KR101295870B1 - Backlight unit for liquid crystal display - Google Patents

Abstract

The present invention relates to a backlight unit for a liquid crystal display device, comprising: a plurality of lamps having first and second electrodes formed at both ends thereof; And applying alternating current voltages having the same magnitude and opposite polarity to the first electrode and the second electrode of each of the lamps, respectively, to drive the lamps in parallel, and to sense the current of the lamps in parallel and apply them to the lamps. Inverter circuit portion for feedback control of the current.

Liquid Crystal Display, Backlight Unit, Inverter, Parallel Drive

Description

Backlight unit for liquid crystal display

1 is a plan view of a backlight unit for a liquid crystal display according to the prior art.

2 is a conceptual diagram of a liquid crystal display according to an exemplary embodiment of the present invention.

FIG. 3 is a plan view of the backlight unit for the liquid crystal display shown in FIG. 2.

FIG. 4 is a rear view of the backlight unit for the liquid crystal display shown in FIG. 2.

FIG. 5 is a diagram illustrating the inverter circuit unit of FIG. 4 in more detail.

6 is a flowchart illustrating a driving method of a backlight unit for a liquid crystal display according to an exemplary embodiment of the present invention.

DESCRIPTION OF THE REFERENCE NUMERALS (S)

200: outer case 210: lamp

220: reflective sheet 230: optical sheet

231: diffusion sheet 232: prism sheet

233: protection sheet 240: inverter circuit portion

250: power conversion unit 251: transformer

252: switching circuit 253: inverter controller

254: current sensing circuit 255: feedback circuit

260: first balancer group 270: second balancer group

The present invention relates to a backlight unit, and more particularly, to a backlight unit applied to a liquid crystal display device.

The liquid crystal display device forms a liquid crystal layer having anisotropic dielectric constant between upper and lower substrates which are transparent insulating substrates. The liquid crystal display device adjusts the intensity of the electric field formed in the liquid crystal layer to change the molecular arrangement of the liquid crystal material, thereby controlling the amount of light transmitted through the upper substrate, which is the display surface, to reproduce the desired image. As a liquid crystal display device, a thin film transistor liquid crystal display (TFT LCD) using a thin film transistor (TFT) as a switching element is mainly used.

Since the liquid crystal display is a light-receiving display device that does not emit light on its own, a backlight unit (BLU) is inevitably required to supply light to a liquid crystal panel that displays an image to maintain uniform brightness of the entire screen. Done.

The backlight unit is divided into an edge type and a direct type according to the location of the lamp. The edge type of the former is a structure in which a lamp is installed on the side of the light guide plate for guiding light, and is relatively similar to a monitor of a laptop computer and a desktop computer. It is applied to a small liquid crystal display device.

The direct type is mainly developed as the size of the liquid crystal display device is increased to 20 inches or more. The direct type is a structure in which light is directly supplied to the front surface of the liquid crystal panel by arranging a plurality of lamps in a row. The direct type is mainly applied to a large liquid crystal display device that requires high luminance because the light utilization efficiency is higher than that of the edge type.

As the lamp, a cold cathode fluorescent lamp (CCFL) or an external electrode fluorescent lamp (EEFL) is used, and a plurality of lamps are generally provided to emit high brightness halo.

The method of driving the lamp is to ground one end of the lamp, and the other end is connected to the ground (Ground) driving method and each inverter circuit part is connected to both ends of the lamp to apply voltage of the same size and different polarity. There is a floating driving method.

In the case of the ground driving method, when the length of the lamp is longer than a certain length, leakage current is generated by the parasitic capacitance and the stray capacitance of the lamp, which causes a difference in luminance on the left and right sides of the lamp. That is, the closer to one end of the grounded lamp, the farther away from the other end of the lamp connected to the inverter circuit portion is to decrease the brightness of the lamp.

In order to prevent this, a floating driving method in which two inverter circuit units are arranged and connected to both sides of the lamp is adopted.

