对于LED（5）的用于照明目的，一个恒流源（2）的用一个晶体管（3）控制被使用。 因此，晶体管（3）可以保持由所述发光二极管的电流恒定，该晶体管的集电极和发射极之间的电压降（3）必须大于晶体管的饱和电压高（3）。 根据本发明，检测在集电极和晶体管（3）和/的发射极或集电极和晶体管（3）的基极之间的电压降（并且相应地，FET晶体管）和恒流源（2）的电源电压以这样的方式被调节 跨越所述晶体管的第一电压降（3）对应于这是稍微晶体管UCESAT（3）的饱和电压以上的目标值。

For controlling the LED's (5) for lighting purposes, a constant current source (2) with a transistor (3) is used. Thus, the transistor (3) can keep the current constant by the light emitting diodes, the voltage drop between the collector and emitter of the transistor (3) must be greater than the saturation voltage of the transistor (3). According to the invention the voltage drop between the collector and the emitter of the transistor (3) and / or the collector and the base of the transistor (3) is detected (and accordingly the FET transistors) and the supply voltage of the constant current source (2) controlled in such a way that the first voltage drop across the transistor (3) corresponds to a target value which is just above the saturation voltage U _CESAT the transistor (3).