JP2007080883A - Led light source - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correct a variance in accuracy of initial light quantity measurement for a light quantity measuring photo diode while suppressing an increase in production cost. <P>SOLUTION: The LED light source is provided with an LED 12, a variable constant current driver 13, a photo diode 14 to detect the quantity of light of the LED 12, a memory 101 wherein a value obtained by directing a reference light to the photo diode 14 is stored as a reference light corresponding value or respective current control values of the LED 12 corresponding to output values obtained from the photo diode 14 are stored in advance, and a control unit 102. When the control unit 102 is activated, it reads the current control values corresponding to the output values given from the photo diode 14 from the memory 101, corrects them on the basis of the reference light corresponding values, and calculates current control correction value. During operation after activation, the current control correction value is given to the variable constant current driver 13 as a variable constant current value, to control a value of current flowing in the LED 12 to be equal to the current control correction value. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an LED light source that includes an LED (light emitting diode) and a photodiode that detects the amount of light emitted by the LED, and that drives the LED with a constant current based on the amount of light detected by the photodiode. .

  Various LED light sources using LEDs as light sources have been proposed. For example, Patent Literature 1 includes at least one red LED that emits red monochromatic light, at least one green LED that emits green monochromatic light, and at least one blue LED that emits blue monochromatic light. A back light source for a display device is provided.

In addition, this back light source further includes a plurality of photodiodes in order to eliminate variations in the amount of light emitted by each LED, detects the light amount of the corresponding LED by each photodiode, and the brightness of white light is determined from each of these light amounts. It is configured to calculate and control the current to each LED so that this is equal to a predetermined table value.
JP 2004-29141 A

  However, when a general-purpose photodiode is mounted on the back light source, since the general-purpose photodiode has a large variation in light amount measurement accuracy, it is not possible to appropriately correct the variation in the amount of light emitted by each LED. In order to solve this problem, it is necessary to use an expensive photodiode, CCD, or the like in which the variation is within an allowable range, which increases the manufacturing cost.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an LED light source capable of correcting variations in initial light amount measurement accuracy of a light amount measurement photodiode while suppressing an increase in manufacturing cost. And

  The LED light source according to the first aspect of the present invention for solving the above-described problem is an LED, variable constant current driving means for adjusting the current flowing through the LED to a variable constant current, and the amount of light emitted by the LED. Obtained from a photodiode, reference light correspondence value storage means for preliminarily storing a value obtained from the output of the photodiode by irradiating the photodiode with reference light, as a reference light correspondence value, and obtained from the output of the photodiode LED control value storage means for storing each current control value for the LED, which is associated with each output value in advance, and a control means, the control means, when activated, from the LED control value storage means, Reads the current control value associated with the output value obtained from the output of the photodiode, and uses this current control value for the reference light A current control correction value is calculated by correction based on the reference light correspondence value stored in the storage means, and the current control correction value is supplied to the variable constant current driving means during the operation after the startup. It is provided as a current value and is controlled so that the value of the current flowing through the LED becomes equal to the current control correction value.

  In this configuration, since the value of the current flowing in the LED is controlled to be equal to the current control correction value, the light quantity measurement photo is compared with the case where the current control value stored in advance in the LED control value storage means is used. Variations in the initial light quantity measurement accuracy of the diode can be corrected. Further, it is not necessary to provide a new physical part substantially, and it is only necessary to secure an area for storing the reference light correspondence value, so that an increase in manufacturing cost can be suppressed.

  Therefore, according to the present invention, it is possible to correct variations in the initial light quantity measurement accuracy of the light quantity measurement photodiode while suppressing an increase in manufacturing cost.

  FIG. 1 is a schematic configuration diagram of an LED light source according to an embodiment of the present invention. The LED light source of this embodiment includes a resistor 11 and an LED 12 connected in series between a positive terminal and a negative terminal (ground) of a constant voltage source, and also includes a variable constant current driving unit 13 and a photodiode 14. And a microcomputer 10.

  The variable constant current drive unit 13 is interposed in series on the cathode side of the LED 12, for example, and adjusts the current flowing through the LED 12 to a variable constant current. Specifically, the current flowing through the LED 12 is adjusted (constant current drive) so as to be equal to a certain level set by a current control signal from the microcomputer 10.

  The photodiode 14 is a general-purpose photodiode, detects the amount of light emitted by the LED 12, and outputs an output signal corresponding to the amount of light to the microcomputer 10.

