PWM refers to Pulse Width Modulation, an electronic control technique in which a PWM signal periodically outputs a voltage for a specific period of time, known as a duty cycle, usually expressed as a percentage.

In fact, PWM is actually to control the output voltage or current of the circuit by changing the pulse width, so as to achieve the speed control of the motor.

Dc fan to achieve PWM control, there are three steps, the first is the design of the control circuit, then the generation of PWM signal, and finally the output of PWM signal.