Chapter 24: Thyristors
MULTIPLE CHOICE
1. ____ are the best known of the thyristors.
a.
SCRs
c.
DIACs
b.
TRIACs
d.
JFETs
2. A(n) ____ is basically a rectifier because it controls current in only one direction.
a.
DIAC
c.
TRIAC
b.
SCR
d.
JFET
3. The advantage of the ____ over a power transistor is that it can control a large current, dependent on
an external circuit, with a small trigger signal.
a.
JFET
c.
TRIAC
b.
DIAC
d.
SCR
4. To switch the SCR off, it is necessary to reduce the ____ voltage below the hold-on value, typically
close to zero.
a.
anode-to-cathode
c.
momentary gate
b.
positive input gate
d.
negative input gate
5. ____ are used primarily to control the application of DC and AC power to various types of loads.
a.
DIACs
c.
SCRs
b.
TRIACs
d.
MOSFETs
6. ____ conduct both directions of AC current flow.
a.
Rectifiers
c.
SCRs
b.
TRIACs
d.
MOSFETs
7. A(n) ____ can be used as an AC switch.
a.
TRIAC
c.
SCR
b.
DIAC
d.
MOSFET
8. The most frequently used triggering device is the ____.
a.
MOSFET
c.
TRIAC
b.
SCR
d.
DIAC
9. The ____ remains in the off state until an applied voltage in either direction is high enough to cause its
reverse-biased junction to break over and start conducting much like a zener diode.
a.
DIAC
c.
MOSFET
b.
TRIAC
d.
SCR
10. In testing DIACs with an ohmmeter, ____ resistance in either direction indicates that the device is not
opened (defective).
a.
zero
c.
low
b.
high
d.
infinite
COMPLETION
1. ____________________ refers to locking onto one of two stable states.
2. ____________________ is a method of obtaining an increased output by feeding part of the output
back to the input.
3. A TRIAC is equivalent to two SCRs connected in ____________________, back to back.
SHORT ANSWER
1. Describe the disadvantages of TRIACs when compared to SCRs.
2. Describe the most common use for DIACs.
