KR100788700B1 - Illumination unit adopting LED, projection display device employing the same and method of operating the illumination unit adopting LED - Google Patents

Abstract

Disclosed are an LED lighting unit, an image projection apparatus using the same, and a method of driving the LED lighting unit. The disclosed LED lighting unit includes a light source unit consisting of a plurality of LEDs; Lighting control means for sequentially dividing the plurality of LEDs into respective lighting time regions within a predetermined time period, wherein the lighting control means is configured to light at least one of the LEDs smaller than a width of the lighting time region; And a drive signal modulator for generating a modulated signal to be turned on with a duty.

The driving method of the disclosed LED lighting unit is a driving method of dividing a plurality of LEDs into respective lighting time regions within a predetermined time period and sequentially lighting the light emitting duty, wherein at least one of the plurality of LEDs is smaller than the lighting time region width. It is characterized in that the lighting.

Description

LED unit, projection display device employing the same and method of operating the illumination unit adopting LED}

1 is a schematic diagram showing a schematic configuration of an image projection apparatus using an LED lighting unit according to a first embodiment of the present invention.

2 is a functional block diagram illustrating a schematic configuration of the LED lighting unit according to the first embodiment of the present invention.

3 is a flowchart for explaining an outline of a modulated signal of a plurality of LEDs in the first embodiment of the present invention.

4 is a signal waveform diagram illustrating a detailed waveform pattern of a modulation signal generated by a driving signal modulator in the LED lighting unit according to the first embodiment of the present invention.

5 is a schematic graph for explaining the human eye's time response to light stimulation.

It is a typical graph explaining the fall of the brightness | luminance of LED.

FIG. 7 is a signal waveform diagram illustrating a detailed waveform pattern of a modulation signal generated by a driving signal modulator in the LED lighting unit according to the second embodiment of the present invention.

8 is a signal waveform diagram illustrating a detailed waveform pattern of a modulated signal in the LED lighting unit according to the modification of the second embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

1. Projection device 2, 200 ... LED lighting unit

3 ... condenser lens 4 ... spatial modulation element

5 ... Projection lens 6 ... Reflective screen

10 ... Control unit 21 ... LED driver circuit

22 ... light source 22R, 22G, 22B ... LED

23 ... Current detector 24,240 ... Drive signal modulator

30R, 30G, 30B, 40R, 40G, 40B, 50R, 50G, 50B ... modulated signal

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an LED lighting unit, an image projection apparatus using the same, and a method of driving an LED lighting unit. The present invention relates to displaying an image by projecting light onto a display medium such as a reflective or transmissive screen.

Background Art Conventionally, for example, LEDs used as light sources in image projection apparatuses such as projectors, rear projection televisions, and light projection apparatuses are often driven by a pulse lighting method.

For example, when projecting a full-color image using LEDs having three emission colors of red (R), green (G), and blue (B) emission wavelengths, R, G, and B are sequentially time-divided and It is known to perform spatial modulation by image signals corresponding to respective colors.

Patent Document 1 (Japanese Patent Laid-Open No. 2005-149132, Figs. 2 and 4) discloses an image processing apparatus for photographing an object and performing image processing, and an electronic component mounting apparatus including such an image processing apparatus, comprising a plurality of LEDs as a light source. Then, it is described to include an LED drive circuit for adjusting the luminance of the emitted light by pulse width modulation of these.

Moreover, as a technique related to an LED driving circuit, Patent Document 2 (Patent No. 2005-5112, Figs. 1, 2, 3) discloses an offset in an LED driving circuit for driving an LED used for lighting or a traffic light of a vehicle. An LED driving circuit is described which generates an excitation triangular wave shaped load current and drives the LED by a constant detection current by means of the current detection means and the switch control means on and off the switching means at an oscillation frequency faster than the response of the human eye.

However, the conventional visible light LED light source device as described above, the image projection device and the driving method of the visible light LED using the same has the following problems.

Since LEDs cause a decrease in output due to self-heating, when the lighting time is prolonged in order to obtain high brightness, the luminous efficiency is lowered, which in turn affects the lifetime.

For example, in the LED light source device in which LEDs having R, G, and B wavelengths are collectively arranged to obtain white light, self-heating of the LEDs may affect each other, and thus there is a problem that luminance decrease is more likely to occur. In addition, since the temperature characteristics are different for each color, and thus the luminance deterioration rate and the lifetime characteristics are different, there is a problem that it is difficult to maintain a balance between luminance during driving and reliability over time.

