JP2009246262A - Light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a burden on a power source by starting generation of pulses of currents supplied to respective light emitting means at different timings. <P>SOLUTION: In a light emitting device, a plurality of LEDs 1, 1, 1 emitting lights of different wavelengths are parallel-connected and the currents are supplied to the LEDs from the power source DC. A photo-sensing element 2 detects the lights emitted from the LEDs. A control section 3 PWM-controls the current supplied to each LED 1 based on a result of detection of each LED 1 by the photo-sensing element 2. The control part 3 controls to start generation of pulses of currents supplied to all the LEDs 1, 1, 1 not at the same timing but at the different timings to always light at least one LED 1 when lighting of the plurality of LEDs 1, 1, 1 is controlled. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a light emitting device using a plurality of light emitting means having different emission wavelengths.

  As a conventional light emitting device using a plurality of light emitting means having different light emission wavelengths, a device that performs PWM control on a supply current to each LED (light emitting means) is known. The conventional light emitting device includes a plurality of LEDs each emitting light having a different wavelength, a detection unit that detects light emitted from each of the plurality of LEDs, and a detection result of each detection unit. And a controller that performs PWM control on the supply current separately. As the plurality of LEDs, a blue LED, a green LED, and a red LED are connected in parallel. The conventional light emitting device obtains white light by mixing blue light, green light and red light. In addition, a power source for supplying current to each LED is connected to the conventional light emitting device.

  In the conventional light emitting device having the above configuration, the control unit, as shown in FIG. 8, based on the detection result of the detection unit, the pulse width of the supply current to each LED (blue LED, green LED, red LED) (or The amount of light emitted from each LED is controlled by adjusting the on-duty in the same period T (time ta to te). The pulse width of the supply current is different for each LED, the pulse width of the supply current to the blue LED is Ta (time ta to tb), the pulse width of the supply current to the green LED is Tb (time ta to tc), to the red LED The pulse width of the supply current is Tc (time ta to td).

  In addition, the conventional control unit matches the start timing of the supply current to each LED at the same timing (time ta). For this reason, the maximum number of LEDs that are simultaneously turned on is three from time ta to tb, and the maximum change amount when the number of LEDs that are turned on is three LEDs at time ta. As described above, the conventional light-emitting device suddenly changes the state of the power source from the no-load state to the maximum load state (three LEDs are lit) at the time ta. There was a problem that had to be used. In addition, since the amount of change in the current flowing from the power source to the LED at time ta is large, the conventional light emitting device also has a problem that noise due to parasitic elements occurs.

As a conventional light emitting device that solves the above problem, there is one that performs PWM control by shifting the timing at the start of a pulse of a supply current to each LED (for example, see Patent Document 1). That is, the light-emitting device of Patent Document 1 shifts the start time of the supply current pulse to the blue LED, the start time of the supply current pulse to the green LED, and the start time of the supply current pulse to the red LED. According to the light emitting device of Patent Document 1, the maximum number of LEDs that can be turned on simultaneously can be suppressed to two, and the maximum amount of change when the number of LEDs that are turned on can be reduced to one LED. Compared with the case of simultaneously starting the pulse of the supply current to the power supply, it is possible to reduce the load on the power source.
JP 2007-080540 A (paragraphs 0035 to 0040, FIG. 4)

  However, although the light emitting device of Patent Document 1 has a time difference at the start of a pulse of supply current to each LED, there is a period in which no current is supplied to all LEDs. From the above, since the light-emitting device of Patent Document 1 frequently switches the state of the power source between the no-load state and the load state during LED lighting control, the light-emitting device of Patent Document 1 still has a burden on the power source. There was a problem that was large.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a light-emitting device that can reduce a burden on a power source.

  The invention of claim 1 is a plurality of light emitting means connected in parallel and each emitting light having a different emission wavelength by a supply current from a power source, and a detecting means for detecting light emitted from the plurality of light emitting means, Control means for PWM-controlling the supply current to the light emitting means based on the detection result of the detecting means for each light emitting means, and the control means supplies each light emitting means so that at least one light emitting means is lit. It is characterized in that there is a time difference at the start of the supply current pulse.

  Each light emitting means may be composed of a single light emitting element, or a plurality of light emitting elements that emit light having the same emission wavelength may be connected in series.

