JP5624438B2 - Lighting device - Google Patents

Description

  The present invention relates to a lighting device.

  Conventionally, lighting devices including a light source unit that emits mixed color light (for example, white light) from a plurality of types of light emitting elements having different emission colors have been researched and developed in various places (for example, Patent Documents 1 and 2). ).

  As this type of illumination device, Patent Document 1 discloses that a light source unit, a light receiving element that receives light from the light source unit, and a lighting period of the light source unit are changed based on the amount of light received by the light receiving element. A light source system including a light source control means for controlling the light source unit is described. In this light source system, the light source unit includes a red LED chip, a green LED chip, and a blue LED chip. In this light source system, the light receiving element is constituted by an optical sensor using a photodiode. The light source system also includes an I / V conversion unit that converts the output current of the optical sensor into a current voltage, and an A / D conversion unit that performs analog / digital conversion of the output voltage of the I / V conversion unit. Here, the I / V conversion unit includes a current-voltage conversion circuit using an operational amplifier and a resistor in association with each of the red LED chip, the green LED chip, and the blue LED chip. That is, the I / V conversion unit includes three current-voltage conversion circuits.

  In Patent Document 1, a red LED chip, a green LED chip, and a blue LED chip are housed in separate packages, and a red LED chip, a green LED chip, and a blue LED chip are included in one package. There is a description of being contained.

  Further, in Patent Document 2, a plurality of LED chips having different emission colors are mounted, and one light detection element for detecting light emitted from each LED chip is provided, and light from each LED chip is provided. A light emitting device including a package from which mixed color light is extracted is described. This light-emitting device adjusts the light output of each LED chip individually by PWM control of each switching element based on the output of the switching element inserted in each LED chip and the light detection element. And a control unit. Here, the light detection element is configured by a photodiode. The control unit is configured by installing an appropriate program in the microcomputer. This control unit is a LED in which a color mixture period in which all LED chips are lit and a monitoring period in which only one LED chip to be monitored by the light detection element is alternately displayed in a time series, and is lit as a monitoring target. A PWM signal to be supplied to each switching element is generated so that the chips are sequentially switched.

JP 2009-162926 A JP 2009-206186 A

  In the light source system disclosed in Patent Document 1, since it is necessary to provide a photosensor and a current-voltage conversion circuit for each LED chip having a different emission color, the cost increases.

  Patent Document 1 also describes that the number of light sensors may be one, and the red LED chip, the green LED chip, and the blue LED chip of the light source unit may be turned on sequentially in time series. . In this case, in the light source system disclosed in Patent Document 1, it is considered that the current / voltage conversion circuit of the I / V conversion unit is also one. However, at present, it is common that LED chips with different emission colors have greatly different emission efficiency, and even if the amount of current supplied to each LED chip of each emission color is the same, the output current of the photodiode is different for each emission color. to differ greatly. In addition, when the amount of current supplied to the LED chips having different emission colors changes, the amount of change in the output current of the photodiode differs for each emission color. On the other hand, in the current-voltage conversion circuit, the resistor functions to convert the output current of the photodiode into a voltage. Therefore, the conversion coefficient (unit: [V / A]) of the current-voltage conversion is determined by the resistance value of the resistor. Is done. Therefore, it is necessary to define the conversion coefficient so as not to exceed the dynamic range of the output voltage of the current-voltage conversion circuit when the LED chip having the highest emission efficiency is turned on. For this reason, in the case where light from a light emitting color LED chip other than the light emitting color LED chip having the highest light emission efficiency is detected by a photodiode, the dynamic range of the output voltage of the current-voltage conversion circuit and the A / D conversion unit The dynamic range of the input voltage cannot be fully utilized, and the quantization error in the A / D conversion unit becomes large. As a result, it is difficult to accurately control the light output of each of the plurality of types of LED chips having different emission colors, and it is difficult to improve the accuracy of the light color and color temperature of the mixed light.