1 is a plan view of a backlight unit for a liquid crystal display according to the related art, and shows a direct type backlight unit employing a floating driving method.

Referring to FIG. 1, a conventional backlight unit for a liquid crystal display includes a plurality of lamps 110 that are fixed at regular intervals on an outer case 100 to emit light.

First and second electrodes 120 and 121 are formed at both ends of the lamp 110, and inverter circuit units 130 and 131 are provided at the first electrode 120 and the second electrode 121 of each lamp 110. Are respectively connected to drive the lamps 110 in parallel. The two inverter circuit units 130 and 131 output an AC voltage having the same size and different polarities by using a DC voltage input from the outside, and applying the same to both ends of the lamp 110 to light the lamp 110. The brightness of the liquid crystal display is adjusted by controlling the lamp 110 according to a control signal input from the system.

When driving the backlight unit of the direct type in parallel, as shown in FIG. 1, two inverter circuit units 130 and 131 are applied to apply high-voltage AC waveforms to the first and second electrodes 120 and 121 of the lamp 110, respectively. Was needed.

However, when two inverter circuit units 130 and 131 are used, the number of printed circuit boards (PCB) is doubled, and since the circuits that can be used in common must be divided into two parts, manufacturing cost increases and structure is increased. There was a problem of becoming complicated.

SUMMARY OF THE INVENTION The present invention provides a backlight unit for a liquid crystal display device which can simplify the overall structure and reduce the manufacturing cost by reducing the number of inverter circuit units and parallelizing transformers and other common circuits in parallel operation. It is.

delete

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not intended to limit the invention to the precise forms disclosed. Other objects, which will be apparent to those skilled in the art, It will be possible.

A backlight unit for a liquid crystal display according to the present invention includes a plurality of lamps having a first electrode and a second electrode formed at both ends thereof; And applying alternating current voltages having the same magnitude and opposite polarity to the first electrode and the second electrode of each of the lamps, respectively, to drive the lamps in parallel, and to sense the current of the lamps in parallel and apply them to the lamps. Inverter circuit portion for feedback control of the current.
The inverter circuit unit includes a primary coil and a secondary coil, and converts an AC waveform supplied to the primary coil to induce the secondary coil, and converts a DC voltage supplied from the outside into an AC waveform to supply the transformer. An inverter controller which receives the feedback signal and controls the transformer so that the current flowing through each of the lamps is constant; a current sensing circuit connected to the lamps in common and sensing the current flowing in the lamps in parallel; and the current sensing A feedback circuit for receiving the sense signal from the circuit and generating the feedback signal; A first balancer group coupled between one side of a secondary side coil of the transformer and a first electrode of each of the lamps to balance the current of the lamps; And a second balancer group coupled to the other side of the secondary coil of the transformer and coupled between the current sensing circuit and the second electrode of each of the lamps to balance the current of the lamps.

delete

delete

delete

delete

delete

delete

delete

delete

The details of other embodiments are included in the detailed description and drawings. Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. Like reference numerals refer to like elements throughout.

Hereinafter, a backlight unit for a liquid crystal display and a driving method thereof according to an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings.

2 is a conceptual diagram of a liquid crystal display according to an exemplary embodiment of the present invention, and illustrates a liquid crystal display having a direct backlight unit.

Referring to FIG. 2, the liquid crystal display according to the exemplary embodiment includes a liquid crystal panel 300 for displaying an image and a backlight unit for supplying light to the liquid crystal panel 300.

The liquid crystal panel 300 includes upper and lower substrates 310 and 320 facing each other and a liquid crystal layer (not shown) formed therebetween.

The backlight unit scatters and condenses the light emitted from the lamp 210 and the reflective sheet 220 and the reflective sheet 220 that reflects the light generated by the lamp 210 and one or more lamps 210 that emit light. It includes an optical sheet 230, an outer case 200 for fixing and supporting the lamp 210.

