F.Y. Diploma : Sem. II [CO/IF/CM/CW] Basic Electronics

Transcription

1 F.Y. Diploma : Sem. [CO/F/CM/CW] asic lecronics Time: 3 Hrs.] Prelim Quesion Paper Soluion [Marks : 70 Q.1 Aemp any FV of he following : [10] Q.1(a) Classify elecronic componens. [2] Ans. Classificaion of elecronic componens lecronic componens Passive componens Acive componens Resisors Capaciors nducors lecron ubes Semiconducor devices Penode Vacuum ub ec. Diode JT JFT ec Q.1(b) Draw he characerisics of PN juncion diode. [2] Characerisics of PN juncion diode. [2 mark] D (ma) Forward characerisic V R (reakdown Volage) S V D (v) V K (arrier poenial volage) Reverse characerisics S is reverse sauraion curren Q.1(c) Draw symbol of npn and pnp ransisor. [2] Symbol of npn ransisor Symbol of pnp ransisor C 1 mark C 1 mark Q.1(d) Lis ypes of MOSFT. [2] Type of MOSFT MOSFTS are of wo ypes (i) Depleion ype MOSFT (ii) nhancemen ype MOSFT ach ype is furher classified ino nchannel and pchannel MOSFT. Q.1(e) Define ransducer. [2] Transducer : An elecronic device ha convers one form of energy ino anoher form is known as ransducer. g.: Microphone; i convers sound energy ino elecrical signal

2 Vidyalankar : F.Y. Diploma Q.1(f) Give example of bipolar and unipolar devices. [2] ipolar Devices : npn and pnp ransisors. Unipolar Devices : JFT and MOSFT Q.1(g) Sae funcion of ransformer in regulaed power supply. [2] Funcion of ransformer in regulaed power supply : [1 mark each] (i) Transformer is used o sepdown he a.c. supply voage. (ii) Transformer is used o provide isolaion beween recifier and a.c. mains. Hence i prevens elecrical shocks. Q.2 Aemp any THR of he following : [12] Q.2(a) Deermine he colour bands for following resisance value. [4] (i) 47 k 5% (ii) % (i) Given resisance value : 47k 5% = % Yellow Voile Orange Gold Hence bands are Yellow Voile Orange Gold (1 s and) (2 nd and) (3 rd and) (4 h and) [2 mark] (ii) Given resisance value : % = % rown lack rown Silver Hence bands are rown lack rown Silver (1 s and) (2 nd and) (3 rd and) (4 h and) [2 mark] Q.2(b) Skech he labelled forward and reverse characerisics of zener diode. [4] [ Symbols 1 mark, Diagram 1 mark and characerisics 2 marks] A zener diode is also called a volage reference, volage regulaor or breakdown diode. Symbols D (ma) Forward bias A K region Anode Cahode V R V Z V F (V) V k (Knee volage) Reverse bias region R differs from recifier diode, in he sense, ha i is operaed in he reverse break down region. The breakdown volage of a zener diode is se by carefully he doping level during manufacure. The zener breakdown occurs when he elecric field across he juncion produced due o reverse volage, is sufficienly high. This elecric field exers a force on he elecron in he ouer mos shell. This force is so high ha he elecrons are pulled away from heir paren nuclei and become free carriers. This lionizaion, which occur due o he elecrosaic forces of aracion, is known as zener effec. The zener diodes, wih breakdown volages of less han 6V, operae predominanly in zener breakdown. Zener diodes are used in volage regulaors

