BASIC ELECTRONICS Electronics is a branch of physics that deals with the emission and effects of electrons in materials. Or  Is a branch of science dealing with the study and development of circuit involving semi conductors, logic gates and other electrical components like resistors, capacitors and inductors.

1. BASIC ELECTRONICS
Electronicsisa branch of physicsthat deals with the emissionand effects
of electronsin materials.
Or
Is a branch of sciencedealing with thestudy and development of circuit
involving semi conductors, logic gatesand other electricalcomponentslike
resistors, capacitorsand inductors.
Or
Thisis thebranch of physics which deals with the movement of electricity
in different materials.
Electronic system or circuitismadeup variouscomponentsconnected to
each other. They are used to perform a widevarietyof tasks. The mainuses
of electronic circuit are;
1. Conversion and distributionof data.
2. Controlling and processing of data.
Electronic componentscanbe passiveor active:
1. PASSIVE COMPONENTS
Consume but do not produceenergy. They do not have the abilityto
produceGAIN that is to increasethepower or AMPLIFY the signal.
They also do not have directionally, that’stheyoperatein the same
way regardlessof thedirectionof the current flowing through them
passivecomponentsinclude power sources (batteryor generator),
resistor, capacitor and inductors.
2. ACTIVE COMPONENTS

2. These are those that havedirectionand or the capacitytoproducegain.
They includesemi conductor devicessuch as diodes, transistorsand
integrated circuits.
Additional terms
Voltmeter –is the device that measurepotentialdifference.
Ammeter – is the devicewhich record electric current.
Inductors – These arecoils wound out soft iron core used to control
alternating currentbyself induction.
Also used to minimizeeffect of excessive alternatingcurrent in
the electric circuit. Usually
inductorsaremadeup by a copper wire.
ENERGY BANDS IN SOLIDS
The energy band in sold is the rangeof energy possessed by an electronin
solid materials(crystals).
Thishappens when atomsof element combineto form solid materials, they
arrangethemselvesin an orderly manner called crystal. Thereforethe
energy levels of the electrons of the atomsin a solid are modified and thus
each electron in any orbit of an atom can have a number of discretebut
closed spaced energy level lying withina certainrange.
The energy bandsformed when the atom combined toform a solid one of
three categories;
1. Valenceband
2. Conductionband
3. Forbiddengap
An important parameter intheband theory is the Fermi level, the top of the
availableelectronenergy levels at low temperatures. Thepositionof the
Fermi level with the relationto the conductionband isa crucialfactor in
determining electricalproperties.
1. VALENCE BAND

3. Thisis therange of energy possessed by valence electron. It hasthe
electrons of highest energy. The band may be completelyor partiallyfilled
with electrons, where theelectrons are normally present at the absolute
zero temperature.
2. CONDUCTION BAND
Thisis therange of energiespossessed by conductionfreeelectrons. The
band may be partiallyor not filled with electrons.
3. FORBIDDEN ENERGY GAP
Thisis theenergy of separationbetweenconductionband and valence
band.
No electrons of solid can stayin this band.
CLASSIFICATION OF SOLIDS WITH ENERGY BANDS
Due to the arrangement ofelectrons in energy bandsleads to the formation
of threetypes of solids in termsof conductivitywhich are;
1. Conductors(metal)
2. Semi conductors
3. Non – conductors(or insulators)
1. ENERGY BAND IN CONDUCTORS(METAL)
CONDUCTORS
Thisis the materialwhich canconduct electricityat any temperature.
Or
Conductorsarethose substanceswhich easily allow the passageof current
by means of free electronsthrough them.
 Absenceof forbiddengap.
 Valenceband and conductionband overlap one another.

4. PROPERTIESOF A CONDUCTOR
 Its electricityconductivitydecreasewith temperature.
 Thisis due to some electronsloss amount of energy due to collision.
2.ENERGY BAND IN THE NON – CONDUCTOR (INSULATED)
NON – CONDUCTOR
Thisis the materialwhich cannot conduct electricityat any
temperature.
Or
These are thematerialswhich do not allow the passageof electric current
by means of free electronsthrough them.
 The energy band in non – conductor arranged asfollows.
 The valence band is completely filled with electrons.
 The conductionband isempty.
 The forbiddenenergy gapeis largeabout 15ev. And therefore valence
electrons from the valence band can never gainenough energy to
overcome theforbiddenenergy gap.
PROPERTIESOF INSULATOR
1. The forbiddengap is higher which makesa given electrons an
efficient to jump from valence band to conductionband.
2. Presence of higher electronsat in force.
3. Cannot conduct electricity.

