FAN6751

www.fairchildsemi.com AN-6073 FAN6751 — Highly Integrated Green-Mode PWM Controller Introduction This application note describes a detailed design strategy for a high-efficiency, compact flyback converter. Design considerations and mathematical equations are presented as well as guidelines for a printed circuit board layout. The highly integrated FAN6751 series of PWM controllers provides several features to enhance the performance for LCDM/TV, NB, and adapters. The green-mode function includes off-time modulation and burst mode to reduce the PWM frequency at light-load and in no-load conditions. To avoid acoustic noise problems, the minimum PWM frequency is set above 18KHz. This greenmode function enables the power supply to meet international power conservation requirements. With the internal high-voltage startup circuitry, the power loss due to bleeding resistors is also eliminated. Built-in synchronized slope compensation achieves stable peak-current-mode control. The proprietary external line compensation ensures constant output power limit over a wide AC input voltage range, from 90VAC to 264VAC. FAN6751 provides many protection functions, as shown in Table 1. In addition to cycle-by-cycle current limiting, the internal open-loop protection circuit ensures safety should an open-loop or output short-circuit failure occur. ƒ ƒ ƒ ƒ ƒ ƒ ƒ ƒ ƒ ƒ ƒ Internal Open-loop Protection GATE Output Maximum Voltage Clamp: 18V VDD Under-Voltage Lockout (UVLO) VDD Over-Voltage Protect...