analog & digital elec. lab

7/28/2019 Analog & Digital Elec. LAB

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Experiment # 1

Name: ________________________________ Roll No: _____________________

Score: _________________ Signature of Tutor: ______________ Date: _______

POWER SUPPLY UNITS & MEASURING INSTRUEMENTS

Object: To become familiar with various Power Sources and Electrical MeasuringInstruments.

Apparatus: All Power Supply Units and Measuring Instruments in the workshop

Theory:

The Electrical quantities are either Varying or non-varying i.e AC or DC. AC stands forALTERNATING CURRENT, whereas DC stands for DIRECT CURRENT. Alternating currents

are those, which vary in some periodic fashion. The voltage which causes Alternating Current, is

called AC voltage and the one, which causes Direct Current, is called DC voltage. For example,figure 1.1 shows waveforms of alternating currents.

Figure 1.1: Various ac waveforms Figure 1.2: Power supply Response

Sinusoidal waveform is the most popular among all. The mains supply in our houses is anexample of ac voltage source, which provides 220 volts ac with sinusoidal waveform. The mains

supply voltage has a frequency of 60 Hz, i.e a time period of 16.667 ms.

Figure 1.2 shows response of an IDEAL DC POWER SUPPLY, which provides either

CONSTANT CURRENT or CONSTANT VOLTAGE irrespective of the load resistance. But

the real power sources are not as accurate as ideal ones. A real power source has a finite internal-


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resistance, which consumes part of the power from the source. Figure 1.3 shows the symbols of

Constant Current and Constant Voltage Sources.

Figure 1.3: The Symbols of power sources

The measuring instruments used to measure POTENTIAL DIFFERENCE (Voltage) are called

VOLTMETER, the ones used to measure CURRENT are called AMPERE-METER (in short

AMMETER), and the ones used to measure RESISTANCE are called the OHMMETER. The

current measurements in the electronic circuits are usually in the range of milli-amperes. Hencein electronic lab, mostly ammeters are with the range of milli-amperes. Hence in electronics lab,

mostly ammeters with the range of milli-amperes are used, which are called MILI-AMMETERS.

Then, there are instruments called MULTIMETER, which can measure Current, Voltage,

Resistance and some other electrical characteristics. These are sometimes called (Ampere-Volts-Ohm) AVO meters. The measuring instruments are generally classified as ANALOG or

DIGITAL. The analog meters have a deflection pointer with a scaled dial, which needs to be

calibrated. The CALIBERATION is the process of correcting any error in the reading of ameasuring instrument. These meters have a CALIBERATION SCREW associated with their

deflection system, which is to be set before use to make the deflection pointer show "ZERO". In

contrast to this, the digital meters have an LCD display like the one in a calculator, and do notneed calibration. Clear advantage of the digital meter is that it shows the exact reading on the

display, and one does not need to read the right scale, which sometimes is non-linear and very

difficult to read. The analog meters with multiple ranges usually have two scales. One must takecare to read the right scale for the selected range. The analog multimeter has a separate scale for

each quantity to be measured. Hence, its scales are very confusing and difficult to read.

1) Take any voltage source, connect a Voltmeter to its output terminal, and turn it ON.Select any voltage from the voltage source, note down the selected value from its scale ordisplay, against the value shown by the voltmeter connected by you, in the Table 1.1. Is

the value same as required? Repeat the same by selecting another magnitude of voltage.

2) Finally try measuring the mains supply ac voltage. Take a digital Multimeter (DMM),and set it to measure ac voltage. Select the measurement range higher than 220 Volts and

insert the DMM probe in any one of the HALF POINTS in the workshop.


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Observation:

S. NO. Selected Voltage

(SV)

Observed Voltage

(OV)

Percent Error=

(OVSV)*100/OV

Conclusion:

Have you become familiar with all Power Supply Units and Measuring Instruments? What

theoretical and practical concepts did you gain from this experiment? Comment.


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Experiment # 2

Name: ________________________________ Roll No: _____________________


FUNCTION GENERATOR AND OSCILLOSCOPE

Object: To learn the operation of Function Generator and Oscilloscope.

