Automatic Fan Controller Circuit Diagram using Temperature Sensor

Here, in this article, we are going to see the circuit diagram, component list, connection procedure, and working principle of the Automatic Fan Controller Circuit Diagram using a Temperature Sensor. An automatic fan controller circuit using a temperature sensor is a practical electronic circuit that controls the speed or operation of a fan based on the temperature of its surroundings. Here, we have built the circuit for a 12V DC fan that will operate with a 12V DC supply. This type of circuit is commonly used in various electronic devices such as CPUs, Amplifiers, Music Systems, Projectors, and many more. You can build this circuit very easily at your home.

Here, we have built this simple temperature-controlled fan circuit using the CA3140 operational amplifier and a thermistor as a temperature sensor. The CA3140 is a CMOS operational amplifier that can be used in various applications, including temperature sensing and control.

Circuit diagram

Here, you can see the circuit diagram for Automatic Fan Controller and the connection between each component.

Component List

• IC CA3140 - 1 PCs
• 12V DC Fan - 1 PCs
• 2N2222 Transistor - 1 PCs
• 1N4007 PN Junction Diode - 1 PCs
• 10uF Capacitor - 1 PCs
• 4.7K NTC Thermistor - 1 PCs
• 500K Preset - 1 PCs
• 1 Kilo-ohm Resistor - 2 PCs
• 1.5 Kilo-ohm Resistor - 1 PCs
• 12V DC Power Source

Connection Procedure

1. Connect the 1N4007 Diode in reverse bias across the fan terminals.
2. Connect the positive terminal of the fan to the positive terminal of the power source.
3. Connect the negative terminal of the fan to the collector terminal of the transistor 2N2222.
4. Connect the emitter terminal of the transistor to the negative terminal of the power source.
5. Connect the base terminal of the transistor to the output terminal(pin 6) of the IC CA3140 in series with a 1 kilo-ohm resistor.
6. Also, connect the 10uF Capacitor across the base and emitter terminal of the transistor.
7. Connect the thermistor in series with a 1 kilo-ohm resist across the power source and then connect the middle joint of the resist and the thermistor to the Inverting Input Terminal(pin2) of the IC CA3140.
8. Connect the 500K Preset in series with a 1.5Kilo-ohm resistor across the power source and then connect the middle terminal of the Preset to the Non-Inverting Input Terminal(pin3) of the IC CA3140.
9. Provide Vcc and Ground to the IC CA3140.

Working Principle

When the temperature changes, the resistance of the thermistor changes and it altering the voltage at the inverting input of the CA3140.

The non-inverting input of the CA3140 is connected to a reference voltage that creates a voltage reference point for comparison.

The operational amplifier compares the voltages at its inverting and non-inverting inputs. When the voltage from the thermistor-resistor network exceeds the reference voltage, the operational amplifier's output swings high.

The high output of the operational amplifier turns On the Transistor 2N2222 and the transistor allows current to flow to the fan, which starts running.

As the temperature decreases and the voltage at the inverting input falls below the reference voltage, the operational amplifier's output swings low.

The low output of the operational amplifier turns off the Transistor 2N2222, stopping the fan.

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