Planar transformer design of LLC DC-DC converters with electromagnetics simulation

A proper magnetic component design is required for the realization of high performance power supply unit design. However there are many tradeoffs between design parameters, such as frequency, AC resistance, leakage inductance, component size, parasitic capacitance and cost demand. To meet these requirements, effective usage of the electromagnetic simulation is gathering attention. Furthermore, multi-physics simulation that combines several physical simulation such as electromagnetics, fluid, thermal conductivity and mechanical stress enables us to make virtual prototypes of the real products. In this paper, design parameters of planar transformers for various LLC DC-DC converters are investigated with iterative EM simulation and optimization of winding structures are demonstrated. Also as an evaluation example of multi-domain simulation, electromagnetics and circuit co-simulation is performed. Transformers and resonance inductors of LLC power supply circuit are 3D-geometrically modeled and AC characteristics of these inductors are simulated with full-wave electromagnetic simulation software. Simulated characteristics are extracted and imported to the circuit simulation software and the circuit simulation with detailed magnetic component model is realized. The evaluation target is 240 W LLC DC-DC converter. Experimental results show that measured and simulated waveforms and conversion efficiency have good correlation. Therefore, the effectiveness of electromagnetics and circuit co-simulation for the precise behavior prediction of the LLC converter circuit is confirmed.