Elevator Mechanic Practice Exam

What keeps the SCR conducting once it's turned on?

1. Gate voltage pulse

2. Steady Anode and Cathode voltage

3. Anode and Cathode current flow

4. Reverse bias

The correct answer is: Steady Anode and Cathode voltage

Once the SCR is turned on, the steady Anode and Cathode voltage keeps it conducting. The other options are incorrect because A: Although a gate voltage pulse is necessary to turn on an SCR, it is not what keeps it conducting once it has been turned on. The gate voltage pulse simply triggers the SCR to start conducting. C: Anode and Cathode current flow is necessary for the SCR to conduct, but it is not what keeps it conducting once it has been turned on. Once the SCR has been triggered by the gate voltage pulse, the steady Anode and Cathode voltage is what keeps it conducting. D: Reverse bias does not play a role in keeping the SCR conducting. Reverse bias is when the voltage applied to the Anode is negative with respect to the Cathode, and this would actually turn off the SCR. It is the steady Anode and Cathode voltage that keeps the SCR conducting. Therefore, the correct answer is B because the steady Anode and Cathode voltage is what maintains conduction through the SCR once it has been turned on by the gate voltage pulse.