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EXPERIMENTS
PN Junction Diode:
Pin Diagram:
Circuit Symbol:
Circuit Diagram:
Forward Bias:
Reverse Bias:
Ex. No.: ____
Date: _ _ / _ _
/____
CHARACTERISTICS OF PN AND ZENER DIODES
Aim:
1
(i) To plot the forward and reverse VI characteristics of PN junction diode
(Silicon diode) and calculate its cut – in voltage, static resistance and dynamic
resistance.
(ii) To study and plot the forward and reverse VI characteristics of Zener diode
and calculate its breakdown voltage, static resistance and dynamic
resistance.
Apparatus Required:
S. No.
Components
Specification
Quantity
1.
Silicon PN diode
1N4007
1
2.
Zener diode
3Z 6.1
1
3.
Voltmeter
0-20 V
1
4.
Ammeter
0-200 mA
1
5.
Ammeter
0-200 µA
1
6.
Power Supply
0-30 V / 2A
1
7.
Bread board
-
1
8.
Connecting Wires
-
As necessary
Formula Used:
Change
in
Voltage
ΔV
Dynamic Resistance, Rd =
=
Resulting Change in Current
Tabulation:
Forward Bias:
Reverse Bias:
Forward Voltage Forward Current
Vf (V)
If (mA)
2
ΔI
Reverse Voltage Reverse Current
Vr (V)
Ir (µA)
Model Graph:
Theory:
PN Diode:
When a P – type and an N – type semiconductor are joined together, a junction
diode is created. It has the unique ability to allow current only in one direction. The lead
connected to the P – type semiconductor is called anode and that connected to the N –
type is called cathode. The P – type and N – type semiconductors are electrically neutral
before the junction is formed. As soon as the junction is formed, the majority carriers are
trying to diffuse through the junction. This happens due to the concentration gradient of
holes and electrons existing inside the diode. Due to the diffusion of majority carriers
from P – region to N- region and vice – versa, neutrality ends and a potential barrier
3
forms across the junction. The barrier potential is 0.6 V for Silicon. The region thus
created is due to the majority carriers. It has a depth of about 1 µm and is called
depletion region.
(i) Forward Bias:
If the anode of the diode is connected to the positive terminal of a battery and
cathode to the negative terminal, the set up is called forward bias. The diode does not
pass any current till the battery voltage exceeds the potential barrier. Once the battery
potential exceeds the barrier potential, high forward current in the order of mA flows
through the diode due to the movement of holes and electrons.
(ii) Reverse Bias:
When the positive terminal of a battery is connected to the N – type and negative
terminal is connected to the P – type, the diode is said to be reverse biased. This
connection makes the majority carriers in the semiconductor move away from the
junction. So the depletion region gets more widened. The minority carriers move towards
the junction and cause a minute current flow through the diode which is in the order of
µA in Germanium diodes and nA in Silicon diodes.
(iii) Static and Dynamic Resistances of the Diode:
When the diode is forward biased, it offers a definite resistance in the circuit. The
static resistance or DC resistance is the ratio of DC voltage across the diode to the DC
current flows through it. Dynamic resistance or AC resistance of the diode at any point is
the reciprocal of the slope of the tangent of the characteristic curve at that point.
Change in Voltage
Dynamic Resistance =
ΔV
=
Resulting Change in Current
Zener Diode:
Pin Diagram:
Circuit Symbol:
Circuit Diagram:
1. Forward Bias:
4
ΔI
2. Reverse Bias:
Zener Diode:
An ordinary diode will not permit current when it is reverse biased. If the reverse
bias voltage exceeds the peak inverse voltage rating, diode may get destroyed due to
avalanche breakdown. Zener diodes are special kinds of diodes designed to operate in
the breakdown region without causing the damage to them. When a diode is heavily
doped, its depletion layer becomes very narrow. When the applied reverse bias voltage
across the diode is increased, the electric field across the depletion layer becomes very
intense and electrons get pulled out from covalent bonds, generating electron – hole
pairs. Thus heavy reverse current flows. This phenomenon is called Zener Breakdown.
Zener diode behaves like an ordinary diode in the forward bias mode. In the V – I
characteristics of the Zener diode, it can be seen that the voltage across the diode
remains constant and independent of the current through it. This property is utilized in
voltage regulation.
5
Procedure:
For PN Junction Diode:
1. The circuit is set up on breadboard keeping the supply voltage at the
minimum position (say 0V).
2. The supply voltage is varied so that the voltmeter readings vary from 0 to 0.7
V or 0.8 V in steps of 0.1 V. Take the readings of voltmeter and ammeter and
enter it in the tabular column for the forward bias connection.
