The invention relates to a transformer construction comprising a plurality of transformer cores configured to share magnetic flux paths and, as a result, at least one of the cores comprises a post and an associated sidewall having an effective cross-sectional area which is less than that of the post. Such a construction may be employed in a power conditioning unit, for example, for a photovoltaic module, which is configured to operate the cores out of phase from each other. Also described is a transformer winding comprising a longitudinal spine having a first turn emanating from a first portion of the spine in a first transverse direction and a second turn emanating from a second portion of the spine in a second transverse direction, wherein the second transverse direction is opposite to the first transverse direction.