A varistor, often referred to by the brand name Thyrite (originally developed by General Electric), is an electronic component used to protect circuits and devices from transient voltage surges or spikes. Transient voltage events can be caused by lightning strikes, power grid fluctuations, electromagnetic interference, and other factors. Varistors are designed to divert excessive voltage away from sensitive components, thereby preventing damage.
Varistors are made from a semiconductor material, typically a ceramic compound such as zinc oxide (ZnO). The material's resistance changes with the applied voltage. At normal operating voltage levels, a varistor has a high resistance and acts as an insulator. However, when a voltage surge occurs, the resistance of the varistor drops dramatically, allowing it to conduct and shunt the excess voltage away from the circuit. Once the surge passes, the varistor returns to its high-resistance state.
Varistors are commonly used in applications like power distribution systems, surge protectors, electronic equipment, and appliances. They are often connected in parallel with the device or circuit that needs protection. Varistors are available in various voltage ratings and sizes to match the specific needs of different applications.
It's important to note that while varistors are effective at protecting against transient voltage surges, they have a limited lifespan and may degrade over time after multiple voltage surge events. Therefore, they might need replacement in critical applications to maintain their protective capability.
Remember that specific information and technologies may have evolved since my last knowledge update in September 2021, so it's a good idea to consult more recent sources for the latest information on varistors and related technologies.