Eced Notes

8/13/2019 Eced Notes

1/34

EC%&& ELECTRIC CIRCUITS AN* ELECTRON *E+ICES

UNIT"I CIRCUIT ANALYSIS TECHNI2UES

Ohm34 La5

Temperature remaining constant, the potential difference (E) across the ends of a

conductor is proportional to the current (I) flowing through it.

Mathematically, V=IR

K!./hh60074 Cu..et La5 (KCL)

The alge!raic sum of all currents entering and e"iting a node must e#ual $eroIin= Iout

%imilarly, at any instant the alge!raic sum of all the currents at any circuit node is $ero.

SI 8 $

K!./hh60074 +69ta1e La5 (K+L)

The alge!raic sum of all &oltages in a loop must e#ual $ero

E = IZ

%imilarly, t any instant the alge!raic sum of all the &oltages around any closed circuit is $ero'

E - IZ = 0

Se.!e4 a: Pa.a99e9 Re4!4t6. C6mb!at!64

There are two !asic ways in which to connect more than two circuit components'%eries and arallel.

*or analysis, series resistors+impedances can !e replaced !y an e#ui&alent resistor+

impedance.

arallel resistors+impedances can !e replaced !y an e#ui&alent resistor+ impedance.

Se.!e4 Re4!4ta/e

Two elements are inseriesif the current that flows through one must also flowthrough the other.

Reqis e#ui&alent to the resistor networ on the left in the sense that they ha&e the

same i-vcharacteristics.

R- R

%ERIE% Req8 R& ; R% ; R


2/34

Pa.a99e9 Re4!4ta/e

Two elements are inparallelif they are connected !etween (share) the same two(distinct) end nodes.

I:u/t6.4

Se.!e4 a: =a.a99e9 !:u/ta/e4

/here, 0 = Inductance in henrys

Ca=a/!t6.4

Se.!e4 a: Pa.a99e9 Ca=a/!ta/e4

/here, 1 = 1apacitance in farads

Me4h /u..et meth6:

TheMesh Current Methoduses simultaneous e#uations, 2irchhoff3s Voltage 0aw,and 4hm3s 0aw to determine unnown currents in a networ. It differs from the 5ranch

1urrent method in that it does not use 2irchhoff3s 1urrent 0aw, and it is usually a!le to

sol&e a circuit with less unnown &aria!les and less simultaneous e#uations.

Ste=4 t6 069965 06. the Me4h Cu..et meth6: 60 aa9>4!4

-. 6raw mesh currents in loops of circuit, enough to account for all components.. 0a!el resistor &oltage drop polarities !ased on assumed directions of mesh currents.

7. /rite 2V0 e#uations for each loop of the circuit, su!stituting the product IR for E

in each resistor term of the e#uation. /here two mesh currents intersect through acomponent, e"press the current as the alge!raic sum of those two mesh currents.

8. %ol&e for unnown mesh currents (simultaneous e#uations).

9. If any solution is negati&e, then the assumed current direction is wrong:

R-

R

7-

----

RRRReq++=;R;00E0


3/34

)

8. ;ssign unnown &oltages (E-)(E) ... (E?)to remaining nodes.

9. /rite a 210 e#uation for each node -,, ... ?. The positi&e coefficient of the first

&oltage in the first e#uation is the sum of conductances connected to the node.Repeat for coefficient of second &oltage, second e#uation, and other e#uations.

These coefficients fall on a diagonal.


4/34

NET@ORK THEOREMS

The?e!74 The6.em

;ny circuit with sources (dependent and+or independent) and resistors can !e

replaced !y an e#ui&alent circuit containing a single &oltage source and a single

resistor. The&eninAs theorem implies that we can replace ar!itrarily complicated networs

with simple networs for purposes of analysis.

N6.t674 The6.em

;ny circuit with &oltage sources, resistances (impedances) and open output

terminals can !e replaced !y a single current source in parallel with single resistance(impedance), where the &alue of current source is e#ual to the current passing through the

short circuit output terminals and the &alue of the resistance (impedance) is e#ual to the

resistance seen into the output terminals.

Su=e. P64!t!6 The6.emIn a linear, lumped element, !ilateral electric circuit that is energi$ed !y two or

more sources the current in any resistor is e#ual to the alge!raic sum of the separatecurrents in the resistor when each sources acts separately. /hile one source is applied, the

other sources are replaced !y their respecti&e internal resistances.

Su=e. P64!t!6 The6.em is not &alid for power responses. It is applica!le only for

computing &oltage and 1urrent responses.

Ma!mum P65e. t.a40e. The6.em

The ma"imum ower transferred to a load resistor occurs when it has a &alue e#ual

to the resistance of the networ looing !ac at it from the load terminals (all sources !eing

replaced !y their respecti&e internal resistances).

*ua9!t>

Two electrical networs which are go&erned !y the same type of e#uations arecalled :ua9!t>

*or the networs to !e duals it is necessary that the &aria!les B elements of one

networ should also !e the duals of &aria!les B elements of other networs.

Meth6: 60 :.a5!1 :ua9!t> (6.) :ua9 et56.k

a) lace a dot in each independent loop of the gi&en networ. These dots placed inside

the loops correspond to the independent node in the dual networ.!) ; dot is placed outside the gi&en networ. This corresponds to the reference node

of the dual networ.

c) ;ll the dots are connected !y dotted lines crossing all the !ranches. The dotted linesshould cross only one !ranch at a time.

d) The dual elements will form the !ranches connecting the corresponding nodes in

the dual networ.


5/34

Sta."*e9ta T.a406.mat!6

The %tarC6elta transformation techni#ues are useful in sol&ing comple" networ.

; star networ of three resistances RA, R-and RCconnected together at common

node ? can !e transformed into a delta networ of three resistances RA-, R-Cand RCA!ythe a!o&e e#uations'

In general terms'

R:e9ta= (sum of R4ta.pair products) + (opposite R4ta.)

