JP2007095391A - Led light source device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact and low-cost LED (Light Emitting Diode) light source device capable of maintaining white balance of white light. <P>SOLUTION: The LED light source device 1 is provided with a plurality of LEDs 21 to 23 with different color of light, a color-mixing means 12 for mixing light of different color of light radiated from the LEDs, driving circuits 40 to 42 for supplying a drive current to each of the LEDs 21 to 23, and a control device 33 for controlling the driving circuits. The control device 33 outputs to the driving circuits 40 to 42 control signals for adjusting the drive current supplied to each LED 21 to 23 based on the temperature detected by an LED temperature sensor 30. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an LED light source device that emits white light, and more particularly to an LED light source device that can maintain white balance of emitted white light.

  Conventionally, an LED light source device that emits white light has been proposed as a light source such as a backlight of a liquid crystal display device. For example, red (R), green (G), and blue (B) light-emitting diodes (LEDs) used in this LED light source device differ in how the luminance changes with respect to the temperature. Therefore, the white balance of white light set at the time of shipment of the LED light source device or the white balance arbitrarily set by the user changes from the set state with the temperature change of the environment used and the self-temperature rise of the device itself. As a result, a phenomenon occurs in which the white balance of white light emitted from the LED light source device is lost.

For example, Japanese Patent Application Laid-Open No. 2004-29141 describes a back light source for an LCD that adjusts the brightness of this type of white light. This light source is composed of LEDs of three primary colors, and each photodiode (light sensor) detects the light quantity of the corresponding LED. On the other hand, a microcomputer chip is provided, which holds a standard value of color temperature and a set value of luminance of white light as table values. This microcomputer chip calculates the color temperature of white light generated by the three LEDs from the light quantity signal, and determines the value of the control signal so that the calculated value becomes equal to the table value. That is, this microcomputer chip individually adjusts the current flowing through each LED, calculates the brightness of white light from the light quantity signal, and provides a common current increase / decrease rate so that the calculated value becomes equal to the table value. Determine the value. That is, the microcomputer chip adjusts the brightness of white light by increasing or decreasing each current at a common rate while maintaining the color temperature.
JP 2004-29141 A

  In Patent Document 1, in order to adjust the brightness of white light, it is necessary to monitor a change in luminance, and a photodiode (light sensor) is used. However, in this type of device, when using the optical sensor, the mounting position is limited and it is necessary to secure a mounting space. For this reason, the use of the optical sensor becomes a factor that hinders downsizing of the liquid crystal display device. Furthermore, the price of the optical sensor is very expensive as an electronic component, which is a major impediment for reducing the cost of an LED light source device using a light emitting diode as a light source.

  Accordingly, an object of the present invention is to solve the above-described problems and provide a small and low-cost LED light source device capable of maintaining white balance of white light.

  The object is to provide a plurality of light emitting diodes having different emission colors, a color mixing means for mixing light of different emission colors emitted from the plurality of light emitting diodes, and a driving current to each of the plurality of light emitting diodes. An LED light source device including a drive circuit for controlling the drive circuit and a control device for controlling the drive circuit, further comprising LED temperature detection means for detecting a temperature of the light emitting diode, wherein the control device detects the LED temperature. This is achieved by an LED light source device that outputs to the drive circuit a control signal for adjusting drive currents respectively supplied from the drive circuit to the plurality of light emitting diodes based on the detected temperature of the means.

  Here, it is preferable that the plurality of light emitting diodes are respectively mounted on a common substrate, and the LED temperature detecting means is mounted on the common substrate. Furthermore, it comprises ambient temperature detection means for detecting the ambient temperature of the LED light source device, and the control device predicts the final temperature reached by the light emitting diode based on the detected temperature of the ambient temperature detection means, and the predicted final temperature reached. Accordingly, a control signal for adjusting a drive current supplied from the drive circuit to the plurality of light emitting diodes can be output to the drive circuit. These LED light source devices can be used as a light source of a liquid crystal display device, for example.