  According to a second aspect of the present invention, in the first aspect of the invention, the control unit sets an individual minimum pulse width for each light emitting unit, and performs PWM control on a supply current to the light emitting unit for each light emitting unit. If the pulse width of the current supplied to the light emitting means becomes the minimum pulse width when the current is being controlled, the control of the current supplied to the light emitting means is fixed to the minimum pulse width from the PWM control. It is characterized by switching to the current control which changes.

  According to a third aspect of the present invention, in the second aspect of the invention, the control means sets the minimum pulse width of the light emitting means to the start of the pulse of the current supplied to the light emitting means and to another light emitting means that starts lighting next. It is characterized in that it is set to be equal to the time difference from the start of the pulse of the supply current.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the control means is configured so that each of the light emitting means is turned on so that one or more n-1 (n: total number of light emitting means) light emitting means are lit. It is characterized in that a time difference is given at the start of the pulse of the supply current to.

  According to a fifth aspect of the invention, in the first or second aspect of the invention, the control means has a period in which one light emitting means and another light emitting means that starts lighting next to the one light emitting means are simultaneously turned on. Is characterized in that there is a time difference at the start of the pulse of the supply current to each light emitting means.

  According to the first aspect of the present invention, at least one light emitting unit is always supplied with a current from the power source by providing a time difference at the start of a pulse of a supply current to each light emitting unit so that the control unit turns on at least one light emitting unit. Therefore, it is possible to prevent frequent switching of the state of the power source between the no-load state and the load state during the lighting control of the light emitting means, and as a result, the burden on the power source can be reduced. it can.

  According to the invention of claim 2, the individual minimum pulse width is set for each light emitting means, and the current control is performed instead of the PWM control by making the pulse width of the supply current to each light emitting means smaller than the minimum pulse width. Thus, the amount of change in the amount of light emitted from each light emitting means can be increased without putting the power supply in a no-load state.

  According to the invention of claim 3, by making the minimum pulse width equal to the time difference at the start of the pulse of the supply current to each light emitting means, the pulse width of the supply current to a certain light emitting means becomes the minimum pulse width, The change in the load state of the power supply when switching from one light-emitting means to the next light-emitting means can be reduced, and the load state of the power supply after switching can be made constant, thus further reducing the load on the power supply Can do.

  According to the invention of claim 4, since it is possible to prevent the power source from supplying current to all the light emitting means at the same time, the burden on the power source can be further reduced. Thereby, it is possible to use a power supply having an allowable current smaller than the sum of the supply currents to all the light emitting means.

  According to the fifth aspect of the present invention, when at least two light emitting units are turned on at the same time, when switching from one light emitting unit to the next light emitting unit, a period in which no current is supplied to all the light emitting units is provided. It can be surely prevented from occurring.

(Embodiment 1)
First, the structure of the light-emitting device of Embodiment 1 is demonstrated using FIG. As shown in FIG. 1, the light emitting device includes a plurality of LEDs (light emitting means) 1 (1a), 1 (1b), 1 (1c) each emitting light having different wavelengths, and a plurality of LEDs 1, 1, 1 includes a light detection element (detection unit) 2 that detects light emitted from 1 and a control unit (control unit) 3 that performs PWM control on the supply current to the LED 1 for each LED 1. In addition, a power source DC that supplies current to each LED 1 is connected to the light emitting device.

  In the present embodiment, as the plurality of LEDs 1, 1, 1, a blue LED 1a that emits blue light, a green LED 1b that emits green light, and a red LED 1c that emits red light are connected in parallel. . White light is obtained by mixing blue light, green light and red light.

  For each LED 1, the light detection element 2 detects the amount of light emitted from the LED 1. That is, the light detection element 2 individually detects the amount of blue light emitted from the blue LED 1a, the amount of green light emitted from the green LED 1b, and the amount of red light emitted from the red LED 1c. In addition, the light detection element 2 is not limited to what detects a light quantity. As another example, the light detection element 2 may detect other physical quantities related to light (for example, light flux, luminous intensity, luminance, illuminance, etc.) instead of the light amount.

  The control unit 3 includes a plurality of switching elements 30, 30, 30 connected in series to the LED 1 in a power supply circuit from the power source DC to the LED 1, and a processing unit 31 that controls on / off of each switching element 30. .

  In each embodiment, a MOSFET is used as each switching element 30. Each switching element 30 which is a MOSFET turns on and off the current flowing between the source and the drain in response to turning on and off of the gate voltage. That is, each switching element 30 turns on and off the current flowing through the LEDs 1 connected in series.

