bca experiments

8/11/2019 bca experiments

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EXPERIMENT NO: DATE:

Department of BCA and B.Sc(CS) ,KSCD.

CAPACTIANCE OF CONDENSER BY

CHARGING AND DISCHARGING

AIM: To determine the time constant of the resistance capacitance series circuit by

charging and discharging characteristics. From the results find the capacitance of a

capacitor.

APPARATUS: High resistance (R), Electrolytic capacitor (C), accumulator charge

and discharge key, tap key, digital stop watch and DMM, bread board and

connecting wires.

INTRODUCTORY INFORMATION: Capacitor in series with resister may be used

in electronic or electronic circuit to control the time required for a current or

voltage to reach a specified value. Operation of this circuit is circuit given below.

R and C are connected in series when we just start charging capacitor, charge on

capacitor is such that potential difference across capacitor Vc is zero but charging

current is maximum as charge starts collecting on C, Vc starts increasing but both

charging current and the potential difference across resistor VRstarts decreasing at

progressively decreasing rate C:

( E = VR + Vc ), Vc is given by Vc = E ( 1 e- t/RC

)where RC = T = Time constant

of the circuit Vc = Voltage across C at time.

NATURE OF GRAPH:


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CIRCUIT DIAGRAM: -

E-transistor power supply (5V)

C = Electronic Capacitor of Capacitance

R = 320 K

DMMDigital millimeter.

C & DCharge and discharge key

T - Tap key

OBSERVATIONS: -

1. Resistance used R = 320 k.

3. theoraticaltical values of time constant T = RC sec


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Table: 1 Table: 2

Charging curve Discharging curve

Sl.

no

Charging

time t

Sec

Voltage

across

capacitor

V. Volt

Obs

No.

Discharging time

t

sec

Time Voltage across C

Vc Volt

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20


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When discharging key is pressed battery is cut of capacitor is short circuited

through R. Hence it starts discharging Voltage value decreases exponentially.

Progressively decreasing value of the Voltage Vc is given by Vc = E(et/Rc

)

Where the product RC is called time constant and t is the time at which voltage

across C is Vc

The time required to rise the voltage across the capacitor to 63. 2 % of the

maximum applied Voltage is called the time constant of Rc circuit

:: Time constant = T = Rc

It is also the time during which the Voltage across the capacitor falls to 37 % of its

initial maximum value.

Equation Vc = E( et/ RC

)

Represents the

decreasing curve.

PROCEDURE: For Table I

Set up the circuit as shown in the figure set the range selection. Switch on

DMM charge the capacitor for s by pressing C and D lay to the position and

simultaneously start the stop watch. After 5 release the C & D key and record Vc

on DMM and time t. Discharge the capacitor fully by closing the tap key T for few

seconds. Now carry out the procedure for time t = 10, 20, 25, ___ until capacitor

voltage reaches the emf of battery

CALCULATION:

Time constant for charging curve = T1

Time constant for discharging curve = T2

Time constant =( T1+T2)/2=

Capacitance of condenser C = T/R=

(Note: for each value of t the capacitor should be discharged before charging).

Tabulate the observations and then plot the charging curve from the charging curve


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determine the time constant the time value corresponding Vc = 0.632 V max is the

time constant T.

For Table II:

First charge the capacitor to the battery voltage by pressing C & D key to

position 1 and holding in this position for about 2 to 3 minutes. Then immediately

press C and D key to the position 2 and simultaneously start the stopwatch. Allow

the capacitor to discharge for 5 After 5 second release the key and record Vc and

time. Again charge the capacitor back to its E value and repeat the procedure as

described already for time interval mentioned in the chart. Record the observations

and plot-discharging curve. From this curve determine the time constant. Time for

which curve Vc = 0.37 Vmax is the time constant.

