KR20090088078A - Device for driving surface light source device and surface light source device and backlight unit using the same - Google Patents

Abstract

A driving unit for a surface light source device, the surface light source device using the same and a backlight unit are provided to apply discharge voltage to the electrode of the surface light source device. A bottom chassis(200) receives a surface light source device(100). An optical member(500) comprises a diffusing plate and a prism sheet. A fixed frame(600) fixes the optical member and is combined with the bottom chassis. A drive unit(700) operates the surface light source device.

Description

Driving device for surface light source device, and surface light source device and backlight unit using same {DEVICE FOR DRIVING SURFACE LIGHT SOURCE DEVICE AND SURFACE LIGHT SOURCE DEVICE AND BACKLIGHT UNIT USING THE SAME}

The present invention relates to a driving device for a surface light source device, a surface light source device and a backlight unit using the same. It is about a unit.

The liquid crystal display displays an image by using electrical and optical characteristics of the liquid crystal. Since the liquid crystal part of the liquid crystal display is a light receiving element that does not generate light by itself, it separately requires a rear light source, that is, a backlight.

Light supplied from the rear light source sequentially passes through the pixel electrode, the liquid crystal, and the common electrode of the liquid crystal display. In this case, the display quality of the image passing through the liquid crystal largely depends on the luminance and luminance uniformity of the rear light source. In general, the higher the luminance and the uniformity of the luminance, the better the display quality.

BACKGROUND ART In the back light source of a conventional liquid crystal display device, a cold cathode fluorescent lamp (CCFL) or a light emitting diode (LED) is mainly used.

Cold cathode fluorescent lamps have the advantage of high brightness, long life, and very low heat generation compared to incandescent lamps. On the other hand, the light emitting diode has a high power consumption, but has an advantage of excellent brightness. However, cold cathode fluorescent lamps or light emitting diodes have poor luminance uniformity. Therefore, existing back light sources require optical members such as a light guide panel (LGP), a diffusion member, a prism sheet, and the like to increase luminance uniformity. As a result, the liquid crystal display has a problem in that the volume and weight of the optical member are greatly increased.

Therefore, a flat fluorescent lamp (FFL) in the form of a flat plate has been proposed.

The conventional surface light source device includes a light source body, a first electrode, and a second electrode.

The light source body has a discharge space in which discharge gas is injected. The light source body includes a first substrate and a second substrate. The first substrate and the second substrate are sealed at edges to have a discharge space between the first substrate and the second substrate.

The first electrode and the second electrode apply a discharge voltage to the discharge gas. When a discharge voltage is applied to the discharge gas, visible light is generated, and the generated visible light is emitted through the substrate.

However, since the conventional surface light source device always generates a constant luminance irrespective of an image signal, there is a problem that it is difficult to realize a realistic image.

For example, in the case of the full white image signal and the peak white image signal, since the luminance of the surface light source device is kept constant, there is a problem that it is difficult to realize a vivid image with low contrast ratio.

The present invention has been made to solve the above problems, an object of the present invention is to provide a surface light source device and a backlight unit that can implement a vivid image by improving the contrast ratio.

In order to achieve the above object, the present invention is a driving device for driving a surface light source device, the discharge voltage to the maximum brightness of the surface light source device is changed to the electrode of the surface light source device according to the magnitude of the load ratio of the image signal It provides a drive device characterized in that.

In addition, the present invention comprises a light source body having a discharge space in which the discharge gas is injected therein, and an electrode for applying a discharge voltage to the discharge space so that the maximum luminance varies depending on the magnitude of the load ratio of the image signal. A surface light source device is provided.

Preferably, the electrode applies a discharge voltage such that the maximum brightness decreases when the load rate increases, and applies a discharge voltage so that the maximum brightness increases when the load rate decreases.

Preferably, the electrode applies a discharge voltage so that the maximum luminance is greater than that of the peak white image signal than that of the full white image signal.

Preferably, when the On area of the screen increases, the load ratio of the video signal is calculated to be large, and when the On area of the screen decreases, the load ratio of the video signal is calculated to be small.

Preferably, when the brightness of the screen increases, the load ratio of the video signal is calculated to be large, and when the brightness of the screen decreases, the load ratio of the video signal is calculated to be small.

Preferably, the electrode includes a first electrode and a second electrode, and at least one of the first electrode and the second electrode is provided to electrically partition the discharge space into a plurality of local regions.

Preferably, the electrode adjusts the luminance by varying the number of discharge sustain voltage pulses applied to the discharge space.

In addition, the present invention provides a backlight unit and a display device comprising the surface light source device.

