PTC Thermistors (POSISTOR)Current-voltage characteristics

Basic Knowledge of PTC Thermistor (POSISTOR)

Maximum voltage / Maximum current
Withstand voltage
Current-voltage characteristics
Basic Knowledge of PTC Thermistor
Related Links

Maximum voltage / Maximum current

It indicates the maximum voltage / current that can be applied to the PTC thermistor at all times within the operating temperature range.

Withstand voltage

Withstand voltage indicates the voltage that can withstand application for 3 minutes in still air at 25 degrees Celsius. The voltage is applied by increasing the voltage from 0V to the withstand voltage by slow boosting.
The higher the thickness of the element and the longer the distance between the electrodes, the higher the breakdown voltage. In other words, the more grains there are, the higher.

Current-voltage characteristics

I-V characteristics, static characteristics

The I-V characteristics of the PTC thermistor are shown in figure 1.
When the internal heat generation and the heat dissipation to the outside are in equilibrium with applied voltage, the relationship between the applied voltage and the stable self-current is determined. In the constant resistance range, V = IR, and the PTC thermistor does not self-heat. It has a maximum point of current and a constant power range.

Figure 1 : Current-Voltage characteristics

Relation with R-T characteristics

Relationship between resistance and temperature characteristics
Exceeding the maximum point of the current is called “tripping”.

Figure 2 : Relationship between PTC I-V and R-T characteristics

Change in I-V characteristics

The characteristics of overcurrent protection PTC are adjusted by controlling the “Initial resistance”, “Curie point”, and “Heat dissipation” in Figure 3.

Change of initial resistance

Change of Curie point

Changes of heat dissipation

Changes of ambient temperature

Figure 3 : Changes in I-V characteristics due to each factor

For a PTC with fixed characteristics, the I-V characteristics will fluctuate due to changes in the ambient temperature, as shown in Fig. 3, “Changes in ambient temperature.” The maximum current point is the trip current. From this graph, it can be confirmed that the trip current value differs depending on the ambient temperature. Therefore, the trip current is defined at a temperature other than 25°C (e.g. −10°C) at the rating.