Fixed operating frequency inverter for cold cathode fluorescent lamp having strike frequency adjusted by voltage to current phase relationship

• US RE44,133 E1
• Filed: 11/13/2009
• Issued: 04/09/2013
• Est. Priority Date: 10/02/2003
• Status: Active Grant

• Current Assignee: Monolithic Power Systems Incorporated
• Original Assignee: Monolithic Power Systems Incorporated
• Inventors: Moyer, James C., Rust, Timothy J.
• Primary Examiner(s): PHILOGENE, HAISSA
• Application Number:
  US12/617,924
• Time in Patent Office: 1,243 Days
• Field of Search: 315/209.R, 315/194, 315/142, 315/224, 315/244, 315/291, 315/276, 315/307, 315/DIG.5, 315/DIG.7, 363/16, 363/17, 363/24, 363/41, 363/132
• US Class Current: 315/291
• CPC Class Codes: H05B 41/2828 using control circuits for the switching elements H05B41/2827 takes precedence
• CPC Class Codes: Y10S 315/05 Starting and operating circuit for fluorescent lamp
• CPC Class Codes: Y10S 315/07 Starting and control circuits for gas discharge lamp using transistors

Abstract

A method of driving a lamp that uses a DC to AC inverter that is connected to a primary winding of a transformer is disclosed. The inverter frequency is variable, and in one embodiment, may be controlled by a voltage controlled oscillator. Circuitry is included that monitors the phase relationship between a voltage across a secondary of the transformer and a current through the primary of the transformer. The circuitry monitors the phase relationship and adjusts the inverter frequency, such as by adjusting voltage controlled oscillator, so that the phase relationship is maintained at a predetermined relationship.

Claims

1. A method of driving a lamp that uses a DC to AC inverter that is connected to a winding of a transformer comprising:

(a) monitoring a phase relationship between a voltage across said winding of said transformer and a current through said winding of said transformer; and

(b) keeping said phase relationship between said voltage across said winding of said transformer and said current through said winding of said transformer at substantially a predetermined relationship.

2. The method of claim 1, wherein said voltage across said winding of said transformer is substantially in phase with said current through said winding of said transformer.

3. The method of claim 1, wherein during an ignition of said lamp, the an operating frequency of said inverter is increased by maintaining in order to maintain said predetermined relationship between said voltage across said winding and said current through said winding.

4. The method of claim 2, wherein said voltage across said winding of said transformer is maintained substantially in phase with said current through said winding by using the a zero-crossing information of said current in through said winding.

5. An apparatus for driving a lamp comprising

a transformer having a primary and a secondary;

means for convertinga circuit configured to convert a DC power into AC power and operating at a frequency, the means for converting driving the primary, wherein the circuit is configured to operate at a frequency and drive the primary of said transformer;

means for monitoring phase comparison that monitors a phase relationship between a voltage across said primary of said transformer and a current through said primary of said transformer; and

means for adjusting frequency control that adjusts the frequency of said means for converting circuit such that said a phase relationship between said voltage across said primary of said transformer and said current through said primary of said transformer is maintained at substantially a predetermined relationship.

6. The apparatus of claim 5, further including a voltage controlled oscillator that is responsive to said means for adjusting frequency control and configured to output an oscillation used by said means for converting circuit to generate said frequency.

7. The apparatus of claim 5, wherein said means for phase comparison and said means for frequency control operate to maintain said phase relationship as being substantially in phase said voltage across said winding of said transformer is maintained at substantially in phase with said current through said winding of said transformer.

8. The apparatus of claim 5 wherein said means for phase comparison further includes a zero-crossing detector for monitoring said current through said primary.

9. A method of driving a lamp that uses a DC to AC inverter that is coupled to a transformer having a primary and a secondary, the method comprising:

(a) determining a phase relationship between a voltage across either the primary or the secondary of the transformer and a current through either the primary or the secondary of the transformer; and

(b) keeping the phase relationship between the voltage across either the primary or the secondary of the transformer and the current through either the primary or the secondary of the transformer at a substantially predetermined relationship.

10. The method of claim 9, wherein the voltage across either the primary or the secondary of the transformer is substantially in phase with the current through either the primary or the secondary of the transformer.

11. The method of claim 9, wherein during an ignition of the lamp, an operating frequency of the inverter is increased in order to maintain the substantially predetermined relationship between the voltage across either the primary or the secondary of the transformer and the current through either the primary or the secondary of the transformer.

12. The method of claim 10, wherein the voltage across either the primary or the secondary of the transformer is maintained substantially in phase with the current through either the primary or the secondary of the transformer by using a zero-crossing information of the current through either the primary or the secondary of the transformer.

13. The method of claim 11, wherein the operating frequency is increased to a strike frequency.

14. A method of striking a lamp comprising:

determining a phase relationship between a voltage across a transformer and a current through the transformer; and

sweeping a frequency of a signal applied to the transformer to a strike frequency based on the phase relationship between the voltage across the transformer and the current through the transformer.

15. The method of claim 14, wherein determining the phase relationship between the voltage across the transformer and the current through the transformer comprises:

determining a phase relationship between a voltage across either a primary or a secondary of the transformer and a current through either a primary or a secondary of the transformer.

16. The method of claim 15, wherein sweeping the frequency of the signal applied to the transformer to the strike frequency based on the phase relationship between the voltage across the transformer and the current through the transformer comprises:

sweeping the frequency of the signal applied to the primary of the transformer to a strike frequency when the voltage across either the primary or the secondary of the transformer is not substantially in phase with the current through either the primary or the secondary of the transformer.

