Patent ID: 7973487

Claim:
A power supply circuit for supplying current to a LED, the circuit comprising: a DC-DC power converter with a power input and a power output; a charge pump coupled to an output of the DC-DC power converter; a first capacitor coupled to the charge pump and adapted to be either connected to be charged by the charge pump to a voltage on top of the converter output during a first mode of operation or to be connected so as to discharge through the LED during a second mode of operation; and a control stage for switching between the first mode of operation and the second mode of operation , wherein the control stage comprises: a first error amplifier with a first input coupled to a first reference voltage source and a second input coupled to a current drain in the current path of the LED, a second error amplifier with a first input coupled to a second reference voltage source and a second input coupled to the output of the power converter, and switching means for connecting a control input of a pulse width modulator in the converter with the output of the first error amplifier in a current regulation mode and with the output of the second error amplifier in a voltage regulation mode.