Phy & Elec 04-08.pdf

Applied Physics and
Electronics
Dr.-Ing Muhammad Rizwan Amirzada

My Introduction
◦Muhammad Rizwan Amirzada
◦MS and PhD in Electrical Engineering from Universität
Kassel, Germany
◦Specialization in MEMS structures (Micromirrors)
APP. PHY & ELEC. 2

Study Material
◦Electronic Principles by Albert Paul Malvino (7th Edition)
◦Electronic Devices and Circuits Theory by Robert L.
Boylestad (9th Ed)
◦And don’t forgot to browse internet for any topic
◦These slides will be available after every lecture
APP. PHY & ELEC. 3

Introduction: Concepts of Electricity
• Electricity is movement of Electrons
• What is an Electron?
• a stable subatomic particle with a charge of
negative electricity, found in all atoms
• Every material has different number of
electrons
• These electrons causes charge
APP. PHY & ELEC. 4

Concepts of Electricity contd.
o Electric Charge is the property of subatomic particles that causes it
to experience a force when placed in an electromagnetic field
oIt can be negative or positive
oElectrons carry negative charge and Protons carry positive charge
oThree basic principles which are important in electricity are
oVoltage
oCurrent
oResistance
APP. PHY & ELEC. 5

oVoltage: it can be defined as, it is the difference in charge between
two points
oIt means one point has more charge than other
oUnit of voltage is Volts
oIt can be AC or DC
oCommon example of voltage sources is battery cells which are
available in market
APP. PHY & ELEC. 6

o Current: The amount of charge flowing through a conductor in a
given time is called current
oUnit of current is Ampere which can be defined as one coulomb
charge flowing in one second
oSymbol for representation of current is “I”
APP. PHY & ELEC. 7

oResistance: Resistance is a measure of the opposition to current
flow in an electrical circuit
oUnit of Resistance is Ohm and can be described as when a constant
potential difference of one volt, applied to two points, produces in
the conductor a current of one ampere
oSymbol of resistance is “R”
APP. PHY & ELEC. 8

o All these three principles are well explained via water tank
philosophy
APP. PHY & ELEC. 9

Ohm’s Law
o Ohm’s Law establishes a relationship between voltage and current
through a resistance
o This relationship established as
𝑉 = 𝐼 × 𝑅
o This is a linear equation means the plot between voltage
and current will be a straight line when resistance is
constant
APP. PHY & ELEC. 10

Ohm’s Law contd.
o Electrical Power (P) in a circuit is the rate at which energy is absorbed or
produced within a circuit
oA source of energy such as a voltage will produce or deliver
power while the connected load absorbs it
oMathematically we can write Power as
𝑃 = 𝑉 × 𝐼
oThe Units of Power is Watt (W), milliwatt (mW) or kilowatt
(KW) is also use extensively in electronics and electrical circuits
APP. PHY & ELEC. 11

Ohm’s Law contd.
o For the circuit shown below find the Voltage (V), the Current (I), the
Resistance (R) and the Power (P)
APP. PHY & ELEC. 12

Voltage and Current Sources
APP. PHY & ELEC. 13

Voltage and Current Sources contd.
APP. PHY & ELEC. 14

Series and Parallel Resistor Comb.
o Resistors are said to be connected in “Series”, when they are daisy
chained together in a single line
o Resistors in series has common current flowing through them
APP. PHY & ELEC. 15

Series and Parallel Resistor Comb. Contd.
o The amount of current will remain same throughout the network
𝐼𝑇 = 𝐼𝑅1 = 𝐼𝑅2 = 𝐼𝑅3
o The equivalent resistance is the sum of all the resistance
𝑅𝑇 = 𝑅1 + 𝑅2 + 𝑅3
APP. PHY & ELEC. 16

o A simple example for calculating the total resistance and current
APP. PHY & ELEC. 17

o Another example for finding the voltage between two points
APP. PHY & ELEC. 18

o In a parallel resistor network the circuit current can take more than
one path as there are multiple paths for the current
o Resistors in Parallel have a Common Voltage across them but
current will divide (depends upon the resistance value)
APP. PHY & ELEC. 19

o The amount of voltage will remain same throughout the network
𝑉𝑇 = 𝑉𝑅1 = 𝑉𝑅2 = 𝑉𝑅3
o The equivalent resistance can be calculated as follows
1
𝑅𝑇
=
1
𝑅1
+
1
𝑅2
+
1
𝑅3
APP. PHY & ELEC. 20

