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MCQOPTIONS
This section includes 257 Mcqs, each offering curated multiple-choice questions to sharpen your Power Electronics knowledge and support exam preparation. Choose a topic below to get started.
| 151. |
In a single-phase full converter, if and are firing extinction angles respectively, then the load current is |
| A. | discontinuous if ( ) < |
| B. | discontinuous if ( ) > |
| C. | discontinuous if ( ) = |
| D. | continuous if ( ) < |
| Answer» B. discontinuous if ( ) > | |
| 152. |
In a single-phase semi converter, with discontinuous conduction and extinction angle < , freewheeling diode conducts for |
| A. | |
| B. | |
| C. | |
| D. | zero degree |
| Answer» E. | |
| 153. |
A converter which can operate in both 3-pulse and 6- pulse modes is a |
| A. | 1-phase full converter |
| B. | 3-phase half-wave converter |
| C. | 3-phase semiconverter |
| D. | 3-phase full converter |
| Answer» D. 3-phase full converter | |
| 154. |
In a 3-phase half-wave rectifier, dc output voltage is 230 V. The peak inverse voltage across each diode is |
| A. | 481 7 V |
| B. | 460 V |
| C. | 345 V |
| D. | 230 V |
| Answer» B. 460 V | |
| 155. |
For a 3-phase, six-pulse diode rectifier, the average output voltage in terms of maximum value of line voltage V |
| A. | (a) |
| B. | (b) |
| C. | (c) |
| D. | (d) |
| Answer» C. (c) | |
| 156. |
In a 3-phase full-wave diode rectifier, the peak inverse voltage in terms of average output voltage is |
| A. | 1 571 |
| B. | 0 955 |
| C. | 1 047 |
| D. | 2 094 |
| Answer» D. 2 094 | |
| 157. |
A dc chopper is fed from 100 V dc. Its load voltage consists of rectangular pulses of duration 1 msec in an overall cycle time of 3 msec. The average output voltage and ripple factor for this chopper are respectively |
| A. | 25 V, 1 |
| B. | 50 V, 1 |
| C. | 33 33 V, |
| D. | <span style=" text-decoration: overline;">2</span> |
| E. | 33 33 V, 1 |
| Answer» D. <span style=" text-decoration: overline;">2</span> | |
| 158. |
A single-phase full-bridge inverter can operate in load commutation mode in caseload consists of |
| A. | RL |
| B. | RLC underdamped |
| C. | RLC overdamped |
| D. | RLC critically damped |
| Answer» C. RLC overdamped | |
| 159. |
For a chopper, V |
| A. | <table><tr><td rowspan="2"> . </td><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>V<sub>s</sub></center></td><td rowspan="2">, <span style=" text-decoration: overline;"> .</span><br></td><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>V<sub>s</sub></center></td></tr><td align="center">R</td><td align="center">R</td></table> |
| B. | <table><tr><td rowspan="2"> <span style=" text-decoration: overline;"> </span><br></td><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>V<sub>s</sub></center></td><td rowspan="2">, <span style=" text-decoration: overline;"> .</span><br></td><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>V<sub>s</sub></center></td></tr><td align="center">R</td><td align="center">R</td></table> |
| C. | <table><tr><td rowspan="2"> <span style=" text-decoration: overline;"> </span><br></td><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>V<sub>s</sub></center></td><td rowspan="2">, .<br></td><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>V<sub>s</sub></center></td></tr><td align="center">R</td><td align="center">R</td></table> |
| D. | <table><tr><td rowspan="2"> (1 - ).<br></td><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>V<sub>s</sub></center></td><td rowspan="2">, (1 - ).<br></td><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>V<sub>s</sub></center></td></tr><td align="center">R</td><td align="center">R</td></table> |
| Answer» D. <table><tr><td rowspan="2"> (1 - ).<br></td><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>V<sub>s</sub></center></td><td rowspan="2">, (1 - ).<br></td><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>V<sub>s</sub></center></td></tr><td align="center">R</td><td align="center">R</td></table> | |
