Patent ID: 8035251

Claim:
An uninterruptible power supply comprising: an input switching circuit receiving an input AC voltage; an AC-to-DC converting circuit interconnected between said input switching circuit and a DC bus for converting said input AC voltage into a bus voltage; a bus capacitor connected to said DC bus; an energy storage unit having an end selectively connected to an energy storage unit connecting node and the other end connected to a common terminal for storing electric energy; a charging circuit connected to said input switching circuit and said energy storage unit connecting node for charging said energy storage unit; a DC-to-DC converting circuit connected to said energy storage unit connecting node and said DC bus for converting said energy storage unit connecting node voltage into a regulated DC voltage; and a system control circuit connected to said input switching circuit, said AC-to-DC converting circuit, said charging circuit and said DC-to-DC converting circuit for controlling operations of said uninterruptible power supply, wherein when said uninterruptible power supply is initiated, said AC-to-DC converting circuit is disabled and said bus capacitor is charged by said DC-to-DC converting circuit under control of said system control circuit.