It is also conceivable to adjust the luminance using the technique described in Patent Literature 1, which describes a general configuration for pulse width modulating the LED. However, since the technique is used as a light source for imaging, it is possible to measure the brightness of an object and Pulse width modulation conditions are set so that exposure energy corresponding to brightness is obtained.

When the light of R, G, and B is sequentially turned on and applied to an LED lighting unit that displays an image on a display medium such as a reflective or transmissive screen, a pulse width modulated irradiates necessary exposure energy. Extend by off duty. As a result, there is a problem that the color switching frequency is lowered, for example, flickering is increased and the image quality is lowered.

In addition, as a technology related to an LED driving circuit, in the technique described in Patent Document 2, in a LED driving circuit of an LED used for lighting or a traffic light of a vehicle, a square wave is modulated by modulating an oscillation frequency faster than the response of a human eye. It is suggested that even if the ripple overlaps the driving current, the driving current is roughly equivalent to the constant current driving. However, the LED driving circuit and method for reducing the luminance deterioration of the LED are not described or suggested.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and when the plurality of visible light LEDs are sequentially turned on to project light onto a display medium to perform image display, the luminance decrease due to heat generation of the visible light LED is reduced to improve reliability. An object of the present invention is to provide an LED lighting unit that can be made, and a driving method of an image projection apparatus and an LED lighting unit using the same.

In order to solve the above problems, the LED lighting unit of the present invention, the light source unit consisting of a plurality of LEDs; Lighting control means for sequentially dividing the plurality of LEDs into respective lighting time regions within a predetermined time period, wherein the lighting control means is configured to light at least one of the LEDs smaller than a width of the lighting time region; And a drive signal modulator for generating a modulated signal to be turned on with a duty.

Moreover, the image projection apparatus of this invention is characterized by employ | adopting the LED illumination unit of this invention.

In addition, the driving method of the LED lighting unit of the present invention is a driving method for dividing a plurality of LEDs into respective lighting time regions within a predetermined time period, and sequentially lighting, at least one of the plurality of LEDs of the lighting time region width It is characterized by making it light with a smaller lighting duty.

According to the present invention, since at least one visible light LED is turned on with a light duty smaller than the lighting time domain width by a modulation signal generated by the drive signal modulator, when at least one visible light LED is turned on at a 100% duty ratio. On the contrary, the duration of self-heating is reduced, and heat is radiated at off-duty turned off in the lighting time region. For this reason, the temperature of a light source part can be reduced.

Here, the duty ratio means a ratio of the lighting time to the time width of the lighting time region, and the waveform of the modulated signal is not limited to the square wave.

In this case, the light is turned off in off-duty, but the human visual sense lasts for some time in accordance with the light brightness level, and maintains a so-called afterimage, so that dark shadows are detected by appropriately setting the brightness level and the time duration of the off-duty. You can't do it. For this reason, an image like the visible light LED continuously lit is observed in the human eye.

For example, in the case of the LED lighting unit of the image projecting device which sequentially lights lights corresponding to R, G, and B and displays a full color image, a certain period of switching between R, G, and B is performed by human vision. Since each color is set to a time width detected by mixing, even if a shorter off duty is provided, dark field is not detected as long as an appropriate luminance level is set.

In addition, when the interval between the off-duty is small enough, the difference between the integral value of physical brightness and the brightness which a human eye feels becomes large, and a human eye feels bright more than the integral value of an actual physical brightness.

The integral value in the lighting time region of the modulated signal is preferably set smaller than the integral value of the modulated signal having a 100% duty ratio. In this case, since the calorific value of the visible light LED is reduced compared to the case of 100% duty ratio, it is possible to suppress the lowering of the luminance more efficiently.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Even if the embodiment is different in all the drawings, the same or corresponding members will be given the same reference numerals and redundant description will be omitted.

The LED lighting unit according to the first embodiment of the present invention will be described together with an image projection apparatus using the same.

1 is a schematic diagram showing a schematic configuration of an image projection apparatus using an LED lighting unit according to a first embodiment of the present invention. 2 is a functional block diagram illustrating a schematic configuration of the LED lighting unit according to the first embodiment of the present invention. 3 is a flowchart schematically illustrating modulation signals of a plurality of LEDs in the first embodiment of the present invention. 4 is a signal waveform diagram illustrating a detailed waveform pattern of a modulation signal generated by a driving signal modulator in the LED lighting unit according to the first embodiment of the present invention.

