Deck 34: Thyristors

Question 1

Because a triac requires different gate currents for each mode of operation, it is ______________.

Answer 1

asymmetrical

Question 2

Some triacs have built-in ______________ which reduces the number of components and connections in some cases.

Answer 2

DIACs

Question 3

The ______________ transistor is a three-terminal semiconductor device that has only one p-n junction.

Answer 3

unijunction

Question 4

The ______________ standoff ratio of a UJT is usually designated as ? or eta.

Question 5

______________ can be designed to handle much higher load currents than triacs.

Question 6

Thyristors (can/cannot) be used for amplification.

Question 7

______________ are primarily used in power control circuits.

Question 8

An SCR differs from an ordinary rectifier diode in that the SCR will remain in a(n) ______________ state, although forward biased, until the forward breakover voltage is reached.

Question 9

The ______________ will automatically turn off when the anode voltage drops to zero or goes negative.

Question 10

A device that can control ac power, because it can conduct in either direction is called a(n) ______________.

Question 11

Which triac triggering mode is the most sensitive?

A) 1
B) 2
C) 3
D) 4

Question 12

What is often used in conjunction with a triac to ensure that the triggering time is the same for both the positive and negative alternation of the applied voltage?

A) zener diode
B) DIAC
C) RC circuit
D) LC tank circuit

Question 13

A three-terminal semiconductor device that has only one p-n junction is a(n)

A) JFET
B) triac
C) unijunction transistor
D) E-MOSFET

Question 14

The ratio ofto the interbase resistance, R_BB is called the

A) resistive interbase ratio
B) interbase standup ratio
C) intrinsic standoff ratio
D) intrinsic interbase ratio

Question 15

The UJT's intrinsic standoff ratio is usually designated as

A) ?
B) ?
C) ?
D) ?

Question 16

Beyond the valley points labeled I_V and V_V (in the saturation region), the UJT's resistance is

A) very low
B) very high
C) negative
D) positive

Question 17

What is the function of D₅ in the circuit shown in Figure 32-14?

A) rectifies ac
B) provides a positive trigger to the SCR
C) provides voltage for the UJT
D) provides ac to the load

Question 18

What component controls the frequency of the UJT relaxation oscillator?

A) D₄
B) D₅
C) R₂
D) R_T

Question 19

Semiconductor devices that are specifically designed for use in high-power switching applications are

A) MOSFETs
B) JFETs
C) thyristors
D) BJTs

Question 20

Which of the following is not an application of high-power thyristors?

A) heaters
B) welders
C) rf amplifiers
D) voltage regulators

Question 21

The region where the voltage drop across a DIAC decreases as the DIAC current increases is called

A) reverse bias region
B) negative resistance region
C) negative breakdown region
D) reverse resistance region

Question 22

A three-layer, two-junction semiconductor device that has only two leads is a(n)

A) SCR
B) zener diode
C) DIAC
D) JFET

Question 23

The DIAC is often used to provide a sharp trigger current pulse that can be used to turn on another thyristor known as a

A) SCR
B) silicon-controlled switch
C) triac
D) JFET

Question 24

A four-layer pnpn device with an anode, cathode, and gate is called a(n)

A) SCR
B) silicon-controlled switch
C) triac
D) JFET

Question 25

SCRs can safely handle anode currents from less than 1 A to

A) 5 A
B) 10 A
C) 100 A
D) 500 A

Question 26

Once an SCR is turned on by gate current, the gate

A) turns it off right away
B) turns it off after the time set up by R and C
C) loses all control
D) current must be removed

Question 27

A bi-directional semiconductor device that remains in a nonconducting state until the forward breakover voltage is reached is a(n)

A) DIAC
B) SCR
C) triac
D) E-MOSFET

Question 28

Which triac triggering mode is the most sensitive?

A) 1
B) 2
C) 3
D) 4

Question 29

Along with transistors and FETs, thyristors can be used for amplification.

Question 30

Thyristors are semiconductor devices that are specifically designed for use in high-power switching applications.

Question 31

Thyristors can operate only in the switching mode, where they act like either an open or closed switch.

Question 32

A DIAC is a three-layer, two-junction semiconductor device that has only two leads.

Question 33

A DIAC is referred to as a unidirectional diode thyristor because it can conduct current in only one direction.

Question 34

DIACs are primarily used in power control circuits.

Question 35

A silicon controlled rectifier is a four-layer pnpn device.

Question 36

An SCR operates in the same way as a rectifier diode.

Question 37

Low current SCRs resemble an ordinary transistor with three leads protruding from the body.

Question 38

SCRs can only handle anode currents of less than 1 A.

Question 39

The SCR remains in the on state as long as the anode current is greater than the holding current.

Question 40

When the SCR is turned on by the gate current, the gate current continues to control the SCR.

Question 41

The capacitor and resistor voltage in a series RC circuit are always 180° out of phase.

Question 42

SCRs can only conduct in one direction.

Question 43

A device that can control ac power, because it can conduct in either direction, is called a triac.