INTERFACE CIRCUIT

The invention relates to an interface circuit for operating a light source, equipped with input terminals for connecting to lamp connection terminals of an electronic fluorescent lamp driver a first string interconnecting a first pair of input terminals to a first terminal, a second string interconnecting a second pair of input terminals to a second terminal, a third string interconnecting the first terminal and the second terminal and comprising a rectifier, wherein output terminals of the rectifier are arranged to be coupled to the light source, and wherein a first switching element is arranged to control the conductive state of the third string, such that the third string delivers a driving current to the light source when the first switching element is conductive, a fourth string coupled to the third string and comprising a sensor circuit, having an output terminal coupled to a control electrode of the first switching element, for sensing the amplitude of a high frequency AC voltage between the first and the second terminal and for rendering the first switching element conductive when the amplitude of the high frequency AC voltage reaches a predetermined value.