U-165 Design Rvw: Isolated 50 W Flyback Converter Using UCC3809 and UC3965

The flyback power stage is a popular choice for single and multiple output DC-to-DC converters at power levels of 150W or less. Without the output inductor required in buck-derived topologies, such as the forward or push-pull converter, the component count and cost are reduced. This application note will re-view the design procedure for the power stage and control electronics of a flyback converter. In these isolated converters, the error signal from the secondary still must cross the isolation boundary to achieve regulation. A UC3965 Precision Reference with Low-Offset Error Amplifier driving an optocoupler on the secondary side and the UCC3809 Economy Primary-Side Controller on the primary side constitute a simple and low-cost 50W isolated power supply.