KR20010003376A - Liquid crystal display - Google Patents

Abstract

PURPOSE: A liquid crystal display is provided to prevent flicker generation by applying an exactly clocked pulse width modulation(PWM) frequency to a plurality of inverters. CONSTITUTION: A liquid crystal display comprises a plurality of inverters(150,153,155) which are electrically connected to corresponding lamps(130) via a wire and supply a power to the corresponding lamps(130). A PWM illuminating part(200) is connected to the inverters(150,153,155) via a wire and applies a PWM frequency to each of the inverters(150,153,155) so as to be synchronized with PWM frequencies of the inverters(150,153,155).

Description

Liquid Crystal Display

The present invention relates to a light control unit of a liquid crystal display, and more particularly, by connecting a plurality of inverters to a single pulse width modulation (PWM) light control unit to accurately synchronize the PWM frequencies of the respective inverters, thereby providing a PWM frequency. The present invention relates to an inverter of a liquid crystal display device which prevents flicker generated due to interference.

Recently, liquid crystal displays developed to replace CRTs (Cathode Ray Tubes) have advantages such as small size, light weight, and low power consumption, and thus are used as large information display devices as well as laptop computers and desktop computers.

Since the LCD does not emit light, the LCD displays information by reflecting extraneous light passing through the LCD panel, or displays an information by installing a separate light source on the back of the LCD panel.

Here, the backlight assembly includes a lamp unit for emitting light, a light guide plate for guiding light emitted from the lamp unit toward the LCD panel, and optical sheets for diffusing and condensing the light guided by the light guide plate to improve light efficiency.

On the other hand, the lamp unit is composed of a lamp used as a light source of the liquid crystal display device, a reflector to reflect the light emitted from the lamp to improve the efficiency of the light, and an inverter device connected to the lamp by a wire to apply a voltage to the lamp.

In general, a small liquid crystal display device obtains sufficient luminance to display information by applying an edge method in which one or two lamps are provided on the side of the light guide plate. By installing a lamp, sufficient brightness cannot be obtained.

Therefore, a large liquid crystal display device uses a diffuser plate instead of a light guide plate and adopts a direct method of providing 12 or more lamps on the lower surface of the diffuser plate to obtain sufficient luminance required for displaying information.

In such a large liquid crystal display device, since a high dimming ratio is required, an PWM dimming inverter device having a much higher dimming ratio is used than an inverter of a current controlled dimming method.

Here, the current control dimming method is a method of dimming by changing the current input to the inverter to adjust the output voltage of the inverter, that is, the voltage applied to the lamp. The dimming ratio is less than 5: 1, which is mainly used for small liquid crystal display devices. do. The reason why the dimming ratio of the current controlled dimming method is low is that the discharge becomes unstable when the voltage applied to the lamp becomes too low because the lamp emits light by the discharge energy.

On the other hand, the PWM dimming method uses a PWM frequency to change the temporal ratio between the lighting period and the unlit period of the lamp, so that dimming is performed time-divisionally, and the dimming ratio is greater than 100: 1. It is used in a large liquid crystal display device requiring a ratio.

However, when 12 or more lamps are installed in a large liquid crystal display, at least three inverter devices for supplying power to the lamps are installed. There is a problem in that flicker occurs due to different mechanical error ranges of the dimming parts, thereby lowering the display quality of the LCD.

In more detail, even when the PWM controllers of the inverter devices are set to the same frequency by manipulating the brightness controllers installed outside the inverter devices, the inverters are generated in each inverter device due to the mechanical error range of the PWM dimming units. The synchronization of the PWM frequencies does not match.

Accordingly, frequency interference occurs between the PWM frequencies generated from the respective inverter devices, causing the lamp to flicker, which causes flickering of the screen when the LCD is driven.

In order to prevent such PWM frequency interference, 12 or more lamps may be electrically connected to one inverter device. However, in this case, the inverter needs to have a large-capacity transformer, thereby increasing the volume of the inverter to realize a thinner LCD. Can't.

Accordingly, an object of the present invention has been made in view of the above problems, and by preventing the interference of the PWM frequency by accurately synchronizing the PWM frequency of each inverter, to prevent the generation of flicker in the liquid crystal display device.

Other objects of the present invention will become more apparent from the following detailed description and the accompanying drawings.

1 is an exploded perspective view showing the structure of a liquid crystal display according to the present invention.

Figure 2 is a block diagram showing a light control unit, an inverter and lamps according to the present invention in a block.

3 is a view showing a process of generating a PWM frequency according to the present invention.

