Circuitry for dimming a fluorescent lamp

The invention relates to a circuit arrangement for the dimmable operation of a fluorescent lamp, in particular for use in motor vehicles as instrument lighting. The prior art discloses corresponding circuit arrangements in which the fluorescent lamp is operated at an operating frequency. The effect achieved by the switching-on and -off of the operating frequency with an apparatus and thus the lamp at a dimming frequency which lies above the visual frequency of the human eye, is that the human eye is given the impression that the fluorescent lamp has a different brightness, depending on the pulse width of the dimming frequency. In order to adjust the lamp current through the fluorescent lamp, it is necessary either to provide an additional regulator or to use a resonant circuit which is stabilized in a complicated manner. The object of the invention, therefore, is to specify a circuit arrangement for dimming a fluorescent lamp which is constructed in a simple manner. In a circuit arrangement for the dimmable operation of a fluorescent lamp at the operating frequency (f), having an apparatus for switching the operating frequency (f) on and off at a dimming frequency (f), the pulse width (W) of the dimming frequency (f) being variable, and where ff