Features of Silicon-Controlled Rectifiers (SCR's)

Question 1

How does the power handling ability of the SCR compare to that of a transistor?

Answer 1

SCR’s can handle more power

Question 2

How does the quantity of control power needed at the gate of an SCR compare to that required for the base of a transistor controlling the same load?

Answer 2

An SCR requires only a small fraction of the power a transistor would require.

Question 3

Name two advantages that an SCR has over a mechanical switch

Answer 3

No contact wear, pitting or corrosion. No contact bounce.

Question 4

In a stud-type SCR, how does the gate terminal compare in physical size to the anode and cathode terminals?

Answer 4

Gate terminal is the smallest terminal

Question 5

SCR’s are available with current ratings in the range of:

a. 1 to 10 A
b. 10 to 100 A
c. 100 to 1000 A
d. 0.25 to 1000+ A

Answer 5

d. 0.25 to 1000+ A (up to 4000A)

Question 6

In general, how does the physical size of an SCR relate to its current rating?

Answer 6

As current rating increases, physical size increases

Question 7

What is likely to happen if the SCR’s current rating is exceeded?

Answer 7

The SCR will overheat and will likely be permanently damaged

Question 8

What happens if the SCR’s reverse-blocking voltage is exceeded?

Answer 8

The SCR will conduct in the reverse direction and will be permanently damaged

Question 9

What happens if the SCR’s forward-blocking voltage is exceeded?

Answer 9

The SCR will turn on without a gate signal

Question 10

What terminal is commonly tied to the heat sink in the SCR?

Answer 10

Anode

Question 11

An SCR is a thyristor, but a thyristor is not necessarily an SCR. True or False?

Answer 11

True

Question 12

What happens to an SCR if the current drops below the holding current?

Answer 12

SCR will switch off

Question 13

How is the SCR turned on?

Answer 13

By applying a small amount of power to the gate terminal