Thermistors

Thermistors are resistors for which the resistance greatly depends on temperature. Recall that temperature also changes the resistance of ordinary resistors.

The circuit symbol for a thermistor is as shown below:

There are two types of thermistors - one where the resistance increases with temperature and the other decreases.

  • PTC (Positive Temperature Coefficient) where the resistance increases with temperature rises.
  • NTC (Negative Temperature Coefficient) where the resistance decreases with temperature rises.

Applications

A PTC type of thermistor is commonly found in overcurrent protection circuits where higher current generates more heat which increases the circuit resistance which acts to limit the current.

A NTC type of thermistor is commonly found in temperature sensors.

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