Method and apparatus for driving discharge lamps in a floating configuration

• US 20060033455A1
• Filed: 08/05/2005
• Published: 02/16/2006
• Est. Priority Date: 08/05/2004
• Status: Active Grant

• Current Assignee: Monolithic Power Systems Incorporated
• Original Assignee: Monolithic Power Systems Incorporated
• Inventors: Chen, Wei, Tsai, Simon
• Granted Patent: US 7,304,441 B2
• Time in Patent Office: Days
• US Class Current: 315/300
• CPC Class Codes: H05B 41/2825 by means of a bridge converter in the final stage H05B41/285 takes precedence

Abstract

A technique is described that facilitates sensing current through a load. A method according to the technique includes mounting a discharge lamp in a floating point configuration, sensing current through the discharge lamp, and controlling current through the discharge lamp to improve power conversion efficiency. A device constructed according to the technique may include two AC voltage sources that are out-of-phase with respect to one another. A current sense circuit may be coupled between the AC voltage sources. When a load is connected to nodes of the AC voltage sources, the current sense circuit may sense current between the nodes that is associated with, or perhaps approximates, current through the load.

Claims

1. A device comprising:

a first AC voltage source having a first node;

a second AC voltage source having a second node, wherein the first AC voltage source is out-of-phase with respect to the second AC voltage source;

a current sense circuit, coupled between the first AC voltage source and the second AC voltage source, effective to sense current at a third node between the first node and the second node, wherein current sensed by the current sense circuit at the third node is associated with current through a load operationally connected to the first node and the second node.

2. The device of claim 1 wherein the current sensed by the current sense circuit at the third node approximates current through the load.

3. The device of claim 1 wherein the current sense circuit further includes a parasitic capacitance compensation component or a parasitic capacitance compensation network.

4. The device of claim 1 wherein the load is operationally connected to the first node and the second node in a floating point configuration.

5. The device of claim 1 wherein the load is a lamp.

6. The device of claim 1 wherein the load is a uniform discharge lamp.

7. The device of claim 1 further comprising a switching network having a DC voltage input, wherein the switching network includes the first AC voltage source and the second AC voltage source having respective AC outputs derived from the DC voltage input.

8. A system comprising:

a switching network module;

a resonant tank module, coupled to the switching network module, effective to convert a signal from the switching network module into a first signal and a second signal, wherein the first signal and the second signal are out-of-phase;

a current sense module, coupled to the resonant tank module, effective to accurately sense current through a load, wherein the load is operationally connected to the resonant tank module in a floating drive configuration and the load is driven by the first signal and the second signal.

9. The system of claim 8, wherein the load is a discharge lamp.

10. The system of claim 8, wherein the load is a uniform discharge lamp.

11. The system of claim 8, wherein the current sense module is magnetically coupled to the load at a zero potential location.

12. The system of claim 8, wherein the current sense module is magnetically coupled to the load at a zero AC potential location.

13. The system of claim 8, wherein the current sense module is magnetically coupled to the load at AC ground.

14. The system of claim 8, further comprising a parasitic capacitance compensation module.

15. The system of claim 8, wherein:

said switching network module, when operationally configured, receives a DC signal and outputs a first square wave signal and a second square wave signal;

said resonant tank module, when operationally configured, receives the first square wave signal from the switching network module and the second square wave signal from the switching network module, wherein the first square wave signal is out-of-phase with respect to the second square wave signal.

16. The system of claim 8, wherein:

said resonant tank module, when operationally configured, outputs a first analog signal and a second analog signal;

said load is driven by the first analog signal at a first end and the second analog signal at a second end.

17. The system of claim 8, further comprising an inverter controller coupled to the resonant tank module.

18. The system of claim 8, wherein the resonant tank module includes a first filter associated with the first signal and a second filter associated with the second signal.

19. A method comprising:

mounting a discharge lamp in a floating point configuration;

sensing current through the discharge lamp;

providing the sensed current as feedback controlling current through the discharge lamp using the feedback.

20. The method of claim 19 further comprising compensating for parasitic capacitance.