JP2007171364A - Visible light led light source apparatus, image projection system using the same, and method of driving visible light led - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the reliability by reducing the brightness reduction of a visible light LED due to heat-generation in the case of successively lighting a plurality of visible light LEDs, projecting the light on a display medium and displaying an image, in a visible light LED light source apparatus, an image projection system using the light source and a method of driving the visible light LED. <P>SOLUTION: Regarding the illumination unit 2 for projecting the light on a reflection type screen 6 and displaying the image, the unit 2 includes: the LED 22 composed of LED chips 22R, 22G and 22B; and a lighting control means 70 for successively lighting the LED chips while dividing the lighting time domain of the LED chips in a periodical fixed time slot. The lighting control means 70 includes a waveform pattern arithmetic formation part for forming a modulation signal of lighting at least one of the LEDs chips 22R, 22G and 22B with a lighting duty smaller than the lighting time range thereof. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a visible light LED light source device, an image projection system using the same, and a visible light LED driving method. For example, the present invention relates to an apparatus that displays an image by projecting light onto a display medium such as a reflective screen or a transmissive screen.

Conventionally, for example, LEDs used as light sources in image projection systems such as projectors, rear projection televisions, and projectors are often driven by a pulse lighting system.
For example, when a full-color image is projected using LEDs that emit light of the three primary colors red (R), green (G), and blue (B), R, G, and B are sequentially time-divisionally lit. In addition, there is known one that spatially modulates with an image signal corresponding to each color.
In Patent Document 1, an image processing apparatus that captures an image of an object and performs image processing and an electronic component mounting apparatus including such an image processing apparatus include a plurality of LEDs as light sources, and performs pulse width modulation on them. A device including an LED drive circuit for adjusting the luminance of emitted light is described.
Further, as a technology related to the LED drive circuit, Patent Document 2 discloses a current detection unit that generates a triangular wave load current having an offset in an LED drive circuit that drives an LED used for vehicle illumination or a signal lamp. In addition, an LED drive circuit is described in which the LED is driven at a substantially constant current by turning on and off the switch means at an oscillation frequency faster than the response of human eyes by the switch control means.
Japanese Patent Laying-Open No. 2005-149132 (FIGS. 2 and 4) Japanese Patent Laying-Open No. 2005-5112 (FIGS. 1, 2, and 3)

However, the above-described conventional visible light LED light source device, the image projection system using the same, and the visible light LED driving method have the following problems.
Since the LED causes a decrease in output due to self-heating, if the lighting time is increased in order to obtain high brightness, the light emission efficiency is lowered, and the life is also affected.
For example, an LED light source device that collects and arranges LEDs having R, G, and B wavelengths to obtain white light has a problem in that the luminance is more likely to be lowered because the self-heating of the LEDs is easily affected. In addition, there is a problem that it is difficult to maintain a balance between luminance at the time of driving and reliability over time because the temperature characteristics are different for each color and the luminance reduction rate and life characteristics are different accordingly.
Although it is conceivable to adjust the brightness using the technique described in Patent Document 1, this technique describes a general configuration for modulating the pulse width of an LED, but is used as a light source for imaging. Is measured, and conditions for pulse width modulation are set so that exposure energy corresponding to a predetermined brightness can be obtained.
When applied to a visible light LED light source device that sequentially displays R, G, and B light and displays an image on a display medium such as a reflective or transmissive screen, the necessary exposure energy is pulse-width modulated and irradiated. For this reason, it is necessary to extend the sequential lighting cycle by the off duty. As a result, there is a problem that the color switching frequency is lowered, and flickering feeling is increased, for example, and the image quality may be lowered.
In addition, as a technique related to the LED drive circuit, the technique described in Patent Document 2 performs modulation of an oscillation frequency faster than the response of the human eye in the LED drive circuit of the LED used for vehicle lighting or signal lights. Thus, it is suggested that even if a ripple is superimposed on the driving current in the rectangular wave, it is equivalent to driving at a substantially constant current, but an LED driving circuit and method for reducing LED luminance reduction are described. Or it is not suggested.

  The present invention has been made in view of the above problems, and in the case where an image is displayed by sequentially lighting a plurality of visible light LEDs and projecting light onto a display medium, the luminance due to the heat generated by the visible light LEDs. It is an object of the present invention to provide a visible light LED light source device capable of reducing deterioration and improving reliability, an image projection system using the same, and a driving method of the visible light LED.

