Cooling fan PWM function Introduction（1）

2 PWM speed control 

The basic principle of PWM speed control is to switch on and off the power supply according to a fixed frequency, and change the time ratio of switching on and off within a cycle (duty ratio) to change the "duty ratio" of the voltage on the DC motor armature, so as to change the average voltage and control the speed of the motor.

In the pulse width speed control system, the speed increases when the motor is powered on, and decreases when the motor is powered off.

As long as the time of on and off power is changed according to a certain law, the motor speed can be controlled.

And the stepless speed control system composed of PWM technology.

There is no impact on the DC system during startup and shutdown, and it has the characteristics of low startup power consumption and stable operation.

When the motor is always powered on, the maximum motor speed is naax, and the duty cycle is D=t/T, then the average speed nd of the motor is: ng= nD According to the formula, when the duty cycle D=t/T is changed, the average speed Vd of the motor can be obtained.

Thus to achieve the purpose of speed regulation.

Strictly speaking, the relationship between average velocity and duty cycle D is not strictly linear, but in general application, it can be regarded as approximately linear.

In the DC motor drive control circuit, the PWM signal is provided by the external control circuit, and after the high-speed photoelectric isolation circuit, motor drive logic and amplification circuit, the switch of MOSFET under the H bridge is driven to change the average voltage on the DC motor armature, so as to control the motor speed and realize the PWM speed regulation of the DC motor.