Patent ID: 6930452

Claim:
A device comprising: an array of semiconductor light emitting devices; a first driver for supplying current to a first portion of the devices in the array, the first driver comprising: a first switch capable of adjusting an amount of current supplied to the first portion; a first control circuit capable of generating a first control signal for controlling the conductive state of the first switch; a first control loop capable of controlling an amount of light generated by the first portion at a level represented by a first reference signal by adjusting a duty cycle of the first control signal; a second driver for supplying current to a second portion of the devices in the array, the second driver comprising: a second switch capable of adjusting an amount of current supplied to the second portion; a second control circuit capable of generating a second control signal for controlling the conductive state of the second switch; a second control loop capable of controlling an amount of light generated by the second portion at a level represented by a second reference signal by adjusting a duty cycle of the second control signal; and a relative intensity control loop capable of limiting the duty cycles of the first and second control signals to a limit value, by decreasing values of the first and second reference signals by the same relative amount.