JP2020034695A - Video projection device, and projection type video display device - Google Patents

Abstract

To provide a video projection device and projection type video display device that can display videos as achieving higher energy efficiency in comparison to a conventional technology upon using a plurality of phosphors different in excitation limit intensity by switching them in a video display system performing a wavelength conversion of light of a semiconductor light source by phosphor, and displaying videos by use of the light having the wavelength converted.SOLUTION: A video projection device according to the present disclosure comprises: a semiconductor light source 110 that is driven in accordance with a PWM modulation signal; and a time division switch wavelength conversion element 120 that performs a wavelength conversion of output light of the semiconductor light source as sequentially alternatively switching a plurality of phosphors including a first phosphor and a second phosphor having excitation intensity saturated by input light of smaller intensity than the first phosphor. A frequency of the PWM modulation signal performing a PWM modulation of electricity driving the semiconductor light source in a period having the second phosphor used is higher than that of the PWM modulation signal in a period having the first phosphor used.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to an image projection device and a projection type image display device of an image display system that converts light from a semiconductor light source into a wavelength using a phosphor and displays an image using the light.

  Patent Literature 1 discloses a light source device, a projection device, and a projection method for projecting an image that is as bright as possible and has high color reproducibility in consideration of luminous efficiency of each color by combining a light emitting element and a phosphor.

  The light source device, the projection device, and the projection method include a semiconductor laser that emits blue light, a color wheel and a motor that generates blue light and green light using blue light, an LED that emits red light, blue light, and green light. A projection light processing unit and a CPU for controlling a semiconductor laser, an LED, a color wheel and a motor so that light and red light are generated cyclically, an input unit for inputting an image signal, and a blue light, a green light and a red light. And a projection system for forming and projecting an optical image using the optical system.

  The color wheel and the motor are set so that the generation time of blue light with higher luminous efficiency is shorter than the generation time of green light. Further, the projection light processing unit and the CPU are set so that the driving power for generating blue light is larger than the driving power for generating green light. Accordingly, it is possible to realize a light source device, a projection device, and a projection method that project an image that is bright and has high color reproducibility.

  However, in such a projector that converts the wavelength of the light from the semiconductor light source with a phosphor and displays an image using the light, when a plurality of phosphors having different excitation limit intensities are switched and used, a low excitation limit is used. However, there is a problem that the phosphor having the above-mentioned characteristic generates heat to lower the energy efficiency.

JP-A-2011-70127

  The present disclosure provides an image projection device and a projection-type image display device that can display an image while achieving higher energy efficiency as compared with the related art.

  An image projection device according to the present disclosure includes a semiconductor light source driven in accordance with a PWM modulation signal, and a first fluorescent substance and a second fluorescent substance whose excitation intensity is saturated by input light having an intensity smaller than that of the first fluorescent substance. A time-division switching wavelength conversion element for wavelength-converting the output light of the semiconductor light source while sequentially and selectively switching a plurality of phosphors including the phosphor, and the frequency of the PWM modulation signal during the period when the second phosphor is used is , During the period in which the first phosphor is used.

  The image projection device and the projection-type image display device according to the present disclosure can display an image while achieving higher energy efficiency as compared with the related art.

FIG. 2 is a block diagram illustrating a configuration example of a video projection device according to Embodiment 1. FIG. 2 is a plan view showing a configuration example of a phosphor wheel included in a time-division switching wavelength conversion element in the video projection device in FIG. 1. FIG. 2 is a block diagram showing a configuration example of the semiconductor light source drive circuit of FIG. A timing chart showing a current flowing through a semiconductor light source in a conventional semiconductor light source driving circuit that does not change the frequency of a PWM modulation signal FIG. 1 is a timing chart showing a current flowing through a semiconductor light source in the semiconductor light source drive circuit of FIG. 1 for changing the frequency of a PWM modulation signal.

  Hereinafter, embodiments will be described in detail with reference to the drawings as appropriate. However, unnecessary detailed descriptions such as detailed description of well-known matters and redundant description of substantially the same configuration may be omitted. This is to prevent the following description from being unnecessarily redundant and to facilitate the understanding of those skilled in the art.

  The inventor provides the accompanying drawings and the following description to assist those skilled in the art with a sufficient understanding of the present disclosure, and these are intended to limit the subject matter described in the claims. is not.