PROCEDURE:

RESULT:

Time constant of the resistance capacitance series circuit=

Capacitance of condenser =


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RESONANCE IN LCR CIRCUIT

AIM ; Set up series and parallel resonance Circuit with the resonance frequency fo

= 2250.5 H Study the response of circuit as a function of frequency. Determine the

band width, resonant frequency & quality factor of the circuit take R = 50 , L =

50 mH and C = 0.1 F

APPARATUS : - Inductor, Capacitor, resistance box, Plug key, frequency

generator, multimeter.

FORMULA:-(i) fo = resonant frequency =

Here L= 50mH = 50 * 103Hz

C= 0.1 F = 0.1* 10-6F

R = 50

(ii) Band Width = f = f2f1

f2Upper half power frequency

f1Lower half power frequency

(iii) Quality factor

Here fo = Resonant frequency determined by experimental method

f = band width

THEORY: - The property of cancellation of reactance when inductive and

capacitive reactance in series or the cancellation of susceptance when inductor and

capacitor are in parallel is called as resonance.


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CIRCUIT DIAGRAM FOR SERIES LCR CIRCUIT:

AFGAudio frequency generator

LInductor = 50 mH

CCapacitor = 0.1 F

RResistor = 50

NATURE OF GRAPH:

From graph ,

Foresonant frequencyI max = mA

There are two types of resonance Circuits

1) LCR series resonance

2) LCR Parallel resonance

1) LCR Series resonance when LCR are in series the effective impedance is a

function of frequency


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Zeff = effective impedance

Zeff = R + J (wL 1/Wc)

At certain frequency fo, the effective impedance drops to minimum &

current in the circuit is of maximum value the frequency at which effective

impedance drops to minimum or current in the circuit maximum is called resonant

frequency. The variation of the current in the circuit with respect to frequency of

current applied voltage is shown in the graph the line drawn parallel to frequency

axis, from a point corresponding to current value 0.707. I max on the current

frequency graph intersects is called lower half & second intersect is called upper

half frequency.

2) LCR Parallel resonance : - When LCR are connected in Parallel the effective

impedance zeff raises current in the circuit drops to minimum. Nature of variationof impedance of the circuit with the frequency as shown in the graph. The frequency

at which Zeff raises to maximum value & current drops to minimum value is called

resonant frequency fo.


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TABULAR COLUMN: -

SL. no Frequency f in (Hz) Current I in (mA)1

2

34

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

2425

In this case fo = At resonance frequency the effective impedance of

circuit. Zeff = Zmax =

In case of parallel resonance circuit the band width is defined as the difference

between the frequencies corresponding to two points on either side of resonant

frequency, where value of the impedance drops to 0.707 times the maximum value

of impedance.

Band width - f = f2f1


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Quality factor

fo =

CIRCUIT DIAGRAM; - LCR PARALLEL RESONANT CIRCUIT

AFG - Audio frequency generator

LInductor50 mH

CCapacitor0.1 F

RResistor50

KPlug Key

NATURE OF GRAPH: -

OBSERVATION: -

1) Vin =

2) Zmax =


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CALCULATION: -

1) Band width, f = f2f1=

2)Quality Factor,

TABUALR COLUMN: -

SL. No Frequency f (Hz) Current I (mA) Impedance Z = VinI

From graph : for parallel

Zmax =


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INVERTING AND NON INVERTING AMPLIFIER

AIM: -

1) Set up an Op- amp IC 741 as inverting amplifier having an absolute value of

gain equal to 10 compare the observed voltage to the theoretical values of the

output for various input voltages sketch the input & output wave forms for

any one of output.

2) Set up an Op amp IC741 as non inverting amplifier having an absolute

value of gain equal to 11 compare the measured output voltages with the

theoretical value of output for various input values. Sketch the input &

output voltages wave forms for any one of inputs.

APPARATUS:- Op amp IC 741, Resistors, audio frequency generator,breadboard, CRO, Connecting wires, DCPower Supply.

