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Basic Electronic Lab Manual
LAB EXPERIMENT # 02
Roll No: ______________
Grade:
Signature:
TO ANALYZE THE VOLTAGE-CURRENT CHARACTERISTICS OF DIODE
Lab Objective:
 To learn how to connect a diode in forward and reverse Bias arrangement.
 To understand V-I Characteristic of diode.
Required Equipment’s:
1. A compatible PC with Multisim installed in it.
2. Diode (any low signal model).
3. Multimeter.
4. DC Power Supply 0V – 12V.
5. Resistor 1k – 10k ohm.
Introduction:
Diode is a two terminal semiconductor device with an ability to conduct current only
in one direction after a certain amount of voltage called barrier potential is applied to it in a
proper way. Diode is one of great invention which is used in many applications such as rectifier
circuits, voltage limiter circuits, voltage clamper circuits, voltage multiplier circuits etc.
Diode biasing methods: There are three “biasing” condition for standard junction diode, are
as follows:
1. Zero Bias: No external voltage is applied to PN junction.
2. Forward Bias: Diode is said to be forward biased; if positive terminal of diode is
connected with positive of voltage source and negative terminal of diode is connected with
negative of voltage source as shown in fig1 (a). Silicon diode will conduct current at 0.7V
and germanium diode will conduct current at 0.3V when diode is forward biased, 0.7volt is
called barrier potential for silicon diode and 0.3V is barrier potential for germanium diode.
Before the value of voltage across diode reaches its barrier potential; there is very small
amount of current that is flowing through diode. The current due to majority carrier is called
forward current and current due to minority carrier is called reverse current. After the value
of voltage across diode reached its barrier potential; there is a rapid change in the value of
current through diode. The graphical representation of this phenomenon is as shown in below
fig 2(b).
3. Reverse Bias: Diode is said to be reverse biased; if positive terminal of diode is
connected with negative of voltage source and negative terminal of diode is connected with
Basic Electronic Lab Manual
positive of voltage source. Reverse bias is a condition that essentially prevents current
through the diode. An ideal diode behaves as an open switch when reverse biased, the VI
characteristic of ideal diode is shown in fig 2(a) whereas practically there is a very small
amount of current (negligible) that is flowing through diode even if diode is reverse biased.
The VI characteristic of forward and reverse bias diode is as shown below fig 2(b).
Figure 1(a) Forward Bias
Fig 2(a) VI Characteristic of an ideal diode
Figure 1(b) Reverse Bias
Fig 2(b) VI Characteristic of practical diode diode
Procedure:
1. Make the circuit as shown in figure 1(a) connect positive terminal of a diode with
positive of battery and connect negative terminal of a diode with negative of battery a
current limiting 1k ohm resistor may also be added in series with diode.
2. Connect the ammeter in series and volt meter in parallel with diode.
Basic Electronic Lab Manual
3. Now switch on the power supply and carefully turn the voltage control clock wise whilst
watching the ammeter.
4. Set the value of voltage and observe the value of current. Plot these values on graph
paper.
5. Make the circuit as shown in figure 1(b) connect positive terminal of a diode with
negative of battery and connect negative terminal of a diode with positive of battery a
current limiting 1k ohm resistor may also be added in series with diode, now repeat the
same procedure from 2 to 4.
Lab Questions:
1. What is barrier potential and write down the values of barrier potential for silicon diode
and germanium diode?
2. How to make a diode forward biased with the help of battery (voltage source)?
3. What are the forward and reverse currents?
4. What is depletion region?
Basic Electronic Lab Manual
LAB EXPERIMENT # 03
Roll No: ______________
Grade:
Signature:
OPERATION AND ANALYSIS OF HALF WAVE RECTIFIER
Objective:
 To understand the operation of half wave rectification.
