MCQ in Electronic Systems and Design Part 7 | ECE Board Exam

This is the Multiple Choice Questions in Electronic Systems and Design Part 7 of the Series as one of the Electronics Engineering Examination topic. In Preparation for the ECE Board Exam make sure to expose yourself and familiarize in each and every questions compiled here taken from various sources including but not limited to past Board Exam Questions in Electronics Engineering field, Electronics Books, Journals and other Electronics References.

MCQ Topic Outline included in ECE Board Exam Syllabi

6. Electronic Systems and Design

• MCQ in SCR’s, UJT, PUT, TRIAC, DIAC, and other Thyristors
• MCQ in Optoelectronic Devices and Sensors
• MCQ in Transducers, Data Acquisition, and Interfacing Techniques
• MCQ in Programmable Logic Controllers
• MCQ in Design and Integration in Building Management Systems and HVAC Controls,
  Security, Safety, and Surveillance Control Systems, and Audio-Video and Lighting
  Controls
• MCQ in Instrumentation and Control
• MCQ in Welding Systems
• MCQ in Robotic Principles
• MCQ in Bioelectrical Principles

Continue Practice Exam Test Questions Part 7 of the Series

Choose the letter of the best answer in each questions.

301. One type of circuit control device which may be manual, automatic or multi-contact

A. fuse

B. breaker

C. switch

D. relay

302. What are the primary methods of controlling electrical power?

A. by using manual switches and rheostats

B. by using variable reactance and transformers

C. by using electronic switches, such as diodes, transistors thyratrons, and thyristors

D. all of the above

303. Common method(s) of controlling electrical power with reactance

A. switching a tapped inductor

B. using a saturable reactor

C. by a matching transformer

D. A and B above

304. A reactive device used in controlling electrical power by using two windings on a common iron core. The control winding is supplied with small dc-current which causes the reactance of large ac-winding to change accordingly.

A. tapped inductor

B. saturable reactor

C. auto transformer

D. LVDT

305. A saturable reactor with regenerative feedback.

A. tapped inductor

B. auto transformer

C. LVDT

D. magnetic amplifier

6. Thyratrons in industrial electronics refers to ____________.

A. a gas-filled diode

B. a vacuum tube

C. gas-filled triode

D. an electron triode

307. An electronic switch that has the highest single-device current capacity and can withstand overloads better.

A. Thyristors

B. ignitrons

C. SCR

D. triac

308. A semiconductor, electronic switch that has the highest single-device current rating

A. thyristor

B. triac

C. SCR

D. Quadric

309. The purpose of installing thyrectors across the incoming power lines to the speed control system is to ___________.

A. cause the motor to caution

B. protect drive circuits from high voltage transient surges

C. increase the counter emf

D. allow the field winding current to continue flowing

310. Semiconductor devices equivalent to thyratrons are generally called

A. thyrector

B. thyristor

C. diac

D. ignitron

11. Using electronic devices as switches, what is(are) the general methods of controlling electrical power?

A. phase control

B. zero-voltage switching

C. static switching

D. all of the above

312. Which power control switching method that greatly generates RFI or EMI and is therefore limited to low-frequency applications?

