Termistorid

Termistorid (the Estonian term for thermistors) are passive electronic components whose resistance changes with temperature. They are primarily of two types: NTC (negative temperature coefficient) thermistors, where resistance decreases as temperature increases, and PTC (positive temperature coefficient) thermistors, where resistance increases with temperature. They are typically made from metal oxide ceramic compounds and come in packages such as beads, discs, rods, or axial leads, often epoxy- or glass-encapsulated.

NTC thermistors are widely used for temperature sensing and compensation because their resistance varies strongly with temperature, allowing relatively small devices to produce measurable signals. Their resistance–temperature relationship is nonlinear, but can often be described by a beta parameter over a limited range, enabling calibration for electronic circuits. PTC thermistors are used for overcurrent protection, self-regulating heaters, and degaussing circuits in older CRT displays; many PTC devices exhibit a sharp resistance rise near a characteristic Curie temperature.

Forms and construction: thermistors are manufactured as beads, discs, or rods and are commonly encapsulated in epoxy or glass to protect the ceramic material. They offer compact size, low cost, and fast response, making them popular in consumer electronics, automotive, and industrial instrumentation.

Applications and limitations: thermistors are used for temperature measurement and control, compensation in semiconductor devices, and protection or inrush limiting in power circuits. Limitations include nonlinear response, tolerance drift with age and humidity, and self-heating effects if driven with excessive current. Typical NTC sensors operate in the kilo-ohm range (for example 10 kΩ at 25°C), while PTC devices for protection span tens to thousands of ohms depending on design.