| 160. |
In dc choppers, per unit ripple is maximum when duty cycle is |
| A. | 0 2 |
| B. | 0 5 |
| C. | 0 7 |
| D. | 0 9 |
| Answer» C. 0 7 | |
| 161. |
A single-phase CSI has capacitor C as the load. For a constant source current, the voltage across the capacitor is |
| A. | square wave |
| B. | triangular wave |
| C. | step function |
| D. | pulsed wave |
| Answer» C. step function | |
| 162. |
In an inverter with fundamental output frequency of 50 Hz, if third harmonic is eliminated, then frequencies of other components in the output voltage wave, in Hz, would be |
| A. | 250, 350, 450, high frequencies |
| B. | 50, 250, 350, 450 |
| C. | 50, 250, 350, 550 |
| D. | 50, 100, 200, 250 |
| Answer» D. 50, 100, 200, 250 | |
| 163. |
In the circuit shown in Fig. 1, L = 5 H and C = 20 F. C is initially charged to 200 V. After the switch S is closed at t = 0, the maximum value of current and the time at which it reaches this value are, respectively |
| A. | 400 A, 15 707 s |
| B. | 50 A, 30 s |
| C. | 100 A, 62 828 s |
| D. | 400 A, 31 414 s |
| Answer» B. 50 A, 30 s | |
| 164. |
The three-phase ac to dc converter which requires neutral point connection is |
| A. | 3-phase semi converter |
| B. | 3-phase full converter |
| C. | 3-phase half-wave converter |
| D. | 3-phase full converter with diodes |
| Answer» D. 3-phase full converter with diodes | |
| 165. |
Types of choppers |
| A. | 3 1 4 2 |
| B. | 2 1 4 3 |
| C. | 3 4 1 2 |
| D. | 3 1 2 4 |
| Answer» B. 2 1 4 3 | |
| 166. |
Chopper configurations |
| A. | 2 4 1 3 |
| B. | 2 4 3 1 |
| C. | 4 2 1 3 |
| D. | 3 4 1 2 |
| Answer» B. 2 4 3 1 | |
| 167. |
In single-pulse modulation used in PWM inverters, V |
| A. | <table><tr><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>2 <span style=" text-decoration: overline;">2</span></center></td><td rowspan="2">V<sub>s</sub>, 120 </td></tr><td align="center"> </td></table> |
| B. | <table><tr><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>4 V<sub>s</sub></center></td><td rowspan="2">, 60 </td></tr><td align="center"> </td></table> |
| C. | <table><tr><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>2 <span style=" text-decoration: overline;">2</span></center></td><td rowspan="2">V<sub>s</sub>, 60 </td></tr><td align="center"> </td></table> |
| D. | <table><tr><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>4 V<sub>s</sub></center></td><td rowspan="2">, 120 </td></tr><td align="center"> </td></table> |
| Answer» B. <table><tr><td style="border-bottom:1px solid #000000;vertical-align:bottom;padding-bottom:2px;"><center>4 V<sub>s</sub></center></td><td rowspan="2">, 60 </td></tr><td align="center"> </td></table> | |
| 168. |
In single-pulse modulation of PWM inverters, the pulse width is 120 . For an input voltage of 220 V dc, the r.m.s. value of output voltage is |
| A. | 179 63 V |
| B. | 254 04 V |
| C. | 127 02 V |
| D. | 185 04 V |
| Answer» B. 254 04 V | |
| 169. |
In single-pulse modulation of PWM inverters, fifth harmonic can be eliminated if pulse width is equal to |
| A. | 30 |
| B. | 72 |
| C. | 36 |
| D. | 108 |
| Answer» C. 36 | |
| 170. |
In single-pulse modulation of PWM inverters, third harmonic can be eliminated if pulse width is equal to |
| A. | 30 |
| B. | 60 |
| C. | 120 |
| D. | 150 |
| Answer» D. 150 | |
| 171. |
A single-phase bridge inverter delivers power to a series connected RLC load with R = 2 , L = 8 . For this inverter-load combination, load commutation is possible in case the magnitude of 1/ C in ohms is |
| A. | 10 |
| B. | 8 |
| C. | 6 |
| D. | zero |
| Answer» B. 8 | |
| 172. |