The image projection apparatus 1 is an image projection apparatus for projecting a full color image according to an external signal, for example, on the reflective screen 6 using the LED lighting unit 2 of the present embodiment.

The schematic structure of the image projection apparatus 1 consists of the LED illumination unit 2, the condensing lens 3, the spatial modulation element 4, the projection lens 5, and the control part 10 which controls the whole system.

In order to display a full color image, the LED illumination unit 2 sequentially generates light having a wavelength corresponding to at least three primary colors R, G, and B at time-divisional timing.

The condenser lens 3 is an optical element that condenses the light generated by the LED illumination unit 2 in the modulation region on the spatial modulation element 4.

The spatial modulation element 4 displays a color-decomposed image by spatially modulating the light focused on the condensing lens 3 in accordance with an image signal of wavelength light corresponding to the irradiation timing, and is controlled by the controller 10. As the spatial modulation element 4, for example, a transmissive element is a liquid crystal display device (LCD), and a reflective element is a digital micro mirror device (DMD, Digigal Micromirror Device) or a reflective liquid crystal panel (LCOS) Devices such as Liquid Crystal On Silicon) can be employed.

The projection lens 5 is an optical element which enlarges and projects the image displayed by the spatial modulation element 4 onto the reflective screen 6.

The detailed configuration of the LED lighting unit 2 will be described.

As shown in FIGS. 1 and 2, the LED lighting unit 2 includes a light source unit 22, an LED driver circuit unit 21, a current detector 23, a drive signal modulator 24, and a light source unit 22. A power supply circuit unit 20 for supplying a driving current is provided.

The light source unit 22 includes LEDs 22R, 22G, and 22B which emit light of wavelengths of R, G, and B, which are three primary colors of light, respectively, which are collectively arranged in a range that thermally affects each other.

The LED driver circuit 21, the current detector 23, and the drive signal modulator 24 are based on the lighting clock transmitted from the controller 10, and the LEDs 22R, 22G, and 22B (hereinafter, referred to as &quot; regulated &quot; , Which may be collectively referred to simply as each chip) is divided into respective lighting time regions to constitute lighting control means 70 which sequentially lights up.

The lighting clock is a clock which acquires timing for setting a periodic constant time period for sequentially lighting each chip, and the same frequency as that of the prior art, for example, a frequency of about 180 Hz to 360 Hz can be adopted. In this embodiment, the fundamental light frequency f0 of 240 Hz is employed.

The LED driver circuit section 21 switches the drive current supplied from the power supply circuit section 20 in accordance with the modulation signals 30R, 30G, 30B transmitted from the drive signal modulator 24, and the LEDs 22R, 22G, 22B. ) Is a driving circuit for driving each independently.

The current detector 23 detects a current flowing through each of the chips 22R, 22G, and 22B of the light source unit 22 at a constant timing, so that the maximum value of the light emission amount of each chip 22R, 22G, 22B of the light source unit 22 is increased. The control signal is set to be maintained at a predetermined value and sent to the drive signal modulator 24.

The drive signal modulator 24 divides the lighting time region of each chip 22R, 22G, 22B of the light source unit 22 into a lighting time region within a predetermined time period set by the lighting clock, and lights it up within each lighting time region. It generates a modulated signal that is turned on with a light duty smaller than the time domain width.

In the present embodiment, as shown in Fig. 3, the LEDs 22R, 22G, and 22B are turned on within one cycle T ₀ = 1 / f ₀ = t ₄ -t ₁ which is set to the lighting fundamental frequency f ₀ . The modulation signals 30R, 30G, and 30B are sequentially generated by time division driving. In other words, the times t _{1 to} t ₂ , the times t _{2 to} t ₃ , and the times t _{3 to} t ₄ are the lighting time regions of the wavelength light of R, G, and B, respectively, provided that t ₁ <t ₂ <t ₃ <t ₄ ).

These lighting time domain widths are set to appropriate widths in consideration of the temperature characteristics of each chip. When T _R = t ₂ -t ₁ , T _G = t ₃ -t ₂ , and T _B = t ₄ -t ₃ , respectively, in this embodiment, the temperature characteristics of the LEDs 22G and 22B are approximately the same. because worse than the temperature characteristic of the LED (22R), for example, and _{T R / T O = 20%} , T g / T 0 = 40%, T B / T 0 = set to 40%.

