Transformer

A transformer comprising:

• a core assembly, which is composed of a pair of E-shaped cores each having two side leg portions and a central leg portion between said two side leg portions, and in which end surfaces of said central leg portions and end surfaces of said side leg portions of said E-shaped cores oppose each other, respectively, and a gap is provided between said end surfaces of said central leg portions;
• a primary coil which is formed by winding a round Litz wire around a perimeter of said central leg portion;
• and
• a secondary coil which is formed by winding a strip-shaped rectangular wire around a perimeter of said central leg portion by edgewise winding and which has a smaller number of windings than a number of windings of the primary coil, whereby the secondary coil outputs a lower voltage than an input voltage to the primary coil and a larger current than an input current to the primary coil,
• wherein said secondary coil is not radially adjacent to said gap so that a space for reducing leakage flux from said gap that acts on said secondary coil is provided between the secondary coil and the gap.