3. For reverse bias connection, the input voltage is varied from 0 to 10V in steps
of 1V and enters the ammeter and voltmeter readings.
4. To measure forward static resistance, consider a point on the forward
characteristics and note the corresponding voltage and current. The ratio of
voltage to current is the static resistance. To measure reverse static
resistance, repeat this step by considering another point on reverse
characteristics.
5. To measure dynamic forward resistance, for a particular DC current, find out
the reciprocal of the slope at the point corresponding to that current. It is
extremely high because the slope is almost zero.
For Zener Diode:
1. The circuit connection is given after testing the components.
Tabulation:
Forward Bias:
Reverse Bias:
Forward Voltage Forward Current
Vf (V)
If (mA)
6
Reverse Voltage Reverse Current
Vr (V)
Ir (mA)
Model Graph:
2. The input voltage is varied and the ammeter and voltmeter readings are noted
down and entered in the tabular column.
3. The reverse characteristics on a graph sheet with voltage along x – axis and
current along y – axis is in the third quadrant. The static resistance is
calculated by taking the ratio of voltage to current at any particular voltage.
4. The dynamic Zener resistance is calculated by taking the ratio of change in
voltage to resulting change in current at a point on the graph after the
breakdown point.
Questions for Discussion:
1. Define peak inverse voltage of a diode.
2. Why Silicon diodes are more popular than Germanium diodes?
3. What do you mean by ‘1N’ in 1N4007?
4. Differentiate Zener and Avalanche breakdown.
5. Write down the applications of PN Junction and Zener diodes.
Result:
(i) Thus the forward and reverse VI characteristics of PN diode are plotted and
the following parameters are obtained.
7
a) Cut – in Voltage of PN junction diode =____________ V.
b) Dynamic Forward Resistance at 10 mA=_____________Ω.
c) Static Forward Resistance at 10 mA =_____________Ω.
(ii) Thus the forward and reverse characteristics of Zener diode are plotted and
the following parameters are obtained.
a) Breakdown Voltage of Zener diode
=_____________V.
b) Dynamic Zener Resistance at 10 mA =_____________Ω.
c) Static Zener resistance at 10 mA
=_____________Ω.
Pre – lab test
(20)
Remarks
Simulation
& Signature
(20)
with Date
Circuit connection (30)
Result
(10)
Post-lab test
(20)
Total
(100)
Pin Diagram:
Circuit Symbol:
Circuit Diagram:
8
Ex. No.: ____
Date: _ _ / _ _
/____
CHARACTERISTICS OF CE CONFIGURATION
Aim:
To plot the input and output characteristics of an NPN transistor in common
emitter configuration and to find out the dynamic input resistance, dynamic output
resistance and common emitter current gain.
Apparatus Required:
S. No.
Components
Specification
Quantity
(0 – 30) V
1
1.
RPS
2.
Ammeters
(0 – 200)mA, (0 – 200 )µA
Each 1
3.
Voltmeter
(0 – 20) V
2
4.
Resistor
1 KΩ
1
5.
Transistor
BC 107
1
9
6.
Bread Board
-
1
7.
Connecting Wires
-
As necessary
Theory:
Transistor can be connected in a circuit in any one of the three different
configurations namely common emitter, common base and common collector. In this
configuration input is applied between base and emitter, and output is taken from
collector and emitter. Here, emitter of the transistor is common to both input and output
circuits and hence the name common emitter configuration. It is also called grounded
emitter configuration. The bias voltage forward biases the base-emitter junction and Vcc
is used
to reverse bias the collector-base junction.
The input voltage in the CE
configuration is the base-emitter and the output voltage is the collector-emitter voltage.
The input current is IB and the output current is Ic.
Tabulation:
Input Characteristics:
VCE = 0V
VCE =
V
VCE =
V
VBE (V) IB (µA) VBE (V) IB (µA) VBE (V) IB (µA)
Output Characteristics:
IB = 0 µA
IB =
µA
IB =
µA
VCE (V) IC (mA) VCE (V) IC (mA) VCE (V) IC (mA)
10
For audio frequency applications common emitter is used. Common emitter is the
most frequently used configuration because it provides voltage, current and power gain
always greater than unity.
(i) Dynamic Input Resistance (ri):
Dynamic input resistance can be calculated from the input characteristic curves. It
is given by the ratio of small change in base to emitter voltage to corresponding change
in base current, keeping collector to emitter voltage constant.
ri = VBE/IB
keeping VCE constant.
