Part 5

B

For an SCR, dv/dt protection is achieved through the use of:</>

A. RL in series with SCR

B. RC across SCR

C. L in series with SCR

D. RC in series with SCR

A

A technique use to turn off a thyristor using an external circuit which causes the anode to become negatively biased.

A. force commutation

B. reverse triggering

C. negative feedback

D. doping

C

The turn-off time of thyristor is 30 m sec at 50°C. Its turn-off time at 100° is

A. same

B. 15 m sec

C. 60 m sec

D. 100 m sec

A

The peak and valley currents of the PUT are typically ___________ those of a similarly rated UJT.

A. lower than

B. the same as

C. higher than

D. None of the above

C

What is a solid state equivalent of a gas filled triode?

A. Triac

B. Thyristor

C. SCR

D. SCS

C

The method(s) for turning off an SCR is (are) categorized as ___________.

A. current interruption

B. forced commutation

C. both current interruption and forced commutation

D. None of the above

B

In a certain UJT rB1 is 2.5 kΩ and rB2 = 4 kΩ. What is the intrinsic standoff ratio?

A. 0.61538

B. 0.38461

C. 2.6

D. 0.8125

A

When SCR starts conducting, then __________ losses all control.

A. gate

B. anode

C. cathode

D. anode supply

B

You have the schematic diagram of several types of circuits. Which of these circuits most likely uses a triac?

A. an oscillator

B. an ac motor control

C. a programmable oscillator

D. an amplifier

D

Determine RB1 for a silicon PUT if it is determined that h = 0.84, VP = 11.2 V, and RB2 = 5 kΩ.

A. 12.65 kΩ

B. 16.25 kΩ

C. 20.00 kΩ

D. 26.25 kΩ

C

Which of the following devices does not have a cathode terminal?

A. SCR

B. SCS

C. TRIAC

D. Shockley diode

B

The UJT operates in what region after peak point?

A. Cut off

B. Negative resistance

C. Saturation

D. Positive resistance

A

What is basically a two-terminal parallel-inverse combination of semiconductor layers that permits triggering in either direction?

A. DIAC

B. TRIAC

C. QUADRAC

D. Shockley Diode

D

Which device does not have a gate terminal?

A. Triac

B. SCR

C. FET

D. Diac

A

The four-layer devices with a control mechanism are commonly referred to as ___________.

A. thyristors

B. transistors

C. diodes

D. None of the above

B

What is that voltage above when the SCR enters the conduction region?

A. Reverse breakover voltage

B. Forward breakover voltage

C. Holding voltage

D. Trigger voltage

C

It is a three-terminal silicon diode with the ability to control a large ac power with a small signal.

A. TRIAC

B. SCR

C. UJT

D. SCS

D

The smallest amount of current that the cathode-anode can have, and still sustain conduction of an SCR is called the:

A. maximum forward current

B. maximum forward gate current

C. holding current

D. reverse gate leakage current

D

It is the minimum additional current that can make up for any missing input (gate) current in order to keep the device ON.

A. leakage current

B. ac current

C. holding current

D. switching current

A

The PUT (programmable unijunction transistor) is actually a type of:

A. UJT thyristor

B. FET device

C. TRIAC

D. SCR

D

What is the typical value of the interbase resistance of UJTs?

A. 20 KΩ

B. Between 4 to 4 KΩ

C. 4 KΩ

D. Between 4 to 10 KΩ

A

Which of the following is a four-layer diode with an anode gate and a cathode gate?

A. SCS

B. SCR

C. SBS

D. SUS

D

SCR is a rectifier constructed of silicon material. Silicon is chosen because

A. it is the most abundant material

B. of its strength and ruggedness

C. it is much cheaper than any other material

D. of its high temperature and power capabilities

C

When the temperature increases, the intrinsic standoff ratio

A. increases

B. decreases

C. essentially constant

D. becomes zero

C

SCRs have been designed to control powers as high as ___________, with individual ratings as high as ___________ at __________.