Apparatus:1) CRT Oscilloscope

2) Function Generator

Theory:

The easiest and normal way to check if an Electronic Circuit is working properly or not is toapply proper input signal to the circuit under test and observe its output. For the purpose two

appliances are used:

1. FUNCTION GENERTOR2. OSCILLOSCPE

The FUNCTION GENERATOR, as the name suggests, generates periodically varying electricalsignals, which are FUNCTIONS OF TIME; i.e they vary with time. A periodic electrical signal

is characterized by its following four parameters:

1. Function or wave shape

2. Time period or Frequency

3. Amplitude

4. DC level

Function Generator:Most Function Generator can produce threebasic wave shapes; i.e Rectangular, Triangular

and Sinusoidal. Many function generators

available have other advanced features besides

generating the three fundamental waves andtheir four composite waves. The three waves

are shown in figure 2.1.This function generator

can generate these wave - shapes with as highfrequencies as 10 MHz, with the maximum

amplitude of 11 Volts; i.e, Peak to Peak Ampli-

-tude of 22volts. The Function Generator alsohelps change DC level of the signal. The dc Figure 2.1 Basic Wave shapes


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level might be kept at positive or negative voltage as desired, given that the peak value

must not exceed +11 volts or -11 volts. For example, Figure 2.1 shows a sinusoidal wave

with following characteristics:

Oscilloscope:

Oscilloscope is the equipment with CATHODE RAY TUBE (CRT) Display used to observeoutput from all kinds of Electronics Circuits with AC, DC, Analog or Digital Output. This

appliance is specially meant for Observing TimeVarying Signals. Mostly, the oscilloscope hastwo inputs called CHANNAELS. The two channels enable the user of simultaneously observingtwo signals as they vary against time in NORMAL mode, or one signal against another in XY

mode. It is often necessary to observe both, input and output of a circuit simultaneously to verify

its proper operation. Therefore, usually Channel 2 is used to observe output signal of a circuit,

whereas Channel 1 is used to observe input applied to the same circuit. Both the oscilloscopechannels are alike in characteristics, and can measure signals with maximum Amplitude of 20

Volts. Each channel has a chord called Probe. These probes are detachable, and can be set to

measure as high voltages as 200 volts, using the X10 switch over them. The two channels can

also be used to observe sum and difference of the two signals applied to them. Before makingany observation with the oscilloscope, one must CALIBRATE both of its channels to make sure

that the observations are correct to the maximum possible accuracy. The oscilloscope generates a

signal called CALIBERATION SIGNAL, which is SQUARE WAVE with the frequency of 1 KHz, i.e Time Period of 1ms. This signal is observed on both channels one by one, and any error

in the observation is corrected before making any other observation. There is a limit to the

highest frequency that can be displayed on an oscilloscope. Most of the oscilloscopes can displaythe signals with the maximum frequency of 20 MHz.

1) Turn the two appliances ON. The power Switches are mostly on the Front Side of

the appliances.

2) Place the coupling switch of both the channels at Ground (GND).3) Select Channel 1. Observe its Ground Line, which appears to be a horizontal line on the

CRT. Rotate the vertical Displacement Switch and move the Ground Line verticallyUP/DOWN to the place you desire to represent "ZERO" Volts.

4) Repeat (3) for channel 2.

5) The Oscilloscope has a knob on the front side, called Calibration Output. Select channel 1,

connect its probe to Calibration output, and place its Volts/Div switch at 0.5 volts perdivision. Now set the associated Calibration Switch so that the square wave signal covers

one division on the vertical axis.

6) Repeat (5) for channel 2.

7) To calibrate Time Scale, select either channel 1 or channel 2, connect its probe to calibration

output, place Time/Div switch at 0.5 ms/div and then set the associated calibration switch,so that each half cycle of the wave covers one division on the horizontal axis.

8) Press SIN key from the three function keys on the Function Generator.9) Set 1 and kHz on the Frequency Select switches to generate 1 kHz signal, i.e signal with

time period of 1 ms.

10) Use attenuation switch to set the signal amplitude at 1 volt (2 V Peak to Peak).11) Connect the probe of Function Generator to the probes of channel 1 and channel 2 of the

Oscilloscope.


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12) Press CH:1 to observe the wave on Channel 1.

13) Set Volts/Div switch of CH:1 on 0.5 Volts/Div.

14) Set Time/Div switch at 0.5 ms/Div.15) Calculate Amplitude of the signal by multiplying the number of vertical divisions covered

by the signal and 0.5 Volts.

16) Calculate frequency of the signal by multiplying number of horizontal divisions coveredby the signal with 0.5 ms.17) Repeat (12) through (16) for Channel 2.

