Lamp grounding and leakage current detection system

• US 6,570,344 B2
• Filed: 05/07/2001
• Issued: 05/27/2003
• Est. Priority Date: 05/07/2001
• Status: Expired due to Fees

• Current Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Original Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Inventors: Lin, Yung-Lin
• Primary Examiner(s): Vu, Bao Q.
• Application Number:
  US09/850,692
• Publication Number:
  US 20020163822A1
• Time in Patent Office: 750 Days
• Field of Search: 315/224, 315/307, 315/DIG.7, 315/DIG.5, 315/219, 315/242, 315/243
• US Class Current: 315/224
• CPC Class Codes: H02M 7/53835 of the parallel type
• CPC Class Codes: H05B 41/2851 for protecting the circuit against abnormal operating conditions
• CPC Class Codes: Y10S 315/05 Starting and operating circuit for fluorescent lamp

Abstract

A common ground system and methodology for one or more loads. In exemplary embodiments, a lamp load is regulated by providing a common ground on the secondary side of the transformer and the load. Lamp regulation is provided, in part, via a current feedback loop provided on the secondary side that is commonly grounded between the bottom of the transformer and the bottom of the lamp through the current feedback loop. In this manner, a feedback signal is developed that includes the leakage current of the lamp.

Claims

1. An common ground circuit, comprising:

a transformer having a primary side and a secondary side, said secondary side having a top and a bottom;

a lamp having a top, a bottom and a leakage current path, said lamp coupled in parallel to said secondary side of said transformer, said top of said secondary side electrically coupled to said top of said lamp;

a common ground connected to a ground node; and

a current feedback loop generating a current feedback signal proportional to the total current delivered to said lamp;

said bottom side of said transformer electrically coupled to said ground node through said current feedback loop, said bottom of said lamp electrically coupled to said ground node and said leakage current path electrically coupled to said ground node.

2. A circuit as claimed in claim 1, wherein at least a portion of power delivered by said transformer causing said total lamp current to flow from said bottom of said transformer through said current feedback loop to said common ground, a lamp current portion of said total lamp current flows from said common ground through said lamp, and a leakage current portion of said total lamp current flows from said common ground through said leakage current path.

3. A circuit as claimed in claim 1, wherein said total current delivered to said lamp comprises a lamp current and a leakage current.

4. A circuit as claimed in claim 2, wherein said lamp current portion and said leakage current portion summing together at the top of said lamp and totaling said total lamp current.

5. A circuit as claimed in claim 1, wherein said leakage current path comprising a leakage capacitance generated by said lamp coupled to said common ground node.

6. A circuit as claimed in claim 1, wherein said current feedback loop comprising a first diode biased away from said bottom of said secondary side, a sense resistor between said first diode and said common node, and a second diode biased toward said bottom of said secondary side in parallel with said first diode and said sense resistor.

7. A circuit as claimed in claim 2, wherein said portion of said power comprising the negative half-cycle of the AC signal generated by said secondary side.

8. A circuit as claimed in claim 1, wherein said common ground comprising a system circuit ground.

9. A lamp regulating circuit, comprising

a DC to AC inverter circuit generating and an AC signal from a DC source;

and

a secondary-side transformer circuit, comprising;

a transformer having a primary side and a secondary side, said secondary side having a top and a bottom;

a lamp having a top, a bottom and a leakage current path, said lamp coupled in parallel to said secondary side of said transformer, said top of said secondary side electrically coupled to said top of said lamp;

a common ground; and

a current feedback loop generating a current feedback signal proportional to the total current delivered to said lamp;

said bottom side of said transformer electrically coupled to said common ground through said current feedback loop, said bottom of said lamp electrically coupled to said common ground and said leakage current path electrically coupled to said common ground.

10. A circuit as claimed in claim 9, wherein at least a portion of energy delivered by said transformer causing said total lamp current to flow from said bottom of said transformer through said current feedback loop to said common ground, a lamp current portion of said total lamp current flows from said common ground through said lamp, and a leakage current portion of said total lamp current flows from said common ground through said leakage current path.

11. A circuit as claimed in claim 9, wherein said total current delivered to said lamp comprises a lamp current and a leakage current.

12. A circuit as claimed in claim 10, wherein said lamp current portion and said leakage current portion summing together at the top of said lamp and totaling said total lamp current.

13. A circuit as claimed in claim 9, wherein said leakage current path comprising a leakage capacitance generated by said lamp coupled to said common ground node.

14. A circuit as claimed in claim 9, wherein said current feedback loop comprising a first diode biased away from said bottom of said secondary side, a sense resistor between said first diode and said common node, and a second diode biased toward said bottom of said secondary side in parallel with said first diode and said sense resistor.

15. A circuit as claimed in claim 10, wherein said portion of said energy comprising the negative half-cycle of the AC signal generated by said secondary side.

16. A circuit as claimed in claim 9, wherein said common ground comprising a system circuit ground.

17. A circuit as claimed in claim 9, wherein said DC to AC converter circuit selected from the group comprising a push-pull inverter, a forward inverter, a flyback inverter, a half bridge inverter or a full bridge inverter.

18. A circuit as claimed in claim 9, wherein said inverter receiving said feedback signal proportional to the total current delivered to said lamp and adjusting the power delivered to said lamp.

