Controlled Rectifiers Flashcards
What are the three leads of an SCR?
Cathode (K)
Anode (A)
Gate (G)
Name some of the different types of an SCR:
Flat Pac or Tab Style
Stud Mount
Puk Style
What are heat sinks generally made of?
Aluminium
An RC snubber circuit is connected across the SCR to limit the rate at which the voltage can increase. T or F?
True
What does Vdrm stand for?
The dynamic repetitive maximum (Vdrm)
When replacing SCRS, you need to consider what five factors?
Voltage rating
Power dissipation
Dv/Dt rating
Gate current rating
Application
Controlling the average voltage is called what?
Phase Control
To operate a dc motor above base speed, the current through the field winding must be reduced. T or F?
True
Most alternators or ac gen-sets, are equipped with rotating exciters, usually a brushless type. T or F?
True
The voltage a zener diode conducts is called the Zener voltage and it only conducts in forward bias under certain conditions. T or F?
False, the zener voltage conducts in reverse bias under certain conditions.
A saturated charge is desired when charging lead-acid batteries. T or F?
False. A tapered charge is desired.
An RC time delay circuit is an effect to gate an SCR. T or F?
True
How does a pulse trigger circuit control an SCR?
By providing a current pulse of sufficient magnitude and duration to trigger the gate of the SCR, turning it on
What components are required for a controlled-bridge rectifier?
Two diodes and two SCRS
Name some of the examples of circuits that are used to provide trigger pulses to SCRS?
Integrated circuits
Digital circuits
Ramp generator
Comparator circuits
What is the purpose of the isolation transformer in a pulse-trigger circuit?
To isolate the low-voltage trigger circuit from the higher-voltage SCR circuit
What are the 3 current levels that may be measured in a convention fire alarm initiating circuit?
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
A triac is an AC solid state switch that conducts in both directions. T or F?
True
Since the triac is used in ac circuits, what is it commutated with?
Class F commutation
How is phase control of triacs accomplished?
By connecting a variable triggering circuit to the gate
Two common applications are of Triacs are
Lighting dimmers
Small ac motor speed control
What single-phase motors are capable of speed control using the phase-control method?
Shaded-pole
Permanent-split capacitor motors
In order to have consistent triggering, what must the polarity of the gate be when T2 is negative?
Negative
What ratings determine the size of a Triac?
The current IT and voltage rating (Vdrm)
