Controlled Rectifiers Flashcards

1
Q

What are the three leads of an SCR?

A

Cathode (K)
Anode (A)
Gate (G)

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2
Q

Name some of the different types of an SCR:

A

Flat Pac or Tab Style
Stud Mount
Puk Style

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3
Q

What are heat sinks generally made of?

A

Aluminium

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4
Q

An RC snubber circuit is connected across the SCR to limit the rate at which the voltage can increase. T or F?

A

True

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5
Q

What does Vdrm stand for?

A

The dynamic repetitive maximum (Vdrm)

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6
Q

When replacing SCRS, you need to consider what five factors?

A

Voltage rating
Power dissipation
Dv/Dt rating
Gate current rating
Application

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7
Q

Controlling the average voltage is called what?

A

Phase Control

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8
Q

To operate a dc motor above base speed, the current through the field winding must be reduced. T or F?

A

True

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9
Q

Most alternators or ac gen-sets, are equipped with rotating exciters, usually a brushless type. T or F?

A

True

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10
Q

The voltage a zener diode conducts is called the Zener voltage and it only conducts in forward bias under certain conditions. T or F?

A

False, the zener voltage conducts in reverse bias under certain conditions.

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11
Q

A saturated charge is desired when charging lead-acid batteries. T or F?

A

False. A tapered charge is desired.

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12
Q

An RC time delay circuit is an effective gate for an SCR. T or F?

A

True

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13
Q

How does a pulse trigger circuit control an SCR?

A

By providing a current pulse of sufficient magnitude and duration to trigger the gate of the SCR, turning it on

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14
Q

What components are required for a controlled-bridge rectifier?

A

Two diodes and two SCRS

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15
Q

Name some of the examples of circuits that are used to provide trigger pulses to SCRS?

A

Integrated circuits
Digital circuits
Ramp generator
Comparator circuits

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16
Q

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

A

To isolate the low-voltage trigger circuit from the higher-voltage SCR circuit

17
Q

What are the 3 current levels that may be measured in a convention fire alarm initiating circuit?

A

10-13mA through an end of line resistor- normal
Zero current - broken wire/trouble
High current - through low Z path of a detector alarm condition

18
Q

A triac is an AC solid state switch that conducts in both directions. T or F?

A

True

19
Q

Since the triac is used in ac circuits, what is it commutated with?

A

Class F commutation

20
Q

How is phase control of triacs accomplished?

A

By connecting a variable triggering circuit to the gate

21
Q

Two common applications of Triacs are

A

Lighting dimmers
Small ac motor speed control

22
Q

What single-phase motors are capable of speed control using the phase-control method?

A

Shaded-pole
Permanent-split capacitor motors

23
Q

In order to have consistent triggering, what must the polarity of the gate be when T2 is negative?

A

Negative

24
Q

What ratings determine the size of a Triac?

A

The current IT and voltage rating (Vdrm)

25
Q

What does SCR stand for?

A

Silicon Controlled Rectifier

26
Q

What material is the Gate made out of?

A

P-Type material

27
Q

What are two differences you can see when looking at an SCR and a TRIAC?

A

They look the same.

Except for…
- Their Part Number
- Their Ratings

TRIAC’s have smaller ratings.