Electronics; Controlled Rectifiers Objective 1

Question 1

When are tab style SCRs typically used?

Answer 1

Low current circuits from 2 amps to 20 amps

Question 2

What “family” of electronic devices do SCRs belong?

Answer 2

Thyristor

Question 3

The threaded stud is generally the __________ (anode/cathode/gate) on most SCRs

Answer 3

Anode

Question 4

What kind of SCR is usually used in medium power circuits?

Answer 4

Stud mount SCRs

Question 5

What type of SCR is generally used for very large power circuits?

Answer 5

Hockey puk

Question 6

What is the threaded stud of a stud mount SCR connected to?

Answer 6

Directly to the heat sink

Question 7

What happens when an SCR gets too hot?

Answer 7

Break over voltage will be reduced

Question 8

What ate heat sinks usually made of?

Answer 8

Aluminum

Question 9

What does silicon grease do in an SCR application?

Answer 9

Provides heat transfer from SCR to heat sink

Question 10

What is the gate of an SCR connected to?

Answer 10

A triggering circuit that controls the SCR

Question 11

What does triggering an SCR mean?

Answer 11

Current pulse applied to gate to make it start conducting

Question 12

What is gating or firing?

Answer 12

Another names for triggering

Question 13

What is commutation with regards to SCRs

Answer 13

Turning off

Question 14

When can an SCR trigger?

Answer 14

1) when its forward biased (anode positive with respect to cathode)
2) current pulse applied from gate to cathode (gate positive with respect to cathode)

Question 15

How long does an SCR stay turned on?

Answer 15

As long as the current from anode to cathode is equal to or greater than a specified value. (HOLDING CURRENT)

Question 16

What is the holding current value for most SCRs?

Answer 16

1mA per ampere of the rated anode current

I(t(av))

Question 17

How long is a positive current pulse?

Answer 17

10 microseconds

Question 18

How much current is required in a “positive current pulse” to turn on an SCR?

Answer 18

5× the minimum gate current rating

Question 19

What normally dictates the value of gate current?

Answer 19

The current rating of the SCR

Question 20

What can be used to prevent gate burnout from excess current?

Answer 20

Resistor in series with the gate

Question 21

How can you accidently trigger an SCR?

Answer 21

Exceed breakover voltage
Fluctuations in voltage
Temperature changes

Question 22

What is an RC snubber circuit?

Answer 22

Paralleled resistor and capacitor used to limit the rate at which the voltage can increase

Question 23

What is dv/dt

Answer 23

Rate of change of voltage

Question 24

At what voltage could an SCR falsely gate?

Answer 24

0.7V

Question 25

What is the problem with heat in semiconductor devices?

Answer 25

Heat can cause leakage current

Question 26

How much leakage current can result from a 10°C of temperature rise?

Answer 26

Leakage current doubles

Question 27

What happens when leakage current = gate current?

Answer 27

Scr will turn on

Question 28

At what point is breakover voltage reached when gate current is provided?

Answer 28

Gate voltage is never reached in this situation

Question 29

What is the dynamic repetitive maximum?

Answer 29

The maximum or peak operating voltage