An electrical ballast system having a toroidal current transformer having a core with a gap of predetermined dimensions, a primary winding, and a secondary winding. The primary winding is connected in series to a lamp load circuit and the secondary winding is connected to a transistor driver having an input. The improvement comprises the reduction of the effective area of the transformer core a sufficient amount to limit the output voltage amplitude of the secondary winding within a predetermined range compatible with the input of the transistor driver. The reduction of the effective area of the core is achieved with a cut or gap that covers up to 75% of the effective cross-sectional area. The resulting transformer will operate linearly for low load currents passing through the lamp and primary. For load currents above a predetermined magnitude, the core is saturated and additional magnetic flux lines pass through the gap, attenuated. The waveform of the current through the primary is thus kept in the secondary, attenuated, thereby protecting the transistors' inputs connected to the secondary.