JP5016324B2 - LED control system - Google Patents

Description

  The present invention relates to an LED control system that measures light output of a plurality of LEDs by a sensor and controls lighting of the LEDs according to the measurement result.

  Conventionally, a light emitting diode (hereinafter referred to as an LED) is used as a light source in an illumination device for producing a wall surface of a building or a backlight of a small liquid crystal display. These lighting devices and backlights generally include a plurality of LEDs that emit three colors of red, green, and blue. By appropriately controlling the light output of these LEDs, combined light of an arbitrary chromaticity can be obtained. Exit. For example, in order to obtain white combined light, each LED needs to be controlled to have an equal light output. However, due to differences in the temperature characteristics of LEDs, etc., the light output varies, and the desired chromaticity may not be obtained.

  Therefore, for example, as shown in Patent Document 1, each LED of red, green, and blue is turned on by an individual power source, and the light output of each LED is detected by a photodiode, and each LED is based on the detection result. There is known an illuminating device in which a combined light having a desired chromaticity can be emitted by adjusting a current value with respect to and mixing colors of LEDs.

  Further, as shown in Patent Document 2, the light output when all red, green, and blue LEDs are turned on is measured, and then the light output when the measurement target LED is turned off is measured. There is known an illumination device that calculates the light output of the LED to be measured by subtracting the latter from the LED and increases the current value for the LED to be lit. This lighting device reduces the number of LEDs that are turned off when measuring the light output, increases the current value for the LEDs that are turned on, and increases the light emission of the LEDs that are turned off, thereby suppressing flickering of the combined light of the entire LEDs. Yes.

JP 2002-533870 A Special table 2004-517445 gazette

  However, since the lighting device described in Patent Document 1 turns off the LED of a color that is not a measurement target when measuring the light output of a certain color LED, the combined light emitted from the lighting device flickers, or the light color May change instantaneously.

  In addition, when a plurality of LEDs are arranged closer to each other in the same package or the like, these LEDs have an optical output when the plurality of LEDs are turned on simultaneously and individually due to the influence of the ambient temperature. May be different. For example, among red, green, and blue LEDs, the red LED is easily affected by the ambient temperature, and when the ambient temperature rises when the green / blue LED is lit near the red LED, the red LED is lit alone. Compared to the case, the light output decreases. Therefore, in the light output measurement method described in Patent Document 1, since the green / blue LEDs are turned off during the measurement of the red LEDs, the ambient temperature of the red LEDs decreases instantaneously, and all of the red / green / blue LEDs are A value different from the light output of the red LED while it is lit is measured.

  In the light output measuring method described in Patent Document 2, for example, in order to measure the light output of a green LED, the light output when all red, green, and blue LEDs are turned on is measured, and then Measure the light output when the red / blue LED is turned on and subtract the latter from the former to calculate the light output of the green LED. However, the light output when the red / blue LED is turned on is Since the green LED is off, the ambient temperature of the red LED drops momentarily, and a value different from the light output of the red / blue LED when all the red / green / blue LEDs are lit is measured. As a result, the light output of the green LED cannot be measured accurately.

  Furthermore, the lighting device described in Patent Document 2 requires an expensive control microcomputer having a high processing capability and a complicated program in order to instantaneously finely control the current value for each LED. It becomes.

  The present invention solves the above-mentioned problems, and with an inexpensive and simple configuration, the combined light emitted from the entire LED does not flicker or the color of the light does not change, and the influence of the ambient temperature like a red LED is affected. An object of the present invention is to provide an LED control system that can accurately measure the light output of an easily received LED and controls the output of the LED according to the measurement result.

In order to solve the above-mentioned problem, the invention of claim 1 includes a plurality of LEDs, a sensor that lights at least a part of the LEDs and measures each light output, and the plurality of LEDs according to the measurement result of the sensors. And an LED control system that individually controls the output of the LED, wherein the LED is controlled to be lit based on an on-duty ratio of a PWM signal, and the control unit outputs light of the LED by the sensor. During the measurement, all the LEDs are turned on without changing the on-duty ratio during normal lighting within one period of the PWM signal, and the measurement of the light output of all the LEDs is completed. Shift the timing to turn on individually, measure the light output of each LED other than the measurement target, from the measured value of the light output of all the LEDs, other than the measurement target By subtracting the sum of the measurements of the LED light output, wherein the calculating the LED light output to be measured, and controls the output of the LED in accordance with the calculated output results.