Equipment:
1. A compatible PC with Multisim installed in it.
2. Multimeter
3. Transformer (single input single output)
4. AC power supply
5. Oscilloscope 2 channel.
6. Diode.
7. Resistor 1k ohm.
Introduction:
A rectifier is a circuit that converts pulsating ac into pulsating dc. There are three basic types of
rectifier circuits: the half wave rectifier, full wave rectifier, full wave (center tapped) and bridge
rectifier, bridge rectifier is most commonly used.
Half Wave Rectifier:
Half wave rectifier is the process, which converts an ac sinusoidal input voltage into a pulsating dc
voltage with the output pulse occurring for each input cycle. The half wave rectifier is made up of
single diode and a resistor (load). The half wave rectifier conducts current only during positive half
cycle of the ac input supply. The negative half cycle of the ac supply is suppressed.
i.e. during negative half cycle, no current is conducted and hence no voltage appear across the load
as shown in figure 3.1. Rectifiers are found in all dc power supplies that operate from an AC voltage
source.
Fig 3.1 half wave rectifier
Basic Electronic Lab Manual
Working Half Wave Rectifier:
Figure 3.2 illustrates the operation of half wave rectification. When the sinusoidal input voltage
Vp(in) goes positive, the diode is forward-biased and conducts current through the load resistor.
The current produces an output voltage across the load R, which has the same shape as the positive
half-cycle of the input voltage.
Fig 3.2 Half wave rectifier operation
During the positive half-cycle, the input voltage must overcome the barrier potential before the
diode becomes forward-biased. This results in a half-wave output with a peak value that is 0.7 V
less than the peak value of the input. The expression for the peak output voltage is as shown below;
Vp(out) = Vp(in) - 0.7 V
where Vrms = vp/2 while Vavg = vp/ π
Note: Vp denotes the peak value of d.c rectified output
Ripple Factor (r): Ripple factor is very important criteria for measuring the efficiencies of
rectifier. Basically the variation in the output voltage due to charging and discharging is called
ripple. Ripple factor is formally define as the ratio of rms value of ac component to the
dc component in the output.
Procedure:
• Design a half wave rectifier circuit given to you in the Lab accordingly in which a diode is
connected with secondary terminal of transformer has turn ratio 10:1 and connect ac signal
with primary terminal of transformer.
• Observe the rectified output signals.
• Calculate the ripple factor and DC voltage using oscilloscope and compared it with
measured voltage.
Basic Electronic Lab Manual
Lab Questions:
1. What is Half Wave and full wave rectification?
2. What is PIV (Peak Inverse Voltage)?
3. What is the common application for conversion of an AC voltage to DC?
4. What are the advantages and disadvantages of half wave rectifier?
5. Compare full wave and half wave rectifier?
Basic Electronic Lab Manual
LAB EXPERIMENT # 04
Roll No: ______________
Grade:
Signature:
Lab Objective:
 To understand the operation of Full wave rectification using bridge circuit.
Required Equipment’s:
1.
2.
3.
4.
5.
6.
A compatible PC with Multisim installed in it.
Four Diodes (1N4001 – 1N4007)
Multimeter
AC voltage source
Ordinary transformer
Oscilloscope
Discussion: Full wave bridge rectification is the process through which an ac sinusoidal input
voltage is converted into a pulsating dc voltage with two output pulses occurring for each cycle.
The full wave rectifier consist of four diodes and load resistors.
Full Wave Bridge Rectifier:
The bridge rectifier uses four diodes connected as shown in Fig 4-1a. When the input cycle is
positive as in part (a), diodes D1 and D2 are forward-biased and conduct current in the direction
shown. A voltage is developed across RL that looks like the positive half of the input cycle.
During this time, diodes D3 and D4 are reverse-biased.
Fig 4-1 Bridge Rectifier
Basic Electronic Lab Manual
When the input cycle is negative as shown in part (b), diodes D3 and D4 are forward biased and
conduct current in the same direction through RL as during the positive half-cycle. During the
negative half-cycle, D1 and D2 are reverse-biased. A full-wave rectified output voltage appears
across RL as a result of this action.
