THYRISTORS

Question 1

(also known as Shockley diode and SUS) is a type of thyristor, which
is a class of devices constructed of four semiconductor layers.

Answer 1

4-Layer Diode

Question 2

The operation of the 4-layer diode may seem unusual because when it is forward-biased, it can act essentially as an open switch.

Answer 2

Forward-Breakover Voltage

Question 3

There is a region
of forward bias, called the _______ , in which the device has a very high forward resistance (ideally an open) and is in the off state.

Answer 3

Forward-blocking region

Question 4

Once the 4-layer diode is conducting (in the on state), it will continue
to conduct until the anode current is reduced below a specified level, called the

Answer 4

Holding Current

Question 5

The value of the anode current at the point where the device switches from the forward-blocking region (off) to the forward-conduction region (on) is
called the

Answer 5

Switching Current

Question 6

is a 4-layer pnpn device similar to the 4-layer diode except with three terminals: anode, cathode, and gate.

Answer 6

SCR (silicon-controlled rectifier)

Question 7

are types of thyristors that can conduct current in both directions (bilateral).

Answer 7

DIAC & TRIAC

Question 8

The difference between the two devices is that a ____ has two terminals, while a ____ has a third terminal, which is the gate for triggering.

Answer 8

diac, triac

Question 9

It functions basically like two parallel 4-layer diodes turned in opposite directions.

Answer 9

Diac

Question 10

It functions basically like two parallel SCRs turned in opposite directions with a
common gate terminal.

Answer 10

Triac

Question 11

A triac can be turned on by a _______ and does not require the breakover voltage to initiate conduction, as does the diac.

Answer 11

Pulse of gate current

Question 12

is a four-terminal thyristor that has two gate terminals that are used to trigger the device on and off.

Answer 12

SCS (silicon-controlled switch)

Question 13

It does not belong to the thyristor family because it does not have a four-layer type of construction.

Answer 13

Unijunction Transistor (UJT)

Question 14

The term ______ refers to the fact that
the UJT has a single pn junction.

Answer 14

Unijunction

Question 15

is a four-terminal thyristor that has two gate terminals that are used to trigger the device on and off.

Answer 15

SCS (silicon-controlled switch)