JP2015219277A - Backlight device and liquid crystal display device with the same, and method of driving backlight device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a backlight device for liquid crystal display device that can suppress color breaking due to persistence characteristics of a phosphor and also actualize a wide color reproduction range.SOLUTION: An LED module as a light source of a backlight device comprises: a magenta color light emission body which has a blue LED element covered with a red phosphor, a green light emission body composed of a green LED element; and a blue light emission body composed of a blue LED element. A backlight drive device controls the level of a lighting current when placing the LED module in an OFF state so that luminance of blue light L(B2) emitted from a blue LED element in the blue light emission body and luminance of green light L(G) emitted from a green LED gradually decrease according to characteristics of a red phosphor (persistence characteristics of the red phosphor).

Description

  The present invention relates to a backlight device, and more particularly to a backlight device for a liquid crystal display device that employs a light emitting element such as an LED (light emitting diode) as a light source.

  In recent years, there has been a remarkable increase in functionality and performance of digital devices, and there has been an increasing demand for higher quality regarding various images. Therefore, in the fields of display devices, printing devices, imaging devices, etc., the color reproduction range (also referred to as “color gamut”) has been conventionally expanded. With respect to liquid crystal display devices such as liquid crystal televisions, the color reproduction range is expanded by improving backlight devices and color filters, for example.

  By the way, in the liquid crystal display device, color display is performed by additive color mixing of the three primary colors. Therefore, a transmissive liquid crystal display device requires a backlight device that can irradiate a liquid crystal panel with white light including a red component, a green component, and a blue component. Conventionally, many cold cathode tubes called CCFLs have been adopted as the light source of the backlight device. However, in recent years, the use of LEDs has increased from the viewpoint of low power consumption and ease of brightness control.

  As described above, a transmissive liquid crystal display device requires a backlight device that can irradiate a liquid crystal panel with white light. Therefore, for example, a backlight device (see FIG. 14) using a white light emitter 950 having a structure in which the blue LED element 952 is covered with a yellow phosphor 954 as a light source, or the blue LED element 962 as a red phosphor 964 and a green phosphor 966. A backlight device (see FIG. 15) using a white light-emitting body 960 covered with a light source is used. Further, a backlight device (see FIG. 16) is also used in which a red light emitter 930 composed of red LED elements 932, a green light emitter 920 composed of green LED elements 922, and a blue light emitter 940 composed of blue LED elements 942 are used as light sources. ing. In each configuration described above, each phosphor emits light when excited by light emitted from the corresponding LED element. In general, a LED element covered with a lens is also referred to as an “LED”. However, in this specification, in order to clearly distinguish the LED element from the LED element, The body. In this specification, a set of light sources composed of a plurality of light emitters as shown in FIG. 16 is referred to as an “LED module”.

  According to the configuration shown in FIG. 16, the drive circuit is complicated, and the cost and power consumption are increased compared to the configuration shown in FIG. 14 and the configuration shown in FIG. 15. However, the color reproduction range is wider when the configuration shown in FIG. 16 is adopted than when the configuration shown in FIG. 14 or the configuration shown in FIG. 15 is adopted. Therefore, conventionally, when realizing a wide color reproduction range, an LED module having the configuration shown in FIG. 16 has often been adopted as a light source. However, due to recent technological advances in phosphors used for light emitters, LED modules that provide a wider color reproduction range than the LED modules having the configuration shown in FIG. 16 have been provided. Specifically, as shown in FIG. 17, an LED module including a magenta light emitter 910 having a structure in which a blue LED element 912 is covered with a red phosphor 914 and a green light emitter 920 including a green LED element 922 is provided. Is provided. According to the LED module having the configuration shown in FIG. 17, light whose two wavelengths (blue wavelength and red wavelength) are the peak wavelengths of the emission spectrum is emitted from the magenta light emitter 910, and the green wavelength is emitted. Light that has a peak wavelength of the spectrum is emitted from the green light emitter 920. The combined light of these lights becomes white light. According to the LED module having the configuration shown in FIG. 17, a wider color reproduction range than that of the LED module having the configuration shown in FIG. 16 can be obtained. As described above, in the liquid crystal display device, the color reproduction range is expanded by using the LED module having the configuration shown in FIG. 17 as the light source of the backlight device.

  In connection with the present invention, Japanese Patent Application Laid-Open No. 2007-141548 discloses color reproducibility of a display screen by adopting an LED module in which white LEDs, red LEDs, green LEDs and blue LEDs are integrated as a light source. A technique for optimizing the above is disclosed.

JP 2007-141548 A

  However, when the LED module having the configuration shown in FIG. 17 is employed, color breaking occurs due to the afterglow characteristics of the red phosphor 914. This will be described in detail below.

  In the configuration shown in FIG. 17, as shown in FIG. 18, blue light is emitted from the blue LED element 912, red light is emitted from the red phosphor 914, and green light is emitted from the green LED element 922. The red phosphor 914 emits light when excited by light emitted from the blue LED element 912. Here, green light emitted from the green LED element 922 is represented by a symbol L (G), blue light emitted from the blue LED element 912 is represented by a symbol L (B), and red light emitted from the red phosphor 914 is represented by a symbol. When represented by F (R), the change in luminance of each light is as shown in FIG. In FIG. 19, the timing for starting the supply of the lighting current to the green LED element 922 and the blue LED element 912 is represented by “ON”, and the timing for interrupting the supply of the lighting current is represented by “OFF”.

  As can be understood from FIG. 19, the green LED element 922 and the blue LED element 912 are immediately turned off when the supply of the lighting current is cut off, but the red phosphor 914 is supplied with the lighting current. After being blocked, the luminance gradually decreases. As described above, the green LED element 922, the blue LED element 912, and the red phosphor 914 have a difference in time from when the supply of the lighting current is interrupted until the light emitting element is completely turned off. For this reason, red color breaking occurs in combination with the high-speed response of the liquid crystal.