  The microcomputer 10 includes a storage unit 101 configured by volatile and nonvolatile storage devices, and a control unit 102 configured by a program stored in the CPU and the nonvolatile storage device, and performs overall control of the LED light source. Execute.

  For example, as shown in FIG. 2, the nonvolatile storage device of the storage unit 101 obtains from the output signal of the photodiode 14 by irradiating the photodiode 14 with the reference light of the reference light source 1 when the LED light source is shipped. To be stored in advance as a reference light correspondence value. That is, the output signal of the photodiode 14 is input to a predetermined A / D conversion port of the microcomputer 10, converted into a digital value, and stored in the nonvolatile storage device as a reference light corresponding value. Further, the value of the reference light received by the photodiode 14 is set to the value of light quantity (design reference value) to be received by the photodiode 14 from the corresponding LED 12.

  In addition, the nonvolatile memory device stores in advance, for example, a table format for each current control value for the LED 12 that is associated with each output value obtained from the output signal of the photodiode 14.

  When the control unit 102 controls the LED light source in general, for example, when it is activated by turning on a switch (not shown) or by an external ON signal, an output obtained from the output signal of the photodiode 14 from the table in the storage unit 101. A current control value associated with the value is read, and the current control value is corrected based on the reference light correspondence value stored in the storage unit 101 to calculate a current control correction value. The current control value is corrected to a current control correction value by, for example, a ratio (%) based on the reference light correspondence value, that is, current control value × reference light correspondence value / current control value.

  In addition, the control unit 102 gives a current control correction value to the variable constant current drive unit 13 as the variable constant current (a constant level) during the operation after startup, and the value of the current flowing through the LED 12 is the current value. Control is made to be equal to the control correction value.

  Next, the operation of this embodiment will be described. When the LED light source is activated, a predetermined current flows through the LED 12 according to the initial setting, the LED 12 emits light, and the photodiode 14 outputs an output signal corresponding to the light emission amount to the microcomputer 10.

  Next, in the microcomputer 10, the current control value associated with the output value obtained from the output signal of the photodiode 14 is read from the table of the storage unit 101, and the current control value is stored in the storage unit 101. A current control correction value is calculated by correction based on the light correspondence value.

  Next, during the operation after startup, the current control correction value is included in the current control signal from the microcomputer 10 to the variable constant current drive unit 13 as a variable constant current value. As a result, the variable constant current drive unit 13 adjusts the current flowing through the LED 12 to be equal to the constant level of the current control correction value, so that the LED 12 emits light with a constant light amount corresponding to the current control correction value.

  According to this embodiment having such a configuration, it is possible to correct variations in the initial light quantity measurement accuracy of the light quantity measurement photodiode while suppressing an increase in manufacturing cost.

  In the present embodiment, the resistor 11, the LED 12, the variable constant current drive unit 13, and the photodiode 14 are each provided one by one. Further, in the configuration, one photodiode 14 is provided for a plurality of LEDs, for example, a red LED, a green LED, and a blue LED, and a reference light correspondence value is stored in advance for each of the plurality of LEDs. It may be configured. Further, the output control of the LED may be divided into timing control by PWM.

  Further, during the operation after the start-up, a means for correcting the light quantity of the LED that changes with the passage of time or the increase in the LED junction temperature may be provided separately.

It is a schematic block diagram of the LED light source of one Embodiment by this invention. It is explanatory drawing of one process performed at the time of shipment of the LED light source of FIG.

Explanation of symbols

10 microcomputer 101 storage unit 102 control unit 11 resistance 12 LED
13 Variable Constant Current Drive Unit 14 Photodiode

Claims (1)

LED,
Variable constant current driving means for adjusting the current flowing through the LED to a variable constant current;
A photodiode for detecting the amount of light emitted by the LED;
Reference light correspondence value storage means for preliminarily storing a value obtained from the output of the photodiode by irradiating the photodiode with reference light as a reference light correspondence value;
LED control value storage means for storing in advance each current control value for the LED, which is associated with each output value obtained from the output of the photodiode;
Control means,
This control means
When activated, a current control value associated with an output value obtained from the output of the photodiode is read from the LED control value storage means, and the current control value is stored in the reference light correspondence value storage means. Correct based on the corresponding value to calculate the current control correction value,
During the operation after the start-up, the current control correction value is applied to the variable constant current driving means as the variable constant current value, and the value of the current flowing through the LED becomes equal to the current control correction value. The LED light source characterized by controlling as follows.

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