5. ENERGY BAND IN SEMICONDUCTOR
SEMICONDUCTOR
Thisis a materialwhich behavesasan insulator at OK and conductor at
273K.
Or
Thisis the materialwhich hasthepropertieslies betweenthat of
insulator and conductor.Examplesof semiconductorsaresilicon,
germanium, cadmiumsulphideand gallium arsenide.
a) At absolutezero temperature(OK)
A semi conductor actslikea non – conductor. Thevalence band completely
filled with electrons, and conductionband iscompletely empty. Forbidden
gap is wide.
b) At room temperature
A semiconductor actslikea conductor:
 The valence band is partiallyfilled.
 Conductionband has few electrons.
 For biddenenergy gap is narrow.

6. PROPERTIESOF SEMICONDUCTOR
1. Presenceof narrow for biddengap.
2. Its conductivityincreaseswith temperature.
3. Presenceof partialelectronsinthe conductionon band.
4. They have negativetemperaturecoefficient ofresistance.
EFFECTSOF TEMPERATURE IN SOLIDS
1. EFFECTSOF TEMPERATURE IN NON CONDUCTOR
(INSULATED)
The temperaturehasno effect on the conductivitypropertyofthe insulator
since theforbiddenenergy gap is very large.
2. EFFECTSOF TEMPERATURE IN A CONDUCTOR
The conductivityofthe conductor decreaseasthe temperatureincreases.
Sincewhen the temperatureincrease, it risesthe amplitudeofvibrationof
atomsand morecollision with atomsare madeby drifting electronsand
thisslow the free electrons and hence conductivitydecrease.
3. EFFECTSOF TEMPERATURE IN SEMI CONDUCTORS
At absolute zero temperature.
At this temperaturethevalence band is full filled and there is a largeenergy
gap betweenvalence and conduction'sband. There is no valence electron
canreach the conductionband tobecomefree electron, thus the material
behaves like an insulator.

7. Above absolutezero temperature, asthetemperaturerisessomevalence
electrons acquiresufficientenergyto enter into the conductionband and
thisbecomesfree elections. Thus the conductivityincreasesasthe
temperatureincreases.
TYPES OF SEMICONDUCTORS
There twotypes of semiconductors:-
a) Intrinsic semiconductor
These are puresemiconductorswhich thechargecarrier originatesinside
the materialitself. Theconductionof electricitytakesplaceby the
promotionof electrons from the valence to the conductionband energy
bandsin intrinsic semiconductor. Theconductivityinthissemiconductoris
due to increasein temperatureand themaincharger carrier is electron.
In intrinsic semiconductor, thenumber of free electrons and the number of
holes areexactlyequal.
b) Extrinsic semiconductors (Impure semi conductor)
Thisis typeof a semiconductor which isconductionareintroduced and
improved through thedoping process. In these types of semiconductor you
canmodify conductionlevel by adding smallamount of impurityup to a
million times.
DOPING
Doping is process of adding impurityatomstointrinsic crystaltoproduce
an extrinsic semiconductor.
OR
Thisis theprocess of adding animpurityisto increasethenumber of free
electrons or holes in the semiconductor. Thepurposeof adding impurities
is to increasethe number of free electrons or holes in the semiconductor in
order to increasetheconductivity ofthe semiconductor. Theimpuritiesare
called dopants.
MECHANISM OF DOPING SEMICONDUCTORS

8. Both silicon and germanium aretetravalent atoms, iethey have for valence
electrons (four electronsto the outermost shell of theatom ). If pentavalent
atom (eg. phosphorus) replacea siliconsemiconductor, four of the
impurityelectronplaythe same role as the four valence electrons of the
replaced sililcon atom and becomepart of thevalence band. The fifth
valence electron is easily detected from the pentavalent atom bythermal
energy and moves freely in the conductionband. Impuritiesthat denote
electrons to the conductionband arecalled donor impurities.
Free electron
Free electron
Fig 1.0
Effect of adding a donor impurity to a silcon
semiconductor.
Doping producestwo types of semiconductorswhich are:-
1. n – type semiconductor
2. p – type semiconductor
Thisis thesemiconductor which themajoritychargecarriers are
electrons. (Negativitycharges)

