KR20080053877A - Surface light source and backlight unit having the same - Google Patents

Abstract

A surface light source apparatus and a backlight unit including the same are provided to reduce an after-image from being produced on a liquid crystal display by dividedly driving the surface light source apparatus. A body of a light source including a first substrate(110) and a second substrate(120) is defined into plural discharge spaces(140) by barrier ribs(130). Electrodes(150a to 150d) are formed on a surface of the body of the light source in the defined discharge spaces, in which a pair of electrodes are formed on both ends of the discharge space. The electrodes are formed on one surface and/or the other surface of the body. The defined discharge space is applied with a voltage which is sequentially divided by the electrodes.

Description

Surface light source device and back light unit having the same {SURFACE LIGHT SOURCE AND BACKLIGHT UNIT HAVING THE SAME}

The present invention relates to a surface light source device and a backlight unit having the same, and more particularly, to a surface light source device that sequentially drives a discharge space into a plurality of regions and a backlight unit having the surface light source device as a light source. .

The liquid crystal display displays an image by using electrical and optical characteristics of the liquid crystal. Liquid crystal displays have the advantages of being very small in volume and light in weight compared to cathode ray tubes (CRTs). As a result, they are widely used in portable computers, communication devices, liquid crystal television receivers, and aerospace industries. .

The liquid crystal display device includes a liquid crystal controller for controlling liquid crystal and a rear light source for supplying light to the liquid crystal. The liquid crystal controller includes a pixel electrode disposed on the first substrate, a common electrode disposed on the second substrate, and a liquid crystal interposed between the pixel electrode and the common electrode. The pixel electrode is formed in plural in correspondence with the resolution, and the common electrode is made of one and facing the pixel electrode. A thin film transistor (TFT) is connected to each pixel electrode to apply pixel voltages having different levels, and a reference voltage of the same level is applied to the common electrode. The pixel electrode and the common electrode are made of a transparent material having conductivity.

Light supplied from the rear light source sequentially passes through the pixel electrode, the liquid crystal, and the common electrode. 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.

Conventionally, the rear light source of the liquid crystal display is mainly used a cold cathode fluorescent lamp (CCFL) having a rod shape or a light emitting diode (LED) having a dot shape. Cold cathode ray tube lamp has 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 the advantage of high power consumption and high brightness. However, cold cathode ray tube type lamps or light emitting diodes have poor brightness uniformity. Accordingly, a rear light source having a cold cathode ray tube lamp or a light emitting diode as a light source is an optical member such as a light guide panel (LGP), a diffusion member, a prism sheet, or the like to increase luminance uniformity. (optical member) is required. As a result, a liquid crystal display using a cold cathode ray tube lamp or a light emitting diode has a problem in that the volume and weight of the optical member are greatly increased.

As a back light source for a liquid crystal display, a flat fluorescent lamp (FFL) in the form of a flat plate has been proposed. Referring to FIG. 1, the conventional surface light source device includes a light source body 10 and electrodes 20 provided on outer surfaces of both edges of the light source body 10. The light source body 10 includes first and second substrates disposed to face each other at predetermined intervals. A plurality of partitions 30 are disposed between the first and second substrates to partition the space between the first and second substrates into a plurality of discharge spaces 50. A sealing member 40 is disposed between the edges of the first and second substrates to isolate the discharge spaces 50 from the outside. Discharge gas is injected into the isolated discharge space 50.

In order to discharge-drive the surface light source device, the electrode 20 is formed on the surface of the light source body 10 to have the same area per discharge space 50 in a band shape. The inverter discharges the same in all channels through the surface light source device.

The liquid crystal display has a disadvantage in that an afterimage remains due to the response characteristics of the liquid crystal. In particular, afterimages in moving images have a problem of degrading display quality. As the size of liquid crystal displays increases, there is an increasing demand for improvement of display quality, and various attempts have been made to solve afterimages, but there are still many things to be improved.

On the other hand, the liquid crystal display device has a problem that excessive power is consumed in the backlight which is the rear light source, and the problem of reducing the power consumption is very urgent as the size of the backlight is increased and the brightness is improved. In addition, the existing fluorescent lamps for backlights mainly use mercury as the discharge gas, but due to environmental problems, for example, restrictions on the use of hazardous substances (RoHs), the need for backlights without mercury is greatly increased. have.

The present invention has been made under the above-described technical background, and an object of the present invention is to provide a surface light source device and a backlight unit capable of improving the display quality of a liquid crystal display device.