  As illustrated in FIG. 2A, the processing unit 31 includes a calculation unit 310 that calculates a light amount detected by the light detection element 2, a storage unit 311 that stores a target value of a preset light amount, and a calculation value. A setting unit 312 that sets the pulse width (or on-duty) of the current supplied to the LED 1 so as to be maintained at the target value, and the pulse signal Vo to the switching element 30 based on the pulse signal V 1 output from the setting unit 312. Is provided. Although only one operational amplifier 313 is shown in FIG. 2A, it is provided for each switching element 30. The processing unit 31 further includes a timer 314 for adjusting the output timing of the pulse signal V1 from the setting unit 312 to each operational amplifier 313.

  The calculation unit 310 outputs a calculation value for each LED 1 to the setting unit 312. The storage unit 311 stores a light amount target value as a target value preset for each LED 1. When the light detection element 2 detects other physical quantities related to light (for example, light flux, luminous intensity, luminance, illuminance, etc.), the calculation unit 310 calculates based on the physical quantities detected by the light detection element 2. I do. The storage unit 311 stores the target value of the physical quantity detected by the light detection element 2.

  The setting unit 312 compares the calculation value of the calculation unit 310 with the target value stored in the storage unit 311. The setting unit 312 that compares the calculated value and the target value sets the pulse width of the supply current to the LED 1 so that the calculated value is maintained at a preset target value for each LED 1. A pulse signal V 1 having a pulse width set by the setting unit 312 is output from the setting unit 312 to the operational amplifier 313.

  In the operational amplifier 313, the pulse signal V1 output from the setting unit 312 is input to the inverting input terminal (− terminal in FIG. 2A), and the LED 1 is switched to the non-inverting input terminal (+ terminal in FIG. 2A). A potential V2 between the elements 30 is input. From the operational amplifier 313, a pulse signal Vo having the same pulse width as the pulse signal V1 is output as the gate voltage of the switching element 30.

  Thereby, the control part 3 can perform feedback control for every LED1 so that the light quantity of LED1 may be maintained at a target value.

  The setting unit 312 sets all the periods of the pulse signals V1 output to the respective operational amplifiers 313 to T (time t1 to t7), but uses the timer 314 to start the pulse of the pulse signals V1 output to the respective operational amplifiers 313. Are shifted by 1/3 period. That is, the setting unit 312 outputs the other pulse signal V1 with a delay of one third period with respect to a certain pulse signal V1. Thereby, the control part 3 can perform PWM control with a time difference at the time of the pulse start of the supply current to each LED1, so that at least one LED1 always lights up during the lighting control of each LED1.

  In addition, the setting unit 312 has a period in which the two pulse signals V1 are turned on, while preventing all the pulse signals V1 from being turned on at the same time. As a result, the control unit 3 performs PWM with a time difference at the start of the pulse of the supply current to each LED 1 so that one LED 1 and the other LED 1 that starts lighting next to this LED 1 have a period during which they are simultaneously turned on. Can be controlled. At the same time, the control unit 3 starts the pulse of the supply current to each LED1 so that one or two (n-1 (n: total number of LED1)) LEDs1 are always lit during the lighting control of each LED1. Sometimes PWM control can be performed with a time difference.

  Next, the operation of the light emitting device of this embodiment will be described with reference to FIG. The control unit 3 drives each LED 1 by shifting the period of the supply current to each LED 1 to T (time t1 to t7) and shifting the pulse start time of the supply current to each LED 1 by (1/3) T. Hereinafter, it demonstrates in order. First, the controller 3 turns on the blue LED 1a for a pulse width T1 from time t1. Subsequently, the control unit 3 turns on the green LED 1b for a pulse width T2 from time t3. Thereafter, the blue LED 1a is turned off at time t4. From time t2 to t4, the total load of the power source DC is equivalent to one LED from time t2 to t3, and equal to two LEDs from time t3 to t4.

  Thereafter, the control unit 3 turns on the red LED 1c for a pulse T3 from time t5. Thereafter, the green LED 1b is turned off at time t6. From time t4 to t6, the total load of the power source DC is equivalent to one LED from time t4 to t5, and is equivalent to two LEDs from time t5 to t6. Thereafter, at time t7, the controller 3 turns on the blue LED 1a again. Thereafter, the red LED 1c is turned off. The total load of the power supply DC is equivalent to one LED at time t6 to t7, and is equivalent to two LEDs at time t7 to t8 (t1 to t2). Thereafter, the light emitting device of the present embodiment repeats the above-described operation, and performs PWM control on the supply current to each of the LEDs 1a to 1c.

