JP4013420B2 - LIGHTING DEVICE AND ITS DRIVE METHOD, LIQUID CRYSTAL DEVICE, AND ELECTRONIC DEVICE - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an illumination device that reduces power consumption and a driving method thereof. The present invention also relates to a liquid crystal display device using the illumination device. The present invention also relates to an electronic apparatus using the liquid crystal display device.
[0002]
[Prior art]
In a liquid crystal device using a transmissive or transflective liquid crystal panel, an illuminating device is provided on the back of the liquid crystal panel in order to improve visibility, and the brightness of the display screen is increased by light supplied from the illuminating device Yes. As a light source of this lighting device, a side-light type cold-cathode tube is cited, and it is used as a relatively bright lighting device that can be used for a color liquid crystal or the like.
[0003]
[Problems to be solved by the invention]
However, the external shape of the fluorescent tube, which is a cold cathode tube, is relatively large, and the device structure is enlarged. In addition, a conventional lighting device using a cold cathode tube requires a booster circuit, a stabilization circuit, and the like in the drive circuit, and thus has a problem that the drive circuit becomes complicated and large in size and consumes a large amount of power. Further, since the light emission luminance cannot be easily changed, it is difficult to adjust the light emission luminance according to the external brightness.
[0004]
In order to solve such a problem, an illumination device using an LED (light emitting diode) as a light source has been proposed. FIG. 12 shows an example of an electric circuit of a conventional lighting device using an LED as a light source. As shown in the figure, the LEDs of the light source are connected in series and are driven by a DC power source.
[0005]
Since the LED does not require a booster circuit or a stabilizing circuit in the drive circuit, it is relatively easy to reduce the size, and the light emission luminance can be easily changed.
[0006]
However, the LED has a problem of high power consumption because its luminous efficiency is lower than that of a cold cathode tube. In addition, it has been proposed to reduce the number of LED chips in order to reduce power consumption. However, if the number of chips is reduced, the distance between the LEDs increases and the luminance unevenness in the vicinity of the light source part deteriorates. did.
[0007]
The present invention has been made in view of such circumstances, and an object of the present invention is to provide an illuminating device that has low power consumption and can improve luminance unevenness, and a driving method thereof.
[0008]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention provides a plurality of light emitting elements arranged in a row and electrically classified into a plurality of groups including the first and second groups, and the light emitting elements from the light emitting elements. A light guide plate that receives light and emits the light in a specific direction, and a driving unit that drives the plurality of light emitting elements for each of the plurality of groups by a pulse signal having a phase difference and a partly overlapping effective time. And the driving means raises the first group pulse signal, then lowers the second group pulse signal, raises the second group pulse signal, and then raises the second group pulse signal. One group of pulse signals is caused to fall.
[0009]
According to such a configuration, since each light emitting element is pulse-driven, the power consumption of each light emitting element can be reduced. Further, since each group is driven by a pulse signal having a different phase and a part of effective time overlapping, display flicker by pulse driving can be minimized.
[0010]
In the above invention, it is preferable that the plurality of light emitting elements of the first and second groups are arranged in rows every other one.
[0011]
With this configuration, display flicker can be reduced most effectively.
[0012]
In the above invention, the light emitting elements in the group are preferably connected in parallel. Thereby, it can drive by a low voltage pulse power supply.
[0013]
Moreover, in the said invention, it is preferable that each light emitting element in a group is connected in series. Thus, it can be driven by a low current pulse power source.
[0014]
In the above invention, the light emitting element is preferably a light emitting diode. The light-emitting diode is effective for pulse driving because of its short response time, and the light emission brightness can be easily adjusted by the value of the current flowing through the element, so that it can be adjusted to the optimum light emission brightness according to the external brightness. The benefits that are possible are obtained. In addition, since the size of the element is very small as compared with the cold cathode tube, there is an advantage that the size can be easily reduced.
[0015]
In the above invention, the light emitting element may be disposed along one side edge of the light guide plate, or may be disposed along two opposing side edges.
[0016]
The arrangement along one side edge has an advantage that the configuration is simple, and the arrangement along two side edges provides an advantage that luminance unevenness can be reduced.