18) Press CHOP or ALT switch to observe Channel 1 and 2 simultaneously.

19) Press CH:1 and CH:2 switches together to observe addition of signals at channel 1 andchannel 2; i.e. CH:1 + CH:2.

20) Press CH:2 INV to observe the difference of signal at channel 1 and the signal at channel 2,

i.e., CH:1-CH:2.

21) Press any two of the three function keys of the function generator.22) Select any one channel of the oscilloscope to observe the composite wave.

23) Press all the three function keys of the Function Generator.

24) Select any channel to observe the composite function, which is combination ofSINUSOIDAL, SQUARE and the TRIANGULAR function.

25) Pull out DC Offset switch of the Function Generator. Set it to lift the signal level up by 2

division on the oscilloscope and then 2 divisions down.


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Observations:

1) Draw all the composite waveforms of the signals, which you could generate from theFunction Generator.

2) Fill the following table to register any inaccuracy in the generation and display of the basicthree signals.

Percent ErrorObserved FrequencySelected FrequencyS.No.

1

2

3

4

5

Conclusion:

Have you become familiar with the two appliances? What theoretical and practical concepts did

you gain from this experiment? Comment.


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WORKSHOP # 3

Name: ________________________________ Roll No: _____________________


RESISTORS

Object: To become familiar with Resistors, Variable Resistors and ResistorColor Coding.

Apparatus:

1) A Digital Multi-meter (DMM)

2) Few Resistors3) Few Variable Resistors

4) A Breadboard

Theory:

The RESISTOR is a component used to limit the flow of Electric Current inside electronic

circuits, or to keep the Electric Current at the required value. The property of Resistor to resistthe flow of Electric Current is called RESISTANCE. i.e.

R= V/Iwhere 'R' represents Resistance in Ohms(), 'V' represents the Voltage in Volts and 'I' representsCurrent in Amperes.

The Resistors are made with fixed resistance as well as with variable resistance. The Resistors,

whose resistance can be varied, are called a VARIABLE RESISTOR or POTENTIOMETER.The fixed resistors are usually made from Carbon, hence they are called CARBON RESISTORS.

The Resistors called WIRE WOUND RESISTORS are also made using wire of metal alloys

wound over ceramic former. The WIRE WOUND RESISTORS are made when very low valuesof resistance are required. The Variable RESISTORS are made using same techniques as fixed

resistors, but they have a slider inside them. The VARIABLE RESISTORS are called

POTENTIOMETERS when the connection is also given to the sliding terminal. The FIXED

VARIABLE RESISTORS have two terminals whereas the potentiometers have three terminals.Their symbols are shown in Figure 3.1.

The Fixed Resistors are available with many different values, which are specified by the

manufacturer, using colorcodes. There are two standards of color coding, i.e. 4- band standardand 5- band standard. The colors used in both standards are same, which are mentioned belowwith their respective values.


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Figure 3.1: Symbols of Resistor

Figure 3.2: The resistors with 4-band and 5-band Color Codes

Black 0 Green 5

Brown 1 Blue 6Red 2 Violet 7

Orange 3 Grey 8

Yellow 4 White 9Gold -1 Silver -2

Gold and Silver are not used in the band of 100s, 10s and units. It is used to code power of 10,

i.e. 3rd

band in 4 band standard and 4th band in 5 band standard. It is also used inTOLERANCE BAND, i.e. the last band from left. Gold represents a tolerance of 5% and the

Silver represents a tolerance of 10%. The word Tolerance means maximum possible deviation inthe resistance of a resistor from one, which is specified by the manufacturer. A resistor with 4 band color code, Brown in first band, Black in second band, Red in third band and a Gold in

fourth band has a resistance of:

Brown Black Red Gold

1 0 102

5%

Minimum Resistance (1000 - 10005/100) (100050) 950

Maximum Resistance (1000 + 10005/100) (1000 + 50) 1050

Commercially, the resistors are available in three series; called E6 (20% Tolerance), E12 (10%

Tolerance) and E24 (5% Tolerance). Resistors with tolerance of 1% or less are also available.

Such a Resistor is called PRECISION RESISTOR.


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The Resistors are available with different Power Ratings. The Resistors with 5% or 10%

tolerance are usually available in power rating of Watt or Watt.

