Dimmable lighting system

1. A lighting system for operation with a dimmer circuit comprising a triac connected to a load, the load comprising a driver circuit for supplying current to a light source comprising one or more LEDs, the current being determined at least in part by an adjusted setpoint value, the system further comprising a setpoint filter circuit for obtaining a dimmer setpoint value determined at least in part by a setting of the dimmer circuit, and for generating an adjusted setpoint value, wherein the sensitivity of the adjusted setpoint value to changes in the dimmer setpoint value is low at low values of the dimmer setpoint value.

2. The lighting system of claim 1 , wherein the setpoint filter circuit is configured to increase the adjusted setpoint at a lower rate at low values of the dimmer setpoint value, and at a higher rate at high values of the dimmer setpoint value.

3. The lighting system of claim 2 , wherein variation of the adjusted setpoint value in response to changes in the dimmer setpoint value approximates an exponential response.

4. The lighting system of claim 1 , wherein the setpoint filter circuit generates the full range of the adjusted setpoint value over less than the full range of the dimmer setpoint value.

5. The lighting system of claim 1 , wherein the setpoint filter circuit generates an adjusted setpoint value having a minimum value greater than zero.

6. The lighting system of claim 1 , wherein the setpoint filter circuit is configured to generate the adjusted setpoint having a first substantially constant value during a first portion of the range dimmer setpoint value, increasing at a low rate during a second portion of the range dimmer setpoint value, increasing at a high rate during a third portion of the range dimmer setpoint value, and having a second substantially constant value during a fourth portion of the range dimmer setpoint value.

7. The lighting system of claim 1 , wherein the setpoint filter circuit includes a second or higher order low pass filter for filtering the received dimmer setpoint value.

8. The lighting system of claim 1 , wherein the setpoint filter circuit comprises a differential amplifier generating an intermediate setpoint value, which controls a transistor to generate the adjusted setpoint value.

9. The lighting system of claim 1 , wherein the driver circuit comprises a voltage control circuit and a current control circuit, wherein the voltage control circuit controls the voltage at an output of the driver circuit according to a voltage setpoint, and the current control circuit modifies the voltage setpoint according to a current setpoint.

10. The lighting system of claim 9 , wherein the current control circuit operates within a predetermined range, the voltage setpoint being maintained at a boundary value when the current control circuit is at a boundary of its operating range.

11. The lighting system of claim 1 , wherein the setpoint filter circuit obtains the dimmer setpoint value from a voltage at an output terminal of the dimmer circuit.

12. The lighting system of claim 1 , wherein the setpoint filter circuit derives the dimmer setpoint value from a firing angle of the dimmer triac.

13. The lighting system of claim 12 , wherein the setpoint filter circuit derives the dimmer setpoint value from a time delay between a zero crossing of a supply voltage and a first triggering of the triac after the zero crossing point.

14. The lighting system of claim 12 , further comprising a dimmer triggering circuit for triggering the dimmer triac, and wherein the dimmer setpoint value is determined at least in part by a time of occurrence of one or more rising and/or falling edges of a current flowing through a dimmer triggering circuit, or a voltage related to the rising edge and falling edge.

15. The lighting system of claim 14 , wherein the dimmer setpoint value is determined at least in part by a time delay between a rising edge and a falling edge of a current flowing through a dimmer triggering circuit, or a voltage related to the rising edge and falling edge.

16. The lighting system of claim 1 , wherein the current through the dimmer circuit when the dimmer triac is on is below a holding current of the dimmer triac.

17. The lighting system of claim 1 , further comprising a dimmer triggering circuit for triggering the dimmer triac, the dimmer triggering circuit comprising a voltage-level detector for detecting whether an input voltage of the dimmer triggering circuit is below a threshold value, and a bipolar current source circuit for providing a current if the voltage detected by the voltage-level detector is below the threshold value and to be deactivated otherwise.

18. The lighting system of claim 17 , wherein the maximum current through the dimmer triggering circuit is below a holding current of the dimmer triac.

19. The lighting system of claim 17 , wherein the current through the dimmer triggering circuit is below a holding current of the triac when the dimmer triac is on.

20. The lighting system of claim 17 , wherein the current through the dimmer triggering circuit is below a holding current of the triac when the dimmer triac is off.

21. The lighting system of claim 17 , wherein the dimmer triggering circuit, in operation, dissipates an average power less than 100 mW.

22. A setpoint filter circuit for use in a lighting system comprising a triac dimmer circuit, a light source comprising one or more LEDs, and a driver circuit for supplying current to one or more LEDs, the current being determined at least in part by an adjusted setpoint value, the setpoint lifter circuit comprising:

an input circuit for obtaining a dimmer setpoint value determined at least in part by a setting of the dimmer circuit; and

an adjustment circuit for generating an adjusted setpoint value, wherein the sensitivity of the adjusted setpoint value to changes in the dimmer setpoint value is low at low values of the dimmer setpoint value.

23. The setpoint filter circuit of claim Z 2 , wherein the adjusted setpoint increases at a lower rate at low values of the dimmer setpoint value, and at a higher rate at high values of the dimmer setpoint value.

24. The setpoint filter circuit of claim 22 , wherein variation of the adjusted setpoint value in response to changes in the dimmer setpoint value approximates an exponential response.

25. The setpoint filter circuit of claim 2 , wherein the adjustment circuit generates the full range of the adjusted setpoint value over less than the full range of the dimmer setpoint value.

