Insulation and Shields Eddy Current Loss Penalty Net Conductor Area 100% 75% 50% 25% 0% Typical Core Window Utilization Low-frequency Transformer Design

T he size, performance and cost of a power electronic system are closely linked to the like parameters of the magnetic components. Since custom power transformers are widely used, transformer design is a frequent design process that has a signifi cant impact on system performance. Yet most high-frequency transformers use less than 25% of the available core window for effi cient current conduction. Two factors cause this relatively poor utilization: insulation requirements and eddy current losses. Insulation requirements generally limit the total winding conductor cross-sectional area to less than half of the available core window. Induced high-frequency eddy currents often increase the apparent winding resistances by 50% or more. Therefore, less than 25% of the available core window is used effectively (Fig. 1). Interleaved windings, multifi lar conductors, Litz wire and other approaches can decrease eddy current effects. However, these techniques add additional insulation penalties, which further reduce the net cross-sectional window area available for the winding conductors.