9. The n – type semiconductor obtained byadding thepentavalent
element to the puresemiconductor (Trivalent element) theadditionof
pentavalent impuritiesprovidesa largenumber of free electrons in a semi
conductor. Thepentavalent impuritiesarecalled donors sincethey
providefree electronsto the semiconductors. Supposea pentavalent
element e.g. antimonyatom is added to a puregermanium trivalent atoms
shown below;
Si – silicon
Sb – Antimonyatom
The form valence electronsof Antimonywill form bonding with the
germanium valenceelectrons. The fifth valence electronof antimonyisnot
involved in bonding, so remainfree to move thus the number of electrons
carriesincreasesand hence theconductivityofmaterialincreases.
ENERGY BAND OF N – TYPE SEMICONDUCTOR
The additionalofdonor impuritiestoanintrinsic semiconductor, creates
extra energylevel called donor energy level just below the bottom of the
conductionband at theforbiddenband.

10. 1. P – Type of semiconductor
Thisis a semiconductor which themajoritychargecarriesarepositive
chargesholes. The p – type semiconductorobtained byadding trivalent
impuritiestothe puresemiconductor. Theadditionalof trivalent impurities
providesa large number of holes in the semiconductor.
The trivalent impuritiesarecalled an acceptor sinceit receives the
electron from the semiconductor. Supposea trivalent element e.g. indium
atom is added to a pure semiconductorofgermanium (trivalent) atom as
shown below;
The threevalence electronof germanium form completebonding inthe
indium thefourth bond is completebeing short of one electron. This
missing electronis called a hole. Therefore each indium atom added one
hole is created. Thenumber of positivechargecarrier’sincreasesand this

11. increasesthe conductivityof thematerial. Thechargecarriesof current are
positivecharge.
ENERGY BAND IN P – TYPE SEMICONDUCTOR
The additionalofacceptor impuritytoan intrinsic semiconductor creates
extra energylevel called acceptor energy level just abovethe top of the
valence band
COMPARISON BETWEEN EXTRINSIC AND INTRINSIC
SEMICONDUCTOR
INTRINSIC
SEMICONDUCTOR
EXTRINSIC
SEMICONDUCTOR
It is a pure semiconductor. It is an impuresemiconductor.
The number of electricityequalsto
the number of holes.
The number of free electronsnot
equalto the number of holes.
The electric conductivityislow. The electric conductivityishigh.
The electric conductivitydepend on
temperature.
The electric conductivitydepend on
the temperatureand amount of
doping.
It has no practicaluse. Used in electronic device.
COMPARISON BETWEEN N – TYPE AND p – TYPE
SEMICONDUCTOR

12. N – TYPE P - TYPE
Produced byadding pentavalent
impuritiestoa pure semiconductor.
Produced byadding trivalent
impuritiestoa pure semiconductor.
The number of free electronexceed
the number of holes.
The number of holes exceeds the
number of free electrons.
The majoritychargearenegative
charges.
The number of holes exceed the
number of free electrons.
The donor energy level is just below
the bottom of the conductionband.
The acceptor energylevel is just
above the valence band.
1. JUNCTION DIODE
Thisis thep – n junctionsemiconductor materialwhich isconnected to
supply voltage.
P–N junction
Thisis thejunctionmadeup by two semiconductormaterialofn – type and
p – type melted together to form a junction.

13. As soon as a p – n junctionisformed electronsfrom n – type materials
diffuse intop – type materialand fill some of theholes there At the same
timeholes from p – type materialsdiffuseinton – type materialsand are
filled by electronsThis diffusionestablishesa potentialdifferencesacross
the junctionand withina very short timeof the junctionbeing madethis
becomea largeenough to prevent any further movement of chargecarriers
thisp–d is called barrier or junction barrier.
DEPLETION LAYER
Thisis theregion of the P-N junctionat which chargesexchangedirection
of moment. The potentialdifferenceset up at the junctionis called
POTENTIAL BARRIE.
BIASING OF A P – N JUNCTION
Thisis thecircuitingprocessof a semiconductordevicesuch that it can
either highly allow or highly prevent movement of chargesthrough it. Is the
process of applying potentialtothe pn–junctiontherearetwo types basing
which are;
1. Forward biasing
2. Reverse biasing
1. FORWARD BIASING
Thisis theprocess of connected thepositiveterminalof the batterytothe
p–type end and negativeterminalof the batterytothe n–type end of the p-
n junction.