(i) Dynamic Output Resistance (rO):
Dynamic output resistance can be calculated from the output characteristic
curves. It is given by the ratio of small change in collector to emitter voltage to
corresponding change in collector current, keeping base current constant.
ro = VCE/IC keeping IB constant.
(iii) Common Emitter Current Gain ():
It is the ratio of the change in collector current to the corresponding change in
base current, keeping the collector to emitter voltage constant.
 = IC /IB keeping VCE constant.
Procedure:
Input Characteristics:
1. The circuit connections are made as shown in figure.
2. Keeping the VCE as 0 V, the input voltage VBE is varied from 0 to 0.8 V in step
of 0.1 and the corresponding input current IB is noted.
3. Step 2 is repeated for several values of output voltage VCE (Say 3V, 6V, etc.).
4. All the readings are tabulated.
11
5. The V-I characteristics curve is plotted by taking VBE along X – axis and IB
along Y axis for each value of VCE.
6. The dynamic input resistance is calculated by taking the ratio of change in VBE
to the resulting change in IB at any point (say 10 µA), which is the inverse of
the slope of the tangent of a curve at that point.
Model Graph:
Input Characteristics:
Output Characteristics:
Calculations:
(i) Dynamic Input Resistance, ri = VBE/IB
(ii) Dynamic Output Resistance, ro = VCE/IC
(iii) Common Emitter Current Gain,  = IC /IB
12
Output Characteristics:
1. The circuit connections are made as shown in figure.
2. Keeping the input current IB as 0 µA, the output voltage VCE is varied from 0 to
10 V in steps of 0.5 V and the corresponding output current IC is noted until it
becomes zero.
3. Step 2 is repeated for several values of the input current IB (say 50 µA, 100
µA).
4. All the readings are tabulated.
5. The V-I characteristics curve is plotted by taking the output voltage VCE along
X – axis and output current IC along Y – axis for each value of IB.
6. The dynamic output resistance is calculated by taking the ratio of change in
VCE to the resulting change in IC at any specific point on the curve, say 10 mA.
7. The common emitter current gain is calculated by using the formulae.
Questions for Discussion:
1. What are the regions of operation of a transistor? Mention its uses.
2. Why CE configuration is preferred as a switch?
3. What is indicated by B, C and 107 in BC 107?
4. Why common collector stage is also called as an emitter follower?
5. Mention the importance of CE amplifier.
Result:
Thus the input and output characteristics of an NPN transistor in CE configuration
is plotted and the following parameters are calculated.
a) Dynamic Input Resistance, ri
=_____________Ω.
b) Dynamic Output Resistance, ro
=_____________Ω.
c) Common Emitter Current Gain,  =_____________.
Pre – lab test
(20)
Remarks
Simulation
& Signature
(20)
with Date
Circuit connection (30)
13
Result
(10)
Post-lab test
(20)
Total
(100)
Pin Diagram:
Circuit Symbol:
Circuit Diagram:
14
Ex. No.: ____
Date: _ _ / _ _
/____
CHARACTERISTICS OF CB CONFIGURATION
Aim:
To plot the input and output characteristics of an NPN transistor in common base
configuration and calculate its dynamic input resistance, dynamic output resistance and
common base current gain.
Apparatus Required:
S. No.
Components
Specification
Quantity
(0 – 30) V
1
1.
RPS
2.
Ammeters
(0 – 100)mA
2
3.
Voltmeter
(0 – 1) V, (0 – 30) V
Each 1
4.
Resistors
1 KΩ, 10 KΩ
Each 1
5.
NPN Transistor
BC 107
1
6.
Bread Board
-
1
7.
Connecting Wires
-
As necessary
Theory:
In common base configuration base of the transistor is common to both input and
output circuits and hence the name common base configuration. Here the input is
applied between emitter and base, and output is taken between collector and base. CB
configuration is also called as Grounded base configuration. An increase in emitter
current causes an increase in collector current. The bias voltage forward biases the
base-emitter junction and Vcc is used
to reverse bias the collector-base junction. The
input voltage in the CB configuration is the emitter-base voltage and the output voltage is
the base-collector voltage. The input current is IE and the output current is IC.
15
The transistor offers low input resistance and very high output impedance when it
is in CB configuration. It provides almost unity current gain and high voltage gain.
Tabulation:
Input Characteristics:
VCB = 0V
VCB =
V
VCB =
V
VEB (V) IE (mA) VBE (V) IB (mA) VBE (V) IB (mA)
Output Characteristics:
IE = 0 mA
IE =
mA
IE =
mA
VCB (V) IC (mA) VCB (V) IC (mA) VCB (V) IC (mA)
(i) Dynamic Input Resistance (ri):
16
Input characteristics are plotted between emitter current IE and the emitter to
base voltage VEB for a constant value of collector to base voltage VCB. The reciprocal of
the slope of the curves gives the value of Dynamic input resistance ri.
ri = VEB/IE
keeping VCB constant.