THEORY: - The operational amplifier is most commonly termed as Op amp. Due

to its use in performing mathematical operations, it has been given the name

operational amplifier. Because of their low cost, small size, flexibility Op amp are

in the field of process control, communications, computers, power and signal

sources delays & measuring systems.

In linear applications output voltage of the amplifier varies linearly wire the

input voltages off their exists a phase difference of 180obetween input and part of

output which is feedback. The feedback maker the gain of the circuit stable, noise

distortion is less, higher band width and improved output & input impedance values

study of such an inverting amplifier gain properly to the purpose of experiment in

case of non inverting amplifier (gain) there is no phase difference between input &

output quantities.


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CIRCUIT DIAGRAM: -

Inverting amplifier.

NonInverting amplifier

AFGaudio frequency generator

R1Resistor = 10 K

R210 K


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IC 741Opamplifier.

Inverting amplifier:

Amplifier which provides a phase difference of 180obetween input & output

is called inverting amplifier.

Closed loop gain of gain of the inverting amplifier

= Vo/ Vin

where

Vooutput voltage

Vininput voltage

The 3 terminals of Op-amp is at potential Vin. Hence the potential of 2

terminal of Op-amp is also equal to Vin

:. VA = VB = Vin

VA = Potential of terminal 2 of Op-amp

VB = Potential of terminal 3 of Op-amp

For outside I = Vo -VA

R2

I = Vo-Vin

R2

At inverting terminal 2 of Op-amp

I = VA-O = Vin (: VA= Vin)

R1 R1

Entire current passes through R2

VOVin = Vin

R2 R1

VO = Vin + Vin = Vin(R1+ R2)

R2 R2 R1 R1R2

VO = R2 (R1+ R2) = (R1+ R2)

Vin R1 R2 R1

:. VO/Vin = gain of amplifier

= 1+R2/R1


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NATURE OF GRAPH OF INVERTING AMPLIFIER

NONINVERTING AMPLIFIER


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Here +ve sign of gain indicates that the input & output are in phase in case of

noninverting amplifier gain will be always greater than 1.

The terminal 3 of Op-amp is ground therefore from concept of virtual

ground; the terminal 2 is also at ground potential.

OBSERVATIONS & TABULAR COLUMNS

Inverting amplifier

R1= . R2=

Gain on amplifier = - R2/R1 =

Frequency =

Input voltage Vin(volt) Output voltage Voin

volt

Calculated output voltage Vo

= - Vin R2/R1

Non Inverting amplifier

R1= R2= gain = 1+(R2/R1) =2

Input voltage Vin(volt) Output voltage Vovolt Calculated output voltage

Vo = -Vin ( 1+R2/R1)


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I = Vin - VA

R

Vininput voltage

VApotential of terminal 2 of Op-amp ground potential = 0

:. I = Vin/R

on output side

R = VAVO O VoOutput voltage

R VApotential at terminals

R = VO/R

Entire current flowing through R1, passes through

R2 :. Vin = VO

R1 R2

VO/Vin = -R2/R1gain of amplifier hereVe sign denotes that input & output are

out of phase.

Here gain can be greater, less than or equal to 1, depending on values of R1&

R2

Noninverting amplifier where in input & output are in phase is called non-

inverting amplifier gain VO/Vin.


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INDENTIFICATION AND MEASUREMENT OF

R ,L AND C IN A BLACK BOX

AIM: - To identify the terminals of R, L and C to determine the values of R, L and

C in the black box.

APPARATUS: - Black box containing R, L and C, Audio Frequency Generator

(AFG) AC voltmeter, bread board connecting wires, resistance box, DC and AC

source etc.