*e9ta"Sta. T.a406.mat!6

; delta networ of three impedances RA-, R-Cand RCAcan !e transformed into a starnetwor of three impedances RA, R-and RCconnected together at common node ? !y the

following e#uations'

In general terms'

R4ta.= (adDacent R:e9tapair product) + (sum of R:e9ta)


6/34


7/34

UNIT"II TRANSIENT RESONANCE IN RLC CIRCUITS

T.a4!et State

If a networ contains energy storage elements, with change in e"citation, the

current and &oltages change from one state to another state is called transient state. The!eha&ior of the &oltage or current when it is changed from one state to another state is

called t.a4!et 4tate.

T.a4!et T!me

The time taen for the circuit to change from one steady state to another steady

state is called the t.a4!et t!me

Natu.a9 .e4=64eIf we consider a circuit containing storage elements which are independent of sources,

the response depends upon the nature of the circuit, it is called atu.a9 .e4=64e.

T.a4!et .e4=64eThe storage elements deli&er their energy to the resistances, hence the response

changes with time, gets saturated after sometime, and is referred to the t.a4!et .e4=64e.

La=9a/e T.a406.m'The 0aplace transform of any time dependent function f(t) is gi&en !y *(s).

/here %; comple" fre#uency gi&en !y %=F G DH

I?e.4e La=9a/e T.a406.m'In&erse 0aplace transforms permits going !ac in the re&erse direction i.e. from s

domain to time domain.

O.:e. 60 a S>4tem

The order of the system is gi&en !y the order of the differential e#uation go&erningthe system. If the system is go&erned !y nthorder differential e#uation, than the system is

called nth order system.

(s) = a> snG a-s

nC-G asnCG JJ..GanC-s Gan

the order of the system is e#ual to KnA.


8/34

I!t!a9 +a9ue The6.em

The initial &alue theorem states that if " (t) and "A (t) !oth are laplace

transforma!le, then

F!a9 +a9ue The6.emThe final &alue theorem states that if " (t) and "A (t) !oth are laplace transforma!le,

then

*.!?!1 P6!t !m=e:a/e

The ratio of the 0aplace transform of the &oltage at the port to the laplace transformof the current at the same port is called dri&ing point impedance.

T.a40e. P6!t !m=e:a/e

The ratio of the &oltage transform at one port to the current transform at the other

port is called transfer point impedance.

Re46at C!./u!t

The circuit that treat a narrow range of fre#uencies &ery differently than all other

fre#uencies are referred to as resonant circuit.

The gain of a highly resonant circuit attains a sharp ma"imum or minimum at itsresonant fre#uency.

Re46a/e

Resonance is defined as a phenomenon in which applied &oltage and resulting

current are in phase.

-a:5!:th

The 5andwidth is defined as the fre#uency difference !etween upper cutCoff

fre#uency (f) and lower cutCoff fre#uency (f-).

Ha90 P65e. 0.eBue/!e4

The upper and lower cutCoff fre#uencies are called the halfCpower fre#uencies. ;t

these fre#uencies the power from the source is half of the power deli&ered at the resonantfre#uency.

Se9e/t!?!t>

%electi&ity is defined as the ratio of !andwidth to the resonant fre#uency ofresonant circuit.

2 0a/t6.

The #uality factor, , is the ratio of the reacti&e power in the inductor or capacitor

to the true power in the resistance in series with the coil or capacitor.

Se.!e4 Re46a/e ! RLC /!./u!t


9/34

In series R01 circuit resonance may !e produced !y either &arying fre#uency for

gi&en constant &alues of 0 and 1 or &arying either 0 and 1 or !oth for a gi&enfre#uency.

;t resonance inducti&e reactance is e#ual to the capaciti&e reactance.

If f L f>the current I leads the resultant supply &oltage V and so the circuit !eha&es

as a capaciti&e circuit at the fre#uencies which are less than f>. ;t f = f>, the &oltage and current are in phase. The circuit !eha&es as pure resisti&e

circuit at the resonant fre#uency with unit power factor.

If f f>, the current I lags the resultant supply &oltage V and so the circuit !eha&es

as an inducti&e circuit at the fre#uencies which are more than f>.

;t resonance series R01 circuit acts as a &oltage amplifier.

%eries resonance circuit is always dri&en !y a &oltage source with &ery small

internal resistance to maintain high selecti&ity of the circuit.

Pa.a99e9 Re46a/e

; parallel circuit is said to !e in resonance when applied &oltage and resulting

current are in phase that gi&es unity power factor condition.

arallel resonance is also nown as ;nti resonance.

;t anti resonance the parallel resonant circuit acts as current amplifier.

Rea/ta/e /u.?e4

The graph of indi&idual reactance &ersus the fre#uency is called Reactance 1ur&e.

T>=e4 60 Tue: /!./u!t4

%ingle tuned circuit

6ou!le tuned circuit

S!19e tue: /!./u!t

In R* circuit design, tuned circuits are generally employed for o!taining ma"imum

power transfer to the load connected to secondary or for o!taining ma"imum possi!le &alueof secondary &oltage.

; single tuned circuit is used for coupling an amplifier and radio recei&er circuits.

*6ub9e tue: /!./u!t

In dou!le tuned circuits, a &aria!le capacitor is used at input as well as output side.

/ith the help of adDusta!le capaciti&e reactance, impedance matching is possi!le if

the coupling is critical, sufficient or a!o&e. It is also possi!le to adDust phase angle such that impedance at generator side

!ecomes resisti&e.

The magnitude matching can !e achie&ed !y adDusting mutual inductance to thecritical &alue, which effecti&ely fulfills ma"imum power transfer condition.


10/34

UNIT"III SEMICON*UCTOR *IO*ES

Ee.1> -a:4

The range of energies possessed !y an electron in a solid is nown as Ee.1>ba:

C9a44!0!/at!6 60 Ee.1> -a:

-. 1onduction !and

. *or!idden !and

7. Valence !and

C9a44!0!/at!6 60 4em!/6:u/t6.4

-. Intrinsic %emiconductors.

. E"trinsic %emiconductors.

It.!4!/ Sem!/6:u/t6.4 ; %emiconductor which is in its e"tremely pure form is nown as an

!t.!4!/ 4em!/6:u/t6.

If potential difference is applied across intrinsic semiconductor, the

electrons will mo&e towards the positi&e terminal while the holes will drift

towards the negati&e terminal.

