Heating, Ventilation, and Air Conditioning (HVAC ) Electrical Practice Test

When the temperature of a positive temperature coefficient (PTC) thermistor increases, what happens to its resistance?

1. It decreases

2. It increases

3. It stays the same

4. It has a linear relation

The correct answer is: It increases

When the temperature of a positive temperature coefficient (PTC) thermistor increases, its resistance increases. This characteristic is fundamental to the behavior of PTC thermistors. A PTC thermistor is a type of resistor that exhibits an increase in resistance as the temperature rises. This property is utilized in various applications such as overcurrent protection and temperature sensing. PTC thermistors typically have a specific threshold temperature known as the transition temperature. Below this temperature, they behave relatively like a conventional resistor, but as the temperature surpasses this point, the resistance can change dramatically and increase significantly. This rise in resistance at higher temperatures makes them useful in circuits that require a reliable response to temperature changes. In contrast, a negative temperature coefficient (NTC) thermistor would show a decrease in resistance with an increase in temperature, which distinguishes it from PTC thermistors. The notion that the resistance stays the same or has a linear relationship is not typical of PTC thermistors, which have a nonlinear relationship between temperature and resistance as they ramp up significantly at certain temperature points.