Hello friends, in this post we are going to make one simple mini project which is temperature controlled DC fan using a thermistor. In this mini project, we are going to control the speed of the DC fan automatically as the surrounding temperature changes. Thus when the temperature of surrounding increases speed of fan also increases and when temperature decrease speed of fan also decreases. This is achieved by using the principle of the thermistor.
- R1 = 4.7K
- R2 = 47 Ohm
- NTC Thermistor = 4.7K
- Potentiometer (Vr) = 500K
- OP AMP IC 741
- Transistor T1 = BD140 (or other PNP transistor may work)
- 12V DC fan which is also used in computer (CPU)
- Diode 1N4007
- 12 V DC power supply
The following figure shows a circuit diagram of temperature controlled DC fan using a thermistor.
The basic working principle of temperature controlled DC fan is based on the working principle of the thermistor. The thermistor is a component which changes its resistance as its temperature changes. There are two types of thermistor available which are NTC i.e. negative temperature coefficient and other is PTC which is positive temperature coefficient.
In temperature controlled DC fan, we have used an NTC type thermistor. It is called NTC because its resistance increases when its temperature decreases and vice verse. Similarly, in PTC, its resistance increases when temperature increases and vice verse.
Op amp IC741 is used as a voltage comparator which compares the voltage between its two inputs i.e. inverting and non-inverting terminals. Pin number 2 is inverting terminal which is connected to the potentiometer and pin number 3 is a non inverting terminal which is connected in between thermistor and R1 which makes a voltage divider circuit. Thus the output of op amp is responsible for the speed of the fan.
When the temperature of surrounding increases, the temperature of thermistor also increases which causes its resistance to decrease, therefore voltage divider circuit causes more voltage across pin number 3. Thus the output voltage increases causing the speed of the fan to increase.
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