Electric lamp and discharge devices: systems – Pulsating or a.c. supply – Transformer in the supply circuit
Reexamination Certificate
2000-08-10
2001-10-30
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Pulsating or a.c. supply
Transformer in the supply circuit
C315S2090SC, C315S219000, C315S224000, C315S276000, C315S291000, C323S361000
Reexamination Certificate
active
06310444
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
The invention relates to an inverter for driving multiple lamps in an LCD display. More specifically, the invention relates to the magnetic coupling of inductors and magnetic coupling of output transformers for each of the multiple lamp driver circuits.
2. Description of the Related Art
An LCD based monitor general needs efficient and low profile backlighting for information display. The narrow diameter cold-cathode fluorescent lamp (CCFL), for example the T1 type by Philips, is widely used in the industry. With the increase of monitor size, multiple lamps are needed for the panel illumination. To drive these CCFLs, high frequency electronic ballasts with high efficiency and low profile are in demand. Due to its low losses and low stresses, the voltage-fed half-bridge resonant converter is used to drive the CCFL and other fluorescent lamps. In developing the electronic inverter for multiple CCFLs, people usually prefer to use one single inverter instead of two or more in order to reduce cost and circuit complexity. In this endeavor, the so-called series structure in FIG.
1
and the parallel structure in
FIG. 2
are currently used for dual lamp inverters. Comparing these two structures, one can have the following observations.
The series structure in
FIG. 1
has a) better lamp current matching due to the series connection of the output transformer primary sides, b) less (3) magnetic components. However, it has higher output transformer turns ratio, which translates to higher primary side winding current, and to more conduction losses. Also, when the output transformer secondary side winding turns increase, the wire size needs to be reduced (e.g. 44AWG) such that the wire fits in the given window area. In addition to contributing to higher conduction losses in the winding, the small size of the wire may cause problems during the manufacturing process.
On the other hand, the parallel structure of
FIG. 2
can use a lower turns ratio output transformer. In addition to clear modularity, the secondary side leakage inductance can be reduced and the system performance is improved. However, the parallel structure in
FIG. 2
suffers from poor lamp current matching and requires more (4) magnetic components for dual lamps. What is needed is a magnetic component integration approach to overcome the shortfalls of the parallel structure.
SUMMARY OF THE INVENTION
In this invention, two magnetic component integration approaches to overcome the shortfalls of the parallel structure are presented. In the first approach, an inverter for driving multiple lamps has a first circuit for driving a first lamp. The first circuit is made up of a first inductor in series with a first output transformer to drive the first lamp. A second circuit drives a second lamp. The second circuit is made up of a second inductor in series with a second output transformer which drives a second lamp. The first and second transformers are coupled together by a first single magnetic core such that magnetic flux from first and second transformers is cancelled in the magnetic core to reduce core losses. In the second approach the inverter described in the first approach further includes a second magnetic core coupling the first and second inductors with the inductors terminals connected to either enhance the flux or to minimize the flux, thus minimizing leakage inductance or balancing the winding currents, respectively.
In the first approach, the inverter has a core with three parallel interconnected branches or legs. Two of the branches are outer branches and one is an inner branch. The first and second transformers are wound on the outer branches and are coupled by the inner branch such that magnetic flux from the first and second transformers is cancelled. The cancellation is accomplished by the first and second transformers having first and second primaries, respectively, located at opposite ends of their respective cores in an anti-parallel arrangement. Similarly, the first and second transformers have first and second secondaries, respectively, located at opposite ends of their respective cores in an anti-parallel arrangement.
REFERENCES:
patent: 4667132 (1987-05-01), Leale
patent: 5034659 (1991-07-01), Taniguchi
patent: 5331253 (1994-07-01), Counts
patent: 5519289 (1996-05-01), Katyl et al.
patent: 5747943 (1998-05-01), Houk et al.
patent: 6114814 (2000-09-01), Shannon et al.
Philips Electronics North America Corporation
Vu Jimmy T.
Wong Don
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