Back lighting source module for liquid crystal display

Details Back lighting source module for liquid crystal display Back lighting source module for liquid crystal display

2000-12-18

2003-03-11

Wong, Don (Department: 2821)

Electric lamp and discharge devices: systems

Current and/or voltage regulation

Automatic regulation

C315S291000, C315S294000, C315SDIG007

Reexamination Certificate

active

06531835

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a back lighting source module for a liquid crystal display (LCD) that is suitable to be used in LCD monitors and LCD televisions. The back lighting source module includes a circuit that is simple and can be modified easily.
2. Description of the Related Art
A liquid crystal display cannot emit light on its own; namely, a back lighting source is required to illuminate the whole panel of the LCD.
FIGS. 3A and 3B
illustrate a conventional back lighting supply circuit for an LCD. The circuit includes a full bridge converter that uses a pulse width modulation (PWM) controller
90
to drive two sets of transistors
91
and
92
(four power transistors in total) for activating two transformers
93
and
94
. Secondary sides of the transformers
93
and
94
are connected in series with each other, and two lighting elements
95
and
96
are connected with the transformers
93
and
94
in series. A feedback circuit
97
formed by several comparators or operational amplifiers feeds current signals of the lighting elements
95
and
96
back to the PWM controller
90
. Thus, by means of continuous feedback control, the lighting elements
95
and
96
are provided with stable power supply and emit light uniformly.
In the above-mentioned LCD back lighting module, it is basically formed by two sets of independent power supplies in order to supply power to the two lighting elements; namely, the uppermost dual transistors
91
and the transformer
93
, and the lower dual transistors
92
and the transformer
94
. They share the PWM controller
90
and the feedback circuit
97
at best. It merely combines two sets of power supplies together without proceeding with an optimal arrangement of the overall circuit. In addition, the above circuit uses four power transistors, which causes high cost, occupies a larger space, and has a complicated structure.
FIGS. 4A and 4B
illustrate another conventional back lighting supply circuit for an LCD. The circuit is a two-stage structure formed by a Buck converter
98
and a Royer converter
99
, which has a low efficiency and high cost and occupies a larger space.
SUMMARY OF THE INVENTION
It is the primary object of the present invention to provide a back lighting source module for an LCD, wherein the module includes only two power transistors for forming a back lighting supply for one ore more lighting elements.
It is another object of the present invention to provide a back lighting source module including a plurality of lighting elements that are connected in series or parallel.
It is a further object of the present invention to provide a back lighting source module that may include a current-limiting circuit when required, thereby balancing the currents in each of the lighting elements such that each lighting element has uniform brightness.
It is still another object of the present invention to provide a back lighting source module including a frequency-variable starting circuit to provide a higher voltage during starting. The voltage returns to a normal value after the lighting elements have been turned on. Thus, the lighting elements are turned on more quickly.
Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.


REFERENCES:
patent: 5612595 (1997-03-01), Maheshwari
patent: 5796213 (1998-08-01), Kawasaki
patent: 5854543 (1998-12-01), Satoh et al.
patent: 6118221 (2000-09-01), Kumasaka et al.

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