14. FLOWOF CURRENT IN A FORWARD BIASED P-N JUNCTION
Under the influence of forward voltage the free electrons in n–typemove
forward the junctionand holes in p-typemove forward the junctionand
due to the largenumber of concentrationof thecharge, the free electrons
and holes crossthe junctionand constitutethecurrent. Thusin n–type
regioncurrent is carried byfree electrons and in p–typeregionthe current
is carried byholes. Thus the forward biased pn-junctionallows thecurrent
to pass through thejunction.

15. Forward and Reverse
bias
1. REVERSE BIASING
Thisis theprocess of connecting thepositiveterminalofthe batterytothe
n–type and negativeterminalofthe batterytothe p–type of the p-n
junction.

16. FLOWOF CURRENT IN THE REVERSE BIASED P – N
JUNCTION
With reverse biasto the p-n junction, thepotentialbarrier at thejunctionis
increased and practicallyno current flow through the circuit bymajority
chargecarrier. However in practicea very small current flow in the circuit
due to the minoritycarrier. Ifthe reverse voltage is increased continuously
the iceof minorityelectronsmaybecome high enough to knockout
electrons from the semiconductor atom.
AI – Thisstagebreakdown of the junctionoccurscharacterized bya
sudden rise of reverse current and a suddenfall of the resistanceofbarrier
region. This maydestroy the junctionpermanently.

17.  Break down voltage
Thisis the reverse voltage at which p-n junctionbreakdown with
the sudden risein reverse current.
 Knee voltage
Thisis the forward biased voltageat which the current through the
junctionstartstoincreaserapidly.
DIODES
A diode is an electricaldeviceallowing current tomove through it in one
directionwith far-greater easethanin theother. The most commonkind of
diode in moderncircuit designisthesemiconductor diode, although other
diode technologiesexist. Thediode they work on thep-n junctionwork.
The n-regionis called the cathodeand the P-regionsis the
anode.

18. Note:
(+) Anodeand (-) Cathode.
N-Regionrepresent Cathodeand P-Regionrepresent Anode.
TYPES OF DIODE
There aredifferent types of diodes used in the electric circuits. The
following are the most commonones:-
1. Semiconductor diode
2. Metalsemiconductor diode
3. Zener diode
4. Light emitting diodes
1. Semiconductor diode
One type of diodeof diode is p-n junctiondiodedescribed above. This
is referred to as semiconductor diode. Most semiconductor diodeare
madeup of siliconor germanium.Consider thefigurebelow shows a
constructionofSemiconductordiode.
2. Metal semiconductor diode
These types of diodesare formed by the deposition of a metal on the
surfaceof metalconductor.

19. Metal
3.Light emitting diode (LED)
A light emitting diode(LED) is a semiconductor diodethat emitslight
when electricalcurrent isapplied in the forward directionofthe
diode.
LEDs are madefrom variety semiconductor materialsdepending on
the wavelength of the light required. Themost used materialsfor the
visible LEDs are gallium phosphideand gallium arsenic phosphide.
Consider thefigure below shows a light emitting diodeand its
symbol.
4. Zener diode
Zener diodes arespecially manufactured diodesdesigned tobe operated in
the reverse breakdownvoltage. Every zener diodeis manufactured for a
specific reversebreakdownvoltage called theZener diode. Consider the
figure below shows a symbol of Zener diode.

