JP2010244801A - Lighting device - Google Patents

Abstract

An illumination device capable of improving illumination efficiency while suppressing an increase in power consumption is provided.
A lighting device that drives a light emitting diode by PWM driving includes a plurality of light emitting diodes that satisfy a condition for causing a Broca-Sulzer effect, and each of the light emitting diodes is PWM driven at a different phase. Features.
[Selection] Figure 5

Description

  The present invention relates to a lighting device.

2. Description of the Related Art Conventionally, some lighting devices that use a light emitting diode (LED) as a light source employ a pulse drive such as PWM in order to suppress the amount of heat generated by the light emitting diode. When the light emitting diode is caused to emit light by pulse driving, there may be a case where flickering may be felt. Therefore, an LED that emits light by shifting the ON times of a plurality of light emitting diodes while partially overlapping each other has been proposed (for example, Patent Document 1). reference).
Similarly, when performing PWM dimming of a light emitting diode, there is an illuminating device that shifts the ON phases of a plurality of diodes from each other to prevent occurrence of uneven brightness and flicker (see, for example, Patent Document 2).

JP 2001-76525 A JP 2008-198430 A

  By the way, although the conventional lighting device described above can suppress flickering perceived by humans by shifting the phases of a plurality of light-emitting diodes, there is a problem that necessary brightness may not be obtained. This is because when the light emission of the light emitting diode is controlled by PWM control, the maximum value of the pulse wave is set to be the same, so that the brightness is proportional to the duty ratio, for example, the DC drive (duty 100%) is the brightest duty This is because the darker the ratio is.

Also, if the duty ratio is increased in order to increase the brightness of the light emitting diode, the power consumption per light emitting diode increases and the amount of heat generation increases, so the graph of FIG. 16 showing the temperature characteristics of the light emitting diode also shows. As can be seen, there is a problem in that it is necessary to enlarge the cooling structure of the light emitting diode because the relative light emission intensity is lowered and the illumination efficiency is lowered as compared with the case where the heat generation amount is small.
On the other hand, in order to further increase the efficiency of the lighting device, for example, when the human eye receives a strong light for a moment, the phenomenon of recognizing it brighter than the actual light amount (Broca-Sulzer effect) is applied to the light repeatedly. In recent years, research has been actively conducted.
However, when the light emitting diode is caused to emit light repeatedly, the apparent brightness improvement due to the above-described Broca-Sulzer effect tends to decrease as the duty ratio increases. When the duty ratio is increased in order to increase the brightness, the apparent brightness improvement due to the Broca-Sulzer effect cannot be expected, and the illumination efficiency may be reduced.

  This invention is made | formed in view of the said situation, and provides the illuminating device which can improve illumination efficiency, suppressing the raise of power consumption.

  In order to solve the above problems, the invention described in claim 1 is directed to a lighting device (for example, a lighting device in the embodiment) that drives a light emitting diode (for example, the light emitting diodes D1 to D4 in the embodiment) by PWM driving. 10 and 30), a plurality of light emitting diodes satisfying conditions for generating the Broca-Sulzer effect are provided, and each light emitting diode is PWM-driven at a different phase.

  According to a second aspect of the present invention, in the first aspect of the present invention, after the output of any one of the plurality of light emitting diodes falls due to the PWM drive, the other is caused by the next rise. The light emitting diodes are lit at intervals.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the plurality of light emitting diodes are arranged in a linear shape or a lattice shape.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, PWM driving is performed in a range of a driving frequency of 60 to 240 Hz and a duty ratio of 1 to 10%. To do.

  According to the first aspect of the present invention, since the plurality of light emitting diodes that satisfy the condition for generating the Broca-Sulzer effect are PWM-driven at different phases, the Broca-Sulzer effect is suppressed while suppressing flicker due to the PWM drive. Since the apparent brightness can be improved with the same power consumption as compared with the case where no occurs, there is an effect that it is possible to improve the illumination efficiency while suppressing the increase in power consumption.