The total current inside the semiconductor is the sum of currents due to

free electrons and holes.

Et.!4!/ Sem!/6:u/t6.4

The conducti&ity can !e increased !y the addition of a small amount of

suita!le metallic impurity. It is also nown as !m=u.!t> 4em!/6:u/t6. The process of adding impurity atoms to the intrinsic semiconductor is

called :6=!1.

The purpose of adding impurity is to increase either the num!er of free

electrons or holes in a semiconductor.

Two types of impurity atoms are added to the semiconductor.

Peta?a9et !m=u.!t> at6m4 "containing fi&e &alance electrons

T.!?a9et !m=u.!t> at6m4 "containing three &alance electrons

E"trinsic semiconductors are classified as,

N"t>=e Sem!/6:u/t6.

P"t>=e Sem!/6:u/t6.

N"t>=e Sem!/6:u/t6.

; small amount of penta&alent impurity is added to a puresemiconductor is nown as N"t>=e Sem!/6:u/t6.

/hen a penta&alent impurity is added to a pure semiconductor, it

displaces some of its atoms. E.g. ;R%E?I1 (;s), ;?TIM4?N (%!)


11/34

In ?Ctype semiconductor, maDor part of the current flows due to the

mo&ement of Electrons. Therefore electrons in an ?Ctype semiconductor arenown as maDority carriers and holes as minority carriers.

P"t>=e Sem!/6:u/t6.

; small amount of tri&alent impurity is added to a pure semiconductor

is nown as P"t>=e Sem!/6:u/t6.

E.g. Oallium (Oa), Indium (In), ;luminium (;l), 5oron (5) etc.

In Ctype semiconductor, maDor part of the current flows due to the

mo&ement of holes. Therefore holes in a Ctype semiconductor are nown asmaDority carriers and electrons as minority carriers.

C6:u/t!?!t> 60 a 4em!/6:u/t6.

Each holeCelectron pair created two charge carrying particles is formed. 4ne is negati&eof mo!ility Pn(free electron) and the other is positi&e of mo!ility Pp (hole). These particles

mo&e in opposite direction in an electric field.

He/e the /u..et :e4!t> J 8 E

/here n , p = magnitude of free electrons B holes respecti&ely.

F = 1onducti&ity of semiconductor

E= applied electric field

# = 1harge of electron or hole.

He/e 8 (Pn; =Pp)E

*or a pure semiconductor n = p = niQ where ni intrinsic semiconductor

CARRIER CONCENTRATIONS IN AN INTRINSIC SEMICON*UCTOR

In order to calculate the conducti&ity of a semiconductor, it is necessary to now the

concentration of free electrons n and the concentration of holes p.

C6/et.at!6 60 E9e/t.64 ()

The num!er of electrons in the conduction !and, 8 N/ e" (E

CDE

F)KT

/here,

N/= h

Smn2T7+


12/34

C6/et.at!6 60 h69e4 (=)

The num!er of holes in the conduction !and, = 8 N? e" (E

FDE

+)KT

/here,

N?=

Ee.1> Ga= (EG)

The energy re#uired to !rea a co&alent !ond in a semiconductor is nown as

energy gap. The Energy gap at any temperature is gi&en !y, EG8 EGOD T

*.!0t Cu..et

6rift current is defined as the flow of electric current due to the motion of the

charge carriers under the influence of an e"ternal electric field applied across thesemiconductor material.

*!00u4!6 Cu..et

In a semiconductor material, the charge carriers ha&e the tendency to mo&e from

the region of higher concentration to that of lower concentration of the same type of chargecarriers. This mo&ement of charge carriers taes place resulting in a current called diffusion

current.

6iffusion current density due to holes, J= 8 " B *=:=: A/m%

6iffusion current density due to electrons, J 8 " B *:: A/m%

T6ta9 Cu..et *e4!t>

Total current is the sum of drift current and diffusion current.

The total current density for Ctype semiconductor J= 8 " B=PpE" B *=:=:

The total current density for ?Ctype semiconductor J 8 " BPnE" B *::

*!00u4!6 Le1th (L)

The a&erage distance that a charge carrier can diffuse during its lifetime is called as

diffusion 0ength 0.

h

Smp2T7+


13/34

The6.> 60 PN Ju/t!6 *!6:e

/hen a Ctype semiconductor s Doined to a ?Ctype semiconductor the contact surface is

called PN u/t!6or ? diode.

The &oltage across ? Dunction can !e applied in two ways.

(i) *orward !iasing

(ii) Re&erse !iasing

The ?Ctype material has high concentration of free electrons and, Ctype material

has high concentration of holes. ;t the Dunction, there is a tendency for the free ?Ctype ofdiffuse o&er to the Cside and holes from the Cside to the ?Cside. This process is called

:!00u4!6.

Thus a !arrier is set up against further mo&ement of charge carriers. This is called

P6tet!a9 ba..!e.or Ju/t!6 ba..!e.(V5).The potential !arrier is of the order of >.-V to>.7 V.

The mo!ile charges ha&e !een depleted in this region. It is nown as :e=9et!69a>e.


14/34

ENER *IO*E

; $ener diode is a special purpose diode that is operated in re&erseC!iased

conditions. Its operation depends on the ee. b.eak:65 =he6me6.

S>mb69

;node 1athode+"I Cha.a/te.!4t!/4 60 ee. :!6:e

The operation of $ener diode is same as that of ordinary pCn diode order forward

!iased condition, whereas under re&erse !iased condition !readown of the Dunction

occurs.

5readown &oltage depends upon the amount of doping. If the diode is hea&ily

doped, depletion layer will !e thin and conse#uently !readown occurs at lower re&erse&oltage and further, the !readown &oltage is sharp. The !readown &oltage can !e

selected with the amount of doping.

The sharp increase in current under !readown condition is due to the following

two mechanisms.

;&alanche !readown

ener !readown


15/34


16/34

A?a9a/he b.eak:65

/hen doping concentration is less lie in ordinary diode then under re&erse !iased

condition a small amount of re&erse saturation current flows and is constant as long as the

temperature is constant.

