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?

17
Q

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

18
Q

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

21
Q

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

22
Q

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

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 ____________.

25
A P-Type material has a net _________ charge.
Neutral
26
The current that flows when a photocell is not exposed to any light is known as ______ _________
Dark current
27
A single phase diode conducts for ______ degrees.
180
28
What conditions must exist in order to properly trigger a silicon-controlled rectifier?
Forward Bias | Positive Gate pulse
29
What is the recommended method of triggering an SCR?
Gate Pulse
30
What are three undesirable methods of triggering an SCR?
- Exceed Breakover Voltage - Fluctuations in voltage - Temperature changes
31
What are three ways to commutate an SCR?
Natural Frequency Forced
32
Is the SCR considered a normally on device?
No; Normally off
33
In a class B fire alarm system, what are the three conditions of a smoke detector?
- normal - alarm - trouble
34
What is the purpose of the FF coil?
Field Failure Coil; prevents motor runaway
35
What is the current limit of a triac?
40 A
36
What is the typical breakover voltage of a diac?
+- 30V
37
What does the potentiometer set?
Output voltage to alternator
38
What is the purpose of the external snubber circuit?
Limit the rate at which voltage can increase