The brushless DC motor is mostly PWM speed regulating motor with built-in drive circuit

　　This kind of DC fan motor has a built-in drive circuit, which only provides four interfaces of power supply voltage, control circuit power supply voltage, speed control voltage and speed feedback signal.

　　The power supply voltage is DC voltage; generally high voltage 280v or low voltage 25V? Is indicated by the symbol vs.

　　The power supply voltage of the control circuit is used for the power supply of the built-in drive circuit; generally, the DC voltage is 15V; it is indicated by the symbol v. Motor power supply voltage CC and control circuit power supply voltage must be treated together.

　　The speed control voltage is indicated by the symbol VSP; the voltage range is generally between 0 (6.5V); the actual voltage regulation range depends on the specific motor. Therefore, when VSP is in the range of 1.7V ~ 6.1v, the output capacity is continuously adjustable from 0 (100), and the speed is continuously adjustable within this range, please refer to "technical specification for brushless DC motor" for specific technical parameters.

　　Speed feedback signal; expressed by V; output 12 pulse frequency per revolution; used to feedback the actual speed; adjust vspfg according to the actual speed

　　Voltage to change the fan speed, in order to achieve the goal of fan speed and stable speed.

　　In order to control the speed of BLDCM with built-in driving circuit, only the power supply voltage needed by built-in driving circuit and the change of speed control voltage VSP are needed to change the speed conveniently. Therefore, the hardware circuit design should be able to generate continuously adjustable VSP conveniently and effectively. We use PWM pulse wave with a certain duty cycle to pulse and discharge the electrolytic capacitor, convert the PWM digital signal output by the chip into analog signal with the same proportion, and obtain the speed control voltage VSP. Adjust the duty cycle of PWM pulse wave; change the analog voltage of input VSP; so that the wind speed can be adjusted continuously; control the speed of fan.

　　PWM wave is pulse width modulation wave; in a certain carrier frequency; duty cycle adjustable rectangular wave; this PWM wave is generated by MCU programming control. The higher the PWM carrier frequency is, the more accurate the adjustment of VSP voltage is.

　　Specific hardware circuit design is as follows; see DC fan drive control circuit schematic diagram.

　　For the above PWM drive circuit, the actual effect can be seen from the following examples. For example. The following is the PWM wave driving signal generated by MCU programming with a duty cycle of 50; the waveform is as follows

　　In the secondary of the optocoupler, the analog signal speed control voltage VSP can be obtained, and the effective value of the voltage VSP is 3.77v. As shown in the figure below

　　When the duty cycle of PWM wave is changed, VSP of different voltage can be obtained.

　　When the DC motor rotates one revolution, the v-end of the speed feedback signal will feedback 12 square wave pulses

　　Detect the period of the square wave pulse; get the frequency of the pulse; calculate the speed. Thus, the VSP voltage can be adjusted according to the current speed, and the speed can be increased, decreased or fine tuned to stabilize the speed.