NTC Thermistor
Publish Time: 2026-08-11
NTC is an abbreviation for Negative Temperature Coefficient, referring generally to semiconductor materials or components with a large negative temperature coefficient. An NTC thermistor is therefore a negative temperature coefficient thermistor.
NTC thermistors are manufactured using ceramic processes, primarily using metal oxides such as manganese, cobalt, nickel, and copper. These metal oxide materials all possess semiconductor properties, and their conductivity is similar to that of semiconductor materials such as germanium and silicon. At lower temperatures, the number of charge carriers (electrons and holes) in the material is relatively small, resulting in a higher resistance; as the temperature increases, the number of charge carriers increases, and the resistance decreases accordingly.
NTC thermistors have a resistance range of 100Ω to 1,000,000Ω at room temperature and a temperature coefficient of approximately -2% to -6.5%/℃. Due to their small size, good stability, and fast response speed, they can be widely used in temperature measurement, temperature compensation, surge current suppression, and other applications.
Main characteristic parameters
1. Resistance-Temperature Characteristics (RT Characteristics)
The RT characteristic refers to the relationship between the zero-power resistance (R) of an NTC thermistor and the resistor's body temperature (T) at a specified voltage. (Note: The resistance decreases as temperature increases.)
2. Rated zero-power resistance value R (Ω or kΩ)
The resistance value is measured at a specified ambient temperature and at a measured power, where the change in resistance due to self-heating of the current is negligible relative to the total detection error.
According to IEC standards, the rated zero-power resistance value refers to the resistance value R25 measured by an NTC thermistor at a reference temperature of 25°C. This is the nominal resistance value of an NTC thermistor. When people say "NTC thermistor resistance value," they are usually referring to this value (unless a specific temperature point is specified).
To ensure testing accuracy, NTC thermistors are typically tested using a high-precision constant-temperature oil bath.
3. B value (material constant/thermal index)
The B value represents the sensitivity of a thermistor to temperature changes. It is usually calculated by the change between two ambient temperatures and is expressed in Kelvin (K).
The value of B is different from the resistance value:
• The resistance value can be changed by adjusting the chip size, but the B value cannot be adjusted;
Engineers typically determine the B-value specification based on the chip's material composition.
Important Notes: Thermistors with a large B value usually also have a high resistance value; therefore, the B value and resistance value cannot be combined arbitrarily. For example, NTCs requiring very high resistance but with a very small B value are difficult to develop.
4. Dissipation coefficient (δ)
The thermistor requires 1°C of electrical power to rise in temperature due to its own heating in a still air environment, and the unit is mW/°C.
The dissipation coefficient is determined by the balance between its own heat generation and heat dissipation; therefore, changes in the environment surrounding the thermistor must be considered.
• If the surrounding materials have high thermal conductivity, it will promote heat release and increase the dissipation coefficient;
• If a low heat dissipation structure is adopted, the dissipation coefficient may be smaller.
After assembly, the dissipation coefficient should be measured in an actual working environment (such as air, water, oil, etc.) to obtain data that conforms to the actual working conditions.
5. Thermal time constant (τ)
This indicates the response speed of a thermistor to changes in ambient temperature. It is defined as: under zero-power conditions, when a sudden temperature change occurs, the time required for the thermistor's temperature change to reach 63.2% of the initial and final temperature differences.
The thermal time constant is directly proportional to the heat capacity and inversely proportional to the dissipation coefficient.
• The smaller the volume of the thermistor, the faster its response speed and the smaller its thermal time constant τ;
• The assembly structure also significantly affects the response speed. Attention should be paid to the working environment, and materials with high thermal conductivity should be given priority.
Factors affecting resistance variation
The higher the temperature, the lower the resistance. Factors affecting resistance variation include:
1. Ambient temperature (T)
2. Self-heating of components caused by electric current
Note: Both the reference resistance value and the B value have precision tolerances. Because the resistance value distribution range is affected by the B value tolerance, the further away from the reference temperature, the wider the resistance value distribution.
Rated power and maximum operating temperature
Rated power (Pn)
Under specified technical conditions, this refers to the power consumption allowed for a thermistor to operate continuously for an extended period. At this power level, the temperature of the resistive element itself does not exceed its maximum operating temperature.
Maximum operating temperature (Tmax)
Under specified technical conditions, the highest temperature at which a thermistor can operate continuously for an extended period of time.
The maximum operating temperature is closely related to the packaging material:
• Glass encapsulation: High temperature resistance, up to 300℃;
• Epoxy resin encapsulation: has a lower temperature resistance rating, with a typical maximum operating temperature of 125℃.
