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PTC Thermistors (POSISTOR)Resistance-Temperature Characteristics

Basic Knowledge of PTC Thermistor (POSISTOR)

Resistance - Temperature Characteristics (R-T characteristics)

Curie Point (C.P.) is defined as a temperature that is twice the resistance value at 25°C.
Between room temperature and the Curie point, the resistance decreases slightly or is almost constant, but above the Curie point the resistance increases logarithmically.

Figure 1 : PTC Res.-Temp. Characteristic Curve and Curie Point

[Reference]

There are types of Curie point (c.p.) as shown in Fig. 2.

Figure 2 : PTC with different Curie points Res.- Temp. characteristics

If the temperature continues to rise beyond the Curie point, it loses its positive temperature characteristics and the resistance decreases. This point is called the TN point.
The rated value of the PTC thermistor is designed with a margin so that it does not exceed the TN point.

Figure 3 : TN point of PTC thermistor