Low-power LLC resonant AC-DC converter for phone charging applications

A single-stage LLC resonant AC-DC converter is presented to replace conventional flyback type converters for phone charging application. Single-stage flyback AC-DC converter is widely used in low-power AC-DC converters, especially phone charging applications. However, for flyback AC-DC converter, the switching frequency is limited due to the hard-switching and switching losses. Its output current ripple is also higher than other topologies. On the other hand, LLC resonant AC-DC converter can achieve higher switching frequency thanks to zero voltage switching (ZVS). Higher switching frequency can reduce the output current ripple, and it allows to reduce the size of the passive components and the cost. For better quality and reliability with long lifespan of a charger, a compact 135 kHz, 10W (5V/2A) single-stage LLC resonant AC-DC converter is implemented and analyzed to verify its feasibility.