In electronic circuit protection, varistors are among the most common overvoltage protection components. However, many engineers encounter severe heating issues with varistors in practical applications. The primary cause of this phenomenon is prolonged exposure to excessively high continuous operating voltages. When grid voltage fluctuations exceed the maximum continuous operating voltage, leakage current significantly increases, leading to severe thermal breakdown in the varistor. Correctly understanding this mechanism is the first step in ensuring safe circuit operation.
In addition to improper voltage matching, severe heating of varistors is closely related to surge impact frequency. In scenarios where frequent lightning strikes or switching overvoltages occur, the grain boundary layers inside varistors gradually deteriorate, leading to a decline in nonlinear characteristics. Each surge absorption generates joule heat, and if heat dissipation conditions are poor or cooling intervals are insufficient, the heat will continue to accumulate, resulting in severe varistor heating. Moreover, excessively high ambient temperatures and overly compact PCB layouts that hinder ventilation can also exacerbate this failure phenomenon.
The aging of components themselves is also a common cause of severe heating in varistors. As usage time increases, the leakage current of varistors gradually rises, creating a positive feedback effect—heat causes the leakage current to increase, and the increased leakage current further raises the temperature. When you notice severe heating in a varistor, you should also check for surface cracks, discoloration, or unusual odors, as these are often early signs of failure. It is recommended to use high-quality varistors with ample voltage margin and safety certification. To address the issue of severe heating in varistors, selecting a reliable supplier is crucial. Yuanlin Electronics has long specialized in the matching and optimization of overvoltage protection components, offering varistor selection evaluation, thermal performance testing, and circuit modification recommendations. This approach effectively resolves the problem of excessive varistor heating from its root cause, enhancing long-term product reliability.