(Embodiment 1)
Hereinafter, the first embodiment will be described in detail with reference to FIGS.

[1-1. Constitution]
First, the configurations of the video projector and the semiconductor light source drive circuit according to the first embodiment will be described in detail with reference to FIGS.

[1-1-1. Configuration of video projection device]
FIG. 1 is a block diagram illustrating a configuration of a video projection device according to Embodiment 1 of the present disclosure. As shown in FIG. 1, the image projection device according to the first embodiment includes a semiconductor light source driving circuit 100, a semiconductor light source 110, a time division switching wavelength conversion element 120, a light modulation element 130, a projection lens 140, a PWM It comprises a modulator 150 and a wavelength conversion element drive circuit 160.

  The video projection device according to the first embodiment of the present disclosure is used for a projection-type video display device that performs color sequential display and the like. By changing the wavelength of the output light of the semiconductor light source 110 by switching a plurality of phosphors, image lights of different colors are generated. Further, by using this image light, the image 171 is projected and displayed on the screen 170 in accordance with the input image signal.

  The PWM modulator 150 generates a PWM modulation signal according to a PWM set value input from an external circuit and a frequency switching signal input from the wavelength conversion element driving circuit 160, and supplies the PWM modulation signal to the semiconductor light source driving circuit 100. The frequency of the generated PWM modulation signal is switched by a frequency switching signal from the wavelength conversion element driving circuit 160. The semiconductor light source driving circuit 100 drives the semiconductor light source 110 according to a target current value input from the outside and a PWM modulation signal from the PWM modulator 150 so that the current flowing to the semiconductor light source 110 is PWM-modulated.

  The semiconductor light source 110 driven by the semiconductor light source driving circuit 100 generates blue light and outputs it to the time division switching wavelength conversion element 120. The wavelength conversion element drive circuit 160 generates a wavelength conversion element drive signal in synchronization with the vertical synchronization signal input from the external circuit, and supplies the generated signal to the time division switching wavelength conversion element 120. Further, the wavelength conversion element drive circuit 160 generates a frequency switching signal in synchronization with the vertical synchronization signal, and supplies the frequency switching signal to the PWM modulator 150.

  The time-division switching wavelength conversion element 120 wavelength-converts the output light of the semiconductor light source 110 while sequentially switching the phosphor used for wavelength conversion according to the wavelength conversion element drive signal. The wavelength-converted output light is output to the light modulation element 130. In the light modulation element 130, the light input according to the video signal input from the outside is intensity-modulated to be video light. The image light is projected onto the screen 170 through the projection lens 140, and the image 171 is displayed on the screen 170.

[1-1-2. Configuration of time division switching wavelength conversion element 120]
The configuration of the time division switching wavelength conversion element 120 will be described with reference to FIG. FIG. 2 is a plan view showing a configuration example of the phosphor wheel 121 included in the time division switching wavelength conversion element 120. The time division switching wavelength conversion element 120 includes a phosphor wheel 121 shown in FIG. 2 and a motor for rotating the phosphor wheel 121.

  The phosphor wheel 121 includes a transmission region 122, a green phosphor region 123, and a red phosphor region 124 formed with a predetermined width in the radial direction so as to divide a region along the exercise. The phosphor wheel 121 is driven by a motor to rotate, thereby selectively switching the regions 122 to 124 that receive the blue light from the semiconductor light source 110. The transmission region 122 transmits the blue light from the semiconductor light source 110 and outputs the blue light to the light modulation element 130 as it is. The green phosphor region 123 is formed of a green phosphor, converts blue light from the semiconductor light source 110 into green light, and outputs the green light to the light modulation element 130. The red phosphor region 124 is formed of a red phosphor, converts blue light from the semiconductor light source 110 into red light, and outputs the red light to the light modulation element 130.

[1-1-3. Configuration of semiconductor light source drive circuit]
FIG. 3 is a block diagram illustrating a configuration example of the semiconductor light source driving circuit 100 according to the first embodiment. 3, the semiconductor light source driving circuit 100 includes a switching power supply 200, a comparator 210, a capacitor 220, an averaging resistor 230, an FET 240, and a detection resistor 250. The switching power supply 200, the semiconductor light source 110, the FET 240, and the detection resistor 250 are connected in series.

