JP4822502B2 - Backlight - Google Patents

Description

The present invention relates to a backlight device used for a liquid crystal display device or the like. More particularly, the present invention relates to a backlight device having a function of using a number of LEDs as a light source and controlling to achieve uniformity in the amount of light of the LEDs .

  A conventional backlight device will be described with reference to FIGS. FIG. 6 is a plan view showing an example of a conventional backlight substrate. Reference numeral 1 denotes an LED substrate showing a part of the LED substrate, on which a large number of LEDs 2 having different emission colors are arranged and mounted. The arrangement state of each LED 2 according to the light emission color is shown with letters R (red), G (green), and B (blue). The problem with such a conventional structure is the variation in the emission intensity between the LEDs having the same emission color and the emission intensity between the color groups of the LEDs having the respective emission colors, which are within a predetermined range. There must be. The latter problem that affects the color tone of the display is more important than the former. In addition, since LEDs having different emission colors have greatly different characteristics, when controlling a plurality of LEDs as a group, LEDs having the same emission color are collectively performed.

  FIG. 5 shows a conventional color tone control drive circuit. Reference numeral 2a denotes an LED driver, which is a constant current circuit using as a load a series circuit of a plurality of LEDs 2 of the same color and one termination resistor 2b. The terminal voltage of the termination resistor 2b is input as a feedback signal to the control terminal F of the LED driver, and the drive current of the LEDs 2 in the group is controlled to a predetermined value, thereby adjusting the light amount and controlling the environmental temperature and the like. This circuit has a simple merit, but for fine adjustment of the light quantity (if it is performed for each color, the color tone will be adjusted as a result), it is necessary to set the termination resistor individually. There was a difficulty that initial setting of was troublesome.

In order to solve the difficulty of individual setting of resistors, there is also a proposal disclosed in the following patent document.
In this example, a termination resistor and a feedback circuit are not provided, a driving current is provided for each color of the LED by a multiple digital-analog converter (MDAC), and one of several (several bits) control terminals included in the MDAC Is kept high (latched) while checking the light amount, thereby adjusting the light amount to a predetermined value. In this example, there is an advantage that an operation for selecting a resistor is unnecessary and color tone setting can be easily performed. However, there are disadvantages that the circuit becomes complicated and expensive, and that the digital operation makes it impossible to perform analog fine adjustment.
JP 2000-340842 A

  Still another conventional example will be described. FIG. 7 is a side view of a liquid crystal display device using the conventional backlight substrate of FIG. Each LED on the LED substrate 1 emits light upward. Reference numeral 4 denotes a transmissive liquid crystal display panel, and 5 denotes a diffusion plate that diffuses and transmits light, and is provided to uniformly mix light emission. An optical sensor 3 is arranged with the light receiving surface of the photodiode 3 b facing the side surface of the diffusion plate 5, and receives light that is scattered and emerges from the side of the diffusion plate 5.

  FIG. 8 is a plan view of a conventional optical sensor. Three light receiving elements (photodiodes 3b) are incorporated, and R, G, and B color filters 3d are provided on the light receiving surface side, respectively, and mixed. The received light is separated into each color, an intensity signal for each color is output, and the light quantity of the LED group is controlled for each emission color (a circuit is not shown).

  The light amount control for each color is based on PWM, and this method is also generally used. That is, each LED group is driven by a continuous pulse current of several tens of Hz, but its pulse width is controlled by negative feedback with a light amount signal from the optical sensor (a circuit is not shown). The advantage of this method is that the amount of light is controlled while keeping the light quality (emission wavelength) constant because the lighting current (pulse peak value) of the LED does not change depending on the control value. This point is ideal, but the difficulty is that the circuit becomes complex and cost increases are unavoidable.

  In addition, since the light receiving portion of the optical sensor is located on the side surface of the diffusion plate, a so-called vague total amount of light in which the light emission of a large number of LEDs is mixed with different complex weights is received. That is, the LEDs cannot be divided into small groups and the light quantity of each group cannot be individually controlled. That means that a large-area backlight equipped with a large number of LEDs corresponding to a large screen cannot be divided into several areas and the amount of light in each area cannot be finely controlled.

  A first object of the present invention is an LED suitable for controlling the amount of light of a relatively small number of LEDs for each group, having a simplified structure, and facilitating the realization of a large (large area) backlight. An optical sensor arrangement structure is provided. The second object is to provide an LED drive circuit with a light quantity control function having an effective and simple circuit configuration.

