Ballasts - Past, Present, and Future: A Review of the Ballasts

The term "ballast" as it is used in this paper is a current limiting device associated with gaseous discharge lamps. They had their beginning about 50 years ago when mercury and fluorescent lamps were introduced. The ballast in its simplest form was a coil wound on an airgapped core of magnetic material. Its inductance limits the lamp current, but introduces an undesirable phase shift affecting its power factor. Lead/lag ballasts were designed next which created a unity, or almost unity power factor by operating one lamp on a lag, another on a lead ballast. Later when grain oriented transformer steel became available, the constant voltage transformer was redesigned into a constant wattage ballast, useful primarily for HID lamps. Their inherent voltage regulation and unity power factor were a great step forward in the design of magnetic ballasts. As of today the magnetic ballast can be considered perfected, and only adaptations to new lamps can be expected in the future. The advancement of power semiconductors led to the design of hybrid and electronic ballasts some 15 years ago. The electronic (solid state) ballasts applicable for HID and fluorescent lamps as well permit closed loop control of either the lamp current, or the lamp intensity. Electronic ballasts have been designed for various purposes, and trial installations have been evaluated. In the future the electronic ballast will gain wider and wider acceptance, and eventually replace many magnetic ballasts. In this paper several typical magnetic and electronic ballasts are discussed, and references cited. A short bibliography is added to aid the review of the evolution of ballasts.