Power Electronics and Digital Electronis

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Cumulative Test Series Anubhav Classes

Subject: Power Electronics and Digital Electronics

Branch: EEDuration: 2 hours 30 minutesOne mark questions: 20Two marks questions: 40Total no of Questions: 60Total no of Pages: 14Date of test: 26/01/14

Each Question Carries One Mark

Q.1 How many two input NAND gates are required to implement= + + .If , , , , , , , are readily available. . 7 B. 8 C. 9 D. 6

Q.2 What is the standard POS expression for the given simplified Boolean expression

= + + + A. = 1,4,5,6,7,8,9,14,15,22,23,24,25,28,29,30,31 B. = 1,3,5,6,7,8,9,12,15,22,23,24,25,28,29,30,31 C.

= 1,3,5,6,7,8,9,12,15,22,23,24,25,28,29,30,31

D. = 1,3,5,8,9,12,15,22,23,24,25,28,29,30,31 Q.3 Designing of 4-bit binary 4 3 2 1 BCD (ABCDE), the expression for C & D is

A. = 4 3 + 3 2 , = 4 3 2 + 4 2 B. = 4 3 + 3 2 , = 4 3 2 + 4 2 C. = 4 3 + 3 2 , = 4 3 2 + 4 2 D. = 4 3 + 3 2 , = 4 3 2 + 4 2

Q.4 8 4 2 1 is an 8421 BCD input to a logic circuit

8 = 0,

4 = 1(or) when

8 = 0

4 = 1. Design the simplest logic circuit.

Q.5 In a 2-bit magnitude comparator circuit ( = 1 0 , = 1 0 ), the expression for > & < isA. > = 1 1 + 11 0 0 < = 1 1 + 11 0 0


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B. > = 1 1 + 11 0 0 < = 1 1 + 11 0 0 C. > = 1 1 + 11 0 0 < = 1 1 + 11 0 0 D. > = 1 1 + 11 0 0 < = 1 1 + 11 0 0

Q.6 What is the MOD value of given counter.

A. Mod 7 B. Mod 5 C. Mod 4 D. Mod 6Q.7 The logic expression realized by the given MOS circuit is

A. + B. + C. + D. +

Q.8 The following program is run on 8085 microprocessor:8000 LXI SP, 1000H

8003 PUSH H

8004 PUSH D

8005 CALL 2050 H

8008 POP H

8009 HLTAt the end of expression of this program, the program counter of 8085contains _______ andSP containsA. PC = 8009 SP = 1000 C. PC = 800B SP = 0FFEB. PC = 800A SP = 1002 D. PC = 800A SP = 0FFE

Q.9 What is the data at 2131 H after the expression of program.LXI H, 2130 H

MVI M, 1BHMOV A, M


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[Analog Electronics & General Aptitude ] ANUBHAV CLASSES


STCCMCRALINX HMOV M, AHLT

A. 26 H B. 46 H C. 36 H D. 56 H

Q.10 What is the operation of the following program? Assume starting address of 10 numberlist is 2200 H.LXI H, 2200 HLXI D, 2300 HMVI C, 0AHBACK: MOV A, MANI 01HJNZ SKIPMOV A, MSTAX DINX DSKIP: INX HDCR CJNZ BACKHLTA. To separate even numbers C. To separate numbers divided by 3B. To separate prime numbers D. To separate numbers divided by 5

Q.11 Consider the following statements in respect of important features of IGBT:

1. It has a high impedance gate as that of a MOSFET.2. It has a low ON state voltage as that of a BJT.3. It can block negative voltages as in the case of GTO.Which of these statements are correct?(A) 1 and 2 (B) 1 and 3 (C) 2 and 3 (D) 1, 2 and 3

Q.12 Consider the following statements:Phase controlled converters1. Do not provide smooth variation of output voltage.2. Inject harmonics into the power system.3. Draw non unity power factor (pf) current for finite triggering angles.Which of these statements are correct?(A) 1,2 and 3 (B) 1 and 2 (C) 2 and 3 (D) 1 and 3

Q.13 Match List I (Converter) with List II (Application).List I List IIA. Fully controlled converter 1. Improved time power factorB. Half controlled converter 2. Soft starter for a c motorC. 3-phase ac voltage controller 3. Speed reversalD. Cyclo converter 4. Smooth low speed reversible high power ac device

