A thyristor works when a small current flows into a gate, allowing a larger current to flow from the anode to the cathode and latch on. The anode is the positive terminal, while the cathode is the negative terminal.
A thyristor is an electronic component that can be used to create a latching circuit. It has three leads called the anode, cathode and gate. Normally, no current flows across a thyristor unless a supply is connected across the device and a small amount of current is applied to the gate.
A thyristor is like two transistors back to back. When a small current flows through the gate, it turns on one of the transistors and causes it to fall toward the cathode. The current then flows through the base of the other transistor and turns it on. Once both transistors are turned on, the current can flow freely through the entire thyristor. The current can only flow in one direction through a thyristor, and no current flows through if a reverse voltage is applied.
The thyristor stays on even if the gate current is removed because the two transistors keep each other switched on. This characteristic makes thyristors very useful in alarm circuits.