Procedure:

1)

Take any Resistor and insert it in to the Breadboard.2) Decode its Resistance from the Color bands (CR).3) Take a Multi-meter. Select the option of Ohmmeter with appropriate range.4) Place the probes on the terminals of the Resistor to measure the Resistance (MR).5) Calculate the Percent Error as CR- MR 100/CR.6) If the Percent Error is less than the Tolerance, the Resistor is reliable and is in accordance

with the Specifications.

7) Repeat (1) through (6) four times.8) Take a Potentiometer and connect its two end-terminals with the Ohmmeter.9) Turn the knob of Potentiometer in any direction, while observing its Resistance.10)Connect the probe of Ohmmeter across middle terminal of the Potentiometer and any one

of the end-terminals.11)Turn the knob of Potentiometer fully clockwise and note down its Resistance.12)Turn the knob of Potentiometer slowly in counter-clockwise direction while observing its

Resistance on the Ohmmeter.

Observation:

S.NO. ecnatsiseR Percent Error ecnareloT noitacilpmI

dedoC derusaeM

1

2

3

4

5

Conclusion:

Have you become familiar with Resistors and their Color coding? What theoretical and practicalconcepts did you gain from this experiment? Comment.


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Experiment # 4

Name: ________________________________ Roll No: _____________________


VOLTAGE- CURRENT CHARACTERISTICS OF A JUNCTION DIODE

Object: To understand the voltageCurrent characteristics of a junction diode.

Apparatus: 1) Oscilloscope

2) 0 - 15 Power Supply

3) Digital Multimeter (DMM)4) IN 4004 diode

5) 1-k resistor

6) Electronics WorkbenchDiscussion:

A diode is a device formed from a junction of n-type and p-type semiconductor materials. The

lead connected to the p-type material is called the anode and the lead connected to the n-typematerial is the cathode. In general, a solid line on the diode, as shown in figure 4.1 marks the

cathode of a diode.

Figure:4.1 The symbol of a diode compared to an actual diode package.

When the positive terminal of diode is connected with positive terminal of battery, this conditionallows the current to flow across the p-n junction, referred as Forward bias, but when the

negative terminal of diode is connected with positive terminal of battery, this condition prevents

the current to flow across the p-n junction, referred as Reverse bias. These two possible

conditions are shown in figure 4.2.

Figure 4.2(a) Forward Bias Figure 4.2(b) Reverse Bias


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The primary function of the diode is the rectification (process of converting a.c into d.c). When it

is forward biased (the higher potential is connected to the anode lead), It will pass current. When

it is reverse biased (the higher potential is connected to the cathode lead), the current is blocked.The characteristic curves of an ideal diode and a real diode are seen in Figure 4.3.

Figure 4.3 Characteristic curves of an ideal diode and a real diode

The voltampere (V-I) characteristics of a diode show how current (I) in that diode varies withthe voltage applies across it experimentally. This can be determined by measuring the current in

the diode for successive number of higher applied voltage and plotting a graph of current versus

voltage, you will note that very little current follows in the diode for low level of the applied

voltage. Thus below (0.7V) forward bias, a silicon diode draws little current. For forward biasvoltages equal to or higher than 0.7V, the diode is turned on and permits the current to flow.

Beyond 0.7V very slight increases in forward biasing voltages result in the increase of current inthe diode dramatically.

The turn on forward bias voltages for silicon diode is typically 0.7V, for Germanium it is 0.3V.

When the diode is reverse biased, the small current due to minority carriers remain relativelyconstant, that is independent of the bias voltage up to certain voltage. Beyond this safe level of

reverse bias, a phenomenon called Avalanche Breakdown takes place when heavy surge ofcurrent occurs which may also destroy the diode. The diode must be operated within the safe

limit. The limit of the safe operation is specified by the manufacturer under the headingmaximum forward voltage (Vfm ), maximum reverse voltage (Vrm) and Peak forward current

(Ifm).

Procedure:

1. Make the circuit as shown in 4.2, using the silicon diode (IN4004) and 10-K resistoron the breadboard.

2. Set the meter indicated by I to its 7.5mA. Set the meter V to read up 4v. Set on theDC supply kit and voltage from zero to 4V and turn the rotary voltage control fully

anticlockwise (0V).


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3. Now switch on the power supply and carefully turn the voltage control clock wisewhilst watching the ammeter.