Another object of the present invention is to provide a surface light source device and a backlight unit capable of improving the driving method, reducing integration power consumption, and providing a high quality image to a liquid crystal display device.

It is another object of the present invention to propose a driving method suitable for a surface light source device in which mercury is excluded.

In order to achieve the above object, the present invention is a light source body having a discharge space enclosed therein and at least one surface is transparent to visible light, and formed on the surface of the light source body and partitioning the discharge space by at least three portions, A surface light source device includes a plurality of electrode parts for applying a voltage to a partitioned area and a driving part for sequentially applying a driving voltage to the plurality of electrode parts in synchronization with an image signal of an external display device.

The plurality of electrode parts may be formed at both ends of the partitioned area of the discharge space, and the driving part may apply an antiphase voltage to both ends of the partitioned area of the discharge space, and the driving part may be partitioned of the discharge space. In the area

The light source body may include a plurality of discharge channels, or may include a single discharge space therein.

The electrode unit may be locally formed on one surface or both surfaces of the light source body, and may include a plurality of surface electrodes that have a large open ratio for emitted light and substantially cover the surface of the light source body.

The present invention also provides a light source body having a discharge space enclosed therein and at least one surface of the light source body transmissive to visible light, formed on the surface of the light source body, and partitioning the discharge space by at least three portions to provide voltage to each partitioned area. A surface light source device including a plurality of electrode portions for applying the light; A case accommodating the surface light source device; And a driving unit configured to sequentially apply driving voltages to the plurality of electrode units in synchronization with an image signal of an external display device.

According to the present invention, the afterimage generated in the liquid crystal display can be reduced by dividing the surface light source device into a plurality of regions and sequentially dividing the partitioned regions. In addition, by dividing and driving the surface light source device, power consumption can be reduced, product life can be extended, and image quality can be improved.

The present invention has a first feature in dividing a light emitting area of a surface light source device into physically or non-physically (by dividing an electrode portion) into several areas and sequentially driving the partitioned areas. In addition, the present invention has a second feature in that the image signal of the liquid crystal display device and the partitioned portion of the surface light source device light emitting region are sequentially driven in synchronization.

The present inventors have found that the afterimage driving of the liquid crystal display device can be significantly reduced by driving the surface light source device by the sequential division driving synchronized with the image signal. 2 is a block diagram schematically showing a system for driving a surface light source device according to the present invention. A synchronization circuit is included to synchronize the image signal of the LCD panel with the driving signal of the backlight, and a sequential division control unit for generating a sequential division driving signal by synchronizing the scanning signal among the image signals to each of the divided regions of the surface light source device. Included. The sequential division controller may be configured as an independent circuit, or may be configured as an inverter and one module provided in the backlight.

3 is a perspective view showing a surface light source device according to a first embodiment of the present invention. The light source body including the first substrate 110 and the second substrate 120 is partitioned into a plurality of discharge spaces 140 by the partition wall 130 (or the sealing member) at the edge and the inside. Electrode portions 150a, 150b, 150c, and 150d are formed on the surface of the light source body in the divided discharge space. The electrode portions are formed in pairs at both ends of the discharge space and may be formed to face one side or both sides of the light source body. Voltages sequentially divided by the electrode parts 150a, 150b, 150c, and 150d are applied to the divided discharge space 140. The divided voltages may be applied sequentially or partially crossing each discharge space.

In the present invention, the driving voltage is preferably a square wave or an impulse waveform. 4A to 4E are graphs showing voltage waveforms according to various driving methods in the surface light source device of the present invention.

Referring to FIG. 4A, a sequential signal application is performed. In the discharge space, the first signal S1 is applied to the discharge space through the first electrode unit 150a, and then the second signal (B) is applied through the second electrode 150b. S2) is applied, and then the third signal S3 is applied through the third electrode 150c, and finally, the fourth signal S4 is applied through the fourth electrode 150d to apply a signal of one cycle. To complete. As the signal applying cycle is repeated, the light emitting surface or the emitting surface of the surface light source device emits light sequentially, and the image quality of the liquid crystal display can be reduced by reducing the afterimage effect of the liquid crystal display.

