WO2008063004A1

WO2008063004A1 - Apparatus of controlling backlight and apparatus of driving backlight comprising the same

Info

Publication number: WO2008063004A1
Application number: PCT/KR2007/005871
Authority: WO
Inventors: Ki Jeom Park; Soo Yeub Yoo
Original assignee: Hee Young Co., Ltd.
Priority date: 2006-11-21
Filing date: 2007-11-21
Publication date: 2008-05-29
Also published as: KR100798111B1

Abstract

A backlight control apparatus and a backlight driving apparatus having the backlight control apparatus are disclosed. The backlight control apparatus includes a serial-parallel conversion shift register outputting parallel data by shifting serial data according to a clock signal, registers storing the parallel data outputted from the serial-parallel conversion shift register, a counter counting the number of clocks of the clock signal and recounting the number of clocks when the counter receives a reset signal, comparators comparing the data stored in the registers with the clock outputted from the counter to output a PWM signal representing which one is greater of the data stored in the registers and the clock, and synchronization gates controlling the PWM signals based on gate signals applied to the synchronization gates to output a PWM control signal having a same duty ratio as the PWM signal, and a portion of which is off.

Description

APPARATUS OF CONTROLLING BACKLIGHT AND APPARATUS OF DRIVING BACKLIGHT COMPRISING THE

SAME

Technical Field

[1] The present invention relates to a backlight control apparatus and a backlight driving apparatus having the backlight control apparatus. More particularly, the present invention relates to a backlight control apparatus capable of uniformly controlling luminance of an entire portion of a backlight and precisely controlling luminance and color characteristics of each portion of the backlight, and a backlight driving apparatus having the backlight control apparatus. Background Art

[2] A fluorescent lamp, for example, a cold cathode fluorescent lamp (CCFL) type is mostly used for a backlight of a liquid crystal display (LCD). However, an environment-friendly, mercury-free product is required. Thus, instead of the CCFL, a light emission diode (LED) is promising as light source.

[3] In addition to environmental advantage, the LED backlight is more effective in energy saving than existing light sources, and may be semipermanently used, so that the LED backlight is becoming popular as the light source of the next generation. As a result, studies are actively carried out in the LED backlight with the improvement in the problems of luminance and cost.

[4] In order to be used for the backlight, white-colored light generated by a white- colored LED is used, or the white-colored light may be obtained from the optical combination of the three primary colors of red, green and blue by using a red-colored LED, a green-colored LED and a blue-colored LED. Particularly, the method of using the three primary colored LEDs is actively reviewed to be used for the television because it is easy to maintain the balance of the colors.

[5] Such a backlight using a red-colored LED, a green-colored LED and a blue-colored

LED as the light sources should optically combine red, green and blue-colored lights at a specific proportion to constantly generate the white-colored light having the fixed chromaticity. Thus, the intensity of the radiation of each colored light is detected by the photosensor of red, green and blue colors, and the above-mentioned three colors are combined at a specific proportion by feedback control, so that the white-colored light having the fixed chromaticity is constantly adjusted.

[6] However, a conventional backlight driving apparatus has a weak function for uniformly controlling luminance of the entire backlight. Furthermore, the conventional backlight driving apparatus cannot precisely control luminance and color characteristics of each portion of the backlight.

[7] In general, a conventional backlight driving circuit employs a steady current circuit for applying steady current to LEDs or a driving circuit capable of controlling the current. However, an error of the resistance of the steady current circuit or an error of a transistor induces a variation in current, resulting in change of luminance of the lamp. Therefore, the change of luminance of the lamp may be reduced by using a precisely controlled resistor or transistor, and thereby reducing luminance variation. However, that is not a fundamental solution.

[8] Furthermore, in a system the control of which is changed depending on such factors as temperature, the control becomes complex. Therefore, such as system is often controlled manually. In order to manually control the system, current that flows through the control circuit needs to be detected. Furthermore, when the LEDs have different performance, each of them has to be controlled manually. Therefore, a device capable of performing such operation is required. Disclosure of Invention Technical Problem

[9] The present invention provides a backlight control apparatus for LED, which is capable of controlling uniformly the brightness of a whole screen and which is capable of precisely controlling the luminance of each portion of the whole screen, and a backlight driving apparatus having the backlight control apparatus.

