MCQOPTIONS
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MCQOPTIONS
This section includes 42 Mcqs, each offering curated multiple-choice questions to sharpen your Power Electronics knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
A step-down chopper is also called as a |
| A. | first-quadrant chopper |
| B. | second-quadrant chopper |
| C. | third-quadrant chopper |
| D. | fourth-quadrant chopper |
| Answer» B. second-quadrant chopper | |
| 2. |
A voltage commutated chopper has the following parameters:Vs = 220 V. Commutation circuit: L = 20 μH and C = 50 μF.Find the effective on period for a constant load current of 80 A and Ton = 800 μsecs. |
| A. | 1.075 μs |
| B. | 10.75 ms |
| C. | 1075 μs |
| D. | 1.075 sec |
| Answer» D. 1.075 sec | |
| 3. |
In a type C chopper, if only one switch is operated |
| A. | only one quadrant operation will be obtained |
| B. | two quadrant operation can be obtained |
| C. | the chopper won't work |
| D. | none of the mentioned |
| Answer» B. two quadrant operation can be obtained | |
| 4. |
Find the expression for effective input resistance of a step down chopper. With R load and duty cycle = α. |
| A. | R x α |
| B. | R/2 |
| C. | 0 |
| D. | R/α |
| Answer» E. | |
| 5. |
Which of the following mentioned control strategy/strategies would require a feedback loop? |
| A. | pwm |
| B. | constant frequency system |
| C. | current limit control |
| D. | none of the mentioned |
| Answer» D. none of the mentioned | |
| 6. |
For a type D chopper, if duty cycle α < 0.5 then the |
| A. | average voltage is positive |
| B. | average voltage is negative |
| C. | average voltage is zero |
| D. | none of the mentioned |
| Answer» C. average voltage is zero | |
| 7. |
The speed of a separately excited dc motor is controlled below base speed by using a type-A SCR based chopper. The supply voltage is 220 V dc and the armature resistance is 0.5 Ω. Calculate the minimum value of firing angle if the motor drives a constant torque load requiring an average armature current of 30 A. |
| A. | 1/2 |
| B. | 3/44 |
| C. | 59/46 |
| D. | 7/12 |
| Answer» C. 59/46 | |
| 8. |
The AC ripple voltage is given by |
| A. | Vrms/Vo |
| B. | Vrms2/π |
| C. | √(Vrms2 – Vo2) |
| D. | √(Vrms + Vo) |
| Answer» D. √(Vrms + Vo) | |
| 9. |
Find the expression for output voltage for a step-up chopper, assume linear variation of load current and α as the duty cycle. |
| A. | Vs |
| B. | Vs/α |
| C. | Vs/(1-α) |
| D. | Vs/√2 |
| Answer» D. Vs/√2 | |
| 10. |
The expression for the thyristor (chopper switch) current is given byI = (α2.Vs - αE)/RFind the value of firing angle α, for which the thyristor current is maximum. |
| A. | 2Vs/π |
| B. | 180° |
| C. | E/2Vs |
| D. | Vs/R |
| Answer» D. Vs/R | |
| 11. |
The type-C chopper or two quadrant type-A chopper has |
| A. | type-A and type-B choppers in series |
| B. | type-A and type-B choppers in parallel |
| C. | two type-A choppers in series |
| D. | two type-A choppers in parallel |
| Answer» C. two type-A choppers in series | |
| 12. |
Find the expression for average output voltage in a type D chopper on RL load. |
| A. | Vs x Duty cycle (α) |
| B. | Vs x T |
| C. | Vs x (T – T)/T |
| D. | Vs2/2 |
| Answer» D. Vs2/2 | |
| 13. |
In a type E chopper, if all the four chopper switches are closed simultaneously then |
| A. | load is short circuited |
| B. | supply is short circuited |
| C. | both load and supply are shorted |
| D. | none of the mentioned. |
| Answer» C. both load and supply are shorted | |
| 14. |
What is the expression for design of commutation capacitance in case of a load commutated chopper circuit? |