/hen the re&erse &oltage is increased width of the depletion layer increases at the

same time the electrons due to force of attraction !y the plates ac#uire some high &elocityand during their motion inside the diode they collide with the electrons in co&alent !onds

and !ring them out.

6ue to this multiplication process a large current flows and this ind of !readown

is called A?a9a/he mu9t!=9!/at!6or !readown. 4nce when this !readown occurs the

diode gets damaged.

ee. b.eak:65

/hen doping is hea&y then in re&erse !ias e&enC!efore the minority charge carries

ac#uire sufficient &elocity the !readown occurs and is nown as ee. b.eak:65.

In re&erse !ias under hea&y doping condition the width of the depletion layer will !e &ery

thin strong electric field e"ists inside the diode. /hen re&erse &oltage increased at once

electric field the electrons which are present in the co&alent !ond are !rought due to strongforce of attraction. ?ow, suddenly a large amount of current flows. ?othing !ut 5readown

occurs. In ener diode first $ener !readown occurs and later a&alanche !readown.

A==9!/at!64 60 ee. :!6:e4

Voltage regulator

*i"ing reference &oltages in electronic circuits such as power supplies and

transistor !iasing.

1lippers in wa&eCshaping circuits.

%#uare wa&e generation.


17/34

UNIT"I+ TRANSISTORS

It.6:u/t!6 60 t.a4!4t6.4

Transistor is a semiconductor de&ice that can amplify electronic signals such as radio and

tele&ision signals.

A:?ata1e 60 the t.a4!4t6.-. %maller in si$e

. ?o filament and no need of power for heating filament

7. 0ow operating &oltage

8. Uigher efficiency

T>=e4 60 the t.a4!4t6.

nipolar Wunction Transistor

5ipolar Wunction Transistor

C64t.u/t!6 60 the t.a4!4t6.

nCpCn transistor

pCnCp transistor

"=" t.a4!4t6.

It is formed !y sand witching pCtype semiconductor !etween two nCtype.

=""= t.a4!4t6.

It is formed !y sand witching nCtype semiconductor !etween two pCtype.

Te.m!a94 06. the t.a4!4t6.

Emitter

1ollector

5ase

Fu/t!64 60 Em!tte., C699e/t6. -a4e

Emitter ' To supply maDority charge carriers.

1ollector' To collect maDority charge carriers.

5ase' It passes most of the inDected charge carriers to the collector.

T.a4!4t6. -!a4!1

;pplying e"ternal &oltage to a transistor is called b!a4!1.

In order to operate transistor properly as an amplifier, it is necessary to correctly !ias the

two pn Dunctions with e"ternal &oltages.

6epending upon e"ternal !ias &oltage polarities used, the transistor wors in one of the

three regions. ;cti&e region.

1utCoff region.

%aturation region.

S9N6 Re1!6 Em!tte. -a4e C699e/t6. -a4e O=e.at!6 60 a t.a4!4t6.

- ;cti&e *orward !iased Re&erse !iased acts as an amplifier

1utCoff *orward !iased Re&erse !iased acts as an open switch


18/34

7 %aturation *orward !iased Re&erse !iased acts as an closed switch

O=e.at!6 60 NPN t.a4!4t6.4

Emitter is forward !iased B as a result large forward current flows across theemitter Dunction due to flow of maDority carriers.

InDected electrons diffuse into the collector region due to the e"tremely smallthicness of the !ase.

1ollector is re&erse !ias and creates a strong electrostatic field !etween !ase

Bcollector.

*ield immediately collects the diffused electrons which enter the collector Dunction.

*low of electrons into the !ase region when confronted with the holes, a few

electrons com!ine B neutrali$e

Rest of the electrons of the inDected electrons diffuse into the collector region and iscollected !y the collector electrode.

O=e.at!6 60 PNP t.a4!4t6.4

*orward !ias causes the holes in the Ctype emitter to flow towards the !ase.

Reduces the potential !arrier at the Dunction

Uoles cross the Dunction B penetrate into the ?Cregion. This constitutes emittercurrent IE.

/idth of the !ase region is &ery thin B lightly dopedQ hence a small amount of the holesrecom!ine with free electrons of ?Cregions. This constitutes !ase current I5B is &ery small.

Rest of the holes drift across the !ase and enter the collector region and are swept

away !y the negati&e collector electrode. This constitutes !ase current I1.

1urrent conduction I ? transistors is !y mo&ement of holes.

1urrent conduction in the e"ternal circuit is !y electrons.

T>=e4 60 /60!1u.at!6

1ommon 5ase configuration

1ommon Emitter configuration

1ommon 1ollector configuration

C6mm6 -a4e /60!1u.at!6

Input is connected !etween emitter B !ase. 4utput is connected !etween

collector B!ase.

EmitterC!ase Dunction is forward !iased. 1ollectorC!ase Dunction is re&erse

!iased.

Emitter current IE flows in the input circuit. 1ollector current I1 flows inoutput circuit.

The ratio of collector current I1, to emitter current IE, is called the Cu..et

am=9!0!/at!6 0a/t6. ()

If there is no input ac signal, then the ratio of I1to IEis called dc alpha (dc).

ac alpha refers to the ratio of change in I1to change in IE.


19/34

The higher the &alue of , !etter the transistor. X can !e increased !y

maing !ase thin and lightly doped.

Cha.a/te.!4t!/4 60 C- /60!1u.at!6

The performance of transistors, when connected in a circuit, may !e determined

from their characteristic cur&es that relate different d.c. currents and &oltages of atransistor.%uch cur&es are nown as Stat!/ /ha.a/te.!4t!/ /u.?e4.

I=ut Cha.a/te.!4t!/4

The cur&e drawn !etween Emitter current and Emitter 5ase &oltage for a

gi&en &alue of collectorC5ase &oltage is nown as input 1haracteristics.

*or a gi&en &alue of V15,the cur&e is Dust lie a forwardC!iased ? Dunction.

/ith an increase in the &alue of V15,it conducts !etter. This is !ecause of

the effect called ea.9> e00e/tor -a4e 5!:th m6:u9at!6.

Out=ut Cha.a/te.!4t!/4

The cur&e drawn !etween 1ollector current and 1ollector 5ase &oltagefor a gi&en &alue of emitter current is nown as output 1haracteristics.

