Labnote PL243 Electronics

7/29/2019 Labnote PL243 Electronics

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LABORATORY MANUAL

(Analog Electronics)

PL 243 (2011-2012)

School of Physical sciences

NATIONAL INSTRITUTE OF SCIENCE EDUCATION AND RESEARCH

(NISER) BHUBANESWAR


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Last updated: December 2011, Dr. P. K. Sahoo 1

LIST OF EXPERIMENTS (Analog Electronics, PL 243)

1. Familiarization with multimeters, power supplies, function generators, Oscilloscopes;Identification of various components, e.g. resistors, diodes, capacitors etc.

2. Study of I~V characteristics of a linear and a nonlinear resistor3. Study of Charging and Discharging of a capacitor in an RC circuit4. Study of filtering and phase shifting networks (RC/LC circuits)5. Study of an LCR resonant circuit6. Study of normal and zener diode characteristics7. Study of Half wave rectifier circuits without and with filters8. Study of Full wave Bridge rectifier circuits without and with filters9. Setting up a Power Supply using a Zener Diode as Voltage Regulator10. Bipolar Junction Transistor Static Characteristics11. Study of Common Emitter Transistor Amplifier circuit12. Study of a single stage and two Stage RC Coupled Transistor Amplifier13. Study of a regulated power supply using transistor as series and voltage regulator


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LAB #1: IDENTIFICATION OF CIRCUIT COMPONENTS

Breadboards:

In order to temporarily construct a circuit without damaging the components used tobuild it, we must have some sort of a platform that will both hold the components in placeand provide the needed electrical connections. In the early days of electronics, most

experimenters were amateur radio operators. They constructed their radio circuits on

wooden breadboards. Although more sophisticated techniques and devices have been

developed to make the assembly and testing of electronic circuits easier, the concept ofthe breadboard still remains in assembling components on a temporary platform.

Fig. 1: (a) A typical Breadboard and (b) its connection details

A real breadboard is shown in Fig. 1(a) and the connection details on its rear side

are shown in Fig. 1(b). The five holes in each individual column on either side of thecentral groove are electrically connected to each other, but remain insulated from all

other sets of holes. In addition to the main columns of holes, however, you'll note four

sets or groups of holes along the top and bottom. Each of these consists of five separatesets of five holes each, for a total of 25 holes. These groups of 25 holes are all connected

together on either side of the dotted line indicated on Fig.1(a) and needs an external

connection if one wishes the entire row to be connected. This makes them ideal fordistributing power to multiple ICs or other circuits.

(a)

(b)


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Last updated: December 201

These breadboard so

handling. However, there auseful life of the electrical co

Always makeyour experimelectrical sho

Never use larwiring) is an

limitation wit

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never be inser

Never force cDoing so can

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solid hookup

If you follow these basic

experimental components wi

Resistors

Most axial resistors use aidentification is the most co

of four colored bands that aralways coded in ohms (). T

1, Dr. P. K. Sahoo

ckets are sturdy and rugged, and can take q

e a few rules you need to observe, in orderntacts and to avoid damage to components. The

sure power is disconnected when constructing

ntal circuit. It is possible to damage componenk if you leave power connected when making cger wire as jumpers. #24 wire (used for nor

excellent choice for this application. Obse

respect to the size of component leads. sible, use watt resistors in your circuits. when necessary; resistors of higher power r

ted directly into a breadboard socket.omponent leads into contact holes on the bread

amage the contact and make it useless.

stranded wire or soldered wire into the breadbo

e stranded wire (as with an inductor or transa wire nut to connect) the stranded wire to a s

ire, and insert only the solid wire into the brea

rules, your breadboard will last indefinitel

ll last a long time.

attern of colored stripes to indicate resistanmonly used color coding scheme on all resisto

painted around the body of the resistor. Resishe color codes are given in the following table i

Fig. 1: Color codes of Resistors

3

uite a bit of

o extend these rules are:

or modifying

ts or incur anhanges.al telephone

ve the same

watt resistorstings should

board socket.

ard socket. If

former lead),ort length of

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y, and your

e. A 4 bandrs. It consists

or values aren Fig. 1.


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band A is first significant figure of component value

band B is the second significant figure

band C is the decimal multiplier

band D if present, indicates tolerance of value in percent (no color means 20%)

For example, a resistor with bands ofyellow, violet, red, and goldwill have first digit 4(yellow in table below), second digit 7 (violet), followed by 2 (red) zeros: 4,700 ohms.Gold signifies that the tolerance is 5%, so the real resistance could lie anywhere

between 4,465 and 4,935 ohms.

Tight tolerance resistors may have three bands for significant figures rather than two,

and/or an additional band indicating temperature coefficient, in units of ppm/K. For largepower resistors and potentiometers, the value is usually written out implicitly as "10 k",for instance.

Capacitors:

You will mostly use electrolytic and ceramic capacitors for your experiments.

Electrolytic capacitors

An electrolytic capacitor is a type of capacitor that uses an electrolyte, an ionic

conducting liquid, as one of its plates, to achieve a larger capacitance per unit volumethan other types. They are used in relatively high-

current and low-frequency electrical circuits.

However, the voltage applied to these capacitorsmust be polarized; one specified terminal must

always have positive potential with respect to theother. These are of two types, axial and radial

capacitors as shown in adjacent figure. The arrowedstripe indicates the polarity, with the arrows

pointing towards the negative pin.

Fig. 2:Axial and Radial Electrolytic capacitors

Warning: connecting electrolytic capacitors in reverse polarity can easily damage or

destroy the capacitor. Most large electrolytic capacitors have the voltage, capacitance,

temperature ratings, and company name written on them without having any special color

coding schemes.

Axial electrolytic capacitors have connections on both ends. These are most frequentlyused in devices where there is no space for vertically mounted capacitors.

Radial electrolytic capacitors are like axial electrolytic ones, except both pins come outthe same end. Usually that end (the "bottom end") is mounted flat against the PCB and


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the capacitor rises perpendicular to the PCB it is mounted on. This type of capacitor

probably accounts for at least 70% of capacitors in consumer electronics.

Ceramic capacitors are generally non-polarized and almost ascommon as radial electrolytic capacitors. Generally, they use an

alphanumeric marking system. The number part is the same as forSMT resistors, except that the value represented is in pF. They mayalso be written out directly, for instance, 2n2 = 2.2 nF.

Fig. 3: Ceramic capacitors

Diodes:

A standard specification sheet usually has a brief description of the diode. Included in

this description is the type of diode, the major area of application, and any specialfeatures. Of particular interest is the specific application for which the diode is suited.

The manufacturer also provides a drawing of the diode which gives dimension, weight,

and, if appropriate, any identification marks. In addition to the above data, the followinginformation is also provided: a static operating table (giving spot values of parameters

under fixed conditions), sometimes a characteristic curve (showing how parameters varyover the full operating range), and diode ratings (which are the limiting values of

operating conditions outside which could cause diode damage). Manufacturers specifythese various diode operating parameters and characteristics with "letter symbols" in

accordance with fixed definitions. The following is a list, by letter symbol, of the major

electrical characteristics for the rectifier and signal diodes.

RECTIFIER DIODESDC BLOCKING VOLTAGE [VR]the maximum reverse dc voltage that will not cause

breakdown.AVERAGE FORWARD VOLTAGE DROP [VF(AV)]the average forward voltage drop

across the rectifier given at a specified forward current and temperature.

AVERAGE RECTIFIER FORWARD CURRENT [IF(AV)]the average rectified forwardcurrent at a specified temperature, usually at 60 Hz with a resistive load.

AVERAGE REVERSE CURRENT [IR(AV)]the average reverse current at a specified

temperature, usually at 60 Hz.PEAK SURGE CURRENT [ISURGE]the peak current specified for a given number of

cycles or portion of a cycle.

SIGNAL DIODESPEAK REVERSE VOLTAGE [PRV]the maximum reverse voltage that can be applied

before reaching the breakdown point. (PRV also applies to the rectifier diode.)

REVERSE CURRENT [IR]the small value of direct current that flows when a

semiconductor diode has reverse bias.MAXIMUM FORWARD VOLTAGE DROP AT INDICATED FORWARD CURRENT

[V F@IF] the maximum forward voltage drop across the diode at the indicated forward

current.REVERSE RECOVERY TIME [trr]the maximum time taken for the forward-bias

diode to recover its reverse bias.


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The ratings of a diode (as stated earlier) are the limiting values of operating conditions,

which if exceeded could cause damage to a diode by either voltage breakdown oroverheating.