A. 1800 MW, 10 A, 2000 V

B. 1800 MW, 2000 A, 10 V

C. 10 MW, 2000 A, 1800 V

D. 2000 MW, 10 A, 1800 V

C

An SCR is a member of what family?

A. Thyrector

B. Thyratron

C. Thyristor

D. Transistor

B

Which of the following can change the angle of conduction in SCR?

A. Changing anode voltage

B. Changing gate voltage

C. Reverse biasing the gate

D. Changing cathode voltage

B

What is the frequency range of application of SCRs?

A. About 10 kHz

B. About 50 kHz

C. About 250 kHz

D. About 1 mHz

C

he minimum operating voltage of the UJT is typically ____________ that of a similarly rated PUT.

A. lower than

B. the same as

C. higher than

D. None of the above

A

A UJT is sometimes called a ___________ diode.

A. double-based

B. single-based

C. a rectifier

D. a switching diode

D

It is like a low current SCR with two gate terminals.

A. UJT

B. PUT

C. SCR

D. SCS

D

What is the typical value of the reverse resistance of SCRs?

A. 1 Ω to 10 Ω

B. 100 Ω to 1 kΩ

C. 1 kΩ to 50 kΩ

D. 100 kΩ or more

A

Which of the following is the normal way to turn on a diac?

A. By breakover voltage

B. By gate voltage

C. By gate current

D. By anode current

D

In a SCR circuit, the angle of conduction can be changed by changing

A. anode voltage

B. anode current

C. forward current rating

D. gate current

A

The function of snubber circuit connected across the SCR is to:

A. Suppress dv/dt

B. Increase dv/dt

C. Decrease dv/dt

D. Decrease di/dt

A

An SCR is made of what material?

A. Silicon

B. Carbon

C. Germanium

D. Gallium-arsenide

A

The SCR can exercise control over ____________ of ac supply.

A. positive or negative half-cycle

B. both positive and negative half-cycles

C. only positive half-cycle

D. only negative half-cycle

A

Which of the following conditions is necessary for triggering system for thyristors?

A. It should be synchronized with the main supply

B. It must use separate power supply

C. It should provide a train of pulses

D. None of these

B

A normally operated SCR has an anode which is ___________ with respect to cathode.

A. negative

B. positive

C. at zero potential

D. at infinite potential

D

Which of the following devices has (have) four layers of semiconductor materials?

A. Silicon-controlled switch (SCS)

B. Gate turn-off switch (GTO)

C. Light-activated silicon-controlled rectifier (LASCR)

D. All of the above

C

How many pn junction does SCRs have?

A. Two

B. Four

C. Three

D. Five

C

The silicon-controlled switch (SCS) is similar in construction to the

A. triac.

B. diac.

C. SCR.

D. 4-layer diode.

B

Which of the following devices has nearly the same turn-on time as turn-off time?

A. SCR

B. GTO

C. SCS

D. LASCR

D

Which of the following is (are) the advantages of the SCS over a corresponding SCR?

A. Reduced turn-off time

B. Increased control and triggering sensitivity

C. More predictable firing situation

D. All of the above

B

An effect that reduces the possibility of accidental triggering of the SCS.

A. Miller effect

B. Rate effect

C. End effect

D. Flywheel effect

D

An SCR whose state is controlled by the light falling upon a silicon semiconductor layer of the device.

A. SCS

B. GTO

C. Thyristor

D. LASCR

D

Power electronics deals with the control of ac power at what frequencies essentially?

A. 20 KHz

B. 1000 KHz

C. Frequencies less than 10 Hz

D. 60 Hz frequency

A

To turn on the UJT, the forward bias on emitter diode should be __________ the peak point voltage.

A. more than

B. less than

C. equal to

D. twice

C

What is the resistance of a certain 4-layer diode in the forward-blocking region if VAK = 15 V and IA = 1 uA

A. 15 Ω

B. 21.21 MΩ

C. 15 M Ω

D. 10.61 MΩ

C

What is the peak-point voltage for the UJT in problem 76 if VBB = 15 V?

A. 10.605

B. 5.76912

C. 6.46915

D. 0.8125