[10] The present invention also provides a backlight control apparatus for LED, which can be applied to a color filter- less (CFL) LCD without a color filter and which can reduce motion blurring of the LCD, and a backlight driving apparatus having the backlight control apparatus.

[11] The present invention also provides a backlight control apparatus for LED, which can be freely controlled by a digital microcomputer to reduce the total power consumption, and a backlight driving apparatus having the backlight control apparatus. Technical Solution

[12] A backlight control apparatus in accordance with an aspect of the present invention includes a serial-parallel conversion shift register, a plurality of registers, a counter, a plurality of comparators and a plurality of synchronization gates. The serial-parallel conversion shift register outputs parallel data by shifting serial data according to a clock signal. The registers store the parallel data outputted from the serial-parallel conversion shift register. The counter counts the number of clocks of the clock signal, and recounts the number of clocks when the counter receives a reset signal. The comparators compare the data stored in the registers with the clock outputted from the counter to output a PWM signal representing which one is greater of the data stored in the registers and the clock. The synchronization gates control the PWM signals, based on gate signals applied to the synchronization gates to output a PWM control signal having the same duty ratio as the PWM signal, and a portion of which is off. [13] A backlight driving apparatus in accordance with another aspect of the present invention includes a backlight unit, a variable voltage source unit, a steady current driving unit, a terminal voltage detecting unit and a control unit. The backlight unit includes a plurality of light emitting regions electrically separated from each other. The variable voltage source unit receives a power source and a voltage control signal to independently output controlled voltages to the light emitting regions. The steady current driving unit includes a plurality of steady current circuits, each of which receives a PWM control signal to independently control a pulse width and a duty of the current applied to the light emitting regions. The terminal voltage detecting unit detects terminal voltages of the steady current circuits. The control unit includes the above- mentioned backlight control apparatus and outputs the voltage control signal to the variable voltage source unit and the PWM control signal to the steady current driving unit, based on the terminal voltages detected by the terminal voltage detecting unit.

Advantageous Effects

[14] The present invention provides the following advantageous effects.

[15] First, according to the present invention, luminance of entire LED backlight may be uniformly controlled by simultaneously controlling duty ratio of the PWM pulse and on/off of the PWM pulse, and luminance and chromaticity of each portion of the LED backlight may be precisely controlled if necessary.

[16] Second, the backlight control apparatus and the backlight driving apparatus according to the present invention may be may be applied to a color filter- less (CFL) LCD not having color filters and, instead, sequentially turning on/off a red-colored LED, a green-colored LED and a blue-colored LED equipped in each pixel by synchronizing them with an LCD display.

[17] Third, the backlight control apparatus and the backlight driving apparatus according to the present invention may be may be applied to a driving method which precisely controls the LEDs of the whole system according to the duration of an image displayed on an LCD in order to prevent motion blurring effects.

[18] Fourth, according to the present invention, luminance of each portion of the backlight may be controlled easily by a digital microcomputer and the total power consumption can be reduced, so that productivity of entire system may be enhanced simply and effectively. Brief Description of the Drawings [19] The above and other advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the accompanying drawings, in which: [20] FIG. 1 is a circuit diagram showing a pixel of a TFT-LCD capable of employing a backlight that is driven according to an exemplary embodiment of the present invention; [21] FIG. 2 is a perspective view roughly showing an LCD capable of employing a backlight that is driven according to an exemplary embodiment of the present invention; [22] FIG. 3 is a diagram showing light emitting regions of a backlight unit of an exemplary embodiment of a backlight driving apparatus according to the present invention; [23] FIG. 4 is a block diagram showing an exemplary embodiment of a backlight control apparatus according to the present invention;

[24] FIG. 5 is a block diagram showing a synchronization gate in FIG. 4;

[25] FIG. 6 shows waveforms of an input signal inputted to the synchronization gate in

FIG. 5, an internal signal of the synchronization gate in FIG. 5, and an output signal outputted from the synchronization gate in FIG. 5; [26] FIG. 7 is a block diagram showing an exemplary embodiment of a backlight driving apparatus according to the present invention; and [27] FIG. 8 is a block diagram showing another exemplary embodiment of a backlight driving apparatus according to the present invention.

