APPARATUS AND METHODS OF OPERATION OF PASSIVE LED LIGHTING EQUIPMENT

• US 20100270942A1
• Filed: 10/20/2009
• Published: 10/28/2010
• Est. Priority Date: 04/24/2009
• Status: Active Grant

• Current Assignee: City University of Hong Kong
• Original Assignee: City University of Hong Kong
• Inventors: Chen, Wu, HUI, Ron Shu Yuen
• Granted Patent: US 9,717,120 B2
• Time in Patent Office: Days
• US Class Current: 315/291
• CPC Class Codes: H05B 45/355 Power factor correction [PFC]; Reactive power compensation
• CPC Class Codes: H05B 45/375 using buck topology
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

This invention is concerned with the control and design of a LED lighting system that does not need electrolytic capacitors in the entire system and can generate light output with reduced luminous flux fluctuation. The proposal is particularly suitable, but not restricted to, off-line applications in which the lighting system is powered by the ac mains. By eliminating electrolytic capacitors which have a limited lifetime of typically 15000 hours, the proposed system can be developed with passive and robust electrical components such as inductor and diode circuits, and it features long lifetime, low maintenance cost, robustness against extreme temperature variations and good power factor. No extra electronic control board is needed for the proposed passive circuits, which can become dimmable systems if the ac input voltage can be adjusted by external means.

Claims

1. An LED lighting system comprising in sequence:

a rectification circuit for rectifying an AC input power and generating a rectified DC power;

a first circuit for reducing the voltage ripple of said rectified DC power;

a second circuit for generating a current source; and

at least one LED receiving said current source as an input.

2. The LED lighting system of claim 1, wherein said first circuit is a valley-fill circuit located between said rectification circuit and said second circuit.

3. The LED lighting system of claim 2, wherein said valley-fill circuit includes a first capacitor and a second capacitor.

4. The LED lighting system of claim 3, wherein the first and second capacitors have the same capacitance.

5. The LED lighting system of claim 3, wherein the first and second capacitors have different capacitances.

6. The LED lighting system of claim 2 including a parallel capacitor connected across the output of the valley-fill circuit.

7. The LED lighting system of claim 2, wherein said valley-fill circuit includes a voltage-doubler.

8. The LED lighting system of claim 1, wherein said second circuit comprises an inductor.

9. The LED lighting system of claim 8, including a capacitor connected in parallel across the inductor.

10. The LED lighting system of claim 1, wherein said second circuit is a current ripple reduction circuit.

11. The LED lighting system of claim 10, wherein said current ripple reduction circuit comprises a coupled inductor with a capacitor.

12. The LED lighting system of claim 1, wherein means are provided for controlling the sensitivity of the LED power to fluctuations in the voltage of the AC input power.

13. The LED lighting system of claim 12, wherein said means for controlling the sensitivity of the LED power to fluctuations in the voltage of the AC input power comprises an input inductor provided in series between the AC input and the diode rectification circuit.

14. The LED lighting system of claim 13, further comprising a capacitor provided in parallel between the said input inductor and the said diode rectification circuit.

15. The LED lighting system of claim 13, wherein the input inductor is inductively coupled to a secondary winding connected in parallel across the AC input before the input inductor.

16. The LED lighting system of claim 15, further comprising a capacitor connected in series between the secondary winding and the AC input before the input inductor.

17. The LED lighting system of claim 13, wherein said input inductor is a variable inductor controllable such that the at least one LED is dimmable.

18. The LED lighting system of claim 12, wherein said first circuit includes an output capacitor connected across said rectification circuit between said rectification circuit and said second circuit.

19. The LED lighting system of claim 1 including an input capacitor connected in series between the AC input and the rectification circuit.

20. The LED lighting system of claim 19 including an anti-surge-component connected in series before the input capacitor.

21. The LED lighting system of claim 20, wherein the anti-surge-component is an inductor or a temperature-dependent resistor.

22. The LED lighting system of claim 1, wherein means are provided for varying the AC input power such that the at least one LED is dimmable.

