temperature controlled dc fan using thermistor

temperature controlled dc fan using thermistor pdf

Working:

The basic working principle of temperature controlled DC fan is based on the working principle of thermistor. Thermistor is component which changes its resistance as its temperature changes. There are two types of thermistor available which are NTC i.e. negative temperature coefficient and other is PTC which is positive temperature coefficient.

In temperature controlled DC fan we have used a NTC type thermistor. It is called NTC because its resistance increases when its temperature decreases and vice verse. Similarly in PTC its resistance increases when temperature increases and vice verse.

Op amp IC741 is used as a voltage comparator which compares the voltage between its two inputs i.e. inverting and non inverting terminals. Pin number 2 is inverting terminal which is connected to the potentiometer and pin number 3 is non inverting terminal which is connected in between thermistor and R1 which makes a voltage divider circuit. Thus the output of op amp is responsible for the speed of fan.

When the temperature of surrounding increases, temperature of thermistor also increases which causes its resistance to decrease, therefore voltage divider circuit causes more voltage across pin number 3. Thus the output voltage increases causing speed of fan to increase.