5. Synchronous motor control

Codes: A B C D


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(A) 3 1 2 4(B) 2 4 5 1(C) 3 4 2 1(D) 2 1 5 4

Q.14 Consider a dc to dc converter Chopper havinvoltage of 232V. If the voltage drop across the converter during ON time is 2 V and thefrequency of operation is 1 KHz at a duty cycle of 0.4 then the average output voltage ofthe converter will be(A) 94.0V (B) 92.8V (C) 92.0V (D) 90.8V

Q.15 In the circuit shown in fig, the switch is operated at a duty cycle of 0.5A large capacitor isconnected across the load. The inductor current is assumed to be continuous. Theaverage voltage across the load and the average current through the diode willrespectively be

(A) 10V, 2A (B) 10V, 8A (C) 40V, 2A (D) 40V, 8A

Q.16 Which one of the following is the most suitable electric device for large power, low speed,reversible drives?(A) Cyclo converter fed 3 phase ac motor drive.(B) CSI fed self controller load commutated synchronous motor drive.(C) Square wave voltage source inverter fed 3 phase ac drive(D) 3 phase induction motor drive fed from a 3 phase ac voltage controller.

Q.17 In a single phase bridge inverter, the maximum value of fundamental component of loadcurrent is I. For a load w hich is highly capacitive in nature, tharmonic component of load current would be(A) (B) (C) 2 (D) I

Q.18 In a single phase voltage controller feeling RL load, when1. Firing angle

(load phase angle), load voltage 0 is sinusoidal.

2. >

, 0 is non sinusoidal3.


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(D) Both pole voltage and live voltage will be free from 3 rd harmonic components.

Q.20 Fig (a) shows an inverter circuit with a dc source voltage . The semiconductor switchesof the inverter are operated in such a manner that the pole voltage 10 20 are asshow in fig (b). What is the rms value of the pole voltage 12 ?

(A) 2 (B) (C) 2 (D)

Each Question Carries Two Marks Q.21 The given sequential circuit is a logic diagram of pulse train generator of 8 bits long. What

is the output of 1 & 2 .

A. 1 = 10011000, 2 = 11101100 C. 1 = 10011000, 2 = 11111100B. 1 = 11011000, 2 = 11111100 D. 1 = 11011000, 2 = 11101100

Q.22 Design a J-K counter that goes through states 3, 4, 6, 7.


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Q.23 How many different output status the following circuit is having?

A. 5 states B. 7 states C. 6 states D. 8 states

Q.24 A lawn-sprinkling system is controlled automatically by certain combinations of thefollowing variables.

Season (S = 1, if summer; 0, otherwise)Moisture content of soil (M=1, if high; 0, if low)Outside temperature (T=1, if high; 0, if low)Outside humidity (H=1, if high; 0, if low)The sprinkler is turned on under any of the following circumstances.1. The moisture content is low in winter.2. The temperature is high and the moisture content is low in summer.3. The temperature is high and the humidity is high in summer.4. The temperature is low and the moisture content is low in summer.5. The temperature is high and the humidity is low.Use a k-map to find the simplest logic expression involving variables S, M, T and H forturning on the sprinkler system.A. = + + C. = + + B. = + + D. = + +

Q.25 How many 1-bit comparators, 2-input AND gates, 2-input OR gates required to design a 2-bit comparator.A. 2,3,2 B. 2,2,3 C. 2,3,3 D. 2,2,2

Q.26 What are the inputs are required for an 8 1 MUX to implement

, , , =

+ +

A. 0 = , 1 = , 2 = , 0 = 0, 1 = , 2 = , 3 = , 4 = 1, 5 = 0, 6 = , 7 =


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MOV B, AMOV A, MSIU 05ANA BMOV E, AMOV A, M

ADD AORA EINX HMOV M, AA. Output =[{( X+5) AND (X 5)} OR (X * 2)]B. Output =[{( X+5) OR (X 5)} AND (X * 2)]C. Output =[{( X 5) AND (X + 5)} AND (X * 2)]D. Output =[{( X+5) OR (X 5)} OR (X * 2)]

Q.32 The contents of memory locations of an 8085 microprocessor based system are shownbelow. The contents of HL pair after execution of the following program will be

LXI H, 3000H

MOV E, M

INX H

3000 023001 303002 003003 30

MOV D, M

LDAX D

MOV L, A

INX D

LDAX D

MOV H, A

HLT

A. 0230 B. 3002 C. 3000 D. 0203

Common Data for Questions 23 24:

Consider the following memory interface diagram with an 8085 microprocessor.