  The present invention also provides a plurality of light emitting diodes having different emission colors, a color mixing means for mixing light of different emission colors emitted from the plurality of light emitting diodes, and a driving current to each of the plurality of light emitting diodes. A control method for an LED light source device comprising a drive circuit for controlling the drive circuit and a control device for controlling the drive circuit, wherein the temperature of the light emitting diode is detected, and the detected light emitting diode is detected by the control device. A drive current to be supplied to each of the plurality of light emitting diodes is obtained based on temperature, and a control signal for supplying the obtained drive current to each of the plurality of light emitting diodes is output to the drive circuit. Furthermore, the ambient temperature of the LED light source device is detected, the final temperature reached by the light emitting diode is predicted based on the detected ambient temperature by the control device, and the plurality of driving circuits are connected to the plurality of driving circuits according to the predicted final temperature reached. A control signal for adjusting the drive current supplied to each light emitting diode can be output to the drive circuit.

  Thus, in the present invention, white balance control can be performed with inexpensive parts by using an inexpensive temperature sensor (LED temperature detecting means) instead of the optical sensor. That is, the biggest factor that the white balance is lost is that the temperature characteristics are different for each LED having a different emission color. For this reason, the amount of light generated from LEDs with different emission colors varies between when the temperature of the LED immediately after power-on is low and when sufficient time elapses after power-on and when the LED temperature rises due to self-heating, etc. However, the chromaticity of white light mixed with these changes. Therefore, the temperature characteristics of LEDs with different emission colors are measured in advance, the relationship between the temperature for maintaining white balance and the current value to be passed to each LED is obtained, and each color is determined according to the relationship and the temperature value detected by the temperature sensor. The current flowing through the LED is changed to control the chromaticity to be constant. Thereby, white balance control of white light can be performed.

  ADVANTAGE OF THE INVENTION According to this invention, the small and low-cost LED light source device which can maintain the white balance of white light can be obtained. That is, in an LED light source device that uses light generated from a plurality of LEDs with different emission colors and uses them as white light, even if the temperature of the light emitting diode changes due to ambient temperature change or self-heating, the white balance of white light is achieved. An apparatus that can be kept constant can be realized at low cost and in a small size. Further, by mounting the temperature sensor on the surface of the substrate near the light emitting diode, it is possible to save space in the liquid crystal display device. Since it is surface-mounted, the effect of shortening the manufacturing time in the manufacturing process can be obtained.

  Hereinafter, an embodiment of an LED light source device according to the present invention will be described with reference to the drawings. In this embodiment, an example of using as a light source of a liquid crystal display device will be described, but the present invention is not limited to this. In this embodiment, a combination of LEDs of three colors of red, green, and blue will be described as an example. However, the present invention is not limited to this, and a combination of a plurality of LEDs having different emission colors ( For example, the LED light source device may be configured by blue and yellow LEDs.

  FIG. 1 is a diagram showing an embodiment of an LED light source device according to the present invention. As shown in FIG. 1, the LED light source device 1 emits white light to the liquid crystal panel 10 via the light guide plate 11. The liquid crystal panel 10 displays a color image by transmitting light from the LED light source device 1 installed on the back surface by a color filter (not shown) disposed on the front surface. If there is a difference in brightness in the image portion of the liquid crystal panel 10, the brightness of the entire screen is kept uniform by adjusting the shutter opening / closing degree of the bright portion.

  As shown in the drawing, the LED light source device 1 stores an LED light source module 20, drive circuits 40 to 42 for driving each light emitting diode (LED) provided in the LED light source module 20, various information, and a drive circuit ( Red) 40, drive circuit (green) 41, and drive circuit (blue) 42, and a control device 33 configured by, for example, a microcomputer, and drive circuits 40 to 42 based on a dimming signal from the control device 33. Is provided with a dimming circuit 43 for outputting a signal for controlling the brightness of the LED. The LED light source module 20 includes a red (R) LED 21, a green (G) LED 22, and a blue (B) LED 23 mounted on a common substrate (LED mounting substrate) 24, and the emission colors of these three types (RGB) LEDs. White light is obtained by color mixing by the color mixing means 12. The LED light source module 20 can include a plurality of red LEDs 21, green LEDs 22, and blue LEDs 23, respectively. White light emitted from the LED light source module 20 is emitted to the liquid crystal panel 10 through the light guide plate 11.

