McqMate
These multiple-choice questions (MCQs) are designed to enhance your knowledge and understanding in the following areas: Electrical Engineering , Electronics and Communication Engineering .
| 1. |
In a flyback converter, the inductor of the buck-boost converter has been replaced by a |
| A. | Flyback capacitor |
| B. | Flyback resistor |
| C. | Flyback transformer |
| D. | Flyback transistor |
| Answer» C. Flyback transformer | |
| 2. |
For bidirectional operation of converters |
| A. | A parallel combination of controllable switch and a diode is used |
| B. | A parallel combination of controllable switch and capacitor is used |
| C. | A series combination of controllable switch and a diode is used |
| D. | A series combination of controllable switch and a capacitor is used |
| Answer» A. A parallel combination of controllable switch and a diode is used | |
| 3. |
For a buck converter to reduce the conduction losses in diode |
| A. | A high on - resistance switch can be added in parallel |
| B. | A low on - resistance switch can be added in parallel |
| C. | A high on - resistance switch can be added in series |
| D. | A low on - resistance switch can be added in series |
| Answer» B. A low on - resistance switch can be added in parallel | |
| 4. |
A step - down choppers can be used in |
| A. | Electric traction |
| B. | Electric vehicles |
| C. | Machine tools |
| D. | All of these |
| Answer» D. All of these | |
| 5. |
The output current in PWM DC - DC converters is equal to |
| A. | Average value of the output inductor current |
| B. | Product of an average inductor current and a function of duty ratio |
| C. | Either (a) or (b) |
| D. | None of these |
| Answer» C. Either (a) or (b) | |
| 6. |
Advantages of Cuk converter is / are |
| A. | Large number of reactive component |
| B. | Low stress on switch |
| C. | Low stress on capacitor |
| D. | None of these |
| Answer» D. None of these | |
| 7. |
In a push - pull converter, the filter capacitor can be obtained as |
| A. | Cmin = V / ( Vr L f2 ) |
| B. | Cmin= ( 1 – D ) V / ( Vr L f2 ) |
| C. | Cmin= ( 1 – 2 D ) V / 32 ( Vr L f2 ) |
| D. | Cmin= ( 1 – 2 D ) V / 42 ( Vr L f2 ) |
| Answer» C. Cmin= ( 1 – 2 D ) V / 32 ( Vr L f2 ) | |
| 8. |
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 |
| Answer» D. All of these | |
| 9. |
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 |
| Answer» B. Current mode control | |
| 10. |
In current commutated DC-DC choppers, the voltage spike appears across the load when |
| A. | Voltage across the commutating inductances collapses |
| B. | The capacitance voltage adds to the supply voltage |
| C. | Both (a) and (b) |
| D. | None of these |
| Answer» C. Both (a) and (b) | |
| 11. |
In a load commutated DC - DC chopper, the capacitor has a |
| A. | Symmetric triangular voltage across itself |
| B. | Symmetric rectangular voltage across itself |
| C. | Symmetric trapezoidal voltage across itself |
| D. | Symmetric sinusoidal voltage across itself |
| Answer» C. Symmetric trapezoidal voltage across itself | |
| 12. |
Voltage commutation circuit can be converted into a current commutation by interchanging the positions of |
| A. | Diode and capacitor |
| B. | Capacitor and SCR |
| C. | Inductor and capacitor |
| D. | Capacitor and load |
| Answer» A. Diode and capacitor | |
| 13. |
During the commutation period in 3 phase converter, overlap time is |
| A. | Dependent on the load current |
| B. | Dependent on the voltage |
| C. | Dependent on both the load current and load voltage behind the short circuit current |
| D. | Independent on both the load current and load voltage |
| Answer» C. Dependent on both the load current and load voltage behind the short circuit current | |
| 14. |
In a three phase converter, the number of notches per cycle is |
| A. | One |
| B. | Three |
| C. | Six |
| D. | Nine |
| Answer» C. Six | |
| 15. |
Unipolar modulation is generally used in |
| A. | AC - AC converters |
