# Electric Drives Questions and Answers – Solid-State Switching Circuits – DC/DC Conversion

This set of Electric Drives Multiple Choice Questions & Answers (MCQs) focuses on “Solid-State Switching Circuits – DC/DC Conversion”.

1. Choppers are used to control the DC voltage level.
a) True
b) False

Explanation: Choppers are used to control the DC voltage level. They can increase, decrease or both the input DC voltage.

2. Which one of the following device is uncontrolled?
a) SCR
b) MOSFET
c) Diode
d) TRIAC

Explanation: Diode is uncontrolled, unidirectional power electronic device. When the voltage across the diode becomes positive it starts conduction otherwise remains off.

3. Cuk-converter is better than Buck converter in terms of the output voltage.
a) True
b) False

Explanation: Cuk-converter is better than Buck converter in terms of the output voltage. The filter is present at the output and input side of the Cuk-converter whereas in Buck there is no filter circuit present at the input side.

4. What is the formula for output voltage for Buck converter?
a) 8D×Vin
b) 5D×Vin
c) 2D×Vin
d) D×Vin

Explanation: The output voltage of the buck converter is Vo = D×Vin. The value of the duty cycle is less than one which makes the Vo < Vin. The buck converter is used to step down voltage. Vin is a fixed voltage and Vo is a variable voltage.

5. What is the formula for output voltage for Buck-Boost converter?
a) D×Vin
b) Vin ÷ (1-D)
c) D×Vin ÷ (1-D)
d) D×Vin ÷ (1+D)

Explanation: The output voltage of the buck-boost converter is Vo = D×Vin ÷ (1-D). 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 duty cycle greater than .5 it will work as a boost converter.

6. What is the formula for output voltage for Boost converter?
a) 8D×Vin
b) 5D×Vin
c) 2D×Vin
d) D×Vin

Explanation: The output voltage of the boost converter is Vo = Vin ÷ (1-D). The value of the duty cycle is less than one which makes the Vo > Vin. The boost converter is used to step up the voltage. Vin is a fixed voltage and Vo is a variable voltage.

7. ____________ is the boundary for C.C.M and D.C.M mode in 3-Φ Half wave bridge rectifier for R load.
a) 60°
b) 10°
c) 80°
d) 30°

Explanation: 30° is the boundary for C.C.M and D.C.M mode in 3-Φ Half wave bridge rectifier for R load. Conduction will only remain from 30°+α to 150°+α.

8. Buck-Boost acts as Buck converter for duty cycle is equal to _________
a) .9
b) .7
c) .6
d) .4

Explanation: The output voltage of the buck-boost converter is Vo = D×Vin ÷ (1-D). 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. The answer is .4.

9. Buck-Boost acts as Boost converter for duty cycle is equal to _________
a) .8
b) .1
c) .2
d) .4

Explanation: The output voltage of the buck-boost converter is Vo = D×Vin ÷ (1-D). 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 more than .5 it will work as a boost converter. The answer is .8.

10. Inductor and Capacitor in Buck converter are used to ___________
a) Increase the cost
b) Decrease the cost
c) Filter out the harmonics
d) Increase the harmonics

Explanation: Inductor and capacitor in Buck converter are used to filter out the harmonics. They remove the ripple from the output voltage.

11. Calculate peak-peak voltage if Vmax=1 V and Vmin=-1 V.
a) 6 V
b) 2 V
c) 3 V
d) 1 V

Explanation: Peak-Peak voltage is equal to the difference between the maximum and minimum voltage. It is mathematically represented as Vp-p=Vmax-Vmin=1+1=2 V.

12. Calculate the value of Crest factor if Vpeak=0 V and Vr.m.s=24 V.
a) 0
b) 3
c) 5
d) 8

Explanation: The value of the crest factor is Vpeak÷Vr.m.s=0÷24=0 V. It signifies the peak value is 0 times than the r.m.s value.

13. Calculate the output voltage of the Buck converter if the supply voltage is 789 V and duty cycle value is .9.
a) 711.1 V
b) 710.1 V
c) 722.2 V
d) 713.2 V

Explanation: The output voltage of the buck converter is Vo = Vin×(D)=789×.9=710.1 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.

14. Calculate the average value of thyristor current in 3-Φ Full wave converter for the load current=27 A and α=6°.
a) 9 A
b) 4 A
c) 5 A
d) 9 A

Explanation: The average value of thyristor current in 3-Φ Full wave converter is Io÷3. It is the average value of the thyristor current. I(r.m.s)= Io÷3=9 A.

15. Calculate the output voltage of the Boost converter if the supply voltage is 156 V and duty cycle value is .4.
a) 260 V
b) 264 V
c) 261 V
d) 268 V

Explanation: The output voltage of the boost converter is Vo = Vin×(1-D)=156×1.66=260 V. The value of the duty cycle is less than one which makes the Vo > Vin. The boost converter is used to step up the voltage.

Sanfoundry Global Education & Learning Series – Electric Drives.

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