  In addition to the red LED 21, the green LED 22, and the blue LED 23, LED temperature detection means (LED temperature sensor) 30 is mounted on the LED mounting substrate 24. The LED temperature sensor 30 monitors the temperature corresponding to the LED junction temperature of the red LED 21, the green LED 22, and the blue LED 23 (the temperature of the light emitting diode) as needed. A plurality of LED temperature sensors 30 mounted on the LED mounting substrate 24 may be used. On the other hand, an ambient temperature detection means (ambient temperature sensor) 31 is installed, for example, around the LED light source module 20, and monitors the ambient temperature of the LED light source device 1 (LED light source module 20) as needed.

  The drive circuit (red) 40 drives the red LED 21 at a constant current. Similarly, the drive circuit (green) 41 and the drive circuit (blue) 42 drive the green LED 22 and the blue LED 23 with constant current, respectively. These drive circuits have a PWM drive function that operates in accordance with the PWM control signal 45 output from the control device 33 and the PWM control signal 46 output from the dimming circuit 43.

  The PWM control signal 45 output from the control device 33 controls the red LED 21, the green LED 22 and the blue LED 23 separately, and adjusts the ratio of the amount of light generated from each color LED to determine the white balance. It is. Here, DUTY control refers to controlling the pulse width of a PWM (pulse width modulation) signal that drives each LED. By changing the pulse width, the ratio of the amount of light generated from each LED can be adjusted.

  On the other hand, the dimming circuit 43 sends the PWM control signal 46 to the drive circuit (red) 40, the drive circuit (green) 41, and the drive circuit (blue) 42 based on the dimming signal 48 output from the control device 33. It outputs with the same signal, and adjusts the whole white light quantity which mixed the emitted light from red LED21, green LED22, and blue LED23. That is, in the present invention, white balance of white light can be achieved by the PWM control signal 45, and the overall brightness of the white light can be controlled by the PWM control signal 46. The dimming circuit 43 may be incorporated into the control device 33 as long as it is functionally equivalent, but will be described here as a separate circuit.

  FIGS. 2A to 2C are graphs showing the relationship between the detected temperature of the LED temperature sensor 30 and the target duty (DUTY) ratio in this embodiment. Here, the DUTY ratio is a ratio between a pulse repetition period and a pulse width of a PWM (pulse width modulation) signal for driving each LED. The horizontal axis represents the LED detection temperature, and the vertical axis represents the target DUTY ratio. For example, in FIG. 2A, 50 characteristic lines are those when the brightness of the red LED 21 is maximum, 51 is a characteristic line when the brightness is half, and 52 is a characteristic line when the brightness is minimum. It is. Similarly, FIG. 2B shows a characteristic line 53 when the brightness of the green LED 22 is maximum, a characteristic line 54 when the brightness is half, and a characteristic curve 55 when the brightness is maximum. ) Shows a characteristic line 56 when the brightness of the blue LED 23 is maximum, a characteristic line 57 when the brightness is half, and a characteristic line 58 when the brightness is minimum.

  2A to 2C depends on the setting by the dimming circuit 43 shown in FIG. 1 in each case of the brightness maximum setting, the brightness half setting, and the brightness minimum setting of each LED in FIGS. That is, the white light formed by the light emitted from each LED is a drive circuit (red) 40 that drives the red LED 21, a drive circuit (green) 41 that drives the green LED 22, and a drive circuit (blue) that drives the blue LED 23. With the white balance maintained by 42, the brightness set by the light control circuit 43 is obtained. The brightness setting value of the dimming circuit 43 can be arbitrarily changed by the user by the user dimming setting 47. This set value is not limited to the maximum, half, and minimum three stages shown in the present embodiment, but can be performed in any plural stages, and can be performed continuously without any stages.