  As described above, if the LED module having the configuration shown in FIG. 17 is adopted, a wide color reproduction range can be obtained, but color breaking occurs due to the afterglow characteristics of the red phosphor 914, so that sufficient display quality is obtained. I can't get it. JP 2007-141548 discloses optimization of color reproducibility, but does not describe any countermeasures against color breaking caused by the afterglow characteristics of the phosphor.

  Accordingly, the present invention provides a backlight device for a liquid crystal display device that can suppress the occurrence of color breaking due to the afterglow characteristics of a phosphor and can realize a wide color reproduction range. With the goal.

1st invention is the backlight apparatus which used the light emitting element for the light source,
A first light emitter composed of a first blue light emitting element and a red phosphor that emits light when excited by light emitted from the first blue light emitting element, and a second light emitter composed of a green light emitting element. , And a backlight body provided with a light emitter module composed of a third light emitter composed of a second blue light emitting element,
The magnitude of the lighting current supplied to the first blue light emitting element, the magnitude of the lighting current supplied to the green light emitting element, and the magnitude of the lighting current supplied to the second blue light emitting element are independently controlled. By doing so, the backlight drive unit controls the luminance of the light emitted from the first blue light emitting element, the luminance of the light emitted from the green light emitting element, and the luminance of the light emitted from the second blue light emitting element And
The backlight driving unit changes the brightness of light emitted from the green light emitting element after changing the second blue light emitting element from the off state to the on state when the light emitter module is turned off. The magnitude of the lighting current supplied to the green light emitting element and the second blue light emitting element so that the luminance of light emitted from the second blue light emitting element gradually decreases in accordance with the afterglow characteristics of the red phosphor. It is characterized by controlling the magnitude of the lighting current supplied to the.

According to a second invention, in the first invention,
The backlight driving unit maintains the second blue light emitting element in a light-off state during a period in which the first blue light emitting element is maintained in a lighted state.

According to a third invention, in the first invention,
The backlight driving unit includes the first blue light emitting element, the green light emitting element, and the second blue light emitting element as control target light emitting elements.
A constant current maintaining circuit for supplying a constant current corresponding to a given control voltage as a lighting current to the light emitting element to be controlled;
A pulse width modulation control circuit for controlling on / off of the supply of the lighting current to the light emitting element to be controlled according to the pulse width of the given control signal;
And a control unit for supplying the control voltage to the constant current maintaining circuit and supplying the control signal to the pulse width modulation control circuit according to a target luminance of the light emitting element to be controlled.

According to a fourth invention, in the third invention,
The backlight driving unit gradually changes a control voltage applied from the control unit to the constant current maintaining circuit when the light emitting module is turned off, thereby emitting light emitted from the green light emitting element. And the luminance of light emitted from the second blue light emitting element are gradually reduced.

According to a fifth invention, in the third invention,
The backlight driving unit is emitted from the green light emitting element by gradually reducing a pulse width of a control signal supplied from the control unit to the pulse width modulation control circuit when the light emitter module is turned off. The brightness of light and the brightness of light emitted from the second blue light emitting element are gradually reduced.

According to a sixth invention, in the third invention,
The backlight driving unit is emitted from the green light emitting device by stepwise changing a control voltage applied from the control unit to the constant current maintaining circuit when the light emitting module is turned off. The brightness of light and the brightness of light emitted from the second blue light emitting element are gradually reduced.

According to a seventh invention, in the third invention,
The backlight driving unit further includes a current detection circuit that detects a lighting current flowing through the light emitting element to be controlled.
The control unit adjusts at least one of the magnitude of the control voltage and the pulse width of the control signal in consideration of the magnitude of the lighting current detected by the current detection circuit.

In an eighth aspect based on the first aspect,
The first blue light emitting element, the green light emitting element, and the second blue light emitting element are light emitting diode elements.

According to a ninth invention, in the first invention,
The first blue light emitting element, the green light emitting element, and the second blue light emitting element are laser diode elements.

A tenth invention is a liquid crystal display device,
A liquid crystal panel including a display unit for displaying an image;
The backlight device according to the first aspect of the present invention irradiates light on the back surface of the liquid crystal panel.

An eleventh aspect of the present invention is composed of a first light emitting element and a green light emitting element which are composed of a first blue light emitting element and a red phosphor which emits light when excited by light emitted from the first blue light emitting element. A driving method of a backlight device in which a second light emitter and a third light emitter composed of a second blue light emitting element are provided as a light source,
A first step of maintaining the first blue light emitting element and the green light emitting element in a lit state and maintaining the second blue light emitting element in a turned off state;
A second step of changing the first blue light-emitting element from a lighting state to a lighting state and changing the second blue light-emitting element from a lighting state to a lighting state;
The green light emitting element is supplied so that the luminance of the light emitted from the green light emitting element and the luminance of the light emitted from the second blue light emitting element gradually decrease in accordance with the afterglow characteristics of the red phosphor. And a third step of controlling the magnitude of the lighting current and the magnitude of the lighting current supplied to the second blue light emitting element.

  According to the first invention, the light emitter module constituting the backlight body includes the first light emitter composed of the blue light emitting element (first blue light emitting element) and the red phosphor, and the green light emitting element. And a blue light emitter composed of a blue light emitting element (second blue light emitting element). When the light emitting module is turned off, the luminance of the light emitted from the green light emitting element (green light) and the light emitted from the second blue light emitting element (blue light) according to the afterglow characteristics of the red phosphor. ) Gradually decreases. Thereby, the influence of the afterglow of the red phosphor after the time when the supply of the lighting current is interrupted is canceled by the green light and the blue light. As a result, the occurrence of red color breaking is suppressed. Further, by including a red phosphor in the first light emitter, the color reproduction range can be widened as compared with the case where a red light emitting element, a green light emitting element, and a blue light emitting element are used as the light source. . As described above, there is provided a backlight device capable of suppressing the occurrence of color breaking due to the afterglow characteristics of the phosphor and realizing a wide color reproduction range.

  According to the second aspect, since the second blue light emitting element functions as a dedicated light emitting element for suppressing the occurrence of red color breaking, the same effect as the first aspect can be obtained more reliably. It is done.