[0018]
The present invention is a liquid crystal device comprising the illumination device according to any one of claims 1 to 8 and a liquid crystal display panel attached to the front surface of the illumination device.
[0019]
According to this liquid crystal device, it is possible to perform display with low power consumption and without uneven brightness.
[0020]
According to another aspect of the present invention, there is provided a lighting device having a plurality of light emitting elements arranged in a row and a light guide plate that receives light from each of the light emitting elements and emits the light in a specific direction. And a plurality of light emitting element groups including the second light emitting element group, and the pulse signals for driving the plurality of light emitting elements have different phases and are effective for the plurality of light emitting element groups. The pulse signal of the first light emitting element group is raised, the pulse signal of the second light emitting element group is lowered, and the pulse signal of the second light emitting element group is changed so that the time overlaps partially. The lighting device driving method is characterized in that the pulse signal of the first light emitting element group is lowered after the start-up.
[0021]
According to such a driving method, since each light emitting element is pulse-driven, power consumption of each light emitting element can be reduced. Further, since each group is driven by a pulse signal having a different phase and a part of effective time overlapping, display flicker by pulse driving can be minimized.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[0023]
FIG. 2 is a plan view showing a configuration of a lighting device according to an embodiment of the present invention. As shown in this figure, in the illumination device of the present invention, LEDs 21a to 21d as light sources are arranged on the side surface of a light guide plate 22 made of a transparent member such as acrylic. Reference numeral 23 denotes a mounting plate on which the LEDs 21a to 21d are installed.
[0024]
3 is a cross-sectional view taken along line AA ′ of FIG. As shown in the figure, a reflection sheet 27 is provided below the light guide plate 22 so that all the illumination light emitted from the LEDs 21 a to 21 d enters the light guide plate 22. The surface of the reflection sheet 27 is subjected to a mirror treatment such as silver plating in order to efficiently reflect the illumination light. In addition, the light guide plate 22 is provided with a light scattering pattern (not shown) for scattering illumination light that has entered the light guide plate 22 from the LEDs 21a to 21d. A diffusion sheet 25 for further scattering the illumination light emitted from the light guide plate 22 is disposed above the light guide plate. Further, on the surface of the diffusion sheet 25, a prism sheet 26 in which a plurality of microprisms are formed on the entire surface of one side is laid. The prism sheet 26 has a characteristic of condensing illumination light emitted from the surface of the light guide plate 22 and transmitted through the diffusion sheet 25. Reference numeral 24 denotes a metal frame, and a mounting plate 23 is attached to the metal frame.
[0025]
Next, a driving method of the illumination device having the above-described configuration will be described with reference to FIGS. FIG. 1 is a diagram showing an electric circuit of the illumination device according to the first embodiment described above.
[0026]
In the present embodiment, a plurality of LEDs that are light sources are divided into two light source groups as shown in FIG. One is a light source group composed of LEDs 21a and 21c, and the other is a light source group composed of LEDs 21b and 21d.
[0027]
In each light source group, the LEDs are connected in series. The light source group constituted by the LEDs 21a and 21c is driven by the pulse voltage V1, and the current limiting resistor R1 is connected to the anode of the LED 21a. The resistor R1 is for suppressing the current flowing through the LEDs 21a and 21c. Similarly, the light source group constituted by the LEDs 21b and 21d is driven by the pulse voltage V2, and the resistor R2 is connected to the anode of the LED 21b. Similarly to the resistor R1, the resistor R2 is for suppressing the current flowing through the LEDs 21b and 21d.
[0028]
FIG. 4 shows pulse waveforms of the pulse voltages V1 and V2. As described above, the phases of the pulse voltages V1 and V2 are different, and further, the pulse voltage V2 falls after the pulse voltage V1 rises, and the pulse voltage V1 falls after the pulse voltage V2 rises. . That is, all the LEDs are not turned off, and two groups are turned on redundantly.
[0029]
In this way, flickering due to pulse driving can be prevented by providing a period in which both light source groups are in the ON state at the same time. The voltage values of the pulse voltages V1 and V2 are determined by the current suppression resistance, the number of LEDs, and the characteristics so that the currents flowing through the LEDs connected to the respective circuits are equal.
[0030]
By applying the voltage pulses as described above to the respective light source groups and controlling the blinking of the light sources, flickering can be prevented and a low power consumption lighting device with improved luminance unevenness can be obtained.
