Comparison of DAB and LLC DC–DC Converters in High-Step-Down Fixed-Conversion-Ratio (DCX) Applications

Abstract

This article compares the dual active bridge (DAB) and LLC converter topologies when utilized in a high-step-down fixed-conversion-ratio application, such as the dc-dc stage in laptop and LED TV adapters. Multiple candidate topologies for this application are compared, motivating the selection of the DAB and the LLC for further investigation. The two converters are first compared using first-order insights, and then using a detailed analytical design methodology focused on zero-voltage switching. Fundamental tradeoffs between conduction and switching losses are analyzed, predicting that the DAB converter should achieve higher efficiency at heavy loads due to lower conduction losses, while the LLC converter should achieve higher efficiency at lighter loads due to lower switching losses. To validate these predictions, design examples are developed for a 1-MHz 400-20 V 330-W application, and experimental prototypes for both converters are built based on these designs. Measured results match well with the predictions. The DAB prototype achieves a peak efficiency of 94.9% at full load, corresponding to a 27% reduction in losses compared to the LLC prototype.