When the lighting is turned on at the 100% duty ratio in the lighting time region, lighting control similar to time division lighting according to the prior art is obtained. That is, in the prior art, the lighting time region is turned on at a 100% duty ratio, whereby the duty ratios for the lighting fundamental frequencies f ₀ are T _R / T _O , T _G / T ₀ , and T _B / T ₀ , respectively. Modulation is being performed. At this duty ratio, the driving current of each chip with respect to the signal level is set so that the optical energy density on the reflective screen 6 becomes a desired value.

As shown in Fig. 4, the modulation signals 30R, 30G, and 30B of the present embodiment have a burst of higher frequency than the lighting fundamental frequency f ₀ within the pulse width modulation lighting time region of such lighting fundamental frequency f ₀ . It is a modulation signal for performing pulse width modulation by the frequency (f _b). In the figure, times t _S and t _E represent 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 performing an experiment or the like, for example, in relation to the amount of decrease in luminance due to self-heating and the brightness felt by a person to be described later. However, it is preferable that the burst frequency f _b is a high frequency at which two or more pulse numbers are generated at least in the lighting time domain width.

For example, a condition of setting the pulse width modulation by the burst frequency f _b may be a condition of f _b = 20 · f ₀ , a period T _b = 1 / f _b , and a duty ratio of 50%.

Under this condition, the driving power required for driving the LEDs 22R, 22G, and 22B is 1/2 compared with the case of 100% duty.

In addition, the peak value I ₀ can be set to the same setting as that of the conventional art. For example, the peak value I ₀ is set to a signal level at which the driving current is 1.5A.

These modulated signals are also sent to the control unit 10 to generate a timing signal for driving the spatial modulation element 4.

The operation of the image projection apparatus 1 will be described centering on the action of the LED lighting unit 2 of the present embodiment.

5 is a schematic graph for explaining the time response of the human eye to light stimulation. It is a typical graph explaining the fall of the brightness | luminance of LED.

When the control unit 10 of the image projecting device 1 receives an image signal separated into colors R, G, and B from the outside, the control unit 10 sends a lighting clock to the LED lighting unit 2.

In the LED lighting unit 2, modulated signals 30R, 30G, and 30B are generated by the drive signal modulator 24 and sent to the LED driver circuit portion 21, whereby the LEDs 22R, 22G and 22B) are supplied with a drive current corresponding to each modulated signal, and each chip is driven to emit light according to the waveform pattern and timing of each modulated signal.

On the other hand, these modulated signals are also sent to the control unit 10, and a modulated timing signal of the spatial modulation element 4 is generated. For this reason, the driving timing of the spatial modulation element 4 is synchronized with the lighting time region of the R, G, and B wavelength light from the light source unit 22, and the spatial modulation element 4 is adapted to correspond to the image signal corresponding to each color. Time-division driven.

For this reason, the light of R, G, B emitted from the LED illumination unit 2 is condensed by the condensing lens 3, and spatially modulated by the spatial modulation element 4 to display a color separation image corresponding to each color. The image displayed on the spatial modulation element 4 is enlarged by the projection lens 5 and projected onto the reflective screen 6. Since this color separation image is synthesized and visible to the human eye, the observer can observe the full color image by seeing the reflected light of the color sequence on the reflective screen 6.

Next, the reason why it can be used as illumination light which does not cause a decrease in luminance even when pulse width modulation is performed at a duty ratio smaller than 100% in the same lighting time region as in the prior art will be described.

Clearly, in this embodiment, since the duty ratio is 50%, the integrated light intensity is lowered. Therefore, for example, when using it as a light source, such as a printer which exposes to the photosensitive member which has a fixed exposure sensitivity, exposure energy will fall with a decrease in duty ratio.

However, the inventors have focused on the fact that in the case of an LED lighting unit which displays an image by projecting visible light onto a display medium such as a reflective or transmissive screen, the light can be made to be equivalent to human eyes even though the physical brightness is different. And earnest research have been made to the present invention.

When the human eye receives a photo stimulus, for some time it feels as if the photo stimulus is continuous. This is known as a so-called afterimage phenomenon. FIG. 5 schematically shows how the sensory light intensity I _V is attenuated over time after seeing the impulse light emission intensity I _i . That is, as shown by the curve 100, it shows a change that initially decays gently and then rapidly decays.

