# Power Electronics (EE 5th Semester) Unit 3: CHOPPERS

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Power Electronics (EE 5th Semester)

Unit 3: CHOPPERS

1

Choppers converter

a) AC to DC

b) DC to AC

c) DC to DC

d) AC to AC

2

A chopper may be thought as a

a) Inverter with DC input

b) DC equivalent of an AC transformer

c) Diode rectifier

d) DC equivalent of an induction motor

3

Which device can be used in a chopper circuit?

a) BJT

b) MOSFET

c) GTO

d) All of the mentioned

4

A chopper is a

a) Time ratio controller

b) AC to DC converter

c) DC transformer

d) High speed semiconductor switch

5

What is the duty cycle of a chopper?

a) Ton/Toff

b) Ton/T

c) T/Ton

d) Toff x Ton

6

The load voltage of a chopper can be controlled by varying the

a) duty cycle

b) firing angle

c) reactor position

d) extinction angle

7

The values of duty cycle (α) lies between

a) 0<α<1

b) 0>α>-1

c) 0<=α<=1

d) 1<α<100

8

If T is the time period for a chopper circuit and α is its duty cycle, then the

chopping frequency is

a) Ton/α

b) Toff/α

c) α/Toff

d) α/Ton

9

Find the output voltage expression for a step down chopper with Vs as the input

voltage and α as the duty cycle.

a) Vo = Vs/α

b) Vo = Vs x α

c) Vo = Vs2/α

d) Vo = 2Vs/απ

10

The below given figure is that of a _________ (IGBT is used as a chopper switch)

a) step-up/step-down chopper

b) step-down chopper

c) step-up chopper

d) none of the mentioned

11

If a step up chopper’s switch is always kept off then (ideally)

a) Vo = 0

b) Vo = ∞

c) Vo = Vs

d) Vo > Vs

12

If a step up chopper’s switch is always kept open then (ideally)

a) Vo = 0

b) Vo = ∞

c) Vo = Vs

d) Vo > Vs

13

Find the average value of output voltage of a basic step-down chopper, with duty

cycle = α and load = R Ω.

a) I = Vs x α

b) I = (Vs x α)/R

c) I = 0

d) I = Vs/R

14

For a step-up chopper, when the duty cycle is increased the average value of the

output voltage

a) increases

b) decreases

c) remains the same

d) none of the mentioned

15

For a step-down chopper, when the duty cycle is increased the average value of

the output voltage

a) increases

b) decreases

c) remains the same

d) none of the mentioned

16

The below given chopper circuit is that of a

a) step-up chopper

b) step-down chopper

c) step-up/step-down chopper

d) none of the mentioned

17

The expression for a step-up/step-down chopper with α as the duty cycle and Vs

as the dc input voltage is

a) Vs/1 – α

b) α x Vs

c) Vs (α/1-α)

d) Vs (α/1+α)

18

For a step-up/step-down chopper, if α (duty cycle) = 0.5 then

a) Vo = Vs

b) Vo < Vs

c) Vo > Vs

d) none of the mentioned

19

In the figure shown below, the capacitor C is used to

a) maintain the load voltage constant

c) protect the chopper switch (SW)

d) maintain the load current constant

20

For a step-up/step-down chopper, if α (duty cycle) < 0.5 then

a) Vo = Vs

b) Vo < Vs

c) Vo > Vs

d) none of the mentioned

21

In the below shown step-up/step-down chopper circuit, when the chopper switch

(SW) if first on and then off, then the current flows from path

a) Vs-CH-L-Vs

d) no current flows

22

A step-down chopper is also called as a

23

For the type-B chopper shown below

a) during Ton, Vo = 0 and L stores energy

b) during Ton, Vo is not 0 and L stores energy

c) during Ton, Vo = 0 and L releases energy

d) during Ton, Vo is not 0 and L releases energy

24

The below given chopper is that of a

a) step-up chopper b) step-down chopper

c) step-up/step-down chopper

d) depends on the duty cycle

25

The type-C chopper or two quadrant type-A chopper has

a) type-A and type-B choppers in series

b) type-A and type-B choppers in parallel

c) two type-A choppers in series

d) two type-A choppers in parallel

26

In case of TRC (Time Ratio Control), _________ is varied

a) duty cycle

b) firing angle

c) supply frequency

d) supply voltage magnitude

27

Name the below given circuit.