Mode for the Invention [28] Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. [29] FIG. 1 is a circuit diagram showing a pixel of a TFT-LCD capable of employing a backlight that is driven according to an exemplary embodiment of the present invention. [30] Referring to FIG. 1, each pixel of the LCD includes a thin film transistor (TFT) 10, a liquid crystal capacitor Cl and a storage capacitor Cst. A source electrode of the TFT is electrically connected to a data line Dm, and a gate electrode of the TFT is electrically connected to a scan line Sn. The liquid crystal capacitor Cl is electrically connected between a drain electrode of the TFT and a common electrode (not shown).

The storage capacitor Cst is electrically connected to the drain electrode. [31] The TFT 10 provides a pixel electrode (not shown) with a data voltage Vd provided by the data line Dm, in response to a scan signal provided by the scan line Sn. When an electric field corresponding to a voltage difference between the data voltage (or pixel voltage Vp) and the common voltage Vcom applied to a common electrode (not shown) is applied to liquid crystal, which is equivalently shown as the liquid crystal capacitor Cl in FIG. 1. The liquid crystal controls light transmittance thereof in accordance with the electric field. The storage capacitor Cst maintains the pixel voltage applied to the liquid crystal capacitor Cl until a next pixel voltage is applied to the liquid crystal capacitor Cl, so that light can be transmitted for a predetermined duration of time.

[32]

[33] FIG. 2 is a perspective view roughly showing an LCD capable of employing a backlight that is driven according to an exemplary embodiment of the present invention.

[34] Referring to FIG. 2, the LCD includes a liquid crystal panel 100. The liquid crystal panel 100 includes a lower substrate 101, an upper substrate 103 and liquid crystal (not shown) disposed between the lower substrate 101 and the upper substrate 103. The lower substrate 101 has a TFT array (not shown) in which a plurality of scan lines, a plurality of data lines and a plurality of common lines are connected to a thin film transistor for switching. The upper substrate 103 includes a common electrode (not shown) providing the common line with the common voltage Vcom.

[35] The LCD further includes a scan line driving circuit 110, a data line driving circuit

120 and a backlight 130. The scan line driving circuit 110 provides the gate lines with scan signals. The data line driving circuit 120 provides the data lines with data signals. The backlight 130 provides the liquid crystal panel 100 with light.

[36] The backlight 130 includes a white-colored light emitting diode (LED) generating white light, or a red-colored LED, a green-colored LED and a blue-colored LED. The backlight 130 may further include a light guide plate.

[37]

[38] FIG. 3 is a diagram showing light emitting regions of a backlight unit of an exemplary embodiment of a backlight driving apparatus according to the present invention.

[39] Referring to FIG. 3, a backlight unit includes nine light emitting regions IA, IB,

1C, 2A, 2B, 2C, 3A, 3B, 3C. In the present invention, the number and the shape of the light emitting regions may be variously changed depending on the application condition.

[40] Each light emitting region may have different luminance due to, for example, nonuniformity of an LED driving circuit or of LED itself. Furthermore, each light emitting region may be controlled to have different luminance. In FIG. 3, the nine light emitting regions are intended to emit light with 100 % luminance, but, in practice, have different luminance from each other. [41]

[42] FIG. 4 is a block diagram showing an exemplary embodiment of a backlight control apparatus according to the present invention.

[43] Referring to FIG. 4, the backlight control apparatus includes a serial-parallel conversion shift register 40, registers 411, 412, ..., 41 n, a counter 42, comparators 431, 432, ..., 43n and synchronization gates 441, 442, ..., 44n.

[44] The serial-parallel conversion shift register 40 outputs parallel data by shifting serial data DATA according to a clock signal CLK. The serial data DATA may be formed by a microcomputer, and are data for a duty ratio of each of PWM signals.