In order to achieve the above object, the backlight of the present invention has the following characteristics.
(1) a large number of LED, and the LED substrate planarly arranged and mounted so as to emit light on the upper surface side, respectively, in the backlight consisting diffusion plate disposed thereabove,
A plurality of photosensors are distributed and arranged at predetermined gap positions on the LED substrate , and each photosensor surrounds the periphery of the sensor element and opens upward higher than the sensor element. By providing a light shielding frame, the light receiving angle from above is limited to a predetermined value smaller than 180 degrees, and the upper end of the photosensor is made higher than the height of the LED, so that the light of the surrounding LED To prevent direct incident on the element,
You have to control the light emission intensity of the LED by the output of the optical sensor.

The backlight of the present invention may also have the following characteristics.
(2) The plurality of LEDs are composed of LEDs of R, G, and B colors, and the light emission intensity for each color of the LEDs is controlled by the output of the light sensor.
(3) Each of the photosensors receives light scattered downward by the diffuser plate at a light receiving angle limited by the shielding frame, is close to the individual photosensors, and the individual photosensors. Grouping the LEDs having good sensitivity to the photosensors for each of the individual photosensors, and controlling the light quantity of the grouped LEDs by the individual photosensors .

The backlight of the present invention may also have the following characteristics.
(4) a reference voltage control type LED driver that drives a series circuit of a plurality of LEDs of the same type, a photodiode provided with spectral sensitivity so as to selectively detect light emitted from the LEDs of the same type, and the photodiode And a photosensor comprising an amplifier circuit for amplifying the generated photocurrent, and feeding back the output of the amplifier circuit as a reference voltage control signal for the LED driver, thereby adjusting the light quantity of the LEDs of the same type.

  It is possible to provide an arrangement structure of a backlight with an optical sensor suitable for controlling the amount of light for each group of LEDs. The position of the light sensor is not limited to the side surface of the diffuser plate, and a necessary number of light sensor positions can be arranged on the light emitting surface. Therefore, it is relatively easy to control a large number of LEDs in a large backlight. Since the LED substrate and the optical sensor substrate are integrated, the number of components of the backlight can be reduced. It is also possible to provide an LED driving circuit with a light quantity control function having an effective and simple circuit configuration.

  A large number of RGB LEDs are arranged in a plane so as to emit light on the upper surface side, and a diffusion plate is disposed above the mounted LED substrate to form a backlight of the liquid crystal display panel. Place the sensor. The light sensor is provided with light receiving angle range limiting means for receiving the diffuse reflected light from the diffuser plate so that the light emission of the adjacent LED is not directly incident. The reference voltage of the LED driver is controlled using the output of the light sensor.

  FIG. 1 is a plan view of a backlight substrate according to an embodiment of the present invention, and FIG. 2 is a side view of a liquid crystal display device using this embodiment. The arrangement of the LEDs 2 of each color may be the same as that of the conventional example shown in FIG. 6, for example, and a repetitive arrangement that looks uniform white when viewed through the diffusion plate is selected. The photosensors 3 are dispersedly arranged on the LED substrate 1 with predetermined intervals as shown in the gaps of the array of the LEDs 2. The light receiving surface of the optical sensor 3 faces upward in the same manner as the main light emission direction of the LED, and is scattered inside the diffusion plate 5 and returns from a surface in a predetermined range (some reflected light from the surface of the diffusion plate 5 is also present). Is included). There is also a reason that detection noise occurs when light emitted from an LED (particularly strong light emitted from a nearby LED) is directly incident. Therefore, the angle of the light receiving range is limited as shown by θ in FIG.

  FIG. 3 is a sectional view of an embodiment of the optical sensor 3 used in the present invention. Reference numeral 3a denotes a sensor substrate, on which a sensor element, for example, a photodiode 3b is mounted to receive light from above. The sensor substrate 3 a is mounted on the LED substrate 1. 3c is a light shielding frame so as to optimize the light receiving range (for example, a large amount of light from LEDs of the same color in a group not controlled by the light sensor is mixed in), and light emission from the LED 2 is directly applied to the photodiode 3b. The light receiving angle limiting means is configured to limit the light receiving angle to a range as indicated by θ in FIG. The inner surface of the light shielding frame 3c may be a reflective surface so as to effectively collect light from the upper surface.

  Reference numeral 3d denotes a filter, which is a color filter that transmits only predetermined color light assigned to the sensor and gives the sensor predetermined spectral sensitivity. Since this photosensor 3 detects the light scattered and returned by the scattering plate 5, it reacts with high sensitivity to the amount of light emitted from the LED that is relatively close to the photosensor and the same color as the received light color. In this way, the LEDs that the sensor can feel are almost grouped. Therefore, even if the backlight is equipped with a large number of LEDs, if the large number of LEDs are divided into small groups and the number of photosensors is increased to control each group, the control of a large backlight is relatively easy. It becomes easy.

