In this paper, the variable transformer solution is presented as a step forward in magnetically controlled electronic ballasts. The proposed technique takes advantage of the device's equivalent series inductance to provide a new flexible way for lamp's luminous flux regulation. Output electrical isolation and constant frequency operation are also guaranteed by the proposed realization. A simple method for large-signal characterization of the variable transformer is described. An FH 14W/840 Osram lamp was chosen to validate this new technique and experimental results clearly show its adequate behavior.