This simple temperature controlled DC fan circuit can be used to control any 5volt DC fan by activating it on a preset temperature. You can use this circuit in many electronic projects, which require a cooling fan. The circuit is very simple circuit to add in 30v dc power supply circuit
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The BD139 transistor is working as a switch here. When the 10K NTC thermistor will receive heat then its resistance will start decreasing and on a preset level the transistor BD139 will become switch ON and activates the 12 volt DC fan or motor.Â
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The 50K variable resistor is used to set the level of temperature or heat on which you want to switch ON the transistor.
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The transistor will dissipate heat during operation therefore it is important to add some distance between the thermistor and transistor or the circuit will not work properly. Also use a suitable heatsink with the transistor.