Fig. RT characteristics of linear silicon PTC thermistor and switching ceramic PTC thermistors
The other major category, and the one that we shall concentrate on in this section, are referred to as switching PTC thermistors. These devices are polycrystalline ceramic materials that are normally highly resistive but are made semiconductive by the addition of dopants. They are most often manufactured using compositions of barium, lead and strontium titanates with additives such as yttrium, manganese, tantalum and silica.
These devices have a resistance-temperature characteristic that exhibits a very small negative temperature coefficient until the device reaches a critical temperature, that is referred to as its “Curie”, switch or transition temperature. As this critical temperature is approached, the devices begin to exhibit a rising, positive temperature coefficient of resistance as well as a large increase in resistance. The resistance change can be as much as several orders of magnitude within a temperature span of a few degrees.
Switching Ceramic PTC Thermistors Characteristics
Ceramic PTC Thermistors Resistance vs. Temperature Characteristic
PTC Thermistor Resistance vs. Temperature means the relation of zero-power resistance of PTC thermistor to PTC thermistor body temperature under a specified voltage. Zero-power resistance should be measured in super slot by using pulse power supply with low output impedance an stable output amplitude. Temperature rise of PTC thernistor induced by measuring current should be so limited that it could be ignored.