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What is a Thermistor?

11 Jul, 2025

A ​​thermistor​​ is a ​​temperature-sensitive resistor​​ whose resistance changes significantly with temperature.

Types of Thermistors:

  1. ​By Structure/Shape​​: Spherical, rod-shaped, tubular, disc-shaped, ring-shaped, etc. 
     
  2. ​By Heating Mode​​: Direct-heating (self-heating) and side-heating (external heating). 
     
  3. ​By Working Temperature Range​​: Normal temperature, high temperature, ultra-low temperature. 
     
  4. ​By Temperature Coefficient​​:
    • ​Positive Temperature Coefficient (PTC)​​: Resistance increases with temperature (e.g., BaTiO₃-based). 
       
    • ​Negative Temperature Coefficient (NTC)​​: Resistance decreases with temperature (most widely used, e.g., MnO₂-based). 
       

Key Characteristics:

  • ​High Sensitivity​​: Resistance changes rapidly with small temperature variations.
  • ​Nonlinearity​​: NTC/PTC resistance-temperature relationships are nonlinear (e.g., exponential for NTC). 
     
  • ​Applications​​: Temperature measurement (e.g., thermostats), overcurrent protection (PTC fuses), temperature compensation (in circuits). 
     

Nominal Value Note:

The ​​nominal resistance​​ is measured at 25°C. Actual resistance may deviate due to self-heating or material characteristics. For example, PTC thermistors show a sharp resistance increase above a critical temperature, while NTC thermistors exhibit exponential decay.