lab5 prelims

7/23/2019 Lab5 Prelims

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Experiment No.5Application of diodes

By Anuj Choudhury

2015CS10214

[email protected]

Lab Partner:Saransh Maheshwari

2015CH70183

CH7150183 IITD.AC.IN

Indian Institute of Technology, Delhi


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Abstract

This laboratory experiment explores the uses of diodes. The objective of this lab is to become familiarwith the functionality of a diode in circuits. We will experiment the use of diodes in rectifying circuits.

We will also observe the clipping and clamping functions of the diode found in our circuit designs.

Introduction

Almost all electric circuits require a DC source of power. A DC power supply is as equipment which

converts the alternating waveform from the power lines into an essentially direct voltage. The powersupply is composed of three main parts. Rectifier, filter and Regulator (the regulator is not considered

in this experiment). Arectifier is a device capable of converting a sinusoidal input waveform, whose

average value is zero, into a unidirectional waveform with non-zero average component. The rectifier

device is usually a semiconductor or vacuum-tube diode.We study the use of a diode as a rectifier,in

first converting a full wave to a half wave.

Other important use of diode is in clipping and clamping circuits. By definition, clipping circuits clipsignals above a selected voltage level, whereas clamping circuits shift the DC voltage of a waveform.

Many wave shapes can be produced with the proper application of these two important diode

functions.


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Objectives:

Study half-wave circuits based on semiconductor

diodes.

To understand the theory of operation of the clipping

and clamping diode circuits


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Materials Required AF Generator

Dual channel Oscilloscope

Silicon Diode

A large Electrolytic Capacitor

Non-electrolytic Capacitor (0.01-0.1 F)

Breadboards


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Theory Required

In this experiment Diode is used in three different circuits.

Half Wave Rectifiers:

Electric current flows through a p - n junction diode when it is forward biased and we get output current through the

load. Let, we supply a sinusoidal voltage Vin= Vsint as a source voltage. Now, if the input voltage is positive, the

diode is forward biased and when that is negative, the diode is in reverse bias condition.

When the input voltage is positive, current flows through the diode. So, the current will flow through the load also

and we obtain output voltage across the load. But for the negative half cycle of the input, the p-n junction get

reverse biased and no current flows through the diode as a result we obtain zero current and zero voltage across the

load.

The basic diagram of half wave diode rectifieris given below,

Source:learn.sparkfun.co
https://learn.sparkfun.com/tutorials/diodes/diode-applicationshttps://learn.sparkfun.com/tutorials/diodes/diode-applicationshttps://learn.sparkfun.com/tutorials/diodes/diode-applicationshttps://learn.sparkfun.com/tutorials/diodes/diode-applicationshttps://learn.sparkfun.com/tutorials/diodes/diode-applications


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Clipping Circuit:

In the following figure,a dc voltage is connected with the diode to show the clipping of the

circuit,which occurs at a voltage which is different from the zero voltage, since the dc voltage is

connected to the diode.the voltage at which the diode turns reverse biased,is at 2 volts(according tothe diagram).This figure shows the clipping of the wave in the circuit.


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Clamping Circuit:

A clamper does is adding a DC component to the signal. In Figure the input signal is a sine-wave, the

clamper pushes the signal upward, so that the negative peaks fall on the 0V level. As can see, the

shape of the original signal is preserved, all that happen is a vertical shift of the signal. We described

an output signal for a positive clamping.The Figure shown represents a positive clamper ideally here

how it is works. On the first negative half cycle of input voltage, the diode turns on.

At the negative peak, the capacitor must charge to Vp with polarity shown. Slightly beyond the

negative peak, the diode shunts off.


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Procedure to the Experiment

Diode Half Wave Rectifier:

Connect the circuit as shown in the figure. Set convenient amplitude (about 5V).

Observe the oscillator waveform across the resistor on the scope.

Measure the peak and dc value of both waveform.

