In an embodiment of the present invention there is provided a device for providing a control voltage that is substantially equivalent to a reference voltage used by a power supply. The device includes a first electronic circuit that is arranged to be connected to a ground via a resistor and to produce a supplementary voltage that is dependant on a resistance of the resistor. The device also includes a second electronic circuit that is arranged to present a resistance to a current in order to provide the control voltage and to receive an output voltage of the power supply and the supplementary voltage to effect the current.