  In the light emitting device disclosed in Patent Document 2, it is conceivable to provide a current / voltage conversion circuit and an A / D converter in the control unit. In this case as well, from the LED chip having relatively low light emission efficiency. When light is detected by a photodiode, there is a possibility that the dynamic range of the output voltage of the current-voltage conversion circuit and the dynamic range of the input voltage of the A / D converter cannot be fully utilized.

  The present invention has been made in view of the above reasons, and an object of the present invention is to provide an illumination device capable of accurately controlling the light output of each of a plurality of types of LED chips having different emission colors while reducing costs. Is to provide.

Lighting apparatus of the present invention, a light source unit emission efficiency different emission colors emit mixed light of the light from each LED chip has a plurality of kinds of LED chips differ, detect light from the respective LED chips and one photodiode for a plurality of switching elements the current having the same current value to the respective LED chips of the respective light emission colors from the power supply unit is inserted, one for each feed line that teapot subjected separately to each, the Based on a current-voltage conversion circuit for converting the output current of the photodiode into current-voltage, an A / D converter for analog / digital conversion of an analog output voltage of the current-voltage conversion circuit, and an output of the A / D converter A control unit that individually adjusts the light output of each of the LED chips by performing PWM control on each of the switching elements, and the current-voltage conversion circuit includes the photodiode. An operational amplifier having an anode cathode connected to the inverting input terminal and an anode connected to the non-inverting input terminal, and a conversion coefficient for current-voltage conversion connected between the inverting input terminal and the output terminal of the operational amplifier. A conversion coefficient determination unit that determines the emission color of the light emission color so that a difference in the dynamic range of the output voltage of the current-voltage conversion circuit between the LED chips having different emission colors is reduced. A conversion coefficient can be selected for each of the different LED chips, and the control unit PWMs each of the switching elements so that a period in which the LED chips of the respective emission colors are lit independently for each of the emission colors is generated. A function to control, and the A / D so that the output voltage of the current-voltage conversion circuit is sampled by the A / D converter during the period. A function of controlling the converter, and a function of controlling the conversion coefficient determination unit so that the conversion coefficient determination unit becomes the conversion coefficient according to the emission color of the LED chip to be lit during the period in the period. It is characterized by having.

  In this lighting device, the conversion coefficient determination unit is configured by a circuit in which a plurality of series circuits in which a resistor and an analog switch that is turned on and off by the control unit are connected in series are connected in parallel. Preferably, the operational amplifier is connected between the inverting input terminal and the output terminal, and the resistance value of each resistor is set to a resistance value corresponding to the conversion coefficient.

  In this lighting device, the conversion coefficient determination unit is formed by connecting a series circuit in which a plurality of resistors are connected in series between the inverting input terminal and the output terminal of the operational amplifier, It is preferable that analog switches that are turned on and off by the control unit are connected in parallel.

  In the illuminating device of the present invention, it is possible to accurately control the light output of each of a plurality of types of LED chips having different emission colors while reducing the cost.

The illuminating device of embodiment is shown, (a) is a schematic circuit diagram, (b) is a principal part circuit diagram. The light-emitting device in an illuminating device same as the above is shown, (a) is a schematic sectional drawing, (b) is a principal part schematic plan view. It is a general | schematic disassembled perspective view of the light-emitting device in an illuminating device same as the above. It is a principal part circuit diagram of the other structural example of an illuminating device same as the above.

  As shown in FIG. 1, the illumination device according to the present embodiment has a plurality of types of LED chips 1a, 1b, and 1c having different emission colors, and emits mixed color light from the LED chips 1a, 1b, and 1c. The unit 1 and one photodiode 4 for detecting light from each of the LED chips 1a, 1b, and 1c are provided. As the plurality of types of LED chips 1a, 1b, and 1c having different emission colors, an LED chip 1a that emits red light, an LED chip 1b that emits green light, and an LED chip 1c that emits blue light are employed. . Therefore, the lighting device can obtain white light as mixed color light of red light, green light, and blue light. In the light source unit 1 of the present embodiment, the LED chip 1b that emits green light has lower light emission efficiency and lower light output than the LED chip 1a that emits red light and the LED chip 1c that emits blue light. . Therefore, in the light source unit 1 in the present embodiment, the number of LED chips 1a that emit red light and the number of LED chips 1c that emit blue light are one by one, and the number of LED chips 1b that emit green light is two. is there.