The PN junction diodes are generally rated for: MAXIMUM AVERAGE FORWARD

CURRENT, PEAK RECURRENT FORWARD CURRENT, MAXIMUM SURGE

CURRENT, and PEAK REVERSE VOLTAGE

Maximum average forward current is usually given at a special temperature, usually25 C, (77 F) and refers to the maximum amount of average current that can be permitted

to flow in the forward direction. If this rating is exceeded, structure breakdown can occur.

Peak recurrent forward current is the maximum peak current that can be permitted to

flow in the forward direction in the form of recurring pulses.

Maximum surge current is the maximum current permitted to flow in the forward

direction in the form of nonrecurring pulses. Current should not equal this value for morethan a few milliseconds.

Peak reverse voltage (PRV) is one of the most important ratings. PRV indicates themaximum reverse-bias voltage that may be applied to a diode without causing junction

breakdown. All of the above ratings are subject to change with temperature variations. If,

for example, the operating temperature is above that stated for the ratings, the ratingsmust be decreased.

There are many types of diodes varying in size from the size of a pinhead (used in

subminiature circuitry) to large 250-ampere diodes (used in high-power circuits).Because there are so many different types of diodes, some system of identification is

needed to distinguish one diode from another. This is accomplished with the

semiconductor identification system shown in Fig. 4. This system is not only used fordiodes but transistors and many other special semiconductor devices as well. As

illustrated in this figure, the system uses numbers and letters to identify different types of

semiconductor devices. The first number in the system indicates the number of junctionsin the semiconductor device and is a number, one less than the number of active

elements. Thus 1 designates a diode; 2 designates a transistor (which may be considered

as made up of two diodes); and 3 designates a tetrode (a four-element transistor). The

letter "N" following the first number indicates a semiconductor. The 2- or 3-digit numberfollowing the letter "N" is a serialized identification number. If needed, this number may

contain a suffix letter after the last digit. For example, the suffix letter "M" may be used

to describe matching pairs of separate semiconductor devices or the letter "R" may beused to indicate reverse polarity. Other letters are used to indicate modified versions of

the device which can be substituted for the basic numbered unit. For example, a

semiconductor diode designated as type 1N345A signifies a two-element diode (1) ofsemiconductor material (N) that is an improved version (A) of type 345.


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Fig. 4: Identification of Diode Fig. 5: Identification of Cathode

When working with different types of diodes, it is also necessary to distinguish

one end of the diode from the other (anode from cathode). For this reason, manufacturers

generally code the cathode end of the diode with a "k," "+," "cath," a color dot or band, orby an unusual shape (raised edge or taper) as shown in Fig. 5. In some cases, standard

color code bands are placed on the cathode end of the diode. This serves two purposes:

(1) it identifies the cathode end of the diode, and (2) it also serves to identify the diode by

number.


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Transistors:Transistors are identified bycase of the transistor. If in d

with one having identical

ensure that an identical repla

Example:2

NUMBER OF JUNCTIONS S

(TRANSISTOR)

There are three main series o

Codes beginningThe first letter B is f

letter indicates the tmeans high power au

of the code identifienumbering system.

identify a special verdifferent case style. I

be used, but if the ge

suitable.

Codes beginninTIP refers to the ma

the end identifies ver

Codes beginniThe initial '2N' identi

the particular transist

TESTING A TRANSISTOis good or bad can be done

or transistor tester. PRECA

taken when working with traare susceptible to dama

overloads, heat, humidityTRANSISTOR LEAD I

plays an important pa

maintenance because beforetested or replaced, its leads

Since there is NO stanidentifying transistor leads, c

lead identification scheme

manual before attemptin

transistor. Identification of

1, Dr. P. K. Sahoo

a Joint Army-Navy (JAN) designation printed dubt about a transistor's markings, always repla

arkings, or consult an equipment or transist

ement or substitute is used.

N 130MICONDUCTOR IDENTIFICATION FIRST M

NUMBER

f transistor codes used:

with B (or A), for example BC1r silicon, A is for germanium (rarely used now

pe; for example C means low power audiodio frequency; F means low power high freque

the particular transistor. There is no obviouometimes a letter is added to the end (eg

ion of the main type, for example a higher curf a project specifies a higher gain version (BC1

neral code is given (BC108) any transistor wit

g with TIP, for exampleufacturer: Texas Instruments Power transistor.

ions with different voltage ratings.

g with 2N, for examplefies the part as a transistor and the rest of the c

r. There is no obvious logic to the numbering s

to determine if itwith an ohmmeter

TIONS should be

nsistors since theye by electrical

, and radiation.ENTIFICATION

t in transistor

a transistor can beust be identified.

dard method ofheck some typical

or a transistor

to replace a

leads for some

8

irectly on thee a transistor

r manual to

AODIFICATION

08, BC478. The second

requency; Dncy. The rest

logic to theBC108C) to

rent gain or a08C) it must

that code is

TIP31AThe letter at

2N3053de identifies

ystem.


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common case styles is show

Testing a transistor

Transistors are basically ma7). We can use this analogy

by testing its Resistancedifferent leads, Emitter, Base

Testing with a multime

Use a multimeter or a simple

resistor and LED) to check e

conduction. Set a digital mul

and an analogue multimeter trange.

Test each pair of leads bot

total):

The base-emitter (Bbehave like a diode a

The base-collector (way only.

The collector-emitteThe diagram shows how t

reversed in a PNP transistor

Transistor Resistance

Between Trans

Collector

Collector

Emitter

Emitter

Base

Base

1, Dr. P. K. Sahoo

in Fig. 6. F

e up of two Diodes connected together back-o determine whether a transistor is of the type

between the threeand Collector.

er

tester (battery,

ch pair of leads for

imeter to diode test

o a low resistance

ways (six tests in

) junction should

d conduct one way only.

C) junction should behave like a diode and co

(CE) should not conduct either way.

e junctions behave in an NPN transistor. T

ut the same test procedure can be used.

Values for the PNP and NPN transist

istor Terminals PNP NP

Emitter RHIGH RHIGBase RLOW RHIG

Collector RHIGH RHIGBase RLOW RHIG

Collector RHIGH RLOEmitter RHIGH RLO

Fig. 7: Testing an NP

9

g. 6

to-back (Fig.PNP or NPN

duct one

e diodes are

r types

N transistor


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Lab # 2: I~V characteristics of Linear and Nonlinear Resistor

Objective:

To study the I ~ V characteristics of a linear and a nonlinear resistor (the filament

of an incandescent lamp)

Brief overview:

One of the most basic properties of any electrical device is the amount of current I

that flows when a known voltage V is applied to the device. A plot of the current as a

function of the voltage is usually called the "I-V characteristic" of the device. The I-Vcharacteristic is often a complicated curve, which may change as the temperature of the

device changes, as light hits the device and so on. Sometimes these changes are used to

sense temperature, light level or some other variable, but at other times any change is a

nuisance. Whatever the I-V curve looks like, it is customary to define the ratio V/I as the

resistance, R, of the device at a particular current, temperature, light level etc. When V is

in volts and I in amperes, R is in ohms.

Ohm's Law:

In a circuit, there exists a definite relationship between the current I flowing a

resistor R and the voltage V applied to the resistor. This relationship is called as Ohm's

law and is expressed as

V = IR

where R is a constant.

Linear Resistor:

A linear resistor is one whose value remains constant, i.e. it does not depend on

applied voltage. Such a resistor obeys Ohm's Law and said to be "ohmic". Thus the I-V

curve for a linear resistor is simply a straight line through the origin.

Nonlinear Resistor:


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It is the resistor in which there is no direct relationship of voltage and current.

Such a resistor has a nonlinear I~V characteristic. Example: A tungsten filament in an

electric bulb.

The electrical resistance depends on the temperature and it can be expressed as

follows

R/R = . T

where R is the change in resistance R due to a change in temperature T and is the

temperature coefficient of resistance. So, if is positive, R is expected to increase with

increase in temperature. Current flowing in a nonlinear resistor heats it and thereby

increasing R. Thus increasing the applied voltage will not increase the current

proportionately due to increased resistance.

Static resistance:

The static resistance at any voltage can be determined from the ratio of the voltage to

current at that particular voltage.

R = V/I

Dynamic Resistance:

The dynamic resistance can be determined at a particular voltage by taking the ratio of an

infinitesimally small change in voltage at that point to the corresponding change in

current.

(Rdynamic)V = (V/I)V

Circuit Components/Equipments:

(i) D.C. Power supply, (ii) a Resistor, (iii) Incandescent Lamp, (iv) 2 multimeters (v)

Connecting wires and (vi) Breadboard.

Circuit Diagram:

R Incandescent Lamp

D.C. Power

SupplymA

V mAV


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Procedure:

1. Read the resistance value of the given resistor from its color code. Use a

multimeter to measure its exact resistance.