[0031]
Next, FIG. 5 shows a driving circuit of the lighting apparatus according to the second embodiment. In the present embodiment, each light source group is configured by connecting each LED in parallel. The light source group composed of the LEDs 21a and 21c is driven by the pulse voltage V1, and current limiting resistors Ra and Rc are connected to the anodes of the LEDs 21a and 21c, respectively. The current limiting resistors Ra and Rc are for suppressing the current flowing through the LEDs 21a and 21c, and are determined by the power supply voltage value and the characteristics of the LEDs 21a and 21c.
[0032]
Similarly, the LEDs 21b and 21d are driven by the pulse voltage V2, and current limiting resistors Rb and Rd are connected to the anodes of the LEDs 21b and 21d, respectively. Similarly, the current limiting resistors Ra and Rc are for suppressing the current flowing through the LEDs 21b and 21d, and are determined by the power supply voltage value and the characteristics of the LEDs 21b and 21d. Further, the cathodes of the LEDs 21a to 21d are grounded.
[0033]
Thus, by connecting the LEDs in parallel, a voltage equal to the voltage value of the pulse voltage is applied to all the LEDs, so that the voltage value of the power supply voltage can be set low.
[0034]
Next, a third embodiment will be described. FIG. 6 is a plan view of the lighting device according to this embodiment. In FIG. 6, LEDs 21 a to 21 e that are light sources are arranged on the right side of the light guide plate 22. The five LEDs 21a to 21e are connected to every other one and divided into a light source group composed of three LEDs and a light source group composed of two LEDs. Thus, in this embodiment, the number of LEDs constituting each light source group is different. FIG. 7 shows an electric circuit diagram in the same embodiment. The LEDs 21a, 21c, and 21e are connected in parallel, and current limiting resistors Ra, Rb, and Re are connected to the anodes of the LEDs 21a, 21c, and 21e, respectively. And the light source group comprised by LED21a, 21c, 21e is driven with the pulse voltage V3.
[0035]
On the other hand, a light source group configured by connecting LEDs 21b and 21d in parallel is driven by a pulse voltage V4. The current limiting resistors Rb and Rd are connected to the anodes of the LEDs 21b and 21d, respectively.
[0036]
FIG. 8 shows pulse waveforms of the pulse voltages V3 and V4 applied to the light source group described above. In this figure, as in the first and second embodiments, the phase of the pulse voltage applied to each light source group is different, and after the pulse voltage V3 rises, the pulse voltage V4 falls, and the pulse voltage V4 After the voltage rises, the pulse voltage V3 falls. That is, all the LEDs are not turned off, and two groups are turned on redundantly. Thereby, the flicker by pulse drive can be prevented.
[0037]
In addition, a pulse voltage is applied so that the power consumption is equal in both light source groups. That is, the pulse voltage value is set so that the light emission luminance of the irradiated surface irradiated by each light source group becomes equal. Therefore, in this embodiment, as shown in FIG. 8, the pulse voltage V4 applied to the light source group constituted by the LEDs 21b and 21d is applied to the light source group constituted by the LEDs 21a, 21c and 21e. It is set higher than the pulse voltage of the pulse voltage V3.
[0038]
By applying the voltage pulse as described above to each light source group and controlling the blinking of the light source, it is possible to prevent flickering and to obtain a lighting device with low power consumption that improves luminance unevenness in the vicinity of the light source. it can.
[0039]
In the above embodiment, the LED connection may be a series connection instead of a parallel connection. In this case, the resistance value of the current limiting resistor and the voltage value of the applied voltage pulse are set so that the power consumption consumed by each light source group becomes equal. The pulse frequency is set to a frequency suitable for suppressing flickering, and each light source group is driven alternately at these pulse frequencies.
[0040]
Moreover, you may increase / decrease the number of LED which comprises each light source group. In this case, the pulse voltage value applied to each light source group needs to be set so that the power consumption in each light source group becomes equal. In addition, a period in which at least two or more light source groups are simultaneously turned on at the rising edge and the falling edge of the pulse is provided. In addition, the drive circuit that drives each light source group also increases or decreases as the light source groups increase or decrease.