  Further, the lighting device includes a plurality of switching elements Qa, Qb, and Qc that are inserted one by one into each power supply path from the power supply unit 8 to each LED chip 1a, 1b, and 1c of each emission color. The lighting device also includes a current-voltage conversion circuit 6 that converts the output current of the photodiode 4 into a current-voltage, and an A / D converter 7 that converts an analog output voltage of the current-voltage conversion circuit 6 from analog to digital. Yes. Further, the lighting device performs PWM control of each of the switching elements Qa, Qb, and Qc based on the output (digital value) of the A / D converter 7, thereby changing the light output of each of the LED chips 1a, 1b, and 1c. The control part 10 to adjust separately is provided. Here, the power supply unit 8 is configured by, for example, a DC / DC converter or the like, and can individually supply currents having the same current value to the LED chips 1a, 1b, and 1c of the respective emission colors. In addition, the illuminating device can change the electric current value supplied to each LED chip 1a, 1b, 1c of each luminescent color by comprising the power supply part 8 with a DC / DC converter, for example. The power supply unit 8 is not limited to a DC / DC converter, and may be, for example, an AC / DC converter, a storage battery, a constant current source, or the like.

  The above-described LED chips 1a, 1b, and 1c for each emission color are housed and mounted in one package 2 as shown in FIGS. 2 and 3, and constitute a light emitting device together with the package 2 and the like. The photodiode 4 is formed in the package 2 described above.

  The package 2 has a mounting recess 2b in which the LED chips 1a to 1c of the respective emission colors are stored on one surface, a mounting substrate 2a on which the LED chips 1a to 1c are mounted, and the one surface side of the mounting substrate 2a. And the translucent member 3 disposed so as to close the housing recess 2b. In the light emitting device, the inside of the housing recess 2b of the package 2 is made of a translucent material (for example, silicone resin, acrylic resin, epoxy resin, polycarbonate resin, glass, or the like) in which the LED chips 1a to 1c are sealed. It is enriched by part 5. The translucent member 3 is not necessarily provided, and an optical member such as a lens may be provided instead of the translucent member 3.

  The mounting substrate 2a includes a first substrate (base substrate) 20, a second substrate (light distribution substrate) 30, and a third substrate (light detection element formation substrate) 40. Each of the substrates 20, 30, and 40 has a rectangular outer peripheral shape and has the same outer dimensions.

  The first substrate 20 is formed using a first silicon substrate 20a whose main surface is a (100) plane, and each LED chip 1a to 1c is mounted on one surface side.

  The second substrate 30 is formed using a second silicon substrate 30a whose main surface is a (100) plane, and a rectangular opening window 31 that exposes the LED chips 1a, 1b, and 1c in the center. Is formed.

  The third substrate 40 is formed using a third silicon substrate 40a whose main surface is a (100) plane, and a circular light extraction for extracting light from the light source unit 1 to the outside at the center. A window 41 is formed.

  The mounting substrate 2a is a portion in which the portion of the third substrate 40 protruding on the opening window 31 of the second substrate 30 protrudes inward from the peripheral portion of the housing recess 2b on the one surface side of the mounting substrate 2a. The protrusion part 2c of a shape is comprised. In the mounting substrate 2a, the light receiving portion 4a of the photodiode 4 is formed on the protruding portion 2c. Here, the light receiving portion 4a of the photodiode 4 is formed so as to surround the circular light extraction window 41 of the third substrate 40. As can be seen from FIG. It is formed so as to surround all the LED chips 1a to 1c in a projected view. In the photodiode 4, a light receiving surface is formed on the surface side facing the housing recess 2 b in the peripheral portion of the light extraction window 41. Here, in the second substrate 30, the opening area of the opening window 31 gradually increases as the distance from the first substrate 20 increases, and the inner surface of the opening window 31 radiates laterally from the LED chips 1a to 1c. A mirror that reflects the emitted light forward (to the protrusion 2c side) is configured. In the light emitting device, the third silicon substrate 40a that is the basis of the third substrate 40 has an n-type conductivity, and the photodiode 4 receives the light from the LED chips 1a, 1b, and 1c. Is constituted by a p-type region. In other words, in the photodiode 4, the light receiving portion 4a is configured by a p-type region, and a region in contact with the light receiving portion 4a in the third silicon substrate 40a is an n-type region.

