Controlled Rectifiers

Question 1

how many degrees does a SCR Conduct for?

Answer 1

180°

Question 2

a triac can be turned off by reversing the polarity of the pulse to the gate?
(T or F)

Answer 2

False

Question 3

what is the difference between a triac and SCR?

Answer 3

current in the triac is bi-directional

Question 4

what is a diac mainly for?

Answer 4

trigger triac

Question 5

a SCR conducts current in how many directions?

Answer 5

1

Question 6

when more load is added to a cap filtered cct the percent ripple would? (increase, decrease)

Answer 6

increase

Question 7

what conditions must exist in order to properly trigger a silicon controlled rectifier?

Answer 7

1. forward bias

2. positive gate pulse

Question 8

what are 3 ways to turn off (commutate) an SCR?

Answer 8

1. natural
2. forced
3. frequency or AC

Question 9

in a class B fire alarm system what are the three conditions of a smoke detector?

Answer 9

• normal(low current 10-13 mA)
• trouble (no current)
• alarm (high current)

Question 10

FA+CA=180°. FA=R×C T or F

Answer 10

true

Question 11

what is the current limit of a triac?

Answer 11

40mA

Question 12

what is the typical breakover voltage of a DIAC?

Answer 12

(+/- ) 30Volts

Question 13

what is the name of a cct used to prevent undesirable triggering of an SCR due to dv/dt?

Answer 13

RC snubber

Question 14

what is commutation of an SCR?

Answer 14

turning off the SCR

Question 15

what is the name of the process of controlling the average voltage with an SCR?

Answer 15

phase contol

Question 16

what is the name of a rectifier that is made by replacing two diodes in a bridge rectifier with two SCRs

Answer 16

a controlled bridge rectifier (hybrid)

Question 17

what does an AVR do

Answer 17

controls the output voltage of an alternator

Question 18

in an RC timing trigger circuit what controls the capacitor charge rate

Answer 18

a variable resistor

Question 19

why do additional pulses within a cycle not have an effect on the SCR

Answer 19

the SCR is already triggered and is conducting

Question 20

what is the purpose of the isolation Transformer in a pulse trigger circuit

Answer 20

to isolate the low voltage trigger circuit from the higher voltage SCR circuit

Question 21

what are the advantages of using SCRs over conventional controlling or switching methods

Answer 21

no arcing,
no moving parts,
less power dissipated

Question 22

which device acts like two SCRs connected in a inverse parallel configuration

Answer 22

Traic

Question 23

what is the recommended method of triggering an SCR

Answer 23

positive gate pulse

Question 24

what are three undesirable methods of triggering an SCR

Answer 24

1. exceeding break over voltage
2. fluctuations in voltage
3. temperature changes