Method and apparatus for interfacing battery backup to power factor correction front end for maintaining power

A battery backup system using a power factor correction (PFC) front end as a DC-to-DC converter of a power supply for supplying a regulated DC input signal to a main power converter. The battery backup system includes a battery backup for supplying power, a switch circuit for connecting the battery in the event of loss of the AC input signal and a detection circuit for detecting the presence or absence of AC power for controlling the switch circuit. The PFC front end preferably receives either a pulsing DC voltage from a bridge rectifier or the battery voltage and switches this voltage through a series inductor for providing the regulated DC input voltage to the main power converter. The battery is switched in to replace the AC source and rectifier in the event of loss of the AC signal. In the preferred embodiment, the PFC circuit includes a series inductor and diode, a switching transistor and a control circuit for providing the regulated DC input voltage. The backup battery is coupled through a diode and a controlled switch to the input of the PFC circuit.