APP. PHY & ELEC. 21

o An example for parallel network
APP. PHY & ELEC. 22

o Another example
APP. PHY & ELEC. 23

o A little complex example
APP. PHY & ELEC. 24

o Task for you
APP. PHY & ELEC. 25

o A complex example
APP. PHY & ELEC. 26

o A complex example
APP. PHY & ELEC. 27

o A complex example
APP. PHY & ELEC. 28

Kirchhoff’s Current Law (KCL)
o Kirchhoff’s Current Law is one of the fundamental law used for
circuit analysis
oIt states that the total current entering a circuits node is exactly
equal to the total current leaving the same node
oMathematically we can write it as
෍ 𝐼𝐼𝑁 = ෍ 𝐼𝑂𝑈𝑇
APP. PHY & ELEC. 29

Kirchhoff’s Current Law (KCL) contd.
o lets take a simple example
APP. PHY & ELEC. 30

o lets take a complex example
APP. PHY & ELEC. 31

o Equivalent circuit will be
APP. PHY & ELEC. 32

o Lets take another simple example
APP. PHY & ELEC. 33

Kirchhoff’s Voltage Law (KVL)
o Kirchhoff’s Voltage Law is the second of his fundamental laws we
can use for circuit analysis
o It states that for a closed loop series path the algebraic sum of all
the voltages around any closed loop in a circuit is equal to zero
oMathematically we can write it as
෍ 𝑉 = 0 𝑓𝑜𝑟 𝑎 𝑐𝑙𝑜𝑠𝑒𝑑 𝑙𝑜𝑜𝑝
APP. PHY & ELEC. 34

Kirchhoff’s Voltage Law (KVL) contd.
APP. PHY & ELEC. 35

Three resistor of values: 10 ohms, 20 ohms and 30 ohms, respectively
are connected in series across a 12 volt battery supply. Calculate: a)
the total resistance, b) the circuit current, c) the current through each
resistor, d) the voltage drop across each resistor e) verify that
Kirchhoff’s voltage law, KVL holds true.
APP. PHY & ELEC. 36

APP. PHY & ELEC. 37

o Another example with two loops where we have values of
resistors and voltage source as follows:
R1=5Ω, R2=10Ω, R3=5Ω and R4=10Ω and V=20V
APP. PHY & ELEC. 38

APP. PHY & ELEC. 39

APP. PHY & ELEC. 40

Semiconductors
◦ What is conductor ?
◦ Copper (29 e-) is a good conductor as it has only one electron is its
valence band
◦ Similarly the materials which has 4 electrons in their valence band
are semiconductor materials
◦ Examples are Si (14 e-), Germanium (32 e-), Carbon (4 e-) etc.
APP. PHY & ELEC. 41

Semiconductors (contd.)
◦ Why silicon is widely used ?
◦ Reason is the atomic structure of both materials
◦ Silicon has 4 electrons in its 3rd shell while Germanium also has 4 electrons
but in 4th shell
◦ Germanium valence e- require small energy to escape from the atom
◦ This makes Germanium unstable at high temperatures
◦ That’s why Silicon is most widely used in electronics
APP. PHY & ELEC. 42

APP. PHY & ELEC. 43

◦ Concept of Hole
◦ At room temp, some valence electrons
absorbs energy and jump to the
conduction band
◦ This causes a vacancy in the valence
band of crystal called hole
◦ Recombination is the process when an e- falls in the hole
APP. PHY & ELEC. 44

◦ When voltage is applied to pure semiconductor, then e- can easily
move towards positive side
◦ Known as electron current
APP. PHY & ELEC. 45

◦ Other type is hole current, which is explained well in diagram
APP. PHY & ELEC. 46

◦ There are two types of semiconductors
◦ n-type semiconductor: in which pentavalent materials added by doping to
achieve certain electrical characteristics
◦ Doped materials can be: Arsenic, Phosphorous, Bismuth and Antimony and
called donner atoms
◦ p-type semiconductor: in which trivalent materials added by doping to
achieve certain electrical characteristics
◦ Doped materials can be: Boron, Indium and Gallium and called acceptor
atoms
APP. PHY & ELEC. 47

