Thyristor Q&A: Everything You Need to Know

Thyristors are solid-state semiconductor devices that share certain similarities with diodes, resistors and transistors. Despite being a small device, a thyristor can reliably conduct a lot of electricity and tolerate extremely high power levels.

If you’re not familiar with thyristors or are wondering how to tell the difference between thyristors and other semiconductor devices, Solid State Inc. can help. As an electronic parts manufacturer, we understand why thyristors are important, what purpose they serve, how they work, and more.

What is a Thyristor?

A thyristor is a powerful electrical component used to control and switch the flow of electricity in both low current and high current applications. Unlike transistors, which act as an amplifier and switch, thyristors control current flow by functioning only as a switch. Due to their superb ability to handle high voltage, thyristors are often utilized in applications such as air conditioning, motor speed control, car ignitions, and surge protectors.

How Does a Thyristor Work?

The most common type of thyristor has three electrodes called the anode (positive terminal), cathode (negative terminal), and gate. Like a transistor, the gate works to control the electric current that travels between the anode and cathode.

When a small current flows through the gate, it triggers a larger current between the anode and cathode. If the small current to the gate is turned off, the larger current will continue to travel from the anode to the cathode, uninterrupted, and the thyristor remains “on.” This feature is the primary difference between transistors and thyristors as well as one of many reasons why thyristors are praised for their ability to deliver reliable, high voltage.

It’s important to note that thyristors can only conduct electricity that travels in one direction. Thyristors will also only function with four layers of alternating P-type and N-type semiconductors (P-N-P-N or N-P-N-P), with three junctions in between. The four layers work like two transistors that are connected together, with the output from each layer acting as the input for each thyristor.

What Are the Three States of a Thyristor?

There are three possible states that a thyristor can be in:

Forward Blocking: This state is initiated when the thyristor blocks the current that would normally be sent forward. The thyristor must be switched off so that no current can flow from the anode to the cathode.

Reverse Blocking: When anode and cathode connections are reversed, no electricity will travel through the thyristor. Thyristors can conduct energy and move it in one direction only and it has to be forward.

Forward Conducting: In this state, the thyristor will conduct energy when an electric current flows into the gate and each transistor activates the other. This process is how a thyristor stays on permanently – even when removing power to the gate. The main current must be interrupted from the anode to the cathode, which can often be done by switching off power to the entire unit.

Types of Thyristors

There are numerous types of thyristors. Some variations include an option to turn off power to the gate (gate turn-off, or GTO) while other thyristors are powered by light.

Despite their differences, all thyristors function in a similar way – an electric current must flow through the gate to activate the upper and lower transistors. Once the transistors are “saturated” with energy, the current can flow through both of them and remain switched on, even if the current at the gate is removed.

Applications for Thyristors

Due to their ability to control high voltage electric power, thyristors are mostly found in light dimmers, logic circuits, oscillator circuits and more, where they act as a switch to channel electricity between nodes.

Contact Solid State Inc.

Need help selecting the best thyristor for your circuit needs? Solid State, Inc. has over 15 different types of thyristors available for purchase. Our high quality, durable thyristors ensure your project will be completed with the best materials on the market. Request a quote for your electrical components today!