What Is a Chip Thermistor?
A thermistor is a semiconductor device whose resistance changes rapidly when the ambient temperature changes, and is made by mixing multiple metals.
Chip thermistors are surface-mountable thermistors on printed circuit boards.
There are two types of thermistors: NTC (negative temperature coefficient) thermistors, whose resistance decreases slowly as the temperature rises, and CTR (critical temperature resistor) thermistors, whose resistance decreases rapidly as the temperature rises. On the other hand, when the temperature rises, the resistance value rapidly increases.
Conversely, there are three types of thermistors called PTC (positive temperature coefficient) thermistors, whose resistance increases rapidly as the temperature rises.
Uses of Chip Thermistors
The resistance of NTC thermistors decreases as the temperature increases. This characteristic is used in sensors for temperature detection and in circuits for temperature control.
PTC thermistors have a temperature at which the resistance value increases as the temperature rises. This characteristic is used in temperature detection sensors, overcurrent protection circuits in place of fuses, and circuits to detect heaters and heating.
An example of actual use is in air conditioners. Both the indoor and outdoor units use thermistors to control the indoor temperature.
In cars, chip thermistors are used to measure engine temperature and outside air temperature to optimize combustion in the engine.
They are also used in home appliances such as refrigerators and coffeemakers.
Principles of Chip Thermistors
NTC thermistors are made by mixing manganese, iron, cobalt, nickel, etc. PTC thermistors are made by mixing barium titanate with ceramics or polymers with carbon black. CTR thermistors are made by mixing vanadium with additives.
Normally, when the temperature of a conductor such as a metal rises, the moving free electrons and cations in the conductor crystal collide violently with each other.
This is because the cations vibrate as the temperature rises. The collision caused by this vibration slows the speed of the free electrons, resulting in a larger resistance value.
This is why the resistance of NTC and CTR thermistors increases as the temperature rises.
On the other hand, in semiconductors, cations increase as temperature rises, and this ratio outweighs the decrease in the speed of free electron movement, resulting in a decrease in resistance.
Thus, taking advantage of the characteristics of each element, thermistors are effectively used in various places around us.