According to the above configuration, the present invention has an effect that can provide a surface light source device and a backlight unit that can implement a vivid image by improving the contrast ratio.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a perspective view showing a surface light source device according to a first embodiment of the present invention, and FIG. 2 is a view showing a first electrode 171 and a second electrode 172 projected on the same surface of the surface light source device of FIG. Drawing.

The surface light source device of FIG. 1 includes a light source body 110 and an electrode.

The light source body 110 includes a first substrate 120 and a second substrate 130. The first substrate 120 and the second substrate 130 are preferably transparent flat glass substrates.

The first substrate 120 and the second substrate 130 are opposed to each other at predetermined intervals, and the sealing member 140 is interposed between the first substrate 120 and the second substrate 130 to form a sealed discharge space 160 therein. According to the exemplary embodiment, the sealed discharge space 160 may be formed by directly bonding or fusing the edges of the first substrate 120 and the second substrate 130 without interposing the sealing member 140. .

A fluorescent layer is coated on the inner surface of the first substrate 120 (or the second substrate 130), and a reflective layer is formed on the inner surface of the second substrate 130 (or the first substrate 120) facing the substrate. A fluorescent layer is formed on the reflective layer.

The spacer 150 is interposed in the discharge space 160 to maintain an interval of the discharge space 160. The spacer 150 may be bonded to or integrally formed with the first substrate 120 and the second substrate 130. For example, an embodiment in which the spacer 150 is integrally formed on the first substrate 120 by molding the first substrate 120 may be possible.

The spacer 150 is preferably made of a material having transparency to visible light.

The spacer 150 is in an island form. Therefore, the interior defined by the first substrate 120 and the second substrate 130 forms a single discharge space 160 having one open structure. The distance between the first substrate 120 and the second substrate 130 is very small in comparison with the substrate area, and is formed in a single space, so that vacuum exhaust and discharge gas can be easily injected.

However, according to the exemplary embodiment, the inner space of the light source body may be partitioned into a plurality of discharge spaces by the partition wall.

Discharge gas is injected into the discharge space 160 of the light source body 110.

As the discharge gas, various kinds of discharge gas may be selected, but preferably, a gas excluding mercury such as xenon, argon, neon, other inert gas, or a mixture thereof is used.

In particular, when a discharge gas excluding mercury is used, it not only provides an environmentally friendly advantage, but also shortens the luminance stabilization time even when driving at low temperature. In addition, due to the temperature sensitivity of the mercury, it provides an advantage that can minimize the problem that the brightness uniformity of the surface light source device in accordance with the temperature deviation.

The electrode applies a discharge voltage to the discharge gas. When a discharge voltage is applied to the discharge gas, ultraviolet rays are generated by the discharge of the discharge gas. The generated ultraviolet rays excite the fluorescent layer to generate visible light, and the generated visible light is transmitted forward through the substrate.

At least, it is preferable that the electrode formed on the emission-side substrate of the visible light has an open ratio of 60% or more to expose the substrate in order to increase the transmittance of the light emitted by the discharge.

The electrode may use a transparent electrode (eg, ITO), other conductive materials may be used, and preferred materials include copper, silver, gold, aluminum, nickel, chromium, ITO, carbon-based conductive materials, conductive polymers, or the like. Any one material selected from composite materials may be used.

The electrode may have various patterns, such as a mesh pattern, in addition to the illustrated stripe pattern.

The electrodes may be formed by directly printing the individual electrodes on the surface of the light source body. Alternatively, the electrodes may be attached to an insulating film to form a multilayer film, and then the multilayer film may be attached to the surface of the light source body. It may be.

The electrode has a first electrode 171 for applying the first discharge voltage to the discharge space and a second electrode 172 for applying the second discharge voltage.

At least one of the first electrode 171 and the second electrode 172 is preferably provided in plural to enable local dimming. 1 and 2, a plurality of first electrodes 171 and a plurality of second electrodes 172 are formed over the entire outer surfaces of the first substrate 120 and the second substrate 130, respectively. In addition, the first electrode 171 and the second electrode 172 are formed to be orthogonal on the projection surface and cause opposite discharge.

According to an embodiment, as shown in FIG. 9 to be described later, the first electrode 171 and the second electrode 172 may be surface discharge type electrodes on one or both surfaces of the first substrate 120 and the second substrate 130. Can be formed.

First discharge voltages may be sequentially applied to the plurality of first electrodes 171. That is, the first discharge voltage may be applied in the order of S1-> S2-> S3-> ...-> Sn.

Meanwhile, the first discharge voltage may be selectively applied to the second electrode 172. That is, the second discharge voltage may be selectively applied in such a manner that the discharge may be performed only in the local region where the discharge is required in synchronization with the external image signal, for example, the external image signal applied to the LCD panel. Accordingly, at some point in time, all of the second electrodes 172 may apply the second discharge voltage to the discharge space, and conversely, no second electrode 172 may apply the second discharge voltage. Only the second electrode 172 may apply the second discharge voltage.

