Design of High Power Density for High Step-Down Ratio Low Voltage High Current LLC-TLVR DC-DC Converter

With the development of big data, cloud computating, the energy consumption of data center is rapidly increasing. This is leading to a change in data center structure from 12V to 48V. The original single-stage converter can no longer meet the demand for high step-down ratio at low voltage and high current, so cascaded converters are required. The pre-stage operates as a pre-step-down stage in an open-loop condition to achieve fixed-ratio power conversion, and the post-stage operates as a regulator stage to achieve precise high-swing rate control. The LLC resonant converter is a favorable choice as pre-stage due to its advantages of Zero Voltage Switch(ZVS), high frequency, power density and electrical isolation. In this paper, an LLC-TLVR cascade structure is proposed, focusing on the analysis of the principle of LLC and TLVR converter, the analysis of the output current swing rate and ripple characteristics of the TLVR converter, the parameter design and simulation verification. Finally, a 200W prototype is built for verification.