Circuit arrangement for operating semiconductor light sources

A circuit arrangement for operating semiconductor light sources comprising:

• a power input for inputting an AC input voltage,
• an output having a first output terminal, and a second output terminal, which is designed to connect a string of semiconductor light sources,
• a control input for controlling the operation of the circuit arrangement with a control signal,
• a rectifier circuit for converting the AC input voltage into a rectified voltage,
• a converter circuit for transforming the rectified voltage into a current which is suitable for the semiconductor light sources,
• a first switch arranged between the converter circuit and the output, for the switching of the current through the semiconductor light sources,
• a first diode arranged between the first switch and the output, or between the converter circuit and the first switch, and
• a series-connected arrangement of a first varistor and a first voltage-dependent switching element, wherein the series-connected arrangement is connected in parallel with the first switch.