    According to the invention described in claim 2, after the output of any one of the plurality of light emitting diodes falls, that is, when the light emitting diode is turned off, the other light emitting diodes are spaced apart. Since it is lit and opened, it is possible to prevent the illumination from flickering by PWM driving.

  According to the invention described in claim 3, there is an effect that it is possible to reduce a feeling of spatial flickering as a whole of the plurality of light emitting diodes.

  According to the fourth aspect of the present invention, flicker may occur when the drive frequency is lower than 60 Hz, and when the drive frequency is higher than 240 Hz, sufficient resolution can be obtained when the light emitting diode is PWM driven. Although it may not be possible, PWM drive of a light emitting diode can be easily performed, reducing a feeling of flicker by setting a drive frequency to 60-240 Hz. Further, by setting the PWM drive duty ratio to 1% to 10%, there is an effect that the illumination efficiency can be improved as compared with the case where the duty ratio exceeds 10%.

It is a circuit diagram which shows the structure of the illuminating device in 1st Embodiment of this invention. It is a figure which shows the attachment state of the light emitting diode in the illuminating device of 1st Embodiment of this invention, (a) is a side view of a board | substrate, (b) is a top view of a board | substrate. It is a timing chart which shows the waveform of the control signal which carries out PWM drive of the light emitting diode in the illuminating device of 1st Embodiment of this invention. It is the arrow line view which looked at the light emission output of the light emitting diode along the time series by the PWM drive in the illuminating device of 1st Embodiment of this invention from the A direction of FIG. It is a graph which shows an example set to the frequency of PWM drive 60Hz, and duty ratio 5% in the illuminating device of 1st Embodiment of this invention. It is the graph which made the gain ratio of PWM drive, and made the horizontal axis the duty ratio at the time of PWM drive. It is a figure which shows the experimental condition of the Broca-Sulzer effect, (a) is a side view, (b) is a front view. It is a figure equivalent to FIG. 2 in the modification of 1st Embodiment of this invention. It is a figure equivalent to FIG. 4 in the modification of 1st Embodiment of this invention. It is a circuit diagram which shows the structure of the illuminating device in 2nd Embodiment of this invention. It is a figure equivalent to FIG. 2 in 2nd Embodiment of this invention. It is a figure equivalent to FIG. 3 in 2nd Embodiment of this invention. It is a figure equivalent to FIG. 4 in 2nd Embodiment of this invention. It is a figure equivalent to FIG. 8 in 2nd Embodiment of this invention. FIG. 10 is a diagram corresponding to FIG. 9 in the embodiment of the present invention. It is a graph of the ambient temperature of a light emitting diode, and a relative luminous intensity.

Next, a lighting device according to a first embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a circuit configuration of a lighting device 10 according to the first embodiment. In the first embodiment, an illumination device including three light emitting diodes is shown as an example.
As illustrated in FIG. 1, the lighting device 10 includes, for example, a meter display of a vehicle such as an automobile, a side mirror winker, a high-mount stop lamp, a room light, and the like. The present invention is applied to various lamps such as a brake lamp, and includes a plurality of light emitting diodes D1 to D3. One end of a current limiting resistor R1 is connected to each of the light emitting diodes D1 to D3 on the anode side, and a switching element (for example, a P-channel shown in FIG. 1) that controls energization of the light emitting diodes D1 to D3 is connected to the cathode side. Sources of Q1 to Q3 are connected to each other. The other end of the resistor R1 is connected to the power source P, and the drains d1 to d3 of the switching elements Q1 to Q3 are connected to the ground E. That is, a circuit in which the resistor R1, the light emitting diode D1, and the switching element Q1 are connected in series, a circuit in which the resistor R1, the light emitting diode D2, and the switching element Q2 are connected in series, and the resistor R1, the light emitting diode D3, and the switching element Q3. Are connected in series between the power source and the ground.

