Two-wire ballast for fluorescent tube dimming

Abstract From the Canadian patent

A two-wire ballast arrangement is disclosed for fluorescent tubes having first and second terminals for supplying variable power to dim the fluorescent tube a, choke coil connected between the first terminal and the fluorescent tube and a filament transformer having a primary connected between the second terminal and a tap on the choke coil, the tap being selected to supply substantially constant voltage to the primary winding, the transformer having secondary windings to supply filament voltage to the fluorescent tube.