KR20080062421A - Circuit for driving backlight and liquid crystal display having the same - Google Patents

Abstract

A backlight driving circuit and an LCD(Liquid Crystal Display) having the backlight driving circuit are provided to stabilize the power consumed by a backlight through feedback control of the power, thereby improving the stability of the backlight when the backlight is used for a long time. A backlight driving circuit(100) includes a driving voltage generator(110) and a consumption power controller(120). The driving voltage generator generates a voltage suitable to drive a backlight(200). The consumption power controller receives power from the driving voltage generator through feedback and controls the driving voltage controller such that initial consumption power of the backlight linearly increases.

Description

TECHNICAL FIELD The backlight driving circuit and a liquid crystal display including the same. {CIRCUIT FOR DRIVING BACKLIGHT AND LIQUID CRYSTAL DISPLAY HAVING THE SAME}

1 is a block diagram illustrating a backlight driving circuit according to an exemplary embodiment of the present invention.

FIG. 2 is a circuit diagram illustrating a power consumption controller of FIG. 1. FIG.

3 is a graph illustrating saturation power consumption versus duty ratio required for adjusting the gain ratio of the amplifier of FIG. 2.

4 is a block diagram illustrating a liquid crystal display according to an exemplary embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

110: backlight driving circuit 110: driving voltage generator

120: power consumption control unit 200: backlight

400: liquid crystal display panel 510: signal controller

520: voltage generator 530: gate driver

540: data driver

The present invention relates to a backlight driving circuit and a liquid crystal display device having the same, and more particularly, to a backlight driving circuit capable of stabilizing initial power consumption of the backlight and a liquid crystal display device having the same.

Recently, the liquid crystal display (LCD), which is one of the flat panel display devices, has better visibility than the cathode ray tube (CRT), and the average power consumption is smaller than that of the CRT of the same screen size, and also generates a small amount of heat. Along with plasma display panels (PDPs) and field emission displays (FEDs), they have recently been in the spotlight as next-generation display devices for mobile phones, computer monitors, and televisions.

The liquid crystal display includes a liquid crystal display panel including an upper substrate on which a black matrix, a color filter, and a common electrode are formed, a lower substrate on which a thin film transistor and a pixel electrode are formed, and a liquid crystal layer positioned between two substrates. It further comprises a polarizing plate attached to both sides of the panel. In addition, since the liquid crystal display panel does not emit light by itself, it requires a backlight for providing light from the back side so that the display contents can be visually recognized.

The power consumption of the backlight can be divided into two categories. One is the initial power consumption immediately after powering the backlight, and the other is the saturated power consumption when the components and internal temperature of the backlight are saturated after a certain time. When the power consumption according to the operation time of the backlight is measured, the power consumption of the backlight rises sharply immediately after the lighting, and becomes unstable, and remains constant after a predetermined time (saturation time) has elapsed. At this time, the initial power consumption is usually about 10 to 20% larger than the saturated power consumption.

In general, the backlight driving circuit is designed based on the maximum power consumption of the backlight, that is, the initial power consumption, and thus the heat generation conditions, because it must ensure stability even in the worst conditions. Thus, there is an excessive performance specification (SPEC) relative to saturation power consumption, which entails cost increase and volume increase. In addition, the conventional backlight driving circuit has a problem that the operation of the backlight is unstable and the backlight life is shortened because the difference between the initial power consumption and the saturated power consumption is large. In particular, the cold-cathode fluorescent lamps, which are mainly used as backlights, are also increasing in line with the recent trend of larger liquid crystal displays. As a result, the share of the power consumption of the backlight among the total power consumption of the liquid crystal display becomes larger, and thus, there is a need to reduce it.

The present invention has been made to solve the above problems, and an object thereof is to provide a backlight driving circuit capable of stabilizing power consumption of a backlight through feedback control of power consumption, and a liquid crystal display device having the same.

In the backlight driving circuit according to the present invention for achieving the above object, the initial power consumption of the backlight is linear by receiving the power consumption from the driving voltage generation unit for generating a voltage suitable for driving the backlight and the front end of the driving voltage generation unit. It includes a power consumption control unit for controlling the driving voltage generator to increase to.

