JP2010061869A - Light-emitting device and controlling method therefor - Google Patents

Abstract

Provided are a light emitting device having a long lifetime and high reliability, and a control method for extending the lifetime of a light source body and increasing the reliability of the light source body.
A light source body and control means for controlling the light emission intensity of light emitted from the light source body, the control means is configured to control the light emission intensity according to an integrated value of lighting time of the light source body. Provided is a light emitting device characterized by adjusting. A method of controlling a light emitting device having a light source body, wherein the light emission intensity of light emitted from the light source body is controlled in accordance with an integrated value of a lighting time of the light source body. Provide a control method.
[Selection] Figure 1

Description

  The present invention relates to a light emitting device including a light source body and a control method thereof.

  Conventionally, cold cathode discharge lamps have been used in backlight light sources for liquid crystal display devices such as liquid crystal televisions and personal computer monitors, but they are gradually being replaced by light emitting diodes (hereinafter referred to as “LEDs”). The LED is small and light, strong against vibrations and shocks, and does not need to use mercury, so it is environmentally friendly and emits light immediately when a current is passed, so it is very responsive, with low voltage and low current. Since it emits light, it has many advantages over the cold cathode discharge lamp, such as good luminous efficiency.

  Backlight light sources using LEDs have been mainly used for small-sized applications such as mobile phones and mobile devices, but now they are used for medium-sized applications such as 10-inch monitors or larger and large-sized applications such as 30-inch or larger liquid crystal televisions. Also tend to be adopted. In particular, in applications such as large liquid crystal display televisions, in order to take advantage of the improvement in color reproducibility of liquid crystal, LEDs having emission wavelengths of three primary colors of red, green, and blue (RGB) are suitable as a backlight light source.

  However, the luminous efficiency of the LED changes due to the deterioration of the constituent material of the LED (chip, resin sealing the phosphor, phosphor, package, etc.) and the influence of heat generated by the LED itself. For this reason, when an LED is incorporated in the backlight device, the luminance and chromaticity of the backlight change due to the deterioration and the influence of heat.

In this regard, there is a planar light source device that includes a sensor that detects light from a light source and adjusts the light amount of the light source based on a value detected by the sensor (Patent Document 1).
JP 2004-21147 A

  In order to keep the luminance and chromaticity of the light emitting device at desired values, a color sensor or a temperature sensor may be used. In this case, the detection values of these sensors are converted to obtain luminance and chromaticity, and these converted values are compared with desired luminance and chromaticity values (reference values) of the light emitting device. Then, the lighting condition of the light source is repeatedly controlled by the control means so that both values match.

  Here, in such a light emitting device, the light emission efficiency decreases as the lighting time of the light source (LED) becomes longer, but a large current is forced to flow in order to obtain the necessary luminance regardless of the decrease in the light emission efficiency. . That is, even when the difference between the converted value obtained from the detection result of the sensor and the reference value becomes large, a large amount of current (correction current) for correcting the converted value to be the reference value is supplied. As a result, in the light source (LED) whose accumulated lighting time has been long and has progressed, a current that does not contribute to light emission among the correction currents increases, and this current accelerates deterioration of the light source (decrease in light emission efficiency).

  As described above, in a light emitting device having a configuration in which luminance or the like is adjusted using a color sensor or a temperature sensor, there is a problem that the lifetime of the light source and the light emitting device is rapidly shortened by repeating the above phenomenon.

  The present invention provides a light-emitting device that has a long lifetime and high reliability, and a control method that increases the lifetime of the light source body and increases the reliability of the light source body.

  According to an aspect of the present invention, the light source body includes a light source body and a control unit that controls a light emission intensity of the light emitted from the light source body, the control unit according to an integrated value of a lighting time of the light source body. The light emitting device is characterized in that the light emission intensity is adjusted.

  According to another aspect of the present invention, there is provided a method for controlling a light emitting device having a light source body, wherein the light emission intensity of light emitted from the light source body according to an integrated value of a lighting time of the light source body. A method for controlling a light emitting device is provided.

  For example, the desired value (reference value) of the luminance and chromaticity of the light emitting device can be obtained from the detection result of the sensor by continuously or stepwise decreasing the luminance deterioration rate corresponding to the cumulative lighting time of the light source. The difference between the converted value and the reference value is reduced, and the correction current for lighting control is reduced. Thereby, it becomes possible to lengthen the lifetime of a light source (LED) and a light-emitting device.

