Power supply circuit and a voltage level adjusting circuit and method for a portable battery-powered electronic device

摘要

A power supply circuit for AC/DC adapter-powered or battery-powered portable electronic devices, which has a linear regulator, and includes a voltage level adjusting circuit coupled to the linear regulator. The voltage level adjusting circuit lowers a voltage supplied from the AC/DC adapter to a predetermined level. In an embodiment, the level-adjusted voltage equals a voltage supplied from the battery. The linear regulator is therefore always provided with a constant voltage regardless of the power sources.