11. Calculate the output voltage of the Buck converter if the supply voltage is 11 V and the duty cycle value is .4. [/bg_collapse]
A. 4.4 V
B. 2.2 V
C. 4.8 V
D. 6.4 V
Answer: A
The output voltage of the buck converter is
Vo = Vin×(D.=11×.4=4.4 V.
The value of the duty cycle is less than one which makes the Vo < Vin. The buck converter is used to step down the voltage.
12. Calculate the output voltage of the Boost converter if the supply voltage is 8 V and the duty cycle value is .6.
A. 40 V
B. 20 V
C. 48 V
D. 51 V
Answer: B
The output voltage of the boost converter is
Vo = Vin ÷ (1-D. = 8÷.4 = 20 V.
The value of the duty cycle is less than one which makes the Vo > Vin as denominator value decreases and becomes less than one. The boost converter is used to step up the voltage.
13. Calculate the output voltage of the Buck-Boost converter if the supply voltage is 78 V and the duty cycle value is .1.
A. 7.2 V
B. 4.5 V
C. 8.6 V
D. 5.1 V
Answer: C
The output voltage of the buck-boost converter is
Vo = D×Vin ÷ (1-D.=.1(78)÷.9=8.6 V.
It can step up and step down the voltage depending upon the value of the duty cycle. If the value of the duty cycle is less than .5 it will work as a buck converter and for a duty cycle greater than .5 it will work as a boost converter.
14. The principle of the Boost converter can be applied for regenerative braking.
A. True
B. False
Answer: A
The Buck converter is used in motoring mode but a Boost converter can operate only in braking mode because the characteristics are in the second quadrant only.
15. The unit of angular acceleration is Joule.
A. True
B. False
Answer: B
Angular acceleration is defined as a derivate of angular velocity with respect to time. It is generally written as α. The unit of angular velocity in rad/sec and of time is second so the unit of angular acceleration in rad/s2.
16. Reluctance motors are singly-excited.
A. True
B. False
Answer: A
Reluctance motors are singly-excited. The stator side of the motor is excited by an AC source. Due to excitation, a revolving magnetic field is created and the rotor rotates with a synchronous speed.
17. Reluctance motor can operate on DC supply.
A. True
B. False
Answer: A
The reluctance motor can operate on AC supply. It cannot operate on DC supply. Reluctance motors are singly-excited.
18. An infinite bus-bar has _____________
A. Constant voltage
B. Constant frequency
C. Constant voltage and frequency
D. constant speed
Answer: C
An infinite bus bar has constant voltage and constant speed. It has many types like single bus-bar, and double bus-bar. It is connected to the grid.
19. Calculate the value of the Input power factor for a 3-Φ Fully controlled rectifier if the firing angle value is 90°.
A. 0
B. .2
C. .3
D. .4
Answer: A
The value of the input power factor for a 3-Φ Fully controlled rectifier is
.95cos(90°)=0.
The input power factor is a product of the distortion factor and displacement factor.
20. Which of the following motor is used in recording instruments?
A. Reluctance motor
B. Induction motor
C. Synchronous motor
D. DC motor
Answer: A
The reluctance motor is used in recording instruments. It is used for many constant speed applications. The starting torque of the motor depends upon the rotor position.