(i) Dynamic Output Resistance (rO):
Output characteristics are plotted between collector current IC and the collector to
base voltage VCB for a constant value of emitter current IE. Dynamic output resistance rO
is obtained from these curves. It has rather high value since the curves are almost flat.
ro = VCB/IC keeping IE constant.
(iii) Common Base Current Gain ():
It is the ratio of the change in collector current to the corresponding change in
emitter current, keeping the collector to base voltage constant.
 = IC /IE keeping VCB constant
Procedure:
Input Characteristics:
1. The circuit connections are made as shown in figure.
2. Keeping the VCB as 0 V, the input voltage VEB is varied from 0 to 0.8 V in step
of 0.1V and the corresponding input current IE is noted.
3. Step 2 is repeated for several values of output voltage VCB (Say 3V, 6V, etc.).
4. All the readings are tabulated.
5. The V-I characteristics curve is plotted by taking VEB along X – axis and IE
along Y axis for each value of VCB.
6. The dynamic input resistance is calculated.
Output Characteristics:
1. The circuit connections are made as shown in figure.
2. Keeping the input current IE as 0 mA, the output voltage VCB is varied from 0
to 10 V in steps of 0.5 V and the corresponding output current IC is noted until
it becomes zero.
3. Step 2 is repeated for several values of the input current IE (say 50 mA, 100
mA).
4. All the readings are tabulated.
Model Graph:
Input Characteristics:
Output Characteristics:
17
Calculations:
(i) Dynamic Input Resistance, ri = VEB/IE
(ii) Dynamic Output Resistance, ro = VCB/IC
(iii) Common Base Current Gain,  = IC /IE
5. The V-I characteristics curve is plotted by taking the output voltage VCB along
X – axis and output current IC along Y – axis for each value of IE.
6. The dynamic output resistance and common base current gain is calculated
by using the formulae.
Questions for Discussion:
18
1. What are the applications of the CB amplifier?
2. Which configuration is good as a constant current source? Why?
3. What is collector power dissipation of a transistor?
4. Why the emitter of a transistor is highly doped and the area of collector is
made large?
5. What does the arrow in the symbol of a transistor indicates?
Result:
Thus the input and output characteristics of an NPN transistor in CB configuration
is plotted and the following parameters are calculated.
a) Dynamic Input Resistance, ri
=_____________Ω.
b) Dynamic Output Resistance, ro
=_____________Ω.
c) Common Base Current Gain, 
=_____________.
Pre – lab test
(20)
Remarks
Simulation
& Signature
(20)
with Date
Circuit connection (30)
Result
(10)
Post-lab test
(20)
Total
(100)
Unijunction Transistor:
Pin Diagram:
Circuit Symbol:
19
Circuit Diagram:
Model Graph:
20
Ex. No.: ____
Date: _ _ / _ _
/____
CHARACTERISTICS OF UJT AND SCR
Aim:
(i) To plot the VI characteristics of a Unijunction transistor and to measure its
intrinsic stand off ratio.
(ii) To study and plot the VI characteristics of SCR.
Apparatus Required:
S. No.
Components
Specification
Quantity
1.
RPS
(0 – 30) V
1
2.
Ammeters
(0 – 10)mA
2
3.
Voltmeter
(0 – 20) V
2
4.
Resistor
1 KΩ
2
Resistor
3.2 KΩ
1
5.
UJT
2N2426
1
6.
SCR
TYN 604
1
7.
Bread Board
-
1
8.
Connecting Wires
-
As necessary
Theory:
Unijunction Transistor (UJT):
A Unijunction transistor consists of a highly doped N-type semi conductor bar to
which a heavily doped P-type rod is attached. Ohmic contacts are made at opposite
ends of the N- type bar, which are called base-1(B1) and base-2 (B2) of the transistor. Ptype rod is called the emitter (E). UJT is a three terminal semiconductor switching device.
It has a unique characteristic that, when it is triggered, the emitter current increases and
it is powered by the emitter power supply.
The inter base resistance RBB of the N-type silicon bar appears as two resistors
RB1 and RB2, where RBB equals the sum of RB1 and RB2.