  According to the third aspect, the same effect as in the first aspect can be obtained without providing a circuit having a complicated configuration.

  According to the fourth aspect of the invention, when the light emitter module is turned off, the luminance of the green light emitted from the green light emitting element and the luminance of the blue light emitted from the second blue light emitting element are the remaining of the red phosphor. It changes in the same way as the brightness of light. For this reason, generation | occurrence | production of the color breaking resulting from the afterglow characteristic of fluorescent substance is suppressed more effectively.

  According to the fifth aspect, the lighting current can be adjusted with a circuit having a relatively simple configuration.

  According to the sixth aspect, the lighting current can be adjusted with a circuit having a relatively simple configuration.

  According to the seventh aspect, the control voltage / control signal for controlling the magnitude of the lighting current is adjusted while detecting the lighting current flowing through the light emitting element. For this reason, generation | occurrence | production of the color breaking resulting from the afterglow characteristic of fluorescent substance is suppressed more effectively.

  According to the eighth aspect of the invention, the light emitting diode element is used as the light source, which can suppress the occurrence of color breaking due to the afterglow characteristics of the phosphor and can realize a wide color reproduction range. A backlight device is provided.

  According to the ninth aspect of the invention, the laser diode element is used as the light source that can suppress the occurrence of color breaking due to the afterglow characteristic of the phosphor and can realize a wide color reproduction range. A backlight device is provided.

  According to the tenth aspect of the present invention, there is provided a liquid crystal display device capable of suppressing the occurrence of color breaking due to the afterglow characteristics of a phosphor and realizing a wide color reproduction range.

  According to the eleventh aspect of the invention, in the invention of the backlight device driving method, it is possible to suppress the occurrence of color breaking due to the afterglow characteristics of the phosphor and to realize a wide color reproduction range.

It is a wave form diagram for demonstrating the drive method of the backlight in the 1st Embodiment of this invention. It is a block diagram which shows the whole structure of the liquid crystal display device provided with the backlight apparatus which concerns on the said 1st Embodiment. It is a figure which shows schematic structure of the backlight apparatus in the said 1st Embodiment. In the said 1st Embodiment, it is a figure which shows the structure of the LED module mounted in an LED board. FIG. 3 is a circuit diagram showing a configuration example of a backlight drive circuit in the first embodiment. It is a wave form diagram which shows the change of the brightness | luminance of the green light in the said 1st Embodiment, blue light, and red light. It is a figure for demonstrating the difference in the emission spectrum by the difference in a structure of an LED module. FIG. 4 is an xy chromaticity diagram for explaining a difference in color reproduction range due to a difference in configuration of an LED module. It is a wave form diagram for demonstrating the drive method of the backlight in the 2nd Embodiment of this invention. In the said 2nd Embodiment, it is a figure for demonstrating how to determine the pulse width in the case of PWM drive. It is a wave form diagram for demonstrating the drive method of the backlight in the 3rd Embodiment of this invention. It is a figure which shows schematic structure of the backlight apparatus which concerns on the modification of the said 1st-3rd embodiment. It is a figure which shows schematic structure of the backlight apparatus which concerns on the modification of the said 1st-3rd embodiment. It is a figure for demonstrating the conventional backlight apparatus. It is a figure for demonstrating the conventional backlight apparatus. It is a figure for demonstrating the conventional backlight apparatus. It is a figure for demonstrating the conventional backlight apparatus. It is a figure for demonstrating light emission in the conventional backlight apparatus. It is a wave form diagram which shows the change of the brightness | luminance of the green light in a conventional backlight apparatus, blue light, and red light.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In addition, regarding the second embodiment and the third embodiment, description of the same points as in the first embodiment will be omitted as appropriate.

<1. First Embodiment>
<1.1 Overall configuration and operation>
FIG. 2 is a block diagram illustrating an overall configuration of a liquid crystal display device including the backlight device according to the first embodiment of the present invention. The liquid crystal display device includes a backlight device 100, a display control circuit 200, a source driver (video signal line driving circuit) 300, a gate driver (scanning signal line driving circuit) 400, and a display unit 500. The backlight device 100 includes a backlight body 102 and a backlight drive circuit 104.

  The display unit 500 includes a plurality (n) of source bus lines (video signal lines) SL1 to SLn, a plurality (m) of gate bus lines (scanning signal lines) GL1 to GLm, and a plurality of these. A plurality of (n × m) pixel forming portions provided corresponding to the intersections of the source bus lines SL1 to SLn and the plurality of gate bus lines GL1 to GLm are included. These pixel forming portions are arranged in a matrix to constitute a pixel array. Each pixel forming portion includes a thin film transistor (TFT) 50 which is a switching element having a gate terminal connected to a gate bus line passing through a corresponding intersection and a source terminal connected to a source bus line passing through the intersection. The pixel electrode 51 connected to the drain terminal of the thin film transistor 50, the common electrode Ec that is a common electrode provided in the plurality of pixel formation portions, and the common electrode Ec provided in the plurality of pixel formation portions. The liquid crystal layer is sandwiched between the pixel electrode 51 and the common electrode Ec. A pixel capacitor Cp is constituted by a liquid crystal capacitor formed by the pixel electrode 51 and the common electrode Ec. In general, an auxiliary capacitor is provided in parallel with the liquid crystal capacitor in order to reliably hold the voltage in the pixel capacitor Cp. However, since the auxiliary capacity is not directly related to the present invention, its description and illustration are omitted.

  The backlight body 102 is provided on the back side of the liquid crystal panel including the display unit 500, and irradiates the back light of the liquid crystal panel with backlight light. The backlight main body 102 includes an LED (light emitting diode) as a light source. The detailed configuration of the backlight body 102 will be described later.

  The display control circuit 200 receives an image signal DAT and a timing signal group TG such as a horizontal synchronization signal and a vertical synchronization signal sent from the outside, and receives a digital video signal DV and a source start pulse for controlling the operation of the source driver 300. The signal SSP, the source clock signal SCK, and the latch strobe signal LS, the gate start pulse signal GSP and the gate clock signal GCK for controlling the operation of the gate driver 400, and the back for controlling the operation of the backlight driving circuit 104 Write control signal BS is output.