According to a second aspect of the present invention, in the LED control system according to the first aspect, when the maximum ON time at the time of the normal lighting matches or approximates the period T of the PWM signal , the control unit The maximum on-time during the measurement of the optical output is a time obtained by subtracting the time from the start timing of the cycle of the PWM signal to the timing when the measurement of the optical output is completed from the cycle of the PWM signal.

  According to a third aspect of the present invention, in the LED control system according to the first or second aspect, the current to the LED is variable when measuring the light output of the LED.

  According to a fourth aspect of the present invention, in the LED control system according to any one of the first to fourth aspects, each of the LEDs emits three colors of red, green and blue.

According to the invention of claim 1, since the light output of each LED can be measured individually while all the LEDs are lit, for example, for an LED that is easily affected by the ambient temperature, It is possible to accurately measure the light output in consideration of the influence. Further, since the on-duty ratio of the PWM signal does not change from that during normal lighting when measuring the light output, the human eye does not flicker the light emitted from the entire LED, and the light color does not change. Further, the control unit that controls the lighting of the LED by the PWM signal is realized by using a general-purpose microcomputer or the like provided with, for example, the number of switching elements such as transistors, so that the apparatus can be made inexpensive.

  According to the invention of claim 2, the measurement time of the sensor is ensured by shortening the maximum on-time at the time of measuring the light output of the LED by the measurement time of the sensor from the cycle of the PWM signal. The light output of the LED can be measured.

  According to the invention of claim 3, for example, when measuring the light output, the brightness of light emitted from the entire LED is kept constant regardless of the maximum on-time by changing the value of the current passed through the LED. Can do.

  According to invention of Claim 4, the balance of the color of the light radiate | emitted from LED can be adjusted to arbitrary colors.

  An LED control system according to an embodiment of the present invention will be described with reference to FIG. The LED control system 1 of the present embodiment includes a plurality of LEDs 2 (2a, 2b,..., 2n), a sensor 3 that lights at least a part of the LEDs 2 and measures each light output, and a measurement by the sensor 3 And a control unit 4 that individually controls the output of the LED 2 according to the result. Moreover, LED2 is connected to the power supply 6 (6a, 6b, ..., 6n) via the switching element 5 (5a, 5b, ..., 5n). Note that the number of the plurality of LEDs 2 (2a, 2b,..., 2n) is arbitrary, and is appropriately determined according to the specifications of the device to which the LED control system 1 is applied. Moreover, in the following description, when it only describes as LED2, it means all or any of several LED2 (2a, 2b, ..., 2n).

  The LED 2 emits three colors of red, green, and blue, and the light output is controlled to be turned on by the PWM signal output from the control unit 4. The LEDs 2 are arranged together to form the light emitting unit 20, and the combined light of the light emitted from the LEDs 2 of each color becomes the light emitted from the light emitting unit 20. The emitted light can be set to an arbitrary color by controlling the light output of the red, green, and blue LEDs 2, respectively. For example, when the light outputs of the red, green, and blue LEDs 2 are substantially equal, the light emitted from the light emitting unit 20 is white light.

  The sensor 3 includes at least three photodiodes using a red, green, or blue filter, or a plurality of photodiodes that output tristimulus values. The sensor 3 converts the light output of the LED 2 into an electrical signal, which is then controlled by a control unit. Output to 4. The sensor 3 may be provided with a memory or the like as necessary, and the light output value of the LED 2 may be temporarily stored in the memory or the like.

  The control unit 4 includes a general-purpose microcomputer, a timer, a memory, and the like, and outputs a PWM signal to the switching element 5 according to the time of the timer, and switches the power supply from the power source 6 to the LED 2 by turning the switching element 5 on and off. Thus, lighting control of the LED 2 is performed.

  Next, the operation of the LED control system 1 of the present embodiment will be described with reference to FIGS. 2 and 3 in addition to FIG. 1 described above. In addition, although the operation | movement which the control part 4 actually performs is ON / OFF of the switching element 5, in the following description, it describes that the control part 4 turns on LED2.

When the LED 2 is normally lit, the control unit 4 sets the period T of the PWM signal for controlling the lighting of the LED 2 as 1 ms, for example, as shown in FIG. Further, the control unit 4 turns on the LED 2 at the start timing S ₀ of the period T of the PWM signal, sets a timer value according to the output value set in the LED 2, and finishes counting the timer value and turns on the LED 2. Turn off. Thereby, the on-duty time t (t _a , t _b ,..., T _n ) is set for each LED 2 (2a, 2b,..., 2n). The LED 2 is controlled to be turned on based on an on-duty ratio D obtained by dividing the on-duty time t by the period T. In the example of FIG. 2, the lighting of the LED 2 a is controlled based on the on-duty ratio D _a (D _a = t _a / T).

