How To Make a Temperature Controlled DC Fan Using LM741

A versatile technique for controlling a DC fan’s speed in response to changes in the surrounding air temperature is provided by the Temperature Controlled DC Fan circuit, which makes use of the LM741 operational amplifier. Applications for this project include climate-controlled spaces, electronic equipment cooling, and temperature-sensing circuit education. It can also be used in other situations where exact temperature control is essential.

The central element is the LM741 operational amplifier, which acts as a comparator to track and react to temperature variations. A temperature sensor, usually a thermistor, which changes resistance in reaction to temperature changes, is included in the circuit. The operational amplifier subsequently transforms this resistance change into a voltage signal.

The LM741 activates the control circuit, which modifies the speed of the associated DC fan, as soon as the temperature is beyond a predetermined threshold that is established by the resistor and thermistor values in the circuit. Effective cooling is ensured by this dynamic regulating technology, which eliminates the need for ongoing human adjustments.

This project gives hobbyists and students a good opportunity to obtain real expertise with sensor interface, Analog electronics, and operational amplifier topologies, in addition to offering a useful application for temperature control. Knowing how temperature, resistance, and voltage relate to one another in this circuit improves understanding of important temperature control system concepts.

This tutorial will provide an informed introduction to the field of temperature-sensing electronics by going over the parts, design factors, and step-by-step assembly of the Temperature Controlled DC Fan Using LM741.



Circuit Schematic



  • 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 resistance of a thermistor, a type of temperature-dependent resistor, varies according to the surrounding temperature.

Types of Thermistor

There are two sorts of Thermistors – NTC and PTC.

As the temperature rises, the Negative Temperature Coefficient Thermistor (NTC) loses resistance. Conversely, as temperature rises, the Positive Temperature Coefficient (PTC) increases its resistance. There are thermistors with resistances ranging from 100 ohms to 10K or higher.

Working Principle of Temperature Controlled DC Fan

A 10K NTC thermistor is used in this temperature-controlled DC fan project. We use an IC 741 op-amp as a voltage comparator to activate the DC fan. Its non-inverting (pin 3) input receives voltage via a potential divider including a 1KΩ resistor and the thermistor, while its inverting input (pin 2) receives an adjustable voltage through the potentiometer. In this way, the thermist’s conductivity determines the voltage at pin 3.

When the temperature is normal, pin 3 receives a higher voltage than pin 2, which raises the IC’s output voltage to a high level, as indicated by a red LED. T1 is kept off by this high output voltage since its base is positive. The DC fan does not turn on in this state. The thermistor’s resistance and the voltage at pin 3 both drop off when the temperature rises above the necessary levels that the potentiometer has set up. As a result, the IC’s output voltage is insufficient to activate T1.

Additionally, a little brushless DC fan is added to improve airflow. The temperature-controlled DC fan shuts off on its own when the temperature becomes normal again. To move back EMF once T1 turns off, diode 1N4007 is necessary.

Applications of Temperature Controlled DC Fan

  • Electronic Devices Cooling: To control the cooling of electronic components including voltage regulators, power supplies, and amplifiers, use the Temperature Controlled DC Fan circuit. To avoid overheating and guarantee peak performance, the fan speed can be changed in response to the outside temperature.
  • Home Automation Systems: To regulate the temperature in particular rooms, connect the circuit to a home automation system. The fan speed rises in response to temperature, providing an affordable and energy-efficient means of preserving a comfortable atmosphere.
  • Greenhouses and Plant Growth Chambers: To maintain the ideal temperature for plant growth, use the Temperature Controlled DC Fan in greenhouses or plant growth chambers. An environment that is controlled and favourable for plants can be developed through the circuit, which can automatically modify the fan speed to maintain the required temperature range.
  • Server Room Cooling: Use the circuit in data centres or server rooms to control the temperature surrounding networking hardware and servers. Ensuring that the electrical components function within safe temperature ranges lowers the possibility of problems and increases the equipment’s longevity.
  • Automotive Cooling Systems: Use temperature-controlled DC fans in automotive applications, such as speed-regulating an automobile’s radiator fan. This contributes to improved fuel economy and overall vehicle performance by keeping the engine temperature within the advised range.

These applications show the versatility of a Temperature Controlled DC Fan with LM741, highlighting its potential in a range of situations where accurate temperature control is necessary for the longevity and performance of electronic components.

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