Tabulation:
21
VB1B2 =
V
VB1B2 =
V
IE (mA) VEB1 (V) IE (mA) VEB1 (V)
Calculation:
Intrinsic Stand off ratio,  = (VP - VD)/VB1B2
The intrinsic stand off ratio is given by,
 = RB1/RBB with IE = 0
Due to the applied voltage at B2 of the transistor, a positive voltage developed
across RB1 equal to VBB. When VE < Voltage across RB1, diode becomes reverse
biased. When VE increases, a forward current flows through the emitter to B1 region. If VE
22
is raised further, a sudden reduction of RB1 occurs. This happens since increase in
current reduces RB1 due to the negative coefficient of resistance of the semiconductor. A
regenerative action takes place at a particular value of VE called the Peak voltage. After
a valley point, IE increases with VE similar to ordinary forward biased diode.
When VE raises, the forward resistance across the junction decreases and the
junction acts as short circuit. The current through EB1 junction increases and the voltage
across the junction decreases. This continues up to a voltage called valley voltage VV
after which the junction acts as an ordinary diode.
Silicon controlled rectifier:
The SCR is a four layer PNPN device and has three terminals namely anode (A),
cathode (K) and gate (G). Keeping the gate open, if the forward voltage is applied across
the SCR, it will remain in OFF state. If the applied voltage exceeds the break over
voltage, it will turn ON and heavy current will flow through it. The break over voltage can
be reduced if a small voltage is applied at the gate. As gate current increases, the break
over voltage decreases. Once the SCR is fired, the gate loses control over the current
through the device. Even if the gate circuit is disconnected, the anode current can not be
brought back to zero. To turn OFF SCR, anode current should be made less than the
holding current.
SCR is a unidirectional power switch and is being extensively used. It is a unique
ac and dc rectifying element, rectifying ac to give controlled dc output and controlling dc
to ac etc. SCR combines the features of the rectifier and a transistor. It can be used as a
switch to perform various functions such as rectification, inversion and regulation of
power flow.
Silicon Controlled Rectifier:
Pin Diagram:
Circuit Symbol:
23
Circuit Diagram:
Model Graph:
24
Procedure:
Unijunction transistor:
1. The circuit connections are given as per the diagram.
2. Keeping VBB = 0V, VE is varied from 0 to 10 V in steps of 0.5V and the
voltmeter and ammeter readings at the input side are noted.
3. The above step is repeated for different values of VBB (say 3V,6V).
4. The VI characteristic is plotted with IE along X-axis and VE along Y-axis
keeping VBB as constant and the intrinsic stand off ratio is calculated from the
graph.
Silicon controlled rectifier:
1. The circuit connections are given as per the diagram.
2. The gate DC supply is switched ON and is adjusted for minimum value of
gate current.
3. IG is increased and the triggering of SCR is watched with the help of DC
ammeter connected in series with the load.
4. For various constant values of IG, the anode and cathode voltages are varied
and the anode current is noted in the tabular column.
5. The characteristic of SCR is plotted taking VAK along X-axis and IA along Yaxis.
25
Tabulation:
IG =
mA
VKA (V)
IA (mA)
26
Questions for Discussion:
1. Which region is called cut – off in UJT?
2. Write the applications of UJT and SCR?
3. Define Latching current and holding current.
4. Why an SCR is called a thyristor?
5. Why SCR turns on at lower anode potential when gate current is applied?
Result:
(i) Thus the VI characteristic of UJT is plotted and the intrinsic stand off ratio is
calculated as  = _____________
(ii) Thus firing characteristic of SCR is studied and the following parameters are
calculated.
a) Latching current
= _______ mA.
b) Holding current, IH = ________mA.
c) Holding current, VH = ________V.
Pre – lab test
(20)
Remarks
Simulation
& Signature
(20)
with Date
Circuit connection (30)
Result
(10)
Post-lab test
(20)
Total
(100)
27
28
Ex. No.: ____
Date: _ _ / _ _
/____
CHARACTERISTICS OF JFET
Aim:
To plot the VI characteristics of a Junction Field Effect Transistor.
Apparatus Required:
S. No.
Components
Specification
Quantity
(0 – 30) V
2
1.
RPS
2.
Ammeter
(0 – 500) A, (0 – 10) mA
Each 1
3.
Voltmeter
(0 – 10) V, (0 – 30) V
Each 1
4.
Resistor
220 Ω
2
5.
JFET
BFW11
1
6.
E-MOSFET
IRE5.6
1
7.
D-MOSFET
IRE5.6
1
8.
Bread Board
-
1
9.