[0041]
Moreover, in embodiment mentioned above, although LED is installed only in one side edge of a light-guide plate, in order to irradiate an irradiation surface more uniformly, LED is installed in the both-sides edge of a light-guide plate, and it irradiates from both sides You can also Hereinafter, a description will be given of a lighting device in which LEDs are arranged on both sides.
[0042]
FIG. 9 is a plan view showing the configuration of the illumination device according to the fourth embodiment. In FIG. 9, 21a-21d and 22a-22d are LEDs. The LEDs 21 a to 21 d are installed on the right side of the light guide plate 22, and the LEDs 22 a to 22 d are installed on the left side of the light guide plate 22.
[0043]
In FIG. 10, the electric circuit of the illuminating device in the embodiment is shown. In this figure, in the LEDs arranged on the right side, LEDs 21a and 21c are connected in series, and a current limiting resistor R10 is connected to the anode of the LED 21a. Similarly, LEDs 22b and 22d are connected in series on the left side, and a current limiting resistor R11 is connected to the anode of 22b. A group consisting of R10 and LEDs 21a and 21c and a group consisting of R11 and LEDs 22b and 22d are connected in parallel and driven by a pulse voltage V2.
[0044]
Similarly, LEDs 21b and 21d arranged on the right side are connected in series, and a current limiting resistor R12 is connected to the anode of the LED 21b. Similarly, LEDs 22a and 22c are connected in series on the left side, and a current limiting resistor R13 is connected to the anode of 22a. A group consisting of R11 and LEDs 21b and 21d and a group consisting of R12 and LEDs 22a and 22c are connected in parallel and driven by a pulse voltage V1.
[0045]
The pulse voltages V1 and V2 for driving each light source group have, for example, the pulse waveforms shown in FIG. In FIG. 4, the voltage values of the pulse voltages V1 and V2 are determined by the number of LEDs connected in series.
[0046]
In the above-described embodiment, the LED connection may be a parallel connection instead of a series connection. That is, 21a and 21c connected in series may be connected in parallel, and a current suppression resistor may be provided at the anode of each LED. Thereby, compared with the light source group comprised by connecting LED in series, the voltage value of a pulse voltage can be set low.
[0047]
As described above, in the fourth embodiment, by providing the light sources on both sides of the light guide plate 22, it is possible to realize an illuminating device that can irradiate the entire irradiation surface brightly with uniform luminance.
[0048]
In the above embodiment, the LEDs may be connected to each side and driven alternately. That is, a light source group composed of LEDs 21a to 21d and a light source group composed of LEDs 22a to 22d are created, and these light source groups are driven by pulse voltages V1 and V2, respectively.
[0049]
As a result, the right side light source and the left side light source are alternately lit.
[0050]
In each light source group described above, current suppression resistors for suppressing current are provided at the anodes of the LEDs 21a and 22a.
[0051]
Next, an electro-optical device using the above-described illumination device will be described. As an electro-optical device using the above-described illumination device, a liquid crystal device using the above-described illumination device as a backlight can be given.
[0052]
In this liquid crystal device, for example, a liquid crystal panel is installed above the diffusion sheet 25 of the lighting device according to the present invention. Further, an optical sheet such as a prism sheet or a wave sheet is disposed between the lighting device and the liquid crystal panel as necessary. As a result, a liquid crystal device provided with an illumination device such as that used in notebook computers is configured.
[0053]
Thereby, the liquid crystal device provided with the illuminating device which can suppress the flicker of a liquid crystal panel and can irradiate a liquid crystal panel uniformly can be comprised.
[0054]
In the above description, a liquid crystal device has been described as an example of the display device in which the illumination device of the present embodiment is used. However, the display device in which the illumination device of this embodiment is used is not limited to a liquid crystal device, and can be widely used in a transmissive display device or a transflective display device provided with a transmissive display element.
[0055]
FIG. 11 is an external view showing an example of an electronic device using a liquid crystal device including the illumination device of the above embodiment.
[0056]
FIG. 11A is a perspective view showing a mobile phone. Reference numeral 1000 denotes a mobile phone body, and 1001 of the mobile phone body is a liquid crystal display unit using a liquid crystal device provided with the illumination device of the present invention.
