EC8353 EDC unit1

Ec8353- electron devices and
circuits
unit-i
Prepared by,
E.ELAKKIA,
ASSISTANT PROFESSOR,
R.M.K.ENGINEERING COLLEGE
15-Jun-20 1

ELECTRONICS
• Electronics is the branch of science that deals
with the study of flow and control of electrons
(electricity) and the study of their behavior
and effects in vacuums, gases, and
semiconductors, and with devices using such
electrons.
15-Jun-20 2

ELECTRICAL AND ELECTRONICS
15-Jun-20 3

BOHR MODEL OF AN ATOM
15-Jun-20 5

BOHR MODEL OF SILICON ATOM
15-Jun-20 6

MATERIALS used in electronics
15-Jun-20 7
Rubber,
plastic,
glass,
mica
,quartz
Silicon,
germaniu
m, arsenic,
GaAs, InP,
SiC etc.
Copper,
Silver,
Gold,
Aluminu
m
•The conductor is applied to any material that
will support a generous flow of charge when a
voltage source of limited magnitude is applied
across its terminals.
•An insulator is a material that offers a very
low level of conductivity under pressure from
an applied voltage source.
•A semiconductor, therefore, is a material that
has a conductivity level somewhere between
the extremes of an insulator and a conductor.

ENERGY DIAGRAM FOR THREE
TYPES OF MATERIAL
15-Jun-20 8
E g = 1.1 eV (Si)
E g = 0.67 eV (Ge)
E g = 1.41 eV (GaAs)
E g > 5 eV

CLASSIFICATION OF
SEMICONDUCTOR
15-Jun-20 9
•Intrinsic materials are those semiconductors that have been carefully refined to
reduce the impurities to a very low level—essentially as pure as can be made
available through modern technology.
•A semiconductor material that has been subjected to the doping process is
called an extrinsic material.

COMPARISON OF SEMICONDUCTOR
TO CONDUCTOR ATOM
15-Jun-20 10

Silicon and germanium atom
15-Jun-20 11
Semiconductor materials such as Ge and Si that show a reduction in resistance
with increase in temperature are said to have a negative temperature
coefficient.

COVALANT BOND IN SILICON
15-Jun-20 12

COVALANT BOND IN SILICON
15-Jun-20 13

CREATION OF ELECTRON-HOLE
PAIR IN A SILICON CRYSTAL
15-Jun-20 14

GENERATION OF ELECTRON
HOLE PAIR
15-Jun-20 15
• An increase in temperature of a semiconductor can result in a
substantial increase in the number of free electrons in the
material.

ELECTRON HOLE CURRENT
15-Jun-20 16

HOLE CURRENT IN INTRINSIC
SILICON
15-Jun-20 17

N-TYPE SEMICONDUCTOR
 Pentavalent impurities are added
 eg. Arsenic(As), phosphorus(P),
bismuth(Bi) and antimony(Sb)
Donor atom
Electrons(doped) are called majority
carrier
Holes(thermally generated) are called
minority carrier.
15-Jun-20 18

p-TYPE SEMICONDUCTOR
 Trivalent impurities are added
 eg. Boron(B), Gallium(Ga), Indium(In)
Acceptor atom
Holes (doped) are called majority carrier
Electron (thermally generated) are called
minority carrier.
15-Jun-20 19

PN JUNCTION DIODE
16-Jun-20 23
• A diode is made from a small piece of
semiconductor material, usually silicon, in which
half is doped as a p region and half is doped as an
n region with a pn junction and depletion region
in between.
• The p region is called the anode and is connected
to a conductive terminal.
• The n region is called the cathode and is
connected to a second conductive terminal.

STRUCTURE AND SYMBOL OF
DIODE
16-Jun-20 24

FORWARD BIAS OF DIODE
16-Jun-20 26

EFFECT OF FORWARD BIAS ON THE
DEPLETION REGION
16-Jun-20 27
As more electrons flow into the depletion region, the number of positive
ions is reduced. As more holes effectively flow into the depletion region on
the other side of the pn junction, the number of negative ions is reduced.
This reduction in positive and negative ions during forward bias causes the
depletion region to narrow

