Thermistors are temperature-sensitive resistors categorized by how their resistance reacts to heat: Positive Temperature Coefficient (PTC) and Negative Temperature Coefficient (NTC). This series focuses on PTC thermistors, which are semiconductor components whose resistance increases sharply once a specific temperature threshold is reached.
A Brief History
The discovery of the PTC effect dates back to 1950 at the Philips Company, where researchers found that certain barium titanate ceramics exhibited this unique property after being made into semiconductors. Commercialization began in the early 1960s, initially as temperature compensation components for transistor circuits. Since then, PTC technology has expanded into motor protection, color TV de-gaussing, and constant-temperature heating, growing into a global industry with hundreds of millions of units sold annually.
Why PTC Matters
Unlike traditional heating wires or fixed resistors, PTC materials possess a unique brain. When they get hot—either from the environment or from the current flowing through them—their resistance spikes. This creates a self-limiting effect: as the resistance goes up, the current goes down. This natural physical property allows PTC devices to act as automatic thermostats and resettable fuses without the need for complex control circuits. Today, these components are everywhere—from the hair curler in your bathroom and the heater in your car to the advanced communication systems and aerospace equipment that power our modern world.
