A control input of an electrical device is disclosed, which is resistant to parasitic currents and which is especially suitable for a large bandwidth of various driving voltages. For this purpose, a control input circuit includes a constant current sink connected to a control line, whose current consumption during the duration of the detection pulse assumes a detection value relative which the power consumption between two successive detection pulses is reduced. The circuit also includes an evaluation module that analyzes the input current flowing in the control line and that indicates a control signal if, during the detection pulse, the input current does not fall below a predetermined switch-on value for a predetermined duty cycle.