Miniaturizing High Step-Down, High Output Current Power Converters

Abstract

Power conversion systems providing high voltage step-down capability at high output current are required in many applications, such as data center servers, electric vehicle charging, and USB power delivery. Converter miniaturization is a critical but especially challenging design goal, and transformers present a key bottleneck in this effort. To address this challenge, a new paradigm for magnetic component design is proposed in which magnetic and electronic elements are viewed as a single ``coupled electronic and magnetic system'' (CEMS).

The first proposed CEMS is the Variable Inverter/Rectifier Transformer (VIRT), which enables a transformer with fractional and reconfigurable effective turns ratios (e.g. 12:0.5, 12:2/3, 12:1, and 12:2). Its wide gain variation and high step-down capability are utilized in a 120-380V input, 5-20V, 5A/36W output dc/dc converter having a peak efficiency of 96% and greater than 93% efficiency across the wide range. The VIRT is also employed in a two-stage universal ac input, 5/9/12V, 5A/50W output portable charger having a component power density of 55W/in3 and a peak end-to-end efficiency of 95.7%.

Challenges associated with leveraging highly interleaved high-layer-count planar windings - another means for handling high current - are elucidated and mitigation strategies are proposed. A novel winding termination strategy is demonstrated to reduce ac resistance by more than 40% in a highly interleaved design.

A CEMS that is especially well suited for processing high output current is derived by combining the VIRT with popular multi-phase concepts. The resulting split-phase half-turn VIRT is employed in a 380V input, 12V/1kW output data center supply having a peak efficiency of 97.7% and a full-load efficiency of 97.1% with a transformer volume up to 36% smaller than best-in-class alternatives. Finally, a generalized modeling framework for developing new CEMS implementations is presented.