EFFECT OF FORWARD BIAS ON
THE DEPLETION REGION
16-Jun-20 28

REVERSE BIAS OF DIODE
16-Jun-20 29

EFFECT OF REVERSE BIAS ON THE
DEPLETION REGION
16-Jun-20 30

COMPARISON OF SEMICONDUCTOR
TO CONDUCTOR ATOM
16-Jun-20 32

V-I CHARACTERISTICS FOR
FORWARD BIAS
16-Jun-20 33

V-I CHARACTERISTICS FOR REVERSE
BIAS
16-Jun-20 34

BREAKDOWN MECHANISMS
16-Jun-20 35
1.Avalanche breakdown
•The minority carriers, under reverse biased conditions, flowing through the
junction acquire a kinetic energy which increases with the increase in reverse
voltage.
•At a sufficiently high reverse voltage (say 5 V or more), the kinetic energy of
minority carriers becomes so large that they knock out electrons from the
covalent bonds of the semiconductor material.
•As a result of collision, the liberated electrons in turn liberate more electrons
and the current becomes very large leading to the breakdown of the crystal
structure itself. This phenomenon is called the avalanche breakdown.
•The breakdown region is the knee of the characteristic curve. Now the
current is not controlled by the junction voltage but rather by the external
circuit.

BREAKDOWN MECHANISMS
16-Jun-20 36
2.Zener breakdown
•Under a very high reverse voltage, the depletion region
expands and the potential barrier increases leading to a very
high electric field across the junction.
•The electric field will break some of the covalent bonds of the
semiconductor atoms leading to a large number of free minority
carriers, which suddenly increase the reverse current. This is
called the Zener effect.
•The breakdown occurs at a particular and constant value of
reverse voltage called the breakdown voltage, it is found that
Zener breakdown occurs at electric field intensity of about 3 x
10^7 V/m.

COMPLETE V-I CHARACTERISTICS
16-Jun-20 37

TEMPERATURE EFFECT ON V-I
CHARACTERISTICS
16-Jun-20 38
• The reverse saturation
current Io will just about
double in magnitude for
every 10°C increase in
temperature.
• The barrier potential
decreases by 2 mV for each
degree increase in
temperature.

DIODE EQUATION
• Where VT = kT/q;
• VD_ diode terminal voltage, Volts
• Io _ temperature-dependent saturation current, µA
• T _ absolute temperature of p-n junction, K
• k _ Boltzmann’s constant 1.38x 10 -23J/K)
• q _ electron charge 1.6x10-19 C
• η= empirical constant, 1 for Ge and 2 for Si
16-Jun-20 39
)1(0  Tv
v
D eII 
Schockley’s Diode characteristics equation for diode junction
current:

STATIC AND DYNAMIC
RESISTANCE
16-Jun-20 40
DYNAMIC RESISTANCE: The resistance offered by the diode to an ac signal is called
dynamic or ac resistance. If a sinusoidal input is applied , the varying input will
move the operating point up and down a region of characteristics and hence
defines specifici change in current and voltage as shown
STATIC RESISTANCE: The resistance of the diode at the operating point can be found
simply by finding the corresponding levels of VD and ID

DIODE EQUIVALENT CIRCUITS
16-Jun-20 41

DIODE EQUIVALENT CIRCUITS
16-Jun-20 42

Diode junction capacitance
16-Jun-20 43
In a p-n junction diode, two types of
capacitance take place. They are,
1. Transition capacitance (CT)
2. Diffusion capacitance (CD)

Transition capacitance
(CT)
16-Jun-20 44
• Just like the capacitors, a reverse biased p-n junction diode also
stores electric charge at the depletion region. The depletion region
is made of immobile positive and negative ions.
• In depletion region, the electric charges (positive and negative
ions) do not move from one place to another place. However, they
exert electric field or electric force. Therefore, charge is stored at
the depletion region in the form of electric field. The ability of a
material to store electric charge is called capacitance. Thus, there
exists a capacitance at the depletion region.
•Otherwise called as space charge, barrier or depletion region
capcitance

Transition capacitance (CT)
16-Jun-20 45
The change of capacitance at the depletion region can be defined
as the change in electric charge per change in voltage.
CT = dQ / dV
Where,
CT = Transition capacitance
dQ = Change in electric charge
dV = Change in voltage
The transition capacitance can be mathematically written as,
CT = ε A / W
Where,
ε = Permittivity of the semiconductor
A = Area of plates or p-type and n-type regions
W = Width of depletion region

DIFFUSION CAPACITANCE
16-Jun-20 46
• Diffusion capacitance occurs in a forward biased p-n
junction diode. Diffusion capacitance is also
sometimes referred as storage capacitance. It is
denoted as CD.
•The diffusion capacitance occurs due to stored
charge of minority electrons and minority holes near
the depletion region.
•Diffusion capacitance is directly proportional to the
electric current or applied voltage. If large electric
current flows through the diode, a large amount of
charge is accumulated near the depletion layer. As a

