Chopper MCQ

1. A chopper may be thought as a

  1. DC equivalent of an induction motor
  2. Diode rectifier
  3. DC equivalent of an AC transformer
  4. Inverter with DC input
Answer. c

2. Which device can be used in a chopper circuit?

  1. GTO
  3. BJT
  4. All of the above
Answer. d

3. A buck regulator has an input voltage of 12 V and the required output voltage is 5 V. What is the duty cycle of the regulator?

  1. 6
  2. 5/2
  3. 12/5
  4. 5/12
Answer. d

4. A chopper circuit is operating on TRC control mode at a frequency of 2 kHz of a 230 V dc supply. For output voltage of 170 V, the conduction and blocking periods of a thyristor in each cycle are respectively

  1. 0.386 ms and 0.114 ms
  2. 0.369 ms and 0.131 ms
  3. 0.390 ms and 0.110 ms
  4. 0.131 ms and 0.369 ms
Answer. b

5. Which of the following regulator provide output voltage polarity reversal without a transformer?

  1. Buck regulator
  2. Boost regulator
  3. Buck-Boost regulator
  4. CUK regulator
Answer. c

6. What is the waveform of the current flowing through the diode in a buck-boost converter?

  1. Square wave
  2. Triangular wave
  3. Trapezoidal wave
  4. Sinusoidal wave
Answer. c

7. In d.c. choppers, the waveforms for input and output voltages are respectively

  1. discontinuous and continuous
  2. both continuous
  3. both discontinuous
  4. continuous and discontinuous
Answer. d

8. A two-quadrant d.c. to d.c. chopper can operate with which of the following load conditions?

  1. +ve voltage, +ve current
  2. -ve voltage, +ve current
  3. -ve voltage, -ve current
  4. +ve voltage, -ve current

Select the correct answer using the code given below.

  1. i and ii
  2. i only
  3. iii and iv
  4. i and iv
Answer. d

9. In the buck-boost converter, what is the maximum value of the switch utilization factor?

  1. 0.75
  2. 1.00
  3. 0.25
  4. 0.50
Answer. a

10. A boost-regulator has an input voltage of 5 V and the average output voltage of 15 V. The duty cycle is

  1. 3/2
  2. 2/3
  3. 5/2
  4. 15/2
Answer. b

11. An ideal chopper operating at a frequency of 500 Hz, supplies a load having resistance of 3 ohms and inductance of 9 mH from a 60 V battery. The mean value of the load voltage for on/off ratio of 4/1, (assuming that load is shunted by a perfect commutating diode and battery is loss-less) is

  1. 240 V
  2. 48 V
  3. 15 V
  4. 4 V
Answer. b

12. For a step up d.c.-d.c. chopper with an input d.c. voltage of 220 volts, if the output voltage required is 330 volts and the non-conducting time of thyristor-chopper is 100 μs, the ON time of thyristor-chopper would be

  1. 66.6 μs
  2. 100 μs
  3. 150 μs
  4. 200 μs
Answer. d

13. A four-quadrant chopper cannot be operated as

  1. one quadrant chopper
  2. cycloconverter
  3. inverter
  4. bi-directional rectifier
Answer. b

14. In a step-up operation, what is the condition to be satisfied for controllable power transfer?

  1. 0 < Vs < E
  2. 0 < Vs > E
  3. Vs > E
  4. Vs < E
Answer. a

15. A dc to dc transistor chopper supplied from a fixed voltage dc source feeds a fixed resistive inductive load and a freewheeling diode. The chopper operates at 1 kHz and 50% duty cycle. Without, changing the value of the average dc current through the load, if it is desired to reduce the ripple content of the load current, the control action needed will be to

  1. Increase the chopper frequency keeping its duty cycle constant
  2. Increase the chopper frequency and duty cycle in equal ratio
  3. Decrease only the chopper frequency
  4. Decrease only the duty cycle
Answer. a

16. An ideal chopper is operating at a frequency of 500 Hz from a 60 V battery input. It is supplying a load having 3 Ω resistance and 9 mH inductance. Assuming the load is shunted by a perfect commutating diode and assuming the battery is lossless, what is the mean load current at an on/off ratio of 1/1?

  1. 10A
  2. 15 A
  3. 20 A
  4. None of these
Answer. a

17. For a step-down d.c. chopper operating with discontinuous load current, what is the expression for the load voltage? (K is duty ratio of chopper)

  1. Vo = Vdc × K
  2. Vo = Vdc/K
  3. Vo = Vdc/(1-K)
  4. Vo = Vdc × (1-K)
Answer. a