  The switching power supply 200 controls the output voltage to the semiconductor light source 110 according to the comparison result signal from the comparator 210. The FET 240 switches conduction on and off according to a PWM modulation signal from the PWM modulator 150, and controls on and off of a current flowing through the semiconductor light source 110. The detection resistor 250 generates a voltage by a current flowing through the detection resistor 250. The generated voltage charges the capacitor 220 through the averaging resistor 230. Comparator 210 compares a reference voltage indicating a target current value input from the outside with an output voltage of capacitor 220, generates a comparison result signal indicating the difference, and outputs the result to switching power supply 200. Thus, the switching power supply 200 is driven and controlled such that the average value of the current flowing through the semiconductor light source 110 is equal to the target current value.

[1-2. motion]
The operations of the video projection device and the semiconductor light source driving circuit configured as described above will be described in detail below.

  In FIG. 1, the PWM modulator 150 generates a PWM modulation signal according to a PWM set value input from an external circuit and a frequency switching signal input from the wavelength conversion element driving circuit 160, and outputs the PWM modulation signal to the semiconductor light source driving circuit 100. The frequency of the output PWM modulation signal is switched by a frequency switching signal from the wavelength conversion element driving circuit 160. Further, the PWM modulation signal is generated such that the duty cycle is equal to a PWM set value (duty cycle instruction value) input from the outside.

  The semiconductor light source drive circuit 100 drives the semiconductor light source 110 according to a reference voltage indicating a target current value and a PWM modulation signal from the PWM modulator 150, which are input from the outside. At this time, the semiconductor light source 110 allows the current to flow through the semiconductor light source 110 only while the PWM modulation signal is on, and as described above, the average value of the current flowing through the semiconductor light source 110 during one cycle of the PWM modulation signal is: Drive control is performed so as to be equal to the target current value.

  The semiconductor light source 110 driven by the semiconductor light source driving circuit 100 generates blue light and outputs it to the time division switching wavelength conversion element 120. The wavelength conversion element drive circuit 160 generates the above-described wavelength conversion element drive signal in synchronization with the vertical synchronization signal input from the external circuit, and outputs the signal to the time division switching wavelength conversion element 120. Further, the wavelength conversion element driving circuit 160 also generates a frequency switching signal for switching the frequency of the PWM modulation signal of the PWM modulator 150 as described later, and outputs the signal to the PWM modulator 150.

  The time-division switching wavelength conversion element 120 is driven according to a wavelength conversion element drive signal from the wavelength conversion element drive circuit 160. The time-division switching wavelength conversion element 120 rotates the semiconductor wheel 121 by a motor and selectively switches the regions 122 to 124 used for wavelength conversion sequentially.

  While the transmission region 122 is used, the blue light from the semiconductor light source 110 passes through the color wheel 121 and is output to the light modulation element 130 as it is. While the yellow phosphor region 123 is being used, the yellow phosphor in the yellow phosphor region 123 receives the blue light from the semiconductor light source 110, emits yellow light, and outputs the yellow light to the light modulation element 130. Similarly, the phosphor in the red phosphor region 124 receives the blue light from the semiconductor light source 110, emits red light, and outputs the red light to the light modulation element 130.

  The light modulation element 130 modulates the intensity of the output light from the time-division switching wavelength conversion element 120 according to a video signal input from the outside, to obtain video light. The image light is projected onto the screen 170 through the projection lens 140, and the image 171 is displayed on the screen 170.

  The intensity of the output light from the semiconductor light source 110 increases as the value of the current flowing through the semiconductor light source 110 increases. As the intensity of the output light of the semiconductor light source 110 increases, the intensity of the output light of the time division switching wavelength conversion element 120 also increases. However, the phosphors have their respective excitation limit intensities, and the intensity of light emission remains constant even when light having an intensity exceeding the excitation limit intensity is input. The phosphor emits heat due to the energy exceeding the excitation limit intensity and lowers the energy efficiency, and consequently the energy efficiency of the image projection device. The excitation limit intensity differs depending on the type of phosphor, and the excitation limit intensity of the red phosphor in the red phosphor region 124 is smaller than the excitation limit intensity of the green phosphor in the green phosphor region 123.