| B. | AC - DC converters |
| C. | DC - AC converters |
| D. | DC - DC converters |
| Answer» D. DC - DC converters | |
| 16. |
Very large values of modulation index (greater than 3.24) lead to |
| A. | Square AC output voltage |
| B. | Sine AC output voltage |
| C. | Triangular AC output voltage |
| D. | Trapezoidal AC output voltage |
| Answer» A. Square AC output voltage | |
| 17. |
With increase in firing angle |
| A. | Both harmonic distortion and quality of input current increases |
| B. | Harmonic distortion increases and quality of input current decreases |
| C. | Harmonic distortion decreases and quality of input current increases |
| D. | Both harmonic distortion and quality of input current decreases |
| Answer» B. Harmonic distortion increases and quality of input current decreases | |
| 18. |
The advantage of using free - wheeling diode in half controlled bridge converter is that |
| A. | There is always a path for the dc current independent of the ac line |
| B. | There is always a path for the ac current independent of the ac line |
| C. | There is always a path for the dc current dependent of the ac line |
| D. | There is always a path for the ac current independent of the ac line |
| Answer» A. There is always a path for the dc current independent of the ac line | |
| 19. |
The input current waveform of a bridge controlled rectifier when the load is perfectly filtered is |
| A. | Sine wave |
| B. | Square wave |
| C. | Saw - tooth wave |
| D. | Trapezoidal wave |
| Answer» B. Square wave | |
| 20. |
A full wave rectifier with resistive load produces |
| A. | Second harmonic |
| B. | Third harmonic |
| C. | Fifth harmonic |
| D. | Do not produce harmonics |
| Answer» D. Do not produce harmonics | |
| 21. |
If all the SCR’s of 3 phase PAC is replaced by diodes, they would be triggered |
| A. | 120 degree after the zero crossing of the corresponding line voltages |
| B. | 60 degree after the zero crossing of the corresponding line voltages |
| C. | 120 degree before the zero crossing of the corresponding line voltages |
| D. | 60 degree before the zero crossing of the corresponding line voltages |
| Answer» B. 60 degree after the zero crossing of the corresponding line voltages | |
| 22. |
An RC snubber network used in BJT |
| A. | Divert the collector current during turn - off |
| B. | Improves the reverse bias safe operating area |
| C. | Dissipates a fair amount of switching power |
| D. | All of these |
| Answer» D. All of these | |
| 23. |
In a 3 phase half wave rectifier, when firing angle is less than 90 degree, then the average dc output voltage becomes |
| A. | Positive |
| B. | Negative |
| C. | Zero |
| D. | None of these |
| Answer» A. Positive | |
| 24. |
In dual converters, |
| A. | Both rectifiers provides positive current to the load |
| B. | Both rectifiers provide negative current to the load |
| C. | One rectifiers provide positive current to the load and the other negative current |
| D. | One rectifier provide positive current to the source and the other negative |
| Answer» A. Both rectifiers provides positive current to the load | |
| 25. |
A single phase ac - dc converter is also known as |
| A. | rectifier |
| B. | inverter |
| C. | chopper |
| D. | regulator |
| Answer» A. rectifier | |
| 26. |
In ac - dc conversion, when the switch is closed then the sum of voltages around the loop is |
| A. | Zero |
| B. | Non zero |
| C. | Equal to the sum of voltage when switch is open |
| D. | Twice of the voltage when switch is open |
| Answer» B. Non zero | |
| 27. |
Choppers are used to control the DC voltage level. |
| A. | True |
| B. | False |
| C. | none |
| D. | all |
| Answer» A. True | |
| 28. |
Cuk-converter is better than Buck converter in terms of the output voltage. |
| A. | True |
| B. | False |
| C. | none |
| D. | all |
| Answer» A. True | |
| 29. |
What is the formula for output voltage for Buck converter? |
| A. | 8D×Vin |
| B. | 5D×Vin |
| C. | 2D×Vin |
