edc lab manual
DESCRIPTION
EDC Lab with VIVA and Some additional topics are also includedTRANSCRIPT
ELECTRONIC DEVICES &
CIRCUITS LAB MANUAL
II BTECH, ECE
1ST SEMESTER
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ELECTRONIC DEVICES AND CIRCUITS LAB MANUAL
SECOND YEAR FIRST SEM
STUDY EXPERIEMENTS:-
1. IDENTIFICATION ,SPECIFICATIONS,TESTING OF R,L,C COMPONENTS (COLOR CODES), POTENTIOMETERS, SWITCHES (SPDT,DPDT &DIP), COILS,GANG CONDENSERS, RELAYS,BREAD BOARDError! Bookmark not defined. 2. SOLDERING PRACTICE- SIMPLE CIRCUITS USING ACTIVE AND PASSIVE COMPONENTS16 3. SINGLE LAYER AND MULTI LAYER PCBs 4. STUDY AND OPERATION OF MULTIMETERS, FUNCTION GENERATOR, REGULATED POWER SUPPLIES 5. STUDY & OPERATION OF CRO
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TABLE OF CONTENTS
1. P-N JUNCTION DIODE CHARACTERISTICS
2. ZENER DIODE CHARACTRISTICS.
3. TRANSISTOR COMMON -BASE CONFIGURATION.AND H-PARAMETER CALCULATIONS.
4. TRANSISTOR COMMON -EMITTER CONFIGURATION AND H-PARAMETER CALCULATIONS.
5. HALF-WAVE RECTIFIER (WITH AND WITH OUT FILTER)
6. FULL-WAVE RECTIFIER (WITH AND WITH OUT FILTER)
7. TRANSISTOR CE AMPLIFIER.
8. FET CHARACTERISTICS.
9. SCR CHARACTERISTICS.
10. UJT CHARACTERISTICS.
11. FREQUENCY MEASUREMENT BY USING LISSAJIOUS FIGURES.
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Identification, Specification & Testing Of Components
AIM: To identify the different component symbols.
APPARATUS: Resistors
Capacitors
Transformers
Semi conductors
Transistors
THEORY:
RESISTORS:
Opposition to flow of currents is called resistance. The elements having resistance are
called resistors. They are of two types
1. Fixed resistor
2. Variable resistor
CAPACITORS:
Capacitors are used to store large amount of static current.
When they are included in circuit it acts open circuit. They are three types
1. Disk capacitor
2. Fixed capacitor
3. Variable capacitor
TRANSFORMERS:
Transformers are used to transfer the current.
They are of two types
1. Step up Transformer
2. Step down Transformer
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SEMICONDUCTORS:
Semiconductors are partial conductors which conducts electricity partially through them.
They play major role in electronics.
1 P-N Junction diode
2. Zener diode
Semiconductor is a material for which the width of the forbidden gap between the valence
band conduction is very small. As gap is every small valence electron acquire required energy
to go in to the conduction band. These free electrons constitute of current under the influence of
applied electric field. The energy band is time for semiconductor. They are a class of material
whose electrical conductivity lies between that of a conductor and an insulator. The
conductivity of a semiconductor lies in a range of10^5 and 10^-4siemens/meter.
INDUCTOR SPECIFICATIONS :
1. Inductance Value
2. Resistance
3. Capacitance
4. Frequency Value
5. Quality Factor
6. Power Losses
7. Current Ratings
8. Electro Magnetic Radiations
9. Temperature Coefficient
SWITCHES:
SPST: Single pole single through
SPDT: Single pole double through
DPST: Double pole single through
DPDT: Double pole double through
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DIODES:
Diodes have more priority now a days. They are mostly used in developing electronic
systems. They are
1. P-N Junction diode
2. Zener diode
Zener diode is background biasing voltage. So it also called voltage requesting diode.
TRANSISTORS:
They are of 4 types
1. BJT: Bi polar junction transistor again 2 types
NPN-BJT
PNP-BJT
Here B-base
C-collector
E-Emitter
2. FET: Field effect transistors again 2 types
P-Channel FET
N-Cannel FET
Here G-Gate terminal
D-Drain terminal
S-Source terminal
3. JFET: Junction field effect transistors they similar to FET.
4. MOSFET: Metal oxide semiconductor field effect transistor
These are of two types
a. Depletion MOSFET:
These are again classified into two types
N-Channel MOSFET
P-Channel MOSFET
Here ss is substrate
b. Enhancement MOSFET:
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These are again classified into two types
N-Channel MOSFET
P-Channel MOSFET
Here G-Gate terminal
D-Drain terminal
S-Source terminal
ss-subsstrate
CIRCUIT DIAGRAM:
RESISTORS:
-fixed resistor
-variable resistor
CAPACITORS:
-fixed capacitor
-variable capacitor
INDUCTORS:
-Fixed inductor
Variable inductor
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TRANSFORMERS:
Primary secondary
SWITCHES:
SPST
SPDT
DPST
DPDT
SEMICONDUCTORS:
P-N Junction diode
Zener diode
BREAD BOARD
An experimental version of a circuit generally lay out on a flat board and assembled with
temporary connections so that circuit elements may be easily substituted or changed. The name
originates from the fact that early electrical circuits were actually wired on wood bread boards.
It is used to connect an electronic circuit temporarily for testing and experimentation.
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A typical bread board is shown in fig.
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RESISTOR COLOR CODE
The resistance value and tolerance of carbon resistor is usually indicated by color coding. Color
bands are printed on insulating body. They consist of four color bands or 5 color bands & they
are read from left to right.
A typical resistor with color bands is shown in figure
The above resistor has 4 color bands.
The first band represents first digit
The second band represent second digit
The third band represent multiplier (this gives the no. of zeros after the 2 digits )
The 4th band represents tolerance in %
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The color codes are presented in below table
COLOR First digit for
the 1st band
Second digit
for the 2nd
band
Multiplier
digit for the
3rd band
Resistance
tolerance
Black 0 0 10^0 -
Brown 1 1 10^1 ±1%
Red 2 2 10^2 ±2%
Orange 3 3 10^3 ±3%
Yellow 4 4 10^4 -
Green 5 5 10^5 -
Blue 6 6 10^6 -
Violet 7 7 10^7 -
Gray 8 8 10^8 -
White 9 9 10^9 -
Gold - - 10^-1 ±5%
Silver - - 10^-2 ±10%
No color - - - ±20%
-
If third band is gold the first two digit are multiplied by 10^-1
If the third band is silver the first two digits are multiplied by 10^-2
If the 4th band is gold the tolerance is ±5%
If the 4th band is silver is the tolerance is ±10%
If the 4th band is no color the tolerance is ±20%
The numerical value associated with each color
B B R O Y G B V G W
black brown red orange Yellow green blue violet gray White
0 1 2 3 4 5 6 7 8 9
EXAMPLES:
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The resistor has a color band sequence green, blue, brown and silver identify the resistance
value.