In order to solve the above-described problems, a visible light LED light source device according to the present invention includes a light source unit including a plurality of visible light LEDs and a plurality of visible lights for projecting light onto a display medium to display an image. A visible light LED light source device having a lighting control means for sequentially lighting an LED by dividing each lighting time region in a periodic fixed time zone, wherein the lighting control means includes at least the visible light LED. A driving signal modulation unit that generates a modulation signal for lighting one with a lighting duty smaller than the lighting time region width is provided.
According to the present invention, since at least one visible light LED is turned on with a lighting duty smaller than the lighting time region width by the modulation signal generated by the drive signal modulation unit, at least one visible light LED has 100% duty. The duration of self-heating is reduced compared to the case where the lamp is turned on, and heat is dissipated during off-duty when the lamp is turned off within the lighting time region. Therefore, the temperature of the light source unit can be reduced.
In this case, the light is turned off at off-duty, but in human vision, light stimulation lasts for a certain period of time in accordance with the luminance level of light and maintains a so-called afterimage. Therefore, the luminance level and the time width of off-duty are set appropriately. Thus, it is possible to prevent the dark change during this period from being detected. For this reason, the human eye observes an image that is the same as when the visible light LED is continuously lit.
For example, in the case of an LED light source device of an image projection system that sequentially lights up light corresponding to R, G, and B and displays a full color image, a certain period of switching RGB is perceived as a mixture of colors by human vision. Since the time width is set, even if an off-duty shorter than that is provided, as long as an appropriate luminance level is set, darkness is not detected.
Also, if the off-duty interval is sufficiently small, the difference between the physical luminance integral value and the brightness perceived by the human eye will be large, and the human eye will exceed the actual physical luminance integral value. It feels bright.
Here, the lighting duty means the ratio of the lighting time to the time width of the lighting time region, and the waveform of the modulation signal is not limited to a rectangular wave.
Also, the integral value of the modulation signal in the lighting time region is preferably set to be smaller than the integral value of the modulation signal with 100% duty. In this case, since the heat generation amount of the visible light LED is reduced as compared with the case of 100% duty, it is possible to more efficiently suppress the luminance decrease.

In addition, the image projection system of the present invention is configured using the visible light LED light source device of the present invention.
According to this invention, since the visible light LED light source device of the present invention is used, the same effects as the visible light LED light source device of the present invention are provided.

Further, the visible light LED driving method of the present invention is a visible light LED driving method for sequentially lighting a plurality of visible light LEDs by dividing each lighting time region within a periodic fixed time zone, A method of lighting at least one of the visible light LEDs with a lighting duty smaller than the lighting time region width is used.
According to the present invention, the visible light LED light source device of the present invention is used to turn on the visible light LED, so that the same effects as the visible light LED light source device of the present invention are provided.

  According to the visible light LED light source device of the present invention, the image projection system using the same, and the driving method of the visible light LED, the duration of self-heating is longer than when at least one visible light LED is turned on with 100% duty. Therefore, it is possible to dissipate heat during off-duty when the light is turned off, so that the reduction in luminance due to heat generation of the visible light LED can be reduced and the reliability can be improved.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In all the drawings, even if the embodiments are different, the same or corresponding members are denoted by the same reference numerals, and common description is omitted.

[First Embodiment]
A visible LED light source device according to a first embodiment of the present invention will be described together with an image projection system using the same.
FIG. 1 is a schematic diagram showing a schematic configuration of an image projection system using a visible light LED light source device according to the first embodiment of the present invention. FIG. 2 is a functional block diagram illustrating a schematic configuration of the visible light LED light source device according to the first embodiment of the present invention. FIG. 3 is a timing chart for explaining an outline of modulation signals of a plurality of visible light LEDs in the first embodiment of the present invention. FIG. 4 is a signal waveform diagram for explaining a detailed waveform pattern of the modulation signal of the visible light LED in the first embodiment of the present invention.

The projector 1 is an image projection system that projects, for example, a full-color image corresponding to an external signal on the reflective screen 6 using the illumination unit 2 that is the visible light LED light source device of the present embodiment.
The schematic configuration of the projector 1 includes an illumination unit 2, a condenser lens 3, a spatial modulation element 4, a projection lens 5, and a control unit 10 that controls the entire system.