The collector current &aries with V15 for &ery low &oltage !ut transistor isne&er operated in this region.

C6mm6 Em!tte. /60!1u.at!6

Input is connected !etween !ase B emitter. 4utput is connected !etween

collector B emitter.

EmitterC!ase Dunction is forward !iased. 1ollectorC!ase Dunction is re&erse!iased.

5ase current I5 flows in the input circuit. 1ollector current I1 flows in

output circuit.

1E is commonly used !ecause its current, &oltage and power gains are #uite

high and output to input impedance ratio is moderate.

The rate of change in collector current I1, to change in emitter current IE, iscalled am=9!0!/at!6 0a/t6. ()


The cur&e drawn !etween 5ase current and 5ase Emitter &oltage for a

gi&en &alue of collectorCemitter &oltage is nown as input 1haracteristics.

*or a gi&en &alue of VE1,the cur&e is Dust lie a forwardC!iased ? Dunction

diode. Input resistance is larger in 1E configuration than in 15 configuration. This

is !ecause the input current I5increases less rapidly with increase in V5E.

;n increment in the &alue of V1E, causes the input current I5to !e lower for

a gi&en le&el of V5E. This is !ecause of the effect called ea.9> e00e/t.

Out=ut Cha.a/te.!4t!/4


20/34

The cur&e drawn !etween 1ollector current I1 and 1ollector emitter

&oltage V1Efor a gi&en &alue of !ase current I5is nown as output 1haracteristics.

4utput characteristics in 1E configuration ha&e some slope while 15

configuration has almost hori$ontal characteristics. This indicates that output

resistance in case of 1E configuration is less than that in 15 configuration.

C6mm6 C699e/t6. /60!1u.at!6

Input is connected !etween !ase B collector. 4utput is connected !etweencollector B emitter.

The 1ollector forms the terminal common to !oth the input and output.

5ase current flows in the input circuit. Emitter current flows in output

circuit.

/ith !ase current I5 e#ual to V14, the emitter current IE is $ero, so no

current flows in the load resistor R0.

/ith increases in input current I5, the transistor passes through the acti&eregion and finally reaches saturation.


To determine the input 1haracteristics, VE1 is ept at a suita!le fi"ed &alue.

The !aseCcollector &oltage V5c is increased in e#ual steps and the

corresponding increase in I5is noted.

This is repeated for different &alues of VE1.

-.eak:65 ! T.a4!4t6.4

;&alanche Multiplication

ReachCThrough (or) unch through

A?a9a/he Mu9t!=9!/at!6

The ma"imum re&erse !ias &oltage which can !e applied !efore !readown

!etween collector and !ase terminals of the transistor under the condition that the

emitter is openCcircuited.

It is represented !y the sym!ol 5V154(for 15 configuration).

This !readown &oltage is a characteristic of the transistor alone.

5readown occurs !ecause of the a&alanche multiplication of current I14that crosses the collector Dunction.

;s a result of this multiplication, the current !ecomes MI14in which M is

the factor !y which the original current I14is multiplied !y the a&alanche effect.

;t a high &oltage 5V154, the multiplication factor M !ecomes infinite andthe region of !readown is then attained.

The current increases a!ruptly and large changes in current accompaniessmall changes in &oltage.

Rea/h"Th.6u1h (6.) Pu/h th.6u1h


21/34

It results from Early effect (i.e.) as a result of increase in V 15 and as the

doping of the !ase is su!stantially smaller than that of the collector and thepenetration of the transition region into the !ase is larger than into the collector

%ince the !ase is &ery thin, the transition region spreads completely across

the !ase to reach the emitter Dunction.

;t this point, normal transistor action ceases and the emitter and collectorare effecti&ely shorted.

Uence, a large current flows from the emitter to collector. This is called

ReachCthrough.

F!e9: E00e/t T.a4!4t6. (FET)

*ET is a semiconductor de&ice which depends for its operation on the control of

current !y an electric field.

The output characteristics of *ET are controlled !y Input &oltage and not !y the

Input current.

%o, it is also nown as &oltageCcontrolled de&ice.

Featu.e4 60 FETThe *ET has se&eral ad&antages o&er the con&entional transistor.

Its operation depends upon the flow of maDority carrier only. %o, it is called as

nipolar de&ice.

It is relati&ely immune to radiation.

It e"hi!its a high input resistance, typically many mega ohms.

It is less noisy than a tu!e of a 5ipolar Transistor.

It e"hi!its no offset &oltage at $ero 6rain current.

It has thermal sta!ility.

T>=e4 60 FET Wunction *ield Effect Transistor (W*ET)

Metal 4"ide *ield Effect Transistor (M4%*ET) (or)

Insulated Oate *ield Effect Transistor (IO*ET)

C64t.u/t!6 60 JFET

W*ET is a three terminal semiconductor de&ice in which current conduction is !y

one type of carrier either Electrons or holes.

The W*ET consists of a Ctype or ?Ctype silicon !ar.

The !ar is made up of ?Ctype material which is nown as ?Cchannel W*ET and if

the !ar is made up of Ctype material, it is nown as channel W*ET.

The current in *ET is carried !y the maDority carriers. 4ne end of the channel is called the source and the other is called the drain.

O=e.at!6 60 JFET

*ET wors under the three conditions.

/hen VOO applied and V66=>

/hen V6%applied and VOO=>

/hen V66 applied and VOO isapplied.


22/34

/here,

VOO Oate supply &oltage.

V6% 6rain %ource &oltage.

V66 6rain supply &oltage.

Cha.a/te.!4t!/4 60 JFET ; family of cur&es that relate the current and &oltage are nown as

characteristics cur&e.

There are the two important characteristics of a W*ET.

Transfer characteristics

6rain characteristics

Cha.a/te.!4t!/4 Pa.amete.4 60 JFET

The parameters of W*ET are

Transconductance

6rain resistance

6rain conductance

;mplification factor

Meta9 O!:e Sem!/6:u/t6. FET (MOSFET)

M4%*ET is a three terminal de&ice. Those terminals are source, gate and drain.

The gate of a M4%*ET is insulated from the channel.

