Patent ID: 8193741

Claim:
A circuit to deliver current from a current source to a light-emitting diode (LED) string, the circuit comprising: a pulse width modulator controller for generating a pulse-width modulated (PWM) drive signal having a duty cycle and driving the LED string with a regular current during an active period of the PWM drive signal; a forward voltage sense controller for driving a sense current, the sense current being driven into the LED string during an inactive period of the duty cycle of the PWM drive signal; a forward voltage sense measuring controller for measuring a forward voltage in the LED string created by the sense current and for outputting the forward voltage; a temperature controller for receiving the forward voltage from the forward voltage sense measuring controller and controlling the regular current, so that the LED string operates at a junction temperature below a maximum allowed operational junction temperature; and a current correction controller for receiving the forward voltage from the forward voltage sense measuring controller and controlling the regular current, wherein the flux of an LED in the LED string is stabilized by driving the LED with a constant power.