Hybrid Magnetic Core to Increase Saturation Limit and Magnetizing Inductance in Integrated High Power Transformers

Abstract:
Integrated magnetics for galvanically isolated dc-dc converters allow for volume and weight improvements which are instrumental in achieving the ever increasing requirements for lighter and more compact dc-dc converters. However, the common integrated transformer concepts are lacking for high power designs. This, among others, can be attributed to the large difference in stray to magnetising inductance requirements for such applications. This paper proposes a hybrid core concept which decouples the design of the transformer and inductance through the use of different materials. An outer core with high magnetic permeability increases the magnetising inductance of the transformer significantly while not affecting the integrated inductance. The inner core made of standard ferrite material allows for orthogonal field lines and is therefore used to integrate the inductor in the design. The concept is compared to a non hybrid core design through numerical FEM simulations and measurements on various prototypes. The new concept increases the saturation limit by 44% and the magnetising inductance by 61% without increasing the volume.