Circuit and method for improved dimming of gas discharge lamps

• US 5,041,763 A
• Filed: 07/13/1990
• Issued: 08/20/1991
• Est. Priority Date: 12/22/1989
• Status: Expired due to Term

• Current Assignee: Lutron Technology Company LLC
• Original Assignee: Lutron Electronics Company Incorporated (Lutron Electronics)
• Inventors: Jurell, Scott R., Sullivan, Charles R., Spira, Joel S., Luchaco, David G., Motto, Eric R.
• Primary Examiner(s): MIS, DAVID C
• Application Number:
  US07/553,201
• Time in Patent Office: 403 Days
• Field of Search: 315/160, 315/171, 315/174, 315/175, 315/176, 315/227 R, 315/283, 315/291, 315/297, 315/301, 315/307, 315/308, 315/311, 315/DIG. 4
• US Class Current: 315/176
• CPC Class Codes: H05B 41/2858 for protecting the lamp against abnormal operating conditions
• CPC Class Codes: H05B 41/3927 by pulse width modulation H05B41/3922 takes precedence
• CPC Class Codes: Y02B 20/00 Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps
• CPC Class Codes: Y10S 315/04 Dimming circuit for fluorescent lamps

Abstract

A dimming circuit provides power from an ac source to a compact fluorescent lamp. The circuit generally includes a resonant circuit driven by a high-frequency switching inverter and a current feedback control system. The circuit is essentially an ac current source of unusually high impedance and provides substantially symmetrical high-frequency current to the lamp. This allows flicker-free dimming of compact fluorescent lamps over a wide range with good light output stability. A small amount of dc or low-frequency ac current may be simultaneously provided to the lamp. The resulting composite current waveform flowing through the lamp substantially eliminates visible striations over a dimming range from about 100% to 1% of full light output.

Claims

1. A control system for providing electrical power from a source to at least one gas discharge lamp comprising:

a) means for producing a composite current waveform, said waveform comprising an ac current component and a dc current component; and

b) means for providing said composite current waveform to said at least one lamp;

whereby visible striations in said at least one lamp are substantially eliminated.

2. The control system of claim 1 wherein said ac current component of said composite current waveform is a high frequency ac current component.

3. The control system of claim 1 wherein said ac current component of said composite current waveform is a substantially symmetrical ac current component.

4. The control system of claim 1 wherein said ac current component of said composite current waveform is a substantially symmetrical high frequency ac current component.

5. The control system of claim 1 wherein said ac current component of said composite current waveform is a pulse duration modulated waveform.

6. The control system of claim 1 wherein said ac current component of said composite current waveform is a substantially sinusoidal waveform.

7. The control system of claim 1 wherein said means for producing a composite current waveform comprises:

a) means for producing an ac current component,

b) separate means for producing a dc current component; and

c) means for combining said ac and dc current components to produce said composite current waveform.

8. The control system of claim 1 wherein said dc current component is less than about 5% of the nominal operating current at full rated light output.

9. A control system for providing electrical power from a source to at least one gas discharge lamp, comprising:

a) means for providing to said at least one lamp an ac component of current at a first frequency; and

b) means for simultaneously providing to said at least one lamp an ac component of current at a second frequency, substantially lower than said first frequency;

whereby a composite current waveform is established in said at least one lamp which substantially eliminates the occurrence of visible striations.

10. The control system of claim 9 wherein said second frequency is between about 30 Hz and about 5 kHz.

11. The control system of claim 9 wherein said first frequency is higher than about 5 kHz.

12. The control system of claim 11 wherein said ac component of current at said first frequency is a substantially symmetrical ac component of current.

13. The control system of claim 9 wherein said ac component of current at said first frequency is a pulse duration modulated ac component of current.

14. The control system of claim 9 wherein said ac component of current at said first frequency is a substantially sinusoidal component of current.

