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Automatic DC FAN controller circuit

Automatic Temperature controlled DC FAN Controller Circuit 

We use many electronic gadgets like power Amplifiers, SMPS, Inverters and AC-DC converters etc. These gadgests uses ICs that generates more heat during opetation and required any temperature controller for Cooling to control the heat for protecting the devices. This circuit is ideal to control the cooling fan of heat generated electronic gadgets like power amplifiers. 

Fan should be small . You can use DC fan of Computer SMPS or CPU FAN .

This circuit switches on a fan automatically when temperature rises to a fix or a set level.  It works by senses a temperature set level. The fan automatically turns off when the temperature returns to normal.

temperature controlled DC motor


The circuit uses an NTC (Negative Temperature Coefficient) Thermister to sense heat. The resistance of NTC Thermister reduces when the temperature in its vicinity increases.

A voltage comparator ic is used to compare its input voltage at pin 2 and 3 which is vary by thermister (as per temperature rises) with two potential dividers. Resistor R1 ( VR) And R2 forms one potential divider connected to the non inverting input of IC (U1) and another potential divider comprising R3 and the 4.7K  Thermister supplying a variable voltage to the inverting input of IC1. VR (R1)is adjusted to give slightly lesser voltage at the non inverting input than the inverting input at normal room temperature. Output of IC (U1) will be low and the Fan remains off in this case.

And when temperature increases near the Thermister, The resistance of its decreases. This drops the voltage at pin 2 of IC and its output becomes high and then Transistor Q1 gets on and fan turn on. Capacitor C1 gives a short lag before Q1 turns on to avoid false triggering of transistor and to give proper bias to Q1.

Attach the Thermistor as possible as near the Heat sink of the Amplifier PCB .

Switch on the amplifier for 5-10 minutes. Then adjust VR till the Fan stop running. When the temperature rises, Fan will automatically switch on.





BC547 or 2N2222-1


NTC 4.7K-1





10uf 25v-1



About the Author


Hi, My name is Aman Bharti, I am interested in making and study of Electronics, circuit diagram, PCB designing and layout etc. I like to share the knowledge and all ideas with people which I get from My Experiment & from different sources. I try to provide any circuit details deeply with test results as possible. If you want to give a suggestion or comments on anything, please leave your comment in the comment box of the related page.

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