  The gates G1 to G3 of the switching elements Q1 to Q3 are respectively connected to the control terminals PWM1 to PWM3 of the microcomputer 20 via the resistor R2. The microcomputer 20 includes a calculation unit (not shown) that performs PWM control of the light emitting diodes D1 to D3 by executing a predetermined program, and turns the switching elements Q1 to Q3 on and off via the control terminals PWM1 to PWM3. Control signal for output.

  Thereby, for example, when an ON signal is output as a control signal from the control terminals PWM1 to PWM3 and the ON signal is input to the switching element Q1, the current supplied from the power supply P is changed to the resistor R1, the light emitting diode D1, When the ON signal flows into the ground E through the switching element Q1 and an ON signal is input to the switching element Q2, the current supplied from the power source P is supplied to the ground E through the resistor R1, the light emitting diode D2, and the switching element Q2. Flows in. Further, when an ON signal is input to the switching element Q2, a current supplied from the power source P flows into the ground E through the resistor R1, the light emitting diode D3, and the switching element Q3.

  The light emitting diodes D1 to D3 have high-speed responsiveness such as a rise time of several hundreds ns and a fall time of several tens of μs, and satisfy the conditions for causing the Broca-Sulzer effect by continuous repeated flashing. Yes. Here, the Broca-Sulzer effect is a phenomenon in which the human eye recognizes brighter than the actual amount of light when it receives a strong light for a moment, but in the case of repeated flash, the apparent brightness is that of the flash. Since it is based on Talbot-Plateau's law that the intensity is a time-averaged value, it has been said that the Broca-Sulzer effect does not occur. "Improvement of effective brightness of LED", IEICE Technical Report, vol.108, no.277, EE2008-41, pp.35-40, October 2008, etc.) Flash light is repeatedly generated using a light emitting diode that satisfies the condition that the fall time is about several tens of μs. It has been confirmed that the apparent brightness due to the Broca-Sulzer effect is improved.

  As shown in FIG. 2, the light emitting diodes D1 to D3 are mounted vertically upward on the substrate B, and a flat imaging surface K is disposed above the light emitting diodes D1 to D3 in parallel with the substrate B. Has been. As shown in the timing chart of FIG. 3, the light emitting diodes D <b> 1 to D <b> 3 are PWM-driven by the microcomputer 20 with different phases. More specifically, any one of the light emitting diodes D1 to D3, for example, after the output of the light emitting diode D1 falls, until the next output of the light emitting diode D1 rises, other light emitting diodes, for example, light emission The diode D2 is turned on (rises) at an interval from the fall of the light emitting diode D1. In addition, after the output of the light emitting diode D2 falls, the light emitting diode D3 is lit at intervals from the falling of the light emitting diode D2 until the light emitting diode D2 rises next time.

  FIG. 4 shows an arrow view of the light emission outputs of the light emitting diodes D1 to D3 along the time series by the PWM drive as viewed from the direction A in FIG. As shown in FIG. 4, the light emitting diode D1 blinks once, the light emitting diode D2 blinks once, the light emitting diode D3 blinks once, and then the light emitting diode D1 blinks again to return to the light emitting diode. Flashes repeatedly in the order of D1, D2, and D3.

  FIG. 5 is a graph showing an example in which the output conditions of the control terminals PWM1 to PWM3 are set to a frequency of 60 Hz and a duty ratio of 5% in order to PWM drive the light emitting diodes D1 to D3. As shown in the graph of FIG. 5, when the output frequency of each of the control terminals PWM1 to PWM3 is set to 60 Hz, the phases are set so that the phases are shifted by 1/3 period. As a result, the blinking frequency of the entire light emitting diodes D1 to D3 viewed through the imaging plane K is 180 Hz as shown by PWMAll in FIG. 5, and the duty ratio for this frequency of 180 Hz is 15%.

