Reference Design:Isolated 50 Watt Flyback Converter Using the UCC3809 Primary Side Controller

The flyback power stage is a popular choice for single and multiple output dc-to-dc converters at power levels of 150 Watts 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 review 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 needs to cross the isolation boundary to achieve regulation. By using the UC3965 Precision Reference with Low Offset Error Amplifier on the secondary side to drive an optocoupler and the UCC3809 Economy Primary Side Controller on the primary side, asimple and low cost 50 Watt isolated power supply is realized.