An operating device for an illuminant, wherein the operating device has - an interface circuit for generating an interface signal (21, 31, 41, 51) depending on a control signal (Vn, 10) generated outside of the operating device, which is designed in the form of a supply voltage control signal, and - a drive circuit for evaluating the interface signal (21, 31, 41, 51) and for the control at least of one illuminant depending on the evaluation of the interface signal (21,31,41,51), - wherein the interface circuit comprises means for detecting an overshooting of an upper threshold value of the control signal (Vn, 10), - wherein the interface circuit is designed to generate a first signal pulse (22, 55) for each detection of the overshooting of the upper threshold value, - wherein the interface circuit comprises a zero-crossing detection circuit, - wherein the zero-crossing detection circuit identifies an overshooting of a lower threshold value of the negative half-cycle of the control signal (Vn, 10), and - wherein for each detection of the overshooting of the lower threshold value of the control signal (Vn, 10) the zero-crossing detection circuit generates a second signal pulse having a low level compared to the first signal pulse (22, 55) in the interface signal (21, 31, 41, 51), characterized in - that the means for the detection is designed to detect an overshooting of the upper threshold value only in one of the two half-cycles of the control signal (Vn, 10); - that the interface circuit is designed to generate the first signal pulse (22, 55) in the interface signal (21, 31, 41, 51) in the range of the peak value of the positive half-cycle of the control signal (Vn, 10); and - that the drive circuit is arranged to identify the presence of the control signal (Vn, 10) on the basis of the first signal pulse (22, 55). - an interface circuit for generating an interface signal (21, 31, 41, 51) depending on a control signal (Vn, 10) generated outside of the operating device, which is designed in the form of a supply voltage control signal, and - a drive circuit for evaluating the interface signal (21, 31, 41, 51) and for the control at least of one illuminant depending on the evaluation of the interface signal (21,31,41,51), - wherein the interface circuit comprises means for detecting an overshooting of an upper threshold value of the control signal (Vn, 10), - wherein the interface circuit is designed to generate a first signal pulse (22, 55) for each detection of the overshooting of the upper threshold value, - wherein the interface circuit comprises a zero-crossing detection circuit, - wherein the zero-crossing detection circuit identifies an overshooting of a lower threshold value of the negative half-cycle of the control signal (Vn, 10), and - wherein for each detection of the overshooting of the lower threshold value of the control signal (Vn, 10) the zero-crossing detection circuit generates a second signal pulse having a low level compared to the first signal pulse (22, 55) in the interface signal (21, 31, 41, 51), - that the means for the detection is designed to detect an overshooting of the upper threshold value only in one of the two half-cycles of the control signal (Vn, 10); - that the interface circuit is designed to generate the first signal pulse (22, 55) in the interface signal (21, 31, 41, 51) in the range of the peak value of the positive half-cycle of the control signal (Vn, 10); and - that the drive circuit is arranged to identify the presence of the control signal (Vn, 10) on the basis of the first signal pulse (22, 55).