Patent ID: 7750579

Claim:
A device for driving a light-emitting-diode element having a variable light intensity and a total threshold voltage, the device comprising: a supply stage having an output to be connected to said light-emitting-diode element, said supply stage being configured so as to have a first operating mode and a second operating mode, wherein, in said first operating mode, said supply stage generates a controlled supply current and, in said second operating mode, said supply stage generates a controlled non-zero supply voltage no greater than said total threshold voltage; a current sensor operable to generate a current-feedback signal correlating to the current flowing in said light-emitting-diode element and further operable to provide said current-feedback signal to said supply stage in the first operating mode; and an intensity-control stage operable to generate a mode-control signal and to provide the mode-control signal to said supply stage to switch between said first and second operating modes according to a desired light intensity, wherein said mode-control signal is a signal defining a first time interval and a second time interval corresponding to said first and said second operating modes, and wherein said intensity-control stage further comprises, a regulation circuit for regulating said first and second time intervals, and an enabling stage connected between said regulation circuit and said supply stage and generating said mode-control signal, wherein said enabling stage comprises a resistive network having a first intermediate node supplying said mode-control signal and a circuit for modifying the dividing ratio, controlled by said regulation circuit.