Basic Action of the SCR Flashcards
To turn on the SCR, what must the polarity of the gate be with respect to the cathode?
The gate must be positive with respect to the cathode
Once an SCR has been turned on, how can it be turned off?
By opening the load circuit or reducing the load current below the SCR holding current rating
What words are used to describe the action of turning an SCR on?
“firing” or “triggering”; sometimes “gating” is used
Why is it not required to maintain the gate signal once the SCR is on?
The gate signal has no effect once the SCR is turned on
Normally, in order for an SCR to conduct, the anode must be _______ with respect to the cathode, and the cathode must be _______ with respect to the gate.
positive, negative
Which of the following ranges of current would be approximate to the typical holding current magnitude in an SCR?
a. microamperes
b. milliamperes
c. amperes
b. milliamperes
When an SCR is conducting, how many volts (to the nearest round number) would appear across the terminals A-K?
1 V
Why must you connect a resistor (load) in series with an SCR?
An SCR in the on mode would represent a short-circuit
If an SCR is triggered at 10° into the cycle, for how many degrees will it conduct?
170°
What is meant by the term “phase control” with reference to an SCR?
The ability to change the shape of the voltage waveform and therefore magnitude of voltage across a load
If the firing angle is large, the average DC output voltage across the load is _____ (small/large)
Small
The maximum number of degrees that the firing angle can have in an SCR is _____ °
180°
When used with a single-phase bridge rectifier, how many SCR’s are needed to give complete phase control for a load?
One
Name on common application of phase control using the SCR
Varying the speed of a DC motor