26. The setpoint filter circuit of claim 22 , wherein the adjustment circuit generates an adjusted setpoint value having a minimum value greater than zero.

27. The setpoint filter circuit of claim 22 , wherein the input circuit comprises a second or higher order low pass filter for filtering the received dimmer setpoint value.

28. The setpoint filter circuit of claim 22 , wherein the adjustment circuit comprises a differential amplifier generating an intermediate setpoint value, which controls a transistor to generate the adjusted setpoint value.

29. The setpoint filter circuit of claim 22 , wherein the dimmer setpoint value is derived from a voltage at an output terminal of the dimmer circuit.

30. The setpoint filter circuit of claim 22 , wherein the dimmer setpoint value is derived from a firing angle of the dimmer triac.

31. The setpoint filter circuit of claim 30 , wherein the dimmer setpoint value is derived from a time delay between a zero crossing of a supply voltage and a first triggering of the triac after the zero crossing point.

32. A lighting system for operation with a dimmer circuit comprising a triac, the system comprising

a light source comprising one or more LEDs, and

a load comprising a dimmer triggering circuit for triggering the dimmer triac and a driver circuit for supplying a current to the one or more LEDs, wherein the current supplied by the driver circuit is determined at least in part by a dimmer setpoint value, and wherein the dimmer setpoint value is derived at least in part from a firing angle of the dimmer triac, and

a setpoint filter circuit for generating an adjusted setpoint value from the dimmer setpoint value, wherein sensitivity of the adjusted setpoint value to changes in the dimmer setpoint value is low at values of the dimmer setpoint value.

33. The lighting system of claim 32 , wherein the driver circuit derives the dimmer setpoint value from a time delay between a zero crossing of a supply voltage and a first triggering of the triac after the zero crossing point.

34. The lighting system of claim 32 , wherein the dimmer setpoint value is determined at least in part by a time of occurrence of one or more rising and/or falling edges of a current flowing through a dimmer triggering circuit, or a voltage related to the rising edge and falling edge.

35. The lighting system of claim 34 , wherein the dimmer setpoint value is determined at least in part by a time delay between a rising edge and a falling edge of a current flowing through a dimmer triggering circuit, or a voltage related to the rising edge and falling edge.

36. The lighting system of claim 32 , wherein the driver circuit comprises a voltage control circuit and a current control circuit, wherein the voltage control circuit controls the voltage at an output of the driver circuit according to a voltage setpoint, and the current control circuit modifies the voltage setpoint according to a current setpoint.

37. The lighting system of claim 36 , wherein the current control circuit operates within a predetermined range, the voltage setpoint being maintained at a boundary value when the current control circuit is at a boundary of its operating range.

38. The lighting system of claim 32 , wherein the current through the dimmer circuit when the dimmer triac is on is below a holding current of the dimmer triac.

39. The lighting system of claim 32 , wherein the dimmer triggering circuit comprises a voltage-level detector for detecting whether an input voltage of the dimmer triggering circuit is below a threshold value, and a bipolar current source circuit for providing a current if the voltage detected by the voltage-level detector is below the threshold value and to be deactivated otherwise.

40. The lighting system of claim 32 , wherein the maximum current through the dimmer triggering circuit is below a holding current of the dimmer triac.

41. The lighting system of claim 32 , wherein the current through the dimmer triggering circuit is below a holding current of the triac when the dimmer triac is on.

42. The lighting system of claim 32 , wherein the current through the dimmer triggering circuit is below a holding current of the triac when the dimmer triac is off.

43. The lighting system of claim 32 , wherein the dimmer triggering circuit, in operation, dissipates an average power less than 100 mW.

44. The lighting system of claim 32 , wherein the setpoint lifter circuit is configured to increase the adjusted setpoint at a lower rate at low values of the dimmer setpoint value, and at a higher rate at high values of the dimmer setpoint value.

45. The lighting system of claim 32 , wherein variation of the adjusted setpoint value in response to changes in the dimmer setpoint value approximates an exponential response.

46. The lighting system of claim 32 , wherein the setpoint filter circuit generates the full range of the adjusted setpoint value over less than the full range of the dimmer setpoint value.

47. The lighting system of claim 32 , wherein the setpoint filter circuit generates an adjusted setpoint value having a minimum value greater than zero.

48. The lighting system of claim 32 , wherein the setpoint filter circuit is configured to generate the adjusted setpoint having a first substantially constant value during a first portion of the range dimmer setpoint value, increasing at a low rate during a second portion of the range dimmer setpoint value, increasing at a high rate during a third portion of the range dimmer setpoint value, and having a second substantially constant value during a fourth portion of the range dimmer setpoint value.

49. A lighting system for operation with a dimmer circuit comprising a triac, the system comprising a light source comprising one or more LEDs and a load comprising a dimmer triggering circuit for triggering the dimmer triac and a driver circuit for supplying a current to the one or more LEDs, the driver circuit comprising a power factor correction circuit, wherein the current supplied by the driver circuit is determined at least in part by an dimmer setpoint value which is derived at least in part from a firing angle of the dimmer triac, and a setpoint filter circuit for generating an adjusted setpoint value from the dimmer setpoint value, wherein sensitivity of the adjusted setpoint value to changes in the dimmer setpoint value is low at low values of the dimmer setpoint value.