The plurality of lamps 210 are arranged side by side in the longitudinal direction of the lamp 210 on the rear surface of the optical sheet 230 in a direct manner, and supplies light to the front surface of the optical sheet 230.

The outer case 200 is made of a material such as aluminum to prevent light leakage of visible light emitted from the lamps 210 and reflect the visible light traveling toward the side and the back of the lamps 210 toward the front surface of the lamp 210. Improve the efficiency of use of light emitted from To this end, a reflective sheet 220 for reflecting light is attached to the bottom of the inner case 200.

The optical sheet 230 is to prevent the shape of the lamp 210 from appearing on the display surface of the liquid crystal panel 300 and to provide a light source having a uniform brightness distribution as a whole, and scattering of light generated from the lamp 210. In order to enhance the effect, various sheets of diffusion sheet 231 and prism sheet 232 may be disposed. The protective sheet 233 may be added to the front surface of the prism sheet 232.

FIG. 3 is a plan view of the backlight unit for the liquid crystal display shown in FIG. 2, and FIG. 4 is a rear view of the backlight unit for the liquid crystal display shown in FIG. 2, and illustrates a direct backlight unit employing a floating driving method. .

Each lamp 210 includes a glass tube and inert gases (Ar, Ne, etc.) inside the glass tube, a first electrode 211 and a second electrode 212 installed at both ends of the glass tube. Inert gases are filled in the glass tube, and phosphors are coated on the inner wall of the glass tube. When an alternating high voltage having the same size and opposite polarity is applied from the inverter circuit unit 240 to the first electrode 211 and the second electrode 212 of the lamps 210, electrons are emitted and an inert gas inside the glass tube. The collision with the field increases the amount of electrons exponentially.

Electric current flows inside the glass tube by the increased electrons, ultraviolet rays are emitted as the inert gas is excited by the electrons, and the emitted ultraviolet rays collide with the phosphor coated on the inner wall of the glass tube to emit visible light.

A first balancer 261 and a second balancer 271 belonging to the first and second balancer groups 270 are respectively connected to the first electrode 211 and the second electrode 212 of each lamp 210. The first electrode 211 and the second electrode 212 of each lamp 210 are connected to the secondary coil 251_2 of the transformer 251 via the first and second balancers 271. Here, the first balancer 261 and the second balancer 271 limit the current supplied to each lamp 210 to uniformize the current balance and provide a resonance vector with the inverter circuit unit 240.

As the lamp 210, an external electrode fluorescent lamp (EEFL) that can be easily driven in parallel and in parallel can be used.

Since the first balancer group 260 and the second balancer group 270 having a symmetrical structure exist at both ends of the lamp 210, a tube voltage having the same magnitude must be applied to both ends. In order to generate a current in the glass tube of the lamp 210, there must be a potential difference at both ends. Therefore, without using a method of fixing a constant voltage such as the ground voltage GND to one of the first electrode 211 or the second electrode 212 of the lamp 210, a power waveform having the same potential difference and different polarities is used. The floating method is applied. That is, an AC voltage having a phase difference of 180 ° is applied to the first electrode 211 and the second electrode 212 of the lamp 210.

The power converter 250 applies an AC voltage having the same magnitude and opposite polarity to the first electrode 211 and the second electrode 212 of each lamp 210 to drive the plurality of lamps 210 in parallel. do.

FIG. 5 is a diagram illustrating the inverter circuit unit of FIG. 4 in more detail.

The inverter circuit unit 240 is largely composed of a first balancer group 260, a second balancer group 270, and a power converter 250. The power converter 250 includes a switching circuit 252 and a transformer 251. , An inverter controller 253, a current sensing circuit 254, a feedback circuit 255, and the like are mounted on a single printed circuit board. The printed circuit board is disposed on the rear surface of the outer case 200 as shown in FIG. 4.

The first balancers 261 constituting the first balancer group 260 correspond one-to-one with each lamp 210, and are disposed between the power converter 250 and the first electrode 211 of each of the lamps 210. Are combined to balance the current of the lamps 210.