Two diodes are always in series with the load resistor during both the positive and negative half
cycles. If these diode drops are taken into account, the output voltage is
Vp(out) =Vp(sec) -1.4 V
The below fig 4.2 shows the diode drops;
Fig 4-2
The number of positive alternations that make up the full-wave rectified voltage is twice that of the
half-wave voltage for the same time interval. The average value, which is the value measured on a
dc voltmeter, for a full-wave rectified sinusoidal voltage is twice that of the half-wave, as shown
in the following formula:
Vavg=2Vp/π
Whereas the AC voltmeter shows RMS value and that is given by
Vrms=Vp/√2 Procedure:
•
•
•
Design a neat and clean circuit in Multisim as shown in figure 4-1with proper labeling for
full wave bridge rectifier in Multisim, realize it on breadboard
Calculate Vp(out),Vavg and Vrms with formulas described above and prove the results
using Multimeter.
Calculate the ripple factor in each case.
Questions:
01: What type of rectifier has high ripple factor?
02: Write down a common application of full wave rectifier
03: Differentiate between full wave center tapped and bridge rectifier
Basic Electronic Lab Manual
LAB EXPERIMENT # 05
Roll No: _____________
Grade:
Signature:
FULL WAVE CENTRE-TAP TRANSFORMER RECTIFICATION
Lab Objective:
 To understand the operation of Full wave rectification by centre-tap rectification.
Required Equipment’s:
1.
2.
3.
4.
5.
6.
A compatible PC with Multisim installed in it.
Four Diodes (1N4001 – 1N4007)
Multimeter
AC voltage source
Ordinary transformer
Oscilloscope
Full Wave Rectifier:
Full wave rectification is the process through which an ac sinusoidal input voltage is converted into
pulsating dc voltage with two output pulses occurring for each input cycle. The full wave rectifier
consists of two diodes and load resistor (RL).
The center tapped rectifier is a type of full wave rectifier that uses two diodes connected to the
secondary of the center tapped transformer as shown in fig 3-2
Fig 3-2 center tapped rectifier
Basic Electronic Lab Manual
Center Tapped Transformer:
The center tapped transformer is more or less same as the normal transformer. It differs only when
an additional wire is connected across the exact middle point of the secondary winding of a
transformer; it is called a center tapped transformer. The wire is adjusted such that it falls in the
exact middle point of the secondary winding and is thus at zero volts, forming the neutral point for
the winding. This is called the “center tap” and this thing allows the transformer to provide two
separate output voltages which are equal in magnitude, but opposite in polarity to each other.
Full Wave Rectifier Operation:
During positive half cycle of input AC signal, diode D1 is forward biased and diode D2 is reverse
biased as shown in fig 3-2. During negative half cycle input AC signal, diode D1 is reverse biased
and diode D2 is forward biased as shown in fig 3-2, which means rectified output is obtained during
both positive and negative half cycle of input AC, whereas amplitude of half wave center tapped
rectified output voltage of center tapped rectifier is always one half of total secondary voltage less
the diode drop, no matter what the turn’s ratio.
Vp(out)=0.5Vp(sec)-0.7
The average output voltage of full wave rectifier is twice of that of half wave and it is given as
Vavg = 2Vp(out)/π
Vrms = Vp(out)/√2
Ripple Factor (r): Ripple factor is very important criteria for measuring the efficiencies of
rectifier. Basically the variation in the output voltage due to charging and discharging is called
ripple.
Ripple factor is formally define as the ratio of rms value of ac component to the dc
component in the output.
Procedure:
1. Design the center tapped full wave rectifier circuit in Multisim as shown above in figure 32 and observes the waveform.
2. Observe the rectified output.
3. Calculate the ripple factor in each case.
Basic Electronic Lab Manual
LAB EXPERIMENT # 06
Roll No: _____________
Grade:
Signature:
Zener Diode Characteristics and Voltage Regulation
Objective:
 Analyze the reverse characteristics of Zener diode.
 Understand voltage regulation provided by Zener.
Components
1.
2.
3.
4.
5.