20. NB: Diode is designed to work in mode of forward and reversing biasing
junction.
RECTIFICATION
Thisis thechangeof alternating current(alternatecurrent todirect current
the diodeused to rectifier of A.C to D.C) to direct current hasso manyuses
comparewith analternatecurrent but isso expensiveto producea direct
current also to reducea cost is necessaryto producean alternatecurrent
then rectified todirect current.
The conversion processis done through a p-n junctionbiased. A junction
diode which is a biased p–n Junctionis denoted by a circuit symbol.
The arrow head show the directionofflow of positivecharges. It has been
observed that p–n junction conductscurrent easilywhenis forward biased
and practicallyno current flow when it is reversed biased. Thisoutstanding
propertyof thesemiconductor for diodepermit to be used as a rectifier i.e.
it changesthe alternating current todirect current.
1. HALF WAVE RECTIFICATION
In a half wave rectificationonly one diodeis used. The diode conducts
current only during thepositionhalf cycles of the input alternatecurrent
supply. During the negativehalf cycle of alternatecurrent nocurrent is

21. conducted and hence no voltage appearsacrossload.
Half Wave Rectifier Operation
To understand theoperationof a half wave rectifier perfectly, you must
know the theory part really well. If you are new to the conceptsof p-n
junctionand itscharacteristics, Irecommend you to read the half wave
rectifier theorypart first.
The operationof a half wave rectifier isprettysimple. From the theory part,
you should know that a p-n junctiondiodeconductscurrent only in 1
direction. In other words, a p-n junctiondiodeconductscurrent only when
it is forward biased. The sameprincipleis madeuse of in a half wave
rectifier toconvert AC to DC.
The input we give here is an alternating current. Thisinput voltageis
stepped down using a transformer. The reduced voltageis fed to the diode
‘D’ and load resistance RL. During thepositivehalf cycles of the input
wave, the diode ‘D’ will be forward biased and during the negativehalf
cycles of input wave, thediode ‘D’ will be reverse biased.
We takethe output acrossload resistor RL. Sincethe diodepasses current
only during one half cycle of the input wave, we get an output asshown in
diagram. Theoutput ispositiveand significant during thepositivehalf
cycles of input wave. At the same timeoutput is zero or insignificant during
negativehalf cycles of input wave. Thisis called half wave rectification.
Before used a d-c current produced in half wave circuit must besmoothed.
The Smoothing Capacitor

22. We saw in theprevious sectionthat thesingle phase half-wave rectifier
producesan output waveevery half cycle and that it was not practicaltouse
thistype of circuit toproducea steadyDC supply... We cantherefore
increaseitsaverageDC output level even higher by connecting a suitable
smoothing capacitor acrosstheoutput ofthe bridgecircuitasshown below.
2. FULL WAVE RECTIFICATION
In full wave rectificationcurrent flow through the load in the same
directionfor both half cycles of the input alternatecurrent voltage.
The following two circuits are commonly used for full wave
rectification;
 Center – tap full rectification
 Full wave bridgerectification
1. CENTER TAP FULL RECTIFICATION
In thistype the two diodesare used and theinput is tapped at the center
hence converted from alternatecurrent todirect current form.
In a central tap Rectifier circuittwodiodesare now used, one for each
half of the cycle. A multiplewinding transformer isused whose secondary
winding is split equally into twohalves with a commoncenter tapped
connection, (C). This configurationresultsin each diodeconducting inturn
when its anodeterminalis positivewith respect to the transformer center
point C producing anoutput during both half-cycles, twicethat for the half
wave rectifier soit is 100% efficient asshown below.
The full wave rectifier circuit consistsoftwo power diodes connected to a
single load resistance (RL) with each diode taking it inturn to supply
current to theload. When point A of the transformer ispositivewith

23. respect to point C, diode D1 conductsintheforward directionasindicated
by the arrows.
When point B is positive(in thenegativehalf of the cycle) with respect to
point C, diode D2 conductsin the forward direction and thecurrent flowing
through resistor R is in the same directionfor both half-cycles. As the
output voltageacrossthe resistor R is the phasesum of the twowaveforms
combined, thistypeof full wave rectifier circuit isalso known as a “bi-
phase” circuit.
As the spacesbetweeneach half-wavedeveloped by each diode is now being
filled in by the other diode theaverage DC output voltageacrossthe load
resistor is now double that of thesingle half-wave rectifier circuit and is
about 0.637Vmax ofthe peakvoltage, assuming no losses.
The peak voltageof the output waveform is thesame as before for the half-
wave rectifier provided each halfof the transformer windingshavethe
samerms voltage value. To obtaina different DC voltage output different
transformer ratioscanbeused. The maindisadvantageofthistype of full
wave rectifier circuit isthat a larger transformer for a given power output is
required with twoseparatebut identicalsecondarywindingsmaking this
type of full wave rectifying circuitcostlycompared tothe “Full Wave Bridge
Rectifier” circuit equivalent.
2. FULL WAVE – BRIDGE RECTIFICATION
The bridge – circuit producesfullwave rectificationwithouttheuse of
center tapped secondary, it consistsfour diodes.

