Study on Flux-Parallel Core Segmentation in High-Frequency Transformers for LLC Converter Applications

Inhalt:
Despite the high DC resistance of ferrite cores, eddy currents are a dominant contributor to core losses at high frequencies, particularly in cores with a large cross-sectional area. This study shows that segmenting an N49 PQ40/40 ferrite core by a single flux-parallel insulation gap in the center leg can reduce the eddy current losses at frequencies above 1MHz by up to 50%. Experimentally, an overall loss reduction of up to 1.25W is measured for an exemplary 2kW LLC converter. This loss reduction can be attributed entirely to the core center leg which is the thermal bottleneck of the magnetic component. Accordingly, the measured temperature of the transformer core is significantly reduced in all operating points. In the worst case operating point the measured maximum core temperature is reduced by 10.5K from 68.3degC to 57.8degC compared to a solid core.