Temperature Controlled Fan with MOSFET

MOSFET or metal oxide semiconductor device is one kind of voltage-controlled device, used in electronic devices & also daily life applications. MOSFET is frequently used as an amplifier & switching in different electronic circuits. These transistors also play a key role in making different electronic projects like motor speed control, controlling light intensity, and many more. They can also provide some key features in terms of their overall performance for the designers of circuits. This article explains how to design one of the MOSFET applications like a temperature-controlled fan with MOSFET.

Temperature-controlled Fan with MOSFET

Generally, fan regulators are used to control the fan speed based on the weather conditions of the room. If the temperature within the room is High then we turn the regulator knob in the clockwise direction and when the temperature is low in the room, we turn the regulator in the anticlockwise direction. But at present to overcome this manual operation, an automatic temperature-controlled fan. This circuit works with a 12V DC fan.

Required Components

The required components of this circuit mainly include; a 12V power supply, 10K NTC, IRFZ44 N channel MOSFET, a 12V Cooling fan, and a 10 kΩ potentiometer.


The temperature-controlled fan with MOSFET circuit connections follows as;

Temperature Controlled Fan Circuit with MOSFET
Temperature Controlled Fan Circuit with MOSFET

Connect the Drain terminal of IRFZ44 N channel MOSFET to the 10K NTC & negative wire of the cooling fan.

A 12v DC battery is connected to the positive & negative polarity of the circuit.


The positive wire of the fan is connected to the positive terminal of the battery and the negative terminal of the battery is connected to the source terminal of MOSFET.

The other NTC connection is given to the Gate terminal of the MOSFET.

The common connection pin of 10k NTC & the gate pin of MOSFET is connected to the source pin of MOSFET through a 10 kΩ potentiometer.


The temperature-controlled fan circuit with MOSFET design is very easy with an IRFZ 44 MOSFET & less number of electronic components. In this circuit, an automatic temperature-controlled fan is turned on whenever it approaches the required temperature region of the temperature sensor and it activates the cooling fan which is connected through the IRFZ44 MOSFET.

The temperature-controlled fan will start running when the sensor detects a temperature above the fixed temperature value & it stops whenever the temperature value returns to its normal condition. Here, a temperature sensor like the NTC thermistor plays a key role in measuring the room temperature & the fan speed can be changed based on the temperature of the room with the potentiometer or PWM technique.   The threshold value is set to 30°C which means if the temperature value goes beyond the threshold value then the fan will automatically start.

Here, the duty cycle can be changed from 0 to 100 to control the speed of the fan based on the temperature of the room. The MOSFET used in this circuit works as a switch. Whenever the thermistor gets the heat then its resistance will start reducing and once it reaches the fixed value then MOSFET will switch ON & enable the DC fan.

Once the temperature value drops under the fixed value then MOSFET will turn OFF & disable the DC fan. The transistor in the circuit dissipates heat throughout its operation thus ensuring that there must be sufficient distance between the MOSFET & thermistor or else this circuit will not work appropriately.

The main advantages of temperature temperature-controlled fan using MOSFET are; very simple to handle, economical, the fan automatically runs, very simple to connect to heat-dissipating devices and it saves energy by simply disabling the fan at room temperature.

This circuit is applicable in different electronic projects which need a cooling fan. This circuit is used for cooling computers and laptops and it also in car engine for cooling.

This circuit is used in different electronic devices like gaming consoles & CPUs when the processors heat up in intensive usage and it leads to turning on the fan. When the processor gets cool, the fan will return to its regular flow or turn OFF.

The above circuit can be used to control our regular fan that runs at home. Let us see

How to connect the temperature controlled fan circuit to control FANS at home ?

To connect the temperature-controlled fan circuit (using a thermistor and a MOSFET) to an existing regulator-controlled fan at home, you will essentially bypass the existing regulator and integrate the above circuit into the fan’s power supply. Here’s a step-by-step guide:

Components Needed:

  • Temperature-controlled fan circuit (as previously described)
  • Existing fan with a regulator
  • Power supply for the existing fan (12V)
  • Additional wires and connectors (if necessary)

Circuit Integration Steps:

  • Identify and Disconnect the Existing Regulator:
    • Locate the existing regulator for the fan. It’s typically found within the fan housing or attached to the power cable.
    • Disconnect the existing fan from its regulator. This will usually involve disconnecting the fan wires from the regulator.
  • Connect the Temperature-Controlled Fan Circuit:
    • Take the wires from your temperature-controlled fan circuit, particularly the wires from the MOSFET’s drain and the fan’s positive and negative terminals.
    • Connect the wire from the MOSFET’s drain to one of the wires that were originally connected to the fan.
    • Connect the wire from the fan’s positive terminal (12V side) to the other wire that was originally connected to the fan.
    • Connect the fan’s negative terminal to the ground (GND) of your temperature-controlled fan circuit.
  • Connect the Power Supply:
    • The power supply for the existing fan (12V) should remain connected to the fan circuit.
    • Ensure that the temperature-controlled fan circuit (including the thermistor and MOSFET) is also powered by the same 12V power supply.
  • Ensure Proper Grounding:
    • Make sure that the ground (GND) of both the temperature-controlled fan circuit and the existing fan’s power supply are connected together to establish a common ground reference.
  • Testing:
    • Power up the temperature-controlled fan circuit and ensure it operates as intended. As the temperature increases, the fan’s speed should adjust accordingly.
    • Adjust the potentiometer in your circuit to set the desired temperature threshold for fan speed control.

By following these steps, you’ve integrated the temperature-controlled fan circuit with your existing fan. The existing regulator has been bypassed, and your circuit now controls the fan speed based on temperature. This setup ensures that your fan operates more efficiently, reducing power consumption when cooling demands are lower and increasing fan speed as needed to maintain a comfortable temperature.