Connecting Wires
-
As necessary
Parameters Used For Calculation:
Drain Characteristics:
Dynamic resistance (rD) = ∆VDS / ∆ ID
Tran conductance (gm) = ∆ ID / ∆VDS
Transfer Characteristics:
Input resistance
(Ri) =VGS / IDSS
Amplification factor (µ) = [∆VDS / ∆VGS] ID constant.
29
Tabulation:
Transfer Characteristics:
VDS=
VGS (V)
VDS=
ID (mA)
VGS (V)
Theory:
30
ID (mA)
FET is a three terminal semi conductor device in which conduction is due to any
one type of majority carriers. So it is also called unipolar device. The three terminals are
Source, Drain and Gate. The current conduction is controlled by the electric field
between the gate and the conducting channel and hence the name FET.
Depending on the construction, the FET can be classified into two types.
1. N-Channel FET
2. P- Channel FET
N-Channel FET:
It consists of n-type silicon bar forming the conducting channel for the charge
carriers. The heavily doped P regions introduced on both sides of the bar forms the gate.
This is used to control the flow of electrons from source to drain. The majority carriers
are electrons which cause the current flow.
P- Channel FET:
It consists of p-type silicon bar forming the conducting channel for the charge
carriers. The heavily doped N region introduced on both sides of the bar forms the gate.
This is used to control the flow of electrons from source to drain. The majority carriers
are holes which cause the current flow.
Procedure:
1. Connections are given as per the circuit diagram.
2. Gate to source voltage is reverse biased.
3. When the voltage is applied between the gate and source (VDD) the electrons
flow from source to drain and this constitutes the drain current ID.
4. The value of drain current will be maximum, when there is no external voltage
applied between gate and source; this current is designated as IDSS.
Transfer Characteristics:
1. Keep a constant value for VDS.
2. Adjust the gate-source voltage (VGS) and note down the ID value.
3. For various VDS values, note down the values of VGS and ID.
4.
Plot a graph between VGS along Y-axis and ID along X-axis.
Drain Characteristics:
VGS(V)
VDS(V)
VGS(V)
ID(mA)
VDS(V)
31
ID(mA)
Drain Characteristics:
1. Adjust gate to source voltage (VGS) to zero volt.
2. Increase VDS and note down the corresponding ID value.
3. Plot the graph for VDS along X-axis and ID along Y-axis.
4. Similarly by placing various values for VGS=1,2,3……..plot the curve and
obtain the drain characteristics.
Questions for Discussion:
1. Why a FET is said to be a voltage controlled device?
32
2. Why FET is called so?
3. What is pinch – off voltage?
4. Compare a FET with a BJT.
5. How a FET functions as a voltage variable resistor?
Result:
Thus the characteristic of JFET was studied and its curves were plotted. The
following parameters are calculated.
(i)
Drain Dynamic Resistance, rd = _______________ Ω.
(ii)
Mutual Conductance, gm
= _______________.
(iii)
Amplification Factor, 
= _______________.
Pre – lab test
(20)
Remarks
Simulation
& Signature
(20)
with Date
Circuit connection (30)
Result
(10)
Post-lab test
(20)
Total
(100)
E-MOSFET:
33
G – Gate
D – Drain
S – Source
Circuit Diagram:
Model Graph:
Ex. No.: ____
Date: _ _ / _ _
/____
CHARACTERISTICS OF E-MOSFET AND D-MOSFET
34
Aim:
To plot the drain characteristics of the E-MOSFET and D-MOSFET.
Apparatus Required:
S. No.
Components
Specification
Quantity
1.
RPS
(0 – 30) V
1
2.
Ammeter
(0 – 10) mA
1
3.
Voltmeter
(0 – 10) V, (0 – 30) V
Each 1
4.
Resistor
220 Ω
2
5.
E-MOSFET
IRE5.6
1
6.
D-MOSFET
IRE5.6
1
7.
Bread Board
-
1
8.
Connecting Wires
-
As necessary
Theory:
Metal Oxide Semiconductor Field Effect Transistors (MOSFET):
Metal-oxide semiconductor field-effect transistor, a common type of transistor in
which charge carriers, such as electrons, flow along channels. The width of the channel,
which determines how well the device conducts, is controlled by an electrode called the
gate, separated from channel by a thin layer of oxide insulation. The insulation keeps
current from flowing between the gate and channel.
The two types of MOSFETs are the depletion type and the enhancement type,
and each has a n /p – channel type. The depletion type is normally on, and operates as a
JFET. The enhancement type is normally off, which means that the drain to source
current increases as the voltage at the gate increases. No current flows when no voltage
is applied at the gate.