| D. | D×Vin |
| Answer» D. D×Vin | |
| 30. |
What is the formula for output voltage for Buck-Boost converter? |
| A. | D×Vin |
| B. | Vin ÷ (1-D) |
| C. | D×Vin ÷ (1 |
| Answer» C. D×Vin ÷ (1 | |
| 31. |
What is the formula for output voltage for Boost converter? |
| A. | 8D×Vin |
| B. | 5D×Vin |
| C. | 2D×Vin |
| D. | D×Vin |
| Answer» D. D×Vin | |
| 32. |
Buck-Boost acts as Buck converter for duty cycle is equal to _________ |
| A. | .9 |
| B. | .7 |
| C. | .6 |
| D. | .4 |
| Answer» D. .4 | |
| 33. |
Buck-Boost acts as Boost converter for duty cycle is equal to _________ |
| A. | .8 |
| B. | .1 |
| C. | .2 |
| D. | .4 |
| Answer» A. .8 | |
| 34. |
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 |
| Answer» C. Filter out the harmonics | |
| 35. |
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 |
| Answer» B. 710.1 V | |
| 36. |
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 |
| Answer» A. 260 V | |
| 37. |
Under harmonic free load voltages, the 3 phase VSI |
| A. | Does not contains second harmonic |
| B. | Does not contains third harmonic |
| C. | Does not contains fifth harmonic |
| D. | Does not contains seventh harmonic |
| Answer» A. Does not contains second harmonic | |
| 38. |
A fully controlled converter uses |
| A. | diodes only |
| B. | thyristors only |
| C. | both diodes and thyristors |
| D. | none of the mentioned |
| Answer» B. thyristors only | |
| 39. |
In a B-2 type full controlled bridge converter |
| A. | one SCR conducts at a time |
| B. | two SCRs conduct at a time |
| C. | three SCRs conduct at a time |
| D. | four SCRs conduct at a time |
| Answer» B. two SCRs conduct at a time | |
| 40. |
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» B. 75 V | |
| 41. |
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» C. Vs/(1-α) | |
| 42. |
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» B. 480 V | |
| 43. |
In the method of phase control, the phase relationship between ___ & ___ is controlled by varying the firing angle |
| A. | supply current, supply voltage |
| B. | end of the load current, end of the load voltage |
| C. | start of the load current, start of the load voltage |
| D. | load current, load voltage |
| Answer» C. start of the load current, start of the load voltage | |
| 44. |
In a single phase half-wave thyristor circuit with R load & Vs=Vm sinωt, the maximum value of the load current can be given by |
| A. | 2Vm/R |
| B. | Vs/R |
| C. | Vm/2 |
| D. | Vs/2 |
| Answer» C. Vm/2 | |
| 45. |
A single-phase half-wave thyristor circuit with R load is triggered at an angle of α = 0°. As such, the maximum value of the average output voltage would be given by Consider Vs = Vm sinωt. |
| A. | Vm |
| B. | 2Vm/π |
| C. | Vm/π |
| D. | Vm/α |
| Answer» C. Vm/π | |
| 46. |
The AC voltage controllers are used in __________ applications. |
| A. | power generation |
| B. | electric heating |
| C. | conveyor belt motion |
| D. | power transmission |
| Answer» B. electric heating | |
| 47. |
A cycloconverter is a: |
| A. | Frequency changer from higher to lower frequency with one-state conversion |
| B. | Frequency changer from higher to lower frequency with two-stage conversion |
| C. | Frequency changer from lower to higher frequency with one-stage conversion |
| D. | Either a or c |
| Answer» D. Either a or c | |
| 48. |
IGT stands for |
| A. | Insulated gate bipolar transistor |
| B. | Insulated gate bidirectional transistor |
| C. | Inductive gate bipolar transistor |
| D. | Inductive gate bidirectional transistor |
| Answer» B. Insulated gate bidirectional transistor | |
| 49. |
Number of PN junction in an SCR is |
| A. | Two |
| B. | Three |
| C. | Four |
| D. | Five |
| Answer» B. Three | |
| 50. |
In a silicon controlled rectifier, the load is connected |
| A. | Across anode |
| B. | In series with anode |
| C. | Across cathode |
| D. | In series with cathode |
| Answer» B. In series with anode | |
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