How To Build Temperature Controlled DC Fan Using LM741 Op-Amp

In this tutorial, we will be going to learn how a temperature controlled DC fan is made and what is its application. This circuit can cool your heat-producing electronic gadgets by working with a DC fan. Its activity is completely programmed and turns off when the temperature returns normally. It utilizes a small 12V DC brushless which is found in the PC cabinet. The circuit exploits the property of the thermistor to work the DC Fan.

Must Read Fire Alarm Using LM358


temperature controlled dc fan

Circuit Diagram

Temperature Controlled DC Fan Using LM741

Components Required

  • LM741 Op-Amp IC
  • 4.7KΩ Thermistor
  • Resistor (1KΩ, 47Ω)
  • 10KΩ Potentiometer
  • BD140 Transistor
  • 1N4007 P-N Diode
  • DC Fan
  • 12V Power Supply

What is a Thermistor?

The thermistor is a sort of Temperature-Dependent Resistor and its resistance differs relying upon the temperature in its region.

Types of Thermistor

There are two sorts of Thermistors – NTC and PTC.

The Negative Temperature Coefficient thermistor (NTC) diminishes its resistance when the temperature increases. While the Positive Temperature Coefficient (PTC) increases its resistance when the temperature increases. Thermistors are available from 100 ohms to 10K or more qualities.

Working of Temperature Controlled DC Fan

Here in this temperature controlled dc fan project, a 10K NTC thermistor is used. To turn on the DC fan, we use an IC 741 op-amp as a voltage comparator. Its inverting input (pin 2) gets an adjustable voltage through potentiometer while its non-inverting (pin 3) input gets voltage through a potential divider involving 1KΩ resistor and the thermistor. In this manner, the voltage at pin 3 relies upon the conductivity of the thermister.

At the point when the temperature is normal, pin 3 gets higher voltage than pin 2 and makes the output voltage of IC high as shown by a red LED. This high output voltage keeps T1 off since its base is positive. In this condition, the DC fan stays off. At the point when the temperature increases over the required values set by the potentiometer, the resistance of the thermistor decreases, and the voltage at pin 3 also decreases. Accordingly, the output voltage of the IC turns out to be low to turn on T1.

A small brushless DC fan goes on to increases the airflow. At the point when the temperature returns normal, the temperature controlled dc fan naturally turns off. Diode 1N4007 is important to evacuate back EMF when T1 turns off.

Leave a Comment