a) Type D chopper

b) Type B chopper

28

In the below given circuit output voltage will be 0 when

a) SW1 is on b) FD is not conducting c) D2 is conducting d) SW2 is on

29

In the below given circuit

a) current can never be zero

b) current can flow in both the directions of the load

c) voltage can never be zero

d) none of the mentioned

30

In the below given type C chopper circuit, _______ and _________ together

operate like type A chopper.

a) CH1, FD

b) CH2, FD

c) CH1, D2

d) CH2, D2

31

In the below given type C chopper circuit, ________ and ___________ together

operate like type B chopper.

a) CH1, FD

b) CH2, FD

c) CH1, D2

d) CH2, D2

32

Which type of chopper is used in the regenerative braking of DC motors?

a) type A

b) type B

c) type C

d) type D

33

Type C chopper consists of

a) two diodes and two switches

b) one diode and one switch

c) one diode and three switches

d) three diodes and two switches

34

In a type C chopper, if only one switch is operated

a) only one quadrant operation will be obtained

b) two quadrant operation can be obtained

c) the chopper won’t work

d) none of the mentioned

35

A type D chopper is a

d) none of the mentioned

36

In a type-D chopper

a) current can flow in both the directions of the load

b) current cannot flow in both the directions of the load

c) voltage can only be positive

d) voltage can only be negative

37

For a type D chopper, the average value of output voltage will be positive when

a) Ton = Toff

b) Ton < Toff

c) Toff = 0

d) Ton > Toff

38

For a type D chopper, if duty cycle = 0.5 then the

a) average voltage is positive

b) average voltage is negative

c) average voltage is zero

d) chopper cannot be operated with duty cycle = 0.5

39

In the below given circuit, if only SW1 is operated then

a) the power flows from load to source

b) the power flows from source to load

c) the average voltage is positive

d) none of the mentioned

40

For a type D chopper, if duty cycle α < 0.5 then the

a) average voltage is positive

b) average voltage is negative

c) average voltage is zero

d) none of the mentioned

41

Identify the given circuit

a) type D chopper

b) two quadrant type C chopper

c) type E chopper

d) type F chopper

42

A type C chopper consists of __________ diodes and _________ switches in anti-

parallel.

a) 2, 2

b) 3, 3

c) 4, 4

d) 3, 4

43

A type C chopper can operate in

c) Ist, IInd and IIIrd quadrants

44

For the first quadrant operation of type E chopper

a) Only CH1 is on

b) CH1 and CH2 is on

c) CH1 and CH3 is on

d) CH1 and CH4 is on

45

What is the expression for load voltage when the chopper is operated in the

a) Vs

b) E

c) 0

d) E + Ldi/dt

46

The load emf E must be reversed for

a) first and second quadrant operation

d) both third and fourth quadrant operation

47

For the type E chopper to be operated in the fourth quadrant

a) only one switch is operated

b) two switches are operated

c) three switches are operated

d) all the switches are operated

48

In a type E chopper, if all the four chopper switches are closed simultaneously

then

b) supply is short circuited

c) both load and supply are shorted

d) none of the mentioned.

49

When CH4 is turned on and then off

a) load current falls to zero b) negative current freewheels through D2, D3 c) positive current freewheels through D2, D3 d) none of the mentioned

50

A type C chopper is operated with only positive load current. Choose the correct

statement.

a) CH1 would remain idle b) D2 would remain idle c) CH2 would remain idle d) Both D2 and CH2 would remain idle

Unit 4: INVERTERS AND UPS

1

Inverters converts

a) dc power to dc power

b) dc power to ac power

c) ac power to ac power

d) ac power to dc power

2

Line-commutated inverters have

a) AC on the supply side and DC on the load side

b) AC on both supply and load side