Miniaturization and Thermal Design of a 170 W AC/DC Battery Charger Utilizing GaN Power Devices

This paper presents the design and analysis of a high-density two-stage battery charger for mid-power applications like small electric vehicles and high-performance laptops utilizing gallium nitride (GaN) power devices. In addition to adherence of maximum junction temperatures, a thermal analysis is carried out for in-housing operation, which is particularly critical for fanless wall chargers. Design measures include calorimetric semiconductor selection, half-bridge miniaturization, thermally conductive epoxy resin and reference-based convection modeling for thermally optimized component placement using 3D-stacking. Furthermore, the remaining optimization potential of the charger is estimated by virtual prototyping. A 170 W hardware prototype is developed and tested, achieving a two-stage power section efficiency of 95.4% with a maximum switching frequency of 550 kHz. This results in a power density in open-housing operation of 1.6 kW/dm$^{3}$. Using epoxy resin, copper and graphite heat spreaders, an in-housing operation power density of 1.1 kW/dm$^{3}$ is achieved with minor reduction of output power due to surface temperature constraints.