The second balancers 271 constituting the second balancer group 270 are configured to correspond one-to-one with each lamp 210, and the second electrode 212 of each of the power converter 250 and the lamps 210 is provided. Coupled between them to balance the current of the lamps 210.

The first balancer group 260 and the second balancer group 270 serve to balance current at both ends of the lamp 210. If the impedance of each lamp 210 is different, more current flows toward the lamp 210 having a lower impedance, which affects the brightness uniformity. Accordingly, in driving the plurality of lamps 210, the first balancer 261 and the second balancer 271 may be mounted as many as the number of lamps 210 to maintain luminance uniformity.

The first balancer 261 and the second balancer 271 may be configured in the form of a coil or a capacitor, and more stable characteristics may be obtained when the coil is formed of a coil. On one side of the lamp 210, a balancer may be configured by a coil on the opposite side and a capacitor on the opposite side to further lower the cost.

The switching circuit 252 switches the switching element according to a switching control signal supplied from the inverter controller 253 to convert the DC power supply Vcc supplied from the outside into an AC waveform.

The transformer 251 converts an AC waveform supplied from the switching circuit 252 into an AC waveform having a high voltage and supplies it to each lamp 210.

The transformer 251 includes a primary coil 251_1 connected to the switching circuit 252 and a secondary coil 251_2 connected to the lamp 210. Here, both ends of the primary coil 251_1 is connected to the switching circuit 252, one end of the secondary coil 251_2 to the first electrode 211 of the lamp 210, the other end is made of the lamp 210 It is connected to the 2 electrodes 212, respectively.

The transformer 251 converts the voltage supplied to the primary coil 251_1 by the turns ratio of the primary coil 251_1 and the secondary coil 251_2 to induce a high voltage AC waveform to the secondary coil. The AC waveform of the high voltage induced by the secondary coil 251_2 is supplied to the lamp 210 through the first electrode 211 and the second electrode 212 of the lamp 210 to light the lamp 210.

The primary coil 251_1 and the secondary coil 251_2 of the transformer 251 are not necessarily configured in one-to-one (1: 1), and the primary and secondary sides of the transformer 251 are one-to-one (1: multi). Even in the case, the paths from the output end of the secondary coil 251_2 to each end of each lamp 210 can be properly configured to drive the lamps 210 in parallel.

The current sensing circuit 254 is connected in common with one electrode of the lamps 210 to sense the output current of each lamp 210 in parallel to output a sensing signal, and the feedback circuit 255 is the current sensing circuit 254. Receives a sense signal output from the to generate a feedback signal corresponding thereto and supplies it to the inverter controller 253.

The inverter controller 253 converts a DC voltage supplied from the outside into an AC waveform and supplies it to the transformer 251. Then, the switching element of the switching circuit 252 is controlled based on the feedback signal supplied from the feedback circuit 255, and the transformer 251 is controlled so that the current flowing through each of the lamps 210 has a constant value.

The inverter controller 253 pulse-modulates the reference voltage and the triangular wave pulse to generate a switching control signal for controlling the switching element, and supplies it to the switching circuit 252. In this case, the inverter controller 253 modulates the pulse width of the switching control signal by varying the reference voltage according to the feedback signal supplied from the feedback circuit 255.

Such a backlight unit for a liquid crystal display may simultaneously drive a plurality of lamps 210 using one inverter circuit unit 240, thereby significantly reducing the required cost.

In the prior art, when two lamps 210 are driven in parallel, two inverter circuit units are mounted at both ends of the lamps 210 connected in parallel, thereby increasing costs due to the use of two or more printed circuit boards or overlapping circuits. A problem occurred. In contrast, the present invention maintains the concept of parallel driving by driving both ends of the lamp 210 at a high voltage as shown in FIGS. 3 and 4, but the transformer 251 and the inverter controller 253, the Other common circuits such as the circuit forming the external power conversion unit 250 can be implemented in one inverter circuit unit 240 to be mounted on a single printed circuit board, thereby simplifying the structure and reducing the circuit cost by reducing the number of components. To save.

delete

The number of the first balancers 261 and the second balancers 271 is maintained to correspond to the number of lamps 210 so as to be connected one-to-one to each end of each lamp 210 to secure driving stability of the lamps 210. To allow parallel operation.

