The flyback converter is an isolated version of the buck-boost converter. Depending on the winding ratio of the coupled power inductor, the input voltage can be higher, lower or equal to the output voltage.
The isolated output feedback can be acquired either directly from a winding of the transformer or by using an optocoupler.
The flyback is the simplest solution for an isolated switching power supply (SMPS) with low power output. For power ratings above 50 W usually more efficient topologies are used.
Würth Elektronik Webinar: Magnetics design & selection – intermediate level