[0057]
FIG. 11B illustrates a wristwatch type electronic device. 1100 is a perspective view showing a watch body. Reference numeral 1101 denotes a liquid crystal display unit using a liquid crystal device including the illumination device of the present invention. Since this liquid crystal panel has high-definition pixels as compared with a conventional clock display unit, it can also display a television image and can realize a watch-type television.
[0058]
FIG. 11C illustrates a portable information processing apparatus such as a word processor or a personal computer. Reference numeral 1200 denotes an information processing apparatus, reference numeral 1202 denotes an input unit such as a keyboard, reference numeral 1206 denotes a display unit using a liquid crystal device including the lighting device of the present invention, and reference numeral 1204 denotes an information processing apparatus main body.
[0059]
【The invention's effect】
As described above, according to the present invention, since each light emitting element is pulse-driven, the power consumption of each light emitting element can be reduced. Further, since each group is driven by a pulse signal having a different phase and a part of effective time overlapping, display flicker by pulse driving can be minimized.
[Brief description of the drawings]
FIG. 1 is an electric circuit diagram of a lighting device according to a first embodiment of the present invention.
FIG. 2 is a plan view showing a configuration of a lighting apparatus according to the first and second embodiments of the present invention.
FIG. 3 is a cross-sectional view taken along the line AA ′ of the illumination device.
FIG. 4 is a timing chart of pulse voltages according to the first, second and fourth embodiments of the present invention.
FIG. 5 is an electric circuit diagram of a lighting device according to a second embodiment of the present invention.
FIG. 6 is a plan view showing a configuration of a lighting apparatus according to a third embodiment of the present invention.
FIG. 7 is an electric circuit diagram of a lighting apparatus according to a third embodiment of the present invention.
FIG. 8 is a pulse voltage timing chart according to a third embodiment of the present invention.
FIG. 9 is a plan view showing a configuration of a lighting apparatus according to a fourth embodiment of the present invention.
FIG. 10 is an electric circuit diagram of a lighting apparatus according to a fourth embodiment of the present invention.
FIG. 11 is a schematic configuration diagram illustrating an application example of a liquid crystal device including the illumination device of the present invention.
FIG. 12 is an electric circuit diagram of a conventional lighting device.
[Explanation of symbols]
21a-21e LED (light emitting element)
R1, R2 Current control resistors

Claims (10)

A plurality of light emitting elements arranged in a row and electrically classified into a plurality of groups including the first and second groups;
A light guide plate that receives light from each of the light emitting elements and emits the light in a specific direction;
Driving means for driving the plurality of light emitting elements for each of the plurality of groups by a pulse signal having a phase difference and a partly overlapping effective time;
The driving means raises the first group of pulse signals, then lowers the second group of pulse signals, raises the second group of pulse signals, and then raises the first group of pulse signals. An illuminating device characterized in that the pulse signal is lowered.   The lighting device according to claim 1, wherein the plurality of light emitting elements of the first and second groups are arranged in a row every other one.   The lighting device according to claim 1, wherein the light emitting elements in the group are connected in parallel.   The lighting device according to claim 1, wherein each light emitting element in the group is connected in series.   The lighting device according to claim 1, wherein the light emitting element is a light emitting diode.   The lighting device according to claim 1, wherein the light emitting element is disposed along one side edge of the light guide plate.   The lighting device according to any one of claims 1 to 5, wherein the light emitting element is disposed along two opposing side edges of the light guide plate.   A liquid crystal device comprising: the illumination device according to claim 1; and a liquid crystal display panel attached to a front surface of the illumination device. In a lighting device having a plurality of light emitting elements arranged in a row and a light guide plate that receives light from each of the light emitting elements and emits the light in a specific direction,
Electrically classifying the plurality of light emitting elements into a plurality of light emitting element groups including first and second light emitting element groups;
The pulse signals of the first light emitting element group are set so that the pulse signals for driving the plurality of light emitting elements have different phases for each of the plurality of light emitting element groups and the effective times partially overlap. The pulse signal of the second light emitting element group is lowered, the pulse signal of the second light emitting element group is raised, and then the pulse signal of the first light emitting element group is lowered. A driving method of the lighting device.   An electronic apparatus comprising the liquid crystal device according to claim 8.

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