Adaptive startup method for constant current LED drivers

1. A controller for an LED driver circuit configured to provide an output current to an LED load, the controller comprising:

at least a first input to receive a sensed current provided to the LED load;

at least a first output to provide driving control signals to the LED driver circuit as a function of the sensed current to maintain the sensed current at a target current;

wherein the controller is programmed during a startup mode of operation to provide driving control signals further as a function of a first defined maximum output voltage value for the LED driver circuit,

wherein the controller is programmed during a steady state mode of operation to provide driving control signals further as a function of a second defined maximum output voltage value;

at least a second input to receive a dimming signal from a dimming circuit; and

wherein the controller is operable to control the current provided to the LED load further as a function of the received dimming signal by adjusting the target current as a function of the received dimming signal.

2. The controller of claim 1 , wherein the controller is programmed to operate in the startup mode for a first time duration after startup of the LED driver circuit.

3. The controller of claim 2 , wherein the controller is further programmed during a transition mode of operation to adjust a maximum output voltage value for the LED driver circuit from the first maximum output voltage value to the second maximum output voltage value over a second time duration.

4. The controller of claim 3 , wherein the controller is programmed during the transition mode of operation to provide a continuous adjustment of the maximum output voltage value for the LED driver circuit from the first maximum output voltage value to the second maximum output voltage value over the second time duration.

5. The controller of claim 3 , wherein the first and second time durations collectively exceed a warm up time associated with the LED load.

6. The controller of claim 3 , wherein the startup mode of operation is initiated by the controller programming upon each startup of the LED driver circuit.

7. The controller of claim 6 , wherein the steady state mode of operation is initiated by the controller programming upon completion of the second time duration and is maintained for the duration of operation of the LED driver circuit.

8. The controller of claim 1 , wherein the first maximum output voltage value for the LED driver circuit is associated with a forward voltage drop for the LED load at a first temperature, and the second maximum output voltage value for the LED driver circuit is associated with a forward voltage drop for the LED load at a second temperature.

9. The controller of claim 8 , wherein the first temperature is −40 degrees Celsius, and the second temperature is 20 degrees Celsius.

10. A method of providing adaptive startup voltage control for an LED driver circuit, the method comprising:

initiating a startup mode of operation based on sensed input power to the LED driver circuit;

during a duration of the startup mode of operation, providing driving control signals to the LED driver circuit as a function of a sensed current provided to an LED load to maintain the sensed current at a target current, and further as a function of a first defined maximum output voltage value;

during a steady state mode of operation, providing driving control signals to the LED driver circuit as a function of a sensed current provided to the LED load to maintain the sensed current at a target current, and further as a function of a second maximum output voltage value;

receiving a dimming signal from a dimming circuit; and

controlling the current provided to the LED load further as a function of the received dimming signal by adjusting the target current as a function of the received dimming signal.

11. The method of claim 10 , the duration of the startup mode of operation comprising a first time duration, the method further comprising:

during a transition mode of operation, adjusting a maximum output voltage value for the LED driver circuit from the first maximum output voltage value to the second maximum output voltage value over a second time duration.

12. The method of claim 11 , wherein during the transition mode of operation the maximum output voltage value for the LED driver circuit is continuously adjusted from the first maximum output voltage value to the second maximum output voltage value over the second time duration.

13. The method of claim 11 , wherein the first and second time durations collectively exceed a warm up time associated with the LED load.

14. The method of 11 , further comprising initiating the steady state mode of operation upon completion of the second time duration and maintaining the steady state mode of operation for the duration of operation of the LED driver circuit.

15. The method of claim 10 , wherein the first maximum output voltage value for the LED driver circuit is associated with a forward voltage drop for the LED load at a first temperature, and the second maximum output voltage value for the LED driver circuit is associated with a forward voltage drop for the LED load at a second temperature.

16. The method of claim 15 , wherein the first temperature is −40 degrees Celsius, and the second temperature is 20 degrees Celsius.

17. A driver circuit operable to provide current to a light source from a direct current (DC) power source having a power rail and a ground, the driver circuit comprising:

an inverter circuit having an input and an output, wherein the input is configured to connect to the power rail and the ground of the DC power source and to provide an alternating current (AC) signal at the output;

a resonant tank circuit having an input connected to the output of the inverter circuit and an output, the resonant tank circuit comprising a resonant inductor and a resonant capacitor connected between the output of the inverter circuit and the ground of the DC power source;

an isolating transformer connected to the output of the resonant tank circuit, the isolating transformer comprising a primary winding connected between the output of the resonant tank circuit and the ground of the DC power source, and a secondary winding;

an output rectifier having an input connected to the secondary winding of the isolating transformer and an output operable to connect to the light source; and

a controller configured to sense current provided to the light source from the output rectifier and adjust a switching frequency of the half-bridge inverter as a function of the sensed current to maintain the sensed current at a target current,

wherein the controller programmed during a startup mode of operation to adjust the switching frequency of the half-bridge inverter further as a function of a first defined maximum output voltage value for the driver circuit, and

wherein the controller is programmed during a steady state mode of operation to adjust the switching frequency of the half-bridge inverter further as a function of a second defined maximum output voltage value.

18. The driver circuit of claim 17 , wherein the duration of the startup mode of operation comprises a first time duration, and

wherein the controller is programmed during a transition mode of operation to adjust a maximum output voltage value for the LED driver circuit from the first maximum output voltage value to the second maximum output voltage value over a second time duration.