5ecause of this, the M4%*ET is also nown as an IO*ET (Insulated gate *ET).

The M4%*ET is a second category of *ET.

The M4%*ET differs from the W*ET is that it has no pn Dunction structureQ instead

the gate of the M4%*ET is insulated from the channel !y a silicon dio"ide layer.

T>=e4 60 MOSFET

6epletion type M4%*ET

Enhance type M4%*ET

C64t.u/t!6 60 MOSFET

Two highly doped n regions are diffused into a lightly doped p type su!strate.

These two highly doped regions are represents source and drain. In some casessu!strate is internally connected to the source terminal.

The source and drain terminals are connected through metallic contacts the nCdoped

regions lined !y an nCchannel.

The gate is also connected to a metal contact surface !ut remains insulted from thenC1hannel !y a &ery thin layer of dielectric material, %ilicon 6io"ide.

This layer act as one parallel plate capacitor.

Thus, there is no direct electrical connection !etween the gate terminal and the

channel of a M4%*ET increasing the input impedance of the de&ice.

Cha.a/te.!4t!/4 60 MOSFET


23/34

The different characteristics of a 6CM4%*ET are

6rain characteristics

Transfer characteristics


24/34

UNIT"+ SPECIAL SEMICON*UCTOR *E+ICES

Tue9 *!6:e4 /hen the impurity concentration is of the order of one part to ->7parts then tunnel

diode is formed. This diode has negati&e resistance region.

6ue to which it is used as an oscillator.

This diode is uses the tunneling phenomenon.

Tue9!1

The process that an electron from nCside of a pn diode directly penetrates throughthe Dunction into the pCside of diode is called tunneling. It is a #uantum mechanical

!eha&iors.

O=e.at!6

/hen a tunnel diode is under un!iased condition then there will not transfer ofelectrons from nCside to pCside hence the net current will !e $ero.

/hen the diode is re&erse !iased under this condition the electrons from nCside are

attracted !y the positi&e plate and hence mo&e away from the Dunction.

;s a result the energy le&el in the nCside decreases when compared to the un!iasedstate.

?ow, there will !e some empty state in &alence !and of pCside #uite opposite to the

empty conduction !and.

Uence tunneling taes place from p to nCside.

;s re&erse !ias is increased this current increase.

A==9!/at!64

Tunnel diode is used as ltraChigh speed switch.

sed in rela"ation oscillator.

sed as an amplifier.

sed as logic memory storage de&ice.

sed as microwa&e oscillator.

A:?ata1e4

Uigh speed operation

Ease of operation

0ow noise 0ow cost

0ow power

*!4a:?ata1e4

It is two terminal de&ice, there is no isolation !etween the input and output circuit.

Voltage range o&er which it can !e operated is - V or less.


25/34

PIN *!6:e It has highly impro&ed switching time in comparison with a ? diode.

I? diodes are used in microwa&e switches.

In I? diode high resisti&ity intrinsic layer is sandwiched !etween the and ?

regions. This results in impro&ed switching time. uite often instead of ICregion we actually use either a high resisti&ity Cregion is

called S region and the high resisti&ity ?Cregion is called Y region.

The ICregion has typically resisti&ity of -> Zm.

A==9!/at!64 60 PIN *!6:e

sed as pulse and phase shifter.

sed as %%T and M%T switches.

sed in amplitude modulation.

sed as photo detectors in fi!er optic systems.

sed as TCR switch.

sed as attenuator and duple"er.

+a.a/t6. :!6:e Varactor diode is a specially manufactured re&erse !iased ? Dunction diode with a

suita!le impurity concentration profile.

It is also called as &aricap or &oltacap.

It is used as a &aria!le reactance capacitance.

Cha.a/te.!4t!/4 60 +a.a/t6. :!6:e

The diode conducts normally in the forward direction.

;t relati&ely low &oltage the re&erse current saturates and then remains constant.

It is rising rapidly at a&alanche point.

;t the saturation point the ma"imum Dunction capacitance is o!tained and a point

Dust a!o&e a&alanche the minimum Dunction capacitance is o!tained.

Therefore there are two conditions which are limiting the re&erse &oltage swing andthe capacitance &ariation.

A==9!/at!64

sed as a tuning de&ice in recei&ers.

It is used in Uigh fre#uency.

It is used in adDusta!le !andCpass filter

It is used in *M modulation.

It is used in automatic fre#uency control de&ices.

It is used in parametric amplifier.

SCR %1R consist of four semiconductor layers forming a ?? structure.

It has three ? Dunctions namely W-, W, W7.

There are three terminals called anode (;), cathode (2) and the gate (O).


26/34

The anode terminal is taen out from -layer, and the gate (O) terminal from the layer. It conducts the current in forward direction only.

O=e.at!6 60 SCR

%1R is forward !ias with a small &oltage, it is in K4**A and no current flows

through the %1R.

The applied forward &oltage is increased, a certain critical &oltage called forward!rea o&er &oltage (V54).It reaches at the Dunction W!readown. ;t this case the

%1R switched K4?A position.

If the %1R is re&erse !ias, the Dunction W-and W7are re&erse !ias and Dunction Wisforward !ias.

It has found that most of the &oltage will drop across Dunction W- only.

/hen the applied re&erse &oltage is small, the %1R is 4**, and there is no currentflow through the de&ice.

SCR /ha.a/te.!4t!/4

It is the relationship !etween the anode cathode &oltage and anode current at

different gate current. Two types of VCI characteristics

*orward 1haracteristics

Re&erse 1haracteristics

F6.5a.: Cha.a/te.!4t!/4

It is the current drawn !etween anodeCcathode &oltage (V;2) and anode current (I;)

at different gate current.

;dDust the gate current to $ero &alue !y eeping the switch open.

Increase the applied &oltage across the %1R in small suita!le steps at each step.

?ote the anode current B plot the graph.

Re?e.4e Cha.a/te.!4t!/4

The re&erse characteristic is o!tained !y re&ersing the connections of the d.c.

supplies V;;and VOO.

;dDust the gate current to any suita!le &alue.

Increase the re&erse applied &oltage in suita!le steps.

?ote the anode current for each steps.

?ow we plot a graph with anode current and anode cathode &oltage.

