Patent ID: 7859381

Claim:
An autotransformer comprising: a transformer core; a printed wire board constructed of a top, inner, and bottom layer framing a core window therethrough for insertion of the transformer core; and at least one electrical trace winding circumventing the transformer core and formed in the inner layer in proximate thermal conductivity with a heat sink interface and in electrical connection between the top and bottom layers; the trace winding comprising: an upper trace portion located a first distance from the heat sink interface; and a lower trace portion located a second distance, smaller than the first distance, from the heat sink interface; wherein the upper trace portion has a first thickness; wherein the lower trace portion has a second thickness smaller than the first thickness so that electrical conductivity of the upper trace portion is higher than electrical conductivity of the lower trace portion; and whereby the lower trace portion, closer to the heat sink interface than the upper trace portion, is heated more than the upper trace portion by passage of current though the trace winding.