19. A transformer circuit, comprising:

a transformer having a primary side and a secondary side, said secondary side having a top and a bottom;

a lamp having a top, a bottom and a leakage current path, said lamp coupled in parallel to said secondary side of said transformer, said top of said secondary side electrically coupled to said top of said lamp;

a common ground connected to a ground node; and

a current feedback loop generating a current feedback signal proportional to the total current delivered to said lamp;

said bottom side of said transformer electrically coupled to said ground node through said current feedback loop, said bottom of said lamp electrically coupled to said ground node and said leakage current path electrically coupled to said ground node;

wherein at least a portion of energy delivered by said transformer causing said total lamp current to flow from said bottom of said transformer through said current feedback loop to said common ground, a lamp current portion of said total lamp current flows from said common ground through said lamp, and a leakage current portion of said total lamp current flows from said common ground through said leakage current path.

20. A common grounding method, comprising:

coupling a top side of a transformer to a top side of a lamp;

coupling a common ground to a ground node; and

coupling a feedback loop circuit to a bottom side of said transformer coupled and to said ground node;

coupling the bottom of said lamp said ground node; and

coupling a leakage current path from said lamp to said ground node.

21. A method as claimed in claim 20, further comprising the step of:

generating a current feedback signal in said current feedback loop proportional to a total current delivered to said lamp.

22. A method as claimed in claim 21, further comprising the steps of:

causing said total lamp current to flow from said bottom of said transformer through said current feedback loop to said common ground;

generating a lamp current portion of said total lamp current flowing from said common ground through said lamp; and

generating a leakage current portion of said total lamp current flowing from said common ground through said leakage current path.

23. A method as claimed in claim 21, further comprising the step of:

regulating power delivered to said lamp based on said a current feedback signal.

24. A transformer circuit, comprising:

a transformer having a primary side and a secondary side, said secondary side having a top and a bottom;

a lamp having a top, a bottom and a leakage current path, said lamp coupled in parallel to said secondary side of said transformer, said top of said secondary side electrically coupled to said top of said lamp;

a common ground connected to a ground node; and

a current feedback loop generating a current feedback signal proportional to the total current delivered to said lamp;

said bottom side of said transformer electrically coupled to said ground node through said current feedback loop, said bottom of said lamp electrically coupled to said ground node and said leakage current path electrically coupled to said ground node;

wherein said total current delivered to said lamp comprises a lamp current and a leakage current.

25. A transformer circuit, comprising:

a transformer having a primary side and a secondary side, said secondary side having a top and a bottom;

a lamp having a top, a bottom and a leakage current path, said lamp coupled in parallel to said secondary side of said transformer, said top of said secondary side electrically coupled to said top of said lamp;

a common ground connected to a ground node; and

a current feedback loop generating a current feedback signal proportional to the total current delivered to said lamp;

said bottom side of said transformer electrically coupled to said ground node through said current feedback loop, said bottom of said lamp electrically coupled to said ground node and said leakage current path electrically coupled to said ground node;

wherein at least a portion of energy delivered by said transformer causing said total lamp current to flow from said bottom of said transformer through said current feedback loop to said common ground, a lamp current portion of said total lamp current flows from said common ground through said lamp, and a leakage current portion of said total lamp current flows from said common ground through said leakage current path and wherein said lamp current portion and said leakage current portion summing together at the top of said lamp and totaling said total lamp current.

26. An common ground circuit, comprising:

a transformer having a primary side and a secondary side, said secondary side having a top and a bottom;

a lamp having a top, a bottom and a leakage current path, said lamp coupled in parallel to said secondary side of said transformer, said top of said secondary side electrically coupled to said top of said lamp;

a common ground connected to a ground node; and

a current feedback loop generating a current feedback signal proportional to the total current delivered to said lamp;

said bottom side of said transformer electrically coupled to said ground node through said current feedback loop, said bottom of said lamp electrically coupled to said ground node and said leakage current path electrically coupled to said ground node.

A capacitor divider in parallel with the secondary side of the transformer.

27. A circuit as claimed in claim 26, further comprising a voltage sense feedback loop coupled in parallel to said transformer through a capacitor divider circuit, said voltage sense feedback loop provides individual lamp ignition and over-voltage protection.

28. An LCD panel display, comprising:

a plurality of transformers each having a primary side and a secondary side, each said secondary side having a top and a bottom;

a plurality of lamps each having a top, a bottom and a leakage current path, each said lamp coupled in parallel to a respective said secondary side of said transformer, said top of each said secondary side electrically coupled to said top of each said lamp;

a common ground connected to a ground node; and

a plurality of current feedback loops, each said feedback loop generating a current feedback signal proportional to the total current delivered to each said lamp;

said bottom side of each said transformer electrically coupled to said ground node through said current feedback loop, said bottom of said lamp electrically coupled to said ground node and said leakage current path electrically coupled to said ground node.

29. A computer system, comprising:

an LCD display panel comprising,

a transformer having a primary side and a secondary side, said secondary side having a top and a bottom;

a lamp having a top, a bottom and a leakage current path, said lamp coupled in parallel to said secondary side of said transformer, said top of said secondary side electrically coupled to said top of said lamp;

a common ground connected to a ground node; and

a current feedback loop generating a current feedback signal proportional to the total current delivered to said lamp;

said bottom side of said transformer electrically coupled to said ground node through said current feedback loop, said bottom of said lamp electrically coupled to said ground node and said leakage current path electrically coupled to said ground node.