What is a unidirectional 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. 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.
If you want to know more, our website has product specifications for thyristors, you can go to Allicdata Electronics Limited to get more information