WO2017029894A1

WO2017029894A1 - Led display device and drive device

Info

Publication number: WO2017029894A1
Application number: PCT/JP2016/069640
Authority: WO
Inventors: 勲米岡; 重教渋江; 浅村　吉範
Original assignee: 三菱電機株式会社
Priority date: 2015-08-20
Filing date: 2016-07-01
Publication date: 2017-02-23
Also published as: JP2018155773A

Abstract

The purpose of the present invention is to provide a technology capable of suppressing LED power consumption. An LED display device equipped with voltage supply units (40), (50) capable of supplying multiple different types of voltage, and a drive unit (5) for driving an LED display unit (1) by using the multiple types of voltage. The drive unit (5) uses time-sharing control and switches the voltage to be supplied to an LED array to be switched on from among the multiple types of voltage, and switches on some of the LEDs to be switched on by using the voltage to be supplied to the LED array, among the multiple LEDs included in the LED array to be switched on.

Description

LED display device and driving device

The present invention relates to an LED display device including an LED display unit having LEDs (Light Emitting Diodes) and a driving device for driving the LED display unit.

LED display devices having LEDs are often used for outdoor and indoor advertisement display. These LED display devices have been used as large display devices having a pixel pitch of 3 mm or more so far, but due to the recent reduction in the cost of LEDs and the narrowing of the pixel pitch, they have become 1.5 mm and 1.9 mm products. Has been put on the market.

Due to the narrowing of the pixel pitch, the LED that constitutes one pixel is composed of a very small package of 1.0 mm × 1.0 mm or less. With the downsizing of the package, depending on the number of terminals, the yield of the soldering process may decrease due to the decrease in the area of the soldering pad, or the pattern may become complicated and the cost may increase due to the increase in the number of layers of the substrate. is doing. As a method for solving these problems, an anode common package in which anodes of red, green and blue LEDs are electrically connected is widely used so that the number of terminals of the package becomes a minimum number. Yes.

However, in the anode common, the voltages supplied to the LEDs of red, green, and blue are common, so if the forward voltage of each LED is different, power corresponding to the forward voltage difference is wasted. Problems such as an increase in power consumption occur. In addition, when the power consumption increases, the heat generation also increases, so that problems such as a reduction in the life of the LED due to an increase in the temperature of the LED itself also occur. On the other hand, in order to reduce the power consumption and extend the life of the LED, a cathode common drive method in which the cathode of the LED is electrically connected has been proposed (for example, Patent Document 1). .

Japanese Patent No. 3564359

However, the drive circuit corresponding to the cathode common has a limited number of manufacturers, and there is a problem that it is difficult to obtain a mass production effect in terms of cost, resulting in an increase in cost.

Therefore, the present invention has been made in view of the above problems, and an object thereof is to provide a technique capable of suppressing the power consumption of an LED.

The LED display device according to the present invention uses an LED display unit including a plurality of LED arrays, a voltage supply unit capable of supplying a plurality of different types of voltages, and the plurality of types of voltages that can be supplied by the voltage supply unit. And a driving unit for driving the LED display unit. Each of the LED arrays has a plurality of LEDs having different emission wavelengths, with anodes or cathodes electrically connected to each other. The drive unit switches a voltage to be supplied to the LED array to be lit from among the plurality of types of voltages by time division control, and among the plurality of LEDs included in the LED array to be lit Then, some of the LEDs to be turned on by the voltage to be supplied to the LED array are turned on in synchronization with the switching.

According to the present invention, the voltage to be supplied to the LED array to be lit is switched by time division control from among a plurality of types of voltages, and the LED array among the plurality of LEDs included in the LED array to be lit Some of the LEDs to be lit according to the voltage to be supplied to are lit in synchronization with the switching. Thereby, the power consumption of LED can be suppressed.

The objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description and the accompanying drawings.

1 is a block diagram illustrating a configuration of an LED display device according to Embodiment 1. FIG. 1 is a block diagram illustrating a configuration of an LED display device according to Embodiment 1. FIG. 3 is a block diagram showing a hardware configuration of the LED display device according to Embodiment 1. FIG. 1 is a circuit diagram showing a configuration of an LED display device according to Embodiment 1. FIG. It is a figure which shows an example of the relationship between the applied voltage and output current in a constant current circuit. 3 is a timing chart showing the operation of the LED display device according to Embodiment 1.

<Embodiment 1>
1 and 2 are block diagrams showing the configuration of the LED display device according to Embodiment 1 of the present invention. The LED display device of FIG. 1 includes an LED display unit 1, an input terminal 2, a video signal processing unit 3, a luminance correction unit 4, and a driving unit 5 corresponding to a driving device.