Tabulation:
E-MOSFET Drain Characteristics:
VGS = +2 V
VDS(V)
ID(mA)
VGS = +3 V
VDS(V)
35
ID(mA)
VGS = +4 V
VDS(V) ID(mA)
Procedure:
1. The positive terminal of VGS is connected to the gate and adjusted to a
constant value.
2. The procedure is continued until the rated VDS is reached.
3. The VDS is brought to zero and the above steps are repeated. The voltage VDS
and the current ID readings are noted down.
4. The graph is plotted for the tabulated readings.
36
D-MOSFET:
G – Gate
D – Drain
S – Source
37
Circuit Diagram:
Model Graph:
Questions for Discussion:
1. Why MOSFET is called insulated gate FET?
2. What is N-channel and P-channel MOSFET?
3. Differentiate Enhancement and Depletion types of MOSFETs.
4. Is it possible for a Depletion type of MOSFET to operate in both modes?
5. What are the disadvantages of MOSFET type and why V-MOS is developed?
38
Tabulation:
D-MOSFET Drain Characteristics:
VGS = -1 V
VDS(V)
ID(mA)
VGS = -2 V
VDS(V)
39
ID(mA)
VGS = -3 V
VDS(V) ID(mA)
40
Result:
Thus the drain characteristics of E-MOSFET and D-MOSFET were studied and
plotted.
Pre – lab test
(20)
Remarks
Simulation
& Signature
(20)
with Date
Circuit connection (30)
Result
(10)
Post-lab test
(20)
Total
(100)
DIAC:
Circuit Symbol:
41
Circuit Diagram:
Forward Bias:
Reverse Bias:
Ex. No.: ____
Date: _ _ / _ _
/____
CHARACTERISTICS OF DIAC AND TRIAC
Aim:
To determine and plot the characteristics of DIAC and TRIAC.
42
Apparatus Required:
S. No.
Components
1.
RPS
2.
Ammeter
Specification
Quantity
(0 – 30) V
1
(0 – 250) A, (0 – 60) mA,
Each 1
(0 – 100) mA
3.
Voltmeter
(0-1)V, (0-30)V
Each 1
4.
DIAC
DB 136
1
5.
TRIAC
BT 136
1
6.
Resistors
1 K Ω/ 10 W, 10 K Ω/ 10 W
Each 1
7.
Bread Board
-
1
8.
Connecting Wires
-
As necessary
Theory:
DIode for Alternating Current (DIAC):
DIAC is a bidirectional trigger diode that conducts current only after its breakdown
voltage has been exceeded momentarily. When this occurs, the resistance of the diode
abruptly decreases, leading to a sharp decrease in the voltage drop across the diode
and a sharp increase in current flow through the diode. The diode remains "in
conduction" until the current flow through it drops below a value called the holding
current. Below this value, the diode switches back to its high-resistance state. When
used in ac applications this automatically happens when the current reverses polarity.
Tabulation:
Forward Bias:
Reverse Bias:
Forward Voltage Forward Current
Vf (V)
If (mA)
43
Reverse Voltage Reverse Current
Vr (V)
Ir (mA)
Model Graph:
Once the voltage exceeds the turn-on threshold, the device turns on and the
voltage rapidly falls while the current increases. This behavior is typically the same for
both directions of current flow. Most DIACs have a breakdown voltage around 30 V.
DIACs are a form of thyristor but without a gate electrode.
DIACs are also called symmetrical trigger diodes due to the symmetry of their
characteristic curve. Since DIACs are bidirectional devices, their terminals are not
labeled as anode or cathode but as A1 and A2 or MT1 ("Main Terminal") and MT2.
TRIode for Alternating Current (TRIAC):
A TRIAC is an electronic component equivalent to two SCRs/thyristors joined in
inverse parallel (paralleled but with the polarity reversed) and with their gates connected
together. This results in a bidirectional electronic switch which conducts current in either
direction when it is turned on. It can be triggered by either a positive or a negative
44
voltage being applied to its gate electrode. Once triggered, the device continues to
conduct until the current through it drops below a certain threshold value. This makes the
TRIAC a very convenient switch for ac circuits, allowing the control of very large power
flows with milliampere-scale control currents. Low power TRIACs are used in many
applications such as light dimmers, speed controls for electric fans and other electric
motors, and in the modern computerized control circuits of many household small and
major appliances. when used with inductive loads such as electric fans, care must be
taken to assure that the TRIAC will turn off precisely at the end of each half-cycle of the
ac power.
TRIAC:
Circuit Diagram:
Forward Bias:
45
Reverse Bias:
Procedure:
DIAC:
1. Connections are given as per the circuit diagram.
2. The power supply is varied in constant steps and the corresponding voltage
and current readings are noted down.
