Circuit for pulsed operation of a discharge lamp

Abstract

To provide for automatic switch-over between a power phase and a holding se in operation of a discharge lamp (EL), a choke or ballast coil (L), serially connected to the discharge lamp, is constructed to have, with respect to current flow therethrough, a non-linear reactance value; the choke or ballast coil is wound on a core which, for example, can be a E-core in which the center leg is of reduced cross-section with respect to the outer legs; or, if one is a torroidal coil on a ring core, the ring core is preferably made of two core elements of different magnetic characteristics, connected together, for example by an adhesive, in which one core element is of low permeability material, such as iron powder or permaloy with high saturation magnetization, and a second core is formed of ferrite with low saturation magnetization. Current flow through the coil and the serially connected lamp is controlled by alternately operating switch elements (S1, S2), typically insulated gate bipolar transistors, to supply power bursts of, for example, between 20 and 30 A during a second operating phase, separated by a first operating phase of between 0.3 A and 0.5 A at a substantially higher frequency than the frequency of the power bursts, and lasting 10 to 30 times as long as the power bursts. An ignition circuit (Z, L-CR) is provided to start or fire the lamp.