​Characteristics of thyristor

Characteristics of thyristor

thyristor are divided into unidirectional thyristors and TRIAC. The unidirectional thyristor has three output pins: anode A, cathode K, and control electrode G. TRIAC has three outgoing pins: anode A1 (T1), second anode A2 (T2) and handle electrode G.

Only when a forward voltage is applied between the anode A and cathode K of a unidirectional thyristor, and the required forward trigger voltage is applied between the control electrode G and the cathode, can it be triggered for conduction. At this point, A and K are in a low resistance conduction state, and the voltage drop between anode A and cathode K is about 1V. After the unidirectional thyristor is turned on, even if the trigger voltage of controller G is lost, as long as the positive voltage between anode A and cathode K is still maintained, the unidirectional thyristor continues to be in a low resistance conduction state. Only when the voltage of anode A is removed or the polarity of the voltage between anode A and cathode K is changed (AC zero crossing), can the unidirectional thyristor transition from a low resistance conduction state to a high resistance cutoff state. Once the unidirectional thyristor is cut off, even if a forward voltage is reapplied between anode A and cathode K, it still needs to be reapplied between the control electrode G and cathode K to conduct. The conduction and cut-off states of unidirectional thyristors are equivalent to the closed and open states of switches, and they can be used to make contactless switches.

Between anode A1 of TRIAC and the second anode A2, no matter whether the applied voltage polarity is positive or negative, as long as the trigger voltage with different positive and negative polarity is applied between the control electrode G and anode A1, the conduction can be triggered to a low resistance state. At this point, the pressure drop between A1 and A2 is also about 1V. Once the TRIAC is turned on, it can continue to be turned on even if the trigger voltage is lost. Only when the current of anode A1 and the second anode A2 decreases and is less than the maintenance current, or when the voltage polarity between A1 and A2 changes and there is no trigger voltage, the TRIAC will be cut off, and only when the trigger voltage is re applied can it be turned on.