A. phase control

B. zero-voltage switching

C. inverter control

D. static switching

313. One of the electronic semiconductor devices known as diac, function as

A. four terminal multi-directional switch

B. two terminal bi-directional switch

C. two terminal unidirectional switch

D. three terminal bi-directional switch

314. Which of the trigger diodes has the highest holding voltage?

A. bidirectional-trigger diac

B. bidirectional-diode-thyristor diac

C. Shockley diode

D. thyrector

315. General term of electronic devices used to control or trigger large-power switching devices.

A. thyristor

B. thyrector

C. break-over devices

D. triggering devices

316. A break-over device that is basically a diode.

A. thyristor

B. thyrector

C. thyratron

D. triggering diode

317. A four-element solid state device that combi9nes the characteristics of both diodes and transistors

A. varactor

B. zener diode

C. tunnel diode

D. SCR

318. The most popular thyristor used in electrical power controllers

A. SCR

B. triac

C. SCS

D. PUT

319. Find the two stable operating conditions of an SCR.

A. Conducting and non-conducting

B. Oscillating and quiescent

C. NPN conduction and PNP conduction

D. Forward conducting and reverse conducting

320. How do you stop conduction during which SCR is also conducting?

A. remove voltage gate

B. increase cathode voltage

C. interrupt anode current

D. reduce gate current

321. How do we turn “ON” or trigger an SCR?

A. by making the gate (G) positive with respect to its cathode (K)

B. by making the gate (G) positive with respect to its anode (A)

C. by making the cathode more positive with respect to the anode

D. A and C above

322. What is true about SCRs after they are being switched “ON”?

A. The anode (A) to cathode (K) continues to conduct even if the gate triggering voltage is removed.

B. The gate (G) must be provided with the required holding current to continue its conduction.

C. A small holding voltage at the gate is required for a continuous conduction.

D. B and C above

323. The voltage across the anode (A) and cathode (K) terminals of an SCR when conducting.

A. holding voltage

B. breakdown voltage

C. breakback voltage

D. trigger voltage

324. The minimum amount of current needed for an SCR to conduct continuously.

A. holding current

B. triggering current

C. threshold current

D. average sustaining current

325. What is(are) the condition(s) in triggering SCR?

A. The gate voltage must be equal to or greater than the triggering voltage.

B. The gate current must be equal to or greater than the triggering current.

C. The anode (A) must be positive with respect to the cathode.

D. all of the above

326. The voltage decreased across the anode (A) and cathode (K) of an SCR from non-conducting state to conducting state.

A. holding voltage

B. forward breakdown voltage

C. triggering voltage

D. breakback voltage

327. An SCR rated 10 A is used as the controlling switch in a circuit powered by 50Vdc. When the SCR fires ON, its anode (A) to cathode (K) voltage was observed to be 2 V. Calculate the breakback voltage of the SCR.

A. 25 Vdc

B. 32 Vdc

C. 41 Vdc

D. 48 Vdc

328. The needed voltage at the gate of an SCR before it conducts.

A. minimum-gate trigger voltage

B. maximum-gate trigger voltage

C. minimum-gate peak-inverse voltage

D. maximum-gate peak-inverse voltage

329. What is(are) the gate limitation(s) of SCRs and triacs?

A. maximum-gate power dissipation

B. maximum-gate peak-inverse voltage

C. maximum-gate trigger current and voltage

D. all of the above

330. How can we extend the rating of SCRs?

A. by external cooling

B. by external circuitry

C. by connecting them in series/parallel

D. all of the above

331. Use of heat sinks, forced air, and water cooling are examples of external cooling in SCRs and other devices. Which of these is the only recommended to be used for the largest power dissipating device?

A. metal heat sinks

B. forced air

C. water cooling

D. A and B above

332. How can we increase the forward-voltage blocking capability of SCRs?

A. by connecting them in series

B. by connecting them in parallel

C. by cascading them

D. by connecting back to back in parallel

333. In connecting two SCRs in series, during “OFF” state, the voltage source must be properly shared between them, but due to devices’ differences, there might be unequal voltages across each SCR. How do we equalize these voltages?

A. by installing a snubber circuit

B. by adding a gate-to-cathode resistor

C. by shunting a capacitor across the anode (A) and cathode (K) of each SCR

D. by using a blocking-equalizing resistor

334. What is true regarding blocking-equalizing resistors in SCRs connected in series?

A. Blocking-equalizing resistors are shunted across each SCR.

B. The value of these resistors is about 10% of the value of the blocking resistance of the SCR it is shunted with.

C. These resistors increases the leakage current towards the load.

D. All of the above

335. A circuit used for voltage equalization during ON-OFF switching action of SCRs in series.

A. snubber circuit

B. crow-bar

C. clipper

D. clamper

336. When a high current is needed, SCRs are connected in parallel. The problem with paralleled SCRs is, when they are not perfectly matched, one will conduct first before the other and carries the full-load current that is for sure greater than its maximum rating. To avoid this situation, both SCRs should be turned ON at the same time. How can we do this?