1ST Band 2nd band 3rd band 4th band
1st digit 2nd digit multiplier tolerance
5 6 10^1 ±10%
The resistance value=56x10^1±10%
=560Ω±10%
Therefore the resistance should be with in the range of 555Ω to 565Ω
SECIFICATIONS FO RLC COMPONENTS
RESISTOR:
1. Resistance value:
This is the value of the resistance expressed in ohms.
Ex: 10Ω, 1MΩ
2. Tolerance:
This is the variation in the value of the resistance i.e. expected from exact indicated value
usually tolerance is represented in %
ex: 1%,2%,20%...
2. Power rating:
The power rating is very important in the sense that it determines the maximum correct that
a resistor can withstand without being destroyed.
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The power rating of resistor is specified as so many watts at a specific temperature such as one
or two watts at 70 degree.
CAPACITOR:
1. Value of capacitance
2. Tolerance
3. Voltage rating
4. Temperature coefficient
5. Leakage resistance
6. Frequency range
7. Dielectric constant
8. dielectric strength
9. power factor
10. Stability
INDUCTOR;
Inductor value:
The inductance is defined as the ability of an inductor which opposes the change in
current. It is denoted by the letter “L” and its unit is Henry(H).Ex:1H.2H…
Mutual inductance:
It is the ability of a varying current in one inductor L1 induced voltage in another
inductor L2 near by .
It is represented by Lm and is measured in Henry.
M=K√ (L1XL2) H
Coefficient if coupling:
It is defined as the ratio of flux linkages between L1 and L2. To total flux produced
by L1. It is represented by K and its typical value is 1.
K=Lm/√ (L1XL2)
Permeability:
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It is denoted by micro’s” and it is return as µ=B/H.
Where B=flux density
H=Flux intensity
PROCEDURE:
Different components can be identified by using their different symbols.
RESULT:
Components should be identified by using their symbols.
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2. SOLDERING PRACTICE- SIMPLE CIRCUITS USING
ACTIVE AND PASSIVE COMPONENTS
Soldering is a process for joining metal parts with the aid of molten metal, where the melting
temperature is situated below that of material joined and where by the surface of part are coated
without turn in becoming molten.
A soldering connection ensures metal continuity on the other hand, when two metals are joined
, behave like a single solid metal by joining disconnected. (or) physically attaching to each
other, the connection could be
Types of soldering:
1. Iron soldering
2. Mass soldering
3. Dip soldering
4. Wave soldering
Solder alloys:
Tin lead, Tin antimony, Tin lead antimony, Tn silver, Tin Zinc.
Soldering is an alloying process between two metals with which it divides some of the metal,
with which it comes into contact. A flux is used to remove this oxide from the area to be
soldered.
Soldering of solder alloy:
Even though the alloy Sb 60/pb 60 is cheaper and still finds a good market, it is advisable to
prefer Sn63/pb 37 for high quality inter connection because
It has a5c higher melting point which means soldering range is 5c higher.
The tensile strength as well as shoal strength of Sn60/pb 37
Is higher in comparison to Sn60/pb 40.
Only tin trans the inter molecular bond with copper of CU3Sn andCU6SN.
The specific gravity of Sn63/ pb 37 is also lesser than that of Sn60/ pb 40.
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Higher composition of tin increases the electrical as well as thermal conductivity. I t also gives
brightness to the joint flux.
FLUX: To aid the soldering process, a substance called flux is used. Flux has below three
purposes.
Remove the film of turnish from the metal surface to be soldered.
To prevent the base metals from being re exposed to oxygen in the air to be avoid oxidation
during heating, which means rotation of welding by preventing from oxidation.
Assist in the transfer of heat to metal being soldered.
The soldering process involves
1. Melting of the solder which makes the higher flux and brings the impurities suspended in it
to the surface.
2. Partial dissolution of some metals in the connection by solder.
3. Cooling and fusing solder with the metal quest often for locating a problem in the
functioning of the circuit.
It is necessary to remove a component from the printed circuit board and carryout the requisite
tests on it.
The process of repair usually involves
Disassembly of a particular component.
Testing of component
Replacing of the component found defective.
4.In this process of removal and replacement of electronic devices, the process of
soldering is employed. specific gravity of Sn63/ pb 37 is also lesser than that of Sn60/p 40 that
makes the equipment lighter.
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3.SINGLE LAYER AND MULTI LAYER PCBs
AIM: To study the single layer and multi layer PCBs.
APPARATUS: PCB
The design of PCB is considered as the last step in electronic design as well as the major step in
the production of PCB. It is a board consisting of printed circuit of electronic equipment on it
and is used for the designing of circuit.
THE STEPS FOR DESIGNING PCB are
1. Layout planning
2. Art work
3. Film master production
4. Pattern transfer (photo/screen printing)
5. Plasting
6. Etching
7. Mechanical matching operations
The layout is the work done before the art work in the PCB. It provides all the information
about the circuit, which has to drawn on PCB.Protection of copper tracks is very much essential
Plasting is such a process which forms a thin layer over copper tracks and protect them.
Generally, it is done with gold.
Types of copper plating: Copper plating
Nickel plating
Gold plating
Tin plating
Tin lead plating
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Etching means to draw on board by the action of acid, especially by coating the surface with
wax and letting the acid cast into the lines or area laid bar with needle.
Spray etching
Laminate etching
Splash etching (Configured force by rotating in centre).
The double sided PCB’s are made with or without plated through holes.
Fabrication of plated through holes type boards is very expensive.
Two types: Plated through holes
No plated through holes.
In plated through holes, the total no. of holes is kept minimum for economy and reliability.
In no plated through holes, contacts are made by soldering the component lead on both sides of
board when required and jumper wires are added. There should be minimum solder joints on
the component sides. Replacing of such components is different.
Result: Single Layer and Multilayer PCB’s are studied
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4. STUDY AND OPERATION OF MULTIMETERS, FUNCTION
GENERATOR, REGULATED POWER SUPPLIES
AIM: To study and operation of multiimeters, function generator, and regulated power supply.
APPARATUS: Multimeter
Function generator
Regulated power supply.
THEORY:
REGULATED POWER SUPPLY
Power supplies provided by a regulated DC voltage facilities fine and coarse
adjustments and monitoring facilities for voltage and current. They will work in constant
voltage and current mode depending on current limit and output load.
The current limit has good stability, load and line regulations. Outputs are protected
against overload and short circuit damages. They are available in single and dual channel
models with different voltage and current capacities. Overload protection circuit of constant
self restoring type is provided to prevent the unit as well as the circuit under use.
The power supplies are specially designed and developed for well regulated DC
output.
These are useful for high regulation laboratory power supplies, particularly suitable
for experimental setup and circuit development in R&D.
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FUNCTION GENERATOR
Designation Specifications
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Wave form : Sine, squares, triangles, TTL square waves
Amplitude : 0-20V for all the functions.
