Thermistor

Thermistor

A Thermistor is a type of resistor whose resistance is dependent on temperature, more so than in standard resistors. The word is a portmanteau of thermal and resistor. Thermistors are widely used as inrush current limiters, temperature sensors (negative temperature coefficient or NTC type typically), self-resetting overcurrent protectors, and self-regulating heating elements (positive temperature coefficient or PTC type typically).

Types of Thermistors

Thermistors can be classified into two types, depending on the sign of k. If k is positive, the resistance increases with increasing temperature, and the device is called a positive temperature coefficient (PTC) thermistor, or posistor. If k is negative, the resistance decreases with increasing temperature, and the device is called a negative temperature coefficient (NTC) thermistor.

Positive Temperature Coefficient (PTC) Thermistors

Positive Temperature Coefficient (PTC) Thermistors are thermistors whose resistance increases when the temperature increases. PTC thermistors are commonly installed in series with a circuit, and used to protect against overcurrent conditions, as resettable fuses.

Negative Temperature Coefficient (NTC) Thermistors

Negative Temperature Coefficient (NTC) Thermistors are thermistors whose resistance decreases when the temperature increases. NTC thermistors are commonly used in a range of applications such as temperature sensing and inrush current limiting.

Applications

Thermistors, both PTC and NTC, are used in a variety of applications. These include temperature sensors, inrush current limiters, self-resetting overcurrent protectors, and self-regulating heating elements.

See Also

• Resistor
• Temperature Coefficient
• Inrush Current Limiter
• Overcurrent Protection
• Self-Regulating Heating Element

References

<references />

• 
  NTC bead thermistor
• 
  Thermistor diagram
• 
  Failed NTC thermistor