Pulse width modulation (PWM) refers to the use of the digital output of a microprocessor to control an analog circuit, and is a method of digitally encoding the level of an 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.

Power supply engineers, especially those designing all-in-one PC power supplies, slim PC adapters, LCD TVs, and LED lighting, need to use a two-switch flyback topology to provide the high efficiency and power savings required by government regulations, while This is not possible with LLC or single flyback solutions. To meet this need, Fairchild Semiconductor has developed an integrated critical conduction mode PFC and quasi-resonant current mode PWM controller product FAN6920MR, which is more than 90% efficient, and it operates in no-load conditions. The lower power consumption is less than 300mW, which has better energy saving effect and can meet regulatory requirements.