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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. [ABSTRACT FROM AUTHOR]

High step-down dc/dc converters are widely utilized in telecom and modern industrial applications. Due to the high step-down ratio, conventional Buck converter cannot provide satisfactory performance. To solve this problem, quite a few new topologies have been proposed to improve the performance of high step-down dc/dc converters, such as series-capacitor Buck (SC-Buck) converter, 3-level Buck converters, tapped inductor Buck converters, and LLC resonant converters. In this paper, the twice step-down benefit of SC-Buck converter and the zero-voltage switching benefit of series-capacitor tapped Buck (SC-TaB) converter are combined together to propose a new topology: interleaved series-capacitor tapped Buck (ISC-TaB) converter. To analyze the performance of the proposed ISC-TaB converter, the operation principles are discussed and the voltage conversion ratio is derived. In addition, to guide the design procedure and optimization, the current waveforms and voltage waveforms of the proposed ISC-TaB are derived. In order to verify the performance of the proposed ISC-TaB, hardware prototype of the proposed ISC-TaB converter and conventional two-phase series-capacitor tapped Buck converter (2ph-TaB) are designed and tested. The application is targeted at telecom with 48-V input and 3.3 V/20 A output. The test results are compared between these two converters. A peak efficiency of 95.6% is achieved on the proposed ISC-TaB and the efficiency of the ISC-TaB over all load range is at least 1% higher than that of 2ph-TaB. [ABSTRACT FROM AUTHOR]