In the car electronic system, temperature treatment has always been a challenge. Generally, the system will be required to work normally under an ambient temperature of -40 ° C ~ + 65 ° C. And the ambient temperature inside the chassis will also have a temperature rise of about 20 ° C, so the maximum ambient temperature that the PCB board actually needs to withstand will be as high as + 85 ° C. Then, further focusing on some areas, such as power supply, CPU and other modules will be a big heat, further aggravating the ambient temperature in the chassis, the harsh environment has now forced the temperature limit of many chips. Therefore, in the early stage of system planning, it is necessary to plan the Thermal Management strategy and the corresponding method of planning.

Relatively simple and crude, but the effective method of heat dissipation is to add a cooling fan, which of course will increase the planning cost and machine noise. Therefore, our requirements when designing fan circuits are also based on these two fundamental starting points:
1). It is necessary to keep the circuit simple and low cost;
2) The speed of the electric fan is proportional to the noise, so the speed of the electric fan should be measurable and controllable. The system will adjust the fan speed according to the ambient temperature, preferably stepless speed regulation, and strive to balance the cooling power and noise.

The structure of the fan:
The core component of the fan is a brushless DC motor with an outer rotor. The so-called outer rotor means that the coil does not move (stator) and the magnet rotates (rotor); the so-called brushless DC motor is a DC motor without brushes, using Hall sensors instead of brushes.

In principle, the intact DC voltage will not allow the motor to continue to work, because it will be firmly attracted by the "heterosexual" and join hands to the white head. The condition for the continuous operation of the motor is that there is a need for one party to "fancy", the rotor or the stator, so the rotor and the stator "separate and combine", constantly looking for new love, and then rolled up. When the motor rotates through 180 ° (this is the phase angle, pay attention to not the physical angle), the N and S poles induced by the coil and the S and N magnets of the magnet attract each other. The change from "heterogeneous attraction" to "homogeneous repulsion" allows the rotor to turn 180 ° again, and then continuously converts the positive and negative poles, and the motor can continue to roll. The equipment that constantly "provokes" the coil to convert the positive and negative poles is called a commutator, which can be either a mechanical brush or an electronic Hall sensor. Obviously, the mechanical commutator is simple and the cost is low, but the noise is large, there is wear and tear, and the life is short.