6.
A PC compatible with Multisim.
Multimeter
Zener diode
Surge resistor
DC signal source
Load resistor
Discussion:
Zener diode is one of the types of diode which was developed by scientist Zener Clarence.
Zener diode is a heavily doped silicon PN junction device that is designed to operate in reverse
breakdown region. In Zener diode two types of reverse breakdowns occur.
i. Zener break down
ii. Avalanche breakdown
i. Zener breakdown:
It occurs at low reverse voltage, Occurs only in Zener diode.
ii. Avalanche breakdown:
Occurs at sufficiently high reverse voltage such that diode will be damaged. Occurs in both rectifier
and Zener diode. Due to heavy doping depletion region becomes thin and there are enough charge
carriers (majority and minority) in P & N region, that’s why less voltage is required by Zener diode
to operate in reverse breakdown region. When Zener diode reaches
Zener break down voltage “Vz”, its voltage remains almost constant even though the current
changes drastically as shown in the figure 6.1. In other words it can also be said that when Zener
Basic Electronic Lab Manual
diode is operating in Zener breakdown region, it acts as voltage regulator for specified range of
reverse current. Zener diode has two states, on state and off state.
ON STATE: When reverse voltage across a Zener diode is equal to or more than breakdown
voltage Vz, the current increases very sharply. In this region, curve is most vertical. It means
voltage across Zener diode is constant even though the current through I change under such
condition. The Zener is said to be in “ON STATE”.
OFF STATE:
When reverse voltage across the Zener diode is less than Vz but greater than 0v, the Zener diode
is said to be in off state, under such condition the Zener diode can be represented by open switch.
Due to characteristic of voltage regulation, Zener diode equivalent circuit is consisting of a voltage
source as shown in figure 6.2. Zener diode does not produce DC voltage, but constant voltage drop
is represented by a constant DC voltage source Zener are available with breakdown voltages from
1.8 to 200 volt with tolerance from 1% to 20%.
Figure 6.1: IV characteristic curve for Zener diode
Figure 6.2: Schematic symbol of Zener diode and it equivalent circuit,
(a) Ideal model (b) Practical model
Basic Electronic Lab Manual
Procedure:
•
•
•
Prepare a series circuit consisting of a resistor, Zener diode and DC voltage source as shown
in figure 6.3.
Take different readings of current through the load at different values of voltage across
Zener diode.
Observe that when input voltage is sufficiently increased then voltage across Zener diode
remains constant even though current is changing w.r.t to input voltage.
Figure 5-3: Zener diode as a voltage regulator
Lab Questions:
01: What is voltage regulator?
02: Describe two types of reverse break downs that can occur in Zener diode.
04: What is the application of Zener diode in DC power supply?
05: what is difference between rectifier and Zener diode?
Basic Electronic Lab Manual
LAB EXPERIMENT # 07
Roll No: _____________
Grade:
Signature:
Filters and Construction of DC Power Source
Lab Objective:
•
Analyze the behavior of filters and need in power supply.
•
Simple construction of DC power supply with regulation.
Equipment’s:
A Compatible PC with Multisim
Oscilloscope (4 channel)
FWB rectifier
Load and Surge resistors
Transformer step-down
Electrolytic capacitor
Light Emitting diode (LED)
Discussion:
The power supply of an electronic system is used to convert the ac energy into dc energy. The basic
power supply can be broken into four circuit groups as shown in figure 7`
AC
DC
Transformer
Rectifier
Filter
Regulator
Figure 6-1 block diagram of Regulated D.C power supply
Transformer: In general, the ac line voltage present in your house wiring is not suitable for
electronic circuits. Most circuits require a considerably lower voltage, while a few require higher
voltage. The transformer serves to convert the ac line voltage to a voltage level more appropriate
to the needs of the circuit to be powered (step down the 220 V ac into the desired level of ac voltage
normally 12v or 15 b). However, a line transformer is generally large and heavy, and is rather
expensive. Therefore, some power supplies (notably for PCs) are deliberately designed to operate
directly from the ac line without a line transformer. The output of the transformer is still an ac
voltage, but now of an appropriate magnitude for the circuit to be powered.
