What are NTC thermistors? And its principle of operation | Basic Knowledge of NTC Thermistor

What are NTC Thermistors?

NTC thermistor is an acronym for Negative Temperature Coefficient thermistor. It was discovered in 1833 by Michael Faraday, who was researching silver sulfide semiconductors, and commercialized by Samuel Reuben in the 1930s. Oxide semiconductor ceramics containing manganese (Mn), nickel (Ni), cobalt (Co), etc.

NTC thermistors are used everywhere in our lives, and because of their resistance characteristics that the resistance value decreases as the temperature rises, they are used in temperature sensors such as thermometers and air conditioners, and in temperature control devices such as smartphones, kettles, and irons. It is also used as a current control for power supply equipment. In recent years, with the electrification of automobiles, there has been a diversification of products for automotive use.

Murata began mass production around 1984, and currently has a lineup of mainly chip types.

Operating principle

General metals have the characteristics that their resistance increases as the temperature rises. This is because heat increases the vibration of the crystal lattice and slows down the average moving speed of free electrons.

In contrast, in semiconductors, heat increases the number of free electrons and holes. The resistance of semiconductors is become s small because the ratio is greater than the decrease in movement speed due to vibration of the crystal lattice.

In addition, since semiconductors have a small energy bandgap, when heat is applied from the outside, electrons in the valence band move to the conductor and conduct electricity. In other words, the resistance decreases as the temperature rises.

Figure 1 : Electrical conductivity of semiconductors

Application

The resistance of NTC Thermistors changes by 3 to 5%/°C to the temperature change. This is used in many electronic devices as a general temperature sensor.

Example, Smart Phones;
When you are using a Smart Phone, have you ever experienced that the “body of the phone gets hot?”
It can be said that thin and highly efficient Smart Phones are small PCs. The body tends to become hot because unlike PCs, there is no fan or etc. to release the heat. Therefore, there is a risk of the precision components which are sensitive to heat being damaged.

The NTC Thermistors come into play in such conditions!
NTC Thermistors measure the temperature inside Smart Phones, and perform various control using the temperature information.