  Further, the temperature of the semiconductor light source 110 increases during a period during which a current flows through the semiconductor light source 110 (hereinafter, referred to as an “on period”), and during a period during which no current flows through the semiconductor light source 110 (hereinafter, an “off period”). Rapidly decreases during the period). Since the forward voltage of the semiconductor light source 110 decreases as the temperature increases, when the switching power supply 200 outputs a constant voltage, the current flowing through the semiconductor light source 110 gradually increases during the ON period and saturates to a constant value. I do. Thereafter, when the OFF period is entered, the temperature of the semiconductor light source 110 is rapidly reduced, and returns to the temperature before the ON period was entered. Therefore, the rising waveform is the same regardless of the value of the duty cycle.

  In the following, it is assumed that the intensity of light emitted by the semiconductor light source 110 when the current flowing through the semiconductor light source 110 is saturated is smaller than the excitation limit intensity of the green phosphor and larger than the excitation limit intensity of the red phosphor. I do. FIG. 4 is a timing chart showing a current flowing through the semiconductor light source 110 in the conventional semiconductor light source driving circuit in which the frequency of the PWM modulation signal is not changed. In FIG. 4, a period in which the green phosphor region 123 is used in the time division switching wavelength conversion element 120 is indicated by T1, and a period in which the red phosphor region 124 is used is indicated by T2. Tc1 indicates the period of the PWM modulation signal.

  In FIG. 4, the current value when the current flowing through the semiconductor light source 110 is saturated is represented by Ip. A current at which the semiconductor light source 110 emits light having an intensity equal to the excitation limit intensity of the red phosphor is indicated by Ipm. In the hatched portion in FIG. 4, an excessive current flows through the semiconductor light source 110, and light having an intensity exceeding the excitation limit intensity is input to the red phosphor. This excess input light is converted into thermal energy inside the red phosphor, and the heated red phosphor reduces energy efficiency.

  FIG. 5 is a timing chart showing a current flowing through the semiconductor light source 110 when the frequency of the PWM modulation signal is switched for each type of phosphor in the semiconductor light source driving circuit 100 of FIG. 5, the periods T1, T2 and the cycle Tc1 are the same as those in FIG. The frequency of the PWM modulation signal in the period T2 is set higher than the frequency of the PWM modulation signal in the period T1. Therefore, the period Tc2 of the PWM modulation signal in the period T2 is shorter than the period Tc1 in the period T1.

  Here, the cycle Tc2 is set to be sufficiently short so that the off-period is entered earlier than the current flowing through the semiconductor light source 110 is saturated. By doing so, the maximum value of the current flowing through the semiconductor light source 110 decreases. If the maximum value of this current is equal to or less than Ipm, the output light of the semiconductor light source 110 does not exceed the excitation limit intensity of the red phosphor. Therefore, the excessive current shown by the hatched portion in FIG. 4 does not flow through the semiconductor light source 110, and the reduction in energy efficiency is solved.

  If the frequency of the PWM modulation signal is increased when the duty cycle is close to 100%, the integrated value of the current flowing through the semiconductor light source 110 over the period T2 decreases. This indicates that the total output of the semiconductor light sources 110 decreases in the period T2. Therefore, in the period T2, the output of the semiconductor light source 110 when the frequency of the PWM modulation signal is switched cannot achieve the maximum output of the semiconductor light source 110 when the frequency is not switched. However, by setting the period T2 longer, a decrease in output can be compensated for, so that the decrease in output does not pose a problem.

[1-3. Effects]
As described above, in the present embodiment, the frequency of the PWM modulation signal in the period T2 using the red phosphor is set higher than the frequency of the PWM modulation signal in the period T1 using the green phosphor. Accordingly, the maximum value of the current flowing through the semiconductor light source 110 can be reduced below a predetermined value, and the intensity of the output light from the semiconductor light source 110 can be adjusted so as not to exceed the excitation limit intensity of the red phosphor. Therefore, energy loss in the phosphor is reduced, and the efficiency of the entire light source device can be increased.

(Other embodiments)
As described above, Embodiment 1 has been described as an example of the technology disclosed in the present application. However, the technology according to the present disclosure is not limited to this, and can be applied to embodiments in which changes, substitutions, additions, omissions, and the like are made as appropriate. Further, a new embodiment can be obtained by combining the components described in the first embodiment. Therefore, another embodiment will be described below.

  In the first embodiment, the voltage by the detection resistor 250 of the semiconductor light source driving circuit 100 is averaged on the time axis by the averaging resistor 230 and the capacitor 220. The averaged voltage is compared with the reference voltage indicated by the target current value by the comparator 210 to control the switching power supply 200. As a result, the current flowing through the semiconductor light source 110 is controlled so as to be PWM-modulated according to the input PWM modulation signal.