The illumination unit 2 sequentially generates light of wavelengths corresponding to at least the three primary colors R, G, and B at a time-division timing in order to display a full-color image.
The condensing lens 3 is an optical element that condenses the light generated by the illumination unit 2 in a modulation region on the spatial modulation element 4.

The spatial modulation element 4 spatially modulates the light collected by the condenser lens 3 in accordance with an image signal of wavelength light corresponding to the irradiation timing, and displays a color-separated image. The drive is controlled by. As the spatial modulation element 4, for example, a liquid crystal display device (LCD) is used as a transmission type element, and a digital micromirror device (DMD, Digigal Micromirror Device) or a reflection type liquid crystal panel (LCOS) is used as a reflection type element. , Liquid Crystal On Silicon) can be used.
The projection lens 5 is an optical element that magnifies and projects the image displayed by the spatial modulation element 4 onto the reflective screen 6.

A detailed configuration of the illumination unit 2 will be described.
As shown in FIGS. 1 and 2, the illumination unit 2 includes an LED 22, an LED driver circuit unit 21, a current detection unit 23, a waveform pattern calculation generation unit 24, and a power supply circuit unit 20 that supplies a drive current to the LED 22.

  The LED 22 is a visible light emitting element in which LED chips 22R, 22G, and 22B that emit light of R, G, and B wavelengths, which are the three primary colors of light, are collectively arranged in a range where they thermally affect each other. .

The LED driver circuit unit 21, the current detection unit 23, and the waveform pattern calculation generation unit 24, based on the lighting clock transmitted from the control unit 10, LED chips 22R, 22G, 22B (hereinafter, These are collectively referred to as “chips” in some cases, and the lighting control means 70 is configured to divide the lighting time regions into respective lighting time regions and sequentially turn them on.
The lighting clock is a clock for acquiring timing for setting a periodic constant time period for sequentially lighting each LED chip, and a frequency similar to that of the prior art, for example, a frequency of about 180 Hz to 360 Hz may be adopted. it can. In this embodiment, the lighting basic frequency f ₀ = 240 Hz is adopted.

  The LED driver circuit unit 21 switches the drive current supplied from the power supply circuit unit 20 according to the modulation signals 30R, 30G, and 30B transmitted from the waveform pattern calculation generation unit 24, and the LED chips 22R, 22G, and 22B. Is a drive circuit for independently driving each other.

  The current detection unit 23 generates a control signal for setting the maximum value of the light emission amount of each chip of the LED 22 to be held at a predetermined value by detecting the current flowing through each chip of the LED 22 at a constant timing. This is sent to the waveform pattern calculation generation unit 24.

The waveform pattern calculation generation unit 24 divides the lighting time regions of the respective chips of the LEDs 22 within a certain time zone set by the lighting clock, and the lighting duty smaller than the lighting time region width within each lighting time region. A modulation signal that is turned on is generated.
In the present embodiment, as shown in FIG. 3, the LED chips 22R, 22G, and 22B are connected within one cycle T ₀ = 1 / f ₀ (= t ₄ −t ₁ ) set at the lighting basic frequency f ₀ . Modulation signals 30R, 30G, and 30B that are sequentially time-division driven are generated. That is, the time t _{1 to} t ₂ , the time t _{2 to} t ₃ , and the time t _{3 to} t ₄ are the lighting time regions of the R, G, and B wavelength lights (where t ₁ <t ₂ < t ₃ <t ₄ ).
These lighting time region widths are appropriately set in consideration of the temperature characteristics of each chip. Assuming that T _R = t ₂ −t ₁ , T _G = t ₃ −t ₂ , and T _B = t ₄ −t ₃ , in this embodiment, the temperature characteristics of the LED chips 22G and 22B are approximately the same, Since the temperature characteristics of the LED chip 22R are remarkably deteriorated, for example, T _R / T ₀ = 20%, T _G / T ₀ = 40%, and T _B / T ₀ = 40% are set.

If lighting is performed with 100% duty in such a lighting time region, the lighting control is similar to the time-division lighting according to the prior art. That is, in the prior art, by lighting up such a lighting time region with 100% duty, the duty ratios at the lighting basic frequency f ₀ are T _R / T ₀ , T _G / T ₀ , and T _B / T, respectively. ₀ become such a pulse width modulation is performed. The drive current of each chip with respect to the signal level is set so that the light energy density on the reflective screen 6 becomes a desired value with this duty ratio.