3 is a diagram illustrating an example of a relationship between a load ratio of an image signal and a maximum luminance of the surface light source device of FIG. 1.

As shown, the surface light source device of the present invention applies a discharge voltage so that the maximum luminance of the surface light source device varies according to the load ratio of the image signal.

The load factor is calculated according to the size of the screen's On area and the brightness of the screen.

If the On area of the screen is increased, the load ratio of the video signal is calculated to be high, and if the On area of the screen is decreased, the load ratio of the video signal is calculated to be low. For example, the load ratio is calculated to be higher than the full white screen in which the entire screen is turned on, compared to the peak white screen in which only a part of the screen is turned on.

In addition, when the brightness of the screen increases, the load ratio of the video signal is calculated to be high, and when the brightness of the screen decreases, the load ratio of the video signal is calculated to be low.

The maximum luminance of the surface light source device is adjusted according to the calculated load ratio of the image signal. In other words, when the load ratio of the image signal is large, a very high power consumption is required to drive the surface light source device. Therefore, the luminance is relatively reduced. When the load ratio of the image signal is low, only a small power consumption is required to drive the surface light source device. The brightness is relatively increased, and the power consumption is constantly consumed.

That is, the electrode applies a discharge voltage to the discharge space so that the maximum brightness of the surface light source device decreases when the load rate increases, and applies a discharge voltage to the discharge space so that the maximum brightness of the surface light source device increases when the load rate decreases.

In FIG. 3, the luminance of the surface light source device is 2500 nits (cd / m2) for a full white image signal having a load ratio of 100%, and for a peak white image signal having a load ratio of 1%. An example is shown in which the luminance is 5000 nit.

4 is a diagram illustrating another example of the maximum luminance value of the surface light source device of FIG. 1 in a full white image signal and a peak white image signal.

As shown in the figure, the luminance of the surface light source device in the case of a full white image signal of which the entire screen is white is different from the case where only local dimming is performed without using the Automatic Brightness Control (ABC) method of the present invention. In the case of using the automatic brightness control method of the present invention, all are equally given as 5000 nit.

In addition, in the case of simple local dimming and the present invention, a maximum power consumption of 300 W is consumed to display the full white screen.

However, in the case of the peak white image signal of which only a part of the screen is white, the luminance of the simple local dimming surface light source device is not changed to 5000 nit, but in the surface light source device of the present invention, the luminance of 15,000 nit is higher than 5000 nit of the full white image signal. By increasing the contrast ratio can be increased three times compared to the former.

From Fig. 4, the present invention enables to provide an improved contrast ratio by backlighting the peak white screen at a higher brightness without reducing the brightness of the surface light source device or increasing the maximum power consumption for displaying the full white screen. do.

Through this, the surface light source device of the present invention can realize an image full of tension and thrill.

5 is a view showing the first electrode 171 and the second electrode 172 of the surface light source device according to the second embodiment of the present invention projected on the same surface.

FIG. 5 illustrates an electrode shape of a surface light source device, which is more practical than that of FIG. 2, and shows that a plurality of rows of electrodes may form a single block to form a unit electrode.

6 is a perspective view illustrating a surface light source device according to a third embodiment of the present invention, and FIG. 7 is a view showing the first electrode 171 and the second electrode 172 projected on the same surface of the surface light source device of FIG. 6. to be.

As shown, the surface light source device of this embodiment has a plurality of discharge spaces therein.

In the illustrated embodiment, an embodiment in which the partition wall 121 partitioned into a plurality of discharge spaces is integrally formed on the first substrate is illustrated, but is not necessarily limited thereto.

In some embodiments, the partition wall may be integrally formed on the second substrate, and the partition wall may be integrally formed on both the first substrate and the second substrate. Furthermore, the partition wall may be interposed between the first substrate and the second substrate as an independent body from the first substrate and the second substrate.

In the present embodiment, the plurality of discharge spaces are partitioned to form independent spaces, but according to the embodiment, the plurality of discharge spaces may be connected to each other to have a serpentine shape.

The discharge space may have various cross-sectional shapes such as trapezoidal, semicircular, circular, semi-elliptic, and elliptical.

In the illustrated embodiment, the first electrode 171 is an embodiment consisting of two electrode pairs formed on both sides of each discharge channel, but is not necessarily limited thereto.

For example, one electrode may be formed in each discharge channel, or electrodes of several discharge channels may be electrically connected to form one first electrode 171.

FIG. 8 is a view showing the first electrode 171 and the second electrode 172 projected on the same surface of the surface light source device according to the fourth embodiment of the present invention.

9 illustrates a second substrate (and a first electrode 171 and a second electrode 172 formed on the second substrate) of the surface light source device according to the fifth embodiment of the present invention.

