Deck 13: Thyristors

Question 1

The operation of a thyristor involves positive feedback.

Answer 1

True

Question 2

A gate voltage can turn an SCR on and off.

Answer 2

False

Question 3

An important application of the SCR is to protect delicate and expensive loads against overvoltages from a power supply.

Answer 3

True

Question 4

One way to overcome soft turn-on caused by the curved zener breakdown knee is to add voltage gain.

Question 5

With an SCR crowbar circuit,a fuse or current limiting is needed to prevent damage to the power supply.

Question 6

The only way to close a transistor latch circuit is by thermal runaway.

Question 7

The angle between the start and end of conduction of an SCR is the

A) conduction angle.
B) production angle.
C) trigger angle.
D) firing angle.

Question 8

The SCR is far more useful than a four-layer diode because the gate triggering is easier than breakover triggering.

Question 9

A transistor circuit that remains in either the closed or opened state indefinitely is referred to as a latch.

Question 10

The angle at which the SCR is triggered on is called the

A) conduction angle.
B) production angle.
C) trigger angle.
D) firing angle.

Question 11

The output of a comparator circuit is negative

A) when the inverting input is greater than the noninverting input.
B) when the noninverting input is greater than the inverting input.
C) when the supply voltage is positive.
D) when the supply voltage is negative.

Question 12

To avoid false triggering,what data sheet rating must not be exceeded?

A) critical rate of breakover
B) critical rate of current rise
C) critical rate of voltage rise
D) critical rate of triggering

Question 13

A transistor latching circuit is opened by increasing the supply voltage (V_CC).

Question 14

The silicon controlled rectifier is the most widely used thyristor.

Question 15

The only way to close a four-layer diode is by applying a trigger signal.

Question 16

Commercially available SCRs have anode currents that extend as high as ________.

A) 50 mA
B) 100 mA
C) 7 A
D) 70 A

Question 17

The ideal approximation of a four-layer diode is an open switch when cut off and a closed switch when saturateD.

Question 18

A silicon unilateral switch (SUS)is another name for the Schockley diode.

Question 19

The voltage gain of an IC comparator is typically about 100.

Question 20

A gate voltage can turn a power FET on and off.

Question 21

The triac can control current

A) in both directions.
B) in only one direction.
C) only if the gate voltage is negative.
D) only if it is dC.

Question 22

The IGBT is a

A) normally off high input impedance device.
B) normally off low input impedance device.
C) normally on high input impedance device.
D) normally on low input impedance device.

Question 23

The programmable unijunction transistor is considered programmable because

A) the gate voltage can be determined by an external voltage divider.
B) the gate voltage is programmed using software.
C) the anode can be modified by adding resistors.
D) the cathode can be modified by adding resistors.

Question 24

If a high-speed switching transient appears on the supply voltage,its rate of rise can be reduced by using a

A) zener diode
B) regulator circuit.
C) Schockley diode.
D) snubber circuit.

Question 25

IGBTs are effective solutions for

A) low voltage and current applications at moderate frequencies.
B) high voltage and current applications at moderate frequencies.
C) high voltage and current applications at low frequencies.
D) low voltage and current applications at high frequencies.

Question 26

What type of thyristors are the diac and triac?

A) two-layer device
B) unidirectional
C) bi-directional
D) unilateral

Question 27

A thyristor that is designed for easy opening with a reverse-biased trigger is the ________.

A) triac
B) SCR
C) gate-controlled switch
D) IGBT

Question 28

The diac is sometimes called a

A) dual inline ac device.
B) silicon bi-directional switch.
C) directional switch.
D) snubber.

Question 29

A low-power thyristor that can be triggered on or off is

A) an SCR.
B) a diaC.
C) an IGBT.
D) a silicon controlled switch.

Question 30

A four layer pnpn device used to produce trigger pulses and sawtooth waveforms is

A) a UJT.
B) an SCR.
C) an IGBT.
D) a PUT.

Question 31

What device is replacing UJTs and PUTs in many of their applications?

A) IGBT
B) power amp
C) MOSFET
D) op amp

Question 32

Commercial triacs have anode currents that extend as high as ________.

A) 100 mA
B) 500 mA
C) 1 A
D) 15 A

Question 33

A device that can be used to form a pulse generating circuit called a relaxation oscillator is

A) a UJT.
B) an SCR.
C) a silicon controlled switch.
D) a diaC.

Question 34

An SCR can be tested by using

A) an ammeter.
B) a voltmeter.
C) a curve tracer.
D) an ohmmeter.

Question 35

The triac acts like two

A) diacs in reverse parallel.
B) zeners in reverse parallel.
C) SCRs in reverse parallel.
D) JFETs in reverse parallel.

Question 36

A semiconductor device that uses internal feedback to produce switching action is a ________.

A) transistor
B) zener diode
C) thyristor
D) rectifier

Question 37

The diac is non-conducting until the

A) voltage across it exceeds the breakover voltage in either direction.
B) voltage across it goes below the breakover voltage.
C) gate triggers it on.
D) snubber turns it on.

Question 38

Analyzing and thinking in terms of functional blocks,or smaller jobs being done by different parts of the overall circuit is referred to as troubleshooting

A) a la cart.
B) at the component level.
C) at the system level.
D) by the numbers.

Question 39

Reducing the supply voltage,interruption,and forced commutation are all methods of accomplishing what?

A) turning on an SCR
B) turning off an SCR
C) turning on a Schockley diode
D) turning on a triac

Question 40

A hybrid device that combines the low conduction loss of a BJT with the switching speed of a power MOSFET is

A) a diaC.
B) an SCR.
C) a D-MOSFET.
D) an IGBT.

Question 41

What is the schematic symbol shown in Figure 13-34(a)?

A) laser
B) triac
C) photo-coupler.
D) photo-SCR

Question 42

A four-layer device,also called a pnpn diode,that allows current flow in only one direction was originally called

A) a triaC.
B) an SCR.
C) a Schockley diode.
D) a PUT.

Question 43

The only way to close a four-layer diode is by

A) applying a trigger.
B) reverse bias.
C) decreasing the supply voltage.
D) breakover.

Question 44

Which thyristor is the most widely used?

A) diac
B) triac
C) SCR
D) four-layer diode

Question 45

With an SCR crowbar,what else is needed to prevent damage to the power supply?

A) coupling capacitor
B) fuse
C) speakers
D) transformer

Question 46

The SCR is turned on by

A) gate voltage.
B) increasing anode voltage.
C) reducing anode voltage.
D) forced commutation.

Question 47

A transistor circuit that can remain in an open or closed state indefinitely is called

A) an amplifier.
B) a multiplexer.
C) a latch.
D) UJT.

Question 48

When light strikes the gate of the device shown in Figure 13-34(a)

A) +V_CC drops to zero.
B) R_L opens.
C) V_CC is dropped across R_L.
D) 0 V is dropped across R_L.

Question 49

An important application for the SCR is

A) amplification.
B) rectification.
C) power supply protection.
D) RF tuning.

Question 50

One method used to reduce the effects of SCR switching transients is by using

A) transformer coupling.
B) a snubber circuit.
C) a slow-blow fuse.
D) a comparator.