2. Make necessary connections as shown in the circuit diagram.

3. Switch on the power supply and start applying different voltages (0-10V) to the

resistor.

4. Measure the current I (mA) flowing in the circuit and the voltage V (Volt) drop

across the resistor using the two multimeters.

5. Plot I (Y-axis) ~ V (X-axis) curve, which should pass through the origin. Find the

slope of the plot to determine the resistance and compare it to the measured value.

6. Now take an incandescent lamp and note down its specifications. Measure its

room temperature resistance.

7. The two terminals of the lamp are connected with wires to facilitate the circuit

configuration on the breadboard. Configure the circuit as shown in the circuit

diagram.

8. Repeat steps 3 and 4 to determine I and V. Keep the intervals as small as possible

in order to acquire more data. Care should be taken that the applied voltage to the

lamp should not exceed its voltage rating.

9. Plot the I~V curve, which will have a varying slope. Determine the static and

dynamic resistance at any operating point. Also plot R ~ V.

Observations:

Resistance of the given resistor = ______ (by color code, see note at the end*)

= ______ (using multimeter)

Ratings of the given incandescent lamp = __________

Resistance of the filament at room temp. = ________ (using multimeter)


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Table: 1.For Linear Resistor

Observation Voltage applied Voltage across R Current Resistance

Number (Volt) V (Volt) I (mA) R = V/I (k)

1

2

..

10

Mean R = ______

Table: 2.For nonlinear resistor

Observation Voltage applied Voltage across R Current Resistance

Number (Volt) V (Volt) I (mA) R = V/I (k)

1

2

..

10

Calculations from Graph:

Resistance of the linear resistor = _________

Static resistance of the nonlinear resistor= __________ at ___ V

Dynamic resistance of the nonlinear resistor = ________ at ___ V

Discussions and Conclusions:

1. Discuss the graphs.

2. Comment on the specific behavior of I~V and R~V curve for incandescent lamp.

Precautions:


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* Appendix: Resistor Color Code

Resistor Color Code

first & second bands(first & second digits)

third band(multiplier)

fourth band(tolerance)

black 0 black 1 none 20%

brown 1 brown 10 silver 10%

red 2 red 100 gold 5%

orange 3 orange 1,000

yellow 4 yellow 10,000

green 5 green 100,000

blue 6 blue 1,000,000

violet 7 silver 0.01

gray 8 gold 0.1

white 9


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Lab # 3: Charging and Discharging of a Capacitor in an RC circuit

Aim:

1. To study the charging and discharging of a capacitor in RC circuit and to estimate

the time constant.

2. To study the current flow in a capacitor during charging and discharging and to

estimate the time constant.

3. To verify Kirchhoffs law during charging and discharging of a capacitor.

Circuit Components:

(ii)D.C. Power supply, (ii) Resistors, (iii) Electrolytic Capacitors, (iv) Multimeters,

(v) Stop watch, (vi) Connecting wires, (vii) Breadboard.

Circuit Diagram:

(* For charging: S1 closed and S2 open. For discharging: S1 open and S2 closed)

Brief Theory:

A capacitor is a passive device that stores energy in its electric field and returns

energy to the circuit whenever required. It consists of two conducting plates separated by

an insulating material or dielectric. When the capacitor is connected to a battery current

will flow and the charge on the capacitor will increase until the voltage across the

capacitor, determined by the relationship C=Q/V, is sufficient to stop current from

mA

VC

S1

S2

R

CV0

+

_

VR


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flowing in the circuit. A fully discharged capacitor initially acts as a short circuit (current

with no voltage drop) when faced with the sudden application of voltage. After charging

fully to that level of voltage, it acts as an open circuit (voltage drop with no current).

In a resistor-capacitor charging circuit (S1 closed and S2 open in the circuit

diagram), capacitor voltage goes from 0 to full source voltage V0 while current goes from

maximum, I0, to zero, both variables changing most rapidly at first, approaching their

final values slower and slower as time goes on. During discharging (S1 open and S2

closed in the circuit diagram), the source is cut out of the circuit and capacitor discharges

through the resistor from its maximum acquired voltage. The voltages across the

capacitor with respect to time during charging and discharging are respectively given by

)(

),1(

0

0

RC

t

C

RC

t

C

eVV

eVV

=

=

Similarly, the time variation of current flowing in the circuit during charging and

discharging, respectively, can be expressed as follows:

)(

)(

0

0

RC

t

RC

t

eII

eII

=

=

Note that the current flow shows the same behavior during charging and dischargingexcept that the direction of flow of discharge current is opposite to that of charging

current, hence the negative sign.

Time constant: The time required to charge a capacitor to 1-(1/e) times its maximum

value (63.2%) or to discharge it to 1/e times (36.8%) its initial voltage is known as the

time constant of the circuit. This is given by the product of resistance and capacitance

(RC) of the circuit, which has the dimension of time. Thus the rate of charging and

discharging of a capacitor in an RC circuit depends on the circuit components. If t1/2 is

defined as the time required by the capacitor to attain to half of its maximum voltage V0,

then it can be easily shown that

RCt 69.02/1 =

The above equation can be used to estimate the time constant of the circuit.


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Kirchhoffs law:

According to Ohms Law, the voltage across the resistor will be VR= IR, while the voltageacross the capacitor will be given by V

C=Q/C. By Kirchhoffs Rule the voltage changes

around the circuit must add to zero so

00 = CR VVV

Since, during charging voltage across capacitor keeps increasing with time, the voltage drop

across resistor goes on falling in order to maintain V0 at a constant value, i.e. at any instant t,

0)()( VtVtV RC =+

During discharging, the capacitor discharges through the resistor and the power supply is out

of the circuit. Around this loop the sum of voltages at any instant is now given by0)()( =+ tVtV RC

Procedure:

(I) Charging and discharging of a capacitor:

1. Connect the circuit as per the circuit diagram. Make sure that the capacitor is

discharged completely before starting the experiment. Please check only one of

the switches is on at a given time.

2. Switch on the power supply and adjust it to be at 15 Volts.

3. Estimate the time constant (RC) of the circuit from the supplied components and

hence the approximate time needed to charge the capacitor fully (practically, this

is about 5RC). Accordingly decide the time interval for which the voltage

readings to be measured.

4. Close S1 (check S2 open), simultaneously start measuring the voltage drop across

capacitor using the multimeter for each prefixed time interval with the help of a

stop-watch, till there is no significant change in the voltage reading for

considerably long time.


19/83


5. Open S1 and close S2. Once again, note down the readings on the multimeter for

the prefixed time interval, till there is no significant change in the voltage reading

for considerably long time.

6. Plot VC~t for both charging and discharging. Find t1/2 from graph corresponding to

VC V0/2. Determine RC = 0.693 t1/2.

(II) Current flow in a capacitor during charging and discharging

1. Repeat the steps from 1-3 of procedure (I). You dont need the second multimeter

reading VC.

2. Close S1, simultaneously start taking the readings of the multimeter for each

prefixed time interval with the help of a stop-watch, till there is no significant

change in the reading for considerably long time.

3. Open S1 and close S2. Once again, note down the current readings on the

multimeter for the prefixed time interval, till there is no significant change in the

reading for considerably long time. Note the negative sign in the current reading.

4. Plot I~t for both charging and discharging. Find t1/2 from graph corresponding to

I I0/2. Determine RC = 0.693 t1/2.

(III) Verification of Kirchhoffs voltage law during charging and dischargingof a capacitor

1. Discharge the capacitor. Connect the circuit for charging as per the circuit

diagram (S1 closed and S2 open). Connect the multimeter across R instead of C

this time. You may not connect the other multimeter in series as you dont need to

measure current in this part of experiment.

2. Measure VR at the same interval as VC was measured earlier.

3. Open S1 and close S2. The circuit for discharging is ready.

4. Measure VR once again in similar fashion as before.

5. Plot VR and VC on the same plot for charging and show that, at any instant

VR + VC = V0.


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6. Plot VR and VC on the same plot for discharging and show that, at any instant

VR + VC = 0.

Observation Tables:

R = -----------, C = -------------, RC = -------------, Supply Voltage = ---------

(I) Charging and discharging of a capacitorTime,t

(sec)

VC (Volt)

Charging Discharging

0..

..

(II)Current flow during charging and discharging

Time,t

(sec)

I (mA)


0

..

..

(III) Verification ofKirchhoffs law during charging and discharging

Time, t(sec)


VR (volt) VR +VC (volt) VR (volt) VR +VC (volt)

0....

Graphs: (I) Plot VC~t for both charging and discharging and estimate time constant.

(II)Plot I~t for both charging and discharging and estimate time constant.

(III) Plot VR and VC on the same plot for charging and discharging and

verify, respectively, VR + VC = V0 and VR + VC = 0.