The driving voltage generator preferably includes a PWM modulator for outputting a pulse width by modulating the input voltage. The driving voltage generator preferably outputs the input voltage by pulse width modulating the input voltage in the form of a sine wave or a square wave.

The driving voltage generator further includes a transformer for boosting and outputting an input voltage from the PWM modulator.

The power consumption controller receives the input voltage and the input current from the front end of the driving voltage generator, calculates the current power consumption, calculates a target power consumption suitable for a dimming signal from the outside, and the current power consumption exceeds the target power consumption. It is preferable to control the driving voltage generator so as not to. The power consumption controller compares an amplifier that receives and amplifies an external dimming signal, a multiplier that multiplies an input voltage and an input current, and an error amplifier that compares an output signal from the amplifier and the multiplier and amplifies the error. And a comparator for outputting a square wave pulse signal by comparing the amplified error voltage with a triangular wave.

A liquid crystal display device according to the present invention for achieving the above object includes a liquid crystal display panel for displaying an image, a backlight for providing light to the liquid crystal table panel and a backlight driving circuit for controlling the backlight, the backlight The driving circuit is configured to control the driving voltage generator so that the initial power consumption of the backlight is linearly increased by receiving power consumption from a driving voltage generator that generates a voltage suitable for driving the backlight and a front end of the driving voltage generator. And a power control unit.

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

However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various forms, and only the embodiments are intended to complete the disclosure of the present invention, and to those skilled in the art the scope of the invention. It is provided for complete information. Like reference numerals in the drawings refer to like elements.

1 is a block diagram illustrating a backlight driving circuit according to an exemplary embodiment of the present invention, FIG. 2 is a circuit diagram illustrating a power consumption controller of FIG. 1, and FIG. 3 is a saturation ratio of duty ratio required for adjusting the gain ratio of the amplifier of FIG. A graph showing power consumption.

1 to 2, the backlight driving circuit 100 according to the exemplary embodiment of the present invention may include a driving voltage generator 110 and a driving voltage generator 110 for generating a voltage suitable for driving the backlight 200. And a power consumption controller 120 controlling the driving voltage generator 110 to linearly increase the initial power consumption of the backlight 100 by receiving power consumption at a front end of the panel.

The driving voltage generator 110 may output a pulse width modulation (PWM) of the input voltage Vin according to the external control signal CS and output the PWM voltage from the PWM modulator 111 and the PWM modulator 111. And a transformer 112 for boosting and outputting the input voltage. The PWM modulator 111 includes a switching circuit (not shown) controlled according to an external control signal CS, thereby controlling the on / off time of the output pulse to vary the width of the output pulse. Meanwhile, the configuration of the PWM modulator 111 and the transformer 112 may vary according to characteristics of the driving voltage of the backlight 200. That is, when using a backlight 200 operating in alternating current, such as a Cold Cathode Fluorescent Lamp (CCFL), the PWM modulator 111 is configured to output a sinusoidal pulse, and the transformer ( 112 is preferably constituted by an AC boosting means such as a transformer. On the other hand, in case of using the backlight 200 operating in direct current, such as a light emitting diode, the PWM modulator 111 is configured to output a square wave pulse, and the transformer 112 is a direct current such as a DC-DC converter. It is preferable that it is comprised by the pressure boosting means.

The power consumption controller 120 receives the input voltage Vin and the input current Iin at the front end of the driving voltage generator 110 to calculate the current power consumption, and target consumption suitable for the dimming signal Vdim from the outside. By calculating the power, the driving voltage generator 110 is controlled so that the current power consumption does not exceed the target power consumption. The power consumption controller 120 controls the total power consumption by controlling a duty ratio during pulse width modulation performed by the driving voltage generator 110 through a control signal CS having a square wave shape. . The power consumption controller 120 receives an external dimming signal Vdim and amplifies an amplifier 121 and a multiplier that multiplies and receives an input voltage Vin and an input current Iin. An error amplifier 123 for comparing the output signals from the amplifier 121 and the multiplier 122 and amplifying the error and an amplified error voltage with a triangular wave to control a square wave; Comparator 124 for generating a signal. At this time, the dimming signal Vdim is input to the non-inverting terminal (+) of the amplifier 121. The output signal from the amplifier 121 is input to the non-inverting terminal (+) of the error amplifier 123 to become a reference signal, and the output signal from the multiplier 122 is an inverting terminal (−) of the error amplifier 123. ) Is entered. In addition, the output signal from the error amplifier 123 is input to the non-inverting terminal (+) of the comparator 124, the triangular wave is input to the inverting terminal (-) of the comparator 124.