| A. | (I x Ton)/Vs |
| B. | Cannot be determined |
| C. | (I x Ton)/2Vs |
| D. | (I x T)/Vs |
| Answer» D. (I x T)/Vs | |
| 15. |
A chopper circuit is fed from an input voltage of 20 V delivers a power of 16 watts. If the chopper efficiency is 80 %, then find the value of input current. |
| A. | 0.64 A |
| B. | 1 A |
| C. | 0.8 A |
| D. | 1.25 A |
| Answer» C. 0.8 A | |
| 16. |
What is the expression for the value of the capacitor in the voltage commutation circuit? Let tc be the circuit turn off time and Io be the constant load current. |
| A. | Io x (dv/dt) |
| B. | Vs/Io |
| C. | (tc x Io)/Vs |
| D. | none of the mentioned |
| Answer» D. none of the mentioned | |
| 17. |
A step down chopper has input dc voltage of 220 V and R = 10 Ω in series with L = 65 mH. If the load current varies linearly between 11 A and 17 A, then find the duty cycle α. |
| A. | 1 |
| B. | 0.4 |
| C. | 0.6 |
| D. | 0.7 |
| Answer» E. | |
| 18. |
Find the average output voltage for a type D chopper if it is given a dc supply of 220 V. Chopper frequency is 2 kHz and both the chopper switches are operated for 0.3 ms. |
| A. | 220 V |
| B. | 108 V |
| C. | 98 V |
| D. | 44 V |
| Answer» E. | |
| 19. |
A voltage commutated chopper feeds power to an electric car (battery-powered). The battery voltage is 60 V. Starting current is 60 A and the SCR turn-off time is 20 μs. Calculate the value of inductance (L) required for the commutating circuit. |
| A. | 400 μH |
| B. | 40 nH |
| C. | 40 μH |
| D. | 0.4 mH |
| Answer» D. 0.4 mH | |
| 20. |
Which type of commutating circuit will have highest switching losses for same rating of all the components? |
| A. | current commutated chopper |
| B. | voltage commutated chopper |
| C. | load commutated chopper |
| D. | forced commutated chopper |
| Answer» D. forced commutated chopper | |
| 21. |
A current commutated chopper is fed from a source of 230 V. Its commutating components are L = 20 μH and C = 50 μF. Find the value of peak commutating current. |
| A. | 233 A |
| B. | 59 A |
| C. | 363 A |
| D. | 198 A |
| Answer» D. 198 A | |
| 22. |
In the current limit control method, when the load current reaches a predefined lower value, then |
| A. | the chopper is switched off |
| B. | the chopper is switched on |
| C. | the source voltage is removed |
| D. | load voltage goes to zero |
| Answer» C. the source voltage is removed | |
| 23. |
The expression for a step-up/step-down chopper with α as the duty cycle and Vs as the dc input voltage is |
| A. | Vs/1 - α |
| B. | α x Vs |
| C. | Vs (α/1-α) |
| D. | Vs (α/1+α) |
| Answer» D. Vs (α/1+α) | |
| 24. |
Find the expression for peak capacitor voltage in case of a current commutated chopper circuit. |
| A. | Io √(L/C) |
| B. | Vs + √(L/C) |
| C. | Vs + Io √(L/C) |
| D. | Zero |
| Answer» D. Zero | |
| 25. |
For the type E chopper to be operated in the fourth quadrant |
| A. | only one switch is operated |
| B. | two switches are operated |
| C. | three switches are operated |
| D. | all the switches are operated |
| Answer» B. two switches are operated | |
| 26. |
A step down chopper has Vs = 230 V and R = 10 Ω. For a duty cycle of 0.4, the power taken by the chopper is 2097 Watts. Find the chopper efficiency. Take the voltage drop across the chopper switch as 2 V. |
| A. | 0.98 |
| B. | 0.8996 |
| C. | 0.9914 |
| D. | 0.9654 |
| Answer» D. 0.9654 | |
| 27. |
The load emf E must be reversed for |
| A. | first and second quadrant operation |
| B. | third quadrant operation |
| C. | fourth quadrant operation |
| D. | both third and fourth quadrant operation |
| Answer» E. | |
