What is the working principle of thyristor?

What is the working principle of thyristor?

On April 24, 2025, Beijing - In modern industrial control systems, a semiconductor device called "thyristor" is quietly playing a key role. Despite its small size, it is hailed as the "switch of the electronic age". So, how does thyristor work? Why does it excel in fields such as frequency converters, power regulation, and motor control?

From "switch" to "control" - the basic principle of thyristor

A thyristor, also known as a thyristor rectifier, is a device with three ports (anode, cathode, and gate) and a four layer semiconductor structure (PNPN). Its core characteristics are "controllable conductivity" and "unidirectional conductivity".

When the anode voltage is higher than the cathode voltage, the device itself does not immediately conduct. Only when a trigger current is applied to the gate (G), will the thyristor "turn on", that is, change from the off state to the on state. Once it is turned on, even if the gate signal is removed, as long as a certain voltage and current condition is maintained between the anode and cathode, it will continue to conduct until the current drops below a certain holding current, at which point it will "turn off".

In short, a thyristor is like a "controllable valve" - it only allows current to pass through when the command to "open the valve" (gate current) arrives.

Principle Analysis: "Positive Feedback Effect" in Microstructure

The four layer structure of a thyristor can be seen as a combination of two transistors - an NPN type and a PNP type. When a forward current is applied to the gate, it triggers charge injection, triggering two internal transistors to conduct in a "positive feedback" manner, causing the entire structure to quickly switch to a conducting state. This mechanism endows thyristors with high sensitivity and fast response characteristics.

Widely used: from electric furnaces to high-speed trains, from lighting to motors

Nowadays, thyristors have become important components in various industrial and civilian power control equipment. For example, in AC dimming lamps, thyristors are used to control the angle of current conduction, thereby adjusting the brightness of the bulb; In the motor speed control system, it is used to adjust the power supply frequency and achieve motor speed control.

In addition, welding machines, induction cookers, induction heating equipment, etc. also extensively use thyristors to achieve effective and accurate energy regulation. In high-voltage direct current transmission systems, high-power thyristors play the role of "rectifier bridges", reliably converting alternating current into direct current.

Advantages and Challenges of Controllable Silicon

The popularity of thyristors cannot be separated from their advantages of simple structure, low cost, large power capacity, and high voltage resistance. However, it also has certain limitations, such as limited turn off process and inability to actively turn off like a transistor. Therefore, in some scenarios, specialized turn off circuits are required.

To address these challenges, researchers have also developed improved devices such as bidirectional thyristors (TRIACs) and gate turn off thyristors (GTOs), which demonstrate stronger flexibility and control capabilities in more complex application scenarios.

Future Promises: The Potential of Controllable Silicon in Smart Grid and New Energy

With the rapid development of new energy technology and smart grid, higher requirements have been put forward for power electronic devices. Controllable silicon, as one of the early power semiconductor devices, is continuously revitalizing through technological innovation.

Industry experts say that in the future, controllable silicon devices based on new materials such as silicon carbide (SiC) and gallium nitride (GaN) are expected to achieve higher frequency, higher voltage, and lower energy consumption control solutions, providing a solid foundation for green energy and intelligent manufacturing.

Conclusion: In the invisible world of electric currents, thyristors are like loyal "gatekeepers", always ready to open the door and release under "instructions". It is this sophisticated technology that enables us to accurately control the power of electricity, leading industry towards a more efficient and intelligent future.