Results and Discussion:

Precautions:


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Pass

Band Stop

Band

|H(j)|

c

Fig. 1: LPF

1. Since the capacitors used here are electrolytic ones, care must be taken to

connect it in the circuit with correct polarity, i.e. positive terminal of capacitor

should be connected to the positive terminal of the power supply.

2. Take extreme care not to close both S1 and S2 simultaneously which might

damage the power supply.

________________________________________________________________________

Lab#4 RC CIRCUIT AS A FILTERING AND PHASE SHIFTING NETWORK

OBJECTIVES:

(I)To study the transfer function and phase shift of a low pass RC filter network.(II) To study the transfer function and phase shift of a high pass RC filter network.

OVERVIEW:

Filter circuits are used in a wide variety of applications. In the field of

telecommunication, band-pass filters are used in the audio frequency range (20 Hz to 20kHz) for modems and speech processing. High-frequency band-pass filters (several

hundred MHz) are used for channel selection in telephone central offices. Data

acquisition systems usually require anti-aliasing low-pass filters as well as low-pass noise

filters in their preceding signal conditioning stages. System power supplies often useband-rejection filters to suppress the 50-Hz line frequency and high frequency transients.

Frequency-selective or filter circuits pass only

those input signals to the output that are in a desiredrange of frequencies (called pass band). The amplitude

of signals outside this range of frequencies (called stop

band) is reduced (ideally reduced to zero). Thefrequency between pass and stop bands is called the cut-

off frequency (c). Typically in these circuits, the inputand output currents are kept to a small value and as such,

the current transfer function is not an importantparameter. The main parameter is the voltage transfer

function in the frequency domain, Hv(j) = Vo/Vi.Subscript v of Hv is frequently dropped. As H(j) iscomplex number, it has both a magnitude and a phase, filters in general introduce a phase

difference between input and output signals.

LOW AND HIGH-PASS FILTERSA low pass filter or LPF attenuates or rejects

all high frequency signals and passes only lowfrequency signals below its characteristic frequency

called as cut-off frequency, c. An ideal low-passfillter's transfer function is shown in Fig. 1. A high

|H(j)|

Pass

Band

Stop

Band

Fig. 2: HPF

c


22/83


1

0.7

|H(j)|

10.7

pass filter or HPF, is the exact opposite of the LPF circuit. It attenuates or rejects all lowfrequency signals and passes only high frequency signals above c.

In practical filters, pass and stop bands are not clearly defined, |H(j)| variescontinuously from its maximum towards zero. The cut-off frequency is, therefore,

defined as the frequency at which |H(j)| is reduced to 1/2 or 0.7 of its maximum value.This corresponds to signal power being reduced by 1/2 as P V2.

c c

Fig.3: Transfer functions of practical low and high pass filter

RC Filter:

The simplest passive filter circuit can be made by connecting together a single resistorand a single capacitor in series across an input signal, (Vin) with the output signal, (Vout)

taken from the junction of these two components. Depending on which way around we

connect the resistor and the capacitor with regards to the output signal determines the

type of filter construction resulting in either a Low Pass or a High Pass Filter. As thereare two passive components within this type of filter design the output signal has

amplitude smaller than its corresponding input signal, therefore passive RC filters

attenuate the signal and have a gain of less than one, (unity).

Low-pass RC Filter

A series RC circuit as shown also acts as a low-pass filter. For no load resistance (output

is open circuit, R ):

RCjV

VjH

VRCj

VCjR

CjV

i

ii

++++========

++++====

++++====

1

1)(

)(1

1

)/1(

)/(1

0

0

To find the cut-off frequency (c), we note

2)(1

1)(

RCjH

++++

====

When 0, |H(j)| is maximum and 1. Fig.4: Low pass RC filter circuit

|H(j)|


23/83


For = c, |H(jc)| = 1/2. Thus

)(tan,

1

1)(,

1

1)(,

1

2

1

)(1

1)(

1

2

2

c

cc

c

c

c

phaseandjH

j

jH

RC

RCjH

====

++++

====

++++

========

====

++++

====

Input Impedance:

22

2 11

CRZand

CjRZ ii

++++====++++====

The value of the input impedance depends on the frequency . For good voltagecoupling, we need to ensure that the input impedance of this filter is much larger than the

output impedance of the previous stage. Thus, the minimum value of Zi is an important

number. Zi is minimum when the impedance of the capacitor is zero (), i.e. Zi|min =R.

Output Impedance:The output impedance can be found by shorting the source and finding the equivalentimpedance between output terminals:

RZ ====0 ||Cj

1

where the source resistance is ignored. Again, the value of the output impedance also

depends on the frequency . For good voltage coupling, we need to ensure that the outputimpedance of this filter is much smaller than the input impedance of the next stage, the

maximum value of Z0 is an important number. Z0 is maximum when the impedance of thecapacitor is (0), i.e. Z0|max = R.

Bode Plots and Decibel

The ratio of output to input power in a two-port network is usually expressed in Bell:

====

====

ii V

V

P

P 010

0

10 log2logBelsofNumber

Bel is a large unit and decibel (dB) is usually used:

====

====ii V

V

P

P 010

0

10 log20log10decibelsofNumber

There are several reasons why decibel notation is used:

1) Historically, the analog systems were developed first for audio equipment. Human earhears" the sound in a logarithmic fashion. A sound which appears to be twice as loud

actually has 10 times power, etc. Decibel translates the output signal to what ear hears.


24/83


2) If several two-port network are placed in a cascade (output of one is attached to theinput of the next), it is easy to show that the overall transfer function, H, is equal to the

product of all transfer functions:

...)()()(

...)(log20)(log20)(log20

...)()()(

21

21011010

21

++++++++====

++++++++====

====

dBdBdBjHjHjH

jHjHjH

jHjHjH

making it easier to understand the overall response of the system.

3) Plot of |H(j)|dB versus frequency has special properties that again makes analysissimpler as is seen below.

For example, using dB definition, we see that, there is 3 dB difference between maximumgain and gain at the cut-off frequency:

dBjH

jHjHjH

c

c 3

2

1log20

)(

)(log20)(log20)(log20

max

10max1010====

========

Bode plots are plots of magnitude in dB and phase of H(j) versus frequency in a semi-log format. Bode plots of first-order low-pass filters (include one capacitor) display the

following typical characteristics:

Fig.5: Bode Plots for low-pass RC filter

At high frequencies, /c>>1, |H(j)| 1/(/c) and |H(j)|dB = 20 log (c)-20 log ,which is a straight line with a slope of -20 dB/decade in the Bode plot. It means that ifis increased by a factor of 10 (a decade), |H(j)|dB changes by -20 dB.


25/83


At low frequencies /c1, 090 and at low frequencies, /c


26/83


Fig.7: Bode Plots for high-pass RC filter

Circuit Components/Instruments:

(i) Resistor (5.6 k

), (ii) Capacitor (10 kpF), (iii) Function generator, (iv) Oscilloscope,

(v) Connecting wires, (vi) Breadboard

Circuit Diagrams:

(Low pass RC filter) (High pass RC filter)


27/83


Procedure:

1. Begin lab by familiarizing yourself with the function generator and oscilloscope.2. Read and also measure the values of R and C.

3. Using the scope set the function generator to produce a 10 V(pp) sine wave. Thissignal will be used for the input. Do not change the amplitude of this signal duringthe experiment.

4. Set up the low/high pass RC filter on the breadboard as shown in the circuitdiagram. Use the function generator to apply a 10 V(pp) sine wave signal to theinput. Use the dual trace oscilloscope to look at both V

inand V

out. Be sure that the

two oscilloscope probes have their grounds connected to the function generator

ground.

5. For several frequencies between 20 Hz and 20 kHz (the audio frequency range)measure the peak-to-peak amplitude of V

out. Check often to see that V

inremains

roughly at the set value and that VOLTS/DIV dials are in their calibrated

positions. Take enough data (at least up to 10 times the cut-off frequency, for lowpass and down to 1/10 times cut-off frequency, for high pass filter) so as to makeyour analysis complete. If needed use the STOP button of oscilloscope at a

desired frequency to acquire data.

6. From your measurements determine the ratio

)(

)()(

ppV

ppV

V

VjH

i

o

i

o========

and compute this ratio by using the formula

2

1

1)(

++++

====

c

jH

, for low pass filter and

2

1

1)(

++++

====

c

jH , for high pass filter

7. For each listed frequency, measure the phase shift angle with proper sign as

shown in the diagram below.


28/83


8. The phase shift angle in degrees is 0360

====

T

T

9. Compute the phase shift angle for each frequency for low/high pass filter.Observations:

R = _____________, C = ___________

(I) For Low Pass Filter: Vin(pp) = _______, c = 1/RC = ________(a)Table for |H(j)|:

Sl.

