This fan controller circuit diagram is build using a 741 operational amplifier, one thermistor and other few components .
In many times in some audio applications or other electronic applications we need a fan controller circuit to keep the temperature of some elements from circuit on a constant temperature or just to keep the device at low temperature .
In many applications we need to cooling the heatsink or ventilate the air inside the device. With this fan controller circuit from this schematic we can make an automatic ventilation .
This fan control circuit will control a 12 volt fan with maximum current required around 200 mA.
For sensing the temperature is use a #271-110 thermistor which turns the fan on when the temperature exceeds 31 degrees C.
If you would like to turn the fan on at a different temperature you can replace the 8.2K resistor ( R4) with a 10K trimmer pot.
For this fan cooling controller circuit you can use a power supply with a output voltage between 12 and 15 volts dc .