  ADVANTAGE OF THE INVENTION According to this invention, the control method which extends the lifetime of a light-emitting device which has a long lifetime and high reliability, and lengthens the lifetime of a light source body, and raises the reliability of a light source body is provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The drawings relate to one embodiment of the present invention, FIG. 1 is a block diagram illustrating a light-emitting device according to this embodiment, and FIG. 2A is an example of the configuration of a light-emitting device (backlight device) according to this embodiment ( 2 is a schematic perspective view showing a specific example 1), FIG. 2B is a schematic circuit diagram of a light emitting device according to the specific example 1, FIG. 3A is a schematic graph showing a luminance maintenance rate with respect to LED lighting time, and FIG. b) is a schematic graph showing the luminance maintenance ratio with respect to the LED lighting time, FIG. 3C is a schematic graph showing the power consumption of the LED with respect to the LED lighting time, and FIG. 4A is a setting of the luminance in the present embodiment. FIG. 4B is a graph illustrating the change in value. FIG. 4B is a graph illustrating the change in power consumption when the luminance is set in this way. In addition, in each drawing, the same code | symbol is attached | subjected to the same component and detailed description is abbreviate | omitted suitably.

  As shown in FIG. 1A, the light emitting device (backlight device or the like) according to this embodiment includes a light source body (light emitting diode or the like) 1 and the luminance (light emission intensity) of light emitted from the light source body 1. And control means Q for controlling.

  The control means Q includes a current control means 100 for controlling the current flowing through the light source body 1, a lighting time integration means 200 for obtaining an integrated value of the lighting time of the light source body 1, and a unit case 3 of the light emitting device emitted from the light source body 1. And color separation detection means 300 for decomposing the light synthesized in the internal space for each wavelength (for example, color separation into RGB) and detecting the emission intensity of each wavelength. Then, as will be described in detail later, the control means Q determines the drive current so that the brightness and hue of the light emitted from the light source body 1 become a predetermined value according to the accumulated value of the lighting time of the light source body 1. Control.

  For example, the control means Q sets a reference value (target value) of the emission intensity for each wavelength detected by the color separation detection means 300, and the emission intensity for each wavelength detected by the color separation detection means 300, the reference value, , And the light emission intensity can be adjusted. In this case, the reference value can be lowered when the light source body 1 is driven for a long time. Accordingly, it is possible to suppress an excessive current from flowing through the light source body 1 in a state in which the light emission efficiency of the light source body 1 is lowered after light emission for a long time. As a result, a light emitting device having a long lifetime and high reliability is provided.

  Further, as illustrated in FIG. 1B, the control unit Q may include a temperature detection unit 400 that detects the temperature of the light source body 1. In this case, for example, the driving current of the light source body 1 can be controlled in consideration of the temperature of the light source body 1. For example, when the temperature of the light source body 1 is high, the light emission efficiency may be reduced. In such a case, it is possible to prevent an excessive current from flowing through the light source body 1 by lowering the reference value.

  Hereinafter, the present embodiment will be described by taking as an example a backlight device using a light emitting diode (LED) 1 that emits monochromatic light in red (R), green (G), and blue (B) as the light source body 1. (Specific Example 1)

  As illustrated in FIG. 2A, the backlight device 1A according to the first specific example includes a plurality of LEDs 1 that emit single color light in red (R), green (G), and blue (B), and a plurality of LEDs 1 in a straight line. LED mounting substrate 2 arranged in a unit, unit case 3 in which LED mounting substrate 2 is arranged in parallel on the inner bottom surface, color sensor 4 (color separation detecting means) disposed on the inner side surface of unit case 3, and unit case 3 A temperature sensor 9 (temperature detection means) disposed on the inner bottom surface of the LED, a control circuit 5 (current control means) connected to the color sensor 4 and the LED mounting board 2 outside the unit case 3, and a lens sheet 6a. An optical sheet 6 composed of a diffusion sheet 6b disposed opposite to each other with the lens sheet 6a interposed therebetween, a diffusion plate 7 provided on the lower surface of the optical sheet 6, and the optical sheet 6 and the diffusion plate 7 It includes a front frame 8 fixed to the unit case 3, a.

  A reflection member such as a white reflection sheet is provided on the inner bottom surface of the unit case 3 except for the region where the LED mounting substrate 2 is disposed, and the reflection member functions as a reflection region. The radiated (emitted) light of the RGB LEDs 1 is synthesized in white in the internal space of the unit case 3 and is emitted to the outside of the backlight device 1 </ b> A via the optical sheet 6 and the reflecting plate 7. Note that the RGB mixing ratio, that is, the number and location of the LEDs 1 arranged in the unit case 3, and the drive current supplied to the LEDs 1 are determined in advance so as to obtain a desired white chromaticity. ing.

