Controller for controlling an LED assembly, lighting application and method for controlling an LED assembly
A controller for controlling an LED assembly is described. The controller is arranged to—receive an input signal representing a required characteristic of the LED assembly,—convert the input signal to a control signal for the LED assembly,—apply a correction to the control signal to obtain a corrected control signal, the correction being based on a predetermined transient characteristic of the LED assembly,—output the corrected control signal. As such, a better correspondence between a required characteristic and an actual characteristic of the LED assembly is obtained.
1. A controller for controlling an LED assembly, the controller being arranged to
receive an input signal representing a required characteristic of the LED assembly;
convert the input signal to a control signal for the LED assembly;
apply a correction to the control signal to obtain a corrected control signal, the correction being based on a predetermined current slope of a current pulse of the LED assembly, the current slope occurring at a beginning and/or an end of the current pulse; and
output the corrected control signal.
2. The controller according to claim 1 wherein the control signal comprises a current set point.
3. The controller according to claim 2 wherein the current set point comprises an amplitude and a duration of a current pulse.
4. The controller according to claim 3 wherein the correction represents an increase of the duration of the required current pulse.
5. A lighting application comprising
an LED assembly comprising a converter arranged to, in use, provide a current to an LED unit; and
a controller according to claim 1 for controlling the LED assembly.
6. The controller according to claim 1 wherein the current slope of the current pulse is determined from a forward voltage over an LED of the LED assembly.
7. The controller according to claim 6 wherein the current slope of the current pulse is determined by subsampling.
8. The lighting application according to claim 5 further comprising the LED unit, the LED unit comprising one or more LEDs, the LED unit being arranged to, in use, receive the current provided by the converter of the LED assembly.
9. The controller according to claim 1 wherein the correction compensates for turn-on losses due to the current slope of the current pulse.
10. The controller according to claim 9 wherein the correction further incorporates a “current-to-light” output transfer function.
11. The controller according to claim 1 wherein the correction is obtained by subsampling.
12. The controller according to claim 1 wherein the correction represents an additional current pulse.
13. The lighting application according to claim 5 wherein the controller is further arranged to receive a voltage over a resistance, the resistance in use receiving the current.
14. The lighting application according to claim 13 wherein the voltage over the resistance is further applied as a feedback signal to the converter, for controlling the current provided by the converter.
15. The lighting application according to claim 13 wherein the controller is further arranged to provide a further feedback signal, preferable via a further resistance, to the controller, for controlling the current provided by the converter.
16. The lighting application according to claim 14 wherein the feedback signal or further feedback signal is increased with at least part of a reference voltage.
17. A method of controlling an LED assembly, the method comprising the steps of
receiving an input signal representing a required characteristic of the LED assembly;
converting the input signal to a control signal for the LED assembly;
applying a correction to the control signal to obtain a corrected control signal, the correction being based on a predetermined current slope of a current pulse of the LED assembly, the current slope occurring at a beginning and/or an end of the current pulse; and
outputting the corrected control signal.
18. The method according to claim 17 wherein the current pulse is determined by a current measurement.
19. The method according to claim 17 wherein the current pulse is determined from a voltage measurement.
20. The method according to claim 17 wherein the correction to the control signal is determined by
applying a signal to the LED assembly corresponding to a required characteristic of the LED assembly;
determining an actual characteristic of the LED assembly from a response to the signal;
determining a difference between the actual characteristic and the required characteristic; and
determining from the difference the correction applicable to the control signal to at least partly compensate the difference.
21. The method according to claim 17 wherein the characteristic comprises an intensity or a colour.