Modulated signal 30R of this embodiment, 30G, 30B, as shown in FIG. 4, such at the lighting fundamental frequency f lighting time of the pulse width modulation ₀ area, lighting the fundamental frequency f ₀ from the high frequency of the burst frequency f _This is a modulation signal for performing pulse width modulation by _b . Times t _S and t _E in the figure indicate the start and end times of the lighting time region, respectively.
The burst frequency f _b and the duty ratio can be appropriately set by conducting an experiment or the like, for example, in relation to the luminance reduction amount due to self-heating and the brightness perceived by the human eye, which will be described later. However, the burst frequency f _b is the least the lighting time region width, it is preferable that the number of two or more pulses with high frequency, such as those generated.
For example, the setting conditions for the pulse width modulation by the burst frequency f _b may be such that f _b = 20 · f ₀ , the period T _b = 1 / f _b , and the duty ratio is 50%.
Under this condition, the driving power required for driving the LED 22 is ½ compared to the case of 100% duty. Further, the number of pulses within the lighting time region width is, for example, four in the case of the modulation signal 30R of R wavelength light having the shortest lighting time region width in the present embodiment.
The peak value I ₀ can be set in the same manner as in the above prior art, and for example, has a signal level at which the drive current is 1.5A.
These modulation signals are also sent to the control unit 10 in order to generate a timing signal for driving the spatial modulation element 4.

The operation of the projector 1 will be described focusing on the operation of the illumination unit 2 of the present embodiment.
FIG. 5 is a schematic graph for explaining the temporal response of the human eye to the light stimulus. FIG. 6 is a schematic graph for explaining a decrease in luminance of the LED.

When the control unit 10 of the projector 1 receives an image signal color-separated into R, G, and B from the outside, it sends a lighting clock to the illumination unit 2.
In the lighting unit 2, modulation signal 30 R, 30 G, 30 B is generated by the waveform pattern calculation generation unit 24, and is sent to the LED driver circuit unit 21, so that each modulation signal is transmitted to the LED chips 22 R, 22 G, 22 B of the LED 22. A corresponding drive current is supplied, and each chip is driven to emit light according to the waveform pattern and timing of each modulation signal.
On the other hand, these modulation signals are also sent to the control unit 10, and a timing signal for modulation of the spatial modulation element 4 is generated. Therefore, the drive timing of the spatial modulation element 4 is synchronized with the lighting time region of the R, G, B wavelength light from the LED 22, and the spatial modulation element 4 is time-division driven corresponding to the image signal corresponding to each color. The
Therefore, the R, G, and B light emitted from the illumination unit 2 is collected by the condenser lens 3 and spatially modulated by the spatial modulation element 4 to display a color separation image corresponding to each color. Then, the image displayed on the spatial modulation element 4 is magnified by the projection lens 5 and projected onto the reflective screen 6. Since this color separation image appears to be synthesized by human eyes, the observer can observe a full-color image by viewing the color sequential reflected light on the reflective screen 6.

Next, the reason why even if the pulse width modulation is performed with a duty ratio smaller than 100% within the lighting time region equivalent to the prior art, the decrease in luminance becomes a problem and the reason why it can be used as illumination light will be described.
Certainly, in this embodiment, since the duty ratio is set to 50%, the integrated light quantity is reduced. Therefore, for example, when used as a light source for a printer or the like that exposes a photosensitive member having a constant exposure sensitivity, the exposure energy decreases as the duty ratio decreases.
However, in the case of a visible light LED light source device that displays an image by projecting visible light onto a display medium such as a reflective screen or a transmissive screen, human beings have different physical brightness. Focusing on the fact that light should be emitted so as to be equivalent to vision, the present invention has been made through extensive research.

When human eyes receive a light stimulus, they feel that the light stimulus continues for a certain amount of time. This is known as a so-called afterimage phenomenon. FIG. 5 schematically shows how the sensory light intensity _IV decays with time after looking at the light having the impulse-like emission intensity I _i . That is, as shown by the curve 100, the change initially attenuates slowly and then rapidly decreases.
It is due to such an afterimage phenomenon that white light that is mixed by sequential lighting of RGB is felt. However, although color mixing occurs at the frequency actually used in the projector, the integrated light quantity and the light intensity perceived by the eyes are not significantly different. This is because white balance is lost when the R, G, and B lighting time region widths are changed, or white light emission that simultaneously lights up R, G, and B light after RGB lighting to increase the apparent brightness of the image. This is easily understood from the fact that
We, the gradually increasing as compared to the burst frequency f _b to the lighting fundamental frequency f _0, the influence of the afterimage is remarkably increased, the human eye detection accuracy for the integral light amount is dull results from integration quantity It is found that the image can be felt brightly, and the modulation signal as in the present embodiment has been conceived.

