Abstract: A power source provides continuous AC power by employing a bi-directional converter which interfaces a rechargable DC power storage device with AC mains power and AC loads. The bi-directional converter includes a transformer having first and second windings coupled in reverse polarity through dual switching means in parallel with one another. The switching means are coupled to a state controller responsive to conditions at the AC mains terminal, the AC load terminal and the DC power terminal. There are two general operating conditions, an active condition wherein DC power is provided to the AC load, and a standby condition wherein power is recovered by the DC storage device. In the standby condition, the converter operates in a so-called "flyback" mode to recover power and to direct it to the DC storage device. In the active condition, the converter is pulse-width modulated according to a predetermined duty cycle to produce an AC sine wave output at the AC load terminals.