DIFFUSION CAPACITANCE
16-Jun-20 47
The formula for diffusion capacitance is
CD = dQ / dV
Where,
CD = Diffusion capacitance
dQ = Change in number of minority carriers
stored outside the depletion region
dV = Change in voltage applied across diode

QUIZ
1. The reverse current in a diode is of the order
of ……………….
A.Ka B.mA C.μA D.pA
2. If the temperature of a crystal diode
increases, then leakage current ………..
A. remains the same
B. decreases
C. increases
D. becomes zero
16-Jun-20 48

QUIZ
3.An ideal crystal diode is one which behaves as a
perfect ……….. when forward biased.
A.Conductor B .insulator C.resistance material
D.none of the above
4. The leakage current in a crystal diode is due to
…………….
A.minority carriers
B.majority carriers
C.junction capacitance
D.none of the above
16-Jun-20 49

QUIZ
5. In a PN junction with no external voltage, the electric
field between acceptor and donor ions is called a
A.Peak B.Barrier C.Threshold D.Path
6. When a PN junction is reverse-biased
A.Holes and electrons tend to concentrate towards the
junction
B.The barrier tends to break down
C.Holes and electrons tend to move away from the
junction
D.None of the above
16-Jun-20 50

BASIC DC POWER SUPPLY
17-Jun-20 51
• Transformer – steps down 230V AC mains to low voltage AC.
• Rectifier – converts AC to DC, but the DC output is varying.
• Filter – smooth the DC from varying greatly to a small ripple.
• Regulator – eliminates ripple by setting DC output to a fixed
voltage.

Rectifier
17-Jun-20 52
• A rectifier is a device, which converts a.c.
voltage (bi-directional) to pulsating d.c.
voltage (Unidirectional).

Types of Rectifier
• Using one or more diodes in the circuit,
following rectifier circuits can be designed.
1) Half - Wave Rectifier
2) Full – Wave Rectifier
3) Bridge Rectifier
17-Jun-20 53

Half wave Rectifier
17-Jun-20 54
During positive half
cycle
During negative half cycle

Full wave rectifier
17-Jun-20 55

Full wave bridge Rectifier
17-Jun-20 56

Full wave bridge Rectifier
17-Jun-20 57

Characteristics of a
Rectifier Circuit
17-Jun-20 58
1.DC output current
2.DC Output voltage
3.R.M.S. Current
4.R.M.S. voltage
5.Rectifier Efficiency (η )
6.Ripple factor (γ )
7.Peak Factor
8.% Regulation
9.Transformer Utilization Factor (TUF)
10.form factor
11.o/p frequency

COMPARISON OF
PERFORMANCE PARAMETER
OF RECTIFIER
17-Jun-20 59
S.NO PARAMETER HWR FWR BR
1 Number of diodes 1 2 4
2 DC voltage Vdc/Π 2Vdc/Π 2Vdc/Π
3 Peak inverse voltage Vm 2Vm Vm
4 Ripple factor 1.21 0.48 0.48
5 Rectifier efficiency 40.6% 81.2% 81.2%
6 Transformer utilization factor 0.286 0.693 0.812
7 Form factor 1.57 1.11 1.11

Light-Emitting Diode (LED)
6018-Jun-20

• When the device is forward-biased, electrons cross the
pn junction from the n-type material and recombine
with holes in the p-type material.
• Free electrons are in the conduction band and at a
higher energy than the holes in the valence band.
• The difference in energy between the electrons and
the holes corresponds to the energy of visible light.
When recombination takes place, the recombining
electrons release energy in the form of photons.
• The emitted light tends to be monochromatic (one
color) that depends on the band gapThis process,
called electroluminescence
6218-Jun-20

63
• Various impurities are added during the
doping process to establish the wavelength of
the emitted light. The wavelength
determines the color of visible light.
• Some LEDs emit photons that are not part of
the visible spectrum but have longer
wavelengths and are in the infrared (IR)
portion of the spectrum.
18-Jun-20

LED Semiconductor Materials
64
MATERIAL USED COLOUR EMITTED
Gallium arsenide(GaAs) Invisible- IR radiation
Gallium arsenide phosphide
(GaAsP)
Visible RED
Gallium phosphide (GaP) Brighter RED, ORANGE, GREEN
Gallium aluminum arsenide
phosphide (GaAlAsP)
RED, YELLOW andGREEN
indium gallium aluminum
phosphide
(InGaAlP)
ultrabright LED in red, orange,
yellow, and green
silicon carbide (SiC) Blue LED
gallium nitride
(GaN)
ultrabright blue LED
indium gallium nitride (InGaN) green and blue LED
18-Jun-20

LED Biasing
6518-Jun-20
•The forward voltage across an
LED is considerably greater than
for a silicon diode. Typically, the
maximum VF for LEDs is between
1.2 V and 3.2 V, depending on the
material.
• Reverse breakdown for an LED is
much less than for a silicon
rectifier diode (3 V to 10 V is
typical).

