A Two-Stage Universal Input Charger With Wide Output Voltage Range

This article presents the design of a two-stage 50 W portable charger architecture with universal ac input and 5 V/25 W, 9 V/45 W, 12 V/50 W output. A 98.5% efficient valley-switched boost converter operating at 0.5-2 MHz enables a 59% reduction in buffer capacitor volume compared to an example electrolytic capacitor while a stacked-bridge LLC converter with a Variable-Inverter-Rectifier-Transformer (VIRT) offers greater than 96% efficiency across the wide output voltage range. The design demonstrates the potential and trade-offs of a two-stage architecture at this operating power and illustrates the benefits of the utilized power stage topologies in achieving both small size and high efficiency over wide input- and output voltage ranges.