No.

Frequency,

f (kHz)

( = 2f) c

V0(pp)

(Volt)

|H(j)|=

)(

)(

ppV

ppV

i

o

|H(j)|dB2

1

1)(

++++

====

c

jH

1 0.02

2 ..

.. ..

.. ..

(b)Table for phase angle:Sl.

No.

Frequency,

f (kHz)

( = 2f) c

T(ms)

T

(ms)0360

====

T

T

(deg)

)(tan 1

c

====

(deg)

1 0.02

2 ..

.. ..

.. ..

(II) For High Pass Filter:Vin(pp) = _______, c = 1/RC = ________(c)Table for |H(j)|:

Sl.

No.

Frequency,

f (kHz)( = 2f)

c V0(pp)

(Volt)

|H(j)|=

)(

)(

ppV

ppV

i

o

|H(j)|dB2

1

1)(

++++

====

c

jH

1 0.02

2 ..


29/83


.. ..

.. ..

(d)Table for phase angle:

Sl.No.

Frequency,f (kHz)

( = 2f)

c T

(ms)T

(ms)0360

====

T

T

(deg)

)(tan 1

c====

(deg)

1 0.02

2 ..

.. ..

.. ..

Graphs: Trace and study bode plots of |H(j)|dB and versus f(2) in a semi-logformat for low/high pass RC filter. Determine the cut-off frequency from graph. Also,estimate the frequency roll-off for each filter.

Discussions:

Precautions:

________________________________________________________________________


30/83


Lab # 5: Study of LCR Resonant Circuit

Objectives:

(i) To study the behavior of a series LCR resonant circuit and to estimate theresonant frequency and Q-factor.

(ii) To study the behavior of voltage drop across inductor and capacitor and henceestimate the resonant frequency.

Overview:

Circuits containing an inductor L, a capacitor C, and a resistor R, have special

characteristics useful in many applications. Their frequency characteristics (impedance,

voltage, or current vs. frequency) have a sharp maximum or minimum at certain

frequencies. These circuits can hence be used for selecting or rejecting specific

frequencies and are also called tuning circuits. These circuits are therefore very important

in the operation of television receivers, radio receivers, and transmitters.

Let an alternating voltage Vibe applied to an inductor L, a resistor Rand a capacitor Call in

series as shown in the circuit diagram. IfI is the instantaneous current flowing through the

circuit, then the applied voltage is given by

IC

LjRVVVVcdCLRi cd

++++====++++++++==== )

1(.... (1)

Here Rd.c. is the total d.c. resistance of the circuit that includes the resistance of the pure

resistor, inductor and the internal resistance of the source. This is the case when the

resistance of the inductor and source are not negligible as compared to the load resistance

R. So, the total impedance is given by

++++==== )

1(..

C

LjRZcd

(2)

The magnitude and phase of the impedance are given as follows:

2/1

22

.. )1

(

++++====

CLRZ cd

(3)


31/83


..

)1

(

tancdR

CL

==== (4)

Thus three cases arise from the above equations:

(a)L > (1/C), then tan is positive and applied voltage leads current by phase

angle .

(b)L < (1/C), then tan is negative and applied voltage lags current by phase

angle .

(c)L = (1/C), then tan is zero and applied voltage and current are in phase. Here

VL = VC, the circuit offers minimum impedance which is purely resistive. Thus

the current flowing in the circuit is maximum (I0) and also VR is maximum andVLC (VL+VC) is minimum. This condition is known as resonance and the

corresponding frequency as resonant frequency (0) expressed as follows:

LCfor

LC

2

1100 ======== (5)

At resonant frequency, since the impedance is minimum, hence frequencies near f0 are

passed more readily than the other frequencies by the circuit. Due to this reason LCR-

series circuit is calledacceptor circuit. The band of frequencies which is allowed to pass

readily is called pass-band. The band is arbitrarily chosen to be the range of frequencies

between which the current is equal to or greater thanI0/2. Letf1andf2 be these limiting

values of frequency. Then the width of the band isBW=f2f1.

The selectivity of a tuned circuit is its ability to select a signal at the resonant frequency

and reject other signals that are close to this frequency. A measure of the selectivity is the

quality factor (Q), which is defined as follows:

CRR

L

ff

fQ

cdcd 0....

0

12

01

========

==== (6)

In this experiment, you will measure the magnitude and phase of VR and VLC with respect

to Vi ((VR/Vi),(VLC/Vi) , R andLC in the vicinity of resonance using following

working formulae.


32/83


Z

R

V

V

i

R==== (7)

====

..

1

1

tancd

RR

CL

(8)

andZ

CL

V

V

i

LC 1

==== (9)

====

CL

R cdLC

1

tan,.1 (10)

Circuit Components/Instruments:

(i) Inductor, (ii) Capacitor, (iii) Resistors, (iv) Function generator, (v) Oscilloscope, (vi)

Multimeter/LCR meter, (vii) Connecting wires, (viii) Breadboard

Circuit Diagram:

Procedure:

(I) Measuring VR, VLC andR,LC:

(a)Using the multimeter/LCR meter, note down all the measured values of the

inductance, capacitance and resistance of the components provided. Also,

1

2

3

4


33/83


measure the resistance of the inductor. Calculate the d.c. resistance of the circuit.

Calculate the resonant frequency.

(b)Configure the circuit on a breadboard as shown in circuit diagram. Set the

function generator Range in 20 KHz and Function in sinusoidal mode. Set an

input voltage of 5V (peak-to-peak) with the oscilloscope probes set in X1

position. Set the function generator probe in X1 position.

(c)Feed terminals 1,4 in the circuit diagram to channel 1 and 3,4 to channel 2 of the

oscilloscope to measure input voltage Vi and output voltage VR, respectively.

Note that terminal 4 is connected to the ground pin of the function generator and

oscilloscope.

(d)Vary the frequency in the set region slowly and record VR and Vi (which may not

remain constant at the set value, guess why?). Read the frequency from

oscilloscope.

For each listed frequency, measure the phase shift angle Rwith proper sign as

shown in the diagram below using the expression, 0360(deg)

====

T

TR .

(e)Replace the resistor with another value and repeat steps (c) and (d). No phase

measurement is required.

(f) Now, interchange the probes of the function generator and oscilloscope, i.e. make

terminal 1 as the common ground so that you will measure VLC output between

terminal 3 and 1 and Vi between 4 and 1. Repeat step-(d) to record VLC, Vi and

LC.

(II) Measuring VL and VC:


34/83


(a)Go back to the original circuit configuration you started with. Interchange R with

L to measure Vi and VL (see steps (c) and (d) of the previous procedure).

Calculate VL/Vi for each frequency.

(b)Now, interchange the inductor with capacitor and measure Vi and VC. Calculate

VC/Vi for each frequency.

Observations:

L = _________ mH, C = ________ F,LC

f2

10 ==== = _________ kHz

Internal resistance of inductor = _________

Output impedance of Function generator = __________

Table:1 R1 = _______ Sl.No. f

(kHz)

Vi

(V)

VR

(V)

VR/Vi VR/Vi

(Calculated)

R R

(Calculated)

Table:2 R2 = _______

Sl.No. Frequency,f

(kHz)

Vi

(V)

VR

(V)

VR/Vi VR/Vi

(Calculated)

Table:3 R1 = _______

Sl.No. Frequency,f

(kHz)

Vi

(V)

VLC

(V)

VLC/Vi VLC/Vi

(Calculated)

LC

(deg)

LC(deg)

(Calculated)


35/83


Table:4 R1 = _______

Sl.No. f

(kHz)

Vi

(V)

VL

(V)

VL/Vi

Table: R1 = _______

Sl.No. f

(kHz)

Vi

(V)

VC

(V)

VC/Vi

Graphs:

(a)Plot the observed values of VR/Vi, VLC/Vi, R and LC versus frequency.

Estimate the resonant frequency.

(b)Plot VR/Vi versus frequency for both the resistors on the same graph-sheet and

compare their behavior. Estimate the Q-factor in each case and compare with

calculated values.


36/83


(c)Plot VL/Vi and VC/Vi versus frequency on the same graph-sheet and estimate the

resonant frequency from the point of intersection and compare with other

estimations.

Discussions/Results:

Precautions: Make the ground connections carefully.

Lab # 6: Study of Normal and Zener Diode Characteristics

Objectives:

i) To study and plot the forward and reverse bias characteristics of a normal diode

and to determine the threshold voltage, static and dynamic resistance.

ii) To study and plot forward and reverse bias characteristics of a zener diode and to

determine the threshold and zener break-down voltage.