  The source driver 300 receives the digital video signal DV, the source start pulse signal SSP, the source clock signal SCK, and the latch strobe signal LS sent from the display control circuit 200, and drives the video signal S (1 (1) to the source bus lines SL1 to SLn. ) To S (n) are applied. At this time, the source driver 300 sequentially holds the digital video signal DV indicating the voltage to be applied to the source bus lines SL1 to SLn at the timing when the pulse of the source clock signal SCK is generated. The held digital video signal DV is converted into an analog voltage at the timing when the pulse of the latch strobe signal LS is generated. The converted analog voltage is applied simultaneously to all the source bus lines SL1 to SLn as drive video signals S (1) to S (n).

  Based on the gate start pulse signal GSP and the gate clock signal GCK sent from the display control circuit 200, the gate driver 400 sends the active scanning signals G (1) to G (m) to the gate bus lines GL1 to GLm. The application is repeated with one vertical scanning period as a cycle.

  The backlight drive circuit 104 controls the luminance of the light source (LED) in the backlight body 102 based on the backlight control signal BS sent from the display control circuit 200.

  As described above, the scanning signals G (1) to G (m) are applied to the gate bus lines GL1 to GLm, and the driving video signals S (1) to S (n) are applied to the source bus lines SL1 to SLn. Is applied and the luminance of the light source in the backlight body 102 is controlled, whereby an image corresponding to the image signal DAT sent from the outside is displayed on the display unit 500.

<1.2 Configuration of backlight body>
FIG. 3 is a diagram showing a schematic configuration of the backlight main body 102 in the present embodiment. FIG. 3 is a side view of the liquid crystal panel 5 and the backlight main body 102. The backlight body 102 is provided on the back side of the liquid crystal panel 5. That is, in this embodiment, a so-called direct type backlight is employed. The backlight main body 102 is irradiated toward the liquid crystal panel 5, the LED substrate 10 on which a plurality of light emitters as light sources are mounted, the diffusion plate 12 for diffusing and uniforming the light emitted from the light emitters. It comprises an optical sheet 14 for increasing the efficiency of light and a chassis 16 that supports the LED substrate 10 and the like.

<1.3 Configuration of LED module>
FIG. 4 is a diagram illustrating a configuration of an LED module mounted on the LED substrate 10. In this embodiment, the LED module includes a magenta light emitter 110 having a structure in which a blue LED element 112 is covered with a red phosphor 114, a green light emitter 120 including a green LED element 122, and a blue light including a blue LED element 132. It is comprised with the light-emitting body 130. FIG. That is, the configuration of the LED module in the present embodiment is a configuration in which a blue light emitter 130 composed of a blue LED element 132 is added to the configuration in the conventional example shown in FIG. By providing the blue light emitter 130, as described later, it is possible to gradually reduce the luminance of the blue light so as to match the afterglow characteristics of the red phosphor 114 when all the light sources are turned off. It has become.

  In the present embodiment, a first light emitter is realized by the magenta light emitter 110, a second light emitter is realized by the green light emitter 120, and a third light emitter is realized by the blue light emitter 130. ing. The blue LED element 112 realizes a first blue light emitting element, the green LED element 122 realizes a green light emitting element, and the blue LED element 132 realizes a second blue light emitting element.

  As shown in FIG. 4, blue light is emitted from the blue LED element 112, red light is emitted from the red phosphor 114, green light is emitted from the green LED element 122, and blue light is emitted from the blue LED element 132. . The red phosphor 114 emits light when excited by light emitted from the blue LED element 112. The combined light of the blue light emitted from the blue LED element 112 and the red light emitted from the red phosphor 114 becomes magenta light. In this way, the magenta light, the green light, and the blue light are emitted from the magenta light emitter 110, the green light emitter 120, and the blue light emitter 130, respectively, so that the liquid crystal panel 5 is irradiated with white light.

  In the present embodiment, an example in which an LED element (light emitting diode element) is used as a light source is described. However, the present invention is not limited to this. The present invention can also be applied when a laser diode element is used as the light source. This also applies to the second embodiment and the third embodiment.

<1.4 Backlight drive circuit configuration>
FIG. 5 is a circuit diagram showing a configuration example of the backlight driving circuit 104 in the present embodiment. In FIG. 5, the light emitting diode elements used for the light source are collectively denoted by reference numeral 19. Further, FIG. 5 shows components for driving the light emitting diode elements 19 for one system connected in series.

  As shown in FIG. 5, a plurality of light emitting diode elements 19 for one system are connected in series between a power supply 700 and a backlight drive circuit 104. The backlight drive circuit 104 includes a current detection circuit 61, a constant current maintenance circuit 62, a PWM control circuit (pulse width modulation control circuit) 63, a resistor 64, and a control unit 65.

  The current detection circuit 61 detects a lighting current (current flowing through the light emitting diode element 19). A detection current value Idet that is a result of the detection of the lighting current by the current detection circuit 61 is given to the control unit 65. The current detection circuit 61 is realized by a known circuit using a shunt resistor or a differential amplifier, for example.

  The constant current maintaining circuit 62 performs control so that a constant current corresponding to the target luminance flows through the light emitting diode element 19. The constant current maintaining circuit 62 includes, for example, an FET (field effect transistor) 622 and an operational amplifier 624 as shown in FIG. Regarding the FET 622, the gate terminal is connected to the output terminal of the operational amplifier 624, the drain terminal is connected to the current detection circuit 61, and the source terminal is connected to the PWM control circuit 63 and the inverting input terminal of the operational amplifier 624. A control voltage Vctl is supplied from the control unit 65 to the non-inverting input terminal of the operational amplifier 624. Since negative feedback is applied to the operational amplifier 624 with the above configuration, the operational amplifier 624 operates so that the voltage between the non-inverting input terminal and the inverting input terminal of the operational amplifier 624 becomes 0 due to an imaginary short. For this reason, the source voltage of the FET 622 is constant at Vctl. Based on this source voltage and the resistance value of the resistor 64, a constant current flows through the light emitting diode element 19. In addition, since the magnitude | size of the control voltage Vctl output from the control part 65 will change if target brightness | luminance changes, the magnitude | size of the electric current which flows into the light emitting diode element 19 also changes according to target brightness | luminance.