| 28. |
Find the expression for the ripple factor in terms of duty cycle α for a type A step down chopper |
| A. | √(1-α/α) |
| B. | α2/2 |
| C. | √α/2 |
| D. | √(1-α) |
| Answer» B. α2/2 | |
| 29. |
Find the output voltage for a step-up chopper when it is operated at a duty cycle of 50 % and Vs = 240 V. |
| A. | 240 V |
| B. | 480 V |
| C. | 560 V |
| D. | 120 V |
| Answer» C. 560 V | |
| 30. |
For a type E chopper operating in the first quadrant, find the expression for average output voltage. |
| A. | Vs |
| B. | E - Ldi/dt |
| C. | 0 |
| D. | E + Ldi/dt |
| Answer» B. E - Ldi/dt | |
| 31. |
In the current limit control method, the chopper is switched off when |
| A. | load current reaches the lower limit |
| B. | load current reaches the upper limit |
| C. | load current falls to zero |
| D. | none of the mentioned |
| Answer» C. load current falls to zero | |
| 32. |
If a step up chopper's switch is always kept off then (ideally) |
| A. | Vo = 0 |
| B. | Vo = ∞ |
| C. | Vo = Vs |
| D. | Vo > Vs |
| Answer» D. Vo > Vs | |
| 33. |
The load commutated chopper circuit consists of |
| A. | two thyristors and one commutating capacitor |
| B. | four thyristors and one commutating capacitor |
| C. | two thyristors and two commutating capacitors |
| D. | four thyristors and two commutating capacitors |
| Answer» C. two thyristors and two commutating capacitors | |
| 34. |
In a voltage commutated SCR, the main SCR is commutated by |
| A. | triggering the auxiliary SCR |
| B. | sending a negative pulse to the main SCR |
| C. | removing the supply Vs |
| D. | none of the mentioned |
| Answer» B. sending a negative pulse to the main SCR | |
| 35. |
For a step-up/step-down chopper, if current increases from I1 to I2 linearly during Ton, then find the energy stored in the inductor during Ton |
| A. | zero |
| B. | Vs x (I1 + I2) |
| C. | Vs x [ (I1 + I2)/2 ] x Ton |
| D. | Vs x [ (I1 + I2)/2 ] x T |
| Answer» D. Vs x [ (I1 + I2)/2 ] x T | |
| 36. |
A voltage commutated chopper has the following parameters:Vs = 220 V. Commutation circuit: L = 20 μH and C = 50 μF.Find the turn-off time for the main SCR with a constant load current of 80 A and Ton = 800 μsecs. |
| A. | 137.5 μs |
| B. | 1075 μs |
| C. | 49.67 μs |
| D. | 200 μs |
| Answer» B. 1075 μs | |
| 37. |
A voltage commutated chopper feeds power to an electric car (battery-powered). The battery voltage is 60 V. The SCR turn-off time is 20 μs. Calculate the value of capacitor (C) required for the commutating circuit. |
| A. | 400 μF |
| B. | 40 nF |
| C. | 40 μF |
| D. | 0.4 mF |
| Answer» D. 0.4 mF | |
| 38. |
For a step-up/step-down chopper, if α (duty cycle) = 0.5 then |
| A. | Vo = Vs |
| B. | Vo < Vs |
| C. | Vo > Vs |
| D. | none of the mentioned |
| Answer» B. Vo < Vs | |
| 39. |
For a step-up/step-down chopper, if α (duty cycle) < 0.5 then |
| A. | Vo = Vs |
| B. | Vo < Vs |
| C. | Vo > Vs |
| D. | none of the mentioned |
| Answer» C. Vo > Vs | |
| 40. |
FIND_THE_EXPRESSION_FOR_OUTPUT_VOLTAGE_FOR_A_STEP-UP_CHOPPER,_ASSUME_LINEAR_VARIATION_OF_LOAD_CURRENT_AND_‚ÂÀ√≠¬¨¬±_AS_THE_DUTY_CYCLE.?$# |
| A. | Vs |
| B. | Vs/α |
| C. | Vs/(1-α) |
| D. | Vs/‚àö2 |
| Answer» D. Vs/‚Äö√Ñ√∂‚àö‚Ć‚àö‚àÇ2 | |
| 41. |
Find_the_output_voltage_for_a_step-up_chopper_when_it_is_operated_at_a_duty_cycle_of_50_%_and_Vs_=_240_V.$ |
| A. | 240 V |
| B. | 480 V |
| C. | 560 V |
| D. | 120 V |
| Answer» C. 560 V | |
| 42. |
In a step down chopper, if Vs = 100 V and the chopper is operated at a duty cycle of 75 %. Find the output voltage. |
| A. | 100 V |
| B. | 75 V |
| C. | 25 V |
| D. | none of the mentioned |
| Answer» C. 25 V | |