Overview:

A diode is a nonlinear circuit element. The symbol of a diode and a real

commercial diode is shown in Fig. 1. Generally there is a band marked at its cathode for

its identification. There exists another type of diode known as zener diode, which has a

heavily doped PN junction.

Fig. 1The theoretical equation for the diode currentID is

==== 1)(exp

T

D

SDnV

VII

ANODE

D1

DIODE

CATHODE


37/83


where VD is the diode voltage drop, IS is the saturation current, n is the emission

coefficient, and VT = kT/q ( 0.026V at T=300K) is the thermal voltage. The emission

coefficient accounts for recombinations of electrons and holes in the depletion region,

which tend to decrease the current. For discrete diodes, it has the value n is 2 .

The I~V characteristic of an ideal diode is shown in Fig. 2-a. Under forward biased

condition of a real PN junction diode, the P-side is connected to the positive and N-side is

connected to the negative terminal of the power supply. This reduces the potential barrier.

As a result current flows from P to N-type in forward direction. When the applied voltage

is more than the barrier potential, the resistance is small (ideally 0) and the current

increases rapidly. This point is called the Knee-point or turn-on voltage or threshold

voltage (Fig. 2-b). This voltage is about 0.3 volts for Ge diodes and 0.7 volts for Si

diodes.

Under reverse biased condition, the P-side of the junction diode is connected to the

negative and N-side is connected to the positive terminal of the power supply. This

increases the potential barrier due to which no current should flow ideally. But in

practice, the minority carriers can travel down the potential barrier to give very small

current. This is called as the reverse saturation current. This current is about 2-20 A

for Ge diodes and 2-20 nA for Si diodes (the values might differ for diodes of different

makes).

However, if the reverse bias is made too high, the current through the PN junction

increases abruptly. The voltage at which this phenomenon occurs is known as the break-

down or reverse voltage and the mechanism involved depends on the construction of the

diode. In conventional diodes with a lightly doped junction, application of higher reverse

voltage leads to large number of carriers produced by collision of thermally generated

electrons and the phenomenon is called avalanche breakdown. When the reverse bias

exceeds this breakdown voltage, a

conventional diode is subject to high

curre

nt.

Unle


38/83


ss this current is limited by external circuitry, the diode will be permanently damaged. If

the junction is heavily doped with narrow depletion layers, break-down occurs when the

reverse voltage is strong enough to rupture the covalent bonds generating large number

of electron-hole pairs. This phenomenon is calledzener breakdown.

Fig. 2 (a) Fig. 2 (b)

Zener diode:

It is a reverse biased heavily doped PN junction diode generally operated in zener

breakdown region. Zener voltage is the reverse voltage above which there is a controlled

breakdown which does not damage the diode. The voltage drop across the diode remains

constant at zener voltage no matter how high the reverse bias voltage is. The forward

characteristic of a zener diode is similar to a normal diode. The symbol of a zener diode

is shown in Figure 3.

Fig. 3

Static and Dynamic Resistance:

At a given operating point, the static

and dynamic resistance of a diode can be

determined from its characteristics as shown in

KNEE

VOLTAGE


39/83


Fig. 4. The static or dc resistance, RD, of the diode at the operating point (the point

where the load line intersects the diode characteristics), Q, is simply the quotient of the

corresponding levels of VD and ID. The dc resistance levels at the knee and below will be

greater than the resistance levels obtained for the vertical rise section of the

characteristics. Fig. 4

RD = VD/ID

The diode circuits generally operate with varying inputs, which will move the

instantaneous operating point up and down a region of the characteristics and defines a

specific change in current and voltage. Dynamic or ac Resistance, rd, is defined as the

quotient of this change in voltage and change in current around the dc operating point.

rd = VD/ID

Components/Equipments:

(i) Junction diodes (Si,Ge), (ii) Zener diode, (iii) A current limiting Resistor (1k), (iv)

D.C. Power supply, (iv) 2 multimeters and (vi) Breadboard, (vii) Connecting wires

Circuit Diagram:

Forward Biasing Reverse Biasing

Procedure:

Before you proceed, identify the p and n-side of the diode in order to connect properly in

forward and reverse bias mode.

(i) Forward and reverse bias characteristics of a normal diode:Forward Bias characteristics:

V

A

V

A


40/83


3. Assemble the circuit on your breadboard as shown in Fig 1(a). Connect to the

0-30V dc power supply.

4. Switch on the power supply. Slowly increase the supply voltage in steps of

0.1 Volt using the fine adjustment knob and note down the corresponding readings of

diode current. When you find the change in current is larger (which means you have

already crossed the threshold point!), increase the supply voltage in steps of 0.5 to note

down current.

5. Using multimeters in appropriate modes, measure voltage drop across the

diode and the current in the circuit. Switch off the supply after taking sufficient readings.

6. Plot the I~V characteristics and estimate the threshold voltage.

7. Choose two operating points below and above the threshold point and

determine the static and dynamic resistance at each of the points.

Reverse Bias characteristics:

1. Assemble the circuit on your breadboard as shown in Fig 1(b). Connect to the

0-30V dc power supply.

2. Switch on the supply. Increase the supply voltage in steps of 0.5 Volt to note

down the diode current.

3. Use multimeters for voltage and current measurements. Keep in mind that

magnitude of current flowing in the circuit will be very small, so choose current range

properly. Switch off the supply after taking sufficient readings.

4. Plot the I~V characteristics on the same graph sheet and estimate the reverse

saturation current.

(ii) Forward and reverse bias characteristics of a zener diode:

Forward Bias characteristics:

1. Assemble the circuit on your breadboard as shown in Fig 1(a). Use a zener

diode this time in your circuit and repeat steps 2-4 of forward bias characteristics of

normal diode.

Reverse Bias characteristics:

1. Assemble the circuit on your breadboard with the zener diode, as shown in

Fig 1(b). Keep in mind that initially the magnitude of current flowing in the circuit will


41/83


be very small.

2. Switch on the power supply. Increase the supply voltage in steps of 0.5 Volt

and note down the corresponding readings of diode current. When you find the change in

current is larger (which means you have already crossed the break-down point!), using

the fine adjustment knob increase the supply voltage in steps of 0.1 to note down diode

current.

3. Plot the I~V characteristics on the same graph sheet and estimate the

threshold and break-down voltages.

Observation:

Code Number of Diode: (i) normal diode: _______ (Si)

_______ (Ge)

(ii) Zener Diode: _______

Table (i) For normal Diode (Si)

Obs.

No.

Forward Biasing Reverse biasing

Voltage

Applied(V)

Voltage, VD

(V)

Current, ID

(mA)

Voltage

Applied (V)

Voltage, VD

(V)

Current, ID

(A)

1

..

..

(ii) For normal Diode (Ge)Same as Table (i)

(iii) For zener Diode:Obs.No.

Forward Biasing Reverse biasing

VoltageApplied

(V)

Voltage, VD(V)

Current, ID(mA)

VoltageApplied (V)

Voltage, VD(V)

Current, ID

(A)

1

..

..

Graphs:

Plot I~V characteristics for both the diodes and estimate the required parameters.


42/83



3. Describe the behavior of the I~V curve for each diode.

4. Threshold voltage for normal diode is ______V (What type of a diode it is,

Si/Ge?)

Static resistance = ------, Dynamic resistance = ------ at operating point Q.

5. Threshold voltage for Zener diode = --------

Zener Break-down voltage = -------

Precautions:

LAB#7: HALF-WAVE RECTIFIER CIRCUIT WITHOUT AND

WITH FILTER

Objectives:

iii)To construct a half-wave rectifier circuit and analyze its output.

iv)To analyze the rectifier output using a capacitor in shunt as a filter.

Overview:

The process of converting an alternating current into direct current is known as

rectification. The unidirectional conduction property of semiconductor diodes (junction

diodes) is used for rectification. Rectifiers are of two types: (a) Half wave rectifier and

(b) Full wave rectifier. In a half-wave rectifier circuit (Fig. 1), during the positive half-

cycle of the input, the diode is forward biased and conducts. Current flows through the

load and a voltage is developed across it. During the negative half-cycle, it is reverse bias

and does not conduct. Therefore, in the negative half cycle of the supply, no current flows

in the load resistor as no voltage appears across it. Thus the dc voltage across the load is


43/83


sinusoidal for the first half cycle only and a pure a.c. input signal is converted into a

unidirectional pulsating output signal.

Fig.1: Half-wave rectifier circuit

Since the diode conducts only in one half-cycle (0-), it can be verified that the d.c.

component in the output is Vmax/, where Vmax is the peak value of the voltage. Thus,

max

max 318.0 VV

Vdc ========

The current flowing through the resistor,

R

VI dcdc ==== and power consumed by the load,

RIP dc2

==== .

