Systems and methods for fault protection in a balancing transformer

• US 7,279,851 B2
• Filed: 10/20/2004
• Issued: 10/09/2007
• Est. Priority Date: 10/21/2003
• Status: Expired due to Fees

• Current Assignee: Microsemi Corporation (Microchip Technology Incorporated)
• Original Assignee: Microsemi Corporation (Microchip Technology Incorporated)
• Inventors: Ball, Newton E.
• Primary Examiner(s): Wong; Don
• Assistant Examiner(s): Lie; Angela M
• Application Number:
  US10/970,248
• Publication Number:
  US 20050093484A1
• Time in Patent Office: 1,084 Days
• Field of Search: 315/274, 315/277, 315/282, 315/219, 315/220, 315/223, 315/224, 315/DIG.2, 315/DIG.4, 336/180, 336/182, 343/846, 343/700.MS
• US Class Current: 315/282
• CPC Class Codes: H05B 41/2827 using specially adapted components in the load circuit, e.g. feed-back transformers, piezoelectric transformers; using specially adapted load circuit configurations

Abstract

An apparatus and methods for balancing current in multiple negative impedance gas discharge lamp loads. Embodiments advantageously include balancing transformer configurations that are relatively cost-effective, reliable, efficient, and good performing. Embodiments include configurations that are applicable to any number of gas discharge tubes, such as cold cathode fluorescent lamps. The balancing transformer configuration techniques permit a relatively small number of power inverters, such as one power inverter, to power multiple lamps in parallel. One embodiment of a balancing transformer includes a safety winding which can be used to protect the balancing transformer in the event of a lamp failure and can be used to provide an indication of a failed lamp.

Claims

1. A two-way balancing transformer assembly for balancing a first current and a second current, the two-way balancing transformer assembly comprising:

a core;

a first balancing winding having about a first number of turns around the core, where the first balancing winding is configured to carry the first current to a first load;

a second balancing winding having approximately the first number of turns around the core, where the second balancing winding is configured to carry the second current to a second load;

a safety winding with a second number of turns around the core, wherein the second number of turns is smaller than the first number of turns; and

a pair of diodes coupled in an anti-parallel configuration across the safety winding to clamp a voltage induced across the safety winding in response to imbalances between the first current and the second current.

2. The two-way balancing transformer assembly as defined in claim 1, where the safety winding is electrically isolated from the first balancing winding and the second balancing winding.

3. The two-way balancing transformer assembly as defined in claim 1, where the second number of turns is 1.

4. The two-way balancing transformer assembly as defined in claim 1, where the second number of turns is 2.

5. The two-way balancing transformer assembly as defined in claim 1, where the first balancing winding and the second balancing winding are wound from coated wire and wherein the safety winding is wound from insulated wire.

6. The two-way balancing transformer assembly as defined in claim 1, wherein none of the windings of the two-way balancing transformer assembly are bifilar.

7. The two-way balancing transformer assembly as defined in claim 1, further comprising a bobbin around which the windings are wound, wherein the first balancing winding and the second balancing winding occupy separate sections of the bobbin.

8. The two-way balancing transformer assembly as defined in claim 7, wherein the bobbin further comprises a third section for the safety winding.

9. The two-way balancing transformer assembly as defined in claim 1, wherein the two-way balancing transformer assembly is further operatively coupled to two cold cathode fluorescent lamps (CCFLs) such that a first CCFL conducts the first current and a second CCFL conducts the second current.

10. A two-way balancing transformer assembly for balancing a first current and a second current, the two-way balancing transformer assembly comprising:

a core;

a first balancing winding having about a first number of turns around the core, where the first balancing winding is configured to carry the first current;

a second balancing winding having approximately the first number of turns around the core, where the second balancing winding is configured to carry the second current;

a safety winding with a second number of turns around the core, wherein the second number of turns is smaller than the first number of turns and the safety winding further comprises a single turn of an uninsulated conductor; and

a bobbin around which the windings are wound, wherein the first balancing winding and the second balancing winding occupy separate sections of the bobbin with a third section for the safety winding.

11. A method of limiting voltage in a two-way balancing transformer, the method comprising:

providing a first balancing winding and a second balancing winding in the two-way balancing transformer to balance a first current and a second current, where the first balancing winding and the second balancing winding have at least approximately the same number of turns;

providing a safety winding with fewer turns than the first balancing winding; and

electrically coupling the safety winding in parallel with anti-parallel diodes to limit voltage in all the windings of the two-way balancing transformer, wherein a winding ratio between the first balancing winding and the safety winding steps down the voltage in the safety winding so that the anti-parallel diodes do not limit voltage when the first current and the second current are substantially balanced.

12. The method as defined in claim 11, wherein the two-way balancing transformer is used to balance currents among at least two negative-impedance gas discharge lamps, and wherein an imbalance between the first current and the second current is caused by a failed lamp.

13. The method as defined in claim 11, wherein the safety winding comprises one turn.

14. The method as defined in claim 11, wherein the safety winding comprises two turns.

15. A method of limiting voltage in a two-way balancing transformer, the method comprising:

providing a first balancing winding and a second balancing winding in the two-way balancing transformer to balance a first current and a second current, where the first balancing winding and the second balancing winding have at least approximately the same number of turns;

providing a safety winding with fewer turns than the first balancing winding;

electrically coupling the safety winding to a circuit that clamps voltage to limit voltage in all windings of the two-way balancing transformer, wherein a winding ratio between the first balancing winding and the safety winding steps down the voltage in the safety winding so that the circuit does not clamp voltage when the first current and the second current are substantially balanced; and

electrically isolating and insulating the safety winding, and monitoring voltage on the safety winding to detect an imbalance between the first current and the second current.

16. A lamp assembly comprising:

a plurality of at least 4 lamps, where the lamps each have a first end and a second end;

a first terminal and a second terminal for receiving power from a secondary winding of an inverter transformer for driving the plurality of lamps in parallel, wherein a first terminal is operatively coupled to first ends of the lamps; and

a straight tree of two-way balancing transformers with at least 2 levels in the tree, wherein at least one of the two-way balancing transformers includes a safety winding electrically coupled to anti-parallel diodes, wherein the straight tree includes a first two-way balancing transformer, a second two-way balancing transformer, and a third two-way balancing transformer, wherein;

the first balancing transformer is operatively coupled to the second terminal, where the first two-way balancing transformer is operatively coupled to and is configured to balance current between the second two-way balancing transformer and the third balancing transformer;

the second two-way balancing transformer is operatively coupled to second ends of at least a first lamp and a second lamp and balances current for the same; and

the third two-way balancing transformer is operatively coupled to second ends of a third lamp and a fourth lamp and balances current for the same.

17. The lamp assembly as defined in claim 16, wherein none of the two-way balancing transformers is bifilar wound.

18. The lamp assembly as defined in claim 16, further comprising capacitors operatively coupled in series with the lamps.

19. The lamp assembly as defined in claim 16, wherein the first terminal and the second terminal are substantially floating and not operatively coupled with respect to ground.

20. The lamp assembly as defined in claim 18, further comprising at least one high-value resistance to ground to discharge static charges.

21. The lamp assembly as defined in claim 16, wherein the first terminal is configured to be operatively coupled to ground.

22. The lamp assembly as defined in claim 16, wherein the second terminal is configured to be operatively coupled to ground.