- Temperature controlled DC fan is a temperature based fan.
- It can cool the devices by operating a DC fan when the temperature in its vicinity increases above the preset level.
- Its operation is fully automatic and turns off when the temperature returns normal.
Op Amp (LM 358)
Transistor (BC 548)
5V DC Motor
9V DC Battery
NTC Thermistor (4.7k Ω)
Potentiometer (4.7k Ω)
LM 358 Op amp is used as a Voltage Comparator, it compares two input voltages at pins 2 & 3.
The output of LM 358 collects at pin1.
BC 548 Transistor is used as a Switch to control Fan.
BC 548 is a NPN transistor
5V DC motor is used to run the Fan.
Thermistor is a Resistor whose resistance varies with respect to Temperature.
Negative Temperature Coefficient(NTC) Thermistor, resistance Decreases as temperature rises.
Thermistors can be classified into two types depending on the sign of k.
If k is positive, the resistance increases with increasing temperature, and the device is called a positive temperature coefficient (PTC) thermistor, Posistor.
If k is negative, the resistance decreases with increasing temperature, and the device is called a negative temperature coefficient (NTC) thermistor.
- The basic working principle of temperature
controlled dc fan is based on the thermistor.
- LM 358 compares the voltage across the NTC thermistor and voltage across the 4.7k Ω resistor.
At room temperature the voltage across the NTC will be greater than or equals to the voltage across the 4.7k Ω resistor. So the Op Amp output will be either negative or zero voltage which can not turn ON the Transistor.
If the temperature rises above the preset value, it leads to decrement of Thermistor resistance and voltage across it.
Then if this voltage lesser than the voltage across 4.7k Ω resistor, the output of Op Amp will be positive voltage which can turn ON the Transistor.
When transistor turns ON, the motor(FAN) will be connected across the DC supply and starts to rotate.
The motor will be turns OFF when the temperature returns back to room temperature.
It is very economical and easy to handle.
Motor fan runs automatically, so that it controls the temperature without using it manually.
It is very easy to install at heat dissipating devices to cool down them.
Saves the energy by turns OFF the motor fan at
normal or low temperature automatically.
Temperature Controlled Fan can be used to control the temperature of devices, rooms, electronic components etc. by monitoring the temperature.
The circuit can be used for Car Engine to reduce the heat.
Cooling Pads in personal computers.
- The electric fan operates automatically according to temperature rises in order to compensate the rise in the temperature and turns off when the temperature returns back to the norml temperature.