Sine distortion : Less than 1% from 0.1 HZ to 100 HZ harmonics
Modulation showed down fundamental for 100K
HZ to 1MHG.
Offset : Continuously variable 10V
Frequency range : 0.1 HZ to 1Μhz in ranges.
Output impedance : 600 ohms, 5%.
Square wave duty cycle : 49% to 51%.
Differential linearity : 0.5%
Range selectors: Decode frequency by multiplying the range selected with the frequency
indicated by dial gives the output frequency, which applies for all functions.
Function selectors: Selected desired output wave form which appears at 600Ω output.
VCO input: An external input will vary the output frequency. The change in frequency is
directly proportional to input voltage.
TTL output: A TTL square wave is available at this jack. The frequency is determined by the
range selected and the setting of frequency dial. This output is independent of amplitude and
D.C OFFSET controls.
Amplitude control: Control he amplitude of the output signal, which appears at 600ohms.
OFFSET control: Control the DC offset of the output. It is continuously variable for ±5V,
±100V.
Fine frequency dial: Multiplying the setting of this dial to the frequency range selected gives
the output frequency of the wave forms at the 600ohms.
MULTIMETER:
DIGITAL MULTIMETER
A multimeter is a versatile instrument and is also called Volt-Ohm-Milliammeter (VOM).
It is used to measure the d.c and a.c voltages and resistance values.
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A digital multimeters essentially consists of an analog to digital converters. It
converters analog values in the input to an equivalent binary forms. These values are processed
by digital circuits to be shown on the visual display with decimal values. The liquid crystal
display system is generally employed. Actually all the functions in DMM depend ion the
voltage measurements by the converter and comparator circuits
Result: The operation of multiimeters, function generator, and Regulated Power Supply are
studied
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5.STUDY & OPERATION OF CRO
AIM: To observe front panel control knobs and to find amplitude, time period and frequency
for given waveforms and also find phase by using the lissajous figures.
APPARATUS: Cathode Ray Oscilloscope, function generator, connecting wires.
THEORY: C.R.O is a versatile instrument used for display of wave forms and is a fast x-y
plotter.
The heart of C.R.O is and the rest is the circuitry to operate C.R.O
The main parts are
1. Electron gun: - it is used to produce sharply focused beam of electron accelerated to very
high velocity.
2. Deflection system: - it deflects the electron both in horizontal and vertical plan.
3. Florescent screen:- the screen which produces, spot of visible light . when beam of electrons
are incident on it the other side of tube is coated with phosphorus material.
FRONT PANNEL:
ON-POWER: toggle switch for switching on power.
INTENCITY: controls trace intensity from zero to maximum.
FOCUS: It controls sharpness of trace a slight adugestement of focus is done after changing
intensity of trace.
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AC-DC: GROUND:
It selects coupling of AC-DC ground signal to vertical amplifier.
X-MAG: It expands length of time base from 1-5 times continuously and to maximum time
base to 40 ns/cm.
SQUARE:
This provides square wave 2v (p-P) amplitude and enables to check y calibration of scope.
SAWTOOTH WAVE FORM:
This provides saw tooth wave form output coincident to sweep speed with an output of saw
tooth wave (p-p)
VERTICAL SECTION: y position:
This enables movement of display along y-axis.
Y-INPUT: It connects input signal to vertical amplifier through AC-DC ground coupling
switch
CALIBRATION: 15mv – 150mv dc signal depending on position selection is applied to
vertical amplifier.
DC BALANCE: It is control on panel electrostatic ally in accordance with waveforms to be
displayed.
VOLTS/CM: Switch adjusts sensitivity.
HORIZANTAL SECTION:
X-POSITION: This control enables movement of display along x-axis.
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TRIGGERING LEVEL: It selects mode of triggering.TIMEBASE: This controls or selects
sweep speeds.
VERNUIS: This control the fine adjustments associated with time base sweep.
SIGN SELECTOR: It selects different options of INT/EXT, NORM/TO.
STAB: Present on panel
EXITCAD: It allows time base range to be extended.
HORIZANTAL INPUT: It connects external signal to horizontal amplifier.
Ext SYN: it connects external signal to trigger circuit for synchronization.
OBSERVATIONS:-
Amplitude = no. of vertical divisions * Volts/div.
Time period = no. of horizontal divisions * Time/div.
Frequency=1/T
Amlitude taken on vertical section (y).
Time period taken on horizontal section(x)
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MODEL WAVE FORMS
MESURMENT OF PHASE :
φ = sin -1 Y1 = sin -1 X1 φ = 180- sin -1 Y1
Y2 X2 Y2
Y1 Y2
x1
X2
Y2 Y1
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APPLICATIONS OF CRO:
1. Measurement of current
2. Measurement of voltage
3. Measurement of power
4. Measurement of frequency
5. Measurement of phase angle
6. To see transistor curves
7. To trace and measuring signals of RF, IF and AF in radio and TV.
8. To trace visual display of sine waves.
RESULT: To calculated the given waveform, frequency, amplitude and phase.
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1. P-N JUNCTION DIODE CHARACTERISTICS
AIM:-To observe and draw the Forward and Reverse bias V-I Characteristics of a P-N
Junction diode.
APPARATUS:-
P-N Diode IN4007.
Regulated Power supply (0-30v)
Resistor 1KΩ
Ammeters (0-100 mA, 0-100uA)
Voltmeter (0-20 V)
Bread board
Connecting wires
THEORY:-
A p-n junction diode conducts only in one direction. The V-I
characteristics of the diode are curve between voltage across the diode and current
through the diode. When external voltage is zero, circuit is open and the potential
barrier does not allow the current to flow. Therefore, the circuit current is zero. When P-
type (Anode is connected to +ve terminal and n- type (cathode) is connected to –ve
terminal of the supply voltage, is known as forward bias. The potential barrier is reduced
when diode is in the forward biased condition. At some forward voltage, the potential
barrier altogether eliminated and current starts flowing through the diode and also in
the circuit. The diode is said to be in ON state. The current increases with increasing
forward voltage.
When N-type (cathode) is connected to +ve terminal and P-type
(Anode) is connected –ve terminal of the supply voltage is known as reverse bias and
the potential barrier across the junction increases. Therefore, the junction resistance
becomes very high and a very small current (reverse saturation current) flows in the
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circuit. The diode is said to be in OFF state. The reverse bias current due to minority
charge carriers.
CIRCUIT DIAGRAM:-
FORWARD BIAS:-
REVERSE BIAS:-
circuit. The diode is said to be in OFF state. The reverse bias current due to minority circuit. The diode is said to be in OFF state. The reverse bias current due to minority
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MODEL WAVEFORM:-
PROCEDURE:-
FORWARD BIAS:-
1. Connections are made as per the circuit diagram.
2. For forward bias, the RPS +ve is connected to the anode of the diode and
RPS –ve is connected to the cathode of the diode,
3. Switch on the power supply and increases the input voltage (supply voltage) in
Steps.