[45] The registers 411, 412, ..., 41n store the parallel data outputted from the serial- parallel conversion shift register 40. The stored data are maintained until new data are inputted.

[46] The counter 42 counts the number of clocks of the clock signal and output the result, and recounts the number of clocks when the counter 42 receives a reset signal.

[47] The comparators 431, 432, ..., 43n compare the data stored in the registers 411,

412, ..., 4 In with the clock outputted from the counter 42 to output a PWM signal representing which one is greater that the other. For example, when the value outputted from the counter 42 is greater than the data stored in the registers 411, 412, ..., 41n, the comparators 431, 432, ..., 43n may output T and when the value outputted from the counter 42 is smaller than the data stored in the registers 411, 412, ..., 41n, the comparators 431, 432, ..., 43n may output '0'. The duty ratio of the PWM signals outputted by the comparators 431, 432, ..., 43n may be controlled independently.

[48] A plurality of synchronization gates 441, 442, ..., 44n control the PWM signals, based on the gate signals applied to the synchronization gates 441, 442, ..., 44n to output a PWM control signal having the same duty ratio as the PWM signal, and a portion of which is off.

[49] The PWM control signals outputted from the synchronization gates 441, 442, ...,

44n may be applied to each of the light emitting regions in FIG. 3, to each of the red- colored LED, the green-colored LED and the blue-colored LED in each of the light emitting regions, or to each of the red-colored LED, the green-colored LED and the blue-colored LED in one pixel.

[50]

[51] FIG. 5 is a block diagram showing a synchronization gate in FIG. 4.

[52] Referring to FIG. 5, the synchronization gate 441 includes a D-flipflop 4411 and an

AND-gate 4412.

[53] The D-flipflop 4411 includes a data input terminal D receiving the gate signal, a clock input terminal receiving the PWM signal, and an output terminal Q outputting the synchronized gate signal. [54] The AND-gate 4412 performs an AND-operation of the synchronized gate signal and the PWM signal to output the PWM control signal.

[55] [56] FIG. 6 shows waveforms of an input signal inputted to the synchronization gate in FIG. 5, an internal signal of the synchronization gate in FIG. 5, and an output signal outputted from the synchronization gate in FIG. 5

[57] Referring to FIGS. 5 and 6, the PWM signal, the duty ratio of which is controlled and outputted by the comparators, is applied to the input terminal of the D-flipflop 4411, and the gate signal for controlling on/off of the PWM signal at a cycle basis is applied to the input terminal D of the D-flipflop 4411. Then, the gate signal synchronized with the PWM signal is outputted from the output terminal Q of the D- flipflop 4411.

[58] When the PWM signal and the synchronized gate signal are applied to the AND- gate 4412, the PWM control signal is outputted. The PWM control signal has the same duty ratio as the PWM signal, and some cycles are off at a cycle basis. By maintaining the duty ratio constant, the gate signal controlling on-off of the PWM pulse may be easily designed.

[59] For example, in the backlight unit including nine light emitting regions as shown in FIG. 3, the luminance of all of the light emitting regions may be controlled to be 90 % as shown in Table 1, by controlling the duty ratio of the PWM signal.

[60] Table 1

[61] In order to control the luminance of the total light emitting regions controlled as shown above to be 50 %, a control signal generating the PWN control signal turning on only five PWM pulses of the nine PWM pulses is applied as a total external gate signal, as shown in Table 2. Of course, a gate signal each providing different luminance may be applied to each light emitting region.

[62] Table 2

[63] [64] FIG. 7 is a block diagram showing an exemplary embodiment of a backlight driving apparatus according to the present invention.

[65] Referring to FIG. 7, an exemplary embodiment of a backlight driving apparatus according to the present invention includes a backlight unit 71, a variable voltage source unit 72, a steady current driving unit 73, a terminal voltage detecting unit 74, a control unit 75, a detection channel selecting unit 76 and a sensor 77.

[66] The backlight unit 71 includes a plurality of light emitting regions electrically separated from each other. In FIG. 7, the backlight unit 71 has, for example, four light emitting regions IA, IB, 2A, 2B.