THEORY: - Black box is a box that contains Resister; Inductor and Capacitor with

one end of the each connected to one common terminal of black box and other ends

to each are connected to different terminals of the black box. Therefore given black

box has four terminals A, B, C, and D

CIRCUIT DIAGRAM:

Observation: -

Tr. No Measure Resistance across Resistance

1 AB

2 AC

3 AD

4 BC

5 BD

6 CD


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INFERENCE: -

1. _____________ Terminal is common for R =

2. _____________ Terminal is one end of the capacitor

3. Resistance across ________&_______ terminals is maximum

4 R and L are in series between terminal ___________and ____________

5. The terminal __ is node for components R, L and C

6. Capacitor is present between _______and _______terminals.

7. Resitance is present between _______and

_______terminals

8. Inductor is present between _______and _______terminals

CIRCUIT DIAGRAM II: -

To determine terminals of L and R, and also to determine values of C L and

R.

AFGAudio frequency generatorR - Resistance box (0-1000)

V1 - dc voltmeter (0-10V)

V2 - dc voltmeter (0-5V) BB Black box with terminals A, B, C & D

OBSERVAITON: -


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1. Resistance RL in resistance box R =

2. Frequency of alternating voltage input =

3. Nodal terminal is ___B

4. Probe is connected to ________terminal of black box

Given : B is a nodal terminal.

Payable RL Voltmeter reading Iac = V1-V2

/R

A

Z = V2/Iac Mean Z

Bet m

V1Volt

Bet N

V2Volt

V1-V2

Volt

A

AB

B

BC

C

BD

CALUCATION: -

C = = __________F

L= =______________mH

INFERENCE: -

1. Nodal terminal is __

2. R and L are in series between __ and__ terminals

3. Resistance across BD determined by II multimeter ___

4. Resistance across XD determined by part II =______

: Resistance across BD determined by multimeter Resistance across XD

determined by Part II


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: Resistance is present in between __ & __ terminals .

5. Capacitor is present between __ and __ terminals

: Inductor must be between __ & __ terminals

: R, L and C Connections in black box are of type.


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ZENER DIODE AS A VOLTAGE REGULATOR

Aim:

To determine Zener diode as a voltage regulator to provide a constant voltage from

a source whose voltage may vary over sufficient range.

Apparatus:

Zener Diode, battery,resistor,resistance box,voltmeter,plug key, connecting wires.

THEORY:

Zener Diode of Zener Voltage Vz is reverse connected across the load RL across

which constant output is derived. The series resistance R absorbs the output voltage

across fluctuations so as to maintain constant voltage across the load. When an

input DC source is applied to the Zener diode, the output voltage will be the same as

the input voltage. When the input voltage exceeds the breakdown voltage of the

Zener diode, the output voltage remains constant even when the input voltage isincreased. Hence Zener diode acts as a voltage regulator.

CIRCUIT DIAGRAM:

Ba - Battery (0 V to 20 V) R - Resistor (220 )

RL - Resistance Box V - Voltmeter

K - Plug Key

NATURE OF GRAPH:


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TABULAR COLUMN:

LOAD REGULATION

INPUT VOLTAGE Vin=

Resistance RL (ohm) Voltage across Zener Diode VZ (volts)


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LINE REGULATION

Load RL=

Input voltage Vin(volts) Voltage across Zener Diode VZ (volts)


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Procedure:

1. Connections are made as shown in the circuit diagram.

2. Supply an input voltage of 10 V.

3. Unplug 100 resistance from the resistance box. Note down the corresponding

voltmeter reading.

4. Continue the procedure for 200 , 300 , 10 K and note down thecorresponding voltmeter reading.

5. Unplug 10 K of resistance from the resistance box

6. Supply an input voltage of 1 V and note down the corresponding voltmeter

reading.

7. Continue the procedure for 2 V, 3 V,.15 V and note down the correspondingvoltmeter reading.

8. Plot the graph of RL v/s Vz and Vin v/s Vz.


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ENERGY GAP OF A SEMICONDUCTOR

THERMISTOR

AIM: Determine the resistance of the thermistor at various temperatures. Plot the

characteristic graph log 10 R (1/T) and hence determine the energy gap of the

given thermistor.