The operation of the backlight driving circuit 100 configured as described above is as follows.

First, the amplifier 121 receives a dimming signal Vdim from the outside and amplifies the dimming signal at a predetermined gain K to output it. The dimming signal Vdim is a signal generated by a user or a system and controls a dimming ratio, that is, a duty ratio of the backlight 200. The gain K of the amplifier 121 is determined through measurement data of saturation power consumption according to the duty ratio of the backlight 200. For example, referring to point A in the graph of FIG. 3, it can be seen that the saturation power consumption is about 90W when the duty ratio is about 40%. Therefore, when a dimming signal Vdim having a duty ratio of 40% is input, the amplifier 121 outputs a signal amplified by a size corresponding to a power consumption of 90W. That is, the magnitude of the output signal from the amplifier 121 means saturation power consumption according to the dimming signal Vdim. The multiplier 122 is connected to the front end of the driving voltage generator 110 to detect the input voltage Vin and the input current Iin, and multiply and output the multiplier. Since power consumption P = V × I, the magnitude of the output signal from multiplier 122 means current power consumption. At this time, the output signal from the multiplier 122 is input to the inverting terminal (-) of the error amplifier 123 after passing through a low pass filter composed of R3 and C1 to reduce the ripple component. The error amplifier 123 uses the output signal from the amplifier 121 as a reference voltage, compares it with the output signal from the multiplier 122, amplifies and outputs the error. The comparator 124 compares the amplified error voltage with a triangular wave and outputs a square wave shaped control signal CS. At this time, since only the portion of the potential higher than the triangular wave is output at the portion where the error voltage is compared with the potential of the triangular wave, the width of the pulse is adjusted to adjust the output to match the reference voltage of the desired error amplifier 123. Meanwhile, the PWM generator 111 modulates the pulse width of the input voltage Vin by adjusting the duty ratio according to the control signal CS from the comparator 124, and the transformer 112 boosts the voltage to a predetermined magnitude. Output to the backlight 200.

In this operation, if the current power consumption of the backlight 200 is greater than or equal to the saturated power consumption suitable for the desired dimming signal Vdim, the duty ratio is adjusted lower than that of the present, resulting in lower power consumption. Therefore, the power consumption of the backlight 200 is initially increased rapidly and then lowered to reach saturated power consumption, but increases linearly from the beginning to reach saturated power consumption. That is, as the initial power consumption of the backlight 200 is stabilized, the difference from the saturated power consumption is reduced. As a result, stability is ensured even when the backlight 200 is used for a long time, and as the initial power consumption is reduced, the performance specification of the backlight driving circuit 100 may be lowered, thereby reducing the cost and reducing the volume. In addition, as the initial power consumption is reduced, the total power consumption of the backlight 200 is reduced.

Meanwhile, the backlight driving circuit 100 according to the exemplary embodiment of the present invention may be used in various systems including the backlight 200. As an example of such a possibility, a liquid crystal display including the backlight driving circuit will be described. . In this case, a description overlapping with the above-described embodiment will be omitted or briefly described.

4 is a block diagram illustrating a liquid crystal display according to an exemplary embodiment of the present invention.

Referring to FIG. 4, the liquid crystal display includes a liquid crystal display panel 400 for displaying an image and a liquid crystal driving circuit 500 for controlling the image, and a backlight 200 for providing light to the liquid crystal display panel and the same. It further includes a backlight driving circuit 100 for controlling.

The liquid crystal display panel 400 includes a plurality of gate lines G1 to Gn extending in one direction and a plurality of data lines D1 to Dm extending in the other direction crossing the gate lines G1 to Gn, and the plurality of gate lines G1 to Gm provided in the intersection area thereof. It includes the unit pixel of. A thin film transistor Q, a liquid crystal capacitor Clc, a liquid crystal capacitor Clc, and the like are formed in the unit pixel.