Repeat the observations for an input signal of one tenth of the previous case.

Connect a large electrolytic capacitor across the resistor. Repeat your observations.


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Diode Clipping Circuit:

Connect the circuit as shown in the figure.

Observe the oscillator waveform and the waveform across diode.

Measure peak to peak and dc value of both waveform.

Repeat the observations for an input ac signal 3 times the previous case.

Reverse the diode polarity and repeat the observation. Reverse the source polarity and repeat the observation.


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Diode clamping circuit:

Connect the circuit as shown.

Observe the oscillator waveform and waveform across diode.

Measure the peak and dc value of both waveform.

Repeat the observations for an input ac signal 3 times the previous case.

Reverse the diode polarity and repeat the observation.

Reverse the source polarity and repeat the observation.


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Rectification of diode

Clipping of diode


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Clamping of diode


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Breadboard Images


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Table of Values and Error Bar:

Frequency= 500 Hz, R= 10 K

For V=10 Volts:

Without Capacitor-

(all units in volts)

S. No. Peak to Peak V from Source Voltage across R

AC DC AC DC

(x) Error (x) error

1. 10+ 0.1 0 2.8 0.1 1.1 0.1


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With Capacitor-

(all units in volts)

S. No. Peak to peak V from Source Voltage across R

AC DC AC DC

(x) error (x) Error

1. 10+ 0.1 0 6.4 0.1 3.4 0.1


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For V=1 Volts:

Without Capacitor-

(all units in microvolts)

S. No. Peak to Peak V from Source Voltage across R

AC DC AC DC

(x) Error (x) error

1. 1+ 0.1 0 100 10 20 10


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With Capacitor-

(all units in microvolts)

S. No. Peak to peak V from Source Voltage across R

AC DC AC DC

(x) error (x) Error

1. 1+ 0.1 0 12 2 64 4


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For clipping of diodes


For V= 5 volts

S. No. Peak to Peak V(Source)

(measured by

oscilloscope)

Output DC voltage

(by source)

Voltage across Diode

(measured by

oscilloscope)

(x) Error (x) error (x) error

1. 5.0 0.1 1.6 0.1 1.0 0.1


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For V= 15 volts


(measured by oscilloscope)

Output DC voltage

(by source)


(measured by

oscilloscope)


1. 15.0 0.1 3.2 0.1 4.8 0.1


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After Changing the Polarity of Diode:


For V= 5 volts



Output DC voltage

(by source)


(measured by

oscilloscope)


1. 5.0 0.1 0.1 0.02 2.5 0.1


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For V= 15 volts



Output DC voltage

(by source)


(By mutlimeter)


1. 15.0 0.1 0.5 0.1 6 0.1


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After Changing the Polarity of DC source:


For V= 15 volts



Output DC voltage

(by source)


(measured by

oscilloscope)


1. 15.0 0.1 3 0.1 4 0.1


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For clamping of diodes

For V= 5 volts



Output DC voltage

(by source)


(By mutlimeter)


1. 5.0 0.1 1. 6 0.1 1.1 0.1

(these images were taken in invert mode)


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For V= 5 volts



Output DC voltage

(by source)


(measured by

oscilloscope)


1. 5.0 0.1 -3.6 0.1 2.5 0.1


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For V= 15 volts



Output DC voltage

(by source)


(measured by

oscilloscope)


1. 15.0 0.1 -8 0.1 7.5 0.1


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After Changing the Polarity of Diode:


For V= 5 volts



Output DC voltage

(by source)




1. 5.0 0.1 0.3 0.02 2.5 0.1


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For V= 15 volts



Output DC voltage

(by source)


(By mutlimeter)


1. 15.0 0.1 4.5 0.1 7.5 0.2


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After Changing the Polarity of DC source:


For V= 5 volts



Output DC voltage

(by source)


(measured by

oscilloscope)

(x) Error (x) Error (x) error

1. 15.0 0.1 -0.3 0.02 2.5 0.1


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For V= 15 volts



Output DC voltage

(by source)


(By mutlimeter)

(x) Error (x) Error (x) error

1. 5.0 0.1 -4.5 0.1 7.5 0.1


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ANALYSIS OF ERRORS:

Though the errors are not very significant, they may be due to following reasons :-

1.The primary reason may be the error in the digital multimeter(machine errors)

2.Error may also be introduced due to heating of resistors(after keeping the circuit closed for a long

time),since the resistance may change of the circuit.

