Build Your Own Fan Control

Circuit Diagram

A straightforward circuit is presented here, designed to accomplish the desired functionality, according to my assessment.

A 15k ohm resistor is utilized within the design.

An NTC Thermistor – measuring 10k ohms – is sourced from Radio Shack in the United States.

Integrated Circuit Details

The circuit incorporates a TL082, a dual operational amplifier, which was readily available. This op-amp is a versatile component frequently employed in analog circuit design, providing amplification and signal conditioning capabilities. It’s a common choice for projects requiring precise voltage control and signal manipulation. The dual nature of the TL082 allows for implementing multiple control functions on a single circuit board, streamlining design and minimizing component count.

Furthermore, an IRF-510 – a 4-amp MOSFET – is included within the design, housed in a TO-220 case. Essentially, as the voltage applied to its gate increases, the MOSFET will conduct greater current. Note that variations like the IRF-520 and 530 can accommodate even higher current levels. Even with a 5-watt dissipation, the MOSFET will generate heat and necessitate a heat sink or placement within an airflow path. The large metallic portion of the MOSFET corresponds to the drain (D) voltage level; it should not be attached to the chassis.

A 1N4001 diode is used as D1, and can be used in place of almost any diode. It facilitates the current's return around the fan when the MOSFET turns off. The fan continues to spin, producing a voltage on the drain lead of the MOSFET. The 1N4001 limits this voltage. Adjustment is easiest with a voltmeter, though it can be accomplished without one. Ensure the thermistor is at room temperature before adjusting. Heat the thermistor to achieve the desired high temperature, triggering full fan speed. Adjust P2 until the fans reach full speed (using a voltmeter to obtain the highest voltage), and then fine-tune P2 to initiate a slight voltage drop as the speed decreases. Fan specifications generally indicate a low voltage limit around 7 volts, though some smaller 80mm fans may operate with a lower limit of 8 volts. Setting the low voltage too low might cause the fans to stall until the thermistor heats up sufficiently. Please share your experiences if you construct this circuit and describe its operation for me.

It is essential to use single-supply voltage op-amps, such as the OP-07, which is a dual voltage op-amp.