Meet The Positive Temperature Coefficient Resistor
A positive temperature coefficient resistor (PTCR) is a resistor that varies its resistance with its temperature. A resistor that changes its resistance characteristics as a function of its temperature is also called a thermistor. So the PTCR is technically a thermistor.
Figure 1 shows a PTCR wired in a circuit. Whenever a thermistor increases its resistance with an increase in temperature, it is said to have a positive temperature coefficient (PTC). If the thermistor decreases its resistance with an increase in its temperature, it is said to have a negative temperature coefficient (NTC).