Tuesday, August 7, 2012

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Automatic DC fan Controller by Thermistor

This circuit will of turn on / off 12V DC fan Pls temperatures of above normal temperatures. You can set the turn on temperature by adjust VR1. This circuit use an NTC Thermistor, the which means Pls Surrounding the temperature decreases the resistance of this thermistor will of increase is. If the temperature increate So the voltage at pin 3 on LM311 will from decreated. The resistance of the NTC is about 10K at 25'c.

Automatic DC fan Controller by Thermistorcircuit diagram of Automatic DC fan
Controller by Thermistor

LM31 pinout
NTC thermistor that is used is a standard type. but Almost any type will do. based on the results experimented with different models from 10K to 100K and all worked fine after replacing the trimmer pot. The one-Used in the above circuit diagram was a 10K model. This 10K was measured at exactly 25 ° C and with 10% tolerance. VR1 is a regular Bourns Trimmer and adjusts a wide range of temperatures for this circuit.

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