15. The control system of claim 9 wherein said means for providing an ac component of current at a first frequency and said means for providing an ac component of current at a second frequency are part of a single current providing means.

16. The control system of claim 9 wherein the RMS value of said ac component of current at a second frequency is less than about 5% of the lamp nominal operating RMS current at full rated light output.

17. A control system for operating a gas discharge lamp at light levels below about 40% of nominal light output, comprising:

means for producing an ac current in said lamp, said means having an output impedance characteristic of greater than about 5,000 ohm.

18. The control system of claim 17 wherein said ac current is a pulse duration modulated current.

19. The control system of claim 17 wherein said ac current is a substantially sinusoidal current.

20. The control system of claim 17 wherein said ac current is at a high frequency.

21. The control system of claim 17 wherein said ac current is substantially symmetrical.

22. The control system of claim 17 further comprising resistor means for obtaining said output impedance characteristic.

23. The control system of claim 17 further comprising inductor means for obtaining said output impedance characteristic.

24. The control system of claim 17 further comprising capacitor means for obtaining said output impedance characteristic.

25. The control system of claim 17 further comprising resonant circuit means for obtaining said output impedance characteristic.

26. The control system of claim 17 further comprising lamp current control means having current feedback means for obtaining said output impedance characteristic.

27. The control system of claim 25 further comprising lamp current control means having current feedback means for obtaining said output impedance characteristic.

28. The control system of claim 17 wherein said output impedance characteristic is greater than approximately 10,000 ohms.

29. The control system of claim 17 wherein said output impedance characteristic is greater than approximately 35,000 ohms.

30. A control system for op rating a gas discharge lamp at light levels below about 40% of nominal light output, said lamp having a cross section <

f average diameter less than about seven-eighths of an in<

h, and a voltage/current characteristic which include;

at least one region of negative resistance, comprising;

means for producing an ac current in said lamp, said means having an output impedance characteristic of greater than about 5,000 ohms.

31. The control system of claim 30 wherein said ac current is a pulse duration modulated current.

32. The control system of claim 30 wherein said ac current is a substantially sinusoidal current.

33. The control system of claim 30 wherein said ac current is at a high frequency.

34. The control system of claim 30 wherein said ac current is substantially symmetrical.

35. The control system of claim 30 further comprising resistor means for obtaining said output impedance characteristic.

36. The control system of claim 30 further comprising inductor means for obtaining said output impedance characteristic.

37. The control system of claim 30 further comprising capacitor means for obtaining said output impedance characteristic.

38. The control system of claim 30 further comprising resonant circuit means for obtaining said output impedance characteristic.

39. The control system of claim 30 further comprising lamp current control means having current feedback means for obtaining said output impedance characteristic.

40. The control system of claim 35, 36, 37, or 38 further comprising lamp current control means having current feedback means for obtaining said output impedance characteristic.

41. The control system of claim 30 wherein said output impedance characteristic is greater than approximately 10,000 ohms.

42. The control system of claim 30 wherein said output impedance characteristic is greater than approximately 35,000 ohms.

43. A control system for operating a gas discharge lamp at light levels below about 40% of nominal light output;

said lamp having a voltage/current characteristic which includes at least one region of negative resistance, comprising;

means for producing a substantially symmetrical ac current in said lamp, said means having an output impedance characteristic of greater than about 5,000 ohms.

44. The control system of claim 43 wherein said substantially symmetrical ac current is a pulse duration modulated current.

45. The control system of claim 43 wherein said substantially symmetrical ac current is a substantially sinusoidal current.

46. The control system of claim 43 wherein said substantially symmetrical ac current is at a high frequency.

47. The control system of claim 43 further comprising resistor means for obtaining said output impedance characteristic.

48. The control system of claim 43 further comprising inductor means for obtaining said output impedance characteristic.

49. The control system of claim 43 further comprising capacitor means for obtaining said output impedance characteristic.

50. The control system of claim 43 further comprising resonant circuit means for obtaining said output impedance characteristic.

