Power Electronics and Drives MCQ-1

1. In a thyristor, anode current is made of

(A) Electrons only
(B) Electrons or holes
(C) Electrons and holes
(D) None of these

2. A DIAC can be terned as :

(A) Diode AC Switch
(B) TRIODE AC Switch
(C) Both (a) and (b)
(D) None of the above

3. A UJT exhibits negative resistance region :

(A) Before the peak point
(B) Between peak and valley points
(C) After the valley point
(D) Both (a) and (c)

4. Inverter converts :

(A) DC to AC
(B) AC to DC
(C) Both (a) and (b)
(D) None of the above

5. Which semiconductor device behaves structurally as consisting of a diode and two resistors :

(A) UJT
(B) TRIAC
(C) SCR
(D) Shockley diode

6. AC power in a load can be controlled by using :

(A) Two SCRs in parallel opposition
(B) Two SCRs in series
(C) Three SCRs in series
(D) Four SCRs in series

7. In a full wave rectifier, the rectification ratio is approximately equal to :

(A) 61%
(B) 71%
(C) 81%
(D) 91%

8. The p-type emitter of a UJT is ______ dopped.

(A) Lightly
(B) Moderately
(C) Heavily
(D) Not

9. For an SCR, di/dt protection is achieved through the use of

(A) R in series with SCR
(B) RL in series with SCR
(C) L in series with SCR
(D) L across SCR

10. In a pulse width modulation of chopper :

(A) T is kept constant & TON is changed
(B) TON is kept constant and T is changed
(C) Both T and TON are changed
(D) Either T or TON is changed

11. Choppers can be used to

(A) Increase a DC voltage
(B) Decrease a DC voltage
(C) Increase or decrease a DC voltage
(D) None of these

12. A single-phase full converter operates as an inverter, when

(A) 0° ≤ α ≤ 90°
(B) 90° ≤ α ≤ 180°
(C) It supplies to a back emf load
(D) 90° ≤ α ≤ 180° and there is a suitable DC source in the load circuit

13. The average value of the output voltage in a step down DC chopper is given by :

(A) Vo = Vs
(B) Vo = KVs
(C) Vo = Vs/K
(D) Vo = Vs/(1-K)

14. The control method used for PWM DC-DC converter is

(A) Voltage mode control
(B) Current mode control
(C) Hysteric control
(D) All of these

15. A fully controlled converter uses :

(A) Diodes only
(B) Thyristors only
(C) Both diodes and thyristor
(D) Insufficient data

16. Which device can be used in chopper circuit :

(A) BJT
(B) MOSFET
(C) GTO
(D) All of the above

17. The load voltage of a chopper can be Controlled by varying the :

(A) Duty cycle
(B) Firing angle
(C) Reactor position
(D) Extinction angle

18. In pule width modulation :

(A) The output voltage is modulated
(B) The input voltage is modulated
(C) The gating pulses are modulated
(D) None of the above

19. The power MOSFET is a :

(A) Current controlled unipolar device
(B) Voltage controlled unipolar device
(C) Current control bipolar device
(D) Voltage controlled bipolar device

20. A step down choppers can be used in :

(A) Electric traction
(B) Electric vehicle
(C) Machine tools
(D) All of these