In addition, according to the present embodiment, in view of luminance reduction due to self-heating, the physical integrated light quantity is more advantageous than the conventional technique, and this point will also be described.
FIG. 6 schematically shows how the brightness decreases due to self-heating of the LEDs. The horizontal axis represents the lighting time, and the vertical axis represents the luminance P.
Because when the LED continuously emitting LED is temperature rises by self-heating, under constant drive current, as shown by curve 101, the light emitting luminance is reduced from the initial brightness P _i in accordance with the temperature characteristics the LED. When the LED temperature reaches equilibrium, the brightness converges to a constant value.
Accordingly, when the lighting time width is turned on with the pulse widths of t ₁₀ and t ₂₀ (where t ₁₀ <t ₂₀ ), the respective luminance decrease amounts, ΔP ₁₀ and ΔP ₂₀ are ΔP ₁₀ <ΔP _20. . Further, the calorific value, since increases with lighting time, who also t ₁₀ time required for heat dissipation is less time. Therefore, if the total sum of the lighting times is the same, the effect of lowering the luminance is less when the high-frequency pulse width modulation is performed, so that more efficient lighting can be performed with respect to the same driving power.
This difference is particularly noticeable in image projection systems such as projectors and rear projection televisions that require high-intensity illumination light.

Thus, in the modulated signal of the present embodiment, in the prior art the same lighting time domain, a smaller duty ratio than 100%, the burst frequency f _b is lit fundamental frequency f ₀ from sufficiently high frequency pulse By performing the width modulation, it is possible to reduce an apparent light amount decrease by using a light amount sensitizing action for human eyes, and to suppress a physical luminance decrease due to self-heating. Therefore, since the temperature of the LED 22 can be reduced, the reliability of the LED 22 can also be improved.

As described above, in the visible light LED device according to the present embodiment, the drive signal modulation unit generates a modulation signal that pulse-width modulates at least one of the visible light LEDs within the lighting time region. .
In this case, luminance reduction can be reduced with a simple configuration that only changes the settings of the pulse width and the duty ratio.

[Second Embodiment]
A visible light LED light source device according to a second embodiment of the present invention will be described.
FIG. 7 is a signal waveform diagram illustrating a detailed waveform pattern of a modulation signal of the visible light LED light source device according to the second embodiment of the present invention.

  As shown in FIGS. 1 and 2, the illumination unit 200 of the present embodiment is a visible light LED light source device that can be suitably used for the projector 1 instead of the illumination unit 2 of the first embodiment. In place of the waveform pattern calculation generation unit 24 of the unit 2, a waveform pattern calculation generation unit 240 which is a drive signal modulation unit is provided. Hereinafter, a description will be given focusing on differences from the above embodiment.

The waveform pattern calculation generation unit 240 used in the illumination unit 200 is different in that it generates modulation signals 40R, 40G, and 40B instead of the modulation signals 30R, 30G, and 30B of the waveform pattern calculation generation unit 24, respectively.
As shown in FIG. 3, the lighting timings of the modulation signals 40R, 40G, and 40B are set in the respective lighting time regions in the same manner as in the first embodiment.
In these detailed waveform patterns, as shown by a curve 102 in FIG. 7, the signal level from the lighting start time t ₁ to t ₂ is I _p , and the signal level from time t ₂ to t ₃ is I _0. Thus, the waveform pattern performs stepwise power modulation. Here, the times t ₁ , t ₂ , and t ₃ are in a relationship of t ₁ <t ₂ <t ₃ <t ₄ , where T _R (T _G , T _B ) = t ₄ −t ₁ . Further, I _p > I ₀ .
The peak value I _p , the stepped lighting duty (t ₂ -t ₁ ), and (t ₃ -t ₁ ) are necessary, for example, by conducting experiments on the amount of decrease in luminance and the change in sensory luminance for the human eye. It can be set appropriately depending on the situation. However, the peak value _Ip is set so as not to exceed the maximum limit of the drive current and its application time that affect the life of the LED 22.