Here, the gate terminal of the thin film transistor Q is connected to the gate lines G1 to Gn, the source terminal is connected to the data lines D1 to Dm, and the drain terminal is a pixel electrode (not shown) of the liquid crystal capacitor Clc. Is connected). The thin film transistor Q operates according to the gate turn-on voltage Von applied to the gate lines G1 to Gn to supply a data signal of the data lines D1 to Dm to the pixel electrode of the liquid crystal capacitor Clc. In addition, the liquid crystal capacitor Clc includes a liquid crystal layer (not shown) positioned as a dielectric between an opposing pixel electrode and a common electrode (not shown). The liquid crystal capacitor Clc is charged with a data signal when the thin film transistor Q is turned on. It serves to control the molecular arrangement of the layers. The sustain capacitor Cst is formed by forming an insulating layer (not shown) with a dielectric between the opposite pixel electrode and the sustain electrode, and the data signal charged in the liquid crystal capacitor Clc is charged until the next data signal is charged. It plays a role of maintaining stability. Of course, the sustain capacitor Cst, which plays an auxiliary role of the liquid crystal capacitor Clc, may be omitted. On the other hand, it is preferable that each unit pixel of the present embodiment uniquely displays one of three primary colors (red, green, blue). To this end, a color filter is provided in each unit pixel, and a black matrix is provided between each unit pixel region to prevent light leakage.

The liquid crystal driving circuit 500 including the signal controller 510, the voltage generator 520, the gate driver 530, and the data driver 540 is provided outside the liquid crystal display panel 400. Various control signals for the operation of the liquid crystal display panel 400 are provided through the liquid crystal driving circuit 500.

The signal controller 510 receives an input image signal and an input control signal from an external graphic controller (not shown). For example, an input image signal including the input image data R, G, and B, and a vertical synchronization signal Vsync, a horizontal synchronization signal Hsync, a main clock MCLK, and a data enable signal DE are included. Is provided with an input control signal. In addition, the signal controller 510 generates an internal image signal, that is, internal image data R ', G', and B 'based on the input image signal, and based on the input control signal, Generate a gate control signal including a vertical synchronization start signal STV and a gate clock signal CPV for controlling the operation of the gate driver 530, and generate a horizontal synchronization start signal for controlling the operation of the data driver 540 ( A data control signal including the STH) and the data latch signal DL is generated.

The voltage generator 520 generates and outputs various driving voltages for driving the liquid crystal display panel 400 using an external power source input from an external power supply device (not shown). For example, a gate turn-on voltage Von for turning on the thin film transistor Q, a gate-off voltage Voff for turning off the thin film transistor Q, and the like are generated and outputted to the gate driver 530. (AVDD) is generated and output to the data driver 540, and a common voltage Vcom is generated and applied to the liquid crystal capacitor Clc and the sustain capacitor Cst.

The gate driver 530 starts operation according to the vertical synchronization start signal STV, and the gate turn-on voltage Von and the gate-off voltage Voff input from the driving voltage generator 400 according to the gate clock signal CPV. ) And a gate signal of an analog form including the ()) is sequentially output to the plurality of gate lines (G1 to Gn) formed on the liquid crystal display panel (400).

The data driver 540 converts the input internal pixel data R ', G', and B 'into analog data signals based on the reference voltage AVDD, and converts the data into the data latch signal DL. Accordingly, the data is output to the plurality of data lines D1 to Dm formed in the liquid crystal display panel 400.

Meanwhile, the backlight 200 including the lamp unit (not shown) is disposed on the rear surface of the liquid crystal display panel 400. Here, it is preferable to use a cold cathode fluorescent lamp (CCFL) as the lamp unit, but is not limited thereto, and various light sources, for example, an electroluminescent lamp (EL) and a light emitting diode ( Light Emitting Diode (LED) or the like may be used. The light generated by the backlight 200 is transmitted through the liquid crystal display panel 400 while the transmittance is changed and colored, and is emitted to the front of the liquid crystal display panel 400 to realize a color image.