It is due to this afterimage phenomenon that they are felt by the white light which mixed them by sequential lighting of RGB. However, although the color mixture actually occurs at the frequency used in the projector, the intensity of light perceived by the eyes by the amount of integrating light does not greatly deviate. This is because the white balance is broken when the lighting time domain widths of R, G, and B are changed, or when white light emission is performed to simultaneously light R, G, and B lights after sequential lighting of RGB in order to enhance the image brightness. It is easy to understand.

The inventors found that when the burst frequency f _b is increased compared to the lighting fundamental frequency f ₀ , the effect of the afterimage is greatly increased, and the detection accuracy of the human eye with respect to the amount of integrating light becomes insensitive. As a result, it was found out that it was brighter than the amount of integrated light, which led to the same modulation signal as in the present embodiment.

In addition, according to the present embodiment, in view of the decrease in luminance due to self-heating, it is advantageous over the prior art in terms of physically integrated light intensity.

Fig. 6 schematically shows a luminance deterioration state caused by self-heating of the LED. The horizontal axis represents the lighting time, and the vertical axis represents the luminance P. FIG.

When the LED emits light continuously, the temperature rises due to self-heating. Therefore, under constant driving current, the emission luminance decreases from the initial luminance Pi according to the temperature characteristic of the LED, as shown by the curve 101. When the temperature of the LED reaches equilibrium, the luminance is also converged to a constant value.

Therefore, when the lighting time widths are each lit at the pulse widths of t ₁₀ and t ₂₀ (t ₁₀ <t ₂₀ ), the respective luminance decrements ΔP ₁₀ and ΔP ₂₀ become ΔP ₁₀ <ΔP ₂₀ . In addition, since the heat generation amount increases with the lighting time, the time required for heat dissipation also ends in a short time as t ₁₀ . Therefore, if the sum of the lighting times is the same, the higher frequency pulse width modulation is less affected by the lowering of the brightness, so that lighting can be performed more efficiently than the same driving power.

In particular, this difference is apparent in an image projection apparatus such as a projector or a rear projection television that requires high luminance illumination light.

As described above, in the modulation signal of the present embodiment, in the lighting time domain as in the prior art, as the duty ratio smaller than 100%, the burst frequency f _b is sufficiently high in pulse width modulation than the lighting fundamental frequency f ₀ . By using the effect of increasing or decreasing the amount of light in the human eye, it is possible to reduce the apparent decrease in the amount of light and also to suppress the decrease in the physical luminance due to self-heating. For this reason, since the temperature of LED can be reduced, the reliability of LED can also be improved.

As described above, the LED lighting unit of the present embodiment is such that the drive signal modulator generates a modulated signal for pulse width modulating at least one of the visible light LEDs in the lighting time region.

In this case, the luminance deterioration can be reduced by a simple configuration that merely changes the settings of the pulse width and the duty ratio.

The LED lighting unit according to the second embodiment of the present invention will be described.

7 is a signal waveform diagram illustrating a detailed waveform pattern of a modulation signal generated by the driving signal modulator 240 of the LED lighting unit 200 according to the second embodiment of the present invention.

The LED lighting unit 200 of this embodiment has a structure as shown in FIGS. 1 and 2 and includes a drive signal modulator 240. Hereinafter, the differences from the first embodiment will be described.

 The drive signal modulator 240 used in the LED lighting unit 200 differs in generating modulated signals 40R, 40G, and 40B.

As shown in Fig. 3, the lighting timings of the modulation signals 40R, 40G, and 40B are set in the same manner as in the first embodiment.

As shown in the graph 102 of FIG. 7, the detailed waveform pattern has a signal level Ip from the lighting start time t ₁ to the time t ₂ , and the time t ₂ to the time t ₃ . It is a waveform pattern which performs step-shaped power modulation so that the signal level up to is ₀ . Here, the time (t ₁ , t ₂ , t ₃ ) is in the relationship of t ₁ <t ₂ <t ₃ <t ₄ when T _R (T _G , T _B ) = t ₄ -t ₁ . In addition, I _P > I ₀ .

The peak value I _P , the stepped lighting duty t _2- t ₁ , and t ₃ -t ₁ are, for example, experimented with the amount of brightness deterioration and the sensory brightness change for the human eye. If necessary, it can be set appropriately. However, the peak value I _P is set so as not to exceed the maximum limit of the drive current and the application time which affect the lifetime of the LEDs 22R, 22G, and 22B.