[67] Each of the light emitting regions IA, IB, 2A, 2B includes a white light emitting diode as a backlight. Though not shown in FIG. 7, the light emitting diodes may be connected with each other in series.

[68] The variable voltage source unit 72 receives an input power from an external power source and a voltage control signal from the control unit 75, and independently outputs a controlled voltage to the light emitting regions IA, IB, 2A, 2B.

[69] The variable voltage source unit 72 is a power source circuit providing the LEDs of the light emitting regions IA, IB, 2A, 2B with current. In order to connect the LEDs in series and turn them on, a high voltage may be required. The variable voltage source unit 72 is a power source circuit precisely controlling the required voltage. Since the LED is a semiconductor device which is sensitive to a temperature variation, the variable voltage source unit 72 should compensate the voltage due to the characteristics change of the LED.

[70] The magnitude of the voltage applied to the LEDs of the light emitting regions IA,

IB, 2A, 2B is determined by a signal from the control unit 75. In detail, the voltage- current characteristics of LEDs are changed according to the temperature. Therefore, the voltage should be controlled to optimize power consumption. The variable voltage source unit 72 controls the voltage. The output voltage is used by the LEDs and the steady current driving unit 73. When the output voltage increases, a heat loss by the steady current driving unit 73 increases and, thus, temperature thereof increases. Therefore, the control unit 75 controls the voltage applied to the steady current driving unit 73, such that a minimum voltage is maintained, by detecting the voltage of the steady current driving unit 73.

[71] The steady current driving unit 73 includes a plurality of steady current circuits 731,

732, 733, 734, each of which receives the PWM control signal from the control unit 75 to independently control the pulse width and duty of the current applied to the light emitting regions IA, IB, 2A, 2B.

[72] The detection channel selecting unit 76 selects steady current circuits which are turned on from the steady current circuits 731, 732, 733, 734, and the terminal voltage detecting unit 74 detects the terminal voltage of the selected steady current circuits. The terminal voltage detecting unit 74 may be an analog-to-digital converter (ADC).

[73] The voltage of the LED and the terminal voltages of the steady current circuits 731,

732, 733, 734 determine the voltage outputted from the variable voltage source unit 72. The voltage of the LED is determined by itself. Therefore, according to the present invention, a voltage required by the variable voltage source unit 72 is calculated by using the terminal voltages of the steady current circuits 731, 732, 733, 734.

[74] The sensor 77 senses a luminance, temperature and/or chromaticity of each light emitting region IA, IB, 2A, 2B or of each LED or LED array contained in each region. Then the sensor provides the control unit 75 with the information of the luminance, temperature and/or chromaticity.

[75] The control unit 75 includes an exemplary embodiment of an LED backlight control apparatus according to the present invention. The control unit 75 provides the variable voltage source unit 72 with a voltage control signal, and the steady current driving unit

73 with the PWM control signal by using the terminal voltage information of the steady current circuits 731, 732, 733, 734 detected by terminal voltage detecting unit

74 and the information of the luminance, temperature and/or chromaticity provided by the sensor 77.

[76] Therefore, the luminance and color characteristics of each of the light emitting regions IA, IB, 2A, 2B may be precisely controlled, so that the entire luminance and color characteristics of the backlight 71 may be controlled uniformly.

[77] The control unit 75 performs a feedback control for independently controlling LED currents applied to the each region using the information of luminance and temperature from all sensors in order to maintain the luminance of each portion of the backlight as set by a user.

[78] Furthermore, the control unit 75 calculates the value of controlled source voltage in order to apply an optimized voltage to a terminal of a transistor by detecting the terminal voltage of the transistor, while the transistor is turned on to allow a current to flow through a backlight driving circuit. The control unit 75 provides the variable voltage source unit 72 with the resultant voltage control signal, in order to reduce power consumption of the entire backlight driving circuit.

