Silicon Controlled Rectifier

Question 1

What is an SCR?

Answer 1

Silicon Controlled Rectifier

Question 2

The name “silicon controlled rectifier” is General Electric’s trade name for a type of ______.

Answer 2

Thyristor

Question 3

SCRs are mainly used in electronic devices that reqire control of ____ voltage and power.

Answer 3

High

Question 4

How many layers of semiconductors does an SCR have?

Answer 4

4 layers

Question 5

Two structures formed within the SCR.

Answer 5

NPNP and PNPN

Question 6

What are the junctions of an SCR?

Answer 6

J1, J2, and J3

Question 7

What are the terminals of an SCR?

Answer 7

Anode, Cathode, Gate

Question 8

What are the modes of operation for an SCR depending upon biasing?

Answer 8

Forward Blocking Mode
Forward Conduction Mode
Reverse Blocking Mode

Question 9

Happens when anode is positive with respect to cathode and gate terminal is open.

Answer 9

Forward Blocking Mode

Question 10

What junction can’t current pass through in forward bias, forward blocking mode?

Answer 10

J2

Question 11

Two ways to bring SCR from blocking to conduction mode.

Answer 11

Increasing voltage between anode and cathode beyond the breakover voltage

Applying a positive pulse at the gate

Question 12

The gate voltage required to maintain an SCR in the ON state.

Answer 12

0

Question 13

The minimum current necessary to maintain SCR in the ON state.

Answer 13

Latching Current

Question 14

A thyristor is brought from forward blocking mode to forward conducting mode by applying required ______.

Answer 14

Gate Voltage

Question 15

Happens when negative voltage is applied to the anode and positive voltage to the cathode.

Answer 15

Reverse Blocking Mode

Question 16

If forward voltage is increase in forward blocking mode, what happens to the J2 junction?

Answer 16

Avalanche Breakdown

Question 17

An SCR incapable of blocking reverse voltage.

Answer 17

Asymmetrical SCR or ASCR

Question 18

Typical reverse breakdown rating of an ASCR

Answer 18

Tens of Volts

Question 19

Reverse conducting diodes used to fabricate ASCRs

Answer 19

RCT or reverse conducting thyristor

Question 20

Thyristor Turn On Methods

Answer 20

Forward-Voltage Triggering
Gate Triggering
Dv/Dt Triggering
Temperature Triggering
Light Triggering

Question 21

Occurs when the anode-cathode forward voltage is increased with the gate circuit opened.

Answer 21

Forward-voltage triggering

Question 22

Occurs when the thyristor should be in forward blocking state where the applied voltage is less than the breakdown voltage.

Answer 22

Gate Triggering

Question 23

Occurs when the width of depletion region decreases as the temperature is increased

Answer 23

Temperature Triggering

Question 24

During a rudimentary test of SCR, where do you put the red test lead?

Answer 24

Gate

Question 25

During a rudimentary test of SCR, where do you put the black test lead?

Answer 25

Cathode

Question 26

What should the ohmmeter show when doing a rudimentary test of SCR?

Answer 26

Continuity/OL

Question 27

"Normal" SCRs that are lacking an internal resistors are sometimes referred to as _____.

Answer 27

Sensitive Gate SCRs

Question 28

A circuit that consists of an SCR placed in parallel with the output of a DC power supply, for placing a direct short-circuit on the output of that supply to prevent excessive voltage from reaching the load.

Answer 28

Crowbar

Question 29

The electron tube version of an SCR

Answer 29

Thyratron

Question 30

An SCR that is specifically designed to be turned off by means of reverse triggering.

Answer 30

Gate-Turn-Off Thyristor (GTO)

Question 31

Thyristors are mainly used in devices where the control of ____ power, possibly coupled with ____ voltage is demanded.

Answer 31

high, high

Question 32

It is the minimum forward voltage, gate being open, at which SCR starts conducting heavily.

Answer 32

Breakover Voltage

Question 33

Commercially available SCRs have what range of breakover voltages?

Answer 33

50V to 500V

Question 34

It is the maximum reverse voltage that can be applied to an SCR without conducting in the reverse direction.

Answer 34

Peak Reverse Voltage

Question 35

It is the maximum anode current, gate being open, at which SCR is turned off from ON conditions.

Answer 35

Holding Current

Question 35

Commercially available SCRs have PRV ratings up to ___.

Answer 35

2.5kV

Question 36

It is the maximum anode current that an SCR is capable of passing without destruction.

Answer 36

Forward Current Rating

Question 37

Commercially available SCRs have forward current ratings of ___.

Answer 37

30A to 100A

Question 38

Indicates the maximum forward surge current capability of SCR.

Answer 38

Circuit Fusing Rating

Question 39

The ____ the firing angle, the ____ is the average current.

Answer 39

greater, smaller