Deck 20: Thyristors and Optoelectronics Devices

Question 1

An SCR has a critical rise rating of 20 V/μs. The device is being used in a circuit where 10 ns rise time) noise signals randomly occur. What noise amplitude is needed to cause false triggering?

A) 200 nV
B) 200 μV
C) 200 mV
D) 20 V

Answer 1

200 mV

Question 2

UJTs are used almost exclusively as

A) breakover devices.
B) amplifiers.
C) thyristor triggering devices.
D) tuned oscillators.

Answer 2

thyristor triggering devices.

Question 3

A photo-detector has a sensitivity rating of 3 μA/mW/cm2. This means that

A) the forward current through the device will increase by 3 μA for every 1 mW/cm2 increase in light intensity.
B) the reverse current through the device will increase by 3 μA for every 1 mW/cm2 increase in light intensity.
C) the forward current through the device will increase by 3 μA for every 1 mW/cm2 decrease in light intensity.
D) the reverse current through the device will increase by 3 μA for every 1 mW/cm2 decrease in light intensity.

Answer 3

the reverse current through the device will increase by 3 μA for every 1 mW/cm2 increase in light intensity.

Question 4

The amount of light per unit area that is received by a photodetector is called

A) light intensity.
B) spectral wavelength.
C) light amplitude.
D) the light-area product.

Question 5

The silicon unilateral switch SUS) is forced into forward conduction when VAK exceeds the rating of the device.

A) forward conducting voltage
B) forward breakover voltage
C) forward trigger voltage
D) forward breakdown voltage

Question 6

Once an SUS is forced into forward conduction, it continues to conduct until IF drops below the rating of the device.

A) minimum forward current
B) forward breakover current
C) holding current
D) dropout current

Question 7

Quadrant I triggering of a triac similar to SCR triggering) is accomplished by applying a gate potential when MT2 is more than MT1.

A) positive; positive
B) positive; negative
C) negative; positive
D) negative; negative

Question 8

A PUT has a value of VGK = +8 V. What value of VAK is needed to trigger the device into conduction?

A) -8 V
B) +16 V
C) +8 V
D) Cannot be determined from the information given.

Question 9

A UJT has the following values: η = 0.72 maximum) and VBB = 12 V. What is the maximum value of VP required to trigger the device into conduction?

A) 8.64 V
B) 17.4 V
C) 12 V
D) 9.34 V

Question 10

A photodiode has a rating of s = 1200 nm. What is the optimum operating frequency for the device?

A) 250 THz
B) 400 THz
C) 250 × 1021 Hz
D) 120 THz

Question 11

The primary difference between the triac phase controller and the SCR phase controller is the fact that the triac circuit

A) requires a higher turn-on voltage.
B) allows conduction through the load during both alternations of the input cycle.
C) requires an added UJT to operate properly.
D) allows for higher load power ratings.

Question 12

What are the two methods that are commonly used to return an SUS to its nonconducting state?

A) Anode current interruption and forced commutation
B) Current holding and forced commutation
C) Anode current interruption and current holding
D) Forced commutation and current dropout

Question 13

False triggering can be prevented by a

A) damping network.
B) snubber network.
C) feedback network.
D) attenuating network.

Question 14

What is the wavelength of a 200 THz signal?

A) 50 pm
B) 6.7 × 10-5 nm
C) 1500 nm
D) 60 nm

Question 15

An object that blocks light is referred to as being

A) transparent.
B) translucent.
C) opaque.
D) solid.

Question 16

An SCR has a circuit fusing rating of 36 A2s. How long can the device withstand a 120 A surge?

A) 360 ms
B) 90 ms
C) 129.6 ms
D) 2.5 ms

Question 17

The forward operating curve of the SCR is identical to that for the SUS.

Question 18

An SCR has a circuit fusing rating of 28 A2s. Will the device be destroyed if it is subjected to a 25 A surge that lasts for 50 ms?

A) Yes
B) No

Question 19

The is commonly used to control triac triggering.

A) SUS
B) diac
C) SCR
D) JFET

Question 20

The primary difference between the diac and the SUS is the fact that

A) the diac has a higher maximum power dissipation rating.
B) the SUS is capable of conducting in only one direction.
C) the diac is no longer used in any practical applications.
D) the SUS requires the use of a snubber.

Question 21

Light current through a photodiode is generally less than dark current.

Question 22

The speed of light c) is .

A) 300 m/s
B) 3 × 10-18 cm/s
C) 3 × 10-17 nm/s
D) 186 m/s

Question 23

An optoisolator is a device that uses light to couple a signal from its input to its output.

Question 24

A phase controller is used to:

A) vary the average value of its load voltage.
B) prevent phase shift oscillations.
C) protect a voltage-sensitive load for excessive voltage.
D) eliminate false triggering.

Question 25

Optoelectronic devices are divided into two types:

A) light sensors and dark sensors
B) light emitters and dark emitters
C) light emitters and light detectors
D) diodes and transistors

Question 26

Photodiodes are normally biased.

A) forward
B) reverse
C) negatively
D) positively

Question 27

The solid-state relay contains an internal

A) optocoupler.
B) optointerrupter.
C) optoviewer.
D) optodivider.

Question 28

Irradiance is:

A) The term used to describe anything that passes light.
B) The forward current through a photo diode with an active light input.
C) The forward current through a photo diode with no active light source.
D) The amount of light per unit area received by a given photo detector.

Question 29

An optocoupler has an isolation source voltage VISO) rating of 5200 Vac. This rating means that

A) the device can handle a 5200 Vac input.
B) the device can provide an output voltage as high as 5200 Vac.
C) 5200 Vac applied across the input/output terminals of the device will destroy the component.
D) the device can be used to drive a 5200 Vac load.

Question 30

A crowbar is used to:

A) vary the voltage to a load.
B) prevent phase shift oscillations.
C) protect a voltage-sensitive load from excessive voltage.
D) eliminate false triggering.
Chapter 20 Thyristors and Optoelectronics Devices Answer Key