  Each characteristic line in FIGS. 2A to 2C has a correlation with the graph of the relationship between the detected temperature of the LED temperature sensor and the luminance shown in FIGS. 3A to 3C. The horizontal axis in FIG. 3 is the detected temperature, and the vertical axis is the luminance. In FIG. 3A, reference numeral 60 denotes a characteristic of the red LED 21 when the brightness is maximum, and there is a correlation with the characteristic line 50 of FIG. Reference numerals 61 and 62 in FIG. 3A indicate characteristics at the minimum and half times of brightness of the LED light source module 20, respectively, and are correlated with the characteristic lines 51 and 52 in FIG. Similarly, in FIG. 3B, when the brightness of the green LED 22 is maximum, half, and minimum, the characteristics are 63, 64, and 65, and the characteristic lines 53, 54, and 55 in FIG. There is a correlation. Similarly, in FIG. 3C, when the brightness of the blue LED 23 is maximum, half, and minimum, the characteristics are 66, 67, and 68, which are correlated with the characteristic lines 56, 57, and 58 of FIG. There is sex. That is, the DUTY ratio for obtaining a desired luminance of each LED corresponding to the temperature can be obtained from FIG. 2 and FIG.

  In the control device 33, data equivalent to the characteristic lines as shown in FIG. 2 and FIG. 3 and white light white balance conditions related to the brightness of each LED are stored in the storage device 34 as a brightness control table. ing. Thereby, the control apparatus 33 can each set the DUTY ratio corresponding to the junction temperature of red LED21, green LED22, and blue LED23. The control device 33 transmits dimming degree information (dimming signal) 48 to the dimming circuit 43 according to the dimming setting 47 performed by the user, and at the same time, the characteristics shown in FIGS. 2 and 3 according to the dimming degree. The white balance of white light is obtained by selecting predetermined data from the brightness control table storing data equivalent to the line and setting the DUTY ratio corresponding to the temperature change of the red LED 21, the green LED 22 and the blue LED 23. Can do.

  The drive circuit (red) 40 is for driving the red LED 21. The brightness of the red LED depends on the output of the target DUTY value determined by the control device 33 according to the detected temperature of the LED temperature sensor 30. Similarly, the drive circuit (green) 41 and the drive circuit (blue) 42 are for driving the green LED 22 and the blue LED 23, respectively, and are targets determined by the control device 33 according to the detected temperature of the LED temperature sensor 30. It depends on the output of the DUTY value.

  Since the above-described drive circuit can reduce power consumption, PWM (pulse width modulation) is applied to turn on / off the drive waveform applied to the LED. Therefore, as a configuration, a circuit that converts a DC voltage output corresponding to each of the red LED 21, the green LED 22, and the blue LED 23 from the control device 33 through a D / A converter into a pulse having a pulse width proportional to the voltage. Constitute.

  The operation of the present invention will be described with reference to FIG. Detection temperature information (LED temperature value) 49 of the LED temperature sensor 30 is given to the control device 33 as needed, and predetermined data is read from the relationship between the temperature and the DUTY ratio stored in the brightness control table of the storage device 34, and the target DUTY is read. Output the ratio. Further, the reading of the brightness control table data stored in the storage device 34 corresponds to the brightness at that time when the brightness desired by the user is set (the dimming circuit 43 controls the brightness). Read data.

  As shown in FIG. 3, the temperature of each color LED gradually increases due to self-heating after the start of operation, but the brightness gradually decreases. As shown in FIGS. 3 (a) to 3 (c), the rate of decrease differs depending on the LED of each color, so that the white balance immediately after the start of operation of the white light emitted from the LED power supply device 1 gradually changes as the temperature rises. become. Therefore, the DUTY ratio of each LED corresponding to the detected temperature information of the LED temperature sensor 30 is read from the brightness control table shown in FIGS. 2A to 2C, and the DUTY for driving each LED is sequentially changed according to each LED temperature. By doing so, the white balance can be kept constant.