Q.33 The capacity of memory ROM shown in the block diagram isA. 1 8 B. 2 8 C. 4 8


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D. The memory IC consists of 4096 locations but width of memory location cannot bespecified.

Q.34 What is the range of addresses 8085 can use to communicate with memory IC?A. 0000H to 07FFHB. 0800 to 0FFFH

C. 0000H to 0FFFH (or) 1000H to 1FFFHD. 0000H to 0FFFH (or) 2000H to 2FFFH

Common Data for Questions 25 26:

A ROM is required to implement the following Boolean expressions1 , , = 0,1,4,5,6

2 = , , = + Q.35 Determine the size of the ROM required.

A. 32 2 B. 2 3 2 C. 2 2 3 D. 3 3 2

Q.36 What is the data present at the memory location address of 110?A. 00 B. 01 C. 10 D. 11

Statement for Linked Answer Questions 27 28:

Consider the following program and some money contents

LXI SP, 2700 H

LXI H, 0002 HDAD SPMOV A, MADD APUSH PSWPUSH HPOP PSWPOP H

Address Data

26FE 00

26FF 01

2700 02

2701 03

2702 04

Q.37 After the execution of above program, what is the content of A, and status of Sign flag,Zero flag.A. = 02, = 0, = 0 C. = 08, = 0, = 0B. = 27, = 1, = 0 D. = 27, = 0, = 0

Q.38 At the end of the above program, if we add the following instructions.INX SPPUSH PSWWhat is the content of SP after the execution of the above instructions? In which memorylocation accumulator register content will be stored.A. = 2701 ; 2700 C. = 2700 ; 2701 B. = 26 ; 2700 D. = 26 ; 2702


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An analog voltage signal whose highest frequency is 1 KHz is to be digitally closed with aresolution of 0.01 percent covering the voltage 0 10 .

Q.39 Determine the minimum number of bit in the digital code.

A. 12 B. 14 C. 16 D. 15

Q.40 What is the aperture time required for the A/D converter?A. 9.71 nsec B. 10.2 nsec C. 5.21 nsec D. 15.21 nsec

Q.41 Ten thyristors are used in a string to with stand a dc voltage of = 15 . The maximumleakage current and recovery charge differences of thyristor are 10mA and 150 C,

respectively. Each thyristor has a voltage sharingof 1 = 0.5 . Calculate the maximum steady state voltage sharing ( ) .(A) 2000 V (B) 1604V (C) 1500V (D) 2004V

Q.42 Latching current for an SCR, inserted in between a dc voltage source of 200V and the load,is 100mA. Compute the maximum width of gate pulse current required to turn on thisSCR incase the load consists of = 20 in series with = 0.2 .(A) 100.503 (B) 111.624 (D) 120.512 (D) 90.10

Q.43 For a thyristor, maximum junction temperature is 125 . The thermal resistance for thethyristor sink combination are = 0.16 = 0.08 /W. for a heat sinktemperature of 70 , compute the load voltage total average power loss in the thyristorsink combination. In case the heat sink temperature is brough down to 60 by forcedcooling, find the percentage increase in the device rating.

(A) 8.00% (B) 9.71% (C) 9.00% (D) 8.71%

Q.44 The tri ac circuit shown in fig. controls the ac output power to the resistive load. The peakpower dissipation in the load is

(A) 3968W (B) 5290W (C)7935W (D) 10100W

Q.45 A 230V, 50Hz one pulse SCR converter is triggered at a firing angle of 40 and the loadcurrent extinguishes at an angle of 210. Find the circuit turn off time & average loadvoltage for = 5

, = 2 = 110 .

(A) = 9.432 0 = 142.532 (C) = 8.126 0 = 112.532 (B) = 9.11 0 = 141.16 (D) = 9.432 0 = 231.63


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Q.46 A three phase semi converter feeds power to a delay of 30, the load takes 5KW. In case load current is made ripple free by connectingan inductor in series with the load. Find the magnitude of per phase input supply voltage.(A) 100V (B) 102.45V (C) 104.16V (D) 111.6V

Q.47 The single phase dual converter is operated from a 120V, 60Hz. Supply and the loadresistance is R = 10. The circulating inducta = 40 , delay angles are1 = 60 2 = 120. Calculate the peak circulating current.