6 is a flowchart illustrating a driving method of a backlight unit for a liquid crystal display according to an exemplary embodiment of the present invention.

In operation S100, the inverter circuit unit 240 generates a first AC voltage and a second AC voltage having the same magnitude and opposite polarities by using an externally applied DC voltage.

In step S110, the inverter circuit unit 240 applies a first AC voltage and a second AC voltage having an antiphase relationship to the first electrode 211 and the second electrode 212 of each of the lamps 210 connected in parallel with each other. Apply each.

In step S120, the first electrode 211 of each lamp 210 by the first balancers 261 of the first balancer group 260 and the second balancers 271 of the second balancer group 270. The current balance of the lamps 210 is balanced at the input of the second electrode 212.

The driving method of the backlight unit for the liquid crystal display may further include steps S130 to S150.

In step S130, the current sensing circuit 254 in the inverter circuit unit 240 detects a current flowing through each of the lamps 210 and outputs a detection signal.

In step S140, the feedback circuit 255 in the inverter circuit unit 240 generates a feedback signal by the sensing signal output from the current sensing circuit 254.

In step S150, the inverter controller 253 in the inverter circuit unit 240 controls the current flowing through each lamp 210 to have a constant value using a feedback signal.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, You will understand.

It is to be understood that the above-described embodiments are provided so that those skilled in the art can fully understand the scope of the invention, and are to be considered in all respects as illustrative and not restrictive, Are only defined by the scope of the claims.

As described above, the backlight unit for the liquid crystal display device according to the present invention can reduce the number of inverter circuit units in parallel driving, implement a transformer and other common circuits, and simplify the overall structure and reduce manufacturing costs. .

The driving method of the backlight unit for a liquid crystal display device according to the present invention can efficiently drive such a backlight unit for a liquid crystal display device.

Claims (9)

A plurality of lamps having a first electrode and a second electrode formed at both ends thereof; And A current is applied to the lamps by applying an alternating voltage having the same magnitude and opposite polarity to the first electrode and the second electrode of each of the lamps, respectively, and driving the lamps in parallel, and sensing the current of the lamps in parallel. Inverter circuit portion for controlling the feedback; The inverter circuit unit, A transformer converting an AC waveform supplied to the primary coil to induce it into a secondary coil, and converting a DC voltage supplied from the outside into an AC waveform to supply the transformer and receiving a feedback signal, and a current flowing through each of the lamps is constant. An inverter controller that controls the transformer to control the current, a current sensing circuit commonly connected to the lamps to sense current flowing in the lamps in parallel, and a feedback for receiving the sensing signal from the current sensing circuit to generate the feedback signal. Circuit; A first balancer group coupled between one side of a secondary side coil of the transformer and a first electrode of each of the lamps to balance the current of the lamps; And And a second balancer group coupled to the other side of the secondary coil of the transformer and between the current sensing circuit and the second electrode of each of the lamps to balance the current of the lamps. . delete delete The method of claim 1, The first balancer group, A plurality of balancers connected to a first electrode of each of the plurality of lamps, The second balancer group, And a plurality of balancers connected to a second electrode of each of the plurality of lamps. delete The method of claim 1, Each of the lamps, A backlight unit for a liquid crystal display device, characterized in that it is an external electrode fluorescent lamp (EEFL). The method of claim 1, An outer case fixing the plurality of lamps in a row; A reflective sheet formed inside the outer case; An optical sheet formed on top of the lamps; And And a printed circuit board on which the inverter circuit unit is mounted. delete delete

Images