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4th Year Electrical - Electronics > Controlled Rectifiers > Flashcards

Controlled Rectifiers Flashcards

1
Q

What are the names of the three (3) terminals of an SCR?

A
  • anode
  • cathode
  • gate
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2
Q

What are the two (2) requirements for an SCR to turn on and conduct?

A

Forward Bias

Positive gate pulse

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3
Q

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

A

Snubber circuit

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4
Q

What is commutation of an SCR?

A

Turning off an SCR

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5
Q

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

A

Phase control

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6
Q

What is the name of a rectifier that is made by replacing two diodes in a bridge rectifier with two SCR’s?

A

Controlled-Bridge Rectifier

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7
Q

What does an AVR do?

A

Controls the output voltage of an alternator

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8
Q

Three configurations of SCRs are

A
  • Flat pac or tab style (low current 2-20A)
  • stud mounted (medium power)
  • put style (large power)
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9
Q

Three ways of accidentally triggering an SCR

A
  • exceeding break over voltage
  • fluctuations in voltage
  • temperature changes
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10
Q

In an RC timing trigger circuit, what controls the capacitor charge rate?

A

A variable resistor

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11
Q

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

A

The SCR is already triggered and is conducting

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12
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.

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13
Q

What are the three (3) current levels that may be measured in a conventional fire alarm initiating circuit?

A
  • normal (10-13mA)
  • trouble (zero current)
  • alarm (high current through low impudence path)
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14
Q

Why must a conventional smoke detector be connected with the correct polarity across the SCR?

A

If reverse-bias, it will not go into conduction.

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15
Q

In what kind of circuits are triacs used?

A

AC

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16
Q

What two (2) devices form an equivalent of a triac when they are connected in inverse parallel?

A

Two SCRs

17
Q

What member of the thyristor family of electronic devices is used in the triggering circuit for a triac?

A

A diac

18
Q

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

A

Negative

19
Q

What are two (2) common applications of circuits containing triacs?

A
  • light dimmers

- small ac motor speed control

20
Q

a SCR conducts current in ______ direction

A

One

21
Q

In order to provide base speed down control of a DC motor an SCR must be placed in the _________ circuit.

A

Armature

22
Q

To ensure proper triggering of a TRIAC, the gate polarity must be the same as __________.

A

T2

23
Q

A TRIAC conducts current in _________ __________.

A

Two directions

24
Q

When more load is added to a cap filtered circuit the percent ripple would ____________.

A

Increase

25
Q

A P-Type material has a net _________ charge.

A

Neutral

26
Q

The current that flows when a photocell is not exposed to any light is known as ______ _________

A

Dark current

27
Q

A single phase diode conducts for ______ degrees.

A

180

28
Q

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

A

Forward Bias

Positive Gate pulse

29
Q

What is the recommended method of triggering an SCR?

A

Gate Pulse

30
Q

What are three undesirable methods of triggering an SCR?

A
  • Exceed Breakover Voltage
  • Fluctuations in voltage
  • Temperature changes
31
Q

What are three ways to commutate an SCR?

A

Natural
Frequency
Forced

32
Q

Is the SCR considered a normally on device?

A

No; Normally off

33
Q

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

A
  • normal
  • alarm
  • trouble
34
Q

What is the purpose of the FF coil?

A

Field Failure Coil; prevents motor runaway

35
Q

What is the current limit of a triac?

A

40 A

36
Q

What is the typical breakover voltage of a diac?

A

+- 30V

37
Q

What does the potentiometer set?

A

Output voltage to alternator

38
Q

What is the purpose of the external snubber circuit?

A

Limit the rate at which voltage can increase

4th Year Electrical - Electronics (5 decks)

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