AN-6747B

www.fairchildsemi.com AN-6747 Applying FAN6747 to Control a Flyback Power Supply with Peak Current Output 1. Introduction Highly integrated PWM controller, FAN6747, is optimized for applications with motor load, such as printers and scanners, that inherently impose some kind of overload condition on the power supply during acceleration mode. FAN6747 provides a two-level OCP function that allows the SMPS to stably deliver peak power during the motor acceleration without causing premature shutdown, while protecting the SMPS from overload condition. Green-mode and burst-mode functions with a low operating current maximize the light-load efficiency so that the power supply can meet stringent standby power regulations. The frequency-hopping function reduces electro-magnetic interference (EMI) of a power supply by spreading the energy over a wider frequency range. The constant power limit function minimizes the component stress in abnormal condition and helps optimize the power stage. Protection functions such as OCP, OLP, OVP, and OTP are fully integrated into FAN6747, which improves the SMPS reliability without increasing system cost. This application note presents design considerations to apply FAN6747 to a flyback power supply with peak load current profile. It covers designing the transformer, selecting the components, and closing the feedback loop. Figure 1 shows a typical application circuit using FAN6747. Figure 1. Typical Application © 2010 Fairchild Semiconductor Corp...