Basic Electronic Lab Manual
Rectifier: The next step is to force current to flow in one direction only, preventing the alternations
that occur in the transformer and the ac line. This process is known as rectification, and the circuit
that accomplishes the task is the rectifier. There are many different rectifier configurations that
may be used according to the requirements of the circuit. The output of the rectifiers a pulsating
dc, which still has some of the variations from the ac line and transformer. To observe better
performer, bridge rectifier is used. The principle advantage of a bridge rectifier is you do not need
a center tape on the secondary of the transformer. A further but significant advantage is that the
ripple frequency at the output is twice the line frequency (i.e 50Hz or 60Hz) and makes filtering
somewhat easier.
Filter: The pulsating dc form the rectifier is generally still not suitable to power the actual load
circuit. The pulsating typically vary from 0V to the peak output voltage of the transformer.
Therefore, insert a circuit to store energy during each voltage peak, and then leaves it to the load
when the rectifier output voltage drops. This circuit is called a filter, and its job is to reduce the
pulses from the rectifier to a much smaller ripple voltage. No filter configuration can be absolutely
perfect, but a properly designed filter will provide a dc output voltage with only a small ac ripple.
Capacitor is use for reducing the variations in the rectifier output signal. In power supply we must
consider surge currents. Initially, when we turn the power supply on, the filter capacitor is fully
discharged and acts as a short circuit. So initially only the resistance of the diode and the winding
resistance of the transformer secondary limit the diode current. Therefore a surge resistor is an
added before capacitor to add some charging time constant. The discharge time depends on the
load resistance.
Regulator/Zener Diode:
The final circuit in the basic power supply is the voltage regulator. In this case we use zener diodes
as voltage regulators, as they are capable of maintaining a constant load voltage despite changes in
the rectifier output voltage.
Procedure:
1. Make the connection as shown in figure
2. Use the digital multimeter to measure the voltages and currents at different points.
Basic Electronic Lab Manual
Lab Questions:
1.
2.
3.
4.
What is DC power supply?
What are the basic building blocks of a dc power supply?
Why do we add surge resistor?
What is the purpose of load resistor if there is LED at the output?
Basic Electronic Lab Manual
LAB EXPERIMENT # 08
Roll No: _____________
Grade:
Signature:
APPLICATION OF DIODES IN WAVEFORM SHAPING
Lab Objective:
 Understand that how a diode can clip/limit the signal.
 Learn that how a diode can clamp the signal.
Equipment’s:
1.
2.
3.
4.
5.
6.
A PC with Compatible Multisim
Resistors
Diodes
DC and AC voltage source
Oscilloscope
Multimeter
7. Capacitor
Discussion:
Diode limiter circuits are usually used to limit the +ve and/or –ve input signal. Positive diode
limiter circuit is shown in figure 7.1(a) and negative diode limiter circuit is shown in figure 7.1(b).
When positive input half cycle of voltage signal is applied to circuit as shown in figure 7.1(a);
diode will be forward biased and it can drop only 0.7volt and remaining input voltage will be
dropped across R1. When negative input half cycle of voltage signal is applied to circuit as shown
in figure 7.1(a); diode will be reverse biased and it will appear as open switch, so input voltage
will be dropped across series combination of R1 and RL.
When negative input half cycle of voltage signal is applied to circuit as shown in figure7.1 (b);
diode will be forward biased and it can drop only 0.7volt and remaining input voltage will be
Basic Electronic Lab Manual
dropped across R1. When positive input half cycle of voltage signal is applied to circuit as shown
in figure 7.1(b); diode will be reverse biased and it will appear as open switch, so input voltage
will be dropped across series combination of R1 and RL.