In order to enhance the afterimage removal effect of the liquid crystal display, it was confirmed that it is effective to divide the light emitting region of the surface light source into three or more portions, preferably four or more portions, to sequentially drive the light sequentially. The partitioned area may receive a signal from a separate driver through each electrode unit or a separate independent signal from a single driver, and coincide with the scan line of the image signal of the liquid crystal display in the sequential division controller that controls the driver. The sequential signal is transmitted to the driver. The signal generated by the sequential division control unit controls the pulse width modulation (PWM) signal of each driving unit so that the surface light source device emits light sequentially in synchronization with the scanning line of the image signal. By sequentially driving the surface light source device as described above, when the image signal is input, the corresponding area is turned on, and there is a section that turns off after a predetermined time, thereby obtaining an effect similar to inserting a black image in the middle of the image.

In order to maximize the effect of the sequential driving, as shown in FIG. 4A, a time point (a) at which the first signal S1 applied to the first area of the partitioned area of the surface light source device ends is an external image signal VS (liquid crystal). And the starting point of the vertical frequency of the display device. In this manner, the afterimage effect of the screen image in the liquid crystal display device can be reduced as much as possible.

In addition, to reduce the afterimage of the LCD, it is confirmed that the duty ratio is 50% or less in the pulse width modulation signal of the driver.

In addition, the contrast ratio of the screen may be improved by changing the on-duty of each pulse width modulation signal sequentially applied to the divided region of the surface light source device in association with the brightness signal of the image signal. For example, referring to FIG. 4B, the driving voltages sequentially applied are on-duty in an I section (duty ratio 40 to 50%) and II section (duty ratio 10 to 20%) according to the external image signal VS. By differentiating, light having different luminance may be generated from the surface light source device in the I section (bright screen) and II section (dark screen). As such, by changing the duty ratio in the range of 10% to 50%, the pulse width modulated signal can actively control the brightness of the surface light source device in conjunction with the image signal in addition to the afterimage removal effect. Therefore, not only the integrated power consumption is reduced, but also the image quality of the liquid crystal display device can be greatly improved.

In addition, the surface light source device according to the present invention may maximize the afterimage suppression effect by applying a pulse signal in the on-duty period while fixing the duty ratio of the pulse width modulation signal. Referring to FIG. 4C, when the image vertical frequency is 60 Hz, the duty ratio of the pulse width modulated signal is fixed to 25% to 40%, and a pulse signal of 1 kHz or more in the on-duty section of the pulse width modulated signal (b). It shows the driving waveform to apply.

The number of pulses of 1 kHz or more in the on-duty period of the pulse width modulation signal may be adjusted according to the brightness of the image signal of the liquid crystal display. By driving the surface light source device as described above, the afterimage suppression effect and the image quality of the liquid crystal display device can be maximized.

On the other hand, the surface light source device according to the present invention can be driven not only the waveform of the square wave form, but also the voltage waveform of the impulse form.

When driving with an impulse-shaped waveform, the driving frequency ranges from 20 kHz to 60 kHz, and the on-duty time ranges from 0.1 Hz to 10 Hz. The shorter the on-duty time, the faster the discharge rise time (Rise-Time) increases the efficiency of the surface light source device. 4D and 4E show examples of impulse voltage waveforms by half-bridge driving and full-bridge driving, respectively. The on-duty time ranged from 0.1 Hz to 10 Hz.

In the present invention, the plurality of electrode portions may be formed at both ends of the partitioned region of the discharge space, and in this case, it is preferable that the driving portion applies an antiphase voltage to the electrode portions at both ends. As a result, when the voltage phase of one electrode is high, the voltage phase of the other electrode becomes low, so that the voltage substantially applied to the discharge space is twice the applied voltage.

In the surface light source device according to the present invention, the plurality of electrode portions are partitioned between the respective electrode portions 150b and 150c as shown in FIG. 5 in order to prevent unwanted discharges into adjacent discharge regions during sequential division driving. The distance between the discharge spaces (for example, the distance between the partition walls 130 of FIG. 5) may be increased. The extended spacing W between the electrode portions may vary depending on the spacing between the discharge spaces.

6 and 7, a surface light source device 200 according to a second embodiment of the present invention is illustrated. The surface light source device 200 includes a light source body 210 and a plurality of electrode portions 250a, 250b, 250c, and 250d provided on outer surfaces of both edges of the light source body 210.

