Abstract: A ballast circuit includes an equalizer transformer for equalizing current between two or more lamps operated in parallel, combined on one core with a choke. In a 2-lamp embodiment, four windings are provided on one main core. The first and second are closely coupled and have N turns each, each connected separately to one of the lamps. A third and fourth winding are loosely coupled with respect to each other, and are arranged symmetrically about the first and second windings on the main core. These latter windings may be connected in series or in parallel to be an inductive impedance in the ballast circuit.

Abstract: The rotary transformer (1) has an inner core portion (3) which is enclosed by an outer core portion (5). The core portions (3, 5) are formed as hollow bodies of revolution of a ferromagnetic material which are rotatable with respect to one another about a common axis (9) and wherebetween an air gap (7) is present. The facing surfaces (11, 13) of the core portions (3, 5) are constructed as double conical surfaces whose bases (23, 25) face one another. In the conical surfaces (11, 13) there are provided first recesses (15) which are shaped as a staircase with substantially flat steps (19) on which transformer windings (21) are provided. The first recesses (15) in the inner core portion (3) are situated opposite first recesses (15) in the outer core portion (5), thus forming a winding chamber (17), windings (21) on the first core portion (3) cooperating with oppositely situated windings (21) on the outer core portion (5). The outer core portion (5) consists of at least two parts.