3 Prelim Quesion Paper Soluion Q.2(c) xplain he working principle of LD wih skech. [4] [xplanaion - 2 marks and Diagram 1 mark, Symbol - 1 mark] Working of LD : A PN juncion diode, which emis ligh when forward biased is known as ligh emiing diode (LD). The emied ligh may be visible or invisible. The amoun of ligh oupu is direcly proporional o he forward curren. Thus, higher he forward curren, higher is he Anode ligh oupu. A (Anode) K (Cahode) Symbol asic srucure Cahode An Nype layer is grown on a Pype subsrae by a diffusion process. Then a hin pype layer is grown on he Nype layer. The meal connecors o boh he layers make anode and cahode erminals as indicaed. The ligh energy is released a he juncion, when he recombinaion of elecron wih holes ake place. The semiconducor maerial used for manufacuring ligh emiing diodes are gallium arsenide, gallium arsenide phosphide. The silicon and germanium is no used for manufacuring lighs emiing diodes because hese are hea producing maerials. Q.2(d) Sae 3 configuraion of JT. Define curren gain for each configuraion. [4] [Name of configuraion 1 mark each and Definiion of curren gain 1 mark each] 3 configuraion of JT. (i) C configuraion C C O/P /P The inpu is applied beween base and emier & O/P is aken across collecor and emier hence i s known as C (common emier) configuraion. C Curren gain, = (ii) C Configuraion : C C /P O/P The inpu is applied beween mier and base & oupu is aken across collecor and base. Hence i is known as C (common ase) configuraion. C Curren gain, = (iii) CC Configuraion : + /P C O/P

4 Vidyalankar : F.Y. Diploma The inpu is applied beween base and collecor & oupu is aken across emuer and collecor hence i s known as CC (common collecor) configuraion. Curren gain, = Q.3 Aemp any THR of he following : [12] Q.3(a) Draw he ransfer characerisics of JFT and explain. (consider nchannel JFT) [4] [xplanaion 2 marks and Diagram 2 marks] The relaionship beween, oupu curren i.e. drain curren ( D ) and inpu volage i.e. V GS is given by equaion 2 V GS D = VP f we plo above equaion as V GS on xaxis and D on yaxis, resulan graph is known as ransfer characerisics. To plo ransfer characerisics D (ma) V GS O 0.3 V P 0.5 V P V P (0, ) D O 2 4 V GS, D (0, ) 0.3V, P 0.5V, 2 P 4 (V P, O) 0.3V, P 2 0.5V, P 4 V GS(v) Transconducance curves, which gives he relaionship beween drain curren ( D ) and gaeosource volage (V GS ) for a consan value of drain o source volage (V DS ). The curve is par of a parabola and herefore expressed by he equaion 2 V GS D = 1 V P The slope of ransconducance curve gives value o ransconducance VGS i.e. g m = When V DS = 0 D (V P, 0) 0.5 V P 0.3 V P Q.3(b) xplain working of piezoelecric ransducer. [4] [xplanaion 2 marks and Diagram 2 marks] Piezoelecric Transducer : A symmerical crysalline maerials such as Quarz, Rochelle sal and arium ianae produce an emf when hey are placed under sress. This propery is used in Piezoelecric ransducers, where a crysal is placed beween a solid base and he forcesumming member, as shown below : Force-semming Oupu Crysal (arium Tianae ase Rochalk Sal Quarz) Piezo-elecric ransducer - 4 -

5 Prelim Quesion Paper Soluion An exernally applied force, enering he ransducer hrough is pressure por, applies pressure o he op of a crysal. This produces an emf across he crysal proporional o he magniude of applied pressure. Since he ransducer has a very good High frequency response, is principal used is in HF acceleromeers. Main advanage of piezoelecric ransducer is i s sabiliy a high frequency. The principal disadvanage is ha volage will be generaed as long as he pressure applied o he Piezoelecric elemen changes. Q.3(c) xplain how inducor and capacior can be used in filer circui. [4] Use of inducor and capacior in filer circui : (i) nducor Filer : is also called choke filer. When recified oupu, passes hrough an inducor, i offers a high resisance o he a.c. componens and no resisance o d.c. componens. Therefore a.c. componens of he recified oupu is block and only d.c. componen reaches a he load. (ii) Capaciive Filer : Capacior filers are suiable for high loads (a load wih large value for resisance) The operaion of a capacior filer depends upon he propery of a capacior o oppose any change in volage, when i is conneced across a pulsaing d.c. volage. The acion of a capacior filer is o smoohed ou (or filer ou) he volage ripple or pulsaions. Q.3(d) Wih a circui diagram, explain how ransisor works as an amplifier. [4] V CC [xplanaion 2 marks and Diagram 2 marks] Amplifier : R 1 R C C ou V O Vin C in R 2 R C C Amplifier Resisors R 1, R 2 and R are used o biasing he ransisor in he acive region. R C is he collecor resisor used for conrolling he collecor curren. When ransisor is used as an amplifier, a ime varying sinusoidal small signal is applied o he base. Thus volage a he base is he d.c. volage superimposed by a sinusoidal - 5 -