In order to explain the operation of such modulation signals 40R, 40G, 40B, for example, I _P = 2 · I ₀ , (t ₂ -t ₁ ) = (1/3) · (t ₄ -t ₁ ), (t ₃ -t ₁ ) = (2/3) · (t ₄ -t ₁ ) will be considered.

In this case, the modulated signal 41 which illuminates the lighting time region of each color at 100% duty with the signal level I shown in the graph 102 of FIG. 7 can have the same amount of heat generation.

In Fig. 7, curves 104 and 105 are shown, respectively, in the luminance deterioration state when the LEDs 22R, 22G, and 22B are driven by the modulation signal and the modulation signal 41 of this embodiment. Will be, but did appear on the waveform after the sake of convenience, the illustrated T _0, ignoring the differences in the following, T ₀ is described.

Since the modulation signal of the present embodiment is driven to the peak value I _P at the start of lighting, the luminance becomes the maximum value indicated by the point a, and is, for example, the curve of FIG. 6 between the times t _{1 to} t ₂ . Along the curve 104, indicated by 101, it drops to point b. Then, at time t ₂ and at time t ₃ , since the light is driven at a signal level I ₀ about half of I _P, the amount of heat generated is halved. _{Becomes 1} It turns off at the times t _{3 to} t ₄ . However, the human eye maintains the luminance P ₁ to some extent and does not detect the extinction.

On the other hand, since the modulation signal 41 is driven at the peak value I ₀ until the times t _{1 to} t ₄ , as indicated by the curve 105, it is lit with the luminance of the point e which is half of the point a. In accordance with the curve 105 showing the curve 101 of FIG. 6 during the time t ₄ -t ₁ , the luminance is lowered to the point f, and the lighting is terminated at the luminance P ₂ (where P ₂ <P ₁ ).

For this reason, although the heat generation amount becomes the same, the modulation signal of the present embodiment is clearly smaller than the modulation signal 41, and the luminance deterioration rate is clearly lowered, and the afterimage phenomenon of the human eye is felt to be brighter depending on each other.

Above, but these descriptive convenience, when a heat value of the same, that the peak value (I _p) of the signal level, by appropriately setting the t _2, t _3, may be a waveform pattern for reducing the heating value is natural.

In this way, the LED lighting unit of the present embodiment is such that the drive signal modulator generates a modulated signal that performs at least one of the visible light LEDs with power modulation having a peak value in the first half of the lighting time region.

In this case, since the maximum luminance is obtained in a state where the heat accumulation due to self-heating is relatively small in the first half of the lighting time region, the luminous efficiency is good and driving of high luminance is possible.

The LED lighting unit of the present embodiment has a waveform pattern in which the modulated signal for performing the power modulation has the peak value at the modulation start timing and monotonically decreases with time.

In this case, it has a peak value at the modulation start timing, and since the signal level is attenuated thereafter, the amount of heat generated is monotonically reduced, so that the decrease in luminance can be effectively suppressed.

Here, the monotonous reduction means a monotonic reduction in a broad sense, and includes a stepped decrease having a constant value area.

Next, a modification of the present embodiment will be described.

FIG. 8 is a signal waveform diagram illustrating a detailed waveform pattern of a modulated signal generated by a drive signal modulator of an LED lighting unit according to a modification of the second embodiment of the present invention.

The drive signal modulator of the present modification generates the modulated signals 50R, 50G, 50B shown in FIG. 8 in place of the modulated signals 40R, 40G, 40B.

A modulation signal (50R, 50G, 50B) has a peak value of the signal level I _q, to time (t ₁ ~t _{5) (single, t 1 <t 5 <t} 4) the signal level I _r during to the linear It has a ladder-shaped waveform pattern that is reduced to (I _r <I ₀ <I _q ).

Peak value (I _q ), signal level (I _r ), lighting duty (t ₅ -t ₁ ) are suitable as necessary, for example, by experimenting with the amount of decrease in brightness and the sensory change in brightness for the human eye. Can be set. However, the peak value I _q is set so as not to exceed the maximum limit of the drive current and the application time which affect the lifetime of the LEDs 22R, 22G, and 22B.