A. by using high triggering gate voltage

B. by using a gate-triggering transformer

C. by using reactors

D. all of the above are possible

337. In controlling electrical power using phase control method with SCR/triac being the active device, what do we call the period of the cycle before the device switches to conduction?

A. trigger time

B. trigger delay time

C. firing frequency

D. firing delay angle

338. How many times per second does an SCR is turned ON and OFF when it is operated in a full-wave phase control at a line frequency of 60 Hz?

A. 30 times

B. 60 times (HV)

C. 90 times

D. 120 times (FW)

339. A three terminal device that behaves roughly like SCR, except that it can conduct current in either direction when at ON.

A. thyristor

B. SUS

C. SBS

D. GTO

340. What is the difference between a triac and a silicon bilateral switch (SBS)?

A. An SBS is usually used as breakover device, while a triac is a load controlling device.

B. An SBS is for low voltage applications, while a triac is generally for high voltage applications.

C. An SBS has better and stable symmetrical-firing voltage than a triac.

D. all of the above

341. A triac can be triggered ON by the application of a

A. positive voltage at the gate with respect to MT1

B. negative voltage at the gate with respect to MT1

C. positive or negative gate voltage with respect to MT2

D. all of the above are correct

342. Which are the three terminals of a TRIAC?

A. Gate, anode 1 and anode 2

B. Gate, source and sink

C. Base, emitter and collector

D. Emitter, base 1 and base 2

343. What are the three terminals of a triac?

A. anode 1 (A1), anode 2 (A2) and gate (G)

B. mainterminal 1 (MT1), mainterminal 2 (MT2), and gate (G)

C. anode (A), cathode (K) and gate (G)

D. both A and B are acceptable

344. A silicon bilateral switch may be considered as s small power triac, and has three terminals namely,

A. anode 1 (A1), anode 2 (A2) and gate (G)

B. mainterminal 1 (MT1), mainterminal 2 (MT2), and gate (G)

C. anode (A), cathode (K) and gate (G)

D. both A and B are acceptable

345. A thyristor that is very similar to an SCR except that it has low voltage and current ratings. It is very temperature stable, and is therefore suitable to be used as triggering

device.

A. UJT

B. GTO

C. SBS

D. SUS

346. Silicon unilateral switches (SUSs) generally have a breakover voltage of 8 V, however, this value can be altered by normally connecting a zener diode. How is the diode installed?

A. across the gate (G) and cathode (K) terminals, with the diode’s anode at the gate

B. anode to anode, cathode to cathode

C. diode’s cathode to SUS’s anode and diode’s anode to SUS’s cathode

D. diode’s cathode to SUS’s gate and diode’s anode to SUS’s cathode

347. A silicon unilateral switch (SUS) has a forward breakover voltage of 8 V. a zener diode is connected between its gate and cathode terminals with the diode’s cathode at SUS’s gate. If the zener voltage is 3.9 V, what is the new forward breakover voltage of the device?

A. 0.49 V

B. 2.05 V

C. 4.50 V

D. 11.9 V

348. Thyristor whose characteristic curve closely resembles that of SCR’s and SUS’s, except that its forward breakover voltage (+VBO) is not alterable, for the device has no gate terminal.

A. diac

B. thyrector

C. UJT

D. Shockley diode

349. What will happen to the forward breakdown or breakover voltage of SCRs and triacs if the gate current is increased?

A. will decrease

B. will also increase

C. will not change

D. will either increase or decrease, it depends on their current coefficient

350. A UJT or unijunction transistor is a three terminal breakover-type switching device. Its three terminals are called base 1, base 2, and emitter. Though this is a transistor and has base and emitter terminals, this operates very different from a BJT and is not used as a linear amplifier. Its applications are for

A. timers and oscillators

B. signal generators

C. triggering control for SCRs and triacs

D. all of the above

Questions and Answers in Electronic Systems and Design

Following is the list of multiple choice questions in this brand new series:

Complete List of MCQ in Electronics Engineering per topic