Tu.!1 ON (T.!11e.!1) SCR

The %1R can !e turned 4?, from 4** position !y anyone of the following methods. Oate triggering

*orward !rea o&er &oltage

0ight triggering

RateCeffect

Lat/h!1


27/34

4nce the %1R is turned 4?, it starts to conduct and remains in conduction state

e&en when the gate signal is remo&ed. This a!ility of the %1R to remain conducting, e&en

when the gate signal is remo&ed, is nown as 9at/h!1.

Tu.!1 OFF

4ne of the following methods is applied to turn 4** the %1R. Re&ersing polarity of anodeCtoCcathode &oltage called as Oate turn 4** switch

(OT4).

The second method is anode current interruption. 1hanging anode current !y meansof momentarily series or parallel switching arrangement.

Third method is forced commutation. In this, the current through %1R is reduced

!elow the holding current.

A==9!/at!64 60 SCR

ower control de&ice

Relay control

Regulated power supplies %tatic switches

Motor control

5attery charges

Ueater controls

hase controls

*or speed control of 61 shunt motor

A:?ata1e4 60 SCR

%1R controls large current in the load !y means of a small gate current.

%1R si$e is &ery compact. %witching speed is high.

U!Ju/t!6 T.a4!4t6. (UJT)

niWunction transistor is a three terminal semiconductor de&ice consisting of onlyone ? Dunction.

It differs from ordinary ? diode in the sense that it has three terminals namely

Emitter, 5ase- and 5ase .

The !eha&ior of WT differs from other transistors lie 5WT and *ET in the sense

that it has no a!ility to amplify.

Uowe&er, it has a!ility to control large ac power with a small signal.

It also e"hi!its a negati&e resistance characteristic which allows it to !e used as anoscillator.

A==9!/at!64 60 UJT

?on sinusoidal oscillator

Timing circuits

%aw tooth generators


28/34

Triggering de&ice for %1R and TRI;1

%witching circuits

Voltage regulated supply

*!a/ (*!6:e AC 45!t/h)

; 6I;1 is two terminal semiconductor de&ice and three layer !idirectional de&ice,which can !e switched form of itAs 4** to 4? state for either negati&e or positi&e

polarity of applied &oltage.

The two leads are connected to pCregion of silicon separated !y an nCregion. It

consists of two 8Clayer diodes connected in parallel in opposite direction.

The diodes are -?-?and ?--?7.

It has two main terminals namely Main terminal - and Main terminal .

A==9!/at!64 60 *IAC

Temperature control

Triggering of TRI;1

0ight dimming circuits

Motor speed control

T.!a/ (T.!6:e AC 45!t/h)

TRI;1 is a three terminal semiconductor switching de&ice which can conduct ineither forward or re&erse direction.

The TRI;1 is the com!ination of two %1RAs connected in parallel !ut in opposite

direction.

The anode of one %1R is connected to the cathode of another %1R.

The gates are connected together.

It consists of two four layer switches in parallel and the switches are -?-?and?--?8.

The TRI;1 has two main terminals namely main terminal- and main terminal and

one Oate terminal.

A==9!/at!64 60 TRIAC

Ueater control

hase control

0ight dimming control

%tatic switch to turn a.c. power 4? and 4**.

%peed control of motor.

L!1ht A/t!?ate: SCR (LASCR)

0;%1R is similar to that of a %1R e"cept the light triggering.

It has a window and lens which focuses light on the gate Dunction area.

It can !e triggered 4? !y a light input on the gate area, !ut does not turn 4**,

when light source is remo&ed.

The 0;%1R acts lie a latch.


29/34

To reduce the holding current, it can !e turned 4**.

6epending on its si$e a 0;%1R is capa!le of handling larger amount of current.

It can !e handled !y a photo transistor or a photo diode.

A==9!/at!64 60 LASCR 4ptical light controls

hase control

In relays

Motor control

LASER *IO*E

The term 0aser comes from the acronym for light amplification for

stimulated emission of radiation.

The 0aser medium can !e a gas, li#uid, amorphous solid orsemiconductor.

Two commonly used 0aser structure

? homoDunction laser

6ou!le hetrostructure laser

La4e. A/t!6

The light tra&eling through a semiconductor, then a single photon is a!le togenerate an identical second photon.

This photon multiplication is the ey physical mechanism of lasing.

The carrier in&ersion is the first re#uirement of lasing.

It is achie&ed at the ? Dunction !y pro&iding the conduction !andwidth electrons

from the ?Cdoped side and the Valence !and with the holes from the Cdoped side.

The photon energy is gi&en !y the !and gap, which depends on the semiconductormaterial. The optical feed!ac and the confinement of photon in an optical

resonator are the second !asic re#uirement of lasing.

Ph6t6:!6:e

It is a light sensiti&ity de&ice used to con&ert light signal into electrical signal.

It is also called hoto detector.

The light energy fall on the Dunction through lens, when, the ? photodiodeDunction is re&erse !ias.

The holeCelectrons pairs are created.

The mo&ement of the holeCelectron pairs in a properly connected circuit results in

current flows.

The current is proportional to the intensity of light and the fre#uency of the light

falling on the Dunction of the photo diode.

It is used in demodulator, encodes and light detectors systems.

Ph6t6t.a4!4t6.

The photo transistor is a light detector.


30/34

It com!ines a photodiode and phototransistor.

The phototransistor cannot !e directly used in control applications. 5ecause, itproduces a &ery low current.

5efore applying to control circuit the current should !e amplified.

; lens focuses the energy on the !aseCcollector Dunction.

It has three terminal, !ut only two leads are generally used (emitter and collector). The !ase current is supplied !y the current created !y the light falling on the 5aseC

collector photodiode Dunction.

In phototransistors, the current is dependent mainly on the intensity of light

entering into the lens and the &oltage applied to the e"ternal circuit.

Ph6t6/6:u/t!?e 4e46.4

hotoconducti&e sensor is also called as 0ight 6epending Resistor (06R).

It is made of thin layer of semiconductor material (cadmium sulfide).

There is no light falls on the sensor the resistance is &ery high and the current islow.

Uence, the &oltage drop across R is high. It is used in control circuits to control the

current.