In sinusoidal PWM, there are m cycles of the triangular carrier wave in the half cycle of reference sinusoidal signal. If zero of the reference sinusoid coincides with zero/peak of the triangular carrier wave, then number of pulses generated in each half cycle are respectively |
| A. | (m 1)/m (b) |
| B. | (m 1)/(m 1) |
| C. | m/m |
| D. | m/(m 1) |
| Answer» B. (m 1)/(m 1) | |
| 173. |
In multiple-pulse modulation used in PWM inverters, the amplitude and frequency for triangular carrier and square reference signals are respectively 4 V, 6 kHz and 1 V, 1 kHz. The number of pulses per half cycle and pulse width are respectively |
| A. | 6, 90 |
| B. | 3, 45 |
| C. | 4, 60 |
| D. | 3, 40 |
| Answer» C. 4, 60 | |
| 174. |
In multiple-pulse modulation used in PWM inverters, the amplitudes of reference square wave and triangular carrier wave are respectively 1 V and 2 V. For generating 5 pulses per half cycle, the pulse width should be |
| A. | 36 |
| B. | 24 |
| C. | 18 |
| D. | 12 |
| Answer» D. 12 | |
| 175. |
In a 3-phase full converter, the output voltage pulsates at a frequency equal to |
| A. | supply frequency, f |
| B. | 2 f |
| C. | 3 f |
| D. | 6 f |
| Answer» E. | |
| 176. |
In circulating-current type of dual converter, the nature of voltage across reactor is |
| A. | alternating |
| B. | pulsating |
| C. | direct |
| D. | triangular |
| Answer» B. pulsating | |
| 177. |
The peak inverse voltage in ac to dc converter systems is highest in |
| A. | single-phase full-wave mid-point converter |
| B. | single-phase full converter |
| C. | 3-phase bridge converter |
| D. | 3-phase half-wave converter |
| Answer» B. single-phase full converter | |
| 178. |
In a 3-phase full converter, the output voltage during overlap is equal to |
| A. | zero |
| B. | source voltage |
| C. | source voltage minus the inductance drop |
| D. | average value of the conducting-phase voltages |
| Answer» E. | |
| 179. |
In a single-phase full converter, the output voltage during overlap is equal to |
| A. | zero |
| B. | source voltage |
| C. | source voltage minus the inductance drop |
| D. | inductance drop |
| Answer» B. source voltage | |
| 180. |
Controlled rectifiers |
| A. | 2 3 4 1 |
| B. | 1 3 4 2 |
| C. | 2 3 1 4 |
| D. | 2 1 4 3 |
| Answer» B. 1 3 4 2 | |
| 181. |
The effect of source inductance on the performance of single-phase and three-phase full converters is to |
| A. | reduce the ripples in the load current |
| B. | make discontinuous current as continuous |
| C. | reduce the output voltage |
| D. | increase the load voltage |
| Answer» D. increase the load voltage | |
| 182. |
A four quadrant operation requires |
| A. | two full converters in series |
| B. | two full converters connected back to back |
| C. | two full converters connected in parallel |
| D. | two semi converter connected back to back |
| Answer» C. two full converters connected in parallel | |
| 183. |
In a 3-phase semi converter, for firing angle less than or equal to 60 , each thyristor and diode conduct, respectively, for |
| A. | 60 , 60 |
| B. | 90 , 30 |
| C. | 120 , 120 |
| D. | 180 , 180 |
| Answer» D. 180 , 180 | |
| 184. |
In a 3-phase semiconverter, for firing angle less than or equal to 60 , freewheeling diode conducts for |
| A. | 30 |
| B. | 60 |
| C. | 90 |
| D. | zero degree |
| Answer» E. | |
| 185. |
In a 3-phase semiconverter, for firing angle equal to 120 and extinction angle equal to 110 , each SCR and diode conduct, respectively, for |
| A. | 30 , 60 |
| B. | 60 , 60 |
| C. | 90 , 30 |
| D. | 110 , 30 |
| Answer» C. 90 , 30 | |
| 186. |
Whan an UJT is used for triggering an SCR, the wave shape of the voltage obtained from UJT circuit is a |
| A. | sine wave |
| B. | saw-tooth wave |
| C. | trapezoidal wave |
| D. | square wave |
| Answer» C. trapezoidal wave | |
| 187. |
In an UJT, maximum value of charging resistance is associated with |
| A. | peak point |
| B. | valley point |
| C. | any point between peak and valley points |