THEORY: Thermistor is temperature sensitive resistor. Its thermal resistance is

related to the body temperature. Thermistor is made up of Germanium, Nickel, and

Manganese. These thermistors are available in different shapes and size. They are in

the form of beads, rods and discs. The compound employed will determine whether

the device has +ve orve temperature coefficient. Thermistors of resistance ranging

from 1200 at 800 k are available.

The energy required to transfer an electron from valence bond to conduction

band is called energy gap. The conductivity J of a semiconductor is given by = ze( -Eg/

2kt) * e((e + n)

where I > Z is total number of carriers per unit value of

semiconductor in conduction band and value band

ii) Eg: Energy gap

iii) K: Boltzmanns constant = 8. 62*10-5 eV/ k

iv) e: Electronic charge

v) e = Mobility of electrons

vi) T = Temperature in Kelvin

vii) n = mobility of holes

viii) = Conductively = 1/s

ix) S = Specific resistance

OBSERVATIONS:

Room temperature =

Applied Voltage V =


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Tabular Column:

Obs No Temp t

in C0

Abs temp

T = t + 273k

Current I

in mA

Resistance

R = V/ I

Log R

1/ T (sec-1

)

1

2

3

4

5

6

7

8

9

10

11

12

13

Nature of graph:

CALCULATION:

Energy gap:- m * 4.606 * 8.62 * 10-5


29/45



SEMICONDUCTOR DIODE

AIM: Obtain current against voltage characteristic for semiconductor diode under

forward bias and condition from the characteristic curves determine important

parameters related to diode.

APPARATUS: Battery, milliammeter, Voltmeter, diode, rheostat, plug key.

THEORY: Forward bias:

When a positive terminal of a dc source is connected to the P side and

negative terminal to the n-side of the PNjunction diode it is said to be forwardbiased. Forward bias Voltage opposes the potential barriers at the depletion layer.

As forward bias voltage is (VF) increases from 0 to the battery potential value

initially there will not be flow of forward current later forward current slowly

increases. When forward voltage is more than barrier potential effect of barrier

potential becomes too less. In this region as the forward potential increases forward

current also increases therefore whenever diode is forward, resistance of diode is

small.

CIRCUIT DIAGRAM: (Forward bias)


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DDiode, BaBattery, RhRheostat, MAMilliammeter (0-25 mA),

V-voltmeter, KPlug key, AAnode, KCathode

NATURE OF GRAPH: -

PROCEDURE: Forward bias

1)

Connections are made as shown in the circuit diagram.

2) Note down the readings of the Vfwith corresponding If until it reaches

to its maximum.

3) Plot the graph of Vfversus If.

4) Find the slope of the graph and calculate if by using the formula,

Where, RFis the forward resistance.


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32/45



DSemiconductor VacacVoltmeter

KPlug key Vdcdc - Voltmeter

CCapacitor = 0.1mf Aammeter

OBSERVATION: -

When the plug key is open, then

Imax=

Vdc =

Vac =

Ripple factor =

TABULAR COLUMN: -

SL.NO Iz (mA) Vdc (V) Vac (V)

ripple factor

ripple factor =


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% voltageregulation =

OBSERVATION : - (Forward bias)

TABULAR COLUMN: -

Obs No Voltmeter reading

Vf Volt

Milliammeter

Reading If(mA)

PROCEDURE:

1) Connections are done as shown in the circuit diagram.

2) Keep the plug key (k) open, switch on the Ac mains note down Vdc and Vac.

3) The plug key is closed and the reading of I, Vac and Vdc are noted down for

corresponding readings.


34/45



4) With the increase of Rheostat it is varied for different readings of I, Vac are

noted.

5) After completion of taking the readings calculate the ripple factor using formula.

6) Calculate the percentage of regulator using the formula.

Where, VNLis the Voltmeter reading when no current is passed through it.

CALCULATIONS: -


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RC PHASE SHIFT OSCILLATOR

AIM: - Set up the RC Phase Shift oscillator using transistor and determine the

frequency of alternating voltage developed by Oscillator.

