAS level is set at 4.0 volts, then the sinusoidal voltage at the diode’s anode terminal must be greater than 2.3 + 0.7 = 3 volts for it to become forward biased. Any anode voltage levels above this bias point are clipped off. Positive Bias Diode Clipping

FIG # 04 Negative Bias Diode Clipping

FIG # 05

Diode Clipping of Different Bias levels

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FIG # 06 The advantage of biased diode clipping circuits is that it prevents the output signal from exceeding present 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.

Circuit Diagram : Task # 01:- Positive Diode Clipping Circuit:

Fig # 07

Task # 02:- Negative Diode Clipping Circuit:

Fig # 08

Task # 03:-

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Clipping of Both Half Cycles:

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Fig # 09

Task # 04:-

Diode Clipping of Different Bias levels:

Fig # 10

Practical Work :Equipment :      

Resistor Diode Connecting Wires Breadboard Oscilloscope Signal generator DC power supply

Procedure : Connect the circuit as shown in the circuit diagram.  Give the input signal as specified.  Switch on the power supply. 4|Pa ge

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 For positive half cycle use 2.2V DC voltage, diode D1 conducts and limits the waveform at +3.0 V. For negative half cycle use 1.0V DC voltage, diode D2 conducts and limits the waveform at -1.8V. Therefore, all positive voltages above +3.0 V and negative voltages below –1.8 V are automatically clipped.  In task 4 we use DC power supply to obtain the given waveforms.  Note down the value of AC and DC voltages from the CRO.  Save the screen shots of waveform of all task from oscilloscope.

Theoretical Calculations:Some common values are: Frequency = f = 50 Hz Period

=

Resister = r = 1.5 Kohm

20 ms

Diod

Vin

Task # 01:-

=

= Vpp = 20 v

Positive Diode Clipping Circuit: Vpp = 10.80V

Vmin = -10.00V

Task # 02:-

Vmax = 0.80V.

Negative Diode Clipping Circuit: Vpp = 11.00V

Vmin = -0.80V

Task # 03:-

Vmax

= 10.20V.

Vmax

= 0.72V.

Clipping of Both Half Cycles: Vpp = 1.44V

Vmin = -0.72V

Task # 04:-

1N4007

Diode Clipping of Different Bias levels: Vpp

=

4.80V

For Vmin add DC 1V by DC power supply into Diode voltage to get 1.80V

Vmin

=

0.8 + 1.0

=

1.80V

For Vmax add DC 2.2V by DC power supply into Diode voltage to get 3.00V

Vmax

=

0.8 + 2.2

=

3.00V

Graphical Data :Task # 01:- Positive Diode Clipping Circuit: 5|Pa ge

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Graph # 01

Task # 02:- Negative Diode Clipping Circuit: Graph # 02

Task # 03:-

Clipping of Both Half Cycles: Graph # 03

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Task # 04:-

Diode Clipping of Different Bias levels: Graph # 04

Course Learning Outcome: o CLO 1: o CLO 2:

=====> =====>

PLO-1 ( Engineering knowledge ) PLO-5 ( Modern Tool Usage )

o CLO 3:

=====>

PLO-3 ( Design & Development )



I have achieved CLO 2 which is mapped to Modern tool usage. This CLO is achieved by working on Oscilloscope, Functional generator, DMM etc.



I have achieved CLO 3 which is mapped to Design & Development of solution. I have design the clipper circuit & developed the solution of given Problem.

Discussion of Results :A In this experiment understand the operating principle of diode clipping circuit. In positive diode clipping circuit a diode clipper that limits or clips the positive part of the input voltage. As the input voltage goes positive, the diode becomes forwards-biased and conduct current. It is because the cathode is at ground potential ( 0 v ), the anode 0.8v(assuming silicon). So the drop at D1 is limited to +0.8v when the input exceeds this value. Next the negative diode clipping circuit. If the diode is tuned around, the negative part of the input voltage is clipped off. When the diode is forward-biased during the negative part of the input voltage. Voltage drop at D1 is limited at -0.8v. when the input voltage goes above -0.8, the diode is no longer forwardbiased and a voltage appears across RL proportional to the input voltage. During the negative half cycle of the input signal, the diode conducts and acts like a short circuit. Also understand the waveform change of diode clipping circuit and clamping circuit when the bias is applied. In this experiment know how to using oscilloscope and to get the wave based on question given. Limiter are used to add a DC voltage to an AC voltage.

Conclusion : 7|Pa ge

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The Clipper circuit design output waveforms have been studied and the required parameters are compared. Today’s lab is about the understanding of clippers that what are clippers circuits how and why they are formed and how to use diodes to make clipper circuits. Moreover, to analyse the working of diode in limiters or clippers and to find the waveforms. At the end, all the required values and circuits are obtained with the help of oscilloscope.

References :  

https://www.electronics-tutorials.ws/diode/diode-clipping-circuits.html https://www.studocu.com/en/document/university-of-engineering-technology-lahore/electriccircuit-analysis/practical/write-an-experiment-on-diode-clipper/3744549/view http://vlab.amrita.edu/?sub=3&brch=60&sim=1115&cnt=2157

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