1) At the beginning, if the control pole G is not applied with voltage, the thyristor will not conduct no matter anode a is applied with forward or reverse voltage, which indicates that the thyristor has forward and reverse blocking ability.

2) When the positive voltage is applied to both anode a and control pole g of the thyristor, the thyristor can be turned on. These are two conditions that must be met for the thyristor to turn on at the same time.

3) After the thyristor is turned on, its control pole g loses its control function. In order to make the thyristor return to the blocking state, the anode current must be reduced to a certain value (less than the maintenance current).