the shape of E cores is derived from the classical iron sheet lamination cores. for the original E range in fact the dimensions of the existing lamination range were taken so that already commercially available coil formers and mounting hardware could be used. the former EF range has been optimized for the use of ferrite as a core material. Cross sections were rearranged resulting in a homogenious magnetic fl ux density in the core and more space for the windings. Main use is as power transformer or choke in SMPS. E cores have a simple shape and can therefore be produced more economically than more complicated cores. A drawback is the rectangular crosssection of the centre pole which makes it more diffi cult to wind, especially with heavy wires. Also the structure of the core is rather open resulting in stray fl ux sometines causing interference problems.