4. Note down the corresponding current flowing through the diode and voltage
across the diode for each and every step of the input voltage.
5. The reading of voltage and current are tabulated.
6. Graph is plotted between voltage and current.
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OBSERVATION:-
S.NO APPLIED VOLTAGE (V) VOLTAGE ACROSS
DIODE(V)
CURRENT
THROUGH
DIODE(mA)
PROCEDURE:-
REVERSE BIAS:-
1. Connections are made as per the circuit diagram
2 . For reverse bias, the RPS +ve is connected to the cathode of the diode and
RPS –ve is connected to the anode of the diode.
3. Switch on the power supply and increase the input voltage (supply voltage) in
Steps
4. Note down the corresponding current flowing through the diode voltage
across the diode for each and every step of the input voltage.
5. The readings of voltage and current are tabulated
6. Graph is plotted between voltage and current.
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OBSEVATION:-
S.NO APPLIEDVOLTAGE
ACROSSDIODE(V)
VOLTAGE
ACROSS
DIODE(V)
CURRENT
THROUGH
DIODE(mA)
PRECAUTIONS:-
1. All the connections should be correct.
2. Parallax error should be avoided while taking the readings from the Analog meters.
RESULT:- Forward and Reverse Bias characteristics for a p-n diode is observed
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VIVA QESTIONS:-
1. Define depletion region of a diode?
2. What is meant by transition & space charge capacitance of a diode?
3. Is the V-I relationship of a diode Linear or Exponential?
4. Define cut-in voltage of a diode and specify the values for Si and Ge diodes?
5. What are the applications of a p-n diode?
6. Draw the ideal characteristics of P-N junction diode?
7. What is the diode equation?
8. What is PIV?
9. What is the break down voltage?
10. What is the effect of temperature on PN junction diodes?
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2. ZENER DIODE CHARACTERISTICS
AIM: - a) To observe and draw the V-I characteristics of a zener diode
b) To find the Zenaer Breakdown voltage,static resistance
and Dynamic resistance after breakdown.
APPARATUS: -
Zener diode.
Regulated Power Supply (0-30v).
Voltmeter (0-20v)
Ammeter (0-50mA)
Resistor (1KOhm)
Bread Board
Connecting wires Theory:-
A zener diode is heavily doped p-n junction diode, specially made to
operate in the break down region. A p-n junction diode normally does not conduct
when reverse biased. But if the reverse bias is increased, at a particular voltage it
starts conducting heavily. This voltage is called Break down Voltage. High current
through the diode can permanently damage the device
To avoid high current, we connect a resistor in series with zener diode.
Once the diode starts conducting it maintains almost constant voltage across the
terminals what ever may be the current through it, i.e., it has very low dynamic
resistance. It is used in voltage regulators.
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CIRCUIT DIAGRAM:- FORWARD BIAS CHARACTERISTICS:-
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REVERSE BIAS CHARACTERISTICS:-
PROCEDURE:- Forward bias characteristics:-
1. Connections are made as per the circuit diagram.
2. The Regulated power supply voltage is increased in steps.
3. The zener current (lz), and the zener voltage (Vz.) are observed and then
noted in the tabular form.
4. A graph is plotted between zener current (Iz) and zener voltage (Vz).
Reverse bias characteristics:-
1. Connection are made as per the circuit diagram.
2. The Regulated power supply voltage is increased in steps untill break down occurs
and note down the corresponding zener current from ammeter.
3. Repeat it for different values of reverse voltage and note the readings.
4. A graph is plotted between zener current (IR) and zener voltage (VR).
5.Identify the reverse saturation current andbreakdown voltage “V” of the zener diode
and calculate the static and dynamic resistance from the graph.
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OBSERVATIONS:- Forward Bias characteristics:-
S.NO ZENER VOLTAGE(VZ)
ZENER CURRENT(IZ)
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Reverse Bias characteristics:- S.NO
ZENER VOLTAGE(VR)
ZENER CURRENT(IR)
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MODEL WAVEFORMS:-
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PRECAUTIONS:-
1. The terminals of the zener diode should be properly identified
2. Parallax error should be avoided while taking the readings from the Analog meters.
RESULT:-
a) V-I characteristics of zener diode are obtained and drawn.
b) The Zener Breakdown voltage,static resistance and Dynamic resistance of Zener
Diode are calculated .
VIVAQUESTIONS:-
1. What type of temp Coefficient does the zener diode have?
2. If the impurity concentration is increased, how the depletion width effected?
3. Does the dynamic impendence of a zener diode vary?
4. Explain briefly about avalanche and zener breakdowns?
5. Draw the zener equivalent circuit?
6. In which region zener diode can be used as a regulator?
7. How the breakdown voltage of a particular diode can be controlled?
8. What type of temperature coefficient does the Avalanche breakdown has?
9. By what type of charge carriers the current flows in zener and avalanche
breakdown diodes?
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3. TRANSISTOR COMMON -BASE CONFIGURATION AND H-
PARAMETER CALCULATIONS
AIM: 1.To observe and draw the input and output characteristics of a transistor
connected in common base configuration.
2. To find α of the given transistor.
APPARATUS: Transistor, BC 107
Regulated power supply (0-30V, 1A)
Voltmeter (0-20V)
Ammeters (0-100mA)
Resistor, 1000Ω
Bread board
Connecting wires
THEORY:
A transistor is a three terminal active device. T he terminals are emitter, base,
collector. In CB configuration, the base is common to both input (emitter) and output
(collector). For normal operation, the E-B junction is forward biased and C-B junction is
reverse biased.
In CB configuration, IE is +ve, IC is –ve and IB is –ve. So,
VEB=f1 (VCB,IE) and
IC=f2 (VCB,IB)
With an increasing the reverse collector voltage, the space-charge width at the
output junction increases and the effective base width ‘W’ decreases. This
phenomenon is known as “Early effect”. Then, there will be less chance for
recombination within the base region. With increase of charge gradient with in the
base region, the current of minority carriers injected across the emitter junction
increases.The current amplification factor of CB configuration is given by,
α= ∆IC/ ∆IE
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Output resistance is the ratio of change of collector emitter voltage ∆VCE , to change in
collector current ∆IC with constant IB. Output resistance or Output impedance hoe =
∆VCE / ∆IC at IB constant.
Input Impedance hie = ∆VBE / ∆IE at VCB constant
Output impedance hoe = ∆VCB / ∆IC at IE constant
Reverse Transfer Voltage Gain hre = ∆VBE / ∆VCB at IB constant
Forward Transfer Current Gain hfe = ∆IC / ∆IE at constant VCB
CIRCUIT DIAGRAM
PROCEDURE:
INPUT CHARACTERISTICS:
1. Connections are made as per the circuit diagram.
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2. For plotting the input characteristics, the output voltage VCB is kept constant at 0V
and for different values of VEB note down the values of IE.
