Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2000-07-28
2002-02-19
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C315S056000, C315S169300, C313S483000, C313S494000
Reexamination Certificate
active
06348765
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the priority benefit of Taiwan application serial no. 89104493, filed Mar. 13, 2000.
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a synchronous switching device for fluorescent lamp. More particularly, the present invention relates to a synchronous switching device for controlling the lighting of a planar fluorescent lamp at the back of a large area liquid crystal display (LCD).
2. Description of Related Art
Liquid crystal display (LCD) is a high image quality, small volume, lightweight, low voltage driven and low power consumption image-displaying device. Nowadays, liquid crystal display (LCD) panels are widely adopted in portable televisions, mobile telephones, camera recorders, notebook computers, desktop computers as well as projectors. In fact, the conventional cathode ray tube (CRT) is gradually being replaced by LCD as the mainstream display device. However, liquid crystal display differs from other display devices such as plasma display panels (PDP), electro-luminescent (EL) displays, and light-emitting diodes (LED) in that the panel does not emit light. An external light source must be available to illuminate the LCD panel. Hence, most LCD panel needs to include a back light at the back of the panel.
Typically, the back light of a LCD panel is a linear fluorescent tube having a diameter between 1.8 mm to 2.6 mm. The linear fluorescent tube has two electrodes, one at each end of the tube, with fluorescent powder coated on the interior sidewall. The interior space of the fluorescent tube is filled with mercury vapor and inert gas. The fluorescent lamp operates by applying a voltage across the two electrodes, thereby leading to an electrode discharge and the production of plasma that emits ultraviolet radiation. When the fluorescent powder coated on the interior sidewalls of the fluorescent tube is activated by ultraviolet radiation, visible light is produced.
As area of a LCD panel increases, a uniformly lit panel capable of serving as a back lighting source is more urgently needed. Since linear fluorescent tubes are incapable of providing planar illumination, special planar fluorescent lamps have been designed.
FIGS. 1A and 1B
are the respective front view and the cross-sectional top view of a conventional planar fluorescent lamp. As shown in
FIGS. 1A and 1B
, the planar fluorescent lamp
100
includes surface panels
102
a
and
102
b
that are parallel to each other. Side panels
102
c
are inserted between and near the edges of the panels
102
a
and
102
b
. The surface panels
102
a
,
102
b
and the side panels
102
c
together form a fluorescent tube
102
enclosing a hollow space
104
. Fluorescent layers
106
are formed on the interior sidewalls of the surface panels
102
a
and
102
b
, respectively. A first electrode
108
a
and a second electrode
108
b
are installed inside the hollow space
104
close to each side panel
102
c.
As surface area of the planar fluorescent lamp
100
increases, overall length of the first electrode
108
a
and the second electrode
108
b
must increase correspondingly. Due to their increased length, a voltage applied to the two electrodes
108
a
and
108
b
may not simultaneously equalize to the same potential level at every point along the entire length instantaneously. Since electric discharge follows the smallest impedance line type route between the electrodes, a line type discharge similar to a linear fluorescent lamp is produced. Hence, the intended uniform fluorescent panel for lighting a large LCD panel is not actually produced.
FIG. 2
is a front view showing the internal structure of another conventional planar fluorescent lamp. The planar fluorescent lamp in
FIG. 2
is very similar to the one shown in
FIGS. 1A and 1B
; hence identical parts are label with the same numerals. The planar fluorescent lamp
200
has sidewall panels
102
c
inserted between the surface panels
102
a
and
102
b
near the edges. The surface panels
102
a
,
102
b
and the side panels
102
c
together form a hollow space
104
. Fluorescent layers
106
are formed on the interior sidewalls of the surface panels
102
a
and
102
b
, respectively. An equal number of first electrodes
208
a
and second electrodes
208
b
are installed inside the hollow space
104
close to each side panel
102
c.
To operate the planar fluorescent lamp shown in
FIG. 2
, each pair of first electrode
208
a
and second electrode
208
b
must be applied synchronous identical voltage so that each pair of electrodes inside the fluorescent tube
102
emits light concurrently. Otherwise, only one pair of electrodes will carry out an electrical discharge similar to the discharge of a linear fluorescent tube. In addition, when an external voltage is applied to various electrode pairs, electric arcs may form between adjacent electrodes leading to mutual interference.
Sequential timing control can be applied to the electrode pairs inside the planar fluorescent lamp so that each electrode pair discharge in turn similar to the horizontal scanning of a cathode ray tube. However, overall brightness attained by the planar fluorescent lamp is greatly reduced compared with a planar fluorescent lamp formed by joining a series of parallel linear fluorescent tubes.
Nevertheless, although a series of fluorescent tubes on a planar panel is capable of having a higher brightness level, a diffusion panel must be inserted between the fluorescent panel and the LCD panel to equalize brightness level across the panel. Moreover, when the planar fluorescent lamp is too close to the LCD panel, layout of the fluorescent tubes inside the lamp may appear on the LCD panel, thereby affecting image quality. On the other hand, if the distance between the planar fluorescent lamp and the LCD panel is increased, overall thickness of the LCD panel and the fluorescent lamp will increase thereby adding weight and volume to the panel.
SUMMARY OF THE INVENTION
Accordingly, one object of the present invention is to provide a synchronous switching device for lighting the planar fluorescent lamp at the back of a large surface liquid crystal display (LCD) panel. A voltage signal is transmitted to the synchronous switching device. The switching device generates synchronous voltage signals and which then pass to a plurality of voltage converters where the voltage signals are amplified. The amplified synchronous signal is fed to the common electrode and a plurality of distributed electrodes inside the planar fluorescent lamp so that the lamp is switched on synchronously and arcing between electrodes is suppressed. Hence, the entire planar fluorescent lamp lights up to obtain a high brightness level and uniform light source.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a synchronous switching device. The switching device includes a common electrode, a plurality of distributed electrodes, a plurality of voltage converters and a signal generator. The distributed electrodes are aligned on a straight line facing the common electrode. Each the distributed electrode has a length smaller than the common electrode. Each voltage converter is electrically coupled to the common electrode as well as one and only one distributed electrode. All voltage converters are electrically coupled to signal generator.
According to a second embodiment, this invention provides a planar fluorescent lamp. The planar fluorescent lamp includes a first panel, a second panel, two side panels, two fluorescent layers, a common electrode, a plurality of distributed electrodes, a plurality of voltage converters and a signal generator. The first and the second panel are parallel to each other with side panels between the first and the second panel near the edges so that a planar lamp enclosing a hollow tube is produced. The fluorescent layer is deposited on the interior surface of the first and second panel, respectively. The distrib
Chen Lai-Cheng
Lin Chie-Ching
Lin Shih-Hsien
Tsai Chun-Hui
Tsai Kuang-Lung
Delta Optoelectronics, Inc.
J.C. Patents
Vu Jimmy T.
Wong Don
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