  The PWM control circuit 63 includes a transistor 630. The PWM control circuit 63 controls the magnitude of the lighting current by controlling on / off of the transistor 630 according to the pulse width of the control signal Sctl supplied from the control unit 65. If the pulse width of the control signal Sctl is large, the time during which the transistor 630 is turned on is relatively long, so that the magnitude of the lighting current is large. On the other hand, if the pulse width of the control signal Sctl is small, the time during which the transistor 630 is turned on is relatively short, so the magnitude of the lighting current is small.

  Based on the target luminance of the light emitting diode element 19 and the detected current value Idet, the control unit 65 controls the constant current maintaining circuit 62 so that a lighting current having a magnitude corresponding to the target luminance flows through the light emitting diode element 19. Vctl is applied, and a control signal Sctl is applied to the PWM control circuit 63.

  In the present embodiment, the backlight drive circuit 104 configured as described above causes the magnitude of the lighting current flowing through the blue LED element 112 in the magenta light emitter 110 to flow through the green LED element 122 in the green light emitter 120. The magnitude of the lighting current and the magnitude of the lighting current flowing through the blue LED element 132 in the blue light emitter 130 are independently controlled. That is, the above components (current detection circuit 61, constant current maintaining circuit 62, PWM control circuit 63, resistor 64, and control unit 65) are the blue LED element 112, the green LED element 122, and the blue LED element 132, respectively. Is provided.

<1.5 Driving method of backlight>
Next, a method for driving the backlight in the present embodiment will be described. In the following, when all the light sources are turned off (when the light emitter module is turned off), the time point when the supply of the lighting current to the blue LED element 112 in the magenta light emitter 110 is cut off is referred to as “ It is called “lighting current cut-off time”. Blue light emitted from the blue LED element 132 is represented by a symbol L (B2), green light emitted from the green LED element 122 is represented by a symbol L (G), and blue light emitted from the blue LED element 112 is represented by a symbol L (B1). ), And the red light emitted from the red phosphor 114 is represented by the symbol F (R), the backlight drive circuit 104 shows the change in luminance of each light when turning off all the light sources as shown in FIG. The blue LED element 132 and the green LED element 122 are driven so as to be like this. In FIG. 1, the lighting start time of the light source is represented by a symbol t0, the lighting current cutoff time is represented by a symbol t1, and the time when no afterglow from the red phosphor 114 is represented by a symbol t2. Further, the period from the time point t1 to the time point t2 is referred to as a “red phosphor afterglow period” for convenience.

  The green LED element 122 is driven so that the luminance gradually decreases from the lighting current cutoff point. The blue LED element 132 is driven from the extinguished state to the lit state when the lighting current is cut off, and is driven so that the luminance gradually decreases from the lighting current cut off point. More specifically, the waveform of the luminance change in the red phosphor afterglow period for the green light emitted from the green LED element 122 and the blue light emitted from the blue LED element 132 has a red fluorescence for the red light emitted from the red phosphor 114. The green LED element 122 and the blue LED element 132 are driven so as to be as identical as possible to the waveform of the luminance change during the afterglow period.

  In the present embodiment, the first step is realized by the control in the period from the time point t0 to the time point t1, the first step is realized by the control in the time point t1 (lighting current cutoff time), and from the time point t1 to the time point t2. The third step is realized by the control in the period (red phosphor afterglow period). That is, the driving method of the backlight device 100 according to the present embodiment includes a first step of maintaining the blue LED element 112 and the green LED element 122 in the lit state and maintaining the blue LED element 132 in the unlit state, and the blue LED element. The second step of changing the LED 112 from the lit state to the unlit state and the blue LED element 132 from the unlit state to the lit state, the luminance of the green light emitted from the green LED element 122 and the blue light emitted from the blue LED element 132 The third step of controlling the magnitude of the lighting current supplied to the green LED element 122 and the magnitude of the lighting current supplied to the blue LED element 132 so that the luminance of the LED gradually decreases according to the afterglow characteristics of the red phosphor 114 And are included.

  Next, a specific method for driving the blue LED element 132 and the green LED element 122 in the red phosphor afterglow period as described above will be described (see FIG. 5). The current detection circuit 61 detects a lighting current flowing through the light emitting diode element 19 (here, the blue LED element 132 or the green LED element 122). A detection current value Idet, which is a result of detection of the lighting current by the current detection circuit 61, is given to the control unit 65 throughout the period during which the liquid crystal display device is operating. Thereby, in the control part 65, the brightness | luminance in each time of the light emitted from the light emitting diode element 19 can be grasped | ascertained based on the detected electric current value Idet. Then, the control unit 65, during the red phosphor afterglow period, changes the luminance change waveform of the green light L (G) emitted from the green LED element 122 and the luminance change of the red light F (R) emitted from the red phosphor 114. The magnitude of the control voltage Vctl applied to the constant current maintaining circuit 62 for the green LED element 122 is gradually changed so that the waveform of is as identical as possible. In addition, during the afterglow period of the red phosphor, the control unit 65 has a waveform of a luminance change of the blue light L (B2) emitted from the blue LED element 132 and a luminance change of the red light F (R) emitted from the red phosphor 114. The magnitude of the control voltage Vctl applied to the constant current maintaining circuit 62 for the blue LED element 132 is gradually changed so that the waveform of is as identical as possible.