  The anode (not shown) and the cathode (not shown) of the photodiode 4 are through-hole wirings 34 b and 34 b formed in the second substrate 30 and through-hole wirings 24 b and 24 b formed in the first substrate 20. Are electrically connected to the external connection electrodes 27b and 27b.

  The anode (not shown) and the cathode (not shown) of each LED chip 1a, 1b, 1c are connected to the external connection electrode 27a via the through-hole wiring 24a formed in the first substrate 20, respectively. Electrically connected.

  In the light emitting device described above, the photodiode 4 is formed on the protruding portion 2c protruding inward from the peripheral portion of the housing recess 2b for housing the LED chips 1a to 1c on the mounting substrate 2a. The light emitted from 1c can be stably and accurately detected by the photodiode 4 provided in the package 2.

  By the way, the control part 10 adjusts the light output of each LED chip 1a-1c separately by carrying out PWM control of each switching element Qa-Qc based on the output of the photodiode 4, and each switching element Qa A PWM signal is given to each of ~ Qc. Therefore, the lighting device of the present embodiment can perform light control and color control. Note that the frequency of each PWM signal is preferably set to 100 Hz or more so that a person does not feel blinking of light.

  The above-described control unit 10 is configured by installing an appropriate program in a microcomputer. The control unit 10 is a single color which is a mixed color period in which the LED chips 1a to 1c of each emission color are turned on and a period in which only a monitoring target (one type of the LED chips 1a to 1c of each emission color) is turned on. PWM signals to be supplied to the respective switching elements Qa to Qc are generated so that periods (monitoring periods) appear alternately in time series and the emission colors to be monitored are sequentially switched. Here, the monochromatic period is a period during which the LED chips 1a to 1c of the respective emission colors are lit independently for each emission color.

  More specifically, the control unit 10 sets the lighting start timing of the monitoring target (timing of rising of the ON period in the PWM signal) in the unit period including at least the color mixture period and the single color period to the lighting start timing other than the monitoring target. By making it faster, each PWM signal is generated so that the monochromatic period appears periodically. Here, the control unit 10 inputs a digital value (output of the A / D converter 7) based on the output current of the photodiode 4 in each monochromatic period, and the digital value is previously assigned to each of the LED chips 1a to 1c. The on-duty of the PWM signal is feedback-controlled so as to be kept at each of the different target values set in a one-to-one correspondence. When the on-duty is feedback controlled, the on-duty is changed by changing the falling timing of the on-period. In addition to the color mixture period and the single color period, the above-described unit period includes an unlit period in which all the LED chips 1a to 1c are unlit. In the above-described unit period, the single color period is set before the mixed color period. However, the single color period may be set after the mixed color period. Further, the control unit 10 sets a target value (reference value for each light emission color) corresponding to each light output of each light emission color (red light, green light, blue light) for realizing the target color mixture light. A storage unit (not shown) including a memory for storage is provided. Here, a setting unit for setting the light color, color temperature, dimming level, and the like of the mixed color light is connected to the control unit 10, and the control unit 10 receives the target value associated with the input from the setting unit from the storage unit. You may make it read. In addition, what is necessary is just to comprise a setting part by a variable resistor etc., for example.

  Further, the control unit 10 may generate a PWM signal to be given to each of the switching elements Qa to Qc so that the monitoring target is the same over a plurality of unit periods. For example, the control unit 10 includes the LED chip 1a, LED chip 1a, LED chip 1b, LED chip 1b, LED chip 1c, LED chip 1c, LED chip 1a, LED chip 1a, LED chip 1b, LED chip 1b,. The PWM signals to be supplied to the respective switching elements Qa to Qc may be generated so that the monitoring targets are sequentially switched in this order. In this case, the control unit 10 performs an operation for obtaining an average value of a plurality of inputs from the photodiode 4 side related to the same monitoring target, compares the average value with the target value, and feedback-controls the on-duty. You may do it.