Ripple factor:

As the voltage across the load resistor is only present during the positive half of

the cycle, the resultant voltage is "ON" and "OFF" during every cycle resulting in a low

average dc value. This variation on the rectified waveform is called "Ripple" and is an

undesirable feature. The ripple factor is a measure of purity of the d.c. output of a

rectifier and is defined as

21.11318.0

5.01

2

2

2

2

22

====

========

========

dc

rms

dc

dcrms

outputdc

ac

V

V

V

VV

V

Vr

In case of a half-wave rectifier Vrms = Vmax/2 = 0.5Vmax. (How?)

Rectification Efficiency:


44/83


Rectification efficiency, , is a measure of the percentage of total a.c. power input

converted to useful d.c. power output.

(((( ))))

(((( ))))

++++

====

++++

====

++++

====

====

====

R

r

R

rV

V

RrI

RI

IVIV

inputatpowercaloadtodeliveredpowercd

dddac

dc

acacdcdc

1

405.0

15.0

318.0

)(

....

2

max

2

max

2

2

Here rdis the forward resistance of diode. Under the assumption of no diode loss

(rd


45/83


The working of the capacitor can be understood in the following manner. When

the rectifier output voltage is increasing, the capacitor charges to the peak voltage Vm.

Just past the positive peak the rectifier output voltage tries to fall. As the source voltage

decreases below Vm , the capacitor will try to send the current back to diode making it

reverse biased. Thus the diode separates/disconnects the source from the load and hence

the capacitor will discharge through the load until the source voltage becomes more than

the capacitor voltage. The diode again starts conducting and the capacitor is again

charged to the peak value Vm and the process continues. Although in the output

waveform the discharging of capacitor is shown as a straight line for simplicity, the decay

is actually the normal exponential decay of any capacitor discharging through a load

resistor. The extent to which the capacitor voltage drops depends on the capacitance and

the amount of current drawn by the load; these two factors effectively form the RC time

constant for voltage decay. A proper combination of large capacitance and small load

resistance can give out a steady output.

Circuit components/Equipments:

(iii)A step-down transformer, (ii) A junction diode, (iii) 3 Load resistors, (iv) 3

Electrolytic Capacitors, (v) Oscilloscope, (vi) Multimeters, (vii) Connecting

wires, (viii) Breadboard.

Circuit Diagram: (As shown in Figs. 1 and 2)

Procedure:

10.Configure the half-wave rectifier circuit as shown in the circuit diagram. Note

down all the values of the components being used.

11.Connect the primary side of the transformer to the a.c. Mains and secondary to the

input of the circuit.

12.Measure the input a.c. voltage (Vac) and current (Iac) and the output a.c. (Vac), d.c.

(Vdc) voltages using multimeter for at least 3 values of load resistor (Be careful to


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choose proper settings of multimeter for ac and dc measurement).

13.Multiply the Vac at the input by 2 to get the peak value and calculate Vdc using

the formula Vdc = Vmax/. Compare this value with the measured Vdc at the output.

14.Feed the input and output (in DC coupling mode) to the two channels of

oscilloscope. We will use oscilloscope here only to trace the output waveform.

Save the data for each measurement using SAVE/LOAD or STORAGE button of

the oscilloscope.

15.Calculate the ripple factor and efficiency.

16.Connect an electrolytic capacitor (with ve terminal connected to ground) across

the output for each load resistor and measure the output a.c. and d.c. voltages once

again and calculate the ripple factor. Trace the input and output waveforms in

oscilloscope and notice the change.

viii) Repeat the above measurement foe all values of capacitors and study the output.

Observations:

6. Code number of diode = ________

7. Input Voltage: Vac = _________ Volt

Table(I): Half wave rectifier w/o filter

Sl.No

LoadR (k)

InputCurrent

Iac (mA)

Output Voltage RippleFactor

r

Efficiency (V2dc/R)/VacIac

(%)

Vac

(Volt)

Vdc

(Volt)

Vmax/

(Volt)

1

2

3

Table(II): Half wave rectifier with filter (C = ____ F) (Make separate tables for

each capacitor)

Sl. No Load

R (k)

Output Voltage Ripple Factor

rVac (Volt) Vdc (Volt)

1


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2

3

(III) Input and output waveforms:

Waveforms without Filter:

R = ______ Input Output

(Paste data here)

Waveforms with Capacitor Filter: C = ______F

R = ______ Input Output

(Paste data here)

Discussions:

Precautions:

LAB#8: FULL-WAVE BRIDGE RECTIFIER CIRCUIT WITHOUT

AND WITH FILTER

Objectives:

v) To construct a full-wave bridge rectifier circuit and analyze its output.

vi)To analyze the rectifier output using a capacitor in shunt as a filter.

Overview:

As you have seen already a half-wave rectifier circuit is unsuitable to applications

which need a "steady and smooth" dc supply voltage. One method to improve on this isto use every half-cycle of the input voltage instead of every other half-cycle. The circuit

which allows us to do this is called a Full-wave Rectifier. Here, unidirectional current

flows in the output for both the cycles of input signal and rectifies it. The rectification can


48/83


be done either by a center ta

rectifier (using four diodes).

The Full-wave Bridge Recti

Another type of circuit that

output as a full-wave recti

Bridge Rectifier (Fig. 1).

phase rectifier uses 4 in

diodes connected in a "brid

to produce the desired ou

require a special centre tappe

its size and cost. The singl

bridge network and the load

to D4 are arranged in "series

half cycle. During the posit

series while diodes D3 and

as shown below (Fig. 2). Du

conduct in series, but diode

current flowing through the l

Fig. 2:

As the current flowing throu

the load is also unidirection

1, Dr. P. K. Sahoo

full wave rectifier (using two diodes) or a ful

n this experiment we will study a full wave bri

ier

produces the same

fier is that of the

his type of single

ividual rectifying

ged" configuration

tput but does not

d transformer, thereby reducing

secondary winding is connected to one side

to the other side as shown in figure. The 4 diod

pairs" with only two diodes conducting curren

ve half cycle of the supply, diodes D1 and

4 are reverse biased and the current flows thr

ring the negative half cycle of the supply, diod

D1 and D2 switch of as they are now revers

oad is the same direction as before.

orking of Full-wave bridge rectifier

h the load is unidirectional, so the voltage dev

al during both the half cycles. Thus, the aver

Fig. 1:Full-wave B

47

wave bridge

ge rectifier.

of the diode

es labeled D1

t during each

2 conduct in

ugh the load

s D3 and D4

biased. The

loped across

ge dc output

idge Rectifier


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voltage across the load resistor is double that of a half-wave rectifier circuit, assuming no

losses.

max

max 637.02

VV

Vdc ========

Ripple factor:

As mentioned in the previous lab the ripple factor is a measure of purity of the

d.c. output of a rectifier and is defined as

48.01637.0

707.01

)(

)(2

2

2

2

22

====

========

========

dc

rms

dc

dcrms

dc

ac

V

V

V

VV

outputV

outputVr

In case of a full-wave rectifier Vrms = Vmax/2 = 0.707Vmax. The ripple frequency is now

twice the supply frequency (e.g. 100Hz for a 50Hz supply).

Rectification Efficiency:

Rectification efficiency, , is given by

(((( ))))

(((( ))))

++++

====

++++

====

++++

====

====

====

L

d

L

dLds

Ldc

acacdcdc

R

r

R

rV

V

RrV

RV

IVIV

inputatpowercaloadtodeliveredpowercd

1

811.0

1707.0

637.0

)(

....

2

max

2

max

2

2

where rdis the forward resistance of diode. Under the assumption of no diode loss

(rd


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Fig.3: Full-wave rectifier circuit with capacitor filter

The full-wave rectifier circuit with capacitor filter is shown in Fig. 3. The

smoothing capacitor converts the full-wave rippled output of the rectifier into a smooth

dc output voltage. The detailed description of its filtering action is already explained in

half-wave rectifier handout. Two important parameters to consider when choosing a

suitable a capacitor are its working voltage, which must be higher than the no-load output

value of the rectifier and its capacitance value, which determines the amount of ripple

that will appear superimposed on top of the dc voltage.

Apart from rectification efficiency, the main advantages of a full-wave bridge

rectifier is that it has a smaller ac ripple value for a given load and a smaller smoothing

capacitor than an equivalent half-wave rectifier. The amount of ripple voltage that is

superimposed on top of the dc supply voltage by the diodes can be virtually eliminated by

adding other improved filters such as a pi-filter.


(iv)A step-down transformer, (ii) 4 junction diodes, (iii) 3 Load resistors, (iv)

Capacitor, (v) Oscilloscope, (vi) Multimeters, (vii) Connecting wires, (viii)

Breadboard.