The backlight driving circuit 100 generates and outputs various driving voltages required for driving the backlight 200 using an external power source input from an external power supply device (not shown). The backlight driving circuit 100 linearly increases the initial power consumption of the backlight 100 by being fed back the power consumption of the driving voltage generator and the front end of the driving voltage generator to generate a voltage suitable for driving the backlight 200. And a power consumption controller configured to control the driving voltage generator so that the power consumption controller includes: an amplifier for receiving and amplifying an external dimming signal; a multiplier for multiplying an input voltage and an input current; It is preferable to include an error amplifier for comparing the output signal from the signal and amplifying the error, and a comparator for comparing the amplified error voltage with a triangular wave to generate a square wave shaped control signal. That is, it is preferable to use the backlight driving circuit 100 in FIG. 1 according to the above-described embodiment.

In the liquid crystal display device configured as described above, the initial power consumption of the backlight 200 increases linearly and is controlled to reach the saturated power consumption after a predetermined time elapses. That is, as the initial power consumption of the backlight 200 is stabilized, the difference from the saturated power consumption is reduced. As a result, stability is ensured even when the backlight 200 is used for a long time, and as the initial power consumption is reduced, the performance specification of the backlight driving circuit 100 may be lowered, thereby reducing the cost and reducing the volume. In addition, as the initial power consumption is reduced, the total power consumption of the backlight 200 is reduced.

As mentioned above, although this invention was demonstrated with reference to the above-mentioned Example and an accompanying drawing, this invention is not limited to this, It is limited by the following claims. Therefore, it will be apparent to those skilled in the art that the present invention may be variously modified and modified without departing from the technical spirit of the following claims.

As described above, the present invention can stabilize the power consumption of the backlight through the feedback control of the power consumption, improves the stability of the backlight when used for a long time, and can reduce the performance specifications of the backlight driving circuit as the initial power consumption is reduced Cost can be reduced and volume can be reduced. In addition, as the initial power consumption is reduced, the total power consumption of the backlight can be reduced.

Claims (11)

A driving voltage generator for generating a voltage suitable for driving the backlight; And a power consumption controller configured to control the driving voltage generator so that the initial power consumption of the backlight is linearly increased by receiving power consumption at the front end of the driving voltage generator. The method according to claim 1, The driving voltage generator, And a PWM modulator for pulse width modulating and outputting an input voltage. The method according to claim 2, The driving voltage generator, And a pulse width modulating the input voltage in a sinusoidal wave form. The method according to claim 2, The driving voltage generator, And a pulse width modulating the input voltage in the form of a square wave. The method according to claim 2, The driving voltage generator, And a transformer for boosting and outputting an input voltage from the PWM modulator. The method according to claim 1, The power consumption control unit, The current voltage is calculated by receiving an input voltage and an input current at the front end of the driving voltage generator, and calculating a target power suitable for a dimming signal from the outside so that the current power does not exceed the target power consumption. Backlight drive circuit for controlling the generator. The method according to claim 6, The power consumption control unit, An amplifier for receiving and amplifying an external dimming signal, A multiplier that multiplies the input voltage and the input current, An error amplifier for comparing an output signal from the amplifier and the multiplier and amplifying the error; And a comparator for outputting a square wave pulse signal by comparing the amplified error voltage with a triangular wave. A liquid crystal display panel displaying an image, A backlight for providing light to the liquid crystal table panel; A backlight driving circuit for controlling the backlight; The backlight driving circuit, A driving voltage generator for generating a voltage suitable for driving the backlight; And a power consumption controller configured to control the driving voltage generator so that the initial power consumption of the backlight is linearly increased by receiving power consumption at the front end of the driving voltage generator. The method according to claim 8, The driving voltage generator, PWM modulator for pulse width modulating the input voltage and outputting; And a transformer for boosting and outputting an input voltage from the PWM modulator. The method according to claim 8, The power consumption control unit, The current voltage is calculated by receiving an input voltage and an input current at the front end of the driving voltage generator, and calculating a target power suitable for a dimming signal from the outside so that the current power does not exceed the target power consumption. A liquid crystal display device for controlling the generator. The method according to claim 10, The power consumption control unit, An amplifier for receiving and amplifying an external dimming signal, A multiplier that multiplies the input voltage and the input current, An error amplifier for comparing an output signal from the amplifier and the multiplier and amplifying the error; And a comparator for outputting a square wave pulse signal by comparing the amplified error voltage with a triangular wave.

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