Flyback Controller Improves Cross Regulation for Multiple Output Applications

摘要

Flyback converters are often used in power supplies requiring low to medium output power at several output voltages. With a flyback, multiple outputs incur little additional cost or complexity—each additional output requires only another transformer winding, rectifier and output filter capacitor. Power over Ethernet (PoE) applications may require several low to medium power outputs and are good candidates for multiple output flyback converters. While multiple output flyback converters are simple and inexpensive, they often suffer from poor cross regulation. Usually, one output is tightly regulated via feedback, while the other outputs are controlled via less accurate transformer action. Schottky diode voltage drops, transformer leakage inductances and transformer winding resistances degrade regulation. Also, outputs remain uncoupled when the rectifiers are off, which contributes to poor cross regulation.