The generation of high temperatures in power components is a well-known issue in electronics. To address this, designers typically mount heatsinks on components to help dissipate heat. However, in many commercial and consumer devices, the embedded heatsink is insufficient. In these cases, faster air circulation is required to lower the temperatures of both the heatsink and the components. Failure to do so can significantly reduce the lifespan of the components.

The solution we propose is an automatic FAN controller board that is simple, compact, and can be easily embedded in commercial devices. The LM35 temperature sensor is affixed to the heatsink using silicone adhesive for accurate temperature measurement.

Users can easily adjust the temperature threshold using a potentiometer. The board can be powered with either a 5V or 12V supply, making it compatible with a variety of miniature fans, including both 5V and 12V PC fans.

The schematic and PCB design were created using Altium Designer 21, with component libraries sourced from SamacSys (via the SamacSys Altium plugin). All components are SMD (except for the connectors), making assembly straightforward and suitable for small-scale production.

Circuit Analysis

Figure 1 below illustrates the schematic diagram of the cooling fan controller, which consists primarily of two key components: a temperature sensor and an operational amplifier (OPAMP).

Figure 1

Schematic diagram of the Cooling Fan Controller (designed using Altium Designer)

The operational amplifier used in this design is the LM358 (U1) [1], configured as a comparator. When the voltage at the positive input (representing the ambient temperature) exceeds the voltage at the negative input (the preset temperature threshold), the output is activated. Conversely, if the ambient temperature is lower than the threshold, the output remains inactive. The LM358 contains two opamps, with the second opamp configured as a voltage follower for stability. R2 is a multi-turn potentiometer that allows users to easily adjust the temperature threshold.

R3 and D2 limit the output voltage to protect the gate of the MOSFET (Q1), which has a maximum gate voltage tolerance of 8V [2]. These components also help regulate the voltage across LED D3 to approximately 4.7V. R4 is fixed at 470Ω to maintain consistent performance regardless of the supply voltage. R5 serves to prevent unwanted gate triggering of Q1.

The chosen MOSFET (Q1) is the SI2302 N-channel SMD MOSFET [2], which can handle up to 2.2A continuously. This component is preferred over a mechanical relay due to its faster switching and smaller form factor. Diode D1 protects Q1 from reverse inductive currents, while capacitor C3 helps reduce switching noise. Capacitors C1 and C2 are bypass capacitors, reducing power supply noise and ensuring smooth operation.

PCB Layout

Figure 2 shows the PCB layout for this design. It features a two-layer PCB, with all components (except for the connectors) implemented as SMD components. The total board size is 3.8cm x 1.9cm, making it compact and suitable for integration into various devices.

Figure 2

PCB layout of the Cooling Fan Controller (designed using Altium Designer)

During the design process, I realized that the component libraries for U1 [3] and Q1 [4] were missing from my local storage. As a solution, I used the IPC-rated SamacSys component libraries, which I imported into Altium Designer using the SamacSys plugin. This plugin allows easy access to schematic symbols, PCB footprints, and 3D models, all of which can be downloaded directly from SamacSys or imported via their CAD plugins.

Figure 3 displays the range of electronic CAD software supported by the SamacSys plugins. As shown, all major CAD platforms are compatible. I used Altium Designer, and the necessary component libraries were quickly imported through the SamacSys Altium plugin (Figure 4).