| D. | after the valley point |
| Answer» B. valley point | |
| 188. |
In a 3-phase full converter, the six SCRs are fired at an interval of |
| A. | 30 |
| B. | 60 |
| C. | 90 |
| D. | 120 |
| Answer» C. 90 | |
| 189. |
In a 3-phase semiconverter, for firing angle equal to 90 and for continuous conduction, freeweeling diode conducts for |
| A. | 30 |
| B. | 60 |
| C. | 90 |
| D. | zero degree |
| Answer» B. 60 | |
| 190. |
A metal oxide varistor (MOV) is used for protecting |
| A. | gate circuit against overcurrents |
| B. | gate circuit against overvoltages |
| C. | anode circuit against overcurrents |
| D. | anode circuit against overvoltages |
| Answer» E. | |
| 191. |
The function of connecting a zener diode in an UJT circuit, used for the triggering of SCRs, is to |
| A. | expedite the generation of triggering pulses |
| B. | delay the generation of triggering pulses |
| C. | provide a constant voltage to UJT to prevent erratic firing |
| D. | provide a variable voltage to UJT as the source voltage changes |
| Answer» D. provide a variable voltage to UJT as the source voltage changes | |
| 192. |
An SCR can withstand a maximum junction temperature of 120 C with an ambient temperature of 75 C. If this SCR has thermal resistance from junction to ambient as 1 5 C/W, the maximum internal power dissipation allowed is |
| A. | 30 W |
| B. | 60 W |
| C. | 80 W |
| D. | 50 W |
| Answer» B. 60 W | |
| 193. |
For series connected SCRs, dynamic equalizing circuit consists of |
| A. | resistor R and capacitor C in series but with a diode D across C |
| B. | series R and D circuit but with across R |
| C. | series R and C circuit but with D across R |
| D. | series C and D circuit but with R across C |
| Answer» D. series C and D circuit but with R across C | |
| 194. |
Practical way of obtaining static voltage equalization in series-connected SCRs is by the use of |
| A. | one resistor across the string |
| B. | resistors of different value across each SCR |
| C. | resistors of the same value across each SCR |
| D. | one resistor in series with the string |
| Answer» D. one resistor in series with the string | |
| 195. |
A single-phase half-wave controlled rectifier has 400 sin 314 t as the input voltage and R as the load. For a firing angle of 60 for the SCR, the average output voltage is |
| A. | 400/ |
| B. | 300/ |
| C. | 240/ |
| D. | 200/ |
| Answer» C. 240/ | |
| 196. |
A resistor connected across the gate and cathode of an SCR increases its |
| A. | (i) Only |
| B. | (i) and (ii) Only |
| C. | (i), (ii) and (iii) Only |
| D. | (ii) and (iv) Only |
| Answer» D. (ii) and (iv) Only | |
| 197. |
Thyristors A has rated gate current of 2 A and thyristor B has rated gate current of 100 mA |
| A. | A is a GTO and B is a conventional SCR |
| B. | B is a GTO and A is a conventional SCR |
| C. | A may operate as a transistor |
| D. | B may operate as a transistor |
| E. | A and C both |
| Answer» F. | |
| 198. |
In a single-phase half-wave circuit with RL load, and a freewheeling diode across the load, extinction angle is more than . For a firing angle , the SCR and freewheeling diode would conduct, respectively, for |
| A. | , |
| B. | , |
| C. | , |
| D. | , |
| Answer» D. , | |
| 199. |
A single-phase one-pulse controlled circuit has resistance and counter emf load and 400 sin 314 t as the source voltage. For a load counter emf of 200 V, the range of firing angle control is |
| A. | 30 to 150 |
| B. | 30 to 180 |
| C. | 60 to 120 |
| D. | 60 to 180 |
| Answer» B. 30 to 180 | |
| 200. |
Turn-on time of an SCR can be reduced by using a |
| A. | rectangular pulse of high amplitude and narrow width |
| B. | rectangular pulse of low amplitude and wide width |
| C. | triangular pulse |
| D. | trapezoidal pulse |
| Answer» B. rectangular pulse of low amplitude and wide width | |