[79]

[80] FIG. 8 is a block diagram showing another exemplary embodiment of a backlight driving apparatus according to the present invention. In FIG. 8, the light emitting regions 811, ..., 8 IN are illustrated as overlapping with each other. However, actually, the light emitting regions 811, ..., 8 IN are represented as configured as in FIG. 7.

[81] Referring to FIG. 8, each of the light emitting regions 811, ..., 81N may include a red-colored LED, a green-colored LED and a blue-colored LED.

[82] The variable voltage source unit 82 includes a variable voltage source 821 for the red-colored LED, a variable voltage source 822 for the green-colored LED and a variable voltage source 823 for the blue-colored LED, and each of steady current driving units 831, 832, 833, 834, 835, 836 is electrically connected to the LEDs of the light emitting regions 811, ... , 8 IN.

[83] The control unit 85 includes an exemplary embodiment of an LED backlight controller according to the present invention, and receives the information of the luminance and temperature from each sensor 87 and the input signal of a user to determine the luminance of red-, green- and blue-colored LEDs of each of the light emitting regions 811, ..., 8 IN.

[84] This invention has been described with reference to the exemplary embodiments. It is evident, however, that many alternative modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, the present invention embraces all such alternative modifications and variations as falling within the spirit and scope of the appended claims. Industrial Applicability

[85] The present invention relates to a backlight control apparatus and a backlight driving apparatus having the backlight control apparatus. More particularly, the present invention relates to a backlight control apparatus capable of uniformly controlling luminance of an entire portion of a backlight and precisely controlling luminance and color characteristics of each portion of the backlight, and a backlight driving apparatus having the backlight control apparatus.

Claims

[1] A backlight control apparatus comprising: a serial-parallel conversion shift register outputting parallel data by shifting serial data according to a clock signal; a plurality of registers storing the parallel data outputted from the serial-parallel conversion shift register; a counter counting the number of clocks of the clock signal, and recounting the number of clocks when the counter receives a reset signal; a plurality of comparators comparing the data stored in the registers with the clock outputted from the counter to output a PWM signal representing which one is greater of the data stored in the registers and the clock; and a plurality of synchronization gates controlling the PWM signals, based on gate signals applied to the synchronization gates to output a PWM control signal having a same duty ratio as the PWM signal, and a portion of which is off.

[2] The backlight control apparatus of claim 1, wherein each of the synchronization gates comprises: a D-flipflop comprising a data input terminal receiving the gate signal, a clock input terminal receiving the PWM signal, and an output terminal outputting a synchronized gate signal; and an AND-gate performing an AND-operation of the synchronized gate signal and the PWM signal to output the PWM control signal.

[3] A backlight driving apparatus comprising: a backlight unit comprising a plurality of light emitting regions electrically separated from each other; a variable voltage source unit receiving a power source and a voltage control signal to independently output controlled voltages to the light emitting regions; a steady current driving unit comprising a plurality of steady current circuits, each of which receives a PWM control signal to independently control a pulse width and a duty of current applied to the light emitting regions; a terminal voltage detecting unit detecting terminal voltages of the steady current circuits; and a control unit comprising the backlight control apparatus of claim 1 or claim 2 and outputting the voltage control signal to the variable voltage source unit and the PWM control signal to the steady current driving unit, based on terminal voltages detected from the terminal voltage detecting unit.

[4] The backlight driving apparatus of claim 3, further comprising a detection channel selecting unit selecting one of the steady current circuits, which is turned on.

[5] The backlight driving apparatus of claim 3, further comprising a sensor sensing luminance, temperature or chromaticity and provides the control unit with information of the luminance, temperature or chromaticity.

[6] The backlight driving apparatus of claim 3, wherein each of the light emitting regions comprises red-colored LEDs, green-colored LEDs and blue-colored LEDs.

[7] The backlight driving apparatus of claim 3, wherein each of the light emitting regions comprises white-colored LEDs.

[8] The backlight driving apparatus of claim 7, wherein the variable voltage source unit comprises a variable voltage source for the red-colored LED, a variable voltage source for the green-colored LED and a variable voltage source for the blue-colored LED, and each of the steady current circuits is electrically connected to LEDs in each of the light emitting regions.