APP. PHY & ELEC. 48

Diode Theory
◦ Intrinsic semiconductor doped with trivalent and pentavalent
material, a boundary called pn-junction is formed between the p-
type and n-type material
◦ Diode created………
APP. PHY & ELEC. 49

Diode Theory (contd.)
◦ For every electron which diffuse at the boundary, a positive charge
is left in the n-region and a negative charge is left in the p-region
◦ This is barrier potential of diode which forbids further diffusion
◦ The region where this electron hole recombination occurs is called
depletion region
◦ Certain amount of voltage equal to barrier potential is required to
flow the electrons across the junction
◦ Typical barrier potential for Silicon diode is 0.7V and for
Germanium 0.3V at 25°C
APP. PHY & ELEC. 50

◦ Typical diode structure and symbol is shown in fig
◦ p-type region is called Anode and n-type region is called Cathode
◦ pn-junction is in between the Anode and Cathode
APP. PHY & ELEC. 51

◦ Biasing of diode is when it is connected with a voltage source
◦ When n-type material is connected with -ive and p-type material is
connected with +ive side of source, it is called forward biasing
◦ Vbias should be greater than the barrier potential
APP. PHY & ELEC. 52

◦ when voltage is greater then the barrier potential, free electrons
crosses the barrier potential and move into the p-type material
◦ Electron current induced inside the diode
APP. PHY & ELEC. 53

◦ More electron flow towards the depletion region, positive charge
reduce and same is true for holes
◦ This causes the depletion region to becomes narrow
◦ Also the concept of energy hill
APP. PHY & ELEC. 54

◦ Reverse biasing is the condition prevents the flow of current
through diode
◦ When p-type is connected with -ive and n-type is connected with
+ive end of source
APP. PHY & ELEC. 55

◦ V-I curve of diode is shown in figure
APP. PHY & ELEC. 56

Diode Models
◦ Ideal Diode Model
◦ It is the least accurate approximate model
◦ The diode can be replace by a simple switch
◦ When diode is forward bias, diode acts like a closed switch
◦ When diode is reverse biased, diode acts like an open switch
◦ The barrier potential, dynamic resistance of diode and reverse current are
neglected
◦ Only used for troubleshooting purpose, whether diode is working or not
APP. PHY & ELEC. 57

Diode Models (contd.)
APP. PHY & ELEC. 58

◦ Since, barrier potential and dynamic resistance is neglected, the
voltage across diode in forward bias is zero and current can be
calculated as
𝐼𝐹 =
𝑉𝐵𝑖𝑎𝑠
𝑅𝐿𝑖𝑚𝑖𝑡
◦ Since, reverse current is neglected, means reverse current is zero
and reverse voltage is equal to the bias voltage
𝐼𝑅 = 0 𝑎𝑛𝑑 𝑉𝑅 = 𝑉𝐵𝑖𝑎𝑠
APP. PHY & ELEC. 59

◦ Practical Diode Model:
◦ In this approximation, the barrier potential is considered i.e. 0.7V for Si
◦ In forward bias, a voltage source is considered with a closed switch
◦ The +ive side of the source is at anode
◦ Bias voltage should be greater then that voltage source in order to conduct a
diode
◦ In reverse bias, voltage source will not effect the circuit as diode acts as an
open switch
APP. PHY & ELEC. 60

APP. PHY & ELEC. 61

◦ As diode has a voltage drop of 0.7V so
𝑉𝐹 = 0.7𝑉
◦ The current through the diode can be calculated by KCL, hence
𝐼𝐹 =
𝑉𝐵𝑖𝑎𝑠 − 𝑉𝐹
𝑅𝐿𝑖𝑚𝑖𝑡
◦ In reverse bias, reverse current is zero and reverse voltage is equal to
the bias voltage
𝐼𝑅 = 0 𝑎𝑛𝑑 𝑉𝑅 = 𝑉𝐵𝑖𝑎𝑠
◦ This approximation is useful when dealing with the low voltage
calculations and designing basic diode circuits
APP. PHY & ELEC. 62

