KR20070054101A - Flat lighting source, luminance correcting circuit, luminance correcting method and liquid crystal display - Google Patents

Abstract

The surface light source is configured to apply illumination light to the entire display area of the display panel. Current or voltage is supplied to each LED from each light emitting diode (LED) drive / calibration circuit. Some of the light emitted from each LED is converted into an electrical signal and the resistance value of each photodiode is reduced in proportion to the brightness. As the brightness of light emitted from each LED is increased, the brightness of light emitted from each LED is reduced and the resistance value of each photodiode is reduced. The resistance value is fed back to each LED drive / correction circuit that changes the drive current or drive voltage, so that the brightness of the light emitted from each LED corresponds to the brightness set voltage. Photodiodes are mounted one-to-one per LED.

Surface light source, luminance correction circuit

Description

Surface light source, luminance correction circuit, luminance correction method and liquid crystal display {FLAT LIGHTING SOURCE, LUMINANCE CORRECTING CIRCUIT, LUMINANCE CORRECTING METHOD AND LIQUID CRYSTAL DISPLAY}

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram showing an electrical configuration of main parts of a surface light source according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing an example of an electrical configuration of the LED drive / correction circuit and drive / detection circuit of FIG.

3 shows an example of the layout of a set of the LED, the photodiode, the LED drive / correction circuit and the drive / detection circuit of FIG.

4 is a diagram showing an example of a layout of an LED drive / correction circuit formed integrally with the LED, the photodiode, and the drive / detection circuit of FIG.

Fig. 5 is a sectional view showing the layout of main parts of the surface light source of the second embodiment of the present invention.

Fig. 6 is a sectional view showing the layout of main parts of the surface light source of the third embodiment of the present invention.

Fig. 7 is a sectional view showing the layout of main parts of the surface light source of the fourth embodiment of the present invention.

Fig. 8 is a sectional view showing the layout of main parts of the surface light source of the fifth embodiment of the present invention.

Fig. 9 is a sectional view showing the layout of main parts of the surface light source of the sixth embodiment of the present invention.

Fig. 10 is a sectional view showing the layout of main parts of the surface light source of the seventh embodiment of the present invention.

Fig. 11 is a circuit diagram showing an electrical configuration of a luminance correction circuit used for the surface light source of the eighth embodiment of the present invention.

The figure which shows the electrical structure of the principal part of the lighting apparatus of patent document 1. FIG.

FIG. 13 is a view for explaining an operation of the lighting device of FIG. 12; FIG.

14 is a diagram showing an example of the configuration of a conventional LED backlight;

FIG. 15 is a diagram illustrating a configuration of an LED used as a conventional backlight described in Patent Document 2. FIG.

FIG. 16 is a diagram showing another configuration of an LED used as a conventional backlight described in Patent Document 2. FIG.

FIG. 17 is a cross-sectional view of the backlight equipped with the LED shown in FIG. 15 or FIG.

FIG. 18 is a block diagram showing a configuration of a correction circuit for correcting the luminance characteristic of the LED shown in FIG. 15 or FIG.

Background of the Invention

Field of invention

The present invention relates to a surface light source, a brightness correction circuit, and a brightness correction method for use in a surface light source, and a liquid crystal display device. In particular, when illumination light of uniform brightness is to be provided in the entire display area of the display panel, For example, in the case of a liquid crystal display device provided with illumination light by a backlight, the present invention relates to a surface light source suitably used, and a brightness correction circuit and a brightness correction method used for the surface light source.

This invention is a priority claim patent application of Japanese application 2005-337871 (2005.11.22).

Conventional technology

Conventionally, a cold cathode fluorescent lamp (CCFL) has been mostly used as a backlight for a liquid crystal display device. Recently, however, LEDs (Light Emitting Diodes) are also increasingly used. In LED backlights, usually, a plurality of LEDs are connected in series and driven at constant current. Therefore, the deviation of the current brightness characteristic of each LED reflects the brightness deviation in the display area of the liquid crystal display device. Here, "deviation" refers to the aging change in luminance characteristic with respect to current and temperature. Conventional techniques for correcting this type of deviation are described, for example, in the following references.

It is a figure which shows the electrical structure of the principal part of the lighting apparatus described in patent document 1 (Unexamined-Japanese-Patent No. 2004-221158, summaries, FIG. 1 and 4). The described lighting device, as shown in FIG. 12, includes an LED printed circuit board (PCB) 10, a constant current source 20, and a temperature compensation circuit 30. Multiple LEDs 11,... 11 are formed in the LED PCB 10. The constant current source 20 has a resistor 21, a transistor 22, an amplifying circuit 23 and a comparison voltage generating circuit 24. The temperature compensation circuit 30 includes a field effect transistor (FET) 31, an LED 32, an amplifying circuit 33, and a photo-detecting device 34.