Figure 01: Diode limiter circuit. (a) Positive limiter (b) Negative limiter
Diode Clamper Circuit:
Diode clamper circuits also known as DC restorer circuits are usually used to add DC level to an
AC signal. Positive diode clamper circuit is shown in figure 7.2 and negative diode clamper
circuit is shown in figure 7.3.
Positive diode clamper circuit inserts a positive DC level in the output waveform. When negative
half cycle of input AC signal is provided to positive diode clamper circuit, diode is forward biased
and capacitor will be charged up to voltage level (Vin-0.7), because diode has to drop 0.7 volts.
During when positive half cycle of input AC signal is provided to positive diode clamper circuit,
diode is reverse biased and as capacitor is already charged up to voltage level (Vin-0.7) volts, now
this capacitor will work as a battery of (Vin-0.7) volts, that’s why capacitor voltage is added with
positive half cycle of AC input signal, furthermore this capacitor voltage will also be added with
next negative half cycle of input AC signal. In result input AC signal is shifted upward by the
magnitude of (Vin-0.7) volts.
Figure 7.2: Positive diode clamper circuit
Basic Electronic Lab Manual
Negative diode clamper circuit inserts a negative DC level in the output waveform. When positive
half cycle of input AC signal is provided to negative diode clamper circuit, diode is forward biased
and capacitor will be charged up to voltage level (Vin-0.7), because diode has to drop 0.7volts.
During when negative half cycle of input AC signal is provided to negative diode clamper circuit,
diode is reverse biased and as capacitor is already charged up to voltage level
(Vin-0.7)volts, now this capacitor will work as a battery of (-Vin+0.7)volts, that’s why capacitor
voltage is added with negative half cycle of AC input signal, furthermore this capacitor voltage
will also be added with next positive half cycle of input AC signal. In result input AC signal is
shifted downward by the magnitude of (Vin-0.7) volts.
Figure 7.3: Negative diode clamper circuit
Input and output signal waveforms are also shown in figure 01 and 02. For good clamping action,
a clamper circuit requires a capacitor with RC time constant at least 10 times the period of input
signal.
Procedure:


Design a circuit according to schematic diagram shown in figure 7.1, 7.2 and 7.3.
Observe the input and output signal waveforms on oscilloscope.
Lab Questions:
1.
2.
3.
4.
What is diode Clipper and Clamper circuits?
What is difference between positive and negative diode clipper circuit?
What is difference between positive and negative diode clamper circuit?
What is biased Clipper and Clamper circuits?
Basic Electronic Lab Manual
LAB EXPERIMENT # 09
Roll No: _____________
Grade:
Signature:
IDENTIFICATION AND CHARACTERISTICS OF TRANSISTORS
Lab Objective:
 Identify the terminals and type of transistors.
 Read out transistors parameters using datasheets.
 Switching characteristics of transistors.
Required Equipment’s:
1.
2.
3.
4.
Transistors.
Multimeter.
Data Sheet.
Breadboard.
Discussion:
In the analog world of continuously varying signals, a transistor is a device used to amplify its
electrical input. In the digital world, a transistor is a binary switch and the fundamental building
block of computer circuitry. Like a light switch on the wall, the transistor either prevents or allows
current to flow through.
The transistor was invented by three scientists at the Bell Laboratories in 1947, and it rapidly
replaced
the vacuum
tube as
an
electronic
signal
regulator.
A
transistor
regulates current or voltage flow and acts as a switch or gate for electronic signals. A transistor
consists of three layers of a semiconductor material, each capable of carrying a current.
There are two types of transistors
1. Bipolar Junction Transistor (BJT)
2. Field Effect Transistor (FET)
Bipolar Junction Transistors:
BJT is semiconductor device; it is constructed of three doped semiconductor materials. Either
n-type material is sandwiched between two p-type materials or p-type material is sandwiched
between two n-type materials and these three materials make three regions of transistor as shown
in figure 01. Three regions of transistor are known as Base (B), Collector (C), Emitter (E), these
regions separated by two pn-junctions known as base-emitter and base-collector junction. A wire
lead is connected to each of three regions, and these leads are labeled as E, B, and C for emitter,
Base, Collector respectively. Emitter is heavily doped, Base is lightly doped, and Collector is
moderately doped. Physically collector is bigger than emitter and base, because collector has to
Basic Electronic Lab Manual
dissipate more power. Transistors are usually used as amplifiers and switches. Schematic symbol
of transistor is shown in figure 02.