In order to describe the operation of such modulated signals 40R, 40G, and 40B, for example, I _p = 2 · I ₀ , (t ₂ −t ₁ ) = (1/3) · (t ₄ −t ₁ ), ( _{t 3 -t 1) = (2/3} ) · ( consider the case of employing the t 4 -t ₁₎ settings.
In this case, the amount of heat generation may be the same as that of the modulation signal 41 for lighting the lighting time region of each color with 100% duty at the signal level I ₀ as shown by the curve 103 in FIG.
The state of luminance reduction when the LED 22 is driven by the modulation signal and the modulation signal 41 of this embodiment is schematically shown as curves 104 and 105 in FIG. Although shown on the waveform after T _{0 for} the convenience of illustration, the following description will be made ignoring the difference of T ₀ .
Because the modulated signal of this embodiment is driven by the peak value I _p at the start of lighting, the brightness becomes the maximum value indicated by point a, between times t ₁ ~t _2, for example, the point in accordance with the curve 101 of FIG. 6 It decreases to b. Then, from time t ₂ to t ₃ , since it is driven at a signal level I ₀ which is half of I _p , the amount of heat generation is halved and falls to point c with a width smaller than the luminance reduction rate from point a to b, the brightness _{P 1.} It is turned off at times t _{3 to} t ₄ . However, the human eye is retained brightness P ₁ to some extent, it is not able to detect the off.
On the other hand, in the case of the modulation signal 41, since it is driven at the peak value I ₀ from the time t _{1 to} t ₄ , as shown by the curve 105, the lighting is started at the luminance of the point e which is half of the point a. ₄ −t ₁ ), the luminance is reduced to the point f according to FIG. 6, and the lighting ends at the luminance P ₂ (where P ₂ <P ₁ ).
For this reason, although the amount of heat generation is the same, the modulation signal of this embodiment clearly has a lower luminance reduction rate than the modulation signal 41, and it feels brighter due to the afterimage phenomenon of the human eye.
Above, for convenience of explanation, the heat generation amount is described in case the same, the peak value I _p of the signal _level, by appropriately setting t _2, t _3, also as a waveform pattern as to reduce the amount of heat generated Needless to say, it is good.

Thus, in the visible light LED light source device of the present embodiment, the drive signal modulation unit generates a modulation signal that performs power modulation having a peak value in the first half of the lighting time region of at least one of the visible light LEDs. It is supposed to be.
In this case, the maximum luminance is obtained in the first half of the lighting time region in a state where heat storage due to self-heating is relatively small, so that the light emission efficiency is good and high luminance driving is possible.
Further, in the visible light LED light source device of the present embodiment, the modulation signal for performing the power modulation has the peak value at the modulation start timing and a waveform pattern that monotonously decreases with time.
In this case, since it has a peak value at the modulation start timing and then attenuates the signal level, the amount of heat generation decreases monotonously, and the luminance reduction can be efficiently suppressed.
Here, monotonic decrease means a monotonic decrease in a broad sense, and includes a step-like decrease having a constant value region.

Next, a modification of this embodiment will be described.
FIG. 8 is a signal waveform diagram illustrating a detailed waveform pattern of the modulation signal of the visible light LED light source device according to the modification of the second embodiment of the present invention.

In this modification, the modulation signals 50R, 50G, and 50B shown in FIG. 8 are used instead of the modulation signals 40R, 40G, and 40B.
Modulated signal 50R, 50G, 50B is the peak value of the signal level _{I q,} the time _t 1 ~t _{5 (however, t 1 <t 5 <t} 4) the signal level until up to _{I r,} linear It has a trapezoidal waveform pattern that decreases to (I _r <I ₀ <I _q ).
The peak value I _q , the signal level I _r , and the lighting duty (t ₅ −t ₁ ) are appropriately set as necessary by conducting experiments on the amount of decrease in luminance and the change in sensory luminance for human eyes, for example. be able to. However, the peak value I _q is set so as not to exceed the maximum limit of the drive current and its application time that affect the life of the LED 22.
This modification is another example of a waveform that monotonously decreases from the peak value, and has the same effect as described above.

  In the above description, the present invention is described as being applied to all the R, G, and B modulation signals. However, it may be applied to at least one depending on the amount of self-heating and the degree of mutual influence. That is, the visible light LED that is less self-heated and less affected by the decrease in luminance may be lit at 100% duty.

