Economic Flat Design (EFD) power transformer cores offer a signifi cant advance in circuit miniaturization. Their low build height and high throughput power-density make them ideally suited to applications where space is at a premium. Throughput power of a ferrite core transformer is essentially proportional to its volume. so the transformer is one of the main limitations in a DC-DC converter's size. Now, with the introduction of the EFD system, a signifi cant reduction in transformer core height has been achieved. EFD transformer cores combine both extreme fl atness with a very high throughput power-density for frequencies up to 1 MHz and higher. Every transformer, based on the EFD range, has a lower building height than any other existing low-profi le design with the same magnetic volume. this is achieved by placing the centre pole of the core always in the centre of the fi nished transformer, thus making maximum use of the winding area.