In the described lighting device, the LEDs 32 having the same temperature characteristics as each LED 11,... 11 emit light that is converted by the light detection device 34 into an electrical signal. The electrical signal is input to the comparison voltage generation circuit 24. The signal output from the comparison voltage generation circuit 24 is input to the amplifying circuit 23, and the current determined by the predetermined reference value through the transistor 22 based on the signal output from the amplifying circuit 23 causes each LED ( 11, ..., 11, and the change in the temperature characteristic of each LED 11, ..., 11 is compensated for. In this state, when the luminance of the LED 32 is changed by the change in temperature (temperature) as shown in the characteristic diagram G2 in FIG. 13, the current output from the constant current source 20 is changed to the characteristic diagram H1. As shown, the luminance is changed by the comparison voltage generating circuit 24, the amplifying circuit 23, and the transistor 22, and the luminance of the light emitted from the LED PCB 10 is corrected. As a result, unlike the state shown in the characteristic diagram G1 in which the luminance changes with respect to the temperature, it shows the characteristic that the luminance does not change with respect to the temperature as shown in the characteristic diagram G3.

It is a figure which shows an example of the structure of the conventional LED backlight. The color emitted from the LEDs 41, ..., 41 made of the LED backlight is a combination of R (red), G (green), and B (blue) or white. The LEDs 41, ..., 41 are mounted on the PCB 42 and connected in series every predetermined number of the LEDs 41, ..., 41. In this case, a plurality of rows each including LEDs emitting white light when the LEDs emitting white light having a number corresponding to each level of the power source are connected in series and the LEDs emitting white light are not included in one column. It is arranged and in some cases connected in parallel. In addition, when each LED of R, G, and B is used, a predetermined number of LEDs are connected in series for each color. In this LED backlight, some of the light components having a predetermined brightness emitted from the entire LEDs 41, ..., 41 are converted into electrical signals by the light-detecting device 43. In this case, by arranging the photodetector 43 and the color filters 44 for each of R, G, and B, or controlling the photodetector 43 so that the light sensing characteristic depends on the wavelength, each R, Light having a predetermined luminance with respect to G and B is converted into an electric signal. The drive current and the drive voltage supplied to the LEDs 41, ..., 41 are adjusted based on the electric signal generated in proportion to the brightness, and controlled so that the brightness of the light received by the light detecting device 43 is constant. do.

As a result, the conventional LED backlight shown in FIG. 14 has a problem. That is, the current and voltage supplied to the LEDs 41, ..., 41 present in the vicinity of the optical detection device 43 by smoothly following the luminance of the light emitted from the LEDs 41, ..., 41. Is well controlled, but it is difficult to follow the change in the luminance of the light emitted from the LEDs 41, ..., 41 which exist at a position away from the light detecting device 43. Another problem is that the heat is difficult to radiate at the center of the PCB 42, so that the temperature is likely to rise, and therefore, the change according to the place of the temperature in the region surrounding the LEDs 41, ..., 41, and the LEDs 41 Due to the temperature dependence of ..., it is difficult to make the luminance distribution uniform. In addition, when there is a change in the luminance of the light emitted from the LEDs 41, ..., 41 due to the aging change of the LEDs 41, ..., 41, the LED present in the vicinity of the optical detection device 43 Only the luminance characteristic of 41 is adjusted, and deviation still occurs in the characteristic of the luminance distribution of all the LEDs 41, ..., 41. In order to solve the above problem, the LED backlight in which the optical detection device is mounted at a plurality of positions instead of one position is disclosed in Patent Document 2 (Japanese Patent Publication No. 2005-115372 (Summary, FIGS. 7A and B, FIG. 8B, and FIG. 10). )).

It is a figure which shows the structure of the LED used by the conventional backlight of patent document 2. FIG. In the described backlight, as shown in FIG. 15, each row with 31 LEDs is disposed on a four row PCB 50 and connected in series.

FIG. 16 is a diagram showing another configuration of the LED used in the conventional backlight described in Patent Document 2. As shown in FIG. In the described backlight, as shown in FIG. 16, a plurality of rows of each LED are arranged with three to seven LEDs connected in series with each other.

FIG. 17 is a cross-sectional view of a conventional backlight equipped with the LED 51 shown in FIG. 15 or 16. In the backlight 52, as shown in FIG. 17, each light detecting device 53 is mounted between the LED 51 and the diffuser 54, and the LCD (Liquid Crystal Display) panel 55 is connected to each LED. Mounted in the direction in which light is emitted from 51.