FORMULA: - Frequency of alternating voltage developed by oscillator

Hz

Where, Rc= Collector resistance

R= Resistance in phase shift network

C= Capacitance of capacitor in phase shift oscillator.

THEORY: - In RC Phase Shift oscillator, three RC Sections are used to provide 180

degree phase shift and the remaining 180 degree phase shift is provided by the transistor.

Therefore there is a total 360 degree phase shift.

CIRCUIT DIAGRAM:


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TABULAR COLUMN: -

Theoretical value of frequency Measured value of frequency

r

o

Capacitance

C(F)

Resistance

R(k)

Frequency(F) Length

of onewave

A(div)

Time base

B(s/div)

Time

periodT=A*B

sec

Frequency

F=1/T Hz

WAVEFORM:-

PROCEDURE:-

1] Connections are made as shown in the circuit diagram.

2] Adjust the potentiometer to obtain a stable wave form on CRO. 3] Find the time

period T.4] Then calculate the frequency f= 1/ T Hz.

5] Compare this value with the theoretical value, repeat the experiment for different

values of R.

CONCLUSION: -


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COLPITTS OSCILLATOR

AIM: - Set up Colpitts Oscillator using transistor determine the frequency of oscillating

for various set of capacitors C1 & C2.

APPARATUS: - BC547, NPN Transistor, resistor, capacitors, power supply.

FORMULA: - Frequency of Oscillator

Where, L=inductance=38.95 H= 38.95 x 10-6

H

C=capacitance= .. microfarads

THEORY: - The tank circuit provides 180-degree phase shift and the amplifier provides

180 degree. Thus, there is a total phase shift of 360-degree. Hence the feedback is +ve.

The frequency of oscillation is,

CIRCUIT DIAGRAM:


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TABULAR COLUMN:

Sl no Theoretical value of frequency Measured value of frequency

Capacitor

C1(F)

C=(C1*C2)/

(C1+C2)

In F

F=1/2L MHz

Length

one wav

(div)

Time ba

B (ms/di

Time peri

AB

Sec-1

Frequency

F=1/T

Hz

PROCEDURE: -

1] Connections are made as shown in the circuit diagram2] Adjust the CRO controls to obtain the wave form on CRO

3] Measure the time period T and find the frequency, f= 1 / T H 4] Measure & compare

this value with expected value

5] Repeat the experiment for different value of C


39/45



FULL-WAVE BRIDGE RECTIFIER

AIM:Set up a Full-Wave Bridge Rectifier with a capacitor filter and study its

performance.

APPARATUS:Transformer, Diode, Capacitor, Resistance Box, Rheostat, DC

Milliammeter, DC Voltmeter, AC Voltmeter, Plug key.

FORMULA:

Ripple Factor =

% Voltage Regulation =

Ripple Factor in absence of filter = r = 0.482

Efficiency of Rectifier = 81.2 %

THEORY:

Rectifier is a device that converts alternating current into unidirectional direct

current. A full-wave rectifier rectifies both the positive and negative half-cycles of

the input ac signal. A bridge rectifier utilizes 4 diodes connected as in the circuit

diagram to accomplish full wave rectification.

Operation of the circuit is like thisDuring positive half cycle of input sine wave,point A is positive w.r.t. point B. Diodes D1 and D2 are forward biased where as

diodes D3 and D4 are reverse biased.. Hence only diodes D1 & D3 conduct during

the positive half cycle while diodes D3 & D4 do not conduct current. If the filtering

condenser C is not in the circuit then always current through (both during +ve & -ve half cycles of input current flows through input resistance) R & Rh (in circuit)will flow in the same direction. But current flowing through load in the absence of

the filter is unidirectional and pulsating one, point D of the diode acts as the Anode

and point C acts as Cathode. Output of the rectifier being pulsating, contains DC

component as well as AC component. This type of output is not useful for driving

sophisticated electronic circuits. In fact, these circuits require steady DC output.