  In any case, in the lighting device, the output current of the photodiode 4 is converted into a current-voltage by the current-voltage conversion circuit 6, and the analog output voltage Vout (see FIG. 1B) of the current-voltage conversion circuit 6 is A / D. It is converted into a digital value by the converter 7 and input to the control unit 10.

The A / D converter 7 converts the analog output voltage Vout of the current-voltage conversion circuit 6 into a digital value based on a value obtained by dividing the specified input voltage range (dynamic range of the input voltage) by the number of bits. To do. Therefore, it is preferable to match the dynamic range of the output voltage Vout of the current-voltage conversion circuit 6 with the dynamic range of the input voltage of the A / D converter 7. Thus, the A / D converter 7, (if the A / D converter 7 is 8-bit A / D converter, 2 ⁸ = 256) the input voltage range bits based on the value obtained by dividing by, The output voltage of the current-voltage conversion circuit 6 can be converted into a digital value from 0 to 255.

  However, the LED chips 1a, 1b, and 1c having different emission colors have different emission efficiencies at present, so that the output of the photodiode 4 can be obtained even if the amount of current supplied to the LED chips 1a, 1b, and 1c of each emission color is the same. The current varies greatly for each emission color. At present, when the amount of current supplied to the LED chips 1a, 1b, and 1c of the respective emission colors is the same, the magnitude relationship of the light output per chip is [LED chip 1c that emits blue light]> [ LED chip 1a emitting red light]> [LED chip 1b emitting green light]. However, in the light source unit 1 in this embodiment, the number of LED chips 1c that emit blue light and the number of LED chips 1a that emit red light are one by one, whereas the LED chip 1b that emits green light. When the light source unit 1 as a whole is considered, [green light output]> [blue light output]> [red light output]. In addition, since the magnitude relationship of these light outputs is decided by the light emission efficiency and the number of each LED chip 1a-1c of each light emission color, it does not necessarily become such a relationship.

  As shown in FIG. 1B, the current-voltage conversion circuit 6 in the present embodiment uses an operational amplifier OP1, the cathode of the photodiode 4 is connected to the inverting input terminal of the operational amplifier OP1, and the anode is It is connected to the non-inverting input terminal of the operational amplifier OP1. The current-voltage conversion circuit 6 includes a conversion coefficient determination unit 61 that is connected between the inverting input terminal and the output terminal of the operational amplifier OP1 and determines a conversion coefficient for current-voltage conversion. Here, the conversion coefficient of the current-voltage conversion circuit 6 is the resistance value of the resistance element existing in the path through which the output current of the photodiode 4 flows between the inverting input terminal and the output terminal of the operational amplifier OP1, that is, conversion coefficient determination. It is determined by the resistance value of the part 61.

  The conversion coefficient determination unit 61 reduces the difference in the dynamic range of the output voltage Vout of the current-voltage conversion circuit 6 between the LED chips 1a, 1b, and 1c having different emission colors (preferably, the difference is caused by the same dynamic range). Conversion coefficient can be selected for each of the LED chips 1a, 1b, and 1c having different emission colors. Here, the conversion coefficient determination unit 61 outputs the output voltage Vout of the current-voltage conversion circuit 6 when only the LED chip 1a is turned on under the condition that the light output of the LED chips 1a, 1b, and 1c of the respective emission colors is maximized. The output voltage Vout of the current-voltage conversion circuit 6 when only the LED chips 1b and 1b are lit is equal to the output voltage Vout of the current-voltage conversion circuit 6 when only the LED chip 1c is lit. Preferably, a conversion factor is selected.