  From the above, the light emitting device of the present embodiment can suppress the maximum number of LEDs 1 that are simultaneously turned on to two, and can also suppress the maximum change amount when the number of LEDs 1 that are turned on is increased or decreased by one LED.

  As described above, according to this embodiment, the control unit 3 always supplies at least one LED 1 from the power source DC by giving a time difference at the start of the pulse of the supply current to each LED 1 so that at least one LED 1 is lit. Since the current is supplied, it is possible to prevent the power source DC from being frequently switched between the no-load state and the load state during the lighting control of the LED 1, and as a result, the burden on the power source DC is reduced. be able to.

  Further, since it is possible to prevent the power supply DC from supplying current to all the LEDs 1 at the same time, the burden on the power supply DC can be further reduced. As a result, it is possible to use a power supply DC having an allowable current smaller than the sum of the supply currents to all the LEDs 1, 1, 1.

  Further, by having a period in which at least two LEDs 1, 1 are lit simultaneously, it is ensured that a period in which no current is supplied to all the LEDs 1, 1, 1 occurs when switching from one LED 1 to the next lit LED 1. Can be prevented.

  As a modification of the first embodiment, as shown in FIG. 2B, the operational amplifier 313 receives the pulse signal V1 output from the setting unit 312 at the non-inverting input terminal (the + terminal in FIG. 2B). The voltage V3 between the switching element 30 and the resistor 32 may be input to the inverting input terminal (-terminal in FIG. 2B). The same applies to Embodiments 2 to 5. Also in the connection configuration shown in FIG. 2B, the operational amplifier 313 outputs a pulse signal Vo having the same pulse width as the pulse signal V <b> 1 as the gate voltage of the switching element 30. However, it should be noted that the connection configuration shown in FIG. 2B is less efficient than the connection configuration shown in FIG.

(Embodiment 2)
The light emitting device of the second embodiment is different from the light emitting device of the first embodiment in that the control unit 3 shown in FIG. 1 switches between PWM control and current control as control of the supply current to each LED 1. In addition, about the component similar to Embodiment 1, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  In the storage unit 311 of this embodiment shown in FIG. 2A, individual minimum pulse width (or minimum duty) set for each LED 1 is stored. That is, the lower limit value of the pulse width of the current supplied to each LED 1 is defined. Specifically, the pulse width T2 shown in FIG. 4 is the minimum pulse width (time t3 to t9 in FIG. 4). In FIG. 4, only the minimum pulse width of the supply current to the green LED 1b is shown, but the minimum pulse width of the supply current to the blue LED 1a and the red LED 1c is also set.

  When the pulse width of the pulse signal V1 becomes the minimum pulse width when the supply current to the LED1 is PWM controlled for each LED1, the setting unit 312 shown in FIG. The voltage value of the pulse signal V1 is lowered while the pulse width is fixed to the minimum pulse width without making the pulse width of V1 smaller than the minimum pulse width. The pulse signal V1 having a low voltage value is output from the setting unit 312 to the operational amplifier 313.

  When the pulse signal V1 having a low voltage value is input, the operational amplifier 313 of this embodiment outputs the pulse signal Vo having a low voltage value to the switching element 30 in the same manner as the pulse signal V1.

  When the pulse signal Vo having a low voltage value is applied as the gate voltage, the switching element 30 of the present embodiment adjusts the current flowing between the source and the drain according to the height of the voltage value.

  From the above, when the pulse width of the supply current to the LED 1 becomes the minimum pulse width when the control unit 3 of the present embodiment performs PWM control on the supply current to the LED 1 for each LED 1, the control unit 3 returns to the LED 1. The supply current control can be switched from PWM control to current control. That is, when the pulse width becomes the minimum pulse width, the control unit 3 controls the supply current to the LED 1 while fixing the pulse width to the minimum pulse width.

  Further, when the current supplied to the LED 1 is under current control, if the current supplied to the LED 1 increases to the current value when switching from PWM control to current control, the control unit 3 The supply current control is switched from current control to PWM control.