4. Set the values of the voltage and observe the values of current. Plot these values on thegraph paper. The resulting graph should show that little current passes until the

voltage has risen to 0.6V (for silicon), but the current rises rapidly with further

increases in voltages.5. Change the resistor value, repeat all previous steps and fill the observation table.6. Finally plot the V-I characteristics of diode on graph paper.7. Also design your circuit on Electronics Workbench, simulate it and note down the

readings to fill the table.

Observation Table:

S.No. Set Voltage Forward Bias(mA) Voltage(V) Reverse Bias(mA)

.1

.2

.3

.4

.5

Review Questions:

1. What do you mean by term Biasing?_____________________________________________________________________

_____________________________________________________________________

2. What is turn on voltage for silicon and germanium at room temperature?_____________________________________________________________________

_____________________________________________________________________

3. What is barrier potential?_____________________________________________________________________

_____________________________________________________________________

4. What is the depletion region?


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_____________________________________________________________________

_____________________________________________________________________

5.

Whether the forward and reverse characteristics of the diode are verified?

_____________________________________________________________________

_____________________________________________________________________


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Experiment # 05

Name: ________________________________ Roll No: _____________________


HALF WAVE RECTIFICATION

Object: To understand the operation of half wave rectification.

Apparatus:1) Oscilloscope


3) IN 4004 diode4) 1-k resistor

5) Electronics Workbench6) Breadboard

Discussion:

A rectifier is a circuit that converts pulsating ac into pulsating dc. There are three basic types ofrectifier circuits: the half wave, full wave (center tapped) and bridge rectifiers. Of them, bridge

rectifier is the most commonly used.

Half wave rectifier:

Half wave rectification is a process, which converts an ac sinusoidal input voltage into a

pulsating dc voltage with the output pulse occurring for each input cycle. The half wave rectifieris made up of a single diode and a resistor. The half wave rectifier conducts the current only

during the positive half cycle of the a.c input supply. The negative half cycle of a.c supply is

suppressed i.e. during the negative half cycle, no current is conducted and hence no voltageappears across the load. Therefore current always flows in one direction (i.e.d.c) through the load

after every half cycle.

Operation:

The a.c voltage is applied across the secondary windings. During the positive half cycle the

diode D1 is forward biased and hence it conducts the current as shown in the Figure 5.1 for the

upper half cycle. During the negative half cycle, diode D1 is reverse bias and no current conductsas shown in Figure 5.1. Therefore the current flows through the diode during the positive half

cycle. In this way, the current flows through the load resistor RL always-same direction. Hence

d.c output is obtained across the RL.


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Figure 5.1 Half wave Rectifier

Ripple Factor (r) :

Ripple factor is very important criteria for measuring the efficiencies of a rectifier. Basically the

variations in the output voltage due to charging and discharging is called ripple. It is formally

defined as the ratio of the ripple voltage in the output voltage delivered to load and the d.ccomponent of the output voltage.

R=Vr.m.s/Vd.cOr alternatively ripple factor can be calculated as

r=(( Vr.m.s/Vd.c)21)

Where Vr.m.s = Vp/2; while Vavg = Vp/

Procedure:

1) Make the half wave circuit diagram as shown in Figure 5-1.2) Observe the rectified output.3) Observe and draw the wave form of (input and output)

Observation:

S.No. p-p(ni)V tuoV

1

2

3

4


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Review Questions:

1. What is Rectification?_____________________________________________________________________

_____________________________________________________________________

2. What is half wave Rectification?_____________________________________________________________________

_____________________________________________________________________

3. What is ripple?_____________________________________________________________________

_____________________________________________________________________

4. What are advantages and disadvantage of half wave rectifier?_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________


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EXPERIMENT # 06

Name: ________________________________ Roll No: _____________________


FULL WAVE RECTIFICATION

Object: To understand the operation of full wave rectification.

Apparatus:1) Oscilloscope



5) Electronics Workbench6) Breadboard

Discussion:

Full wave rectification is the process through which an ac sinusoidal input voltage is converted

into a pulsating dc voltage with two output pulses occurring for each input cycle. There are twomethods to achieve the full eave rectifier.

Center tapped full wave rectification. Bridge full wave rectification.

Center tapped full wave rectification:

The positive half cycle of a.c input voltage makes the diode D1 forward biased and D2 reversebiased. Therefore D1 conducts the current and D2 does not conduct the current, so current will

only flow across D1 through the load resistor RL in upper half cycle as shown in Figure 6-1.

