Automatic Fan Controller Circuit

The above circuit is a Automatic Fan Controller Circuit .This circuit is used for turn on/off DC fan or CPU fan. working principle of this circuit is we can set turn On temperature by adjust VR1.When temperature goes from the above normal temperature the fan will be automatically on.This circuit consist NTC (Negative temperature coefficient )which is a thermistor.when the zero power resistance decreases temperature will increases.So when temperature increases the voltage at pin 3 of LM311 will decreased. The resistance limit of NTC is 10k at 25'c. Relay is 12V relay which we are using in this circuit.The diode D1 (1N4148) is used for the purpose of high speed switching.