  Next, the operation of the light emitting device of this embodiment will be described with reference to FIG. The basic operation is the same as that of the light emitting device of the first embodiment. Here, as shown in FIG. 4, when the pulse width T2 of the supply current to the green LED 1b becomes the minimum pulse width (time t3 to t9 in FIG. 4), control is performed to reduce the light amount of the green LED 1b. The case will be described. When the minimum pulse width of the green LED 1b is 45% of the period T and the green LED 1b requires 36% of the light amount for all lighting, the control unit 3 determines the pulse width of the supply current to the green LED 1b. T2 is fixed to the minimum pulse width, and the control of the current supplied to the green LED 1b is switched from PWM control to current control to reduce the current flowing through the green LED 1b. Thereby, the energy given to the green LED 1b is adjusted. Thereafter, when the current flowing through the green LED 1b increases to the current value at the time of switching from PWM control to current control, the control unit 3 switches the control of the supply current to the green LED 1b from current control to PWM control. The same applies to the blue LED 1a and the red LED 1c. The above operation is performed independently for each of the control of the supply current to the blue LED 1a, the control of the supply current to the green LED 1b, and the control of the supply current to the red LED 1c.

  As described above, according to the present embodiment, the individual minimum pulse width is set for each LED 1 and the pulse width of the supply current to each LED 1 is made smaller than the minimum pulse width, not by PWM control but by current control, The amount of change in the amount of light emitted from each LED 1 can be increased without leaving the power supply DC in an unloaded state.

(Embodiment 3)
In the light emitting device of the third embodiment, the control unit 3 shown in FIG. 1 sets the minimum pulse width of the LED 1 at the start of the pulse of the supply current to the LED 1 and the start of the pulse of the supply current to the other LED 1 that starts lighting next. It is different from the light emitting device of Embodiment 2 in that it is set to be equal to the time difference with time. In addition, about the component similar to Embodiment 2, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  In the present embodiment, as shown in FIG. 5, the minimum pulse width of the pulse width T2 of the current supplied to the green LED 1b is set to times t3 to t5. When the pulse width T2 becomes the minimum pulse width, the control unit 3 of the present embodiment switches the control of the current supplied to the green LED 1b from PWM control to current control. The same applies to the blue LED 1a and the red LED 1c.

  In the present embodiment, when the pulse width T2 becomes the minimum pulse width, unlike the case of the second embodiment, the total load of the power source DC remains unchanged for one LED at times t5 to t7. Although only the minimum pulse width of the supply current to the green LED 1b is shown in FIG. 5, the minimum pulse width of the supply current to the blue LED 1a and the red LED 1c is also set. Specifically, the minimum pulse width of the pulse width T1 is set to times t1 to t3, and the minimum pulse width of the pulse width T3 is set to times t5 to t7.

  Next, the operation of the light emitting device of this embodiment will be described with reference to FIG. The basic operation is the same as that of the light emitting device of the second embodiment. Here, as shown in FIG. 5, when the pulse width T2 of the current supplied to the green LED 1b becomes the minimum pulse width (time t3 to t5 in FIG. 4), control is performed to reduce the light amount of the green LED 1b. The case will be described. When the minimum pulse width of the green LED 1b is 33.3% of the period T and the light amount of 16.7% is necessary for all lighting in the green LED 1b, the control unit 3 supplies the green LED 1b. The current pulse width T2 is fixed to the minimum pulse width, and the control of the current supplied to the green LED 1b is switched from PWM control to current control, so that the current flowing through the green LED 1b is halved. Thereby, the energy given to the green LED 1b is adjusted. Thereafter, when the supply current to the green LED 1b increases to the current value at the time of switching from PWM control to current control, the control unit 3 switches the control of the supply current to the green LED 1b from current control to PWM control. The same applies to the blue LED 1a and the red LED 1c.

  As described above, according to this embodiment, the pulse width of the supply current to a certain LED 1 becomes the minimum pulse width by making the minimum pulse width equal to the time difference at the start of the pulse of the supply current to each LED 1. Since the change state of the load state of the power supply DC when switching from the LED 1 to the next lighting to 1 can be reduced and the load state of the power supply after the switch can be made constant, the burden of the power supply DC can be further reduced. .

(Embodiment 4)
As shown in FIG. 6, the light emitting device of the fourth embodiment is different from the light emitting device of the first embodiment (see FIG. 3) in that the pulse widths T <b> 1 to T <b> 3 of the current supplied to each LED 1 are different. In addition, about the component similar to Embodiment 1, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  In the present embodiment, the ratio of the pulse widths T1 to T3 is T1: T2: T3 = 2: 4: 3. At the start of the pulse of the supply current to each LED 1, it is adjusted according to the ratio of the pulse widths T1 to T3. That is, time t1 to t3: time t3 to t5: time t5 to t7 = 2: 4: 3. Accordingly, it is possible to prevent a period in which no current is supplied to all the LEDs 1, 1, 1, and to prevent a period in which a current is supplied to all the LEDs 1, 1, 1.