FIG. 18 is a diagram showing the configuration of a correction circuit for correcting the luminance characteristic of the LED 51 shown in FIG. 15 or FIG. In the correction circuit, the signal 'a' output from the optical detection device 53 is detected by the detector 61, and the luminance characteristic of the LED 51 is controlled by the control unit 62 based on the detected signal 'b'. Is corrected by

In the backlight control unit of the liquid crystal display device described in Patent Document 3 (Japanese Patent Publication No. 2003-215534), the amount of light emitted from the LED mounted as a backlight on the back side of the liquid crystal display device is controlled in accordance with the brightness around the liquid crystal panel. Even if the use temperature of the LED changes, the amount of emitted light is controlled to be a predetermined value.

However, the prior art has the following problems. In the illumination device described in Patent Document 1 and the backlight described in Patent Document 2, it is impossible to detect and correct the luminance of light emitted from each of the plurality of LEDs consisting of LED light sources. As a result, the luminance due to secular variation in the LED changes, causing a problem that the luminance distribution occurs in the liquid crystal panel. Another problem is that the total change in the brightness of the light emitted from the LED caused by the change in temperature can be corrected, but the change in the brightness of the light emitted from the individual LED among the LEDs cannot be corrected, and as a result, the liquid crystal panel Causes a change in the luminance distribution at.

Moreover, the lighting apparatus described in patent document 1 has another problem. That is, in the conventional lighting device, when the temperature change of the LED or the aging change of the LED is detected, the luminance of light emitted from the LED different from the LED actually used as the light source is referred to, but the LED used as the reference and the LED used in practice are referred to. It is very rare that the temperature, temperature characteristics, and aging characteristics (life characteristics) coincide with each other, and it is difficult to accurately correct these characteristics. Further, in the backlight described in Patent Document 2, although a plurality of LEDs are connected in series with each other, it is impossible to correct luminance characteristics such as the luminance of light emitted from each of the plurality of LEDs. In practice, the drive current and the like for the entire group of the plurality of LEDs connected in series can be adjusted, and the brightness of the light emitted from the group of LEDs cannot be changed as a whole. Further, in the backlight adjusting device described in Patent Document 3, since the luminance of light emitted from the LED is controlled in accordance with the brightness of the peripheral portion of the liquid crystal panel, therefore, the object of the conventional invention is different from the object of the present invention, and thus the problems are It cannot be solved by these prior arts.

In view of the above, it is an object of the present invention to provide a surface light source capable of providing illumination light of uniform brightness to the entire display area of a display panel such as a liquid crystal display device and a brightness correction circuit used therein.

According to a first aspect of the present invention, there is provided a surface light source having a plurality of light emitting devices arranged to form a flat surface and allowing illumination light to enter a display area of a transmissive display panel from the rear surface thereof,

The luminance of the light emitted from each of the plurality of light emitting devices is set as the target value for each light emitting device, and the deviation amount of the brightness of the light is detected from the target value generated when each of the plurality of light emitting devices is turned on, and based on the detected deviation amount And a plurality of luminance correction circuits for matching the luminance of light with a target value.

In a first aspect, the luminance correction circuit is:

Mounted to correspond to each of the plurality of light emitting devices in a one-to-one relationship, receiving light emitted from each of the plurality of light emitting devices, and receiving a luminance detection signal having a level corresponding to the brightness of the light emitted from each of the plurality of light emitting devices; A plurality of light detecting devices to generate; And

Mounted to correspond to each of the plurality of light emitting devices in a one-to-one relationship,

And a plurality of drive / correction circuits for supplying driving power to each of the plurality of light emitting devices, detecting a deviation of the luminance of light emitted from each of the plurality of light emitting devices from the target value, and correcting the driving power to compensate for the deviation. Good.

Further, it is preferable that each of the plurality of light emitting devices be arranged in a 1: 1 relationship in the vicinity of the plurality of light detecting devices.

Further, each of the plurality of light emitting devices and each of the plurality of light detection devices is preferably mounted in the same package.

According to a second aspect of the present invention, there is provided a plurality of light emitting devices arranged to form a flat surface, and having a luminance correction circuit used for a surface light source for causing illumination light to enter a display area of a transmissive display panel from its rear surface, Each luminance correction circuit sets the luminance of light emitted from each of the plurality of light emitting devices to a target value for each light emitting device, and the plurality of light emitting devices are turned on. It is preferable to detect the luminance deviation of light from the target value generated at the time, and to make the luminance of the light coincide with the target value based on the detected deviation amount.

