Controlled rectifiers

Question 1

What does scr stand for

Answer 1

Silicon controlled rectifier

Question 2

What is a rectifier

Answer 2

Its an electrical device that changes AC in to DC, by blocking the negative sine wave of one alteration. “

Question 3

What are the 3 leads of an scr

Answer 3

Cathode (k)
Anode (a)
Gate (g)

Question 4

What 3 configurations is an scr available in?

Answer 4

Flat puck or tab style
Stud mount
Puck style

Question 5

The threaded stud is the ___

The large flexible lead is the ___
The small wire is connected to the ___

The ___ is the smaller terminal or lead

Answer 5

Anode
Cathode
Cathode
Gate

Question 6

If the temperature exceeds the rating of the scr what is used?

Answer 6

Heat sink

Question 7

What material are Heat sinks generally made of

Answer 7

Aluminum

Question 8

Cathode connects to the ___ side of the cct

Anode connects to the ___ side of the cct

Gate connects connects to a ___

Answer 8

Negative

Positive

Triggering cct

Question 9

The structure of an scr can be described as

Answer 9

Two pn-junction diodes or two switches in series

Question 10

Applying a positive current pulse from the gate to the cathode turns on a scr.
What is that called and how long is it?

Answer 10

Gate pulse

10 micro seconds long

Question 11

What are three undesirable triggering of an scr?

Answer 11

Exceeding breakover voltage

Fluctuations in voltage

Temperature change

Question 12

What are two ways of commutating an scr

Answer 12

Natural commutating

Forced commutating

Question 13

5 things to consider when replacing an scr

Answer 13

Voltage
Power dissipation
Dv/dt
Gate current
Application

Question 14

What are the functions of an scr

Answer 14

Control the average voltage applied of a dc load from an ac source

Control the output voltage of an alternator

Act as a switch

Question 15

An scr can only turn on when it is?

Answer 15

Forward biased

Question 16

Firing angle plus conduction angle always equals?

Answer 16

180 degrees

Question 17

The ___ supplies the current to the field of an alternator

Answer 17

Exciter

Question 18

___ is desired when charging lead acid batteries

Answer 18

Tapered charge

Question 19

To have a battery charging current the charging voltage must be ___ than the battery voltage

Answer 19

Higher

Question 20

What is the name of a circuit used to prevent the undesirable triggering of an scr due to dv/dt

Answer 20

Snubbed circuit

Question 21

What does an avr do?

Answer 21

Controls the output voltage of an alternator

Question 22

An scr needs a pulse of current between __mA and __mA on the gate and the scr to be forward biased for the current to begin flowing

Answer 22

20

40

Question 23

___ diodes and ___ scrs are required in the controlled bridge tectifier

Answer 23

2

2

Question 24

When is a pulse transformer used?

Answer 24

Where isolation is needed

Question 25

What is the purpose of an isolation transformer in a pulse trigger circuit

Answer 25

To isolate the low voltage trigger circuit from the higher voltage scr circuit

Question 26

The initiating circuit of a fire alarm system operate with three levels of current. What are they

Answer 26

10 - 13 mA through an end if line resistor indicating normal condition Zero current indicating a broken wire High current through the low impedance path of a detector in alarm condition

Question 27

What is a triode or triac?

Answer 27

It's an ac solid state switch that conducts in both directions and requires gate trigger current

Question 28

A triac is equivalent to two scrs connected in?

Answer 28

Inverse parallel

Question 29

What breakover voltages are diacs typically in?

Answer 29

30v

Question 30

Can a diac conduct before it has 30v across it?

Answer 30

No

Question 31

In what kind of circuits are triacs used?

Answer 31

Ac