  The above-described operation is an operation for keeping the white balance of white light constant, and does not have a function for keeping the brightness of the entire white light constant. However, as shown in FIGS. 3A to 3C, each LED has a characteristic that the brightness decreases as the temperature rises. Therefore, for example, when the temperature is low immediately after the operation starts, the overall brightness is high. Is brighter, and the phenomenon that it gradually becomes dark as the temperature of each LED rises occurs. Therefore, the final reached temperature (equilibrium temperature) of each LED is predicted based on the detected temperature information (ambient temperature value) 44 of the ambient temperature sensor 31, and the DUTY ratio of the signal for driving each LED is controlled accordingly. . Thereby, the brightness of the whole white light can be kept constant, and thus the brightness of the screen can also be kept constant.

  That is, immediately after the start of the operation of the LED power supply device 1, when the temperature of the attachment portion of the LED temperature sensor 30 is still rising, the final value of each LED is determined from the detected temperature of the ambient temperature sensor 31 and the brightness setting value desired by the user. The temperature reached is predicted, and the brightness of the white light corresponding to the final temperature reached is predicted. Then, the DUTY ratio is sequentially set based on the temperature measured by the LED temperature sensor 30 so that the predicted brightness of the white light is obtained immediately after the start of the operation. After the operation starts, the detected temperature of the LED temperature sensor 30 gradually increases, but each LED is driven at a DUTY ratio determined according to the brightness control table stored in the control device 33 according to the detected temperature. As described above, the brightness of the white light at the predicted final temperature can be maintained immediately after the start of operation until after the temperature is stabilized.

  As described above, according to the present invention, by outputting the target DUTY ratio from the detected temperature of the LED temperature sensor 30, the change in the white balance of the white light due to the luminance change of each LED due to the temperature change is invalidated, Stable chromaticity white light can be maintained. Furthermore, by predicting a finally stable temperature from the detected temperature of the ambient temperature sensor 31, a change in the brightness of the white light (screen brightness) that occurs in the process of the LED temperature rising immediately after the start of the operation is detected. It can be suppressed.

  FIG. 4 is a structural schematic diagram showing an example of an LED mounting substrate used in the LED light source device according to the present invention. As shown in the figure, the LED mounting board 24 of this example is a board in which a plurality of LED units 70 in which one red LED 21, two green LEDs 22, and one blue LED 23 are arranged in a square shape on a board are arranged one-dimensionally. However, this may be arranged two-dimensionally. In this example, one LED temperature sensor 30 is arranged in the middle of the substrate, but a plurality of LED temperature sensors 30 may be arranged. The LED of each LED unit 70 has an anode connected to the connector 71 via a wiring 73 and a cathode connected to the connector 72 via a wiring 74. The connector 71 is connected to the anode side of the drive circuits 40 to 42, and the connector 72 is connected to the cathode side of the drive circuits 40 to 42. The detection signal (LED temperature value) of the LED temperature sensor 30 is transmitted to the control device 33 via the wiring 75 and the connector 71 in this example.

  By mounting the LED temperature sensor 30 on the LED mounting substrate 24 that is the same substrate as the red LED 21, the green LED 22, and the blue LED 23, it is possible to detect a temperature change due to self-heating of the LEDs mounted thereon. Since the LED temperature sensor 30 is mounted at a position as close as possible to the LED junction portion, the temperature can be detected with high sensitivity and high sensitivity. In order to detect the temperature with higher accuracy, a plurality of LED temperature sensors 30 may be mounted close to each LED unit 70, and an average value of the detected values may be used as the LED temperature value. Moreover, since the LED temperature sensor 30 is surface-mounted on the LED mounting substrate 24, the LED temperature sensor 30 can be easily mounted and the mounting position can be made uniform.

  According to the LED light source device according to the present invention, by using the temperature sensor for detecting the temperature of the LED and the temperature sensor for detecting the ambient temperature of the LED light source device, white light can be obtained without using an expensive photosensor. The white balance can be kept constant. For this reason, when this LED light source device is used for a liquid crystal display device, for example, an inexpensive liquid crystal display device can be provided as a product.

