PWM refers to the use of the digital output of the microprocessor to control the analog circuit, and it is a method of digitally encoding the level of the analog signal. Controlling analog circuits digitally can greatly reduce the cost and power consumption of the system. A PWM controller is included in many microcontrollers.

The basic principle of PWM control is based on: narrow pulses with the same impulse and different shapes have the same effect when they are applied to the link with inertia. According to the PWM control principle, the waveform is divided into 6 equal parts, which can be replaced by 6 square waves. There are many classification methods of pulse width modulation, such as unipolar and bipolar, synchronous and asynchronous, rectangular wave modulation and sine wave modulation. The unipolar PWM control method means that the carrier only changes in one direction in a half cycle, and the resulting PWM waveform only changes in one direction, while the bipolar PWM control method changes the carrier in two directions in a half cycle, and the resulting PWM The waveform also changes in both directions.