The optical sheet 6 and the diffusing plate 7 function as a light emitting surface in the backlight device 1A. The diffusion plate 7 has an optical diffusion effect of diffusing light, and the optical sheet 6 increases the brightness of the diffused light more effectively.
Next, each component will be described.

(LED1)
The LED 1 functions as a light source of the backlight device 1A. The emission spectrum peaks of the RGB LEDs 1 exist at wavelengths of 610 to 650 [nm] for R, wavelengths of 515 to 535 [nm] for G, and wavelengths of 440 to 470 [nm] for B. The LED 1 is configured as a monochromatic LED 1 by packaging RGB light emitting elements.
Instead of the single-color LED 1, a configuration in which a plurality of light-emitting elements are packaged to form a multi-color LED 1 is possible, and RGB light-emitting elements may be directly disposed on the upper surface of the LED mounting substrate 2.

(Color sensor 4)
The color sensor 4 has a function of detecting the emitted light of the LED 1.
The color sensor 4 is composed of a photodiode such as silicon. For example, an RGB photodiode having RGB wavelength sensitivity characteristics shown in FIG. These are configured to be integrated or close to each other. In the photodiodes corresponding to RGB, a color filter is formed in the light receiving portion of the photodiode to eliminate light of other colors. For example, in the case of a photodiode that receives red light, a color filter that excludes blue light and green light is formed in the light receiving portion of the photodiode. The color sensor 4 is not limited to a photodiode, and a light receiving element such as a photomultiplier tube or a CCD (charge coupled device) may be used as a sensor.
The color sensor 4 can be provided in an arbitrary place where light synthesized in the internal space of the light emitting device can be received. For example, as illustrated in FIG. 2A, the unit case 3 may be disposed on the inner side surface, or may be disposed on the inner bottom surface of the unit case 3.

(Temperature sensor 9)
The temperature sensor 9 has a function of detecting the temperature of the LED 1.
The temperature sensor 9 may be composed of a component or a device that can read the temperature, such as an IC or a thermistor.
As shown in FIG. 2A, the temperature sensor 9 may be disposed on the inner bottom surface of the unit case 3 in the vicinity of the LED 1, or a value close to the junction temperature (the temperature of the junction) of the LED 1. It may be arranged at an arbitrary place as long as it can be detected.

(Control circuit 5)
As shown in FIG. 2B, the control means Q is provided with a control circuit 5. The control circuit 5 includes an A / D processing unit 51 that converts a detection value detected by the color sensor 4 from an analog value to a digital value, and a light amount value (reference value) of light having the detection value, desired luminance, and desired chromaticity. ) And an LED drive unit 53 that controls the drive current of the LED 1 based on the comparison result.
Further, the control means Q has a timer 10. By the timer 10, the lighting time of the light source body 1 can be measured and integrated. In this case, the timer 10 may measure and integrate the lighting time, or the timer 10 may measure the lighting time, and the comparison calculation unit 52 may accumulate the lighting time. In any case, a data storage unit such as a nonvolatile memory for storing data relating to the accumulated time can be provided as appropriate.

Furthermore, the measurement data of the temperature sensor 9 is input to the comparison calculation unit 52. The comparison operation circuit 52 can also determine the current output from the LED drive unit based on the measurement data from the temperature sensor 9.
The control function in each part will be described later. Each part constituting the control circuit 5 can be combined with a microcomputer, an IC, or the like.

Next, it will be described with reference to FIG. 3 to suppress the overcurrent from flowing through the LED 1 and thereby to extend the life of the LED 1 and to provide high reliability.
FIG. 3A shows an example of the luminance maintenance rate (Comparative Example B) when the LED 1 emits light with a constant current. FIG. 3A shows that the luminance decreases with time when the current value is constant. This is because the light emission efficiency of the LED is due to deterioration of the constituent material of the LED (chip, resin sealing the chip, phosphor, package, etc.). Further, such deterioration may be accelerated by the influence of heat generated by the LED itself.

  In order to avoid a decrease in luminance due to such deterioration, for example, it is conceivable to control the current flowing through the LED 1 so that the luminance of the emitted light of the LED 1 is maintained at a constant value (Comparative Example C). For example, feedback control may be performed using the color sensor 4 shown in FIG.

  FIG. 3B shows an example of the luminance maintenance rate of the LED 1 when the current flowing through the LED 1 is controlled as described above (Comparative Example C). FIG. 3B shows that the luminance of the emitted light from the LED 1 can be kept constant by appropriately controlling the current. However, in this case, since a large current is passed to maintain the luminance of the deteriorated LED, there is a possibility that the deterioration of the LED is accelerated.

