# Power Electronics Questions and Answers – Choppers-1

This set of Power Electronics Multiple Choice Questions & Answers (MCQs) focuses on “Choppers-1″.

1. In the ___________ type of chopper, two stage conversions takes place.
a) AC-DC
d) None of the mentioned

Explanation: In AC link chopper, DC is converter to AC than stepped up/down than again AC to DC conversation takes place.

2. Choppers converter
a) AC to DC
b) DC to AC
c) DC to DC
d) AC to AC

Explanation: Choppers are used to step up or step down DC voltage/current levels. Hence, they are DC to DC converters.

3. 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

Explanation: It is a DC equivalent of an AC transformer because it behaves in the similar manner i.e. converting fixed DC to variable DC.

4. Which device can be used in a chopper circuit?
a) BJT
b) MOSFET
c) GTO
d) All of the mentioned

Explanation: All of the devices which can be used as a switch can be used in a chopper.

5. A chopper is a
a) Time ratio controller
b) AC to DC converter
c) DC transformer
d) High speed semiconductor switch

Explanation: It is a high speed on/off semiconductor switch. Note that it behaves like a DC transformer, does not mean it is a DC transformer. There is no DC transformer.

6. What is the duty cycle of a chopper ?
a) Ton/Toff
b) Ton/T
c) T/Ton
d) Toff x Ton

Explanation: It is the time during which the chopper is on (Ton) relative to the whole period (T = Ton+Toff).

7. The load voltage of a chopper can be controlled by varying the
a) duty cycle
b) firing angle
c) reactor position
d) extinction angle

Explanation: The output voltage can be changed by changing the duty cycle (Ton/T).

8. The values of duty cycle (α) lies between
a) 0<α<1
b) 0>α>-1
c) 0<=α<=1
d) 1<α<100

Explanation: The duty cycle is between 0 and 1. It can be 0 if the chopper switch is never on and it can be 1 when the chopper switch is always on.

9. 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

Explanation: α = Ton/T
T = Ton/ α
f = 1/T = α/Ton.

10. 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
d) Vo = 2Vs/απ

Explanation: The chopper output voltage is Duty cycle x the input voltage (ideal condition).

Sanfoundry Global Education & Learning Series – Power Electronics.

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