Figure 6-1. Center tapped full wave rectifier

During the negative half cycle of a.c input voltage diode D2 is forward biased while diode D1 is

reverse biased. Therefore D2 conducts the current because D2 is in forward biased conditionwhile D1 does not conduct the current because the D1 is in reverse biased condition. Therefore


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current flows only D2 through the load resistor RL in the upper half cycle as shown in Figure 6-

1.

Bridge full wave rectification

A bridge rectifier makes use of four diodes in a bridge arrangement to achieve full waverectification as shown in Figure 6-2.

Figure 6-2. Bridge full wave rectifier

The bridge rectifier is the most commonly used full wave rectifier circuit for several reasons.1. It does not require a center tapped transformer and therefore can be coupled directly to

the ac power line if desired.

2. Using a transformer with the same secondary voltage produces a peak output voltage thatis nearly double the voltage of the full wave center tapped rectifier. This results in a

higher dc voltage from the supply.

Procedure:

1. Make the center tapped full wave and full wave bridge circuit as shown in Figures

2-1and 6-2 respectively and observe the rectifier output.2. Observe the wave form and draw it on the graph paper.

Observation:

S.No. p-p(ni)V tuoV

1

2

3

4


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Review Questions:

1. What is Full wave Rectification process?_____________________________________________________________________

_____________________________________________________________________

2. What is full wave Bridge Rectification?_____________________________________________________________________

_____________________________________________________________________

3. Compare the two full wave rectifiers?_____________________________________________________________________

_____________________________________________________________________

4. Why cant we implement the Center tapped full wave rectifier without center-tappedtransformer?

_____________________________________________________________________

_____________________________________________________________________

5. Which type of rectifier has high ripple factor?______________________________________________________________________

______________________________________________________________________

6. In bridge rectifier, how many diodes are forward biased during one cycle?______________________________________________________________________

_______________________________________________________________________


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EXPERIMENT # 07

DIODE AS A SERIES CLIPPER

Object: To become familiar with the diode application as series clipper (Diode

Limiter).

Apparatus:

Diode (IN914) Oscilloscope Function Generator Resistor Breadboard Hardwires

Theory:

A circuit which removes the peak of a waveform is known as a clipper. A negative clipper is

shown in Figure 6.1(a). During the positive half cycle of the 5 V peak input,

Figure 6.1(a) Negative Clipper Figure 6.1(b) Positive Clipper

the diode is forward biased. The diode conducts. It is as if the diode were not there. The

positive half cycle is unchanged at the output V(2) in Figure 6.2. Since the output positive

peaks actually overlays the input sine wave V(1), the input has been shifted upward in theplot for clarity.

Figure 6.2: Output of Negative Clipper


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As can be observed from Figure 6.2 the input 5 Vp-p sine wave denoted by V(1) and output

clipped at -0.7 denoted by V(2). During the negative half cycle diode is reverse biased, that

is, non-conducting. The negative half cycle of the sine wave is shorted out. The negative halfcycle of V(2) would be clipped at 0 V for an ideal diode. The waveform is clipped at -0.7 V

due to the forward voltage drop of the silicon diode. The clipping action is only effective

after the input sine wave exceeds -0.7 V.

Positive Series Clipper is shown in Figure 6.1(b) in which the +ve half cycle of input sine

wave is clipped at +0.7V while negative half cycle appears completely.

Procedure:

1. Using the solderless breadboard, construct the circuit shown in Fig.6.1(a) using thefollowing components:

R1 = 3.9 k ohms

D1 = 1N914

2. Calibrate the Oscilloscope by setting it at 1KHz frequency and 1Vp-p voltage.3. Generate the 5 Vp-p from function generator and verify it on oscilloscope.4. Construct the clipper designed in Figure 6.1(a). Use 3.9 k ohms resistor to

limit the current.

5. Make sure you take into account the use of real diodes. Drive the circuit with a 5Vp-psine wave.

6. Visualize the output on oscilloscope across 3.9 K resistor and note down the peakvoltage and frequency of the signal in Table 2.

7. Measure and sketch the input and output waveforms.8.

Repeat the steps from 3-7 for Figure 6.1(b) and note down the peak voltage andfrequency of the signal.

9. Also calculate theoretical values for circuit and draw output waveform from it.Observation:

S.No. Selected

Frequency

Selected Vp-p Output Frequency Output Vp-p

1.

2.

3.

4.


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EXPERIMENT # 08

DIODE APPLICATION AS PARALLEL CLIPPER

Object: To become familiar with the diode application as parallel clipper (Diode

Limiter).

