The SEPIC converter represents a topology of a switching controller where the input voltage can be greater than, less than or equal to the desired output voltage. The input voltage can vary while the output voltage remains constant.
It is a combination of a boost converter and a inverted buck-boost converter. Central components for energy transfer are either two individual power inductors or a coupled power inductor, each in combination with a capacitor, depending on the design. The advantages are short-circuit resistance and a non-inverted output. The disadvantage is the more complex and thus more susceptible design.
Würth Elektronik Webinar: Magnetics design & selection – intermediate level