02. Thermistor

Most metals have a positive temperature coefficient (PTC), which means that they conduct the better the colder they are.

Most semiconductors have a negative temperature coefficient (NTC), which means that they conduct the better the hotter they are.

However, some metal alloys can have a tiny NTC.

And some semiconductors will, once their temperature is higher than the Curie temperature, display a huge resistance increase when the temperature is rising, until 30°C.

You can set where the Curie temperature is by changing the alloy of the material (range from -50°C to 250°C for barium titanate).

This is then called a Thermistor.

Unfortunately, a high current flowing through a thermistor will cause it to heat up and so the resistance changes.

If you leave it alone, it will be:

Where α is the temperature conduction coefficient, A the area of the thermistor, ΔT the temperature of the thermistor relative to the environment.

Author: Danny (remove the ".nospam" to send)

Last modification on: Thu, 09 May 2013 .