  4 is a circuit diagram of an embodiment of a light emission control circuit used in the present invention. The LED driver 2a, which is substantially the same as the conventional example (FIG. 5), drives a group consisting of a plurality of the same kind of LEDs 2 (the LEDs are of the same color because the characteristics of the LEDs differ greatly depending on the emission color). There is no feedback from the terminating resistor 2b to the control terminal F of the LED driver 2. Since the emitted light 6 is scattered by the scattering plate 5 and mixed with the light of other LEDs, other colors mixed through the filter 3d of the same color of the optical sensor 3 are cut and incident on the photodiode 3b. .

  The output of the photodiode 3b is input to the positive and negative input terminals of an amplifier 3e which is an operational amplifier. 3f is a feedback resistor, and 3g is a load resistor. The output 3h of the amplifier 3e is input to the control terminal F of the LED driver 2a as a feedback signal. Since this circuit has such a configuration, (1) since it is not PWM modulation, there is no need for an IC for that purpose, and the control circuit can be simply configured accordingly. (2) Since it is analog control, linear and smooth light quantity control is possible. (3) Since the optical sensor circuit section is composed of a photodiode and an operational amplifier, variations in sensitivity characteristics are small, and initial adjustment is almost unnecessary (compared to selecting a termination resistor). It has the features such as.

Next, some examples of configurations and modifications not described in the above embodiment will be described.
For example, R, G, B LEDs are arranged in a plane with other repeating patterns. Also, R, G, and B sensors are not separately distributed, but three photosensors having sensitivity to each color of R, G, and B are brought close together to form one set, and each set is placed between LED arrays. Distribute. In addition, LEDs and optical sensors are arranged close at random. Change the number of colors. The sensor photodiode is also mounted on the LED substrate together with the LED. On the contrary, the inner surface of the light shielding frame of the optical sensor is a non-reflective surface. A commercially available RGB sensor should be used in place of the above-described embodiment structure (photosensor of color filter + photodiode). Omitting termination resistor (LED-only series drive circuit). Use in combination with other control drive circuits. Various modifications and embodiments are conceivable.

According to the present invention, it is possible to reliably control the amount of light even in a large-sized backlight, and the substrate configuration and circuit configuration can be simplified.

It is a top view of the backlight board | substrate which is an Example of this invention. It is a side view of the liquid crystal display device which is an Example of this invention. It is sectional drawing of the optical sensor used for the Example of this invention. It is a circuit diagram of the Example of the light emission control circuit used for this invention. It is a circuit diagram of an example of the conventional light emission control circuit. It is a top view of an example of the conventional backlight board | substrate. It is a side view of the liquid crystal display device of a prior art example. It is a top view of the optical sensor of a prior art example.

Explanation of symbols

1 LED board 2 LED
2a LED driver 2b Terminating resistor 3 Optical sensor 3a Sensor substrate 3b Photo diode 3c Shading frame 3d Filter 3e Amplifying circuit 3f Feedback resistor 3g Load resistor 3h Feedback signal 4 Liquid crystal display panel 5 Diffusion plate 6 Light θ Light receiving angle F Control terminal

Claims (4)

A large number of LED, and the LED substrate planarly arranged and mounted so as to emit light on the upper surface side, respectively, in the backlight consisting diffusion plate disposed thereabove,
A plurality of photosensors are distributed and arranged at predetermined gap positions on the LED substrate , and each photosensor surrounds the periphery of the sensor element and opens upward higher than the sensor element. By providing a light shielding frame, the light receiving angle from above is limited to a predetermined value smaller than 180 degrees, and the upper end of the photosensor is made higher than the height of the LED, so that the light of the surrounding LED To prevent direct incident on the element,
Backlight is characterized in that so as to control the light emission intensity of the LED by the output of the optical sensor. 2. The backlight according to claim 1, wherein the plurality of LEDs include LEDs of R, G, and B colors, and the emission intensity of each color of the LEDs is controlled by the output of the photosensor. . Each of the photosensors receives light scattered downward by the diffuser plate at a light receiving angle limited by the light shielding frame, and is close to and close to the individual photosensors. 3. The back according to claim 1, wherein the LEDs having good sensitivity are grouped for each of the individual photosensors, and the light quantity of the grouped LEDs is controlled by the individual photosensors. Light. Reference voltage control type LED driver for driving a series circuit of a plurality of LEDs of the same type, a photodiode provided with spectral sensitivity so as to selectively detect light emitted from the LEDs of the same type, and light generated from the photodiode And an optical circuit configured to amplify a current. The light sensor adjusts the amount of light of the LED of the same type by feeding back an output of the amplifier circuit as a reference voltage control signal of the LED driver. Item 4. The backlight according to any one of Items 1 to 3 .

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