Figure 01: Structure of npn (on left side) and pnp (on right side) transistor
Figure 02: Schematic symbol of transistor (a) npn (b) pnp
Transistor Terminal Identification
Transistor terminals can be identified with any of following methods:
1. Ohm meter
2. Diode option on digital multimeter
3. Case identification
1. Using Ohm (Ω) Meter In transistor there are two PN-Junctions, when ohm meter is connected
with any of two leads and if that junction of transistor is forward biased then it will show some
Basic Electronic Lab Manual
value of resistance else it will show “OUT of Range”. So find out both junctions with the help
of ohm meter, such that both junctions are forward biased. Now check if common terminal of
transistor is connected with positive probe of ohm meter; transistor is said to be NPN else PNP.
This common terminal is base. Junction with slightly higher resistance is base emitter, so
emitter terminal is also identified. Junction with slightly lower resistance is base collector, so
collector terminal is also identified.
RBE>RBC very minor difference (forward resistance is round about in the range of kilo ohms)
2.
Using Diode Option in Meter. First identify common terminal and type of transistor such as
npn or pnp. Then junction with slightly higher forward voltage drop is base emitter and
junction with slightly lower forward voltage drop is base collector. All three terminals are
identified.
VBE>VBC very minor difference (forward voltage drop is round about 0.7 volt)
3. Through Case Structure Identification:
Transistor terminal identification with the help of case is very easy as shown in figure 03. But care
must be taken, because same case may have different terminal configuration by different
manufacturers.
Figure 03: Transistor terminal identification with the help of its case output
Characteristics of BJT:
When dealing with transistor configurations, characteristics curves are very important
because they can predict the performance of a transistor. There are three curves, an input
characteristic curve, a transfer characteristic curve and output characteristic curve. Of these
curves, the most useful for predicting the transistor performance is the output characteristic curve.
Output characteristic curves of BJT are displaying the output voltages and currents for different
input currents. It simply provides the V-I relationship at the output terminals, with either the input
current or input voltage as parameters. For each transistor configuration, CE, CC and CB, the
input curves are slightly different.
Basic Electronic Lab Manual
Common Emitter Output Characteristic Curves.
In common emitter configuration, the input is applied between base and emitter and output is taken
from the collector and emitter as shown in figure 9-2. In CE input current is Ib and output current
Ic.
Figure 9.2 Common Emitter Configuration (a) NPN (b) PNP
In order to determines the output characteristic of CE configuration Ib is maintained constant at
several convenient levels. At each fixed level of base current (Ib), collector emitter voltage (Vce)
is adjusted in step and corresponding values of collector current (Ic) are recorded. Then for each
level of Ib , Ic is plotted v/s Vce. At typical output characteristic for a BJT in CE mode shown in
figure 9.3
Figure 9.3 output characteristics of BJT in CE mode
Basic Electronic Lab Manual
PROCEDURE:
1.
2.
3.
4.
5.
Make the connections according to the figure 9.4.
Rotate both variable control to minimum.
Switch ON the power supply
Set 10 k() to give a base current of 2.5 ()
Starting from 0.5V vary Vce to according to table and note down the corresponding values
of Ic.
6. Take similar reading with different reading values of Ib.
7. Fill the following table and plot the graph representing the output characteristic of NPN
transistor for CE mode.
Figure 9-4: BJT Common Emitter Configuration Circuit
Keeping the base current Ib fixed at some values say (2.5µA) and varies the values Vce say some
values (0.5V) and cheeks increase or decrease within the current on ammeter. after checking the
current increase (0.8mA) then plot reading on graph paper, taking Ic along y-axis and Vce along
x-axis this gives the output characteristics at (Ib=2.5µA).
