Solid state lighting device and method for operating the same
View Patent ↗A lighting device employs at least one string of LEDs as a lighting source. The string of LEDs may be coupled in series between a power supply node and ground. In order to accurately determine a drive current running through or drive voltage across the string of LEDs, the drive current through the string of LEDs or the drive voltage across the string of LEDs is sampled randomly or semi-randomly, and a moving average is determined from each one of the samples. By sampling the drive current through or drive voltage across the string of LEDs randomly or semi-randomly, inaccuracies due to synchronization of the sampling with interference in the drive current signal or the drive voltage signal are effectively prevented. Accordingly, an accurate measurement of the drive current through or the drive voltage across the string of LEDs may be obtained.
1. A lighting device comprising:
an array of light emitting diodes (LEDs) coupled between a power supply node and ground; and
a system controller configured to:
sample a drive signal provided to the array of LEDs at random or semi-random intervals to generate a plurality of drive signal samples;
determine a moving average of the plurality of drive signal samples to generate a drive signal measurement; and
generate one or more control signals based on the drive signal measurement.
2. The lighting device of claim 1 wherein the one or more control signals are used to adjust the color temperature of the array of LEDs as the array of LEDs is dimmed to accomplish a sunset dimming feature.
3. The lighting device of claim 1 wherein the one or more control signals are used to adjust the drive signal provided to the array of LEDs.
4. The lighting device of claim 1 wherein the drive signal is a drive current through the array of LEDs.
5. The lighting device of claim 4 further comprising a current sensing resistor coupled between the array of LEDs and ground.
6. The lighting device of claim 5 wherein the drive current is sampled by the system controller by measuring the voltage across the current sensing resistor.
7. The lighting device of claim 1 wherein the drive signal is a drive voltage across the array of LEDs.
8. The lighting device of claim 7 further comprising a voltage divider coupled between the power supply node and ground, the voltage divider including an output that is proportional to the drive voltage across the array of LEDs.
9. The lighting device of claim 8 wherein the drive voltage across the array of LEDs is sampled by the system controller by measuring the voltage at the output of the voltage divider.
10. The lighting device of claim 1 wherein the array of LEDs comprises a first string of series connected LEDs coupled between the power supply node and ground.
11. The lighting device of claim 10 wherein the array of LEDs further comprises a second string of series connected LEDs coupled in parallel with the first string of series connected LEDs between the power supply node and ground.
12. The lighting device of claim 1 wherein the system controller uses the drive signal measurement to adjust the color temperature of the light emitted from the array of LEDs.
13. The lighting device of claim 1 wherein a first subset of LEDs in the array of LEDs are red and a second subset of LEDs in the array of LEDs are blue-shifted yellow (BSY).
14. The lighting device of claim 13 wherein the system controller is adapted to adjust the color temperature of the light emitted from the array of LEDs by adjusting the intensity of one or more of the LEDs in the first subset of LEDs or the second subset of LEDs.
15. The lighting device of claim 14 wherein the one or more control signals are used to adjust the color temperature of the array of LEDs as the array of LEDs is dimmed to accomplish a sunset dimming feature.
16. A method of measuring a drive signal through an array of light emitting diodes (LEDs) coupled between a power supply node and ground in a lighting device comprising:
sampling the drive signal at random or semi-random intervals to generate a plurality of drive signal samples;
determining a moving average of the plurality of drive signal samples to generate a drive signal measurement; and
generating one or more control signals based on the drive signal measurement.
17. The method of claim 16 further comprising adjusting the color temperature of the array of LEDs based on the one or more control signals as the array of LEDs is dimmed to accomplish a sunset dimming feature.
18. The method of claim 16 further comprising adjusting the drive signal provided to the array of LEDs based on the one or more control signals.
19. The method of claim 16 wherein the drive signal is a drive current through the array of LEDs.
20. The method of claim 19 wherein the lighting device further comprises a current sensing resistor coupled between the array of LEDs and ground.
21. The method of claim 20 wherein the drive current is sampled by the system controller by measuring the voltage across the current sensing resistor.
22. The method of claim 16 wherein the drive signal is a drive voltage across the array of LEDs.
23. The method of claim 22 wherein the lighting device further comprises a voltage divider coupled between the power supply node and ground, the voltage divider including an output that is proportional to the drive voltage across the array of LEDs.
24. The method of claim 23 wherein the drive voltage across the array of LEDs is sampled by the system controller by measuring the voltage at the output of the voltage divider.
25. The method of claim 16 wherein the array of LEDs comprises a first string of series connected LEDs coupled between the power supply node and ground.
26. The method of claim 25 wherein the array of LEDs further comprises a second string of series connected LEDs coupled in parallel with the first string of series connected LEDs between the power supply node and ground.
27. The method of claim 16 wherein the system controller uses the drive signal measurement to adjust the color temperature of the light emitted from the array of LEDs.
28. The method of claim 16 wherein a first subset of LEDs in the array of LEDs are red and a second subset of LEDs in the array of LEDs are blue-shifted yellow (BSY).
29. The method of claim 28 wherein the system controller is adapted to adjust the color temperature of the light emitted from the array of LEDs by adjusting the intensity of one or more of the LEDs in the first subset of LEDs or the second subset of LEDs.
30. The method of claim 29 wherein the one or more control signals are used to adjust the color temperature of the array of LEDs as the array of LEDs is dimmed to accomplish a sunset dimming feature.