The light source body 210 includes a first substrate 212 and a second substrate 214 disposed to face each other at predetermined intervals, and a space between the first substrate and the second substrate by the plurality of partitions 225. Is divided into a plurality of discharge channels 220. The discharge channel 220 and the partition 225 may be formed by, for example, molding the first substrate 212, or may be formed by molding a second substrate instead of the first substrate. A sealing member 230 is disposed between the edges of the first substrate 212 and the second substrate 214 to isolate the discharge channels 220 from the outside. Discharge gas is injected into the discharge space 240 inside the discharge channel 220. Although not shown, a fluorescent layer and a protective layer may be further included in the discharge channel 220, and a reflective layer may be formed on any one of the first substrate and the second substrate.

In order to drive the surface light source device, a plurality of 250a, 250b, 250c, and 250d are formed on the first substrate 212 and / or the second substrate 214 so that the discharge channels 220 may be formed in four or more regions. And partitioned. The electrode unit applies a divided voltage sequentially to the divided discharge channels.

8 and 9 show a surface light source device 300 according to a third embodiment of the present invention. The surface light source device 300 includes a planar first substrate 310 and a planar second substrate 320 having the same shape. The first substrate 310 and the second substrate 320 are opposed to each other at predetermined intervals, and the sealing member 330 is inserted into the edge to form a sealed space.

In the surface light source device 300, a plurality of electrode portions 350a, 350b, 350c, and 350d having a large area are formed on an outer surface of the light source body formed by the first substrate 310 and the second substrate 320. . The electrode portion is formed of a surface electrode in the form of a flat plate covering substantially the entire substrate area. The electrode portion preferably has an open ratio of 60% or more for exposing the substrate to increase the transmittance of light emitted by the discharge from the light source body.

The interior defined by the first substrate 310, the second substrate 320, and the sealing member 330 forms a discharge space 340 having an open structure, not a plurality of discharge spaces partitioned by partition walls. do. The plurality of electrode portions 350a, 350b, 350c, and 350d non-physically partition the discharge space 340, and the divided driving voltage applied sequentially to each electrode portion sequentially discharges the discharge space locally.

The spacing between the first substrate 310 and the second substrate 320 is very small compared to the substrate area, and the internal space is formed in one open structure, so that it is easy to inject the vacuum exhaust and discharge gas. Moreover, it is suitable to comprise a surface light source device using gas other than mercury as a discharge gas, for example, xenon, argon, neon, other inert gas, or a mixture thereof. The vertical space of the discharge space 240 between the first substrate 210 and the second substrate 220 may be determined by the spacer 235.

As illustrated in FIG. 9, the plate type electrode part may include an upper electrode part 350 formed on the surface of the first substrate 310 and a lower electrode part 360 formed on the surface of the second substrate 320. In addition, any one of the upper electrode portion and the lower electrode portion may be formed in the discharge space 340.

In this embodiment, the shape of the electrode portion can be variously modified. For example, as shown in FIG. 10, a plurality of electrode portions 350a, 350b, 350c, and 350d are formed on the surface of the first substrate 310, and One surface electrode 360 may be formed on the second substrate 320. Alternatively, as illustrated in FIG. 11, the first substrate 310 may include a plurality of first electrode portions 350a, 350b, 350c, and 350d. And a plurality of second electrode portions 360a, 360b, 360c, 360d, 360e, and 360f disposed perpendicular to the first electrode portion on the second substrate 320.

12 is an exploded perspective view showing a backlight unit including a surface light source according to the present invention. As shown, the backlight unit includes a surface light source 200, upper and lower cases 1100 and 1200, an optical sheet 900, and an inverter 1300.

The lower case 1200 includes a bottom portion 1210 and a plurality of sidewall portions 1220 extending to form an accommodation space from an edge of the bottom portion 1210 to accommodate the surface light source 200. The surface light source 200 is stored in the storage space of the lower case 1200.

The inverter 1300 is disposed on the rear surface of the lower case 1200 and generates a discharge voltage for driving the surface light source 200. The discharge voltage generated from the inverter 1300 is applied to the plurality of electrode portions 250 of the surface light source 200 through the first and second power lines 1352 and 1354, respectively.

The inverter 1300 may include the above-described sequential division control unit, or may separate the sequential division control unit as a separate unit. The driving voltage applied through the inverter is sequentially applied to each of the plurality of electrode units 250 to locally emit the surface light source 200 sequentially.

The optical sheet 900 may include a diffusion plate for uniformly diffusing the light emitted from the surface light source 200, and a prism sheet for imparting linearity to the diffused light. The upper case 1100 is coupled to the lower case 1200 to support the surface light source 200 and the optical sheet 900. The upper case 1100 prevents the surface light source 200 from being separated from the lower case 1200. Unlike the illustrated figure, the upper case and the lower case may be formed as one integrated case. Meanwhile, the backlight unit according to the present invention may not include the optical sheet 900.

