Introduction to the Basic Types of Thermistors 1

Based on the varying characteristics of thermistor resistance with temperature, thermistors can be fundamentally classified into three types.

1. NTC thermistor  NTC thermistors are primarily composed of mixed sintering of transition metal oxides such as Mn, Co, Ni, Fe, and Cu. By altering the composition and ratio of the mixture, NTC thermistors with different temperature measurement ranges, resistance values, and temperature coefficients can be obtained.  An NTC thermistor is a negative temperature coefficient thermistor, whose resistance-temperature characteristics follow a negative exponential law, with the relationship expressed as:diode

In the formula:  RT — the resistance of the thermistor at absolute temperature T (Ω);  Ro — the resistance of the thermistor at absolute temperature ro (Ω);  To, T1 — the initial and varying temperatures of the medium (K);  to, t — the initial and varying temperatures of the medium (°C);  B — the material coefficient of the thermistor, typically ranging from 2000 to 6000 K.  The magnitude of B depends on the material used to manufacture the thermistor. For oxide semiconductor thermistors, the material constant B isdiode

In the formula: △E — ionization energy of impurities in semiconductors; K — Boltzmann constant. The figure shows the characteristic curve of resistivity versus temperature for a thermistor made from CdO-Sb2O3-WO3 material. It can be seen that within a relatively wide temperature range, its resistivity exhibits a linear relationship with temperature, making it a relatively ideal thermistor. To accommodate high-temperature applications, thermistors made from titanium oxide and yttrium oxide have a working temperature range of 200°C to 1000°C, and their characteristic curve is as shown in the figure.  diode