Non-linear resistors

Non-linear resistors, i.e. thermistors and varistors have been playing a major role in the history of electrical engineering. Technologically, they are based on intensive research into ceramic materials and the fact that additives and special mixtures can significantly change the electrical and thermal properties of the ceramic material.

PTC thermistors and varistors

PTC (positive temperature coefficient) thermistors perform several functions in electronics – one of them is heating. In motor vehicles for instance, they provide additional heating in heat exchangers, protect wiper nozzles from freezing and prevent diesel fuel from becoming viscous. Their safety properties are particularly important. As PTC heating elements are self-regulating, they cannot overheat like heating wires and cause fires. What’s more, their ceramic material can be made in almost any shape.

As the resistance of PTC thermistors rises with temperature, they are ideal protective components for power supplies. Thermally coupled with power semiconductors, they limit control currents if overheating is imminent and thus protect the entire unit against damage or destruction. They are also used as sensors in a wide variety of designs and complete with terminals, e.g. as limit value sensors for overflow protection of tanks filled with liquids such as fuel or beverages.

Varistors for overvoltage and ESD protection are found throughout electronics and electrical engineering. They protect high-voltage grids just as reliably as automotive electronic networks, telecom equipment and computers. Despite the large quantities of energy that they may have to absorb in an emergency, even heavy-duty varistors can be made in more and more compact designs. Multilayer varistors and integrated products

Thanks to the ongoing development of multilayer ceramic technology, varistors can be made even smaller and new and integrated products can be realized. The evolution of multilayer varistors lead among others to CeraDiodes®, varistor arrays and ESD/ EMI modules. They are used throughout mobile and consumer electronics as well as in data systems. Complete dual PI filters with integrated varistors likewise offer more customer benefits.

NTC thermistors

NTC (negative temperature coefficient) thermistors are virtually unbeatable when it comes to accurate temperature measurement. They are made of ceramic materials whose resistance falls as temperature rises. Depending on the ceramic mixture, the R/T curve is approximately linear across certain temperature ranges, making NTC thermistors ideal for almost every application where temperatures have to be measured or monitored. They measure the operating temperatures of coolant and oil in motor vehicles. They are located in the control unit of the air conditioning system, or alert the driver if the outside temperature drops below freezing. In homes, they regulate and protect refrigerators and cookers. They also help save energy in heating systems. And they prevent destruction of computers and telecom equipment by overheating.

This variety of applications is reflected in the wide range of sensor designs: from SMDs through tiny glass-encapsulated types to variants with screw terminals or special thermistors for tube mounting – nothing is impossible. Today, temperatures ranging from around -55 to +1000 °C can be measured.

NTC thermistors can also limit inrush currents. They protect networks and fuses against high pulses and ensure soft starting for powerful motors and transformers.