6 Vidyalankar : F.Y. Diploma volage. Thus, he base volage also varies wih respec o ime collecor curren also varies wih he base curren. Thus, he oupu volage V C also varies wih ime, D.C. biasing of he ransisor ensures ha he ransisor is on, no only in posiive half cycle, bu also in negaive half cycle of he inpu volage. The collecor o emier volage V C, is he oupu volage, which is 180ou of phase wih C &. n amplificaion process, he frequency of signal remains unchanged. Q.4 Aemp any THR of he following : [12] Q.4(a) xplain various selecion crieria for ransducers. [4] Selecion crieria for ransducers : [1 mark for each crieria] The following poins should be considered while selecing a ransducer. 1. Operaing range : Chosen o mainain range requiremens and good resoluion. 2. Sensiiviy : Chosen o allow sufficien oupu. 3. Frequency response and resonan frequency : fla over he enire desired range. 4. nvironmenal compaibiliy : Temperaure range, corrosive fluids, pressure, shocks ec. 5. Accuracy : Repeaabiliy and calibraion errors as well as errors expeced due o sensiiviy o oher simuli. Q.4(b) Draw he circui diagram for full wave bridge recifier and also draw oupu waveform for a sinusoidal inpu. Full wave bridge recifier [4] A.C. supply V 1 V 2 D 4 D 2 R L V O + D 1 D 3 Circui diagram V in O 2 3 V O D 1 & D 2 D 3 & D 4 D 1 & D 2 conducs conducs conducs O 2 3 npuoupu waveforms for fullwave recifier Q.4(c) Define ransconducance for JFT and ransconducance if drain resisance [4] (r d ) = 50k and amplificaion facor () = 1.5. Transconducance for JFT Transconducance is defined as raio of change in drain curren wih respec o change in gae o source volage. D i.e. g m = a V DS consan [ 1 mark] Vgs = g m r d 1.5 = g m 50 k 1.5 g m = 50k g m = g m =

7 Prelim Quesion Paper Soluion Q.4(d) Why filer are needed in regulaed power supply. Lis various ypes of filers. [4] Need of filer : The oupu of recifier conains d.c. componen as well as an a.c. componen. The presence of an a.c. componen is mos undesirable and herefore mus be removed from he recifier oupu. is achieved by a circui called filer : wih wihou V in V o Recifier Oupu filer filer npu Volage Filer V 0 0 A filer circui may be defined as a ck which removes (or minimizes) he unwaned a.c. componen of he recifier oupu and allows only he d.c. componen o reach he load. Oupu Volage Classificaion of filers (i) nducor filer (ii) Capacior filer (iii) nducorcapacior or LC filer (iv) Filer Q.5 Aemp any TWO of he following : [12] Q.5(a) Draw he sinusoidal, riangular and square level ampliude, ime period and peak [6] value on each wave forms. [1 mark for each waveform and 1 mark for labeling] (i) Sinusoidal Wave : Ampliude Peak Value (V m) (ii) Triangular Wave : Ampliude Time period (T) Peak Value (V m) Time period (T) (iii) Square wave Ampliude (V m) (V m) Time period (T) Q.5(b) n C configuraion if = 150, leakage curren CO = 50 A. f base curren [6] is 0.5 ma Deermine collecor curren C, emier curren and common base, dc curren gain (). C configuraion = 150, CO = 50 A, = 0.5 ma, C =?, =?, =? (i) Common base curren gain, = 1 = =

