Mixed mode control for dimmable fluorescent lamp

• US 7,923,939 B1
• Filed: 08/29/2008
• Issued: 04/12/2011
• Est. Priority Date: 01/29/2004
• Status: Active Grant

• Current Assignee: Marvell Asia Pte Limited (Marvell Technology Group Limited)
• Original Assignee: Marvell International Limited (Marvell Technology Group Limited)
• Inventors: Hamdad, Fatemeh, Notohamiprodjo, Hubertus
• Primary Examiner(s): Vo; Tuyet Thi
• Application Number:
  US12/202,017
• Time in Patent Office: 956 Days
• Field of Search: 315/224, 315/225, 315/209.R, 315/247, 315/246, 315/291, 315307-311
• US Class Current: 315/224
• CPC Class Codes: H05B 41/3925 by frequency variation H05B41/3922 takes precedence
• CPC Class Codes: H05B 41/3927 by pulse width modulation H05B41/3922 takes precedence

Abstract

A mixed mode control for dimmable fluorescent lamp provides a smooth and continuous control of output of the lamp. A load threshold, below which the output of the discharge lamp could not be effectively controlled by the conventional frequency control, is determined. During the dimming of the discharge lamp, when the load is not lower than the load threshold, the conventional frequency control is employed. However, when the load is lower than the load threshold, a complementary duty cycle control is used.

Claims

1. A method for controlling a lamp, the method comprising:

comparing a load of the lamp with a threshold; and

controlling an output of the lamp based on the comparison by complementarily adjusting a first frequency of a first control signal and a second frequency of a second control signal.

2. The method according to claim 1, further comprising:

controlling the output of the lamp by adjusting a frequency of third and fourth control signals based on the comparison.

3. The method according to claim 1, wherein when one of the first and second control signals turns off, the other control signal turns on substantially immediately.

4. The method according to claim 3, wherein the time between the turn on time of one of the control signals and the turn off time of the other control signal differs only by a delay sufficient to prevent a short circuit.

5. The method according to claim 1, wherein there is no overlap between the turn on time of one of the control signals and the turn off time of the other control signal.

6. The method according to claim 1, wherein the first frequency is a first duty cycle and the second frequency is a second duty cycle.

7. The method according to claim 6, wherein a duty cycle of the first and second control signals is lower than 50% when the load is lower than the threshold.

8. An apparatus for controlling a lamp, the apparatus comprising:

a load detector, comparing a load of the lamp with a threshold; and

a controller, which receives inputs from the load detector and outputs a first control signal and a second control signal based on the comparison to control an output of the lamp by complementarily adjusting a first frequency of the first control signal and a second frequency of the second control signal.

9. The apparatus according to claim 8, further comprising a first driver through which the controller outputs the first and second control signals.

10. The apparatus according to claim 8, wherein the controller outputs a third control signal and a fourth control signal to control the output of the lamp by adjusting a third frequency of the third control signal and a fourth frequency of the fourth control signal based on the comparison.

11. The apparatus according to claim 10, further comprising a second driver through which the controller outputs the third and fourth control signals.

12. The apparatus according to claim 8, wherein when one of the first and second control signals turns off, the other control signal turns on substantially immediately.

13. The apparatus according to claim 12, wherein the time between the turn on time of one of the control signals and the turn off time of the other control signal differs only by a delay sufficient to prevent a short circuit.

14. The apparatus according to claim 12, wherein there is no overlap between the turn on time of one of the control signals and the turn off time of the other control signal.

15. The apparatus according to claim 8, further comprising an under voltage lock-out module.

16. The apparatus according to claim 8, further comprising an over voltage protection module.

17. The apparatus according to claim 8, further comprising a power control module.

18. The apparatus according to claim 8, further comprising a phase detector.

19. The apparatus according to claim 8, wherein the lamp comprises a discharge lamp.

20. The apparatus according to claim 8, wherein the lamp comprises a fluorescent lamp.

21. An apparatus for controlling a lamp, the apparatus comprising:

means for detecting whether a load of the lamp is lower than a threshold; and

controlling means, which receives inputs from the detecting means and outputs a first control signal and a second control signal based on the comparison to control an output of the lamp by complementarily adjusting a first frequency of the first control signal and a second frequency of the second control signal.

22. The apparatus according to claim 21, further comprising first driving means through which the controlling means outputs the first and second control signals.

23. The apparatus according to claim 21, wherein the controlling means outputs a third control signal and a fourth control signal to control the output of the lamp by adjusting a third frequency of the third control signal and a fourth frequency of the fourth control signal based on the comparison.

24. The apparatus according to claim 23, further comprising second driving means through which the controlling means outputs the third and fourth control signals.

25. The apparatus according to claim 21, wherein when one of the first and second control signals turns off, the other control signal turns on substantially immediately.

26. The apparatus according to claim 25, wherein the time between the turn on time of one of the control signals and the turn off time of the other control signal differs only by a delay sufficient to prevent a short circuit.

27. The apparatus according to claim 25, wherein there is no overlap between the turn on time of one of the control signals and the turn off time of the other control signal.

28. The apparatus according to claim 21, further comprising means for under voltage protection.

29. The apparatus according to claim 21, further comprising means for over voltage protection.

30. The apparatus according to claim 21, further comprising means for power control.

31. The apparatus according to claim 21, further comprising means for phase detecting.

32. The apparatus according to claim 21, wherein the lamp comprises a discharge lamp.

33. The apparatus according to claim 21, wherein the lamp comprises a fluorescent lamp.