AN-6858 is a Fairchild Semiconductor application note that describes a detailed design strategy for a high-efficiency, compact flyback converter. The note presents design considerations, mathematical equations, and guidelines for printed circuit board layout.
The document describes a detailed design strategy for a high-efficiency, compact flyback converter utilizing the SG6858 controller. Key features include Green-mode PWM to reduce standby power, low start-up and operating currents, leading-edge blanking, constant output power limit, and universal input support.
| Start-up current | 10uA |
|---|---|
| Operating current | 2.5mA |
| Gate output voltage clamp | 17V |
It uses a proprietary green mode that provides off-time modulation to linearly decrease the switching frequency.
The SG6858's output driver clamps the gate output voltage at 17V.
The SG6858 introduces a leading-edge blanking time of about 300ns.
A gate drive resistor in the range of 47 to 100 ohms is recommended.