This application note presents practical step-by-step design considerations for a power supply system employing Fairchild’s FAN6920 PFC / PWM combination controller, an integrated Boundary Conduction Mode (BCM) Power Factor Correction (PFC) controller and Quasi-Resonant (QR) PWM controller. Figure 1 shows the typical application circuit, where the BCM PFC converter is in the
front end and the dual-switch quasi-resonant flyback converter is in the back end.