Lab Questions:
1. How many regions of operation does BJT have?
2. How to identify transistor terminals?
3. What are the applications of transistor?
4. Draw schematic symbol for pnp and npn transistor.
Basic Electronic Lab Manual
LAB EXPERIMENT # 10
Roll No: _____________
Grade:
Signature:
BIASING, SWITCHING AND AMPLICATION OF TRANSISTORS
Objective:
 Learn that how a transistor can operate as amplifier.
 Learn that how a transistor can operate as a switch.
Equipment’s:
1. PC compatible with Multisim
2. Transistor BC547/2N3004
3. DC and AC Power Source
4. Multimeter
5. Resistors
Theory:
BJT is semiconductor device; it is constructed of three doped semiconductor materials. Either
n-type material is sandwiched between two p-type materials or p-type material is sandwiched
between two n-type materials and these three materials make three regions of transistor. Three
regions of transistor are known as Base (B), Collector (C), Emitter (E), these regions separated by
two pn-junctions known as base-emitter and base-collector junction. A wire lead is connected to
each of three regions, and these leads are labeled as E,B,C for emitter, Base, Collector respectively.
Emitter is heavily doped, Base is lightly doped, and Collector is moderately doped. Physically
collector is bigger than emitter and base, because collector has to dissipate more power. Transistors
are usually used as amplifiers and switches.
Transistor as a Switch
The majority application of transistor is that it can be utilize for switching operation when it’s
used as a electronic switch, in this condition a switch normally operates alternatively in cutoff
and saturation.
Transistor can be operated in one of three following configurations, when common terminal is
grounded.
1. Common Base Configuration
2. Common Emitter Configuration
3. Common Collector Configuration
Basic Electronic Lab Manual
Transistor can be operated in following regions

Cutoff region (Both junction BE and BC are reversed biased)

Active Region (BE junction is forward biased and BC junction is revere biased)

Saturation Region (Both junction BE and BC are forward biased)
 Breakdown region (Transistor currents and/or voltages exceed than maximum specified
values in data. Transistor should not be operated in this region, because it will be damaged)
Transistor works as an open switch in any of the following conditions



IB=0v, IC =0v VCE ( cutoff ) =VCC
Both junctions of transistor are reversed biased
Transistor works in its cut off region
Transistor works as a close switch in any of the following conditions
 I C=IC ( Sat ) VCE=VCE ( Sat )
 Both junctions of transistor are forward biased
 Transistor works in its saturation region
Transistor as an open switch and close switch is shown in figure 10.1
Figure 10.1: Switching action of Ideal Transistor
Transistor as an Amplifier:
Amplification is the process of linearly increasing the amplitude of an electrical signal. Transistor
amplifier circuit, input and output voltage signal waveforms are shown in figure 02. Where input
AC signal is superimposed on VBB, which causes IB to change. Smaller change in IB causes higher
change in IC. Using equation (VCC = I CRC+VCE), it can be noticed that Increase in IC causes
Basic Electronic Lab Manual
decrease in VCE vice versa. That is why both input and out voltage signal waveforms are 180
degree out of phase.
Figure 10.2: Transistor as an amplifier in common emitter configuration
Voltage gain is the ratio of Vc / Vb
Procedure:- Prepare following circuit as shown in figure 10.1 and figure 10.2. Depending upon
the transistor model, set the values of RC, RB, VCC and Vin such that transistor should be operated
in its saturation and then cutoff regions continuously.
Observation:- It is observed that when transistor is in its saturation region, LED is turning on for
one second and when transistor is in its cutoff region, LED is turning off. From figure observe the
magnitude of output signal is grater then input signal.
Lab Questions
1. Draw and discus the transistor switching circuit and what are the values of RC, Rb, VCC
and Vin that you have considered during this practical?
2. What is amplification? Draw the circuit diagram for a transistor amplifier circuit with
values of different components and energy sources that is observed during practical.