  However, the voltage of the sensing resistor 250 is averaged over a period including the off period. Since no current flows through the semiconductor light source 110 during the off period, the voltage value of the detection resistor 250 is zero. When the value of the duty cycle of the PWM modulation signal is small, for example, 5% or less, the off period in which the voltage value of the detection resistor 250 is 0 occupies most of the entire period. Therefore, in this case, the average voltage value used for comparison by the comparator 210 is close to zero. Therefore, the accuracy of current control is reduced due to the influence of noise or variations in element performance, and the accuracy of intensity control of optical output is also reduced.

  Therefore, a configuration is assumed in which a switch is inserted in series immediately before or immediately after the averaging resistor 230, and the switch is turned on and off by a PWM modulation signal from the PWM modulator 150. The switch conducts while the PWM modulation signal is on and disconnects while the PWM modulation signal is off. In such a configuration, the capacitor 220 does not perform charging / discharging during the off-period, so that the charge of the capacitor 220 is stored during the off-period. Thus, the averaging resistor 230 and the capacitor 220 average the voltage only during the ON period. Therefore, the output voltage Vc of the capacitor 220 becomes substantially constant even if the value of the duty cycle changes. Thus, even when the duty cycle is as small as 5% or less, for example, the output voltage Vc used for comparison by the comparator 210 is maintained at the above-described substantially constant level, and highly accurate control is possible.

  In the first embodiment, the phosphor wheel 121 is composed of two kinds of phosphors, a green phosphor and a red phosphor whose excitation limit intensity is smaller than the green phosphor. However, the plurality of phosphors used in the time-division switching wavelength conversion element are not limited to this, and are configured to include a first phosphor and a second phosphor having an excitation limit intensity smaller than that of the first phosphor. You may.

  As described above, the embodiments have been described as examples of the technology in the present disclosure. For that purpose, the accompanying drawings and the detailed description have been provided.

  Therefore, among the components described in the accompanying drawings and the detailed description, not only those components that are essential for solving the problem, but also components that are not essential for solving the problem, in order to illustrate the above technology. May also be included. Therefore, based on the description of the non-essential components in the accompanying drawings and detailed description, it should not be immediately determined that the non-essential components are essential.

  Further, since the above-described embodiments are intended to exemplify the technology in the present disclosure, various changes, substitutions, additions, omissions, and the like can be made within the scope of the claims or equivalents thereof.

  The present disclosure is applicable to a video projection device and a projection type video display device. In an image display system in which light from a semiconductor light source is wavelength-converted by switching two or more types of phosphors having different excitation limit intensities and an image is displayed using the light, the maximum value of the intensity of light output from the semiconductor light source is determined by Adjustment is made so as not to exceed the excitation limit intensity of the phosphor, and the efficiency can be increased.

REFERENCE SIGNS LIST 100 semiconductor light source driving circuit 110 semiconductor light source 120 time division switching wavelength conversion element 121 phosphor wheel 122 transmission area 123 green phosphor area 124 red phosphor area 130 light modulation element 140 projection lens 150 PWM modulator 160 wavelength conversion element driving circuit 200 Switching power supply 210 Comparator 220 Capacitor 230 Averaging resistor 240 FET
250 detection resistor

Claims (4)

A semiconductor light source driven according to a PWM modulation signal;
While selectively switching a plurality of phosphors sequentially including a first phosphor and a second phosphor whose excitation intensity is saturated with input light having an intensity smaller than that of the first phosphor, the semiconductor light source includes A time-division switching wavelength conversion element for wavelength-converting the output light,
The frequency of the PWM modulation signal that PWM modulates the current for driving the semiconductor light source during the period in which the second phosphor is used is higher than the frequency of the PWM modulation signal in the period in which the first phosphor is used.
Video projection device. The time-division switching wavelength conversion element, selectively switches the plurality of phosphors sequentially in synchronization with a vertical synchronization signal input from the outside,
The video projection device according to claim 1. The image projection device further includes:
According to a video signal input from the outside, an optical modulator that modulates and outputs output light from the time-division switching wavelength converter,
And a projection lens for projecting output light from the light modulation element,
The image projection device according to claim 1.   A projection-type image display device, comprising the image projection device according to claim 1.

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