23. The LED lighting system of claim 22, wherein said means for varying the AC input power comprises a variable inductor provided in series between the AC input and the diode rectification circuit.

24. The LED lighting system of claim 23, wherein said variable inductor is provided with tapping control.

25. The LED lighting system of claim 23, wherein said variable inductor is provided with an auxiliary winding having a current to alter a magnetic property of the core in order to vary the inductance value of said variable inductor.

26. The LED lighting system of claim 1, wherein the power supplied to said at least one LED is permitted to vary, and wherein the operating and/or design parameters of said at least one LED are chosen such that the variation in luminous flux resulting from the variation in power is not observable to the human eye.

27. An LED lighting system comprising:

an AC input power source;

a rectification circuit for rectifying an AC input power and generating a rectified DC power; and

an input inductor provided in series between the AC input power source and the rectification circuit.

28. The LED lighting system of claim 27, further comprising a capacitor provided in parallel between the said input inductor and the said diode rectification circuit.

29. The LED lighting system of claim 27, wherein the input inductor is inductively coupled to a secondary winding connected in parallel across the AC input before the input inductor.

30. The LED lighting system of claim 29, further comprising a capacitor connected in series between the secondary winding and the AC input before the input inductor.

31. The LED lighting system of claim 27, wherein said input inductor is a variable inductor controllable such that the LED lighting system is dimmable.

32. The LED lighting system of claim 31, wherein said variable inductor is provided with tapping control.

33. The LED lighting system of claim 31, wherein said variable inductor is provided with an auxiliary winding having a current to alter a magnetic property of the core in order to vary the inductance value of said variable inductor.

34. A method of operating a LED lighting system comprising:

rectifying an AC input voltage to generate a rectified DC power;

reducing the voltage ripple of said rectified DC power;

generating a current source from said voltage ripple reduced rectified DC power; and

providing said current source as an input to at least one LED, wherein the power supplied to said at least one LED is permitted to vary, and wherein the operating and/or design parameters of said at least one LED are chosen such that the variation in luminous flux resulting from the variation in power is not observable to the human eye.

35. The method of claim 34, wherein a thermal characteristic of the at least one said LED is chosen such that the variation in luminous flux resulting from the variation in power is not observable to the human eye.

36. The method of claim 35, wherein said thermal characteristic comprises the design of the heatsink.

37. The method of claim 35, wherein said thermal characteristic comprises the provision of forced cooling or natural cooling.

38. The method of claim 34, wherein a valley-fill circuit is used to reduce the voltage ripple of the rectified DC power.

39. The method of claim 38, wherein the valley-fill circuit is provided with a first capacitor and a second capacitor.

40. The method of claim 39, wherein the first capacitor and the second capacitor have the same capacitance.

41. The method of claim 39, wherein the first capacitor is selected with a different capacitance to the second capacitor.

42. The method of claim 38, wherein a parallel capacitor is connected across the output of the valley-fill circuit to further reduce the voltage ripple of the rectified DC power.

43. The method of claim 38, wherein said valley-fill circuit includes a voltage-doubler.

44. The method of claim 34, further comprising the step of reducing the current ripple of said current source.

45. The method of claim 44, wherein an inductor is used to reduce the current ripple.

46. The method of claim 45, wherein a capacitor is connected in parallel across the inductor.

47. The method of claim 44, wherein a coupled inductor with a capacitor is used to reduce the current ripple.

48. The method of claim 34, further comprising reducing the sensitivity of the LED power to fluctuations in the AC input voltage.

49. The method of claim 48, further comprising providing an input inductor to reduce the sensitivity of the LED power to fluctuations in the AC input voltage before rectifying the AC input voltage.

50. The method of claim 49, further comprising providing a capacitor in parallel after the said input inductor before rectifying the AC input voltage.

51. The method of claim 49, further comprising inductively coupling the input inductor to a secondary winding connected in parallel across the AC input before the input inductor.

52. The method of claim 51, wherein a capacitor is connected in series between the secondary winding and the AC input before the input inductor.