  FIG. 6 is a graph in which the vertical axis represents the PWM drive gain, that is, the power saving due to the Broca-Sulzer effect for DC drive, and the horizontal axis represents the duty ratio during PWM drive. The graph shown in FIG. 6 was measured in the arrangement shown in FIG. 7, that is, in a state where a DC-driven light emitting diode and a PWM-driven light emitting diode are arranged 100 mm apart from each other at a position 1 m away from the subject. Is.

  The current of the DC drive light emitting diode can be adjusted by a knob (not shown) installed at the subject's hand, and the duty ratio of the PWM drive can be set with the subject looking directly at the two light emitting diodes 1 meter ahead. A predetermined value (1%, 5%, 10%, 20%, 30%) and a frequency are set to a predetermined value (60 Hz, 120 Hz, 180 Hz, 240 Hz), and the test subject determines the brightness of the PWM light emitting diode and the DC Adjust the knob so that the brightness of the driving light emitting diode feels the same brightness, measure the driving conditions (current, voltage) of the DC driving light emitting diode at that time, and compare with the PWM driving light emitting diode By processing, the gain of the PWM driving light emitting diode is obtained. In addition, as for the light emitting diode used for the said measurement, all used the yellow light emitting diode made from OSRAM (luminous intensity; 54000 mcd, wavelength; 587 nm, model number: DX1-Y2-L30W).

  As shown in FIG. 6, the PWM drive gain is gradually decreased from 1% to 5% in the average value (Ave) of each frequency, and then from 5% to 10%. It became almost flat. Then, the gain of PWM drive gradually decreased from around 20% to 20% and became the lowest gain at 20%. Then, the difference in gain between each frequency increases from the point where the duty ratio exceeds 10%. Moreover, the Broca-Sulzer effect was similarly recognized in all the frequencies in the frequency of the PWM drive set by the said measurement. It should be noted that when the duty ratio is 20% or more, according to the so-called Weber-Fechner rule in which the magnitude of the sense is proportional to the logarithm of the intensity of the stimulus, the difference in change by the subject becomes more difficult to perceive as the brightness increases. This is considered to be the cause of the large variation in gain.

  Therefore, according to the illuminating device 10 of 1st Embodiment mentioned above, since the several light emitting diodes D1-D4 which satisfy | filled the conditions which generate | occur | produce the Broca-Sulzer effect are each PWM-driven by a different phase, flicker by PWM drive is carried out. The apparent brightness can be improved with the same power consumption as compared with the case where the Broca-Sulzer effect does not occur while preventing the increase in power consumption, thereby improving the illumination efficiency.

  Further, after the output of any one of the plurality of light emitting diodes D1 to D3 falls, that is, when any one light emitting diode is turned off, the other light emitting diodes are turned on at intervals. Therefore, it is possible to prevent the illumination from flickering by PWM driving.

The present invention is not limited to the first embodiment described above. In the first embodiment described above, the case where the light emitting diodes D1 to D3 are erected vertically with respect to the substrate B has been described. However, as shown in the modified example of FIG. The upper ends of the two light emitting diodes D1 and D3 arranged on the outside are arranged so that the extension lines of the respective axes of the diodes D1 to D3 intersect on the imaging plane K. You may make it arrange | position to incline. As a result, when viewed through the image plane K, all of the light from the light emitting diodes D1 to D3 having relatively high directivity blinks at the approximate center in the upward direction of the light emitting diodes D1 to D3 arranged in series (see FIG. 9). ), It is possible to reduce the spatial flickering caused by the change in the shining position.
Further, although the case where three light emitting diodes are used has been described, three or more light emitting diodes may be arranged in a straight line so that the PWM phases are shifted from each other and blinked.

