Heat Extraction from Ferrite Cores Using Metallic Laminations

Designers of power magnetic devices face thermal constraints at all power and frequency levels and must optimize core size to ensure proper operating temperatures. Ferrite cores, commonly used for medium to high frequency designs, are poor thermal conductors which complicates effective heat extraction when cooling is only available on the surface. We propose that the addition of metallic laminations (i.e. metallic cooling planes) within the core can improve heat extraction without adverse effects to the performance of the magnetic component. We demonstrate this conclusion with an analytic solution of the expected eddy current loss in the plate(s) and a calculation of the expected impact on the overall component’s loss which is largely independent of the details of the component design and applies across broad frequency ranges. Through FEA and experiment, we demonstrate improved natural convection of a prototype transformer with a metallic lamination in the center of ferrite core sets. We first demonstrate the improvement in heat extraction and the negligible loss of the plate using Ansys Maxwell and Icepak simulations. We further validate the proposed approach by testing a prototype transformer in a 2 kW, 150 kHz LLC converter.