  As is apparent from the above description, the control unit 10 controls each switching element Qa so that a period in which each LED chip 1a, 1b, 1c of each emission color is lit independently for each emission color (the above-described single color period) is generated. , Qb, and Qc have a function of PWM control. The control unit 10 also has a function of controlling the A / D converter 7 so that the output voltage Vout of the current-voltage conversion circuit 6 is sampled by the A / D converter 7 during the single color period. Further, the control unit 10 controls the conversion coefficient determination unit 61 so that the conversion coefficient determination unit 6 has a conversion coefficient corresponding to the light emission color of any of the LED chips 1a, 1b, and 1c that are turned on during the single color period. It has a function.

  Here, the conversion coefficient determination unit 61 is configured by a circuit in which a plurality of series circuits in which analog switches SWa, SWb, and SWc that are turned on and off by the control unit 10 are connected in series are connected in parallel. This circuit is connected between the inverting input terminal and the output terminal of the operational amplifier OP1. In the conversion coefficient determination unit 61, the resistance values of the resistors Ra, Rb, and Rc are set to resistance values corresponding to the desired conversion coefficients on a one-to-one basis. On the other hand, when the control unit 10 turns on the red LED chip 1a in the single color period, only the analog switch SWa connected in series to the resistor Ra among the plurality of analog switches SWa, SWb, SWc is selected. Turn it on. Further, when the green LED chip 1b is lit in the single color period, the control unit 10 selectively selects only the analog switch SWb connected in series to the resistor Rb among the plurality of analog switches SWa, SWb, and SWc. Turn it on. In addition, when the blue light LED chip 1c is lit in the single color period, the control unit 10 selectively selects only the analog switch SWc connected in series to the resistor Rc among the plurality of analog switches SWa, SWb, SWc. Turn it on.

  Therefore, in the illuminating device of this embodiment, the resistance values of the resistors Ra, Rb, and Rc are set to the resistance values corresponding to the desired conversion coefficients on a one-to-one basis. The dynamic range of the output voltage Vout and the dynamic range of the input voltage of the A / D converter 7 can be fully utilized, and the quantization error in the A / D converter 7 can be reduced. As a result, it is possible to accurately control the light output of each of the plurality of types of LED chips 1a, 1b, and 1c having different emission colors, and it is possible to improve the accuracy of the light color and color temperature of the mixed color light.

  In the illumination device according to the present embodiment described above, a plurality of different emission colors can be achieved while reducing costs by adopting a configuration including one photodiode 4, one current-voltage conversion circuit 6, and one A / D converter 7. It becomes possible to accurately control the light output of each of the LED chips 1a, 1b, and 1c.

  Further, in the illumination device of the present embodiment, as described above, the control unit 10 has a mixed color period in which the LED chips 1a to 1c of the respective emission colors are lit and a single color period in which only the monitoring target by the photodiode 4 is lit. Since PWM signals to be supplied to the respective switching elements Qa to Qc are generated so that they appear alternately in series and the monitoring targets are sequentially switched, the LED chips 1a to 1c of the respective emission colors can be obtained simply by providing one photodiode 4 in the package 2. Each light can be detected with high accuracy, and the accuracy of the light color and color temperature of the mixed color light can be improved, so that the reliability is high and the cost can be reduced.

  By the way, the emission color of each LED chip 1a-1c is not specifically limited, What is necessary is just to select suitably according to desired color mixing light.

  Also, the emission color is not limited to three types, and may be a plurality of types. For example, white light may be obtained by mixing four types of red light, green light, blue light, and yellow light. Good.

  Further, the conversion coefficient determination unit 61 is not limited to the circuit configuration of FIG. 1B, and may have a circuit configuration as shown in FIG. In the circuit configuration of FIG. 4, a series circuit in which a plurality of resistors R1, R2, and R3 are connected in series is connected between the inverting input terminal and the output terminal of the operational amplifier OP1, and each of the resistors R1, R2, and R3 is connected. Analog switches SW1, SW2, and SW3 that are turned on and off by the control unit 10 are connected in parallel to each other.