Ph6t6?69ta!/ 4e46.4

It is a lightCsensiti&e semiconductor de&ice, and it produces a &oltage, when the&oltage increases and the intensity of light falling on the semiconductor Dunction of

this photo&oltaic cell increases.

It consists of a piece of semiconductor material (silicon or germanium).

The photo&oltaic cells are produced more power, as in solar cells. These are called

photo&oltaic de&ices.

It is used in light meters.

LIGHT EMITTING *IO*E (LE*)

;n 0E6 is a semiconductor pCn Dunction diode which con&erts electrical energy to

light energy under forward !iasing.

It emits light in !oth &isi!le and IR region.

The amount of light output is directly proportional to the forward current.

0E6 structure can !e di&ided into two categories.

%urface C emitting 0E6

Edge C emitting 0E6

%urface emitting 0E6As emit light perpendicular to the ? Dunction plane.

EdgeCemitting 0E6 emits light parallel to the ? in the plane.

P.!/!=9e a: @6.k!1

InDection luminescence is the principle used in 0E6As.

/hen 0E6 is forward !iased, the maDority charge carriers mo&es from p to n and

similarly from n to p region and !ecomes e"cess minority carriers.


31/34

These e"cess minority carriers diffuse through the Dunction and recom!ines with the

maDority carriers in n and p region respecti&ely to produce light.

The light thus produced is emitted from the pCn Dunction of the diode.

A:?ata1e4 60 LE*

They are smaller in si$e. Its cost is &ery low.

It has long life time.

It operates 0E6As are a&aila!le in different colours at low cost.

e&en at &ery low &oltage.

Response time of 0E6 is &ery fast in the order of -> [seconds.

Its intensity can !e controlled easily.

It can !e operated at a wide range of temperature (>C>\) 1.

A==9!/at!64 60 LE*

sed for numeric display in pocet calculators.

sed for applying input power to lasers.

sed for entering information into optical computer memories

sed for solid &ideo displays.

sed in image sensing circuits.

L!Bu!: C.>4ta9 *!4=9a> (LC*)

0i#uid crystal display is not a semiconductor de&ice as 0E6.

016As display the light, it doesnAt radiate light energy.

Therefore, 016As re#uire an e"ternal (or) internal source of light so that it can

either transmit (or) reflect the incident light.

016 is a passi&e type display de&ice used to display alpha numeric character and isse&en segment display, watches calculators etc., in which the digits are displayed

!y the transmission (or) deflection of the incident light, with &ery low power

consumption.

Molecules in ordinary li#uids ha&e random orientation !ut in a li#uid crystal theyare oriented in a definite crystal pattern.

Types of 016As

o 6ynamic %cattering 6isplays.

o Twisted nematic display (or) *ield effect display

A:?ata1e4 60 LC*

0ow power is re#uired

Oood contrast

0ow cost

*!4a:?ata1e4 60 LC*

%peed of operation is slow

016 occupy a large area


32/34

016 life span is #uite small, when used on d.c. Therefore, they are used with a.c.

suppliers.

A==9!/at!64 60 LC*

sed as numerical counters for counting production items.

;nalog #uantities can also !e displayed as a num!er on a suita!le de&ice. (e.g.)6igital multimeter.

sed for solid state &ideo displays.

sed for image sensing circuits.

sed for numerical display in pocet calculators.


33/34

RAJALAKSHMI INSTITUTE OF THCHNOLOGY

Kuttambakkam (PO), Chea!"#$% &$'

EC%&& ELECTRIC CIRCUITS AN* ELECTRON *E+ICES

SEMII -.a/h CSE Sta00"!"Cha.1e KKIRU-A RANI

ASSIGNMENT 2UESTIONS

UNIT D I

-. 6efine the following terms' i) Mesh ii) 0oop iii) ?ode i&) 5ranch

. %tate and e"plain 2irchhoffAs laws7. E"plain &oltage di&ision B current di&ision method using suita!le e"ample.

8. 6eri&e the relationship to e"press three delta connected resistances into star.

9. Two resistances -9Z and >Z are connected in parallel. ; resistance of -Z isconnected in series with the com!ination. ; &oltage of -> V is applied across the

entire circuit. *ind the current in each resistance, &oltage across -Z resistance and

power consumed in all the resistances.

> watts

when the applied &oltage is >>V. 1alculate the &alue of R.

. E"plain the loop analysis of analy$ing a gi&en networ, with a suita!le e"ample.@. %tate and e"plain %uperposition theorem.

[. %tate and e"plain The&eninAs theorem.

->. ; !ridge networ formed !y four arms is as ;5=Z, 51=7Z, 16=8Z, 6;=9Z. ;< Z resistance is connected !etween 5 and 6. ; !attery source of [V is connected

with internal resistance of - Z !etween ; and 1 such that ; is G&e and 1 is &e.

1alculate current through &olts

(Rg=>), R-=R= 9Z, 0-=0= 7 ^U, M =>^ U, secondary side capacitance 1 =

>.9^ *. 6etermine the resonant fre#uency and the output &oltage at this fre#uency.9. 6eri&e the e"pression of ma"imum &alue of E>and I>.

UNIT D III

-. E"plain the ? Dunction diode.. E"plain the diode current e#uation.

7. 6eri&e the e"pression for transition capacitance and diffusing capacitance.

8. E"plain different methods of !readown in ? Dunction diodes.9. 6escri!e the operation of ener diode and e"plain its characteristics.


34/34

UNIT D I+

-. 6escri!e 1ommon Emitter configuration and its characteristics.

. E"plain the !readown in transistor.7. 6escri!e the transistor switching times.

8. E"plain the 1haracteristics of W*ET with the help of neat setches.

9. /ith the help of suita!le diagrams e"plain the woring of different types ofM4%*ET.

UNIT D+

-. E"plain the operation of I? diode.

. E"plain the following terms' i) hotoconducti&e sensor ii) hoto emissi&e sensor

7. 6escri!e the operation of 0E6 and 016.8. E"plain the operation of TRI;1 and 6I;1.

9. 6raw the e#ui&alent circuit of WT and e"plain its operation.

Documents

Eced Notes