In the second aspect, the

A plurality of light detection devices corresponding to each of the plurality of light emitting devices in a one-to-one relationship and mounted to receive light emitted from each of the plurality of light emitting devices; And

Corresponding to each of the plurality of light emitting devices in a one-to-one relationship, supplying driving power to each of the plurality of light emitting devices, and based on the level of the luminance detection signal, the luminance deviation of the light emitted from each of the plurality of light emitting devices from the target value. It is preferred to include a plurality of drive / calibration circuits that detect and correct drive power such that deviations are compensated for.

According to a third aspect of the present invention, there is provided a luminance correction method applied to a surface light source having a plurality of light emitting devices arranged to be formed in a plane and allowing illumination light to enter a display area of a transmissive display panel from the back surface. Setting a luminance of light emitted from each of the plurality of light emitting devices to a target value for each light emitting device;

Each of the plurality of light emitting devices is turned on? Detecting a luminance deviation of light from a target value generated at the time; And

And matching the luminance of the light to the target value based on the detected amount of deviation.

According to a fourth aspect of the invention, the surface light source is:

A plurality of light emitting devices;

A plurality of luminance detection devices which are provided in a one-to-one relationship with each of the plurality of light emitting devices, and receive light emitted from the corresponding light emitting devices; And

On the basis of the difference between the detected luminance value obtained from the corresponding luminance detection device and the predetermined desired luminance value, provided in a one-to-one relationship with each of the plurality of light emitting devices, so as to maintain the uniformity of the luminance of each of the light emitting devices, And a plurality of luminance correction circuits for correcting the luminance of the light emitted from the corresponding light emitting device.

In a fourth aspect, it is preferable that the light emitting devices each include a light emitting diode.

According to a fifth aspect of the present invention, there is provided a liquid crystal display device having a surface light source for backlight, wherein the surface light source is:

A plurality of light emitting devices;

q a plurality of luminance detection devices provided in a one-to-one relationship with each of the light emitting devices to receive light emitted from the corresponding light emitting devices; And

It is provided in a one-to-one relationship with each of the plurality of light emitting devices, and on the basis of the difference between the detected luminance value obtained from the corresponding luminance detection device and the predetermined desired luminance value in order to maintain the uniformity of the luminance of each of the light emitting devices, And a plurality of luminance correction circuits for correcting the luminance of the light emitted from the corresponding light emitting device.

In the fifth aspect, it is preferable that the light emitting devices each include a light emitting diode.

With this configuration, the luminance of light emitted from each of the light emitting devices is set to a predetermined target value, the luminance deviation of the light emitted from each of the light emitting devices is detected from the predetermined target value, and emitted from each of the light emitting devices based on the deviation amount. A plurality of luminance correction circuits are provided for matching the luminance of the light to a predetermined target value, so that the luminance of the light emitted from each light emitting device and the brightness of the entire display area of the display panel can be made uniform. Light having a predetermined brightness emitted from each light emitting device is converted into a brightness detection signal by each of the photodetecting devices in a one-to-one relationship, and the brightness detection signal is fed back to each of the driving / correction circuits, and thus emitted from each of the light emitting devices. Changes and deviations in the luminance of the emitted light can be compensated for automatically. The light having a predetermined luminance emitted from each light emitting device is fed back, and a process of extracting only the amount of temperature change for the return is unnecessary, so that each temperature correction circuit for each light emitting device is unnecessary. Each light emitting device and each light detecting device are mounted in close proximity to each other in a one-to-one relationship in the same package. Therefore, even if there is a variation in the luminance characteristic between the light emitting device and the photodetecting device, the luminance of the light emitted from each light emitting device can be made uniform by appropriately setting the target value of the luminance. Each light emitting device is mounted so as to correspond to each of the light detecting devices in a one-to-one relationship, and therefore, even if light of any of R, G, and B is emitted by each light emitting device, the color balance is changed without using a color filter. Can be compensated. As a result, when the surface light source is used as a backlight in the transmissive liquid crystal panel, it becomes possible to provide illumination light having uniform luminance over the entire display area of the liquid crystal panel.

Best Mode for Carrying Out the Invention The best mode for carrying out the present invention will be described in detail using various embodiments with reference to the accompanying drawings. Light having a predetermined luminance emitted from each LED used as a light emitting device is converted into a luminance detection signal in a one-to-one relationship, and the luminance correction circuit is used for the surface light source and the surface light source to which the signal is returned to each luminance correction circuit. Is provided.