In the above, it has been described with reference to preferred embodiments of the present invention, but those skilled in the art or those skilled in the art from the spirit and scope of the invention described in the claims to be described later Various modifications and variations can be made in the present invention without departing from the scope thereof.

1 is a plan view showing an example of a surface light source device.

Figure 2 is a system block diagram for the operation of the surface light source device or backlight of the present invention.

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

4A to 4E are graphs showing various driving voltage waveforms applied to the surface light source device of the present invention.

5 is a partially enlarged view of the electrode unit of FIG. 3;

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

FIG. 7 is a sectional view taken along the line X-X 'of FIG. 6; FIG.

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

9 is a cross-sectional view taken along the line Y-Y 'of FIG.

FIG. 10 is a plan view showing electrode portions on the upper and lower surfaces of the surface light source device of the embodiment of FIG. 8;

11 is a plan view showing another embodiment of the electrode portion on the upper and lower surface of the surface light source device of the embodiment of FIG.

12 is an exploded perspective view of a backlight unit including the surface light source device of the present invention.

*** Explanation of symbols for the main parts of the drawing ***

110: first substrate 120: second substrate

130: partition 140: discharge space

150a, 150b, 150c, 150d: electrode part

Claims (15)

A light source body having a discharge space sealed therein and at least one surface thereof being transparent to visible light; A plurality of electrode portions formed on a surface of the light source body to divide at least three portions of the discharge space and apply voltage to each of the divided regions; And a driving unit configured to sequentially apply driving voltages to the plurality of electrode units in synchronization with an image signal of an external display device. Surface light source device. The surface light source of claim 1, wherein the plurality of electrode parts are respectively formed at both ends of the partitioned region of the discharge space, and the driving unit applies an antiphase voltage to both ends of the partitioned region of the discharge space. Device. The surface light source device of claim 1, wherein the driving unit drives the time point at which the signal applied to the first area of the partitioned region ends to coincide with the start time point of the vertical frequency of the image signal of the external display device. The surface light source device according to claim 1, wherein the driving unit applies a voltage of an impulse waveform having a driving frequency in a range of 20 kHz to 60 kHz and an on-duty time in a range of 0.1 Hz to 10 Hz. The surface light source device of claim 1, wherein the driving unit applies a pulse width modulation signal having a duty ratio of 50% or less to a partitioned area of the discharge space. The surface light source device according to claim 5, wherein the duty ratio of the pulse width modulated signal varies in a range of 10% to 50% according to the brightness signal of the image signal of the external display device. 6. The pulse width modulation signal of claim 5, wherein the duty ratio of the pulse width modulation signal is fixed in the range of 25% to 40%, and a pulse signal of 1 kHz or more is applied in the on-duty period of the pulse width modulation signal, and the number of the pulse signals is displayed on the external display. Surface light source device characterized in that the adjustment according to the image brightness signal of the device. The surface light source device of claim 1, wherein an interval between the electrode portions is larger than an interval between partitioned regions of the discharge space. The surface light source device of claim 1, wherein the light source body includes a plurality of discharge channels. The surface light source device of claim 9, wherein the light source body includes a first substrate and a second substrate, and a plurality of discharge channels are formed on at least one of the first substrate and the second substrate. The surface light source device of claim 1, wherein the light source body includes a first substrate and a second substrate on a flat plate, and the first substrate and the second substrate form an interior space. The surface light source device of claim 11, wherein the electrode part is a surface electrode formed on at least one surface of the light source body and has an aperture ratio of 60% or more. A light source body having a discharge space sealed therein and at least one surface of the light source body transmissive to visible light, and formed on a surface of the light source body and partitioning the discharge space by at least three or more portions to apply voltage to each partitioned area. A surface light source device including an electrode portion; A case accommodating the surface light source device; And And a driving unit configured to sequentially apply driving voltages to the plurality of electrode units in synchronization with an image signal of an external display device. Backlight unit. The backlight unit of claim 13, wherein the plurality of electrode parts are respectively formed at both ends of the partitioned region of the discharge space, and the driving unit applies an antiphase voltage to both ends of the partitioned region of the discharge space. . The backlight unit of claim 13, wherein the driving unit comprises a plurality of inverters that sequentially apply driving voltages to the plurality of electrode units.

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