A circuit that converts pulsating output from rectifier into a steady DC level is

known as Filter, because it filters off or smoothens the output.

The filter used here is a Shunt Capacitor Filter. Here, capacitor of suitable value C1

is connected across the rectifier and is parallel to the load resistance R & Rh. Thistype of filter is Capacitor Input Filter. It often allows impedance path for DC

portion of the output. The filtering action is shown in the output wave form. By

looking at it, one can see that even after filtering action, small amount of AC

remains unfiltered in the output. The remaining AC in DC component of the output

is called Ripple (unfiltered AC remains in outut). and is written a r = 1 / 4 .

This indicates that ripple factor depends on C and load resistance.


40/45



CIRCUIT DIAGRAM:

OBSERVATION:

Sl. No.Load

Resistance

Vdc

(Volt)

Vac

(Volt)

Iac

(mA)

Ripple

Factor

Vac / Vdc

% Voltage

Regulation

1

2

3

4

5

6

7

8

9

10


41/45



PROCEDURE:

1) Connections are done as shown in the circuit diagram.

2) Keep the plug key (k) open, switch on the Ac mains note down Vdc and Vac.

3) The plug key is closed and the reading of I, Vac and Vdc are noted down for

corresponding readings.

4) With the increase of Rheostat it is varied for different readings of I, Vac are

noted.

5) After completion of taking the readings calculate the ripple factor using formula.

6) Calculate the percentage of regulator using the formula.

Where, VNLis the Voltmeter reading when no current is passed through it.

CALCULATIONS:


42/45



ZENER DIODE CHARACTERISTICS

AIM: - Set up electronic circuit to study the reverse current characteristics of

zenerdiode of power 0.5w and breakdown voltage 6.2v and hence determine.

1. Knee current I

2. Incremental zener resistance Rz

3. Range of Iz over which Vz remains constant

APPARATUS: - Transistor, power supply, Rheostat, current limiting resistor,

Zener diode, digital multimeter, to measure Vz, digital multimeter Iz.

THEORY: - Zener diode is reverse biased, heavily doped P.N diode that is operated

in the breakdown region, where current is limited by both external resistance and

power rating of the diode.

Zener diode at breakdown voltage VB breakdown due to zener effect and

avalanche effect usually at breakdown voltage one of the above two effects will

predominate depending upon breakdown potential difference.

In case of zener effect, breaking of the bond i.e covalent bond by strong

electric field occurs. Avalanche effect occurs due to at higher voltage, when

thermally generated electrons acquire enough to produce more carriers by collision.

Maximum current required to sustain breakdown is called knee current Ik

The maximum current which zener diode can withstand without getting overheated

or burnt is represented by I max. If the current is more than this maximum value,

zener diode will burn out due to overheating.

To reduce overheating, a limiting resistance Rs is connected in series with

zener diode.

Value of Rs is calculated as follows:

P = Power of zener diode = Vz Iz

:. Iz = P

Vz

Where, Vz = break down voltage of diode


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Iz = Current

I max = Selected maximum current allowed to pass through zener diode = 50% of

Iz

Then Rs = VinVz

Imax

Where, Vin = applied voltage.

Reverse current character of zener diode is as shown in the nature of graph.

Diode passes some resistance called zener dynamic resistance Rz. Ideal

zener diode characteristic is not truly vertical, however the zener dynamic R is

very small. This means for considerable increase in Iz the value of Iz remains almost

same. Vz value of diode remain constant over range IkI amx

CIRCUIT DIAGRAM:


44/45



NATURE OF GRAPH:

OBSERVATIONS:-

1. Voltage selected in TPS = Vin =

2. Zener diode break down voltage =

3. I amx

4.

Limiting resistance =

5. Actual value of Rs, selected =

TABULAR COLUMN:

SI. NO. IZin

mA

VZ

(VOLTS)


45/45


CACULATIONS:

AB=

BC=

RZ=

Range of current = IK to Imax

bca experiments

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