To cut off a forward-conducting unidirectional thyristor, as a forward-conducting thyristor will form a maintaining current within itself, which will maintain its conductivity; only by making this maintaining current 'zero' can we stop its conductivity.
In the circuit for the "electronic candle" we are making:
Point movement switch S1: Used to apply a positive voltage to the G pole; press it once, and the controllable silicon will conduct, and the candle lamp will light up;
Trigger switch S2: Used to short-circuit the A pole and K pole for a moment, at that instant, the current through the thyristor becomes zero (the original current through the thyristor has 'detoured' to the copper sheet), the internal maintaining current is lost, and the thyristor breaks, the candle lamp will also be extinguished.