Apparatus:

Diode (IN914) Oscilloscope Function Generator Resistor Breadboard Hardwires

Theory:

Diode application as a parallel clipper is also of two types:

1. Positive Parellel / Shunt Clipper2. Negative Parellel / Shunt Clipper

1. Positive Parallel Clipper:

The circuit for positive parallel clipper is as shown in Figure 7.1.. Here the output is taken across

the diode. During positive half input cycle the output is nearly zero, since, the forward biaseddiode resistance is very small. And during negative half cycle of the input the output is anegative half sinusoidal wave, as shown in Figure 7.1.

Figure 7.1 Positive Parallel Clipper

2. Negative Parallel Clipper:

The action of the negative parallel clipper is quite to that of negative series clipper as during thepositive half input cycle, the diode does not conduct and hence the entire input voltage appears

across the diode. During negative half cycle of the input, diode is forward biased and current


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flows through it, but the voltage drop is nearly zero, hence the output voltage is zero, for ideal

case.

Figure 7.2 Negative Parallel Clipper

Procedure:

1. Using the solderless breadboard, construct the circuit shown in Fig. 7.1 using thefollowing components:

R1 = 3.9 k ohms

D1 = 1N914R2 = 4.7 k ohms

2. Calibrate the Oscilloscope by setting it at 1KHz frequency and 1Vp-p voltage.3. Generate the 5 Vp-p from function generator and verify it on oscilloscope.4. Construct the clipper designed in Figure 7.3.5.

Make sure you take into account the use of real diodes. Drive the circuit with a 5Vp-psine wave from Function Generator.

6. Visualize the output on oscilloscope across 4.7 K resistor and note down the peakvoltage and frequency of the signal.

7. Measure and sketch the input and output waveforms.8. Repeat the steps from 3-7 for inverted diode in Figure 7.3 and note down the peak

voltage and frequency of the signal.

9. Also calculate theoretical values for circuit and draw output waveform from it.

Figure 3.3 Positive Parallel Clipper


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Observation:

Note: Also implement the circuit using Square wave and Rectangular wave from the function

generator.

Conclusion:

Have you become familiar with different types of Parallel/ shunt clipper? What other results u

observed in response to the other signal wave shapes? Comment.

S.No. Selected

Frequency

Selected Vp-p Output Frequency Output Vp-p

1.

2.

3.

4.


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EXPERIMENT # 09

DIODE APPLICATION AS A CLAMPER

Object: To become familiar with the diode application as a Clamper.

Apparatus:

Diode (IN914) Oscilloscope Function Generator Capacitor (1 F) Resistor (3.3 K ohms) Breadboard Hardwires

Theory:

A circuit that places either the positive or negative peak of signal at a desired d.c. level is known

as a clamping circuit. On the other hand we can say that a clamping circuit (or a clamper)essentially adds a d.c. component to the signal.

Clamping circuit broadly divided into two groups namely

Positive Clamper Negative Clamper

Figure 8.1 shows the key idea behind clamping. The input signal is a sine wave having a peaktopeak value of 20 V. the clamper adds the d.c. component and pushes the signal upwards sothat the negative peaks fall on the zero level.

Figure 8.1: General Clamper Response

From Figure 8.1 it is observed that the shape of original signal has not changed: only there is

vertical shift in the signal such as a clamper is called a Positive Clamper. The Negative Clamper

does the reverse i.e. it pushes the signal downwards so that positive peaks fall on the zero level.While observing the output of the clamping circuit following points should be mentioned:


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The clamping circuit does not change the peaktopeak or rms value of the waveform.The input waveform and the clamped output has the same peaktopeak value i.e., 20V from the Figure 8.1.

A clamping circuit changes the peak and average value of a waveform. As in Figure 8.1 itis clear that the input waveform has a peak value of 10V and average value over a cycleis zero. The clamped output voltage varies between 20V and 0V. therefore the peak value

of clamped output is 20V and average value (or d.c. value = (20 + 0)/2 = 10V ) is 10V.

Positive Clamper:

Figure 8.2 shows a circuit of a positive clamper.

Figure 8.2: Positive Clamper

For the proper operation of circuit the charging time is ( Tc = Rf C ) between the diode and

input supply is small as compared to the discharging time ( Td = RL C ). This condition isbased on the fact that voltage across the capacitor will not change during the diode is non conducting. Therefore the discharging time is deliberately made much greater than the charging

time.