◦ Complete Diode Model:
◦ It is the most accurate diode approximation
◦ It includes the barrier potential, a small forward internal dynamic resistance
and a large internal reverse resistance
◦ Reverse resistance is taken because it provides a path for reverse current
which is included in the approximation
APP. PHY & ELEC. 63

APP. PHY & ELEC. 64

◦ The values for the forward voltage and current can be calculated
as:
𝑉𝐹 = 0.7𝑉 + 𝐼𝐹𝑟𝑑
and
𝐼𝐹 =
𝑉𝐵𝑖𝑎𝑠 − 0.7𝑉
𝑅𝐿𝑖𝑚𝑖𝑡 + 𝑟𝑑
APP. PHY & ELEC. 65

ELECTRONIC DEVICES AND CIRCUITS 66

Half Wave Rectifier
◦ Diodes are mainly used in the power supply circuits
◦ Power supply converts the standard 230V AC to some DC voltage level
◦ Main part of a dc supply is the rectifier
◦ There are two types of rectifiers
◦ Half wave rectifier
◦ Full wave rectifier
APP. PHY & ELEC. 69

Half Wave Rectifier (contd.)
APP. PHY & ELEC. 70

◦ During the positive cycle diode conducts and current flow through
the resistor
◦ For a negative cycle, diode goes into reverse biasing and do not
operate, no current flows through resistor
◦ Net result is that only positive cycle of AC source appears across
load resistor
◦ No polarity change at the output so a pulsating dc voltage appears
across diode
APP. PHY & ELEC. 71

◦ Average value of half wave output voltage can be calculated as:
𝑉𝐴𝑣𝑔 =
𝑉𝑃
𝜋
◦ Equation shows that Vavg is approx. 31.8% of Vp (Ideal Diode Case)
◦ When a practical model is used peak output voltage can be
calculated as:
𝑉𝑃(𝑜𝑢𝑡) = 𝑉𝑃(𝑖𝑛) − 0.7𝑉
APP. PHY & ELEC. 72

Full Wave Rectifier
◦ Full wave rectifier allows unidirectional current for entire 360° of
input cycle
◦ It is combination of two half wave rectifiers
◦ For this purpose two diodes are used with a centre taped
transformer which provides two separate voltages (out of phase)
across its secondary winding
◦ One diode conducts and other diode is reverse biased during
positive input cycle and vice versa
◦ As a result current is continuously flow through the load resistor
APP. PHY & ELEC. 73

Full Wave Rectifier (contd.)
APP. PHY & ELEC. 74

APP. PHY & ELEC. 75

◦ The average value of full wave rectifier can be calculated as:
𝑉𝐴𝑣𝑔 =
2𝑉𝑃
𝜋
◦ Equation shows that Vavg is approx. 63.6% of Vp (Ideal Diode Case)
◦ The frequency of full wave rectifier will be equal to
𝑓𝑜𝑢𝑡 = 2𝑓𝑖𝑛
APP. PHY & ELEC. 76

◦ Another type of full wave rectifier is Bridge Rectifier
APP. PHY & ELEC. 77

APP. PHY & ELEC. 78

◦ the bridge output voltage in case of ideal approx. can be calculated
as:
𝑉𝑃(𝑜𝑢𝑡) = 𝑉𝑃(𝑠𝑒𝑐)
◦ By using the second approx. the bridge output voltage can be
calculated as:
𝑉𝑃(𝑜𝑢𝑡) = 𝑉𝑃(𝑠𝑒𝑐) − 1.4𝑉
APP. PHY & ELEC. 79

APP. PHY & ELEC. 80

Power Supply Filtering
◦ For a power supply there must be a constant voltage amplitude
without fluctuations
◦ The output of a Full wave or Half Wave rectifier is not constant
◦ There must be some filtering to smoothen the output of rectifiers
APP. PHY & ELEC. 81

Power Supply Filtering (contd.)
◦ Capacitor input filter is used for filtering
◦ Capacitor is attached at the output of rectifier
◦ when the positive cycle arrived, diode becomes forward bias
◦ The capacitor start charging and it continues as voltage is
increasing, when voltage starts decreasing, capacitor starts
discharging and diode becomes reverse bias
◦ The time constant RC determines the discharging rate of capacitor
◦ Larger the time constant, lesser the capacitor discharge
APP. PHY & ELEC. 82