LED Biasing
• An increase in IF
corresponds
proportionally to an
increase in light output.
The light output (both
intensity and color) is
also dependent on
temperature
6618-Jun-20

SPECTRAL OUTPUT CURVES FOR
LED
6718-Jun-20

RADIATION PATTERN OF LED
• LEDs are directional light
sources (unlike filament or
fluorescent bulbs). The
radiation pattern is generally
perpendicular to the emitting
surface.
• It can be altered by the shape of
the emitter surface and by
lenses and diffusion films to
favor a specific direction.
• Directional patterns can be an
advantage for certain
applications, such as traffic
lights, where the light is
intended to be seen only by
certain drivers
18-Jun-20 68

Applications OF LED
• Standard LEDs are used for indicator lamps and readout
displays on a wide variety of instruments , ranging from
consumer appliances to scientific apparatus
• Infrared LED is in remote control units for TV, DVD, gate
openers, etc
• IR light-emitting diodes are used in optical coupling
applications such as, industrial processing and control,
position encoders, bar graph readers, and optical switching.
• Bright LEDs are becoming popular for home and business
lighting applications because of their superior efficiency
and long life.
18-Jun-20 69

Applications OF LED
• LED for lighting can deliver 50–60 lumens per
watt, which is approximately five times greater
efficiency than a standard incandescent bulb.
• LEDs for lighting are available in a variety of
configurations, including even flexible tubes for
decorative lighting and low-wattage bulbs for
outdoor walkways and gardens.
• High intensity LEDs are used in many applications
including traffic lights, automotive lighting,
indoor and outdoor advertising and informational
signs, and home lighting.
18-Jun-20 70

SEVEN SEGMENT LED DISPLAY
7218-Jun-20

CONCEPT OF COUNTING AND CONTROL
MECHANISM
7318-Jun-20

LED TRAFFIC LIGHT
7418-Jun-20
An LED array has three major advantages over the incandescent bulb:
brighter light, longer lifetime (years vs. months), and less energy
consumption (about 90% less).

CONCEPT OF RGB PIXEL USED
IN LED DISPLAY Screen
7518-Jun-20

PARTIAL DATASHEET OF LED
7618-Jun-20

PARTIAL DATASHEET OF LED
7718-Jun-20

LASER DIODE
• The term LASER stands for Light Amplification by
Stimulated Emission of Radiation.
• Laser light is monochromatic, which means that
it consists of a single color and not a mixture of
colors
• Laser light is also called coherent light, a single
wavelength, as compared to incoherent light,
which consists of a wide band of wavelengths.
• The laser diode normally emits coherent light,
whereas the LED emits incoherent light.
18-Jun-20 78

LASER DIODE- CONSTRUCTION
18-Jun-20 80
•A pn junction is formed by two layers of doped
gallium arsenide. The length of the pn junction
bears a precise relationship with the wavelength
of the light to be emitted.
•There is a highly reflective surface at one end of
the pn junction and a partially reflective surface
at the other end, forming a resonant cavity for
the photons.

LASER DIODE WORKING
18-Jun-20 82
•The laser diode is forward-biased by an external voltage source. As electrons
move through the junction, recombination occurs just as in an ordinary diode.
As electrons fall into holes to recombine, photons are released.
•A released photon can strike an atom, causing another photon to be
released. As the forward current is increased, more electrons enter the
depletion region and cause more photons to be emitted.
•Eventually some of the photons that are randomly drifting within the
depletion region strike the reflected surfaces perpendicularly. These reflected
photons move along the depletion region, striking atoms and releasing
additional photons due to the avalanche effect.
•This back-and-forth movement of photons increases as the generation of
photons “snowballs” until a very intense beam of laser light is formed by the
photons that pass through the partially reflective end of the pn junction.

