Resistance-Temperature Characteristic
　　
This shows the resistance-temperature relation of a PTC thermistor. The resistance is shown logarithmically due to the sharp exponential increase whereas temperature is given linearly.

Taking advantage of these characteristics, when the temperature becomes more than the detection temperature, a PTCR can reduce the current flow. Since the resistance of a PTCR increases suddenly, the digital conversion of the temperature information is not required. The temperature can be detected with a simple circuit.
　　
Current-Voltage Characteristic (Static Characteristic)
　　
The PTCR indicates a self-heated function when voltage is applied.In this case, for practical usage a current-voltage characteristic is suitable.This shows a current-voltage relation of a PTCR in still air at a temperature of 25°C. The maximun current through a PTCR is also called a tripping current (I_T) and suffices for heating the thermistor to the reference temperature. This current determines the range of PTCR application as a current limiter for current overloading protection.

Taking advantage of these characteristics, the PTC thermistor can be applied to:
● Constant temperature heating elements, heaters and etc.
The PTCR is different than a Nichrome heater, etc., and maintains a constant temperature without performing ON/OFF control. No complex or additional control circuits;
● Overcurrent Protection
When an abnormality occurs in an electronic circuit, a large current (overcurrent) will flow. The PTCR limits the current in the circuit, so that an overcurrent does not flow into other electronic components, when this overcurrent flows. The PTCR limits the current in a circuit, to protect from overcurrents.
　　
Current-Time Characteristics (Dynamic Characteristic)
　　
This shows the relation between current and time before inner heating and outer thermal dissipation arrive at equilibrium state. This featuree having large initial current and abruptly continuous attenuating portion.

The PTCR allows for the initial inflow of a large current, and subsequently the current can be decreased by the self-heating. Taking advantage of these characteristics, the PTC thermistor can be applied to relay for motor starting.