  In this embodiment, the control signal Sctl is given to the PWM control circuit 63 for the blue LED element 112 so that the transistor 630 is turned on during the period from the time point t0 to the time point t1. The PWM control circuit 63 is supplied with a control signal Sctl so that the transistor 630 is turned on during the period from time t0 to time t2, and the PWM control circuit 63 for the blue LED element 132 is supplied to the PWM control circuit 63 from time t1 to time t2. The control signal Sctl is supplied so that the transistor 630 is turned on during the period up to.

  As described above, as the luminance of each light changes as shown in FIG. 1, each of the green light L (G), the blue light L (B1 + B2), and the red light F (R) emitted from the LED module. The waveform of the luminance change is as shown in FIG. 6 are blue light L (B1) emitted from the blue LED element 112 in the magenta light emitter 110 and blue light L emitted from the blue LED element 132 in the blue light emitter 130. The blue light L (B1 + B2) in FIG. (B2) is synthesized.

  As can be seen from FIG. 6, during the red phosphor afterglow period, the luminance of the green light L (G), the blue light L (B1 + B2), and the red light F (R) changes in the same way. That is, the influence of the afterglow of the red phosphor 114 after the lighting current is cut off is canceled out by the green light L (G) and the blue light L (B1 + B2). Thereby, occurrence of red color breaking is suppressed.

<1.6 Color reproduction range>
In order to obtain white light, when an LED module is configured by a red light emitting element composed of a red LED element, a green light emitting element composed of a green LED element, and a blue light emitting element composed of a blue LED element (that is, the structure shown in FIG. 16). When the LED module is employed), the emission spectrum from the LED module is represented by a curve as indicated by reference numeral 81 in FIG. On the other hand, in the case where an LED module is constituted by a magenta light emitter having a structure in which a blue LED element is covered with a red phosphor to obtain white light and a green light emitter made of a green LED element (that is, in FIG. 17). When the LED module having the configuration shown is adopted), the emission spectrum from the LED module is represented by a curve as indicated by reference numeral 82 in FIG. Based on these emission spectra, the color reproduction range when the LED module having the configuration shown in FIG. 16 is employed is represented by a triangle indicated by reference numeral 9 in FIG. 8, whereas the configuration shown in FIG. The color reproduction range when the LED module is adopted is represented by a triangle denoted by reference numeral 7 in FIG. As described above, the configuration of the LED module in the present embodiment is a configuration in which the blue light emitter 130 including the blue LED element 132 is added to the configuration illustrated in FIG. Therefore, in this embodiment, a color reproduction range that is at least equivalent to the case where the LED module having the configuration shown in FIG. 17 is employed can be obtained.

<1.7 Effect>
According to the present embodiment, the LED module constituting the backlight body 102 includes a magenta light emitter 110 having a structure in which a blue LED element 112 is covered with a red phosphor 114, and a green light emitter 120 including a green LED element 122. , And a blue light emitter 130 made of a blue LED element 132. When all the light sources are turned off, the backlight drive circuit 104 changes the luminance change in the red phosphor afterglow period for the green light emitted from the green LED element 122 and the blue light emitted from the blue LED element 132. The green LED element 122 and the blue LED element 132 are driven so that the waveform is as similar as possible to the luminance change waveform in the red phosphor afterglow period for the red light emitted from the red phosphor 114. Thereby, the influence by the afterglow of the red fluorescent substance 114 after the lighting current interruption | blocking time is canceled by green light and blue light. As a result, the occurrence of red color breaking is suppressed. Further, since the red phosphor 114 is used, an LED module composed of a red light emitter made of a red LED element, a green light emitter made of a green LED element, and a blue light emitter made of a blue LED element is adopted. Compared with the case where the color is reproduced, the color reproduction range is widened. As described above, according to the present embodiment, the backlight for a liquid crystal display device that can suppress the occurrence of color breaking due to the afterglow characteristics of the phosphor and can realize a wide color reproduction range. An apparatus is provided.

<2. Second Embodiment>
A second embodiment of the present invention will be described. Since only the backlight driving method is different from that of the first embodiment, description of other points is omitted.

  In the present embodiment, when all the light sources are turned off, the backlight drive circuit 104 causes the blue LED element 132 and the green LED element 122 so that the change in luminance of each light becomes as shown in FIG. Drive. In FIG. 9, as in FIG. 1, the blue light emitted from the blue LED element 132 is represented by L (B2), the green light emitted from the green LED element 122 is represented by L (G), and the blue LED Blue light emitted from the element 112 is represented by a symbol L (B1), and red light emitted from the red phosphor 114 is represented by a symbol F (R).

  The green LED element 122 is driven so that the ratio of the lighting period in the predetermined period gradually decreases after the lighting current is cut off. The blue LED element 132 is driven from the extinguished state to the lit state when the lighting current is interrupted, and is driven so that the ratio of the lighting period in the predetermined period gradually decreases after the lighting current is interrupted. Thus, during the red phosphor afterglow period, the green LED element 122 and the blue LED element 132 are driven by PWM (pulse width modulation). Since this PWM drive is performed at a very high speed based on the human eye recognition ability, the blue light L (B2) emitted from the blue LED element 132 and the green light L (G) emitted from the green LED element 122 are used. 1 is recognized by human eyes as shown in FIG.

  Next, a specific method for driving the blue LED element 132 and the green LED element 122 in the red phosphor afterglow period as described above will be described (see FIG. 5). As in the first embodiment, the control unit 65 can grasp the luminance at each time point of the light emitted from the light emitting diode element 19 based on the detected current value Idet. Then, the control unit 65 supplies a constant control voltage Vctl to the constant current maintaining circuit 62 so that the brightness is constant when the green LED element 122 and the blue LED element 132 are in a lighting state. In the state where the control voltage Vctl having a constant magnitude is applied to the constant current maintaining circuit 62 in this manner, the control unit 65 performs the blue light L (B2) and the red light afterglow period as shown in FIG. A control signal Sctl is given to the PWM control circuit 63 so that the luminance of the green light L (G) changes. The waveform of the control signal Sctl is the same as the waveform of the luminance change of the blue light L (B2) and the green light L (G) shown in FIG. Thereby, the on / off state of the transistor 630 in the PWM control circuit 63 is switched in accordance with the waveform of the control signal Sctl.