24. The Full Wave Bridge Rectifier
Another type of circuitthat producesthesameoutput waveform as thefull
wave rectifier circuit aboveisthat of the Full Wave Bridge Rectifier.
Thistype of single phaserectifier uses four individualrectifyingdiodes
connected in a closed loop “bridge” configurationtoproducethedesired
output. The mainadvantageofthisbridgecircuitisthat it does not require
a specialcenter tapped transformer, therebyreducingitssize and cost. The
single secondarywinding is connected to one side of thediode bridge
network and the load to the other sideas shown below.
The Diode Bridge Rectifier
The four diodes labeled D1 to D4 arearranged in“series pairs” with only
two diodesconducting current during each half cycle. During thepositive
half cycle of the supply, diodes D1 and D2 conduct inseries while diodes
D3 and D4 are reverse biased and the current flows through the load as
shown below.
The Positive Half-cycle

25. During the negativehalf cycle of the supply, diodes D3 and D4 conduct in
series, but diodes D1 and D2 switch “OFF” asthey arenow reversing
biased. The current flowing through theload is thesame directionas
before.
The Negative Half-cycle
As the current flowing through the load is unidirectional, sothe voltage
developed across theload is also unidirectional, thesameas for the
previoustwo diode full-wave rectifier.
TRANSISTOR
A transistor isa semiconductor deviceused to amplifyand switch electronic
signalsand electricalpower. It is composed of semiconductor materialwith
at least three terminalsfor connectionto an externalcircuit. A voltageor
current applied toone pair of the transistor'sterminalschangesthecurrent
through another pair of terminals. Becausethe controlled (output) power
canbe higher than thecontrolling (input) power, a transistor canamplifya
signal. Today, some transistorsarepackaged individually, but manymore
are found embedded inintegrated circuit.

26. A bipolar junctiontransistor (BJT or bipolar transistor) isa type of
transistor that relieson the contact of twotypes of semiconductor for its
operation. BJTscan be used as amplifiers. Switchesor inoscillatorsBJTs
canbe found either as individualdiscretecomponents, or in large numbers
as partsof integrated circuits.
Bipolar transistorsareso named becausetheir operationinvolves both
electrons and holes. These two kinds of chargecarriersarecharacteristic of
the two kindsof doped semiconductor material; electronsaremajority
chargecarriersinn-typesemiconductors, whereasholes aremajority
chargecarriersinp-typesemiconductors. Incontrast, unipolar transistors
such as the field effect transistor haveonly one kind of chargecarrier.
Chargeflow in a BJT is due to diffusionof chargecarrieracrossa junction
betweentwo regionsof different chargeconcentrations. Theregionsof a
BJT are called emitter, collector, and base. A discretetransistorhasthree
leads for connectionto these regions. Typically, emitter isheavily doped
compared toother twolayers, whereasmajoritychargecarrier
concentrationsinbaseand collector layers are about thesame. By design,
most of the BJT collector current is due to the flow of chargesinjected from
a high-concentrationemitterintothebase where thereare minority
carriersthat diffusetoward thecollector, and so BJTs are classified as
minority-carrier devices.
BJTs come in twotypes, or polarities, knownas PNP and NPN based on the
doping types of thethree mainterminalregions. An NPN transistor
comprisestwosemiconductor junctionsthat sharea thinp-doped anode
region, and a PNP transistor comprisestwosemiconductorjunctionsthat
share a thin n-doped cathoderegion.
Thisis thedielectric deviceby joining either twoN–typesemiconductor
sand mixed by one p–type OR two p–typesend mixed by one N–type
semiconductor. Therearetwotypes of transistor which are;

27. TERMINALS OF A TRANSISTOR
Base (B)- centralpoint of a transistor.
Emitter (E)- line at which the electric signalsflows intoor out of the
transistor. Theline carrying signalinthe input circuit.
Collector (C)- line at which the signalis takenfrom the transistor tothe
appliancei.e. the line taking signalfrom the transistor into
Emitter circuit isalwaysin the forward BIAS meanwhile the collector
circuit isinthe reverse bias.