What is a one-way thyristor?

What is a one-way thyristor?

SCR is a three-terminal semiconductor device composed of PNPN four-layer semiconductor material.The names of the three lead electrodes are anode A,cathode K and gate G ( also known as control pole).The anode and the cathode of the unidirectional thyristor have a unidirectional conductivity,and the internal circuit can be equivalent to a PNP transistor and an NPN transistor the internal structure,the equivalent circuit and the symbols of the circuit diagram of the compound pipe are shown in Figure. 

As can be seen from figure,when the negative power supply of the unidirectional thyristor anode A ends and the positive power of the cathode K end,the unidirectional thyristor anode A and the cathode K are disconnected regardless of the polarity of the gate G and the polarity of the voltage.When the anode A end of the unidirectional thyristor anode is connected to the positive power supply and the cathode K end,the unidirectional thyristor anode A and the cathode K will be turned from disconnected to the conduction state as long as the G end of the gate pole is added to the negative power supply.The voltage drop between the anode A and the cathode K is low, and the pressure drop between the A and K poles is (0.8~1V).If the trigger voltage of gate G is negative,the one way thyristor will not be connected.

Once the unidirectional thyristor is triggered, even if the trigger voltage is cancelled at the G end of the gate,the thyristor will maintain a low resistance state if the positive voltage is still maintained between the anode A end and the cathode K end.Only when the voltage of the anode A end is reduced to a certain critical value or the voltage polarity between the anode A end and the cathode K end is changed (such as the zero crossing),the unidirectional thyristor anode A and the cathode K are converted from the low resistance conduction state to the high blocking state.The unidirectional thyristor is disconnected.Even if the positive voltage is added between the anode A end and the cathode K end,it will not be redirected again.Only the positive triggering voltage can be made only after the positive trigger voltage is added between the gate G end and the cathode K end.