  Note that the pulse width in the PWM drive is generated from the integral value (area integration) 83 of the luminance and the green LED element 122 by the blue light L (B2) emitted from the blue LED element 132 in a very short time as shown in FIG. The integral value (area integral) 83 of luminance due to the green light L (G) is determined to be equal to the integral value (area integral) 84 of luminance due to the afterglow characteristic of the red phosphor 114.

  As described above, as the luminance of each light changes as shown in FIG. 9, each of the green light L (G), the blue light L (B1 + B2), and the red light F (R) emitted from the LED module. The change in luminance is recognized by the human eye as shown in FIG.

  As described above, also in this embodiment, as in the first embodiment, the occurrence of color breaking due to the afterglow characteristics of the phosphor can be suppressed, and a wide color reproduction range can be realized. A backlight device for a liquid crystal display device is provided. In addition, since the lighting current control of the blue LED element 132 and the green LED element 122 during the red phosphor afterglow period is performed by PWM control, the circuit configuration is simplified as compared with the first embodiment. For this reason, compared with the said 1st Embodiment, cost is reduced.

<3. Third Embodiment>
A third embodiment of the present invention will be described. Since only the backlight driving method is different from that of the first embodiment, description of other points is omitted.

  In the present embodiment, when all the light sources are turned off, the backlight drive circuit 104 causes the blue LED element 132 and the green LED element 122 so that the change in luminance of each light is as shown in FIG. Drive. In FIG. 11, as in FIG. 1, blue light emitted from the blue LED element 132 is represented by L (B2), green light emitted from the green LED element 122 is represented by L (G), and the blue LED Blue light emitted from the element 112 is represented by a symbol L (B1), and red light emitted from the red phosphor 114 is represented by a symbol F (R).

  The green LED element 122 is driven so that the luminance gradually decreases stepwise from the time when the lighting current is cut off. The blue LED element 132 is driven from the extinguished state to the lit state when the lighting current is cut off, and driven so that the luminance decreases stepwise from the lighting current cut off point. At this time, the luminance change of the blue light L (B2) emitted from the blue LED element 132 and the green light L (G) emitted from the green LED element 122 is recognized by human eyes as shown in FIG.

  Next, a specific method for driving the blue LED element 132 and the green LED element 122 in the red phosphor afterglow period as described above will be described (see FIG. 5). As in the first embodiment, the control unit 65 can grasp the luminance at each time point of the light emitted from the light emitting diode element 19 based on the detected current value Idet. Then, the control unit 65 controls the constant current maintaining circuit 62 so that the luminance of the blue light L (B2) and the green light L (G) changes during the red phosphor afterglow period as shown in FIG. The magnitude of the voltage Vctl is changed stepwise.

  In this embodiment, the control signal Sctl is given to the PWM control circuit 63 for the blue LED element 112 so that the transistor 630 is turned on during the period from the time point t0 to the time point t1. The PWM control circuit 63 is supplied with a control signal Sctl so that the transistor 630 is turned on during the period from time t0 to time t2, and the PWM control circuit 63 for the blue LED element 132 is supplied to the PWM control circuit 63 from time t1 to time t2. The control signal Sctl is supplied so that the transistor 630 is turned on during the period up to.

  As described above, as the luminance of each light changes as shown in FIG. 11, each of the green light L (G), the blue light L (B1 + B2), and the red light F (R) emitted from the LED module. The change in luminance is recognized by the human eye as shown in FIG.

  As described above, also in this embodiment, as in the first embodiment, the occurrence of color breaking due to the afterglow characteristics of the phosphor can be suppressed, and a wide color reproduction range can be realized. A backlight device for a liquid crystal display device is provided. In addition, since the light emission control of the blue LED element 132 and the green LED element 122 during the red phosphor afterglow period is performed by changing the lighting current in a step shape, the circuit configuration is compared with the first embodiment. It will be easy. For this reason, compared with the said 1st Embodiment, cost is reduced.

<4. Modification>
In each of the above embodiments, a direct type backlight device is employed, but the present invention is not limited to this. The present invention can also be applied when an edge-light type backlight device is employed. Therefore, as a modification, a configuration of an edge light type backlight device will be described. In this modification as well, the backlight device is constituted by a backlight body and a backlight drive circuit.

  12 and 13 are diagrams showing a schematic configuration of the backlight body in the present modification. 12 is a schematic view of the liquid crystal panel 5 and the backlight body viewed from above, and FIG. 13 is a view of the liquid crystal panel 5 and the backlight body viewed from the side. The backlight body includes an LED substrate 10 on which a plurality of light emitters as light sources are mounted, a light guide plate 18 for emitting light emitted from the light sources toward the liquid crystal panel 5 in a planar shape, and toward the liquid crystal panel 5. And an optical sheet 14 for increasing the efficiency of the irradiated light. The light guide plate 18 and the optical sheet 14 are provided on the back side of the liquid crystal panel 5. The optical sheet 14 is provided between the light guide plate 18 and the liquid crystal panel 5. The LED substrate 10 is provided near the end of the light guide plate 18. In FIGS. 12 and 13, the chassis is omitted.

  Even in the case where the edge light type backlight device as described above is adopted, the occurrence of color breaking due to the afterglow characteristics of the phosphor is suppressed and a wide color can be obtained in the same manner as in the above embodiments. A reproduction range can be realized.

<5. Other>
In general, the color temperature is adjusted by adjusting the gains of the three primary colors (red, green, and blue) (the intensity of the color that is actually displayed with respect to the intensity of the input signal). In this regard, according to the LED module having the configuration shown in FIG. 17, the luminance of the magenta color is controlled by controlling the light emission from the magenta light emitter 910, and the green color is controlled by controlling the light emission from the green light emitter 920. Is controlled. However, since only two colors (magenta and green) can be controlled independently, the color temperature cannot be changed by adjusting the luminance of the light source. In this regard, according to each of the embodiments described above, the LED module that constitutes the backlight body 102 includes the blue light-emitting body 130 including the blue LED element 132 in addition to the components in the prior art shown in FIG. (See FIG. 4). For this reason, the luminance of the three colors magenta, green, and blue can be independently controlled by controlling the light emission from each light emitter. Therefore, the color temperature can be changed. Thereby, since the white point can be adjusted, the display quality is improved. According to the above embodiments, such an effect can also be obtained.

