PTC thermistor

 
PTC thermistor

What are PTC thermistors? PTC stands for „Positive Temperature Coefficient“. PTC thermistors are resistors with a positive temperature coefficient, which means that the resistance increases with increasing temperature. PTC thermistors are divided into two groups, based on the materials used, their structure and the manufacturing process. The first group of PTC thermistors is comprised of silistors, which use silicon as the semiconductive material. They are used as PTC temperature sensors for their linear characteristic. The second group is the switching type PTC thermistor. This type of PTC thermistors is widely used in PTC heaters, sensors etc. Polymer PTC thermistors, made of a special plastic, are also in this second group, often used as resettable fuses. The switching type PTC thermistor has a highly nonlinear resistance-temperature curve. When the switching type PTC thermistor is heated, the resistance starts to decrease at first, until a certain critical temperature is reached. As the temperature is further increased above that critical value, the resistance increases dramatically. This article will focus on the switching type PTC thermistors. PTC thermistor definition A PTC thermistor is a thermally sensitive resistor whose resistance increases significantly with temperature. Characteristics of PTC thermistors Switching PTC thermistors are usually made of poly-crystalline ceramic materials that are highly resistive in their original state and are made semi-conductive by the addition of dopants. They are mostly used as PTC self-regulating heaters. The transition temperature of most switched PTC thermistors is between 60°C and 120°C. However, there are special application devices manufactured that can switch as low as 0°C or as high as 200°C. Silistors have a linear resistance-temperature characteristic, with a slope that is relatively small through most of their operational range. They may exhibit a negative temperature coefficient at temperatures above 150 °C. Silistors have temperature coefficients of resistance of about 0.7 to 0.8% °C. Transition temperature [… read more]