In order to achieve the object of the present invention, the present invention electrically connects a plurality of inverters to one PWM dimming unit to synchronize the PWM frequency of each inverter.

Hereinafter, an inverter of a liquid crystal display according to the present invention will be described with reference to FIGS. 1 and 2.

As shown in FIG. 1, the liquid crystal display device 100 according to the present invention is installed on the LCD panel 110 and the lower surface of the LCD panel 110 to display information using electrical and optical properties. Diffusion plate 120 to diffuse and transmit to the LCD panel 110, a plurality of lamps 130 are installed on the bottom surface of the diffusion plate 120 to emit light and the lamps 130 by the wire 140 and A plurality of inverters 150, 153, 155, which are electrically connected to each of the lamps 130, and a plurality of inverters 150, 153, 155 and a plurality of inverters 150, 153, 155 are connected to each other by a wire 160 to supply a PWM frequency to each of the inverters 150, 153, 155. One PWM dimming unit 200 is applied.

Here, the lamps 130 are spaced apart from each other by a predetermined distance and are arranged in the longitudinal direction of the diffusion plate 120, and electrodes in which power supplied from the inverters 150, 153, and 155 are input to both ends of the lamps 120 in the longitudinal direction. (Not shown) are formed, and one end of the wire 140 is connected to each electrode.

In addition, the other end of the wire 140 is connected to the plurality of inverters 150, 153, and 155, which converts a low voltage direct current into a high voltage and high frequency AC voltage and supplies the lamps 130 to the lamps 130.

Here, in general, one inverter 150, 153, 155 is a plurality of lamps 130 are electrically connected, for example, 12 lamps 130 on the lower surface of the diffusion plate 120 When installed, as shown in FIG. 1, three inverters are installed, and four lamps 130 are electrically connected to the inverters 150, 153, and 155, respectively.

Meanwhile, according to the present invention, the three inverters 150, 153, and 155 are electrically connected to one PWM dimming unit 200 via a wire 160, wherein the PWM dimming unit 200 is connected to the lamps 130. In order to adjust the brightness, a PWM frequency is generated and applied to the inverters 150, 153, and 155, respectively.

The reason for installing the plurality of inverters 150, 153, and 155 in one PWM dimming unit 200 is to apply the PWM frequency generated by the PWM dimming unit 200 to each of the inverters 150, 153, and 155. This is to synchronize the PWM frequency.

As shown in FIG. 1, a brightness controller 210 is installed outside the PWM dimming unit 200 so that an operator can adjust the luminance of the lamps 130, and inside the PWM dimming unit 200. As shown in FIG. 2, the period of the triangular wave signal is connected to the triangular wave oscillation circuit 220 and the triangular wave oscillation circuit 220 for generating a triangular wave signal in order to determine a period of turning on and off the lamps 130. Waveform setting unit 230 for determining the waveform, the operational amplifier 240, which is electrically connected to the brightness controller 210 and outputs a signal corresponding to the DC voltage level of the control signal input from the brightness controller 210, operational amplifier A NAND gate 260 connected to the 240 and the waveform setting unit 230 to generate a PWM frequency and a NAND gate 260 connected to the comparator 250 to invert the PWM frequency output from the comparator 250. Is installed.

Here, the waveform setting unit 230 is composed of two resistors 232 and 234 and one capacitor 236.

Referring to the operation of the liquid crystal display device configured as described above with respect to the PWM dimming unit is as follows.

As shown in FIG. 2, when a triangular wave signal that determines the driving period of the lamp 130 from the triangular wave oscillation circuit 220 is output at a constant period as shown in FIG. 3A, the waveform setting unit 230 generates a triangular wave oscillation. The waveform and period of the triangular wave signal output from the circuit 220 are set.

More specifically, as illustrated in FIG. 3A, the triangular wave signal waveform from time t ₀ to time t _f is determined by the time constants of the first resistor 232 and the condenser 236, and from time t _f . The triangular signal waveform up to time t ₀ ′ is determined by the time constants of the second resistor 234 and the condenser 236. In general, to generate 100% luminance, the PWM frequency is changed from t _f to time t ₀ ´. Makes the time of low level signal.

Here, from time t ₀ to time t _f of the triangular wave signal waveforms of one period (t ₀ to t ₀ ′) is a section in which a high level frequency is generated as shown in FIG. 3B, and time t _f to time t _{Up to 0} ′ is a period generated by the low level frequency, and the light emission of the lamps 130 is stopped and turned off during the low level period.

