Abstract: The disclosure relates to a ballast unit for gas discharge lamps, particularly fluorescent lamps, by which a substantially constant burning current is supplied to the lamp. The ballast unit includes a transformer mounted on a core having a defined air gap. The transformer is provided with a leakage inductance having a value resulting in a voltage drop of between approximately 15 and 30 percent of an input voltage applied thereto. One or more capacitors are connected in series with the transformer output supply to the lamp. The one or more capacitors provide a capacitance in series with the lamp substantially equal to the ratio of the burning current to the angular frequency of the input voltage multiplied by the secondary no-load voltage supplied to the secondary circuit.