Driver of an LED array

1. A driver of an array of current-driven light emitting diodes (LEDs), comprising:

a voltage converter arranged to generate a supply voltage to the LED array and to adjust the supply voltage in response to a feedback signal;

a plurality of current regulators arranged to drive the LEDs of the LED array, wherein the cathode of each LED is connected to a current regulator; and

a monitoring arrangement adapted to monitor a current regulator voltage relative to a voltage headroom and to generate the feedback signal on the basis of headroom monitoring results, the monitoring arrangement comprising a plurality of window comparators, and wherein the cathode of each current-driven LED is also connected to an input of a window comparator, and wherein the window comparator is realized to generate a high comparator output when the LED cathode voltage is lower than a first input voltage defining a lower bound of the voltage headroom and to generate a low comparator output when that LED cathode voltage is higher than a second input voltage defining an upper bound of the voltage headroom, and wherein the feedback signal comprises bundled comparator outputs.

2. The driver according to claim 1 , wherein the current regulator comprises a controlled active device.

3. The driver according to claim 2 , wherein the current regulator comprises a bipolar transistor or a MOSFET.

4. The driver according to claim 1 , wherein the window comparator comprises:

a first operational amplifier and a first diode connected in forward direction between the output of the first operational amplifier and the comparator output; and

a second operational amplifier and a second diode connected in reverse direction between the output of the second operational amplifier and the comparator output.

5. The driver according to claim 4 , wherein

inverting inputs of the operational amplifiers are connected to an electrode of an LED;

a non-inverting input of the first operational amplifier is connected to the first input voltage; and

a non-inverting input of the second operational amplifier is connected to the second input voltage.

6. The driver according to claim 5 , wherein the window comparator comprises a resistor between the cathode of the first diode and the anode of the second diode so that a single comparator with a high output level on its first operational amplifier is adapted to push the feedback signal above a threshold level.

7. The driver according to claim 1 , wherein an electrode of each LED is connected to a dedicated current regulator.

8. A device comprising:

the LED array comprising a plurality of current-driven LEDs; and

the driver according to claim 1 , arranged to drive the LEDs.

9. The device according to claim 8 , wherein the LED array is realized as a segmented flash comprising at least nine LEDs.

10. The device according to claim 8 , in the form of a mobile phone.

11. The device according to claim 8 , wherein the voltage converter is realized as any of a boost converter, a buck converter, or a buck-boost converter.

12. The device according to claim 8 , comprising the plurality of current regulators, each configured to control the current through an LED of the LED array, and wherein an electrode of each LED is connected to a current regulator.

13. A method of driving the array of current-driven LEDs using the driver according to claim 1 , which method comprises:

increasing the supply voltage (V boost ) of the voltage converter when the feedback signal from the monitoring arrangement (M) is higher than a threshold level (V 20 ); and

decreasing the supply voltage (V boost ) of the voltage converter ( 10 ) when the feedback signal from the monitoring arrangement (M) is lower than a threshold level (V 20 ).