DESCRIPTION OF SYMBOLS 5 ... Liquid crystal panel 10 ... LED board 12 ... Diffusion plate 14 ... Optical sheet 16 ... Chassis 18 ... Light guide plate 61 ... Current detection circuit 62 ... Constant current maintenance circuit 63 ... PWM (pulse width modulation) control circuit 64 ... Resistor 65 ... Control unit 100 ... Backlight device 102 ... Backlight body 104 ... Backlight drive circuit 110 ... Magenta light emitter (first light emitter)
112 ... Blue LED element (first blue light emitting element)
114 ... Red phosphor 120 ... Green light emitter (second light emitter)
122... Green LED element (green light emitting element)
130... Blue light emitter (third light emitter)
132 ... Blue LED element (second blue light emitting element)
200: Display control circuit 300: Source driver (video signal line drive circuit)
400: Gate driver (scanning signal line driving circuit)
500: Display unit F (R): Red light emitted from the red phosphor in the magenta light emitter L (B1) Blue light emitted from the blue LED element in the magenta light emitter L (B2) ... Blue in the blue light emitter Blue light emitted from the LED element L (G) ... Green light emitted from the green LED element in the green light emitting body

Claims (11)

A backlight device using a light emitting element as a light source,
A first light emitter composed of a first blue light emitting element and a red phosphor that emits light when excited by light emitted from the first blue light emitting element, and a second light emitter composed of a green light emitting element. , And a backlight body provided with a light emitter module composed of a third light emitter composed of a second blue light emitting element,
The magnitude of the lighting current supplied to the first blue light emitting element, the magnitude of the lighting current supplied to the green light emitting element, and the magnitude of the lighting current supplied to the second blue light emitting element are independently controlled. By doing so, the backlight drive unit controls the luminance of the light emitted from the first blue light emitting element, the luminance of the light emitted from the green light emitting element, and the luminance of the light emitted from the second blue light emitting element And
The backlight driving unit changes the brightness of light emitted from the green light emitting element after changing the second blue light emitting element from the off state to the on state when the light emitter module is turned off. The magnitude of the lighting current supplied to the green light emitting element and the second blue light emitting element so that the luminance of light emitted from the second blue light emitting element gradually decreases in accordance with the afterglow characteristics of the red phosphor. A backlight device characterized by controlling a magnitude of a lighting current supplied to the battery.   2. The backlight unit according to claim 1, wherein the backlight driving unit maintains the second blue light emitting element in a light-off state during a period in which the first blue light emitting element is maintained in a lighting state. Backlight device. The backlight driving unit includes the first blue light emitting element, the green light emitting element, and the second blue light emitting element as control target light emitting elements.
A constant current maintaining circuit for supplying a constant current corresponding to a given control voltage as a lighting current to the light emitting element to be controlled;
A pulse width modulation control circuit for controlling on / off of the supply of the lighting current to the light emitting element to be controlled according to the pulse width of the given control signal;
2. A control unit that applies the control voltage to the constant current maintaining circuit and applies the control signal to the pulse width modulation control circuit in accordance with a target luminance of the light emitting element to be controlled. The backlight device described in 1.   The backlight driving unit gradually changes a control voltage applied from the control unit to the constant current maintaining circuit when the light emitting module is turned off, thereby emitting light emitted from the green light emitting element. The backlight device according to claim 3, wherein the luminance of the light and the luminance of light emitted from the second blue light emitting element are gradually reduced.   The backlight driving unit is emitted from the green light emitting element by gradually reducing a pulse width of a control signal supplied from the control unit to the pulse width modulation control circuit when the light emitter module is turned off. 4. The backlight device according to claim 3, wherein the luminance of light and the luminance of light emitted from the second blue light emitting element are gradually reduced.   The backlight driving unit is emitted from the green light emitting device by stepwise changing a control voltage applied from the control unit to the constant current maintaining circuit when the light emitting module is turned off. 4. The backlight device according to claim 3, wherein the luminance of light and the luminance of light emitted from the second blue light emitting element are gradually reduced. The backlight driving unit further includes a current detection circuit that detects a lighting current flowing through the light emitting element to be controlled.
The control unit adjusts at least one of a magnitude of the control voltage and a pulse width of the control signal in consideration of a magnitude of a lighting current detected by the current detection circuit. 4. The backlight device according to 3.   The backlight device according to claim 1, wherein the first blue light emitting element, the green light emitting element, and the second blue light emitting element are light emitting diode elements.   The backlight device according to claim 1, wherein the first blue light emitting element, the green light emitting element, and the second blue light emitting element are laser diode elements. A liquid crystal display device,
A liquid crystal panel including a display unit for displaying an image;
A liquid crystal display device comprising: the backlight device according to claim 1, which irradiates light on a back surface of the liquid crystal panel. A first light emitter composed of a first blue light emitting element and a red phosphor that emits light when excited by light emitted from the first blue light emitting element, and a second light emitter composed of a green light emitting element. , And a driving method of a backlight device in which a third light emitter composed of a second blue light emitting element is provided as a light source,
A first step of maintaining the first blue light emitting element and the green light emitting element in a lit state and maintaining the second blue light emitting element in a turned off state;
A second step of changing the first blue light-emitting element from a lighting state to a lighting state and changing the second blue light-emitting element from a lighting state to a lighting state;
The green light emitting element is supplied so that the luminance of the light emitted from the green light emitting element and the luminance of the light emitted from the second blue light emitting element gradually decrease in accordance with the afterglow characteristics of the red phosphor. And a third step of controlling the magnitude of the lighting current and the magnitude of the lighting current supplied to the second blue light emitting element.

Images