When measuring the light output of the LED 2, for example, when the light output of the LED 2 a among the LEDs 2 (2 a, 2 b,..., 2 n) is measured, the control unit 4 first starts the on-duty ratio during normal lighting. All the LEDs 2 including the LED 2a to be measured are turned on without changing D. In this case, the sensor 3, the measurement timing _{s a,} shown in FIG. 3, measuring the light output of all LED2. After the measurement of the light output of all the LEDs 2 is completed, the control unit 4 sequentially turns on the LEDs 2 (2b,..., 2n) other than the LED 2a to be measured individually. Also at this time, the on-duty ratios D (D _b ,..., D _n ) of the other LEDs 2 (2b,..., 2n) are not changed from the time of normal lighting. The sensor 3 is measured timing _s b shown in FIG. 3, ..., in _{s n,} LED2 other than the measurement object (2b, ..., 2n) are measured separately the light output of the. Thereafter, the control unit 4 calculates the light output of the measurement target LED 2a by subtracting the total of the light output measurement values of the LEDs other than the measurement target from the measurement values of the light output of all the LEDs.

  As described above, the total of the measured values of the light outputs of the LEDs 2 (2b,..., 2n) other than the measurement target from the measured values of the light outputs of all the LEDs 2 (2a, 2b,..., 2n). , The light output of the LED 2a when all the LEDs 2 are lit can be individually measured. For example, even when the LED 2a is easily affected by the ambient temperature, the influence of the ambient temperature Can be measured accurately.

  In this embodiment, when measuring the light output, the on-duty ratios D of all the LEDs 2 are not changed during normal lighting and when measuring the light output. Therefore, the human eyes do not flicker the combined light emitted from the entire LED 2 or change the light color. In the above description, the measurement of the light output of the LED 2a has been described, but the light outputs of the LEDs 2b,..., LED 2n are individually measured in the same procedure.

  In the present embodiment, preferably, the light output of the LED 2 that is easily affected by the ambient temperature is measured first, and the measurement result is used to calculate the light output value of the other LED 2. For example, when measuring the light output of a green LED that is not easily affected by ambient temperature among red, green, and blue LEDs, first measure the light output value of the red LED while all the LEDs are lit. Then, using this measurement result, the light output value of the green LED while all the LEDs are lit is calculated. That is, when the red LED is turned on alone, the green / blue LED is turned off, so the ambient temperature of the red LED drops momentarily, and all the red, green, and blue LEDs are turned on. A value different from the light output of the red LED is measured, and as a result, the light output of the green LED cannot be accurately measured while all the red, green, and blue LEDs are lit. However, as described above, when the light output of the red LED that is easily affected by the ambient temperature is measured first, and the measurement result is used to calculate the light output value of the green LED, all of the red, green, and blue LEDs are It is possible to accurately measure the light output of the green LED while it is lit.

In addition, for example, in the measurement of the light output of the LED 2 (2b,..., 2n) that is not the measurement target, the control unit 4 determines the maximum ON time of the LED ₂ from the start timing S0 of the period T of the PWM signal. A time (T− (s _b −S ₀ )) obtained by subtracting the time until the completion of output measurement s _b (for example, s _b −S ₀ ) from the period T of the PWM signal. Normally, the measurement of the light output by the sensor 3 is performed in a short time, but it takes at least several tens to several hundreds of μs. Therefore, if the maximum on-time is equal to or approximate to the period T of the PWM signal, it is not possible to secure the timing when only the LED 2 that is not the measurement target is on, and the light output of the LED 2 cannot be measured individually. Therefore, as described above, the maximum ON time of the LED 2 is shortened by the measurement time of the sensor 3 from the period T of the PWM signal, so that the measurement time of the sensor 3 is secured and the light output of the LED 2 is reliably measured. It can be so.

  The maximum on-time of the LED 2 described above is assigned to the LED 2 for which the largest on-duty ratio D is set among the plurality of LEDs 2. For example, in order to obtain light having a color temperature of 3000 K by mixing the LEDs 2 of three colors (red, green, and blue), the ratio of each on-duty ratio D is set to red: green: blue = 10: 11: 9. . The measurement time of the sensor 3 is 200 μs, and the period T is 1 ms. At this time, the maximum on-time of the LED 2 is 800 μs, and this maximum on-time is assigned to the green LED 2 having the largest on-duty ratio D among the three color LEDs. If it carries out like this, at the time of a light output measurement, it can suppress to the minimum that the brightness of the synthetic light which LED2 radiate | emits falls.