FIG. 3C shows the transition of the power consumption of the LED 1 in the example of FIG. 3B (Comparative Example C: when the current is controlled so that the luminance of the LED 1 is constant). As shown in FIG. 3C, the current flowing through the LED 1 increases with time, and the power consumption of the LED 1 also increases.
Thus, in the backlight device 1A, when the light from the light source is detected by the sensor and the current is controlled so that the light amount of the light source is constant with respect to time, even if the LED deteriorates, the luminance and chromaticity are reduced. Is controlled to remain at the initial value. For this reason, an excessive current flows through an LED whose light emission efficiency is reduced due to progress of deterioration so that the initial luminance is maintained. Thereby, deterioration of LED may be further accelerated. When the deterioration of the LED is accelerated, the luminous efficiency is further reduced, and a vicious circle may occur in which the LED current value is further increased and the deterioration is accelerated.

  For this reason, in this embodiment (specific example 1), the lighting time of LED1 is integrated | accumulated and the brightness | luminance of the emitted light of LED1 is controlled according to this integrated value. Specifically, as described above with reference to FIG. 3B, the target luminance is not maintained as it is as the initial value, but is reduced as the lighting time elapses.

  FIG. 4A is a graph illustrating the change in the set value of luminance in the present embodiment. FIG. 4B is a graph showing the change in power consumption when the luminance is set in this way. In these graphs, Embodiment A and Comparative Examples B and C shown in FIG. 3 are shown.

In the specific examples shown in FIGS. 4A and 4B, when the integrated value of the lighting time increases, correction is performed to relatively lower the target value of the luminance of the emitted light. In this way, a large current can be suppressed from flowing even when the lamp is lit for a long time. That is, the accelerated deterioration of the LED 1 can be prevented.
And in this Embodiment A, compared with the comparative example B represented to Fig.3 (a), a target brightness | luminance can be determined so that the fall of a brightness | luminance may be suppressed. If it does in this way, it will become possible to maintain the lifetime of LED1 long, preventing a big fall of a brightness | luminance.

The integrated value of the lighting time of the LED 1 can be calculated by, for example, the time during which the color sensor 4 is operated. More specifically, for example, the operating time of the color sensor 4 can be calculated as the lighting time of the LED 1. it can. In this case, a timer 10 may be provided in the control means Q as shown in FIG.
Further, the integrated value of the lighting time of the LED 1 is stored in a storage device (an integrated circuit (IC) having storage performance) such as an EEPROM (Electronically Erasable and Programmable Read Only Memory). It may be configured as follows. Corresponding to the lighting of LED 1, the integrated lighting time stored in the storage device is called, and the integration is newly continued. When the lighting of LED 1 is finished, the integrated lighting time at that time can be stored in the storage device. it can. The next time when the LED 1 is turned on, the luminance can be controlled by determining the target value of the luminance of the emitted light from the LED 1 based on the integrated value stored in the storage device.

Here, the luminance of the LED 1 can be controlled by appropriately setting a target value of the luminance of the emitted light from the LED 1 detected by the color sensor 4 and performing feedback control. This target value can be, for example, the light emission intensity for each wavelength when desired brightness and hue are obtained. For example, it can prescribe | regulate by the function of the integrated value of lighting time of LED1. Specifically, for example, a function represented by the following formula (1) can be given.

y = Ax ² −Bx + initial target value (1)

(Here, x is an integrated value of the lighting time of the LED 1, and y is a target value of the luminance of the emitted light of the LED 1 detected by the color sensor 4. A and B are real numbers, and the required service life of the LED 1 is obtained. It can be set to any value according to the deterioration characteristics, etc.)

According to the quadratic function of Equation (1), y is an initial target value in the initial stage (x = 0) by appropriately setting the coefficients A and B, but the value of y decreases thereafter as time passes. . That is, with the passage of time, the target value of the brightness of the LED1 emitted light decreases. As a result, the amount of current gradually decreases with time in the LED 1, and as a result, the load is reduced, thereby extending the life and improving the reliability of the LED 1.

  In addition, the value of A and B can be set so that the assumed LED lifetime may be a numerical value within the range of “0 to B / 2A”, for example. That is, in equation (1), y is minimal when x = B / 2A, and thereafter, the value of y increases as x increases (after the time of “B / 2A”, the luminance target value of LED 1 is However, in order to reduce the load on the LED 1 over time, the service life is preferably in the range of “0 to B / 2A”.