51. The control system of claim 43 further comprising lamp current control means having current feedback means for obtaining said output impedance characteristic.

53. The control system of claim 43 wherein said output impedance characteristic is greater than approximately 10,000 ohms.

54. The control system of claim 43 wherein said output impedance characteristic is greater than approximately 35,000 ohms.

55. The control system of claim 43 wherein said lamp has a substantially circular cross section of average diameter less than about seven-eighths inch.

56. The control system of claim 43 further comprising means for producing a dc component of current in said lamp to substantially eliminate visible striations.

57. The control system of claim 43 further comprising means for producing a low frequency ac component of current in said lamp to substantially eliminate visible striations.

52. The control system of c]aim 47, 48, 49, or 50 further comprising lamp current control means having current feedback means for obtaining said output impedance characteristic.

58. A control system for operating a gas discharge lamp at light levels below about 40% of nominal light output, said lamp having a maximum negative resistance greater than about 330 ohms, comprising:

means for producing an ac current in said lamp, said means having an output impedance characteristic of greater than about 5,000 ohms.

59. The control system of claim 58 wherein said ac current is a pulse duration modulated current.

60. The control system of claim 58 wherein said ac current is a substantially sinusoidal current.

61. The control system of claim 58 wherein said ac current is at a high frequency.

62. The control system of claim 58 wherein said ac current is substantially symmetrical.

63. The control system of claim 58 further comprising resistor means for obtaining said output impedance characteristic.

64. The control system of claim 58 further comprising inductor means for obtaining said output impedance characteristic.

65. The control system of claim 58 further comprising capacitor means for obtaining said output impedance characteristic.

66. The control system of claim 58 further comprising resonant circuit means for containing said output impedance characteristic.

67. The control system of claim 58 further comprising lamp current control means having current feedback means for obtaining said output impedance characteristic.

68. The control system of claim 63, 64, 65, or 66 further comprising lamp current control means having current feedback means for obtaining said output impedance characteristic.

69. The control system of claim 58 wherein said output impedance characteristic is greater than approximately 10,000 ohms.

70. The control system of claim 58 wherein said output impedance characteristic is greater than approximately 35,000 ohms.

71. A control system for operating a gas discharge lamp at light levels below about 40% of nominal light output, said lamp having a cross section of average diameter less than about seven-eighths of an inch, and a voltage/current characteristic which include:

at least one region of negative resistance, comprising;

means for producing a substantially symmetrical ac current in said lamp, said means having an output impedance characteristic of greater than about 5,000 ohms.

72. The control system of claim 71 wherein said substantially symmetrical ac current is a pulse duration modulated current.

73. The control system of claim 71 wherein said substantially symmetrical ac current is a substantially sinusoidal current.

74. The control system of claim 71 wherein said substantially symmetrical ac current is at a high frequency.

75. The control system of claim 71 further comprising resistor means for obtaining said output impedance characteristic.

76. The control system of claim 71 further comprising inductor means for obtaining said output impedance characteristic.

77. The control system of claim 71 further comprising capacitor means for obtaining said output impedance characteristic.

78. The control system of claim 71 further comprising resonant circuit means for obtaining said output impedance characteristic.

79. The control system of claim 71 further comprising lamp current control means having current feedback means for obtaining said output impedance characteristic.

80. The control system of claim 75, 76, 77, or 78 further comprising lamp current control means having current feedback means for obtaining said output impedance characteristic.

81. The control system of claim 71 wherein said output timpedance characteristic is greater than approximately 10,000 ohms.

82. The control system of claim 71 wherein said output impedance characteristic is greater than approximately 35,000 ohms.

83. A control system for op rating a gas discharge lamp at light levels below about 40% of nominal light output, said control system having a maximum output impedance characteristic of at least about 5,000 ohms and comprising:

a) a high frequency source having a relatively low output impedance;

b) at least one passive impedance element connected in series between said source and said lamp;

c) current sensing means for sensing an actual current in said lamp; and

d) amplifier means responsive to said current sensing means for increasing the effective output impedance characteristic of said control system beyond that of said passive impedance element alone.

