Patent ID: 8427267

Claim:
An apparatus comprising: a printed circuit board having a winding to generate a first magnetic field; and a core structure having a first core piece having a back section and a first leg approximately normal to the back section for directing the first magnetic field along a flux path in the first leg and the back section; the back section having an exterior back surface and an interior back surface separated by a back thickness, the back thickness being generally normal to the flux path; the first leg having an exterior leg surface and an interior leg surface separated by a leg thickness, the leg thickness being generally normal to the flux path; the flux path making a first turn between the first leg and the back section, the first turn being bounded on the inside by the interior leg surface and the interior back surface and forming a first angle that is approximately a right angle; wherein the first core piece includes a first feature for reducing flux crowding in the first core piece at the first turn, the first feature comprising a fillet formed between the interior back surface and the interior leg surface at the first turn; the fillet having a fillet surface comprising a rounded concavity or one or more segments approximating a rounded concavity; the fillet having an effective radius that is greater than or equal to 15% of the back thickness; wherein the effective radius is defined by the radius of a circle that is simultaneously tangent to the interior leg surface, the interior back surface, and an intersection of the fillet surface and a bisector of the first angle.