As described above, when the operator manipulates the brightness controller 210 after the waveform and period of the triangular wave signal are set by the waveform setting unit 230, a control signal corresponding to the manipulated amount is input to the operational amplifier 240 to calculate the operation. The amplifier 240 outputs a signal corresponding to the DC voltage level of the input control signal to the comparator 250 as shown in FIG. 3C.

Meanwhile, the comparator 250 compares the signal output from the operational amplifier 240 (see FIG. 3C) with the triangular wave signal output from the waveform setting unit 230 (see FIG. 3A). The frequency is output to the NAND gate 260.

The NAND gate 260 inverts the PWM frequency output from the comparator 250 to apply the inverted PWM frequency to the inverters 150, 153, and 155, and inputs the PWM frequency transmitted from the PWM dimming unit 200. Reference numerals 150, 153, and 155 invert the PWM frequency again to generate a signal having the same waveform as that shown in FIG. 3D and output the signal toward the lamps 130.

Here, as shown in FIG. 3F, the lamp 130 is turned on during the high level period (t ₁ to t _f ) among the PWM frequencies output from the inverters 150, 153, and 155, and the low level period (t ₀ to t _1). The lamp 130 is turned off to output the luminance desired by the operator.

As described above, when one PWM dimming unit 200 generates a PWM frequency and applies it to each of the inverters 150, 153, and 155, the synchronization of the PWM frequencies input to the inverters 150, 153, and 155 is exactly the same, thereby interfering with each other. Can be prevented at the source.

If the PWM frequency interference does not occur as described above, the flicker phenomenon that the screen of the liquid crystal display is not shaken because the lamps 130 are stably driven without flickering.

In addition, without the PWM dimming unit 200 embedded in each of the inverters 150, 153, and 155, one PWM dimming unit 200 may be separately installed outside the inverters 150, 153, and 155 as described above, respectively. Because of the electrical connection to the size of the inverters 150, 153, 155 according to the present invention can be formed smaller than the size of the conventional inverter.

In this way, the inverters, which are not built-in PWM dimming unit and controlled by a separate component PWM dimming unit, are applicable to not only the above-described direct type liquid crystal display device but also edge type liquid crystal display device.

The edge type liquid crystal display device is provided with a frame having a receiving groove, a reflecting plate installed on the base surface of the receiving groove for reflecting light, a light guide plate placed on the upper surface of the reflecting plate to guide the light, and installed on both sides of the light guide plate in the width direction to emit light. It consists of a lamp assembly, an optical sheet for diffusing and condensing light placed on the upper surface of the light guide plate, and an LCD panel placed on top of the optical sheets to display information.

The lamp assembly may include a plurality of lamps arranged on both sides of the light guide plate horizontally or vertically with the light guide plate, for example, three lamps arranged on one side of the light guide plate in the width direction of the light guide plate, and three lamps from the width direction side of the light guide plate. It consists of at least two inverters which are all wrapped and electrically connected to the electrodes of the lamps by means of reflectors and wires reflecting light towards the light guide plate to power the lamp.

For example, assuming that three lamps are electrically connected to one inverter, two inverters are installed in an edge type liquid crystal display according to the present invention, and two inverters are wired as in a direct type liquid crystal display. Is electrically connected to a single PWM dimmer.

As described above, the present invention electrically connects a plurality of inverters installed in a liquid crystal display to a single PWM dimming unit, thereby applying a precisely synchronized PWM frequency to each inverter, thereby providing a frequency between the PWM frequencies input to the inverters. Interference can be prevented.

As such, if the PWM frequencies output from the inverters to the lamps are not subjected to frequency interference, the lamps operate stably without flickering, thereby improving display quality of the LCD.

Claims (3)

An LCD panel on which information is displayed by electric and optical properties; An optical sheet unit installed at a lower surface of the LCD panel to improve light uniformity and light efficiency and to transmit the light to the LCD panel; A plurality of lamps disposed below the optical sheet unit to emit light; A plurality of inverters electrically connected to the lamps to supply high voltage and high frequency AC power to the lamps; And And a PWM dimming unit electrically connected to the inverters through a wire, the PWM dimming unit transmitting a PWM frequency to each of the inverters to adjust the brightness of the lamp. The diffuser plate of claim 1, further comprising a diffuser plate configured to diffuse light onto a lower surface of the optical sheet unit, wherein the lamps are arranged in a line along a longitudinal direction of the diffuser plate at predetermined intervals from each other. Liquid crystal display device characterized in that. The liquid crystal display of claim 1, wherein a light guide plate for guiding light is further provided on a lower surface of the optical sheet unit, and at least two lamps are installed on opposite sides of the light guide plate.