(A) 10.24A (B) 11.25A (C) 16.41A (D) 9.36A

Q.48 An impulse commutated chopper feeds inductive load requiring a constant current of260A. the source voltage is 220V dc and the chopping frequency is 400 Hz. Turn off timefor main thyristor is 18s. peak current through main thyristor is limited to 1.8 times theconstant load current. Taking a factor of safety 2 for the main thyristor, calculate thevalue of commutating components C and L.(A) = 41.545 , = 46.596 (C) = 42.545 , = 47.596 (B) = 34.214 , = 44.72 (D) = 36.712 , = 37.16

Q.49 A single phase half wave ac voltage controller feeds a load of = 20 with an inputvoltage of 230V, 50Hz. Firing angle of thyristor is 45. Determine average input current.(A) = 0.7585 (B) + 0.5424 (C) = 0.5624 (D) = 0.7585

Q.50 A single phase half wave ac voltage controller feeds a load of = 20 with an inputvoltage of 230V, 50Hz. Firing angle of thyristor is 45. Calculate power delivered to loadand input pf.(A) 2524.1W;0.97(lag) (C) 2612W; 0.91(lag)

(B) 2124.12W; 0.92(lag) (D) 2131.4W; 0.94(lag)

Q.51 The single phase full wave controller in figure, supplies an RL load. The input rms voltageis = 120 , 60 . The delay angles of thyristors are equal: 1 = 2 = /2. Determinethe rms output voltage 0 .

(A) 0 = 69.12 (B) 0 = 61.16 (C) 0 = 61.24 (D) 0 = 68.09

Q.52 In the single phase voltage controller circuit shown in fig. for what range of triggeringangle( ) the output voltage ( 0 ) is not controllable.


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(A) 0 < < 135 (B) 45 < < 135 (C) 90 < < 180 (D) 135 < < 180

Q.53 Circuit shown in figure is fed from dc source such that fundamental component of outputvoltage is 230 V. Find the rms value of thyristor current for the load = 2 , =8, = 6

(A) 54.818A (B) 61.243A (C) 51.216A (D) 70.324A

Q.54 A single phase bridge inverter delivers power to a series connected RLC with= 2 = 10 . The periodic time T = 0.1 msec. Whave in order to obtain load commutation for th

10sec. Take circuit turnoff time as 1.5 . Assume that load current contains onlyfundamental component.(A) = 1.002 (B) = 0.998 (D) = 2.012 (D) = 1.248

Q.55 A dc series motor is fed from 600v dc source through a chopper. The dc motor has thefollowing parameters:

= 0.04 , = 0.06 , = 4 1 0 3 / 2 The average armature current of 300A is ripple free. For a chopper duty cycle of 60%determine motor speed .(A) 2104.4rpm (B) 2912 rpm (C) 2626.1 rpm (D) 2416 rpm

Common Data Question 26, 27 and 28:

For a current commutated chopper, peak commutating current is twice the maximumpossible load current. The source voltage is 230V dc and main SCR turn off is 30 . Fora maximum load current of 200A.

Q.56 The calculate values of the commutating L and C?(A) = 15.147 ; = 51.6 (C) = 16.473 ; = 49.822 (B) = 16.01 ; = 40.822 (D) = 17.73 ; = 40.921

Q.57 Maximum capacitor voltage (or) peak capacitor voltage ( ) is(A) 316V (B) 312V (C) 335V (D) 345V


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Q.58 Peak commutating current ( ) is(A) 350A (B) 400A (C) 450A (D) 200A


A 230V, 1500rpm, 220A separately excited dc motor is fed from 3-phase full converter.Motor armature resistance is 0.6 . Full converter is converted to 400V, 50Hz sourcethrough a delta star transformer. Motor terminal voltage is rated when converter firingangle is zero.

Q.59 Calculate the transformer phase turns ratio from primary to secondary.(A) 4.999 (B) 4.067 (C) 3.645 (D) 4.000

Q.60 Calculate the firing angle delay of the converter when the motor is running at 1000 rpmat rated torque.(A) 44.01 (B) 40.12 (C) 46.84 (D) 42.03

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