 # WHAT IS A THERMISTOR AND HOW DO THEY WORK?

A thermistor is a kind of resistor that has a variable resistance depending on the temperature. It’s a special type of resistor that measures heat and responds to changing temperatures. A thermistor’s resistance varies based on the temperature it measures, making it an ideal sensor for heat-sensitive applications. In simple terms, a thermistor is a device that measures temperature electronically by its resistance to current. Thermistors are available as solid-state devices, which makes them ideal for use in electronic circuits. There are Two main types of thermistors: negative coefficient (NTC), positive coefficient (PTC). Each type has different properties and uses. See this article to learn more about these different types of thermistors

## Thermistor symbol

The US standard and international standard symbol of thermistor is shown in the below figure.

## Types of thermistors

Thermistors are classified into two types

• PTC (Positive Temperature Coefficient) Thermistor
• NTC (Negative Temperature Coefficient) Thermistor

PTC and NTC linear equation for the relation between the change in temperature and resistance.

ΔR = k ΔT

Where,

• ΔR = Change in resistance
• k = Temperature Coefficient
• ΔT = Change in Temperature

The temperature coefficient can be either positive or negative and it completely changes the electrical property of the component. A thermistor having a positive coefficient is called PTC while a negative coefficient thermistor is called NTC.

### PTC (Positive Temperature Coefficient) Thermistor

The primary function of a thermistor is to measure temperature. There are different types of thermistors available, each with its own specific use case. PTC thermistors are one such type that stands for positive temperature coefficient. They are known as POSITIVE because they have an opposite response to heat. When they get hotter, their resistance decreases instead of increasing like in the case of NEGATIVE type thermistors. PTC stands for Positive Temperature Coefficient that means this particular device has a property such That it’s resistance decreases when its temperature rises above a certain threshold. PTC stands for Positive Temperature Coefficient that means this particular device has a property Such That it’s resistance decreases when its temperature rises above a certain threshold

## Types of PTC Thermistor

There are two types of PTC (Positive Temperature Coefficient) thermistors.

• Silistors
• Switching Type PTC

### Silistors

The silistor is a PTC thermistor made from silicon having the linear characteristic. The resistance will increase linearly with the increase in the temperature.

### Switching Type PTC

The switching type PTC thermistor has a highly nonlinear resistance-temperature curve. When the switching type PTC thermistor is heated, the resistance starts to decrease at first, until a certain critical temperature is reached

## NTC (Negative Temperature Coefficient) Thermistor

Negative Temperature Coefficient (NTC) thermistor is used for many purposes from temperature sensing to control.

NTC thermistors are widely used for various purposes in many applications where a negative temperature coefficient is required.

As the name indicates, the NTC thermistor provides a reduction in resistance for an increase in thermistor body temperature.

Thermistors can physically take many forms. NTC thermistors can be manufactured as pressed discs, rods, plates, beads or even semiconductor chips, for example using sintered metal oxide.

Often metal oxide NTC thermistors are made of fine wires that are compressed and sintered at high temperatures. The materials used include Mn2O3, NiO, Co2O3, Cu2O, Fe2O3, TiO2, etc. They can also be manufactured from silicon or germanium crystals that are doped to provide the required level of conductivity.

### Characteristics of NTC Thermistors

NTC thermistors are widely used in the electronics industry for many basic temperature sensing applications. Thermistors themselves can be very small, often the size of a small bead, but have two leads coming out of them. Other types and sizes exist that offer a variety of features.