8 Vidyalankar : F.Y. Diploma (ii) O/P curren, C = + CO = m + 50 A = ma (iii) mier curren, = + C = 0.5 ma ma = ma Q.5(c) Skech he block diagram of a regulaed power supply. Sae he funcion of [6] reach block. Draw he waveforms a he oupu of each block. Regulaed Power Supply [Waveforms 1 mark] V in (i) A ransformer supplies a.c. volage a he required level (mosly seps down he supply volage). also provides isolaion. (ii) The bidirecional a.c volage is convered ino a unidirecional pulsaing d.c. using a recifier. (iii) The unwaned ripple conens of his pulsaing d.c are removed by a filer o ge pure d.c. volage (iv) The o/p he filer is fed o a regulaor which gives a seady d.c. oupu independen of load variaions and inpu supply flucuaion. [3 mark] Q.6 Aemp any TWO of he following : [12] Q.6(a) Draw and explain srucure, working of ype MOSFT. [6] Working : Operaion wih V GS = 0 f V GS = 0 and posiive volage is applied beween is drain and source hen due o he absence of he n-ype channel, a zero drain curren will resul. Operaion wih V GS is posiive The posiive poenial a he gae erminal will repel he holes presen deeper ino he P-sub. The minoriy carriers i.e. he elecron in he p-ype subsrae will be araced owards he gae erminal and gaher near he surface of SiO 2 as shown. The drain curren hen sars flowing hrough his induced channel. The value of V GS a which his conducion begins is called as he hreshold volage and indicaed by V T or V GS (TH). P- sub - 8 -

9 Prelim Quesion Paper Soluion Q.6(b) Draw he oupu characerisics of C mode configuraion of JT. And explain each region in brief. Oupu characerisics in C mode : Sauraion region C (ma) Acive Region = 4 = 3 = 2 = 1 = 0 reakdown region Cu-off region OFF V C (Vols) Oupu characerisics : These are curves of variaion of oupu curren ( c ) agains oupu volage (V C ) a consan inpu curren ( ). Oupu characerisics of C configuraion is divided ino 4 regions : (i) Cu-off region : When boh he juncions are reverse biased, hey assis flow of minoriy charge carriers, ransisor operaes in cu-off region. The minoriy charge carrier consiue curren CO. n his region ransisor acs as OFF swich. (ii) Acive region : n his region, inpu juncion i.e. base-emier juncion is forward biased and oupu juncion is reverse biased. n his region ransisor acs as an amplifier. (iii) Sauraion region : When boh he juncions are forward biased, due o large number of charge carriers are injeced ino base from emier and collecor. Large variaion in curren is observed wih small variaion in applied poenial. This region is non-ohmic and offers leas resisance and in his region device acs as ON swich. (iv) reakdown region : n his region ransisor undergoes permanen damage and occurs due o punch hrough effec. [1 mark for each region] Q.6(c) Wih he help of nea labeled diagram explain working of phooransisor. [6] Phooransisor : Collecor A phoodiode canno produce any amplificaion acion. A phooransisor can provide he inernal curren muliplicaion and can generae a large oupu signal. ase The ligh is allowed o fall on he collecor base juncion of he ransisor. The phoocurren produced here acs mier as he base curren for he ransisor and ges muliplied Symbol of Phooransisor imes. [6] Oupu Characerisics : Oupu characerisics are very much similar o hose of convenional ransisor. C (ma) [3 marks] 50 mw/cm 2 40 mw/cm 2 30 mw/cm 2 20 mw/cm 2 Dark Curren V C (Vols)