First embodiment

1 is a block diagram showing an electrical configuration of a main part of a surface light source according to a first embodiment of the present invention. The surface light source of this embodiment is used as a backlight of a transmissive liquid crystal panel mounted on a liquid crystal display panel, and as shown in Fig. 1, an LED 71, a photodiode 72 which is a light detection device (luminance detection device), and an LED drive / Correction circuit 73, and drive / detection circuit 74. In Fig. 1, only one LED 71 is shown, but the surface light source consists of a plurality of LEDs serving as backlights and is arranged to be formed in a plane. Each photodiode 72 is mounted for each of the LEDs 71 in a one-to-one relationship, and receives the light emitted from each of the LEDs 71 and has a level corresponding to the luminance of the received light. Create Each driving / detecting circuit 74 is mounted on each photodiode 72 in a one-to-one relationship, supplies power to each of the photodiodes 72, and supplies a photodiode to each of the LED driving / calibration circuits 73. 72) The luminance detection voltage 'a' generated by each is sent out as the luminance detection voltage V2.

Each LED driving / correction circuit 73 is mounted for each LED 71 in a one-to-one relationship, supplies driving power 'c' to each of the LEDs 71, and is supplied from each of the driving / detecting circuits 74. On the basis of the luminance detection voltage V2, the driving power is detected to detect a deviation from each target value (value corresponding to the luminance setting voltage V1) of the luminance of the light emitted from each LED, and to compensate for the deviation from each target luminance value. Correct 'c'. Specifically in this embodiment, each LED drive / correction circuit 73 increases the current supplied in response to a decrease in the brightness of the light emitted from each LED 71, for example. Each photodiode 72, LED drive / correction circuit 73, and drive / detection circuit 74 constitute respective luminance correction circuits. Each luminance correction circuit sets the luminance of the light emitted from each LED 71 as the target value, detects the deviation amount from the target value of the luminance of the light emitted from each LED 71, and the deviation amount from the target value. Based on this, the luminance of the light emitted from each LED 71 is made to match the target value.

FIG. 2 is a circuit diagram showing an example of each electrical configuration of the drive / detection circuit 74 and the LED drive / correction circuit 73 in FIG. 2. Each of the LED drive / correction circuits 73 includes resistors 81, 82, 83, 84, operational amplifiers 85, resistors 86, 87, 88, and operational amplifiers 89, as shown in FIG. , A register 90 and an operational amplifier 91, and a register 92. Each drive / detection circuit 74 includes a constant current circuit 93 and an operational amplifier 94.

3 is a diagram showing an example of the layout of a set of the LED 71, the photodiode 72, the LED drive / correction circuit 73, and the drive / detection circuit 74 in FIG. As shown in FIG. 3, one of a set of LEDs 71, a photodiode 72, an LED drive / correction circuit 73, and a drive / detection circuit 74 is disposed on the PCB 75. In this case, each LED 71 has various forms. That is, each LED 71 may be weld sealed or have a bare chip shape. In the case of a bare chip, it is preferable that a part or all part of the PCB 75 to which each LED 71 is mounted is weld-sealed by resin etc. In particular in this embodiment, each LED 71 is mounted in the vicinity of each photodiode 72 in a one-to-one relationship, and each LED drive / correction circuit 73 is integrated with each drive / detection circuit 74. Is formed.

4 is an example of the layout of the LED drive / correction circuit 73 formed integrally with the LED 71, the photodiode 72, and the drive / detection circuit 74 of FIG. As shown in FIG. 4, 20 sets of LED drive / correction circuits 73 are integrally formed with an LED 71, a photodiode 72, and a drive / detection circuit 74 on the OCB 75. do. In this case, if either photodiode 72 receives light from any one of the LEDs 71 included in the adjacent set in either set, the photodiode 72 receiving the light must provide the original light. Is affected by light emitted from any one of the LEDs other than the LED 71, and therefore, structural means for shielding the photodiode from the light emitted from the other LED 71 is taken.

According to the luminance correction method used for the surface light source of the present invention, the luminance of light emitted from each LED 71 is set to a predetermined target value, and the amount of deviation from the target value generated when each LED 71 is turned on. The luminance of the light emitted from each LED 71 is detected and based on the deviation amount, so as to coincide with the target value already set. At this time, each LED drive / correction circuit 73 whose current or voltage is shown in FIG. ) Is supplied to each LED 71. In this case, constant current driving or constant voltage driving can be applied as the driving method. A portion of the light component having a predetermined luminance emitted from each LED 71 is received by each photodiode 72, converted into an electrical signal, and the resistance value of each photodiode 72 is proportional to the luminance of the received light. Is lowered. That is, when the brightness of the light emitted from each LED 71 is increased, the resistance value of each photodiode 72 is lowered while the brightness of the light emitted from each LED 71 is lowered, so that each of the photodiodes 71 The resistance value increases. The resistance value is detected by each drive / detection circuit 74, and the resistance value is returned to the LED drive / correction circuit 73. Each LED drive / correction circuit 73 changes the drive current or drive voltage so that the luminance of the light emitted from each LED 71 is at a level corresponding to the brightness setting voltage V1.