The LED temperature sensor has an important mounting position, and if it is not mounted uniformly in manufacturing, there is a problem that the temperature value to be detected is not appropriate. However, the LED temperature sensor is mounted with each LED as in the present invention. By mounting on the mounting substrate, the problem can be avoided.
As described above, in the present invention, in an LED light source device including a plurality of LEDs having different emission colors, the relationship between the temperature and the luminance of each color LED is measured in advance, and the white light emitted from the LED light source device based on the measured relationship. The relationship between the temperature of each color LED for maintaining the white balance of light and the value of the current passed through each color LED is obtained. Then, a temperature sensor for detecting the temperature of the LED is provided, and the current to be supplied to each color LED is set from the detected temperature, the temperature of each color LED for maintaining the white balance and the relationship between the current value to be supplied to each color LED. Thereby, even if the temperature of an apparatus changes with the temperature of the environment to use or the self temperature rise of LED itself, the white balance of white light can always be maintained.

  The present invention relates to an LED light source device that emits white light, and more particularly to an LED light source device that can maintain the white balance of the emitted white light and has industrial applicability.

It is a figure which shows one Example of the LED light source device which concerns on this invention. (A)-(c) is a graph which shows the relationship between the detection temperature of LED temperature sensor 30, and the target duty (DUTY) ratio in a present Example. (A)-(c) is a graph which shows the relationship between the detection temperature of a LED temperature sensor, and a brightness | luminance. It is a structural schematic diagram which shows an example of the LED mounting board used for the LED light source device which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Liquid crystal panel 11 Light guide plate 12 Color mixing means 20 LED light source module 21 Red LED
22 Green LED
23 Blue LED
24 LED mounting board 30 LED temperature sensor 31 Ambient temperature sensor 33 Controller 40, 41, 42 Drive circuit 43 Dimming circuit

Claims (6)

  A plurality of light emitting diodes having different emission colors; color mixing means for mixing light of different emission colors emitted from the plurality of light emitting diodes; and a driving circuit for supplying a driving current to each of the plurality of light emitting diodes. An LED light source device comprising a control device for controlling the drive circuit, further comprising LED temperature detection means for detecting the temperature of the light emitting diode, wherein the control device detects the temperature detected by the LED temperature detection means. And a control signal for adjusting a driving current supplied from the driving circuit to each of the plurality of light emitting diodes, to the driving circuit.   2. The LED light source device according to claim 1, wherein each of the plurality of light emitting diodes is mounted on a common substrate, and the LED temperature detecting means is mounted on the common substrate.   Furthermore, it comprises ambient temperature detection means for detecting the ambient temperature of the LED light source device, and the control device predicts the final temperature reached by the light emitting diode based on the detected temperature of the ambient temperature detection means, and the predicted final temperature reached. 3. The LED light source device according to claim 1, wherein a control signal for adjusting drive currents respectively supplied from the drive circuit to the plurality of light emitting diodes is output to the drive circuit.   A liquid crystal display device using the LED light source device according to claim 1 as a light source.   A plurality of light emitting diodes having different emission colors; color mixing means for mixing light of different emission colors emitted from the plurality of light emitting diodes; and a driving circuit for supplying a driving current to each of the plurality of light emitting diodes. , A control method of an LED light source device comprising a control device for controlling the drive circuit, wherein the temperature of the light emitting diode is detected, and the plurality of light sources are detected based on the detected temperature of the light emitting diode. A control method for an LED light source device, wherein a drive current to be supplied to each of the light emitting diodes is obtained and a control signal for supplying the obtained drive current to each of the plurality of light emitting diodes is output to the drive circuit. .   Furthermore, the ambient temperature of the LED light source device is detected, the final temperature reached by the light emitting diode is predicted based on the detected ambient temperature by the control device, and the plurality of driving circuits are connected to the plurality of driving circuits according to the predicted final temperature reached. 6. The method of controlling an LED light source device according to claim 5, wherein a control signal for adjusting a drive current supplied to each light emitting diode is output to the drive circuit.

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