84. The control system of claim 83 wherein said high frequency source is a pulse duration modulated source.

85. The control system of claim 83 wherein said high frequency source is a substantially sinusoidal source.

86. The control system of claim 83 wherein the output impedance of said high frequency source is less than about 500 ohms.

87. The control system of claim 83 wherein said passive impedance element has an impedance of less than about 4,500 ohms.

88. The control system of claim 83 wherein said lamp has a substantially circular cross section, said cross section having a diameter of less than about seven-eighths inch.

90. The control system of claim 83 further comprising means for producing a dc component of current in said lamp to substantially eliminate visible striations.

91. The control system of claim 83 further comprising means for producing a low frequency ac component of current in said lamp to substantially eliminate visible striations.

92. The control system of claim 83 wherein said output impedance characteristic is greater than approximately 10,000 ohms.

93. The control system of claim 83 wherein said output impedance characteristic is greater than approximately 35,000 ohms.

89. The control system of c[aim 83 wherein said high frequency source is a substantially symmetrical high frequency source.

94. A control system for operating a gas discharge lamp at light levels below about 40% of nominal light output, said control system having a maximum output impedance characteristic of at least about 5,000 ohms and comprising:

a) a high frequency source having a relatively low output impedance;

b) at least one passive impedance element connected in series between said source and at least one lamp;

c) means for sensing an actual current in said lamp and producing a first signal indicative of said actual lamp current;

d) means for comparing said first signal to a reference value and producing a second signal indicative of the difference between said first signal and said reference value; and

e) means responsive to said second signal for adjusting said high frequency source such that the difference between said first signal and said reference value tends towards zero.

95. The control system of claim 94 wherein said high frequency source is a pulse duration modulated source.

96. The control system of claim 94 wherein said high frequency source is a substantially sinusoidal source.

97. The control system of claim 94 wherein the output impedance of said high frequency source is less than about 500 ohms.

98. The control system of claim 94 wherein said passive impedance element has an impedance of less than about 4,500 ohms.

99. The control system of claim 94 wherein said lamp has a substantially circular cross section of average diameter less than about seven-eighths inch.

100. The control system of claim 94 wherein the output waveform of said high frequency source is substantially symmetrical.

101. The control system of claim 94 further comprising means for producing a dc component of current in said lamp to substantially eliminate visible striations.

102. The control system of claim 94 further comprising means for producing a low frequency ac component of current in said lamp to substantially eliminate visible striations.

103. The control system of claim 94 wherein said output impedance characteristic is greater than approximately 10,000 ohms.

104. The control system of claim 94 wherein said output impedance characteristic is greater than approximately 35,000 ohms.

105. A method of substantially eliminating the occurrence of visible striations in a gas discharge lamp, comprising the steps of:

a) providing to said lamp ac current to strike and maintain an electric discharge therethrough; and

b) simultaneously providing to said lamp a dc component of current;

whereby a composite current waveform is established in the lamp which substantially eliminates the occurrence of visible striations.

106. A method of substantially eliminating the occurrence of visible striations in a gas discharge lamp comprising the steps of:

a) providing to said lamp an ac component of current at a first frequency;

b) simultaneously providing to said lamp an ac component of current at a second frequency substantially lower than said first frequency;

whereby a composite ac current waveform is established in said lamp which substantially eliminates the occurrence of visible striations.

107. A method of substantially eliminating the occurrence of visible striations in a gas discharge lamp comprising the steps of:

a) generating an ac current at a first frequency;

b) generating an ac current at a second frequency substantially lower than said first frequency;

c) adding together said first and second frequency ac currents to obtain a composite ac current; and

d) providing said composite ac current to said gas discharge lamp to substantially eliminate the occurrence of visible striations.