As shown in Fig. 2, the luminance setting voltage V1 is input to detect the driving current of each LED 71, and the luminance of the light emitted from each LED 71 is set according to the luminance setting voltage V1. do. And the current I0 is supplied to each LED 71 from each LED drive / correction circuit 73. The current I0 is represented by the following equation (1).

I0 = V3 / RSC ... (1)

'RSC' represents a resistance value of the resistor 90. The voltage V3 for determining the current I0 is the output voltage from the addition and subtraction circuit composed of the operational amplifier 85 and is represented by the following equation (2).

V3 = (-R2 / R1) × V1 + (R4 / R3) × V2 ... (2)

'R1' represents the resistance value of the resistor 81. 'R2' is the resistance value of the resistor 82, 'R3' is the resistance value of the resistor 83, and 'R4' is the resistance value of the resistor 84.

The luminance detection voltage V2 is the drive voltage of each photodiode 72 supplied in advance through each operational amplifier 94 which functions as a voltage follower to each LED drive / correction circuit 73. Since each photodiode 72 is driven by each constant current circuit 93, each photodiode 72 has a resistance value corresponding to the luminance of light emitted from each LED 71. That is, when the luminance of light emitted from each LED 71 is lowered, the resistance value of each photodiode 71 is increased and the driving voltage of each photodiode 72 is increased, thus increasing the luminance detection voltage V2. Done. When the luminance voltage V2 is increased, the voltage V3 is increased so as to be a voltage R4 / R3 times larger than the luminance detection voltage V2 according to equation (2).

An increase in voltage V3 causes an increase in the drive current of each LED 71 and also causes an increase in the brightness of the light emitted from each LED 71. Therefore, by selecting the resistance values R1, R2, R3, and R4 and the current Id of each constant current circuit 93, the voltage is returned from each photodiode 72, and as a result, each LED 71 The change in the brightness of the light emitted from it is compensated.

Therefore, in the surface light source of the first embodiment, the light having the predetermined luminance emitted from each LED 71 is converted by the photodiode 72 into the luminance detection voltage V2 in a one-to-one relationship, and the luminance is achieved. Since the detection voltage V2 is fed back to each drive / detection circuit 74, the luminance change and fluctuation of the light emitted from each LED 71 are automatically compensated for. In addition, since light having a predetermined luminance emitted from each LED 71 is fed back, a process of extracting only the amount of temperature change for the return is not necessary, and it is not necessary to attach a temperature correction circuit to each LED 71. In addition, since each LED 71 is mounted in the vicinity of each photodiode 72 in a one-to-one relationship, the luminance of light emitted from each LED 71 is respectively corrected, thus, between the LEDs 71 and the light. Even if the luminance characteristic between the diodes 72 varies, the luminance of the light emitted from each LED 71 is made uniform by appropriately setting the subsequent set voltage V1. In addition, each LED 71 corresponds to each photodiode 72, so that even if any of R, G, and B colors are emitted from each LED 71, the change in color balance is compensated without using a color filter. do.

Second embodiment

FIG. 5 is a cross-sectional view showing the layout of the principal part of the surface light source of the second embodiment of the present invention, and the same reference numerals are given to the components having the same functions as the first embodiment shown in FIG. In the surface light source of the second embodiment, as shown in FIG. 5, each LED 71, a photodiode 72, an LED drive / correction circuit 73, and a drive / detection circuit 74 have the same package ( 76). Package 76 is equipped with terminals (not shown) and the like used to contact external components. According to the surface light source of the second embodiment, each LED 71 is disposed in the vicinity of each photodiode 72 in the same package 76 in a one-to-one relationship, and each LED drive / correction circuit 73 and Each drive / detection circuit 74 is integrally formed, and therefore, the second embodiment has the same advantages as the first embodiment.

Third embodiment

FIG. 6 is a cross-sectional view showing the layout of the principal part of the surface light source of the third embodiment of the present invention, and the same reference numerals are given to components having the same functions as the second embodiment shown in FIG. In the light source of the third embodiment, as shown in Fig. 6, each photodiode 72, each LED drive / correction circuit 73, and each drive / detection circuit 74 are integrally formed so that one IC It operates as an integrated circuit 77. As in the case of the first embodiment, each LED 71 is disposed in the vicinity of the photodiode 72 in a one-to-one relationship, and thus the same advantages as those obtained in the first embodiment can be obtained. .

