Abstract: A supply circuit for a fluorescent tube installation with a high-voltage transformer (T) which is connected, input-end, to a supply voltage with a frequency of several hundred Hz, and which is formed without an air gap. To replace the air gap in the transformer, an electronic regulator (EST) is nonetheless used in the supply circuit, which emulates the current-limiting function of an air gap. The frequency of the supply voltage is between 300 and 800 Hz, preferably 400 Hz. As these frequencies are higher than the usual network frequency of 50/60 Hz, the size and weight of the transformer can be considerably reduced.