Thermistors are thermally sensitive resistors whose key function is to show a large, predictable and precise change in electrical resistance when subjected to a corresponding change in body temperature.Its resistance varies more significantly with temperature than in standard resistors. Generally, the resistance increases with the temperature for most of the metals but the thermistors respond negatively i.e. the resistance of the thermistors decrease with the increase in temperature.
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 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. PTC thermistor is used as a sensor when the effect of environmental conditions on the electrical characteristics is supervised. PTC thermistors can be used in place of fuses for circuit protection. As the circuit heats up, resistance increases to prevent overload.
They are also used as timing devices in televisions. When the unit is switched on, the degaussing coil is activated to eliminate the magnetic field; the thermistor automatically switches it off when the temperature reaches a certain point. The Global Positive Temperature Coefficient (PTC) Thermistors Market is segmented on the basis of type, applications, and region. On the basis of type, the global market is classified into Silistor, Switching PTC Thermistor.
Silistor uses a semiconductor as its base material and it is characterized by a linear characteristic. Accordingly, this type of device is used in temperature sensors. The silistor PTC thermistor is mostly manufactured from incapacitated silicon. It exhibits a resistance / temperature characteristic that is virtually linear, the exact characteristic depending upon the semiconductor used and the level of doping.
Switching PTC Thermistor: is used in heaters, sensors and specialized versions are also used as resettable fuses. Switching type NTC thermistors have a highly non-linear curve. The resistance at first falls with increasing temperature, and then at a critical temperature the resistance increases intensely, thereby acting virtually as a switch. On the basis of production technology, the global market is classified into Ceramic PTC (Barium Titanate), Polymer PTC (Carbon Doped Polymer). On the basis of modes, the global market is classified into Self Heating Mode, and Sensor Mode.
Self heating mode: in this mode current is passed through the thermistor, often in series with the item being controlled. As it heats up as a result of the current, it reaches a point where the critical temperature is reached and the resistance increases significantly. It can be used as a safety cut-out or regulator. Sensor mode: in this mode, virtually no current is passed through the device and PTC thermistor senses the surrounding temperature. The self-heating effect is negligible and it is only the surrounding temperature at which point the resistance will significantly increase.
On the basis of application, the global market is classified into Audio-visual Equipment, Information Equipment, Communication Equipment, Automobile Electronics, Home Electronics, Power Supply, Other. Geographically, the global market is segmented into North America (U.S., Canada and Mexico), Europe (Germany, France, England, Russia and Italy), Asia Pacific (China, Japan, Korea, India, and Southeast Asia), South America, Middle East and Africa. The key players are TE, Polytronics, CYG Wayon, Littelfuse, Bourns, Fuzetec, Sea & Land, Keter, Hollyland, TDK (EPCOS), VISHAY, Amphenol (GE SENSING), Jinke, MURATA, Thinking, Uppermost, HIEL, HGTECH, and Hansor.
Research Support Specialist, USA