3.The voltage in a part of the circuit may be contributed to by both the resistor itself and the

wire(which has some finite non-neglectable resistance)

4.Another source of error is the leakage current through the capacitor.

5.Also,the diode is not ideal(in case of 1 Vpp,it should show 0 current ideally)

6.There is some error due to the least count errors of the oscilloscope(which is an analog instrument).


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Discussion

According to the figure obtained from oscilloscope, we notice that input and output voltages are in phase, however

the output voltage has its negative part rectified. This is due to the diode property, which lets current flow only in

one direction. Moreover, input voltage has higher amplitude during positive half. In my understanding, this smallvoltage (difference) is needed to switch the diode on (breakdown voltage).

In the following experiment, for the half wave rectification part,we observe that for large Vpp(like 10 V) there is

good(observable)half wave rectification. for the 1V part, the observed ideal value should be 0,since the ideal diode

would not allow even the small (visible) part to flow. The figure, which is seen could be that of disturbance, noise

etc.

Clipping is the process of making the output voltage constant after a certain voltage level. It is a device designed toprevent the output of a circuit from exceeding a particular voltage level without distorting the remaining part of the

applied waveform.In the following experiment,we see significant clipping in both the cases(i.e. the 5 V and the 15 V

case) .If the diode polarity is reversed,the clipping just takes place in the opposite direction,as can be seen from the

experiment as well.If the source polarity is reversed then the voltage at which the clipping takes place changes,which

can be again,seen from the images posted.

Clamping is the process of adding a certain amount of dc throughout the ac waveform. The result is a sinusoidal

waveform that is shifted from the symmetric position about the x-axis to a different dc level.


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Application in Real life

Uses of Half Wave Rectifier circuits:

These are used to convert ac supply to dc based on principle that diodes have zero resistance in forward bias

and very large resistance when reverse bias. We can see the use of rectifiers in mobile and laptop chargers as

supply at our home is in the form of ac and mobile chargers run on dc supply.

Modern electronic devices like CD players, computers, television etc require DC supply. The power we get

from wall outlets is AC. Rectifiers are used to convert AC to DC.

Uses of clipping circuits:

The diode clipper can be used for the protection of different types of circuits. For example, a digital circuit

against transients which may cause considerable damage.

They are frequently used for the separation of synchronizing signals from the composite picture signals.

The excessive noise spikes above a certain level can be limited or clipped in radio transmitters by using series

clippers.A combination of half wave rectifier circuits and clipping circuits can be used as a convertor for ac to dc

power supply.

Uses of clamping circuits:

The complex transmitter and receiver circuitry of television clamper is used as a base line stabilizer to define

sections of the luminance signals to preset levels.

Clampers are also called as direct current restorers as they clamp the wave forms to a fixed DC potential.

These are frequently used in test equipment, sonar and radar systems.

For the protection of the amplifiers from large errant signals clampers are used.


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Conclusion

In this part of the laboratory, the principle of diode operation was practically understood. Initially, the behavior of

half wave rectifier was analyzed with the help of oscilloscope. Finally, we learnt about clipping and clamping circuits

and their uses in various fields. We also learnt about the potential uses of the diode.

References

ELL Lab Manual

Anant Agarwal: fundamentals of AD electronic circuits

http://www.elprocus.com/types-of-clipper-and-clamper-circuits-and-applications/

learn.sparkfun.com/

Wikipedia

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