17. The method of claim 16 further comprising:

changing from the strike frequency to a normal operating frequency.

18. The method of claim 17, wherein changing from the strike frequency to the normal operating frequency occurs when the voltage across either the primary or the secondary of the transformer is substantially in phase with the current through either the primary or the secondary of the transformer.

19. A method of converting a DC input voltage to an AC signal for driving a lamp, comprising:

controllably switching the DC input voltage ON and OFF to generate an AC signal;

monitoring two or more signals, wherein the two or more signals comprise at least a drive voltage signal and a drive current signal;

determining a phase relationship between the drive voltage signal and the drive current signal to generate a control signal; and

controlling a frequency of the AC signal based on the control signal.

20. The method of claim 19, wherein the two or more signals further comprise either a lamp current signal or a lamp voltage signal.

21. The method of claim 20 further comprising:

controlling the frequency of the AC signal based on either the lamp current signal or the lamp voltage signal.

22. The method of claim 19, wherein controlling a frequency of the AC signal based on the control signal comprises:

sweeping a frequency of the AC signal to a strike frequency when the control signal indicates the phase relationship between the drive voltage signal and the drive current signal is not substantially in phase; and

changing from the strike frequency to a normal operating frequency when the control signal indicates the phase relationship between the drive voltage signal and the drive current signal is substantially in phase.

23. A method comprising:

receiving a DC voltage;

generating one or more switching signals;

generating an AC signal from the DC voltage based on the switching signals;

monitoring two or more signals, wherein the two or more signals comprise at least a drive voltage signal and a drive current signal;

determining a phase relationship between the drive voltage signal and the drive current signal to generate a control signal; and

sweeping a frequency of the AC signal based on the control signal.

24. The method of claim 23, wherein determining a phase relationship between the drive voltage and the drive current signal to generate the control signal comprises:

determining a phase relationship between the drive voltage and a zero crossing of the drive current signal to generate a control signal.

25. The method of claim 23, wherein sweeping a frequency of the AC signal comprises:

increasing the frequency to a strike frequency when the control signal indicates the phase relationship is not substantially in phase.

26. The method of claim 25, further comprising:

changing the frequency from the strike frequency to a normal operating frequency when the control signal indicates the phase relationship is substantially in phase.

27. An inverter circuit for driving a lamp, the circuit comprising:

one or more switches to controllably switch an input voltage ON and OFF to generate an AC signal; and

a control circuit configured to;

monitor a drive voltage signal and a drive current signal,

determine a phase relationship between the drive voltage signal and the drive current signal to generate a control signal, and

control a frequency of the AC signal based on the control signal.

28. The inverter circuit of claim 27, wherein the control circuit is further configured to determine a phase relationship between the drive voltage signal and a zero crossing of the drive current signal to generate the control signal.

29. The inverter circuit of claim 27, wherein the control circuit is further configured to increase the frequency of the AC signal to a strike frequency when the control signal indicates the phase relationship is not substantially in phase.

30. The inverter circuit of claim 29, wherein the control circuit is further configured to change the frequency from the strike frequency to a normal operating frequency when the control signal indicates the phase relationship is substantially in phase.

31. An integrated inverter controller comprising:

a first circuit configured to monitor at least two or more signals, wherein the two or more signals comprise at least a drive voltage signal and a drive current signal;

a second circuit configured to determine a phase relationship between the drive voltage signal and the drive current signal to generate a control signal;

a third circuit configured to control the frequency of an AC signal based on the control signal.

32. The integrated inverter controller of claim 31, wherein the third circuit is further configured to:

sweep the frequency of the AC signal when the control signal indicates the phrase relationship is not substantially in phase.

33. The integrated inverter controller of claim 31, wherein the AC signal is externally generated by controllably switching a DC input voltage ON and OFF.

34. The integrated inverter controller of claim 31, wherein the third circuit is further configured to increase the frequency of the AC signal to a strike frequency when the control signal indicates the phase relationship is not substantially in phase.

35. The integrated inverter controller of claim 34, wherein the third circuit is further configured to change the frequency from the strike frequency to a normal operating frequency when the control signal indicates the phase relationship is substantially in phase.

36. The integrated inverter controller of claim 31, wherein the two or signals further comprise either a lamp voltage signal or a lamp current signal.

37. An inverter controller for driving a lamp, the controller comprising:

a first circuit configured to monitor at least two or more signals, wherein the two or more signals comprise at least a drive voltage signal and a drive current signal;

a second circuit configured to determine a phase relationship between the drive voltage signal and the drive current signal to generate a control signal;

a third circuit configured to control the frequency of an AC signal based on the control signal.

38. The inverter controller of claim 37, wherein the third circuit is further configured to sweep the frequency of the AC signal when the control signal indicates the phase relationship is not substantially in phase.

39. The inverter controller of claim 37, wherein the AC signal is externally generated by controllably switching a DC input voltage ON and OFF.

40. The inverter controller of claim 37, wherein the third circuit is further configured to increase the frequency of the AC signal to a strike frequency when the control signal indicates the phase relationship is not substantially in phase.

41. The inverter controller of claim 40, wherein the third circuit is further configured to change the frequency from the strike frequency to a normal operating frequency when the control signal indicates the phase relationship is substantially in phase.

42. The inverter controller of claim 41, wherein the two or signals further comprise either a lamp voltage signal or a lamp current signal.