Introduction to symbols and performance of thyristor

Introduction to symbols and performance of thyristor

thyristor, also known as thyristors, are components composed of PNPN four layer semiconductors with three electrodes, anode A, cathode K, and control electrode G.

thyristor can achieve contactless control of AC power in circuits, controlling large currents with small currents, and not producing sparks when controlled like relays. They also have fast action, long lifespan, and good reliability. It has its presence in various control circuits such as speed regulation, light regulation, voltage regulation, temperature regulation, and so on.

thyristor are divided into unidirectional and bidirectional, with different symbols. Unidirectional silicon controlled rectifier has three PN junctions, with two electrodes called anode and cathode led out from the outermost P-pole and N-pole, and one control electrode led out from the middle P-pole.

Unidirectional thyristor has its unique characteristics: when the anode is connected to a reverse voltage, or when the anode is connected to a forward voltage but the control electrode is not applied voltage, it does not conduct. However, when both the anode and the control electrode are connected to a forward voltage, it becomes conductive. Once it is connected, the control voltage loses its control effect on it. Regardless of whether there is a control voltage or not, and regardless of the polarity of the control voltage, it will remain in a conductive state. To turn off, the only way is to reduce the anode voltage to a certain critical value or reverse it.

The pins of the bidirectional thyristor are mostly arranged from left to right in the order of T1, T2, and G (with the electrode pins facing downwards and facing the side with characters). When the size or time of the trigger pulse added to the control pole G changes, the magnitude of its conduction current can be changed.

The difference between bidirectional thyristor and unidirectional thyristor is that when the polarity of the triggering pulse on the G pole of the bidirectional thyristor changes, its conduction direction changes with the polarity, thus controlling the AC load. After triggering, unidirectional thyristor can only conduct in one direction from the anode to the cathode, so there is a distinction between unidirectional and bidirectional thyristor.