3. Repeat the above step keeping VCB at 1V, 2V, and 3V.All the readings are
tabulated.
4. A graph is drawn between VEB and IE for constant VCB.
OUTPUT CHARACTERISTICS:
1. Connections are made as per the circuit diagram.
2. For plotting the output characteristics, the input IE iskept constant at 1m A and for
different values of VCB, note down the values of IC.
3. Repeat the above step for the values of IE at 2 mA, 4 mA, and 6 mA, all the
readings are tabulated.
4. A graph is drawn between VCB and Ic for constant IE
OBSERVATIONS:
INPUT CHARACTERISTICS:
S.No VCB=0V VCB=1V VCB=2V
VEB(V) IE(mA) VEB(V) IE(mA) VEB(V) IE(mA)
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OUTPUT CHARACTERISTICS:
S.No
IE=1mA IE=2mA IE=3mA
VCB(V) IC(mA) VCB(V) IC(mA) VCB(V) IC(mA)
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MODEL GRAPHS:
INPUT CHARACTERISTICS
OUTPUT CHARACTERISTICS
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PRECAUTIONS:
1. The supply voltages should not exceed the rating of the transistor.
2. Meters should be connected properly according to their polarities.
RESULT:
1. The input and output characteristics of the transistor are drawn.
2.The α of the given transistor is calculated. .
3.H-Parameters for a transistor in CE configuration are calculated from the input and
output characteristics.
1. Input Impedance hie =
2. Reverse Transfer Voltage Gain hre =
3. Forward Transfer Current Gain hfe =
4. Output conductance hoe =
VIVA QUESTIONS:
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1. What is the range of α for the transistor?
2. Draw the input and output characteristics of the transistor in CB configuration?
3. Identify various regions in output characteristics?
4. What is the relation between α and β?
5. What are the applications of CB configuration?
6. What are the input and output impedances of CB configuration?
7. Define α(alpha)?
8. What is EARLY effect?
9. Draw diagram of CB configuration for PNP transistor?
10. What is the power gain of CB configuration?
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4.TRANSISTOR CE CHARACTERSTICS AND
H-PARAMETER CALCULATIONS
AIM: 1. To draw the input and output characteristics of transistor connected in
CE configuration
2. To find β of the given transistor.
APPARATUS:
Transistor (BC 107)
R.P.S (O-30V) 2Nos
Voltmeters (0-20V) 2Nos
Ammeters (0-200µA)
(0-500mA)
Resistors 1Kohm 1No
10 Kohm 1No
Bread board
Connecting wires
THEORY:
A transistor is a three terminal device. The terminals are emitter, base,
collector. In common emitter configuration, input voltage is applied between base and
emitter terminals and out put is taken across the collector and emitter terminals.
Therefore the emitter terminal is common to both input and output.
The input characteristics resemble that of a forward biased diode curve. This
is expected since the Base-Emitter junction of the transistor is forward biased. As
compared to CB arrangement IB increases less rapidly with VBE . Therefore input
resistance of CE circuit is higher than that of CB circuit.
The output characteristics are drawn between Ic and VCE at constant IB. the
collector current varies with VCE unto few volts only. After this the collector current
becomes almost constant, and independent of VCE. The value of VCE up to which the
collector current changes with V CE is known as Knee voltage. The transistor always
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operated in the region above Knee voltage, IC is always constant and is approximately
equal to IB.
The current amplification factor of CE configuration is given by
Β = ∆IC/∆IB.
The transistor always operates in the active region. I.e. the collector current
IC increases with VCE very slowly. For low values of the VCE the IC increases
rapidly with a small increase in VCE .The transistor is said to be working in saturation
region.
Output resistance is the ratio of change of collector emitter voltage ∆VCE , to
change in collector current ∆IC with constant IB. Output resistance or Output
impedance hoe = ∆VCE / ∆IC at IB constant.
Input Impedance hie = ∆VBE / ∆IB at VCE constant
Output impedance hoe = ∆VCE / ∆IC at IB constant
Reverse Transfer Voltage Gain hre = ∆VBE / ∆VCE at IB constant
Forward Transfer Current Gain hfe = ∆IC / ∆IB at constant VCE
CIRCUIT DIAGRAM:
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PROCEDURE:
INPUT CHARECTERSTICS:
1. Connect the circuit as per the circuit diagram.
2. For plotting the input characteristics the output voltage VCE is kept constant at 0V
and for different values of VBE . Note down the values of IB
3. Repeat the above step by keeping VCE at 1V and 2V.
4. Tabulate all the readings.
5. plot the graph between VBE and IB for constant VCE
OUTPUT CHARACTERSTICS:
1. Connect the circuit as per the circuit diagram
2. for plotting the output characteristics the input current IB is kept constant at
10µA and for different values of VCE note down the values of IC
3. repeat the above step by keeping IB at 20 µA ,40 µA
4. tabulate the all the readings
5. plot the graph between VCE and IC for constant IB
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OBSERVATIONS:
INPUT CHARACTERISTICS:
S.NO
VCE = 0V VCE = 1V VCE = 2V
VBE(V) IB(µA) VBE(V) IB(µA) VBE(V) IB(µA)
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OUT PUT CHAREACTARISTICS:
S.NO
IB = 10 µA IB = 20 µA IB = 40 µA
VCE(V) IC(mA) VCE(V) ICmA) VCE(V) IC(mA)
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MODEL GRAPHS:
INPUT CHARACTERSTICS:
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OUTPUT CHARECTERSTICS:
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PRECAUTIONS:
1. The supply voltage should not exceed the rating of the transistor
2. Meters should be connected properly according to their polarities
RESULT:
1. The input and out put characteristics of a transistor in CE configuration are
Drawn
2.the β of a given transistor is calculated
3.H-Parameters for a transistor in CE configuration are calculated from the
input and output characteristics.
5. Input Impedance hie =
6. Reverse Transfer Voltage Gain hre =
7. Forward Transfer Current Gain hfe =
8. Output conductance hoe =
VIVA QUESTIONS:
1. What is the range of β for the transistor?
2. What are the input and output impedances of CE configuration?
3. Identify various regions in the output characteristics?
4. what is the relation between βα and
5. Define current gain in CE configuration?
6. Why CE configuration is preferred for amplification?
7. What is the phase relation between input and output?
8. Draw diagram of CE configuration for PNP transistor?
9. What is the power gain of CE configuration?
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10. What are the applications of CE configuration?
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5. HALF – WAVE RECTIFIER
AIM: - To obtain the load regulation and ripple factor of a half-rectifier.
1. with Filter
2. without Filter
APPARATUS:-
Experimental Board
Multimeters –2No’s.
Transformer (6-0-6).
Diode, 1N 4007
Capacitor 100µf.