  At this time, the control unit 4 keeps the ratio of each on-duty ratio D constant. That is, in the above example, since the maximum ON time of the green LED 2 is 800 μs, the maximum ON time of the red LED 2 is 800 × 10/11 = 727 μs, and the blue LED is 800 × 9/11 = 655 μs. As described above, when the ratio of the on-duty ratio D of each LED is kept constant during normal lighting and measurement of light output, the chromaticity of the combined light emitted from the LED 2 does not change.

  Desirably, the control unit 4 makes the current to the LED 2 variable when measuring the light output. That is, in the above example, the maximum on-duty ratio of the LED 2 is 80% (maximum on-time 800 μs / cycle T1 ms). Therefore, if the maximum on-duty ratio during normal lighting is 100%, the light output The brightness of the combined light emitted from the entire LED 2 during the measurement is reduced by 20%. At this time, the control part 4 enlarges the electric current value sent through LED2. For example, in the above example, if a current of 30 mA flows through the LED 2 during normal lighting, the control unit 4 supplies a current of 37 mA (30 mA / 0.8 (80%)) to the LED 2 when measuring the light output. To make it flow. By doing in this way, the brightness of the synthetic | combination light radiate | emitted from the LED2 whole can be kept constant before and after the measurement of light output.

  The light output values of the LEDs 2 individually measured as described above are written in a memory or the like provided in the control unit 4 or the sensor 3, and the control unit 4 controls the lighting of the LEDs 2 based on these light output values. . This lighting control varies depending on the specification of the device to which the LED control system 1 is applied. For example, during the operation of the LED 2, the lighting control is periodically performed once every 10 seconds. When the measurement result of the sensor 3 is A, the control unit 4 sets the on-duty ratio (reference value) of the dimming signal for controlling the lighting of the LED 2a to, for example, 50%. When the measurement result of the next light output is B, the control unit 4 sets the on-duty ratio (target value) for the LED 2a to 50% × A / B. In addition, by using LEDs that emit three colors of red, green, and blue for each LED 2 described above, and by periodically controlling the lighting output to these LEDs 2, the balance of the color of the light emitted from the entire LED 2 can be set to any color. Can be adjusted.

  The present invention shifts the timing of turning on without changing the on-duty ratio D for controlling the lighting of the LEDs, measures the light output when all the LEDs are turned on, and then outputs the light output of the LEDs not being measured. Is not limited to the above as long as the light output of the LED is calculated from these differences. In addition, the present invention enables accurate measurement of the light output of an LED that is easily influenced by the ambient temperature, such as a red LED, and for an LED that is not easily affected by the ambient temperature, for example, a green LED, You may make it switch a measuring means suitably according to the characteristic of LED, such as measuring the light output directly.

The block block diagram of the LED control system which concerns on one Embodiment of this invention. The figure which shows the PWM signal output pattern at the time of normal lighting in the system. The figure which shows the PWM signal output pattern at the time of the measurement of the optical output in the same system.

Explanation of symbols

1 LED control system 2 LED (light emitting diode)
3 Sensor 4 Control unit

Claims (4)

A plurality of LEDs, a sensor for lighting at least a part of the LEDs to measure each light output, and a control unit for individually controlling the outputs of the plurality of LEDs according to the measurement results of the sensors. In LED control system,
The LED is controlled to be lit based on the on-duty ratio of the PWM signal,
The controller turns on all the LEDs without changing the on-duty ratio during normal lighting within one cycle of the PWM signal when measuring the light output of the LEDs by the sensor, and outputs the light of all the LEDs. After completing the measurement, individually shift the timing of turning on the LEDs other than the measurement target, measure the light output of each LED other than the measurement target, and from the measured values of the light output of all the LEDs, The light output of the LED to be measured is calculated by subtracting the total measured value of the light output of each LED other than the measurement target, and the output of the LED is controlled according to the calculation result. LED control system. When the maximum on-time at the time of normal lighting matches or approximates the period T of the PWM signal , the control unit determines the maximum on-time at the time of measuring the light output of the LED as the period of the PWM signal. 2. The LED control system according to claim 1, wherein a time from the start timing to the timing when the measurement of the light output is completed is set to a time obtained by subtracting from the period of the PWM signal.   The LED control system according to claim 1, wherein a current to the LED at the time of measuring the light output of the LED is variable.   The LED control system according to any one of claims 1 to 3, wherein each of the LEDs emits three colors of red, green, and blue.

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