APP. PHY & ELEC. 83

◦ Capacitor quickly charge and slowly discharge during the complete
cycle
◦ Variation in the capacitor voltage due to charging and discharging
is known as ripple voltage
◦ Smaller the ripple, better the filtering
APP. PHY & ELEC. 84

◦ Full wave rectifier has double the frequency as compare to half
wave rectifier
◦ It is easier to filter the full wave rectifier output as there is short
time between peaks
◦ When filtered with same load resistor and capacitor, full wave
rectifier has small ripple as compared to half wave rectifier
◦ Because capacitor discharges less during the short intervals
between full peaks
APP. PHY & ELEC. 85

APP. PHY & ELEC. 86

◦The ripple factor (r) (amount of AC content present in DC
output) is effectiveness of filter and defined as
𝑟 =
𝑉𝑟
(𝑝𝑝)
𝑉𝐷𝐶
APP. PHY & ELEC. 87

Zener Diode
◦ Zener diode is a typical diode which is designed to operate in
reverse-breakdown region
APP. PHY & ELEC. 89

Zener Diode (contd.)
◦ Two types of reverse breakdown in Zener diodes are observed i.e.
avalanche and Zener
◦ Avalanche breakdown occurs at higher voltage levels but Zener
breakdown occurs at low voltages
◦ Zener diode is heavily doped to reduce the breakdown voltage
◦ An intense electric field is generated in depletion region
◦ When applied voltage is near Zener breakdown voltage, the field is
intense enough to pull the electrons from valence band to
conduction band
APP. PHY & ELEC. 90

Avalanche and Zener Effect
◦ Avalanche effect is observed when the material is lightly doped
◦ Zener effect is observed when material is heavily doped
◦ Width of the depletion layer is depend on the amount of doping
◦ Heavily doped diodes has narrow depletion layer and lightly doped
diodes has wider depletion layer
APP. PHY & ELEC. 91

Avalanche and Zener Effect (contd.)
◦ In reverse bias, a small reverse current is observed due to minority
carriers
◦ When the applied voltage increases, it accelerate those minority
carriers
◦ Those minority carriers then collide with majority carriers and
knock them out
◦ This knocking out effect continues and hence current start to flow
because of those majority carriers
APP. PHY & ELEC. 92

Zener Diode (contd.)
◦ Main applications of Zener diode are voltage regulators
◦ It can be used where a constant voltage is required (without
fluctuations)
APP. PHY & ELEC. 93

Bipolar Junction Transistors (BJT)
◦ BJT is constructed when three different semiconductor regions are
joined together
◦ Three semiconductor regions are separated by two pn junctions
◦ Three regions are called Emitter, Base and Collector
APP. PHY & ELEC. 94

Bipolar Junction Transistors (contd.)
◦ The pn junction joining the base region and the emitter region is
called Base Emitter junction (Emitter Diode)
◦ The pn junction joining the base region and collector region is
called Base Collector junction (Collector Diode)
◦ Base region is lightly doped and very thin
◦ Emitter is heavily doped and collector is
moderately doped
◦ Schematic symbol of BJT is shown in fig
APP. PHY & ELEC. 95

◦ In normal configuration/operation Emitter diode is forward biased
and Collector diode is reverse biased
◦ Emitter has a job to emits its electrons so that they can inject in
the base region
◦ When emitter diode is forward biased, electrons can enter from
emitter to base
APP. PHY & ELEC. 96

◦ Because of biasing, the electrons which enter in base has two
options
◦ To enter to the collector OR
◦ To go out from the base
◦ Majority of the electrons will enter the collector as base is lightly
doped and very thin
◦ Lightly doped means electrons have longer life in base and
because of very thin base electrons have to move very short
distance to enter into collector
APP. PHY & ELEC. 97
E B C

◦ When electrons enter into the collector, they feel a strong
attraction because of the source voltage
◦ Because of this electrons flow through the collector and reach to
the positive terminal of the source
◦ There are three useful configurations of transistors
◦ Common Emitter
◦ Common Base and
◦ Common Collector
APP. PHY & ELEC. 98

APP. PHY & ELEC. 99

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