3. For particular values of applied forward voltage , the current increases.
Then the voltage across DIAC decreases with increase in current.
4. The same procedure is repeated for reverse voltage of DIAC.
5. The VI characteristics is drawn from the tabulated readings.
TRIAC:
1. Connections are given as per the circuit diagram.
2. Set the value of IG to be constant by adjusting the power supply.
3. The terminal voltage is varied in steps and the corresponding readings are
noted down.
4. The same procedure is repeated for reverse polarity of TRIAC.
46
5. The voltage and current readings are noted down.
6.
The characteristics curve is plotted for the tabulated readings.
Tabulation:
Forward Bias:
Reverse Bias:
IG = 2.5 mA
Forward Voltage Forward Current
Vf (V)
If (mA)
47
IG = 6 mA
Reverse Voltage Reverse Current
Vr (V)
Model Graph:
Questions for Discussion:
1. Why the DIAC is said to be a symmetrical trigger diode?
2. Draw the SCR equivalent circuit of TRIAC.
3. How can you control the phase using TRIAC?
4. Give few applications of DIAC.
5. Give few applications of TRIAC.
48
Ir (mA)
Result:
Thus the characteristics of DIAC and TRIAC were plotted. The breakdown
voltage of TRIAC is ________ V and its reverse break down voltage is __________ V.
Pre – lab test
(20)
Remarks
Simulation
& Signature
(20)
with Date
Circuit connection (30)
Result
(10)
Post-lab test
(20)
Total
(100)
49
50
Ex. No.: ____
Date: _ _ / _ _
/____
CHARACTERISTICS OF PHOTO DIODE AND PHOTO TRANSISTOR
Aim:
To study the characteristics of Photo diode and Photo transistor.
Apparatus Required:
S. No.
Components
Specification
Quantity
1.
Ammeter
(0-10) mA
1
2.
Voltmeter
(0-10)V,(0-30)V
Each 1
3.
Resister
1 KΩ,680 KΩ
Each 1
4.
Photo diode
-
1
5.
Photo transistor
-
1
7.
Bread Board
-
1
8.
Connecting Wires
-
As necessary
Theory:
Photo Diode:
Generally silicon and germanium can be used for the fabrication of PN photo
diodes. A PN junction diode under reverse biased conditions carries reverse saturation
current. This is due to flow of minority carriers which are nothing but the hole – electron
pairs generated by the thermal energy which is absorbed by the crystal at room
temperature. When the thermal energy is increased by increasing the temperature, the
reverse saturation current increases .If now the PN junction is irradiated by light instead
of thermal energy ,the reverse current through the diode increases.
For maximum
activity, sometimes, a lens is placed on the junction to focus the incident light. The
changes in the output voltage are proportional to the incident light. These photo diodes
are used in industries, process control and automation, instrumentation and
communication.
Photo Transistor:
51
The photo transistor is a much more sensitive semiconductor photo device than
PN photo diode. It is usually connected in a common emitter configuration with base
open for the illumination. The radiation is concentrated on the region near the emitter
base junction. It is similar to photo diode but has a sensitivity 50 to 100 times more. In
the absence of radiation excitation, minority carriers are generated thermally and the
electrons crossing base to the collector as well as holes crossing collector to the base
constitute the reverse saturation current.
If the light is now incident on the base, additional minority carriers are generated
and these constitute additional reverse saturation current. The reverse saturation current
due to light is designated as Ic which is the total collector current.
Procedure:
Photo Diode:
1. Connections are made as per the circuit diagram.
2. For minimum, medium, maximum illumination the diode voltage and current
are noted.
3. Graph is plotted between diode voltage (VD) and current (ID).
Photo Transistor:
1. Connections are made as per the circuit diagram.
2. For minimum, medium, maximum illumination the transistor output or collector
voltage and current are noted.
3. Graph is plotted between transistor voltage (VT) and current (IT).
Tabulation:
S.No.
Minimum Illumination
ID(mA )
VD (V)
Medium Illumination
ID(mA )
52
VD (V)
Maximum Illumination
ID(mA )
VD (V)
Photo Diode:
Photo Transistor:
S.No.
Minimum Illumination
IT(mA )
VT (V)
Medium Illumination
IT(mA )
VT (V)
Maximum Illumination
IT(mA )
Questions for Discussion:
1.
Result:
Thus the characteristics of photo diode and photo transistor were studied.
53
VT (V)
Pre – lab test
(20)
Remarks
Simulation
& Signature
(20)
with Date
Circuit connection (30)
Result
(10)
Post-lab test
(20)
Total
(100)
54