Next, a lighting device according to a second embodiment of the present invention will be described with reference to the drawings. Note that the illumination device of the second embodiment is the same as the illumination device of the first embodiment described above and the number and arrangement of the light emitting diodes are changed, and therefore the same parts are denoted by the same reference numerals.
FIG. 10 shows a circuit configuration of the illumination device 30 of the second embodiment. In addition to the circuit configuration of the lighting device 10 of the first embodiment described above, the circuit configuration of the lighting device 30 includes a circuit in which a resistor R1, a light-emitting diode D4, and a switching element Q4 are connected in series in this order. E is added in parallel between E. The microcomputer 40 includes a control terminal PWM4 in addition to the control terminals PWM1 to PWM3 of the microcomputer 20 described above, and can output a control signal for turning on / off the switching element Q4 via the control terminal PWM4. It has become.

  As shown in FIG. 11A, the four light emitting diodes D1 to D4 are erected on the substrate B along the vertical direction of the substrate B, and as shown in FIG. The two light emitting diodes D1 to D4 are arranged so as to have a lattice shape when viewed from above, that is, when the left and right adjacent light emitting diodes are connected by a line, they are arranged in a substantially rectangular shape. Above these light emitting diodes D <b> 1 to D <b> 4, a flat imaging surface K is arranged in parallel with the substrate B. Then, as shown in the timing chart of FIG. 12, these light emitting diodes D <b> 1 to D <b> 4 are PWM-driven by the microcomputer 40 with different phases.

  More specifically, as one of the light emitting diodes D1 to D4, for example, after the output of the light emitting diode D1 falls, the other light emitting diodes until the output of the light emitting diode D1 rises next time. For example, the output of the light emitting diode D2 rises at intervals from the falling of the light emitting diode D1. In addition, after the output of the light emitting diode D2 falls, the output of the light emitting diode D3 rises at an interval from the fall of the light emitting diode D2 until the next light emitting diode D2 rises. After the output falls, the output of the light emitting diode D4 rises at an interval from the fall of the light emitting diode D3 until the light emitting diode D3 rises next time.

  FIG. 13 shows the state of the light emission output of the light emitting diodes D1 to D4 by the PWM driving as seen through the imaging plane K. FIG. As shown in FIG. 4, the light emitting diode D1 blinks once, the light emitting diode D2 blinks once, and the light emitting diode D3 blinks once, and then the light emitting diode D4 blinks. Then, after the light emitting diode D4 blinks, the light emitting diode D1 returns to blinking again, and the light emitting diodes D1, D2, D3 and D4 are repeatedly blinked in this order.

  Therefore, according to the second embodiment described above, when the number of light emitting diodes is increased, even if the light emitting diodes are arranged in a lattice shape, that is, in a plane, the spatial flicker is reduced as in the first embodiment. be able to.

In the above-described second embodiment, the case where the light emitting diodes D1 to D4 are erected vertically with respect to the substrate B has been described. However, as shown in FIGS. The upper ends of the light-emitting diodes D1 to D4 may be provided so as to be inclined toward the approximate center when viewed from above so that the extension lines of the axes D1 to D4 intersect on the imaging plane K. As a result, when viewed through the imaging plane K, all the light of the light emitting diodes D1 to D4 having relatively high directivity blinks at the approximate center in the upward direction of the light emitting diodes D1 to D3 arranged in a lattice shape (FIG. 15). See), and it is possible to reduce the spatial flickering caused by the change in the shining position.

  Further, in the second embodiment described above, the case where four light emitting diodes are used has been described. However, four or more light emitting diodes may be arranged in a lattice pattern so that the PWM phases are shifted from each other and blinked.

Next, Example 1 of the illumination device of the present invention will be specifically described.
The first embodiment shows a case where it is applied to a car interior light as an example required to reduce flicker by PWM driving. The frequency, duty ratio, the number of light emitting diodes (LEDs), and the arrangement method in the first embodiment are shown. Each condition is shown below.