Resistor 1KΩ.
Connecting wires
THEORY: -
During positive half-cycle of the input voltage, the diode D1 is in forward bias
and conducts through the load resistor R1. Hence the current produces an output
voltage across the load resistor R1, which has the same shape as the +ve half cycle of
the input voltage.
During the negative half-cycle of the input voltage, the diode is reverse biased
and there is no current through the circuit. i.e, the voltage across R1 is zero. The net
result is that only the +ve half cycle of the input voltage appears across the load. The
average value of the half wave rectified o/p voltage is the value measured on dc
voltmeter.
For practical circuits, transformer coupling is usually provided for two
reasons.
1. The voltage can be stepped-up or stepped-down, as needed.
2. The ac source is electrically isolated from the rectifier. Thus preventing
shock hazards in the secondary circuit.
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CIRCUIT DIAGRAM:-
With out Filter:
With Filter:
PROCEDURE:-
1. Connections are made as per the circuit diagram.
2. Connect the primary side of the transformer to ac mains and the secondary side to
the rectifier input.
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3. By the multimeter, measure the ac input voltage of the rectifier and, ac and dc
voltage at the output of the rectifier.
4. Find the theoretical of dc voltage by using the formula,
Vdc=Vm/П
Where, Vm=2Vrms, (Vrms=output ac voltage.)
The Ripple factor is calculated by using the formula
r=ac output voltage/dc output voltage.
REGULATION CHARACTERSTICS:-
1. Connections are made as per the circuit diagram.
2. By increasing the value of the rheostat, the voltage across the load and current
flowing through the load are measured.
3. The reading is tabulated.
4. Draw a graph between load voltage (VL and load current ( IL ) taking VL on X-
axis and IL on y-axis
5. From the value of no-load voltages, the %regulation is calculated using the
formula,
Theoretical calculations for Ripple factor:-
Without Filter:-
Vrms=Vm/2
Vm=2Vrms
Vdc=Vm/П
Ripple factor r=√ (Vrms/ Vdc )2 -1 =1.21
With Filter:-
Ripple factor, r=1/ (2√3 f C R)
Where f =50Hz
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C =100µF
RL=1KΩ
PRACTICAL CALCULATIONS:-
Vac=
Vdc=
Ripple factor with out Filter =
Ripple factor with Filter =
OBSERVATIONS:-
WITHOUT FILTER
USING
DMM
Vac(v) Vdc(v) r= Vac/ Vdc
WITH FILTER
USING
DMM
Vac(v) Vdc(v) r= Vac/ Vdc
WITHOUTFILTER:-
Vdc=Vm/П, Vrms=Vm/2, Vac=√ ( Vrms2- Vdc 2)
Vm(v) Vac(v) Vdc(v) r= Vac/ Vdc
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USING
CRO
WITHFILTER
USINGCRO
V1(V) V2(V) Vdc=
(V1+V2)/2
Vac=
(V1- V2)/2√3
r=
Vac/
Vdc
PRECAUTIONS:
1. The primary and secondary sides of the transformer should be carefully identified.
2. The polarities of the diode should be carefully identified.
3. While determining the % regulation, first Full load should be applied and then it
should be decremented in steps.
RESULT:-
1. The Ripple factor for the Half-Wave Rectifier with and without filters is measured.
2. The % regulation of the Half-Wave rectifier is calculated.
VIVA QUESTIONS:
1. What is the PIV of Half wave rectifier?
2. What is the efficiency of half wave rectifier?
3. What is the rectifier?
4. What is the difference between the half wave rectifier and full wave
Rectifier?
5. What is the o/p frequency of Bridge Rectifier?
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6. What are the ripples?
7. What is the function of the filters?
8. What is TUF?
9. What is the average value of o/p voltage for HWR?
10. What is the peak factor?
6. FULL-WAVE RECTIFIER
AIM:-To find the Ripple factor and regulation of a Full-wave Rectifier with and without
filter.
APPARATUS:-
Experimental Board
Transformer (6-0-6v).
P-n Diodes, (lN4007) ---2 No’s
Multimeters –2No’s
Filter Capacitor (100µF/25v) -
Connecting Wires
Load resistor, 1KΩ
THEORY:-
The circuit of a center-tapped full wave rectifier uses two diodes
D1&D2. During positive half cycle of secondary voltage (input voltage), the diode D1 is
forward biased and D2is reverse biased.
The diode D1 conducts and current flows through load resistor RL. During
negative half cycle, diode
D2 becomes forward biased and D1 reverse biased. Now, D2 conducts and
current flows through the load resistor RL in the same direction. There is a continuous
current flow through the load resistor RL, during both the half cycles and will get
unidirectional current as show in the model graph. The difference between full wave
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and half wave rectification is that a full wave rectifier allows unidirectional (one way)
current to the load during the entire 360 degrees of the input signal and half-wave
rectifier allows this only during one half cycle (180 degree).
CIRCUIT DIAGRAM:-
Without Filter:
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With Filter :
PROCEDURE:
1. Connections are made as per the circuit diagram.
2. Connect the ac mains to the primary side of the transformer and the secondary
side to the rectifier.
3. Measure the ac voltage at the input side of the rectifier.
4. Measure both ac and dc voltages at the output side the rectifier.
5. Find the theoretical value of the dc voltage by using the formula Vdc=2Vm/П
6. Connect the filter capacitor across the load resistor and measure the values of
Vac and Vdc at the output.
7. The theoretical values of Ripple factors with and without capacitor are
calculated.
8. From the values of Vac and Vdc practical values of Ripple factors are
calculated. The practical values are compared with theoretical values.
THEORITICAL CALCULATIONS:-
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Vrms = Vm/ √2
Vm =Vrms√2
Vdc=2Vm/П
(i)Without filter:
Ripple factor, r = √ ( Vrms/ Vdc )2 -1 = 0.482
(ii)With filter:
Ripple factor, r = 1/ (4√3 f C RL) where f =50Hz
C =100µF
RL=1KΩ
PRACTICAL CALCULATIONS:
Without filter:-
Vac=
Vdc=
Ripple factor, r=Vac/Vdc
With filters:-
Vac=
Vdc=
Ripple factor=Vac/Vdc
Without Filter:
USING
DMM
Vac(v) Vdc(v) r= Vac/ Vdc
With Filter
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USING
DMM
Vac(v) Vdc(v) r= Vac/ Vdc
Without Filter
Vrms = Vm/ √2 , Vdc=2Vm/П , Vac=√( Vrms2- Vdc 2)
USING
CRO
Vm(v) Vac(v) Vdc(v) r= Vac/ Vdc
With Filter
USINGCRO
V1(V) V2(V) Vdc=
(V1+V2)/2
Vac=
(V1-
V2)/2√3
r=
Vac/
Vdc
PRECAUTIONS:
1. The primary and secondary side of the transformer should be carefully identified
2. The polarities of all the diodes should be carefully identified.
RESULT:-
The ripple factor of the Full-wave rectifier (with filter and without filter) is calculated.