(With capacitor)

Smoothing

Capacitor

C Charges C Disharges

(Output waveform

without capacitor)


51/83


Circuit Diagram: (As shown in Fig. 1 and 3)

Procedure:

17.Configure the full-wave rectifier circuit as shown in the circuit diagram. Note

down all the values of the components being used.

18.Connect the primary side of the transformer to the a.c. Mains and secondary to the

input of the circuit.

19.Measure the input a.c. voltage (Vac) and current (Iac) and the output a.c. (Vac) and

d.c. (Vdc) voltages using multimeter for at least 3 values of load resistor (Be

careful to choose proper settings of multimeter for ac and dc measurement).

20.Feed the input and output to the oscilloscope (we will use oscilloscope here only

to trace the output waveform) and save the data for each measurement. BE

CAREFUL NOT TO MEASURE THE INPUT AND OUTPUT VOLTAGES

SIMULTANEOUSLY.

21.Multiply the Vac at the input by 2 to get the peak value and calculate Vdc Using

the formula Vdc = 2Vmax/ . Compare this value with the measured Vdc at the

output.

22.Calculate the ripple factor and efficiency.

23.Connect the capacitor across the output for each load resistor. Measure the output

a.c. and d.c. voltages once again and calculate the ripple factor. Trace the input

and output waveforms in oscilloscope and notice the change. (If time permits you

could also use different values of capacitors and study the output)

Observations:

8. Code number of diode = ________

9. Input Voltage: Vac = _________ Volt

Table(I): Full-wave rectifier w/o filter


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Sl.

No

Load

RL

(k)

Input

Current

Iac (mA)

Output Voltage Ripple

Factor

r

Efficiency

(Vdc2/RL)/VacIac

(%)

Vac

(Volt)

Vdc

(Volt)

2Vmax/

(Volt)

1

2

3

Table(II): Full-wave rectifier with filter (C = ____F)

Sl. No Load

RL (k)

Output Voltage Ripple Factor

rVac (Volt) Vdc (Volt)

1

2

3

(III) Input and output waveforms:

Waveforms without Filter:

RL = ______

Input Output

(Paste data here)

Waveforms with Capacitor Filter:

RL = ______

Input Output

(Paste data here)


53/83


Discussions:

Precautions:

Lab#9: Setting up a Power Supply using a Zener Diode as Voltage

Regulator

Objectives:

To set up a power supply using a zener diode as a voltage regulator and to calculate

percentage of regulation.

Overview:

Zener diodes are generally used in the reverse bias mode. You have seen already in one

of your previous experiments that the zener diode has a region of almost a constant


54/83


voltage in its reverse bias characteristics, regardless of the current flowing through the

diode. This voltage across the diode (zener Voltage, Vz) remains nearly constant even

with large changes in current through the diode caused by variations in the supply voltage

or load. This ability to control itself can be used to great effect to regulate or stabilize a

voltage source against supply or load variations. The zener diode maintains a constant

output voltage until the diode current falls below the minimum Iz value in the reverse

breakdown region, which means the supply voltage, VS, must be much greater than Vz for

a successful breakdown operation. When no load resistance, RL, is connected to the

circuit, no load current (IL = 0), is drawn and all the circuit current passes through the

zener diode which dissipates its maximum power. So, a suitable current limiting resistor,

(RS) is always used in series to limit the zener current to less than its maximum rating

under this "no-load" condition.

From the previous experiments on rectifiers, you know that the d.c. output voltage from

the half or full-wave rectifiers contains ripples superimposed on the d.c. voltage and that

the average output voltage changes with load. As shown in the circuit diagram, a more

stable reference voltage can be produced by connecting a simple zener regulator circuit

across the output of the rectifier. The breakdown condition of the zener can be confirmed

by calculating the Thevenin voltage, VTH, facing the diode is given as:

S

LS

LTH V

RR

RV

++++====

This is the voltage that exists when the zener is disconnected from the circuit. Thus, VTH

has to be greater than the zener voltage to facilitate breakdown. Now, under this

breakdown condition, irrespective of the load resistance value, the current through the

current limiting resistor, IS, is given by

S

ZS

SR

VVI

====


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The output voltage across the load resistor, VL, is ideally equal to the zener voltage and

the load current, IL, can be calculated using Ohms law:

L

LLZL

R

VIandVV ========

Thus the zener current, IZ, is LSZ III ==== .

Now that you have constructed a basic power supply, its quality depends on its load and

line regulation characteristics as defined below.

Load Regulation: It indicates how much the load voltage varies when the load

current changes. Quantitatively, it is defined as: %100====FL

FLNL

V

VVregulationLoad ,

where VNL = load voltage with no load current (IL = 0) and VFL = load voltage with full

load current. The smaller the regulation, the better is the power supply.

Line Regulation: It indicates how much the load voltage varies when the input line

voltage changes. Quantitatively, it is defined as: %100

====

LL

LLHL

V

VVregulationLine ,

where VHL = load voltage with high input line voltage, and VLL = load voltage with low

input line voltage. As with load regulation, the smaller the regulation, the better is the

power supply.


(i) A variable transformer, (ii) 4 junction diodes, (iii) A zener diode, (iv) Current limiting

resistor, (v) Load resistors, (vi) Capacitor, (vii) Multimeters, (viii) Connecting wires, (ix)

Breadboard.

Circuit Diagram:


56/83


Procedure:

1. Use the full-wave rectiffilter minus the load). Co

the secondary as the a.c.

the magnitude of input v

You can use only those

zener breakdown voltage

2. Complete the rest part othe values of the compon

3.

Keeping input voltage suoutput d.c. voltage and

unregulated d.c. voltage

and ensure that the zener

4. Similarly, keeping RL fixvoltage, current and inp

before each measuremen

5. Tabulate all your data an

Observations:

Specifications of zener di

RS = _________k

1, Dr. P. K. Sahoo

ier circuit configured in your previous lab (

nnect the primary of a variable transformer to a

source for the rectifier circuit. This will facilit

oltage to rectifier by choosing different second

secondary terminals whose voltage is much

you are using.

the circuit as shown in the circuit diagram.

ents being used including the zener breakdown

itably fixed, use different values of RL and mecurrent using multimeter (in d.c. mode).

across capacitor. Calculate VTH before each

is operating in breakdown region.

ed, vary the input voltage and measure again t

t unregulated d.c. voltage across capacitor.

.

calculate percentage regulation in each case.

ode: Breakdown voltage = ________ V

55

ith capacitor

.c. mains and

ate to change

ry terminals.

ore than the

ote down all

voltage.

sure both theeasure input

measurement

e output d.c.

alculate VTH


57/83


Table (i) Load Regulation: Input unregulated d.c. voltage = _________V

Table (ii) Line regulation: RL = _______ k

Graphs:

Plot graphs RL (X-axis) vs VL (Y-axis) and Vi (X-axis) vs VL (Y-axis) using data of

tables (ii) and (iii), respectively. Also plot IL (X-axis) and VL (Y-axis) for each set of

observations.


Precautions:

________________________________________________________________________

Sl.

No

Load

(RL)

(k)

D.C. input

voltage (V)

(unregulated)

S

LS

L

TH VRR

RV

++++====

(V)

Output D.C.

Voltage (VL)

(V)

Output

Current

(IL)

(mA)

Percentage

Regulation

(%)

1 .. VFL=..

100

FL

FLNL

V

VV

..

.. VNL = .. 0

Sl.

No

Input D.C.

Voltage (Vi)

(V)

S

LS

L

TH VRR

RV

++++====

(V)

Output D.C.

Voltage (VL)

(V)

Output

Current (IL)

(mA)

Percentage

Regulation

(%)

1 VLL= ..

100

LL

LLHL

V

VV

..

.. VHL= ..

Increasing

order

Increasing

order


58/83


Lab# 10: Bipolar Junction Transistor Static Characteristics

Objective:

(i) To study the input and output characteristics of a PNP transistor in CommonBase mode and determine transistor parameters.

(ii) To study the input and output characteristics of an NPN transistor in CommonEmitter mode and determine transistor parameters.

Overview:

A Bipolar Junction Transistor, or BJT is a three terminal device having two PN-

junctions connected together in series. Each terminal is given a name to identify it and

these are known as the Emitter (E), Base (B) and Collector (C). There are two basic types

of bipolar transistor construction, NPN and PNP, which basically describes the physicalarrangement of the P-type and N-type semiconductor materials from which they are

made. Bipolar Transistors are "CURRENT" Amplifying or current regulating devices thatcontrol the amount of curre

Labnote PL243 Electronics

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Transcript of Labnote PL243 Electronics