  As described above, according to the present embodiment, the pulse widths T1 to T3 of the supply current to each LED 1 are different, and the pulse start time of the supply current to each LED 1 is adjusted according to the ratio of the pulse widths T1 to T3. Even if it exists, there exists an effect similar to Embodiment 1. FIG.

(Embodiment 5)
As shown in FIG. 7, the light-emitting device of Embodiment 5 is different from the light-emitting device of Embodiment 1 (see FIG. 3) in that it includes a yellow LED that emits yellow light. At the start of the pulse of the supply current to the yellow LED, the time is t10, and the pulse width is T4. In addition, about the component similar to Embodiment 1, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  The control unit 3 of the present embodiment has a time difference at the start of a pulse of the supply current to each LED 1 so that one or two (n-1 (n: total number of light emitting means) or less) LEDs 1 are lit. PWM control. Therefore, the total load of the power source DC is equal to two LEDs at time t10 to t11, and equal to one LED at times t11 to t7.

  As mentioned above, according to this embodiment, even if it is a case where the number of LED1 becomes four, there exists an effect similar to Embodiment 1. FIG. Further, by providing the yellow LED, the color rendering property of white light can be enhanced.

  As a modification of the fifth embodiment, an orange LED that emits orange light may be provided instead of the yellow LED. Also in this case, the color rendering property of white light can be improved.

  Moreover, in Embodiments 1-5, LED1 is used as a light emission means, However, As a modification of Embodiments 1-5, you may use organic EL for a light emission means. Moreover, you may use for a light emission means the combination of LED and the fluorescent substance which is excited by the light radiated | emitted from this LED and radiates | emits the light of a different color.

  Furthermore, in Embodiments 1 to 5, one LED 1 is used as the light emitting means, but as a modification of Embodiments 1 to 5, a plurality of LEDs 1 that emit light having the same emission wavelength are connected in series. May be used as the light emitting means.

It is a circuit diagram of Embodiments 1-5. (A) is a circuit diagram of the control part in the light-emitting device which concerns on the same as the above, (b) is a circuit diagram of the control part in the light-emitting device which concerns on the modification same as the above. 3 is a time chart illustrating a supply current to each LED and a total load of a power source in the light emitting device according to Embodiment 1. 6 is a time chart showing a current supplied to each LED and a total load of a power source in the light emitting device according to Embodiment 2. 6 is a time chart showing a current supplied to each LED and a total load of a power source in the light emitting device according to Embodiment 3. 6 is a time chart showing a supply current to each LED and a total load of a power supply in the light emitting device according to Embodiment 4. 10 is a time chart showing a supply current to each LED and a total load of a power supply in the light emitting device according to Embodiment 5. It is a time chart which shows the total load of the supply current and power supply to each LED in the conventional light-emitting device.

Explanation of symbols

1 LED (light emitting means)
2 Light sensing element (detection means)
3 Control unit (control means)
30 switching element 31 processing section

Claims (5)

A plurality of light emitting means that are connected in parallel and each emit light having a different emission wavelength by a supply current from a power source;
Detecting means for detecting light emitted from the plurality of light emitting means;
Control means for PWM-controlling the current supplied to the light emitting means based on the detection result of the detecting means for each light emitting means,
The light emitting apparatus characterized in that the control means gives a time difference at the start of a pulse of a current supplied to each light emitting means so that at least one light emitting means is lit.   The control means sets an individual minimum pulse width for each light emitting means, and when the current supplied to the light emitting means is PWM controlled for each light emitting means, the pulse width of the supply current to the light emitting means is The control of the supply current to the light emitting means is switched from PWM control to current control in which the pulse width is fixed to the minimum pulse width and the magnitude of the supply current is changed when the minimum pulse width is reached. The light emitting device according to 1.   The control means makes the minimum pulse width of the light emitting means equal to the time difference between the start of the pulse of the supply current to the light emission means and the start of the pulse of the supply current to the other light emission means that starts lighting next. The light emitting device according to claim 2, wherein   2. The control unit according to claim 1, wherein a time difference is provided at the start of a pulse of a supply current to each light emitting unit so that one or more n-1 (n: total number of light emitting units) light emitting units are lit. 4. The light emitting device according to any one of 3.   The control means gives a time difference at the start of a pulse of a supply current to each light emitting means so as to have a period in which one light emitting means and another light emitting means that starts lighting next to the one light emitting means have a simultaneous lighting period. The light-emitting device according to claim 1 or 2.

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