VIVA QUESTIONS:-
1. Define regulation of the full wave rectifier?
2. Define peak inverse voltage (PIV)? And write its value for Full-wave rectifier?
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3. If one of the diode is changed in its polarities what wave form would you get?
4. Does the process of rectification alter the frequency of the waveform?
5. What is ripple factor of the Full-wave rectifier?
6. What is the necessity of the transformer in the rectifier circuit?
7. What are the applications of a rectifier?
8. What is ment by ripple and define Ripple factor?
9. Explain how capacitor helps to improve the ripple factor?
10. Can a rectifier made in INDIA (V=230v, f=50Hz) be used in USA (V=110v,
f=60Hz)?
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7. FET CHARACTERISTICS
AIM: a). To draw the drain and transfer characteristics of a given
FET.
b). To find the drain resistance (rd) amplification factor (µ) and
Transe conductance (gm) of the given FET.
APPARATUS: FET (BFW-11)
Regulated power supply
Voltmeter (0-20V)
Ammeter (0-100mA)
Resistors 100 Ώ 1No
560 Ώ 1No
Bread board
Connecting wires
THEORY:
A FET is a three terminal device, having the characteristics of high input impedance
and less noise, the Gate to Source junction of the FET s always reverse biased. In
response to small applied voltage from drain to source, the n-type bar acts as sample
resistor, and the drain current increases linearly with VDS. With increase in ID the ohmic
voltage drop between the source and the channel region reverse biases the junction
and the conducting position of the channel begins to remain constant. The VDS at this
instant is called “pinch of voltage”.
If the gate to source voltage (VGS) is applied in the direction to provide
additional reverse bias, the pinch off voltage ill is decreased.
In amplifier application, the FET is always used in the region beyond the
pinch-off.
FDS=IDSS(1-VGS/VP)^2
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CIRCUIT DIAGRAM
PROCEDURE:
1. All the connections are made as per the circuit diagram.
2. To plot the drain characteristics, keep VGS constant at 0V.
3. Vary the VDD and observe the values of VDS and ID.
4. Repeat the above steps 2, 3 for different values of VGS at 1V and 3V.
5. All the readings are tabulated.
6. To plot the transfer characteristics, keep VDS constant at 1V.
7. Vary VGG and observe the values of VGS and ID.
8. Repeat steps 6 and 7 for different values of VDS at 1.5 V and 2V.
9. The readings are tabulated.
10. From drain characteristics, calculate the values of dynamic resistance (rd) by using
the formula
rd = ∆VDS/∆ID
11. From transfer characteristics, calculate the value of transconductace (gm) By using
the formula
Gm=∆ID/∆VDS
12. Amplification factor (µ) = dynamic resistance. Tran conductance
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µ = ∆VDS/∆VGS
OBSERVATIONS:
DRAIN CHARACTERISTICS:
S.NO VGS=0V VGS=1V VGS=3V
VDS(V) ID(mA) VDS(V) ID(mA) VDS(V) ID(mA)
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TRANSFER CHARACTERISTICS:
S.NO VDS=0.5V VDS=1V VDS =1.5V
VGS (V) ID(mA) VGS (V) ID(mA) VGS (V) ID(mA)
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MODEL GRAPH:
TRANSFER CHARACTERISTICS
DRAIN CHARACTERISTICS
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PRECAUTIONS:
1. The three terminals of the FET must be care fully identified
2. Practically FET contains four terminals, which are called source, drain, Gate,
substrate.
3. Source and case should be short circuited.
4. Voltages exceeding the ratings of the FET should not be applied.
RESULT :
1. The drain and transfer characteristics of a given FET are drawn
2. The dynamic resistance (rd), amplification factor (µ) and Tran conductance (gm)
of the given FET are calculated.
VIVA QUESTIONS:
1. What are the advantages of FET?
2. Different between FET and BJT?
3. Explain different regions of V-I characteristics of FET?
4. What are the applications of FET?
5. What are the types of FET?
6. Draw the symbol of FET.
7. What are the disadvantages of FET?
8. What are the parameters of FET?
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9. TRANSISTOR CE AMPLIFIER
AIM: 1. To Measure the voltage gain of a CE amplifier
2. To draw the frequency response curve of the CE amplifier
APPARATUS:
Transistor BC-107
Regulated power Supply (0-30V, 1A)
Function Generator
CRO
Resistors [, 10KΩ, Ω, 100KΩ,/1kΩ] 1No
2.2KΩ 1No
Capacitors- 10µF -2No
100µF 1No
Bread Board
Connecting Wires
THEORY:
The CE amplifier provides high gain &wide frequency response. The
emitter lead is common to both input & output circuits and is grounded. The emitter-
base circuit is forward biased. The collector current is controlled by the base current
rather than emitter current. The input signal is applied to base terminal of the transistor
and amplifier output is taken across collector terminal. A very small change in base
current produces a much larger change in collector current. When +VE half-cycle is
fed to the input circuit, it opposes the forward bias of the circuit which causes the
collector current to decrease, it decreases the voltage more –VE. Thus when input
cycle varies through a -VE half-cycle, increases the forward bias of the circuit, which
causes the collector current to increases thus the output signal is common emitter
amplifier is in out of phase with the input signal.
CIRCUIT DIAGRAM:
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PROCEDURE:
1. Connect the circuit as shown in circuit diagram
2. Apply the input of 20mV peak-to-peak and 1 KHz frequency using Function
Generator
3. Measure the Output Voltage Vo (p-p) for various load resistors
4. Tabulate the readings in the tabular form.
5. The voltage gain can be calculated by using the expression Av=
(V0/Vi)
6. For plotting the frequency response the input voltage is kept Constant at 20mV
peak-to-peak and the frequency is varied from 100Hz to 1MHz Using function
generator
7. Note down the value of output voltage for each frequency.
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8. All the readings are tabulated and voltage gain in dB is calculated by Using The
expression Av=20 log10 (V0/Vi)
9. A graph is drawn by taking frequency on x-axis and gain in dB on y-axis
On Semi-log graph.
The band width of the amplifier is calculated from the graph
Using the expression,
Bandwidth, BW=f2-f1
Where f1 lower cut-off frequency of CE amplifier, and
Where f2 upper cut-off frequency of CE amplifier
The bandwidth product of the amplifier is calculated using the
Expression
Gain Bandwidth product=3-dBmidband gain X Bandwidth
OBSERVATIONS:
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FREQUENCY RESPONSE: Vi=20mv
FREQUENCY(Hz) OUTPUT
VOLTAGE (V0)
GAIN IN dB
Av=20 log10 (V0/Vi)
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MODELWAVE FORMS:
INPUT WAVE FORM:
OUTPUT WAVE FORM
FREQUENCY RESPONSE
FREQUENCY RESPONSE
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RESULT: The voltage gain and frequency response of the CE amplifier are obtained.