Fourth embodiment

7 is a cross-sectional view showing the layout of the principal part of the surface light source of the fourth embodiment of the present invention. In the surface light source of the fourth embodiment, as shown in Fig. 7, each LED drive / correction circuit 73 and drive / detection circuit 74 are mounted outside the package 76, and the package 76 and Together on the PCB 75. PCB 75 is made of an organic material or an inorganic material. According to the surface light source of the fourth embodiment, as in the first embodiment, each LED 71 is arranged in the vicinity of the photodiode 72 in a one-to-one relationship, and therefore, the same as that obtained in the first embodiment. The same advantage can be obtained.

Fifth Embodiment

Fig. 8 is a sectional view showing the layout of the pouring portion of the surface light source of the fifth embodiment of the present invention. In the surface light source of the fifth embodiment, as shown in FIG. 8, the package 76 shown in FIG. 8 is mounted on the PCB 75, and each correction device 78 is, for example, a variable register. And a thick * film printed resistor device trimmed by a laser, a Zener device consisting of a resistor and a Zener diode, a memory device capable of recording data corresponding to a target value of the luminance of each LED, and the like. It is configured to provide the brightness setting voltage V1 to the maintenance circuit 73. Therefore, even if there is a change in the luminance characteristic between the LEDs 71 and the photodiode 72, the light emitted from each LED 71 by appropriately setting the luminance setting voltage V1 using each of the correction devices 78 is obtained. The brightness can be controlled to be uniform.

Sixth embodiment

FIG. 9 is a cross-sectional view showing the layout of the principal part of the surface light source of the sixth embodiment of the present invention, and the same reference numerals are given to the components having the same functions as the fourth embodiment shown in FIG. In the surface light source of the sixth embodiment, as shown in FIG. 9, each correction device 78 shown in FIG. 8 is mounted to the PCB 75 shown in FIG. Therefore, even if there is a change in the luminance characteristic between the LEDs 71 and the photodiode 72, the LEDs emitted from the respective LEDs 71 by appropriately setting the luminance setting voltage V1 using each of the correction devices 78 are obtained. The brightness of the light can be controlled to be uniform.

Seventh embodiment

FIG. 10 is a cross-sectional view showing the layout of main parts of the surface light source of the seventh embodiment of the present invention, and the same reference numerals are given to the constituent parts having the same functions as the sixth embodiment shown in FIG. In the surface light source of the seventh embodiment, as shown in Fig. 10, each of the LED drive / correction circuits 73, the drive / detection circuits 74, and the correction device 78 are integrally formed so that one IC ( 79). Therefore, as in the case of the sixth embodiment, even if there is a change in the luminance characteristic between the LEDs 71 and the photodiode 72, the luminance setting voltage V1 using each correction device 78 is appropriately set. By doing so, the luminance of the light emitted from each LED 71 can be controlled to be uniform.

Eighth embodiment

FIG. 11 is a cross-sectional view showing the electrical configuration of the luminance correction circuit of the eighth embodiment of the present invention, and the same reference numerals are given to the components having the same functions as the first embodiment shown in FIG. Each luminance correction circuit of the eighth embodiment has an LED drive / correction circuit 73A different from the LED drive / correction circuit shown in FIG. 2, as shown in FIG. Each LED drive / calibration circuit 73A0 includes resistors 81, 82, 83, and 84, operational amplifier 85, operational amplifier 95, n-channel MOSFET [Metal Oxide Semiconductor Field Effect Transistor (nMOS)] ( 96), and variable registers.

In this luminance correction circuit, the current I0 flowing through the LED 71 is represented by the following equation (3).

I0 = V4 / RICC ... (3)

'RICC' represents a resistance value of the variable register 97.

Each luminance correction circuit operates so that the voltage V3 of the non-inverting input terminal (+) of the operational amplifier 95 is equal to the voltage of the inverting input terminal (-). As a result, the voltage V3 becomes the voltage V4. Almost the same as). The current I0 flowing through each LED 71 is determined by the voltage V4 and the resistance value RIC of the variable resistor 97. By adjusting the resistance value RIC, a desired current flows through each LED 71, and each LED 71 emits light having a desired brightness. In addition, the operational amplifier 85 constitutes the addition and subtraction circuit of the first embodiment, and thus changes the voltage V3 by changing the luminance setting voltage V1. Therefore, in the luminance correction circuit having a configuration different from that of the first embodiment, the same advantages as those obtained in the first embodiment can be obtained.

