Power Electronics 5

Which chopper is used for the DC motor speed control and regenerative braking of

the DC motor

• Chopper A

• Chopper B

• Chopper C

• Chopper D

In a DC-DC boost converter, the duty ratio is controlled to regulate the output voltage

at 48 V. The input DC voltage is 24 V. The output power is 120 W. The switching

frequency is 50 kHz. Assume ideal components and a very large output filter

capacitor. The converter operates at the boundary between continuous and

discontinuous conduction modes. The values of the boost inductor (in µH) is

• 12

• 24

• 28

• 14

Which of the following is a disadvantage of choppers?

• High efficiency

• Simple control

• High-frequency operation can cause EMI issues

• Ability to handle high power

Which of the following is incorrect?

• Class-B chopper - one quadrant Operation

• Class-C chopper - four quadrant operation

• Class-D Chopper - two-quadrant operation

• Class-E chopper - four-quadrant operation

In the Flyback converter, the inductor of the buck-boost converter has been replaced

by

• Flyback capacitor

• Flyback resistor

• Flyback transformer

• Flyback transistor

For the bidirectional operation of converters

• A parallel combination of controllable switch and a diode is used

• A parallel combination of controllable switch and capacitor is used

• A series combination of controllable switch and a diode is used

• A series combination of controllable switch and a capacitor is used

The step-up chopper is used to feed a load at 400 V DC from a 250 V DC source. The

inductor current is continuous. If the ‘off ‘time of the switch is 20 µs, the switching

frequency of the chopper in kHz is

• 16

• 31.2

• 38.25

• 45.75

Which of the following statement is wrong about cuk converter?

• The Ćuk converter can produce an output voltage that is either higher or lower

  than the input voltage

• This can produce a output voltage of reverse polarity with respect of input voltage

• High Component Count

• This can produce a output voltage of same and reverse polarity with respect of input

  voltage

The buck dc-dc converter of has Vs = 50 V, D = 0.4, L = 400 𝜇H, C = 100 𝜇F, f = 20

kHz, and R = 20 ohm, Assuming ideal components, calculate the maximum and

minimum inductor current, respectively

• 1.75 A, 0.25A

• 2 A, 0.25 A

• 3.75A, 0.50 A

• 1.75 A, 1 A

A flyback converter has the following circuit parameters: Vs = 24 V, N1/N2 = 3.0,

Vo= 5 V. find the required duty ratio

• 0.125

• 0.250

• 0.385

• 0.40