Here, the frequency and duty ratio in the above table are values per light emitting diode (LED), respectively, and the linear arrangement in the arrangement method is the linear arrangement (in the above-described first embodiment ( For example, refer to FIG.
When one light-emitting diode is PWM-driven under the above conditions, the same apparent brightness can be obtained with about 33% power consumption as compared with the case of DC driving.

  Therefore, the power consumption is equivalent to that of DC driving using three light emitting diodes, and each light emitting diode is PWM driven at different phases as in the first embodiment described above. As a result, the blinking frequency of the entire light emitting diode is 360 Hz, and thus flickering can be further prevented by the increase in frequency.

Furthermore, the following brightness-related effects can be obtained.
In the human visual system, it is known to integrate and perceive light temporally (Block's law). Although the block rule varies depending on the light stimulus presentation conditions, it is assumed that the rule is established if the presentation time is within a range of about 20 ms. When the indoor lamp is intermittently PWM driven within the range in which the block law is established, the time characteristics of the visual system can be effectively utilized by the number of the light emitting diodes. In Example 1, as described above, the blinking frequency of the entire light emitting diode is 360 Hz, and the duty ratio is 1 [%] × 3 [pieces] = 3%, so the presentation time is 8.3 ms or less. The block law is established, and three brightnesses can be perceived cumulatively.
Therefore, as a result, it is possible to realize about three times the brightness of the case where one light emitting diode is PWM-driven (same as the brightness at the time of DC driving) with the same power consumption as that of DC driving.

Next, a second embodiment of the lighting device according to the present invention will be specifically described.
The second embodiment is a case where the present invention is applied to a winker of an automobile as an example in which sufficient brightness is required. The conditions of frequency, duty ratio, number of light emitting diodes (LEDs), and arrangement methods in the second embodiment are as follows. Shown in

Here, the frequency and duty ratio in the above table are values per light emitting diode (LED), respectively, as in the first embodiment, and the linear arrangement in the arrangement method is the first implementation described above. This means a linear arrangement of forms (see, for example, FIG. 2).
When one light emitting diode is PWM-driven under the above conditions, the same apparent brightness can be obtained with about 50% power consumption as compared with the case of DC driving.

  Therefore, the power consumption is equivalent to that of DC driving using two light emitting diodes, and each light emitting diode is PWM driven at different phases as in the second embodiment described above. As a result, the blinking frequency of the entire light emitting diode is 240 Hz, so that flickering can be prevented as the frequency increases.

Further, when the winker is PWM-driven, the overall duty ratio is 3 [%] × 2 [pieces] = 6%, so that the brightness is further increased by the block law as described above, so that the DC drive It is possible to obtain twice or more brightness as in the case of. In Example 2, the brightness magnification is as low as 2 times or more compared to 4 times or more of Example 1 described above, but the duty ratio per light emitting diode is set to be about 3 times larger. Therefore, the overall apparent brightness of the winker of the second embodiment is larger than that of the room light of the first embodiment.
In the case where two light emitting diodes are arranged as in the second embodiment described above, for example, two light emitting diodes are arranged in an inclined manner like the three light emitting diodes D1 and D3 shown in FIG. The same result can be obtained even if the upper end portion is arranged close to the intermediate position of each light emitting diode.

D1, D2, D3, D4 Light emitting diode 10 Lighting device 30 Lighting device

Claims (4)

In an illumination device that drives a light emitting diode by PWM drive,
A plurality of light emitting diodes satisfying the conditions for producing the Broca-Sulzer effect are provided,
Each of the light emitting diodes is PWM-driven with a different phase.   The output of any one of the plurality of light emitting diodes falls by the PWM drive, and then the other light emitting diodes are lit at intervals until the next rise. The lighting device according to 1.   The lighting device according to claim 1, wherein the plurality of light emitting diodes are arranged in a straight line shape or a lattice shape.   4. The lighting device according to claim 1, wherein PWM driving is performed in a range of a driving frequency of 60 to 240 Hz and a duty ratio of 1 to 10%.

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