The present invention is not limited to the above embodiments, and various changes and modifications can be made without departing from the scope and spirit of the present invention. For example, the luminance correction circuit shown in FIG. 2 or 11 may use any configuration as long as it has the same function as that shown in FIG. 2 or FIG.

In addition, the present invention can be applied to the general field when illumination light having a uniform brightness is to be provided in the entire display area of the display panel, for example, when illumination light is supplied by the backlight.

According to the present invention, there is provided a surface light source capable of providing illumination light of uniform brightness to the entire display area of a display panel such as a liquid crystal display device and a brightness correction circuit used therein.

Claims (11)

In the surface light source having a plurality of light emitting devices arranged to form a flat surface, the illumination light enters the display area of the transmissive display panel from the back, For each light emitting device, the luminance of light emitted from each of the plurality of light emitting devices is set as a target value, and the deviation amount of the luminance of light is detected from the target value generated when each of the plurality of light emitting devices is turned on, and the detected deviation amount is And a plurality of luminance correction circuits for causing the luminance of the light to coincide with the target value. The method of claim 1, The luminance correction circuit, Luminance detection mounted to correspond to each of the plurality of light emitting devices in a one-to-one relationship, receiving light emitted from each of the plurality of light emitting devices, and detecting luminance having a level corresponding to the brightness of light emitted from each of the plurality of light emitting devices. A plurality of photodetectors for generating a signal; And Mounted to correspond to each of the plurality of light emitting devices in a one-to-one relationship, supplying driving power to each of the plurality of light emitting devices, and emitted from each of the plurality of light emitting devices from a target value based on the level of the luminance detection signal; And a plurality of drive / correction circuits for detecting a deviation in luminance of light and correcting the drive power such that the deviation is compensated for. The method of claim 2, And each of the plurality of photodetectors is arranged in a one-to-one relationship in the vicinity of each of the plurality of light emitting devices. The method of claim 3, wherein And said plurality of light emitting devices and said plurality of light detecting devices are mounted together in the same package. In a luminance correction circuit having a plurality of light emitting devices arranged to form a flat surface, and used for a surface light source for causing illumination light to enter the display area of the transmissive display panel, Each of the brightness correction circuits sets the brightness of light emitted from each of the plurality of light emitting devices as a target value for each light emitting device, and detects an amount of deviation of the brightness of light from the target value generated when each of the plurality of light emitting devices is turned on. And the luminance of the light coincides with the target value based on the detected deviation amount. The method of claim 5, A plurality of light detection devices mounted on each of the plurality of light emitting devices in a one-to-one relationship, for receiving light emitted from each of the plurality of light emitting devices; And Mounted in a one-to-one relationship to each of the plurality of light emitting devices, supplying driving power to each of the plurality of light emitting devices, and emitted from each of the plurality of light emitting devices from a target value based on the level of the luminance detection signal; And a plurality of drive / correction circuits for detecting deviations in luminance of light and correcting the drive power so that the deviations are compensated for. In the luminance correction method applied to a surface light source having a plurality of light emitting devices arranged to form a flat surface, the illumination light enters the display area of the transmissive display panel from the back, Setting a luminance of light emitted from each of the plurality of light emitting devices as a target value for each light emitting device; Detecting a deviation amount of brightness of light from the target value generated when each of the plurality of light emitting devices is turned on; And And adjusting the luminance of the light to match the target value based on the detected deviation amount. A plurality of light emitting devices; A plurality of luminance detection devices which are provided in a one-to-one relationship with each of the plurality of light emitting devices, and receive light emitted from the corresponding light emitting devices; And On the basis of the difference between the detected luminance value obtained from the corresponding luminance detection device and the predetermined desired luminance value, provided in a one-to-one relationship with each of the plurality of light emitting devices, so as to maintain the uniformity of the luminance of each of the light emitting devices. And a plurality of luminance correction circuits for correcting the luminance of the light emitted from the corresponding light emitting device. The method of claim 8, Each of the light emitting devices includes a light emitting diode. In the liquid crystal display provided with a surface light source for backlight, The surface light source is: A plurality of light emitting devices; A plurality of luminance detection devices which are provided in a one-to-one relationship with each of the plurality of light emitting devices, and receive light emitted from the corresponding light emitting devices; And On the basis of the difference between the detected luminance value obtained from the corresponding luminance detection device and the predetermined desired luminance value, provided in a one-to-one relationship with each of the plurality of light emitting devices, so as to maintain the uniformity of the luminance of each of the light emitting devices. And a plurality of luminance correction circuits for correcting the luminance of the light emitted from the corresponding light emitting device. The method of claim 10, Wherein each of said light emitting devices comprises a light emitting diode.

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