53. The method of claim 49, further comprising controllably varying the input inductor such that the at least one LED is dimmable.

54. The method of claim 48, wherein an output capacitor connected across the rectified DC power is used to reduce the voltage ripple of the rectified DC power.

55. The method of claim 34, further comprising providing an input capacitor connected in series with the AC input before rectifying the AC input voltage.

56. The method of claim 55, further comprising providing an anti-surge-component connected in series before the input capacitor.

57. The method of claim 56, wherein the anti-surge-component is provided as an inductor or a temperature-dependent resistor.

58. The method of claim 34, further comprising varying the AC input voltage such that the at least one LED is dimmable.

59. The method of claim 58, further comprising providing a variable inductor to vary the AC input voltage.

60. The method of claim 59, further comprising controlling the variable inductor with tapping control.

61. The method of claim 59, further comprising providing the variable inductor with an auxiliary winding having a current and altering a magnetic property of the core in order to vary the inductance value of said variable inductor.

62. A method of providing power to a LED lighting system comprising:

providing an AC input;

reducing the sensitivity of the power provided to the LED lighting system to fluctuations in the voltage of the AC input power; and

rectifying the AC input power and generating a rectified DC power that is provided to the LED lighting system.

63. The method of claim 62, further comprising providing an input inductor to reduce the sensitivity of the LED power to fluctuations in the AC input voltage before rectifying the AC input voltage.

64. The method of claim 63, further comprising providing a capacitor in parallel after the said input inductor before rectifying the AC input voltage.

65. The method of claim 63, further comprising inductively coupling the input inductor to a secondary winding connected in parallel across the AC input before the input inductor.

66. The method of claim 65, wherein a capacitor is connected in series between the secondary winding and the AC input before the input inductor.

67. The method of claim 63, wherein the input inductor is a variable inductor to vary the AC input voltage such that the LED lighting system is dimmable.

68. The method of claim 67, further comprising controlling the variable inductor with tapping control.

69. The method of claim 67, further comprising providing the variable inductor with an auxiliary winding having a current and altering a magnetic property of the core in order to vary the inductance value of said variable inductor.

70. A system including a valley-fill circuit for generating a DC output voltage, said system including a parallel capacitor connected across said valley-fill circuit such that the voltage ripple of the DC output voltage is reduced.

71. The system of claim 70, further comprising a current source circuit to receive and convert said voltage ripple reduced DC output voltage into a current source, said current source thereby having a reduced current ripple.

72. The system of claim 71, wherein the current source circuit includes an inductor.

73. The system of claim 71 connected as an input to a load requiring a relatively constant current source.

74. The system of claim 73, wherein said load is an LED lighting system.

75. A method of generating a DC output by using a valley-fill circuit and a parallel capacitor connected across said valley-fill circuit such that the DC output voltage is generated with reduced voltage ripple.

76. The method of claim 75, further comprising converting the DC output voltage to a current source having a reduced current ripple.

77. The method of claim 76, wherein an inductor is used to convert the DC output voltage to a current source.

78. The method of claim 76, further comprising connecting the current source as an input to a load requiring a relatively constant current source.

79. The method of claim 78, wherein said load is an LED lighting system.

80. An LED lighting system comprising:

an AC input power source;

a rectification circuit for rectifying an AC input power and generating a rectified DC power; and

an input capacitor provided in series between the AC input power source and the rectification circuit.

81. The LED lighting system of claim 80 including an anti-surge-component connected in series before the input capacitor.

82. The LED lighting system of claim 81, wherein the anti-surge-component is an inductor or a temperature-dependent resistor.

83. A method of providing power to a LED lighting system comprising:

providing an AC input;

providing an input capacitor to receive power from the AC input; and

rectifying the AC input power from the input capacitor and generating a rectified DC power that is provided to the LED lighting system.

84. The method of claim 83, further comprising providing an anti-surge-component connected in series before the input capacitor.

85. The method of claim 84, wherein the anti-surge-component is provided as an inductor or a temperature-dependent resistor.