Editing Thermistor (section)

===NTC (negative temperature coefficient)===
[[Image:Failed NTC thermistor.png|thumb|A failed (blown) NTC thermistor that worked as an inrush current limiter in a [[switched-mode power supply]]]]
Many NTC thermistors are made from a pressed disc, rod, plate, bead or [[casting|cast]] chip of [[semiconductor|semiconducting]] material such as [[sintering|sintered]] metal [[oxides]]. They work because raising the temperature of a semiconductor increases the number of active [[charge carrier]]s by promoting them into the ''[[conduction band]]''. The more charge carriers that are available, the more [[current (electricity)|current]] a material can conduct. In certain materials like ferric oxide (Fe<sub>2</sub>O<sub>3</sub>) with titanium (Ti) doping an ''n-type'' semiconductor is formed and the charge carriers are [[electron]]s. In materials such as nickel oxide (NiO) with lithium (Li) doping a ''p-type'' semiconductor is created, where [[Electron hole|holes]] are the charge carriers.<ref name=EERB>{{cite book |title=Electronics Engineer's Reference Book |year=1976 |publisher=Butterworths |isbn=0408001682 |pages=6-29 to 6-41 |edition=4 |editor=L. W Turner}}</ref>

This is described in the formula
: <math>
I = n \cdot A \cdot v \cdot e,
</math>
where
: <math>I</math> = electric current (amperes),
: <math>n</math> = density of charge carriers (count/m<sup>3</sup>),
: <math>A</math> = cross-sectional area of the material (m<sup>2</sup>),
: <math>v</math> = drift velocity of electrons (m/s),
: <math>e</math> = charge of an electron (<math>e = 1.602 \times 10^{-19}</math> coulomb).

Over large changes in temperature, calibration is necessary. Over small changes in temperature, if the right semiconductor is used, the resistance of the material is linearly proportional to the temperature. There are many different semiconducting thermistors with a range from about 0.01&nbsp;[[kelvin]] to 2,000&nbsp;kelvins (−273.14&nbsp;°C to 1,700&nbsp;°C).<ref>{{Cite web|url=http://www.thermalfluidscentral.org/encyclopedia/index.php/Temperature_measurements_and_instrumentation|title = Thermal-FluidsPedia {{pipe}} Temperature measurements and instrumentation {{pipe}} Thermal-Fluids Central}}</ref>

The [[International Electrotechnical Commission|IEC]] standard symbol for a NTC thermistor includes a "−t°" under the rectangle.<ref>{{cite web |url=http://www.resistorguide.com/ntc-thermistor/ |title=NTC thermistor » Resistor Guide }}</ref>