Also gain bandwidth product of the amplifier is calculated.
VIVA QUESTIONS:
1. What is phase difference between input and output waveforms of CE amplifier?
2. What type of biasing is used in the given circuit?
3. If the given transistor is replaced by a p-n-p, can we get output or not?
4. What is effect of emitter-bypass capacitor on frequency response?
5. What is the effect of coupling capacitor?
6. What is region of the transistor so that it is operated as an amplifier?
7. How does transistor acts as an amplifier?
8. Draw the h-parameter model of CE amplifier?
9. What type of transistor configuration is used in intermediate stages of a multistage
amplifier?
10. What is Early effect?
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10. SILICON-CONTROLLED RECTIFIER(SCR) CHARACTERISTICS
AIM: To draw the V-I Charateristics of SCR
APPARATUS: SCR (2P4M)
Regulated Power Supply (0-30V)
Resistors 3.3kΩ, 1kΩ
Ammeter (0-50) µA
Voltmeter (0-10V)
Breadboard
Connecting Wires.
THEORY:
It is a four layer semiconductor device being alternate of P-type and N-type silicon. It
consists os 3 junctions J1, J2, J3 the J1 and J3 operate in forward direction and J2
operates in reverse direction and three terminals called anode A, cathode K , and a
gate G. The operation of SCR can be studied when the gate is open and when the
gate is positive with respect to cathode.
When gate is open, no voltage is applied at the gate due to reverse bias of
the junction J2 no current flows through R2 and hence SCR is at cutt off. When anode
voltage is increased J2 tends to breakdown.
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When the gate positive,with respect to cathode J3 junction is forward biased
and J2 is reverse biased .Electrons from N-type material move across junction J3
towards gate while holes from P-type material moves across junction J3 towards
cathode. So gate current starts flowing ,anode current increaase is in extremely small
current junction J2 break down and SCR conducts heavily.
When gate is open thee breakover voltage is determined on the minimum
forward voltage at which SCR conducts heavily.Now most of the supply voltage
appears across the load resistance.The holfing current is the maximum anode current
gate being open , when break over occurs.
CIRCUIT DIAGRAM:
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PROCEDURE:
1. Connections are made as per circuit diagram.
2. Keep the gate supply voltage at some constant value
3. Vary the anode to cathode supply voltage and note down the readings of voltmeter
and ammeter.Keep the gate voltage at standard value.
4. A graph is drawn between VAK and IAK .
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OBSERVATION
VAK(V) IAK ( µA)
MODEL WAVEFORM:
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RESULT: SCR Characteristics are observed.
VIVA QUESTIONS
1. What the symbol of SCR?
2. IN which state SCR turns of
3. What are the applications of SCR?
4. What is holding current?
5. What are the important type’s thyristors?
6. How many numbers of junctions are involved in SCR?
7. What is the function of gate in SCR?
8. When gate is open, what happen
9. What is the value of forward resistance offered by SCR?
10. What is the condition for making from conducting state to non conducting state?
SCR Characteristics are observed.
What the symbol of SCR?
IN which state SCR turns of conducting state to blocking state?
What are the applications of SCR?
What is holding current?
What are the important type’s thyristors?
How many numbers of junctions are involved in SCR?
What is the function of gate in SCR?
When gate is open, what happens when anode voltage is increased?
What is the value of forward resistance offered by SCR?
What is the condition for making from conducting state to non conducting state?
conducting state to blocking state?
s when anode voltage is increased?
What is the condition for making from conducting state to non conducting state?
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11. UJT CHARACTERISTICS
AIM: To observe the characteristics of UJT and to calculate the Intrinsic Stand-Off
Ratio (η).
APPARATUS:
Regulated Power Supply (0-30V, 1A) - 2Nos
UJT 2N2646
Resistors 10kΩ, 47Ω, 330Ω
Multimeters - 2Nos
Breadboard
Connecting Wires
THEORY:
A Unijunction Transistor (UJT) is an electronic semiconductor device that
has only one junction. The UJT Unijunction Transistor (UJT) has three terminals an
emitter (E) and two bases (B1 and B2). The base is formed by lightly doped n-type bar
of silicon. Two ohmic contacts B1 and B2 are attached at its ends. The emitter is of p-
type and it is heavily doped. The resistance between B1 and B2, when the emitter is
open-circuit is called interbase resistance.The original unijunction transistor, or UJT, is
a simple device that is essentially a bar of N type semiconductor material into which P
type material has been diffused somewhere along its length. The 2N2646 is the most
commonly used version of the UJT.
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Circuit symbol
The UJT is biased with a positive voltage between the two bases. This causes a
potential drop along the length of the device. When the emitter voltage is driven
approximately one diode voltage above the voltage at the point where the P diffusion
(emitter) is, current will begin to flow from the emitter into the base region. Because
the base region is very lightly doped, the additional current (actually charges in the
base region) causes (conductivity modulation) which reduces the resistance of the
portion of the base between the emitter junction and the B2 terminal. This reduction in
resistance means that the emitter junction is more forward biased, and so even more
current is injected. Overall, the effect is a negative resistance at the emitter terminal.
This is what makes the UJT useful, especially in simple oscillator circuits.When the
emitter voltage reaches Vp, the current startsto increase and the emitter voltage starts
to decrease.This is represented by negative slope of the characteristics which is
reffered to as the negative resistance region,beyond the valleypoint ,RB1 reaches
minimum value and this region,VEB propotional to IE.
CIRCUIT DIAGRAM
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PROCEDURE:
1. Connection is made as per circuit diagram.
2. Output voltage is fixed at a constant level and by varying input voltage
corresponding emitter current values are noted down.
3. This procedure is repeated for different values of output voltages.
4. All the readings are tabulated and Intrinsic Stand-Off ratio is calculated using
η = (Vp-VD) / VBB
5. A graph is plotted between VEE and IE for different values of VBE.
MODEL GRAPH:
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OBSEVATIONS:
VBB=1V VBB=2V VBB=3V
VEB(V) IE(mA) VEB(V) IE(mA) VEB(V) IE(mA)
CALCULATIONS:
VP = ηVBB + VD
η = (VP-VD) / VBB
η = ( η1 + η2 + η3 ) / 3
RESULT: The characteristics of UJT are observed and the values of Intrinsic Stand-
Off Ratio is calculated.
VIVA QUESTIONS
1. Wha is the symbol of UJT?
2. Draw the equivalent circuit of UJT?
3. What are the applications of UJT?
4. Formula for the intrinsic stand off ratio?
5. What does it indicates the direction of arrow in the UJT?
6. What is the difference between FET and UJT?
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7. Is UJT is used an oscillator? Why?
8. What is the Resistance between B1 and B2 is called as?
9. What is its value of resistance between B1 and B2?
10. Draw the characteristics of UJT?
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