As shown, the surface light source device of FIG. 9 shows that the first electrode 171 and the second electrode 172 are formed on the same substrate to cause surface discharge.

10 is an exploded perspective view showing a backlight unit according to a sixth embodiment of the present invention.

As shown, the backlight unit includes a bottom chassis 200, an optical member 500, a fixing frame 600, and a driving device 700 in addition to the surface light source device 100.

The bottom chassis 200 accommodates the surface light source device 100.

The surface light source device 100 employs the surface light source device of FIG. 6 for illustration, but of course, the surface light source device of various structures may be used.

The optical member 500 may include a diffusion plate and a prism sheet. The diffusion plate diffuses the light emitted from the surface light source device 100 to increase the luminance uniformity. The prism sheet imparts straightness to the light diffused by the diffuser plate to increase the front luminance.

The fixed frame 600 is coupled to the bottom chassis 200 to fix the optical member 500. In the LCD, the liquid crystal panel is positioned in front of the fixed frame 600.

The driving apparatus 700 generates a high discharge voltage and supplies a first discharge voltage and a second discharge voltage to the first electrode 171 and the second electrode 172 through the first output terminal and the second output terminal, respectively. The surface light source device 100 is driven.

FIG. 11 is a diagram conceptually illustrating signal processing between a driving device and a surface light source device in the backlight unit of FIG. 10.

As shown, when there is an input of an external video signal from the video circuit, the driving device extracts the luminance component of each local region from the video signal to calculate the load ratio, and adjusts the brightness of the surface light source device according to the calculated load ratio to adjust the contrast ratio. To improve. The luminance of the surface light source device can be adjusted by varying the number of discharge sustain voltage pulses. For example, when the luminance is to be increased, the number of discharge holding voltage pulses is increased. On the contrary, when the luminance is to be decreased, the number of discharge holding voltage pulses is decreased.

1 is a perspective view showing a surface light source device according to a first embodiment of the present invention.

FIG. 2 is a view showing the first electrode and the second electrode of the surface light source device of FIG. 1 projected on the same surface.

3 is a diagram illustrating an example of a relationship between a load ratio of an image signal and a maximum luminance of the surface light source device of FIG. 1.

4 is a diagram illustrating still another example of the maximum luminance value of the surface light source device of FIG. 1 in a full white image signal and a peak white image signal.

5 is a view showing the first electrode and the second electrode of the surface light source device according to the second embodiment of the present invention projected on the same surface.

6 is a perspective view showing a surface light source device according to a third embodiment of the present invention.

FIG. 7 is a view showing the first electrode and the second electrode of the surface light source device of FIG. 6 projected on the same surface.

8 is a view showing the first electrode and the second electrode of the surface light source device according to the fourth embodiment of the present invention projected on the same surface.

9 is a view showing a second substrate (and a first electrode and a second electrode formed on the second substrate) of the surface light source device according to the fifth embodiment of the present invention.

10 is an exploded perspective view showing a backlight unit according to a sixth embodiment of the present invention.

FIG. 11 is a diagram conceptually illustrating signal processing between a driving device and a surface light source device in the backlight unit of FIG. 10.

Claims (9)

A drive device for driving a surface light source device, And a discharge voltage applied to the electrodes of the surface light source device so that the maximum luminance of the surface light source device varies according to the magnitude of the load ratio of the image signal. A light source body having a discharge space into which discharge gas is injected; And an electrode for applying a discharge voltage to the discharge space so that the maximum luminance varies according to the magnitude of the load ratio of the image signal. The method of claim 2, And the electrode applies a discharge voltage such that the maximum brightness decreases when the load rate increases, and applies a discharge voltage so that the maximum brightness increases when the load rate decreases. The method of claim 2, The electrode is a surface light source device, characterized in that for the peak white video signal, the discharge voltage is applied so that the maximum luminance is larger than that of the full white video signal. The method of claim 2, If the On area of the screen increases, the load ratio of the video signal is calculated to be large, and if the On area of the screen is reduced, the surface light source device characterized in that to calculate a small load ratio of the video signal. The method of claim 2, The surface light source device characterized in that the load ratio of the video signal is calculated to be larger when the brightness of the screen is increased, and the load ratio of the video signal is calculated to be smaller when the brightness of the screen is decreased. The method of claim 2, The electrode has a first electrode and a second electrode, At least one of the first electrode and the second electrode is provided with a plurality of surface light source device, characterized in that to electrically partition the discharge space into a plurality of local area. The method of claim 2, The electrode is a surface light source device, characterized in that the brightness is adjusted by varying the number of discharge sustain voltage pulse applied to the discharge space. A backlight unit comprising the surface light source device according to any one of claims 2 to 8.

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