The function of the luminance target value and the integrated lighting time is not limited to the above specific example, and can be flexibly defined according to the usage mode of the light emitting device and the like. For example, the luminance target value can be set by a straight line or a curve that continuously decreases from the initial target value as the lighting time elapses, or by a stepped broken line that decreases stepwise at regular intervals.
In this case, the setting of these target values (reference values) can be registered in the storage medium in advance. That is, the setting of the target value to be compared with the detected value is registered in the storage medium so as to linearly decrease with respect to the cumulative lighting time (b) or curvilinearly decreases with respect to the cumulative lighting time. It can be registered in the storage medium as described above, or (c) it can be registered in the storage medium so as to be lowered step by step with respect to the accumulated lighting time.

  Thus, the vicious circle mentioned above is suppressed by controlling the brightness | luminance of the emitted light of LED1 according to the integrated value of lighting time of LED1. That is, it is possible to suppress a large current from flowing through the LED 1, including the case where the luminance is reduced due to the deterioration of the LED 1. For this reason, according to the present embodiment, a light-emitting device having a long lifetime and high reliability while correcting a decrease in luminance with time is provided.

As described above, according to the present embodiment, it is possible to prevent deterioration due to a large current while suppressing a change in luminance over time, and to have a long life and high reliability. Is provided.
The embodiments of the present invention have been described above with reference to specific examples. However, the present invention is not limited to these specific examples. In other words, those specific examples that have been appropriately modified by those skilled in the art are also included in the scope of the present invention as long as they have the characteristics of the present invention. For example, the elements included in each of the specific examples described above and their arrangement, materials, conditions, shapes, sizes, and the like are not limited to those illustrated, and can be changed as appropriate.

  For example, the light source used in the present embodiment is not limited to the light emitting diode described above, and may be various light sources such as EL (Electro-Luminescence). Further, the colors used in the present embodiment are not limited to the red, green, and blue colors described above, and may be other colors. Also, the number of types of colors is not limited to the above-described three colors, and may be one or a plurality of other numbers within a range that can be applied to each form of the present embodiment. Furthermore, the light emitting device according to the present embodiment is not limited to the above-described backlight device, and may be other various illumination devices.

  Moreover, each element with which each embodiment mentioned above is provided can be combined as long as technically possible, and the combination of these is also included in the scope of the present invention as long as it includes the features of the present invention.

Block diagram illustrating the light emitting device according to this embodiment (A) is a model perspective view showing an example (specific example 1) of the structure of the light-emitting device (backlight apparatus) which concerns on this embodiment, (b) is a schematic circuit diagram of the light-emitting device which concerns on the specific example 1. FIG. (A) is a schematic graph showing the luminance maintenance rate with respect to the LED lighting time, (b) is a schematic graph showing the luminance maintenance rate with respect to the LED lighting time, and (c) is a schematic showing the power consumption of the LED with respect to the LED lighting time. Graph (A) is a graph illustrating the change in the set value of luminance, and (b) is a graph illustrating the change in power consumption.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source body, LED, 1A Light-emitting device, backlight apparatus, 2 LED mounting board, 3 Unit case, 4 Color sensor, 5 Control circuit, 6 Optical sheet, 6a Lens sheet, 6b Diffusion sheet, 7 Diffusion plate, 8 Front frame 9 temperature sensor, 10 timer, 11 R LED, 12 G LED, 13 B LED, 41 R sensor, 42 G sensor, 43 B sensor, 51 A / D processing unit, 52 comparison operation unit, 53 LED drive unit, Q control means

Claims (8)

A light source;
Control means for controlling the emission intensity of light emitted from the light source body;
With
The light emitting device according to claim 1, wherein the control means adjusts the light emission intensity according to an integrated value of a lighting time of the light source body.   The control means reduces the light emission intensity so that a decrease in the light emission intensity that occurs with an increase in the integrated value of the lighting time is smaller than when the light source body is driven with a constant current. The light emitting device according to claim 1. The control means includes
It has a detection means which has a function which decomposes | disassembles the light radiate | emitted from the said light source body in the interior space of the said light-emitting device for every wavelength, and the function which detects the said light emission intensity | strength for every said wavelength. The light emitting device according to claim 1.   The light emitting device according to claim 3, wherein the control unit calculates the integrated value based on a time during which the detection unit operates. The control means includes
Set a reference value of the emission intensity for each wavelength detected by the detection means,
5. The light emitting device according to claim 3, wherein the light emission intensity is adjusted by comparing the light emission intensity for each wavelength detected by the detection unit and the reference value.   6. The light emitting device according to claim 5, wherein the reference value is defined by a function of the integrated value.   The light emitting device according to claim 6, wherein the reference value is set so as to decrease as the integrated value increases. A method of controlling a light emitting device having a light source body,
A method for controlling a light emitting device, comprising: controlling light emission intensity of light emitted from the light source body according to an integrated value of lighting time of the light source body.

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