The following circuit diagram shows a simplified AC/DC SMPS front end with active PFC boost converter. The purpose of the active PFC converter is to force the input current (blue waveform in the graph) to be in phase and the same wave shape as the AC input voltage (red waveform in the graph). This is achieved through the use of controller chips running advanced algorithms. The switching element Q1 is driven to provide the required load current while drawing power in correct Power Factor from the grid.