  When the conversion coefficient determination unit 61 has the circuit configuration of FIG. 4, the control unit 10 controls the plurality of analog switches SW1, SW2, and SW3 to turn on / off the analog switches SW1, SW2, and SW3. By changing the combination, the conversion coefficient of the conversion coefficient determination unit 61 can be changed. Therefore, there are many variations of conversion coefficients that can be realized by the conversion coefficient determination unit 61.

  By the way, although the switching device Qa-Qc is comprised by MOSFET in the illuminating device of this embodiment, you may comprise not only MOSFET but a bipolar transistor, for example. Further, in the configuration shown in FIG. 1A, only one light source unit 1 is provided, but a plurality of light source units 1 are provided, and a single control unit 10 controls the light output of the plurality of light source units 1 simultaneously. You may make it do. In this case, for example, it can be set as the lighting fixture which provided the some light source part 1 in the one surface side of one wiring board, and was accommodated in the fixture main body. Moreover, in the above-mentioned example, LED chips 1a, 1b, and 1c of all emission colors are mounted on one package 2, but LED chips 1a to 1c having different emission colors are mounted on individual packages, and these packages are mounted. Alternatively, one photodiode 4 may be provided. Moreover, the mounting member for mounting the LED chips 1a to 1c of the respective emission colors is not limited to the above-described package 2, and may be a ceramic package, for example. In addition, a package is not necessarily required, and the LED chip 1a to 1c is mounted on a flat mounting board or wiring board, and a translucent sealing portion that covers these LED chips 1a to 1c is provided. Also good.

DESCRIPTION OF SYMBOLS 1 Light source part 1a, 1b, 1c LED chip 4 Photodiode 6 Current-voltage conversion circuit 7 A / D converter 8 Power supply part 10 Control part 61 Conversion coefficient determination part OP1 Operational amplifier Qa, Qb, Qc Switching element Ra, Rb, Rc Resistor SWa, SWb, SWc Analog switch

Claims (3)

A light source unit emission efficiency different emission colors emit mixed light of the light from each LED chip has a plurality of kinds of LED chips differ, and one photodiode for detecting light from the respective LED chips, current and a plurality of switching elements the current having the same current value to the respective LED chips of the respective light emitting colors are inserted, one for each feed line that teapot subjected to each separate from the power supply unit, the output current of the photodiode A current-voltage conversion circuit for voltage conversion, an A / D converter for analog / digital conversion of an analog output voltage of the current-voltage conversion circuit, and PWM for each of the switching elements based on the output of the A / D converter A control unit that individually adjusts the light output of each LED chip by controlling, and the current-voltage conversion circuit includes a cathode of the photodiode. An operational amplifier having an anode connected to a non-inverting input terminal and an anode connected to a non-inverting input terminal; and a conversion coefficient connected between the inverting input terminal and the output terminal of the operational amplifier to determine a conversion coefficient for current-voltage conversion The conversion coefficient determination unit for each LED chip having a different emission color so that a dynamic range of an output voltage of the current-voltage conversion circuit is reduced between the LED chips having different emission colors. A conversion coefficient can be selected, and the control unit performs PWM control of each of the switching elements so that a period in which the LED chip of each light emitting color is lit independently for each light emitting color is generated, and A function of controlling the A / D converter so that the output voltage of the current-voltage converter circuit is sampled by the A / D converter during a period; And a function of controlling the conversion coefficient determination unit so that the conversion coefficient determination unit becomes the conversion coefficient corresponding to the emission color of the LED chip to be lit during the period. .   The conversion coefficient determination unit is configured by a circuit in which a plurality of series circuits each having a resistor and an analog switch that is turned on and off by the control unit are connected in series, and the circuit is the inversion of the operational amplifier. The lighting device according to claim 1, wherein the lighting device is connected between an input terminal and the output terminal, and the resistance value of each resistor is set to a resistance value corresponding to the conversion coefficient.   The conversion coefficient determination unit includes a series circuit in which a plurality of resistors are connected in series between the inverting input terminal and the output terminal of the operational amplifier. Each of the resistors is turned on and off by the control unit. The lighting device according to claim 1, wherein the analog switches are connected in parallel.

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