The present invention relates to a circuit for controlling at least one LED and to a light- and/or signal element including said circuit, wherein the circuit facilitates an optimum utilization of any input voltage provided by an energy source and provides constant light intensity of the LEDs independent from an input voltage. For this purpose, the circuit contains a step-up converter arranged in the circuit in a way such that the step-up converter outputs a voltage adapted to a forward voltage of the at least one LED at a constant current independent from an input voltage provided by the energy source.