Lamp ballast with near unity power factor and low harmonic content

摘要

A magnetic ballast circuit for a fluorescent lamp providing improved power factor, reduced harmonic content and increased efficiency. A ballast circuit with three inductances connected at a junction, preferably with the first and second inductances comprising a tapped autotransformer, with the third inductance connected between a line terminal and the tap, with the first inductance connected in series with a capacitance to the other line terminal, and with the second inductance connected to the load. The first inductance may be provided totally as part of the autotransformer, or may be supplemented with a second inductance in series. In an alternative embodiment, separate inductances may be utilized. Alternative lamp filament power sources and alternative functionally equivalent core and winding configurations are disclosed.