LASER DIODE APPLICATION
18-Jun-20 83
•Laser diodes and photodiodes are used in the pick-up system of
compact disk (CD) players.
•Laser diodes are also used in laser printers and fiber-optic
systems.
•Medical equipment used in surgery
•Laser diode emitting visible light are used as pointers
•Laser diode emitting visible and infrared light are used to
measure range(or distance)

DAY 5
zener diode as voltage
regulator
Ms. E.ELAKKIA,
ASSISTANT PROFESSOR/EEE,
R.M.K.ENGINEERING COLLEGE
8419-Jun-20

ZENER Diode
8518-Jun-20
• A zener diode is a silicon pn junction
device that is designed for operation in
the reverse-breakdown region. The
breakdown voltage of a zener diode is
set by carefully controlling the doping
level during manufacture.
• when a diode reaches reverse
breakdown, its voltage remains almost
constant even though the current
changes drastically, and this is the key to
zener diode operation.

ZENER DIODE VI
CHARACTERISTICS
18-Jun-20 86

ZENER BREAKDOWN
• Zener diodes are designed to operate in reverse
breakdown. Two types of reverse breakdown in a zener
diode are avalanche and zener.
• The avalanche effect occurs in both rectifier and zener
diodes at a sufficiently high reverse voltage.
• Zener breakdown occurs in a zener diode at low reverse
voltages. A zener diode is heavily doped to reduce the
breakdown voltage. This causes a very thin depletion
region. As a result, an intense electric field exists within the
depletion region. Near the zener breakdown voltage (VZ),
the field is intense enough to pull electrons from their
valence bands and create current.
18-Jun-20 87

ZENER BREAKDOWN
• Zener diodes with breakdown voltages of less
than approximately 5 V operate predominately in
zener breakdown.
• breakdown voltages greater than approximately 5
V operate predominately in avalanche
breakdown.
• However Both types are called zener diodes.
Zeners are commercially available with
breakdown voltages from less than 1 V to more
than 250 V with specified tolerances from 1% to
20%.
8818-Jun-20

Breakdown Characteristics
89
• As the reverse voltage (VR) is increased, the reverse
current (IR) remains extremely small up to the “knee”
of the curve. The reverse current is also called the
zener current, IZ.
• At this point, the breakdown effect begins; the internal
zener resistance, also called zener impedance (ZZ),
begins to decrease as the reverse current increases
rapidly.
• From the bottom of the knee, the zener breakdown
voltage (VZ) remains essentially constant although it
increases slightly as the zener current, IZ, increases.
18-Jun-20

Breakdown Characteristics
18-Jun-20 90

Zener Regulation
• The ability to keep the reverse voltage across its
terminals essentially constant is the key feature
of the zener diode.
• A zener diode operating in breakdown acts as a
voltage regulator because it maintains a nearly
constant voltage across its terminals over a
specified range of reverse-current values.
• A minimum value of reverse current, IZK, must be
maintained in order to keep the diode in
breakdown for voltage regulation.
18-Jun-20 91

Zener Regulation
• when the reverse current is reduced below the knee of
the curve, the voltage decreases drastically and
regulation is lost.
• Also, there is a maximum current, IZM, above which
the diode may be damaged due to excessive power
dissipation.
• Basically, the zener diode maintains a nearly constant
voltage across its terminals for values of reverse
current ranging from IZK to IZM.
• A nominal zener voltage, VZ, is usually specified on a
datasheet at a value of reverse current called the zener
test current.
18-Jun-20 92

Zener Equivalent Circuit
9318-Jun-20
• Ideal model (first approximation) of a zener
diode has a constant voltage drop equal to the
nominal zener voltage.
• This constant voltage drop across the zener
diode produced by reverse breakdown is
represented by a dc voltage symbol even
though the zener diode does not produce a
voltage.

ZENER DIODE DATASHEET
18-Jun-20 96

ZENER DIODE AS VOLTAGE
REGULATOR
18-Jun-20 98
• The zener diode can be used as a type of
voltage regulator for providing stable
reference voltages.
• Zener Regulation with a Variable Input
Voltage
• Zener Regulation with a Variable Load

Zener Regulation with a
Variable Input Voltage
• Zener diode regulators can provide a reasonably
constant dc level at the output, but they are not
particularly efficient. For this reason, they are limited
to applications that require only low current to the
load.
• As the input voltage varies (within limits), the zener
diode maintains a nearly constant output voltage
across its terminals. However, as VIN changes, IZ will
change proportionally so that the limitations on the
input voltage variation are set by the minimum and
maximum current values (IZK and IZM) with which the
zener can operate.
18-Jun-20 99

18-Jun-20 100

18-Jun-20 101

Variable Load
• Zener voltage regulator with a variable load
resistor across the terminals.The zener diode
maintains a nearly constant voltage across as
long as the zener current is greater than IZK
and less than IZM.
18-Jun-20 102

Variable Load
18-Jun-20 103

EC8353 EDC unit1

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