This modification is another example of the waveform monotonically decreasing from the peak value, and has the same effects as described above.

In the above description, the present invention is applied to all modulated signals of R, G, and B. However, the present invention may be applied to at least one according to the amount of self-heating and the degree of mutual influence. That is, the visible light LED which has little self-heating and little influence of brightness fall can also be lighted with 100% duty ratio.

In addition, although the above description demonstrated the example in which three visible light LEDs were provided, two or more may be sufficient. For example, two LEDs each of R, G, and B may be installed. In addition, as long as the plurality of visible light LEDs are thermally affected by each other, the plurality of visible light LEDs may not be integrated as a single device.

In the above description, the case where one cycle of the lighting fundamental frequency coincides with a periodic constant time zone is described as an example, but a plurality of visible light LEDs may have a timing of simultaneous lighting in one cycle of the lighting fundamental frequency. For example, in order to increase the apparent luminance of the image, timings for simultaneously lighting R, G, and B may be provided.

In the above description, the image projection apparatus has been described as an example of displaying an image on a reflective screen. However, the image display may be performed by projecting light onto a transmissive screen. For example, it may be a rear projection television.

In addition, in the above description, the example using the LED lighting unit of the present invention has been described taking the case of using the image projection apparatus as an example. However, if the projection of light onto a display medium such as a reflective or transmissive screen, in particular, the image It can be used not only as a device for projecting the light, but also as a suitable lighting device and part of a light transmitting device.

In addition, the component described in each said embodiment can be implemented in combination suitably within the range of the technical idea of this invention, if technically possible.

According to the LED lighting unit of the present invention, and an image projection apparatus and a driving method of the LED lighting unit using the same, since at least one LED is turned on with a duty ratio less than 100%, the self-heating duration is reduced, and the off duty is turned off. Since the heat radiation can be carried out in this manner, it is possible to reduce the decrease in luminance due to the heat generation of the LED and to improve the reliability.

The above embodiments are merely exemplary, and various modifications and equivalent other embodiments are possible to those skilled in the art. Therefore, the true technical protection scope of the present invention should be defined within the following claims.

Claims (12)

A light source unit comprising a plurality of LEDs; Lighting control means for dividing the plurality of LEDs into respective lighting time regions within a predetermined time period and sequentially lighting the light; The lighting control means includes a drive signal modulator for generating a modulation signal for lighting at least one of the LEDs with a lighting duty smaller than the lighting time domain width, And the drive signal modulator generates a modulated signal for power modulating at least one of the plurality of LEDs to have a peak value in the first half of its lighting time region. The method of claim 1, And the drive signal modulator generates a modulated signal for pulse width modulating at least one of the plurality of LEDs within a lighting time region thereof. The method of claim 2, The drive signal modulator is pulse width modulated with a predetermined frequency, The predetermined frequency is the LED lighting unit, characterized in that the frequency for generating two or more pulses in the lighting time domain width. delete The method of claim 1, And said modulated signal has said peak value at a modulation start timing. The method of claim 5, The modulating signal LED lighting unit, characterized in that having a waveform pattern monotonically reduced with respect to time. The method of claim 5, The modulating signal is an LED lighting unit, characterized in that it has a waveform pattern that decreases stepwise with respect to time. An image projection apparatus for displaying an image by magnifying and projecting light onto a screen, the illumination unit illuminating the light, A light source unit consisting of a plurality of LEDs, Lighting control means for dividing the plurality of LEDs into respective lighting time regions within a predetermined time period and sequentially lighting the light; The lighting control means includes a drive signal modulator for generating a modulation signal for lighting at least one of the LEDs with a lighting duty smaller than the lighting time domain width, And the drive signal modulator generates a modulated signal for power modulating at least one of the plurality of LEDs to have a peak value in the first half of its lighting time region. The method of claim 8, And the drive signal modulator generates a modulated signal for pulse width modulating at least one of the plurality of LEDs within a lighting time region thereof. delete The method of claim 8, wherein the modulated signal, Has the peak value at a modulation start timing, And a waveform pattern that monotonically decreases with time. In the driving method of the LED lighting unit for dividing a plurality of LEDs into respective lighting time region within a predetermined time period in order to sequentially light, At least one of the plurality of LEDs is turned on with a lighting duty smaller than its lighting time domain width, And generating a modulated signal for power modulating at least one of the plurality of LEDs to have a peak value in the first half of the lighting time region.

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