  In the above description, the example in which three visible light LEDs are provided has been described. For example, two R, G, and B LEDs may be provided. In addition, the plurality of visible light LEDs may not have a configuration integrated as a single element as long as they are thermally affected by each other.

  In the above description, an example in which one cycle of the lighting basic frequency coincides with a periodic constant time zone has been described, but the timing at which a plurality of visible light LEDs are simultaneously turned on within one cycle of the lighting basic frequency. May be provided. For example, in order to increase the apparent brightness of the image, a timing for simultaneously lighting R, G, and B may be provided.

  In the above description, an example of a projector that displays an image on a reflective screen has been described as the image projection system. However, a projector that displays an image by projecting light onto a transmissive screen may be used. For example, a rear projection television may be used.

  In the above description, as an example of using the visible light LED light source device of the present invention, an example in the case of using it in an image projection system has been described. However, light is projected onto a display medium such as a reflective screen or a transmissive screen. If there is, it can be used not only as a device for projecting an image, but also as a part of an appropriate illumination device or light projection device.

  Further, the constituent elements described in each of the above embodiments can be appropriately combined and implemented within the scope of the technical idea of the present invention, if technically possible.

Here, a case will be described where the names of the correspondence relationships between the terms of the above embodiments and the terms of the claims are different.
The projector 1 is an embodiment of an image projection system. The illumination units 2 and 200 are an embodiment of a visible light LED light source device. LED22 is one Embodiment of a light source part. The LED chips 22R, 22G, and 22B are an embodiment of a visible light LED. The waveform pattern calculation generation units 24 and 240 are an embodiment of the drive signal modulation unit.

It is a schematic diagram which shows schematic structure of the image projection system using the visible light LED light source device which concerns on the 1st Embodiment of this invention. It is a functional block diagram explaining schematic structure of the visible light LED light source device which concerns on the 1st Embodiment of this invention. It is a timing chart explaining the outline of the modulation signal of several visible light LED in the 1st Embodiment of this invention. It is a signal waveform diagram explaining the detailed waveform pattern of the modulation signal of visible light LED in the 1st Embodiment of this invention. It is a typical graph for demonstrating the time response of the human eye with respect to a light stimulus. It is a typical graph explaining the brightness fall of LED. It is a signal waveform diagram explaining the detailed waveform pattern of the modulation signal of the visible light LED light source device which concerns on the 2nd Embodiment of this invention. It is a signal waveform diagram explaining the detailed waveform pattern of the modulation signal of the visible light LED light source device which concerns on the modification of the 2nd Embodiment of this invention.

Explanation of symbols

1 Projector (image projection system)
2,200 Illumination unit (visible LED light source device)
DESCRIPTION OF SYMBOLS 3 Condensing lens 4 Spatial modulation element 5 Projection lens 6 Reflective type screen 10 Control part 21 LED driver circuit part 22 LED (light source part)
22R, 22G, 22B LED chip 23 Current detection unit 24 Waveform pattern calculation generation unit (drive signal modulation unit)
30R, 30G, 30B, 40R, 40G, 40B, 50R, 50G, 50B Modulation signal 70 Lighting control means

Claims (6)

In order to perform image display by projecting light onto a display medium, a light source unit composed of a plurality of visible light LEDs and the plurality of visible light LEDs are divided into respective lighting time regions within a periodic fixed time period. And a visible light LED light source device having a lighting control means for sequentially lighting,
The visible light LED light source device, wherein the lighting control unit includes a drive signal modulation unit that generates a modulation signal for lighting at least one of the visible light LEDs with a lighting duty smaller than a lighting time region width.   2. The visible light LED light source device according to claim 1, wherein the drive signal modulation unit generates a modulation signal that performs pulse width modulation of at least one of the visible light LEDs within a lighting time region thereof.   3. The visible signal according to claim 1, wherein the drive signal modulation unit generates a modulation signal for performing power modulation having a peak value in the first half of the lighting time region of at least one of the visible light LEDs. Light LED light source device.   The visible light LED light source device according to claim 3, wherein the modulation signal for performing the power modulation has a waveform pattern that has the peak value at the modulation start timing and monotonously decreases with time.   The image projection system using the visible light LED light source device in any one of Claims 1-4. A visible light LED driving method for sequentially lighting a plurality of visible light LEDs by dividing each lighting time region in a periodic fixed time zone,
A driving method of a visible light LED, wherein at least one of the visible light LEDs is lit with a lighting duty smaller than a lighting time region width.

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