Figure 8.3(a):During Negative half cycle Figure 8.3(b):During Positive half cycle

Operation:

During the negative half cycle as in Figure 8.3(a), the diode is forward biased and it behaves asshort circuit, under this condition capacitor will charge to V volts and the output voltage is

directly across the short circuit.

During the positive half cycle, the diode is reversed biased and behaves as an open circuit. Sincethe discharging time is much greater than the time period of the input signal, the capacitor

remains almost fully charged to V volts during the off time of diode, Now by applying KVL to

the input loop:


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V + VVout = 0

Vout = 2V

The resulting waveform is shown in Figure 8.2 where input has been pushed upward by V voltsso that negative peaks fall on the zero level.

Negative Clamper:

Figure 8.4 shows a circuit of a negative clamper where the terminals of diode are reversed.

Figure 8.4: Negative Clamper

Procedure:

1. Use DMM to test the diode.2. Calibrate the oscilloscope.3. Generate the 10Vp-p from function generator and verify it on oscilloscope.4. Construct the circuit shown in Figure 8.2 and 8.4 respectively..5. Visualize the output on oscilloscope across the resistor and note down the peak voltage

and frequency of the signal.

6. Also check the DC level of the signal.7. Construct the output waveform on graph paper.8. Also calculate theoretical values for circuit and draw output waveform from it.


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Observations:

Note: Also implement the circuit using Sinusoidal and Rectangular wave from the function

generator.

Conclusion:

Have you become familiar with different types of clampers? What other results you have

observed in response to other signal shapes?Comment.

S.No. Selected

Vp-p

Selected

Frequency

Output

Vp-p

Output Frequency

1.

2.

3.

4.


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EXPERIMENT # 10

Name: ________________________________ Roll No: _____________________


REVERSE CHARACTERISTICS OF ZENER DIODE

Object: To familiar with reverse characteristics of zener diode and its operation as a

regulator.

Apparatus:

1) Oscilloscope


4) Electronics Workbench5) Breadboard6) Digital Multimeter

7) Variable Power Supply

Discussion:

The Zener diode is a silicon p-n junction device that differs from rectifier diodes because it is

designed for operation in the reverse breakdown region. It is known that when a diode reaches

reverse breakdown, its voltage remains almost constant even though the current changersdrastically. The symbol for Zener diode is given in Figure 9-1.Thus, Zener diode is extensively

used as voltage regulator in power supply circuits. A Zener regular is an electronic device that

maintains a constant output voltage for a range of input voltage.

Figure: 9.1 Zener diode

Zener Breakdown:

Two types of reverse breakdown in a Zener diode are avalanche and Zener. The avalanche

breakdown occurs in both rectifiers and Zener diodes at a sufficiently high reverse voltage due to

the multiplication of the conduction electrons. The zener breakdown occurs in a Zener diode atlow reverse voltages. As Zener diode is heavily doped, the depletion region is very thin. As a

result near the Zener breakdown voltages the field within the depletion region is intense enough

to pull electrons from their valence bands and create current. Zener didoes with breakdownvoltages of less than approximately 5V operate predominately in Zener breakdown. Those with

breakdown voltages greater than 5V operate in avalanche breakdown.


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Characteristics:

The rectifier only operates in forward bias condition, while the Zener diode works in bothforward and reverse bias. In forward bias, Zener diode acts same as the rectifier diode. In reverse

bias, Zener diode limits the current until the breakdown voltage is attained. After the breakdown

voltage, the device enters the region of constant voltage, i.e. the voltage drop across the zenerdiode is essentially constant but the current through the device increases drastically.

Procedure:

1. Make the connections according to Figure 9. 2 (a). In this case the Zener diode isforward biased. Tabulate the different values of voltages and current.

2. Rearrange the circuit as in Figure 9. 2 (b). Again take different readings of currentthrough the load at different values of voltage across Zener diode. Observe the voltagedrop across Zener diode at different input voltages.

3. Draw the characteristic curve of Zener diode (V-I) for both forward and reverse bias andplot them on the graph paper.

Fig 9. 2(a) Forward biased zener diode Fig 9. 2(b) Reverse biased zener diode

Observation Table:

S.No. Forward Bias

Reverse Bias

Voltage (Zener)

Current (mA) Voltage (zener)

tnerruC )Am(

1

2

3


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