Patent ID: 7705489

Claim:
An uninterruptible power supply comprising: a first input having an input line connection and an input neutral connection to receive a first input voltage from a first voltage source; a battery; a second input to receive a second input voltage from the battery; a boost circuit configured to provide a positive output DC voltage with respect to the input neutral connection and a negative output DC voltage with respect to the input neutral connection in both a line mode of operation and a backup mode of operation; a first connection circuit to couple the first input to the boost circuit in the line mode of operation; and a second connection circuit to couple the second input to the boost circuit in the backup mode of operation; wherein the uninterruptible power supply is constructed and arranged to isolate the battery from the input neutral connection in the line mode of operation; wherein the boost circuit has a positive input, a negative input and a neutral input, wherein the neutral input is coupled to the input neutral connection, and wherein the second connection circuit includes a first diode coupled between a positive terminal of the battery and the positive input and a second diode coupled between a negative terminal of the battery and the negative input; wherein the uninterruptible power supply is configured to operate with an AC voltage source at the first input having a peak AC voltage that is less than the positive output DC voltage, and wherein the battery has a battery voltage that is less than the positive output DC voltage and greater than the peak AC voltage.