First, the hardware of each component will be described. For example, an LED display panel is applied to the LED display unit 1. The video signal processing unit 3 and the luminance correction unit 4 (hereinafter referred to as “video signal processing unit 3 etc.”) are realized by, for example, the processor 92 in FIG. 3 executing a program stored in the memory 91.

The memory 91 includes, for example, a nonvolatile or volatile semiconductor memory such as a RAM, a ROM, a flash memory, an EPROM, and an EEPROM, a magnetic disk, a flexible disk, an optical disk, a compact disk, a mini disk, and a DVD. The processor 92 includes, for example, a CPU (Central Processing Unit), a central processing device, a processing device, a computing device, a microprocessor, a microcomputer, a processor, and a DSP. The program causes a computer to execute procedures and methods such as the video signal processing unit 3 and is realized by, for example, software, firmware, or a combination of software and firmware.

Note that the video signal processing unit 3 or the like is not limited to a configuration realized by operating according to a software program, and may be, for example, a signal processing circuit that realizes the operation with a hardware electric circuit. Alternatively, the video signal processing unit 3 or the like may be a combination of a configuration realized by a software program and a configuration realized by hardware. Similarly, the drive unit 5 may be realized by hardware, or may be realized by a combination of software and hardware.

Next, each component of the LED display device of FIGS. 1 and 2 will be described.

The LED display unit 1 is used for displaying a desired image such as a character or a figure. The LED display unit 1 has a plurality of LED arrays arranged in a matrix. In the example of FIG. 1, a total of 16 LED arrays of 4 × 4 are arranged in a matrix.

As shown in FIG. 2, the LED array 100, which is one of a plurality of LED arrays, has a total of three

LEDs

100R, 100G, and 100B of red (R), green (G), and blue (B) having different emission wavelengths. is doing. Although not shown in FIGS. 1 and 2, other LED arrays are configured in the same manner.

The input terminal 2 receives a video signal from the outside. The video signal processing unit 3 selects a region necessary for display based on the video signal received at the input terminal 2 and performs processing such as gamma correction. The luminance correction unit 4 corrects the luminance of the output signal of the video signal processing unit 3. The drive unit 5 performs, for example, LED lighting control (flashing control) of the LED display unit 1 by driving the LED display unit 1 based on the output signal corrected by the luminance correction unit 4.

<LED display unit 1 and drive unit 5>
FIG. 4 is a circuit diagram showing configurations of the LED display unit 1 and the drive unit 5 according to the first embodiment.

First, the LED display unit 1 will be described. In general, an LED display device with a narrow pixel pitch scans in units of several lines. FIG. 4 shows a configuration in which drive control is performed with 2 rows × 2 lines scan as an example.

In the example of FIG. 4, the

LED arrays

100 and 101 are LED arrays on the first line, and the LED arrays 110 and 111 are LED arrays on the second line. The

LED arrays

100 and 110 are the first row LED arrays, and the LED arrays 101 and 111 are the second row LED arrays. Note that the number of columns and lines is not limited to this, and is generally larger than this. For example, as shown in FIG. 1, in a 4 × 4 LED array, drive control is performed with 4 columns × 4 lines scan.

The LED array 100 has R, G, and

B LEDs

100R, 100G, and 100B as described above. The anodes of the

LEDs

100R, 100G, and 100B are anode common terminals and are electrically connected to each other. Similarly, the LED array 101 includes R, G, and

B LEDs

101R, 101G, and 101B whose anodes are electrically connected to each other. The LED array 110 includes R, G, and

B LEDs

110R, 110G, and 110B whose anodes are electrically connected to each other. The LED array 111 includes R, G, and

B LEDs

111R, 111G, and 111B whose anodes are electrically connected to each other.

Next, the drive unit 5 will be described. The drive unit 5 comprehensively controls the

switches

20, 21, 30, the green and blue power supply circuit 40, the red power supply circuit 50, the constant current circuit block 60, and the on / off circuit block 70. And a control circuit 80.

Here, the green and blue power supply circuit 40 and the red power supply circuit 50 having an output voltage different from the power supply circuit 40 constitute a voltage supply unit (power supply circuit). Thereby, the voltage supply part (power supply circuit) can supply a plurality of different voltages Vgb and Vr.

The driving unit 5 drives the LED display unit 1 using a plurality of types of voltages Vgb and Vr that can be supplied by the voltage supply unit (the green and blue power supply circuits 40 and the red power supply circuit 50). In the first embodiment, the voltage supply units (the green and blue power supply circuits 40 and the red power supply circuit 50) are provided in the drive unit 5, but may be separate from the drive unit 5. .

Next, each component of the drive unit 5 will be described in detail.

The anode common terminals of the

LED arrays

100 and 101 are connected to the switch 20. When the switch 20 is set to ON by the control of the control circuit 80, the

LED arrays

100 and 101 are turned on, and these LEDs can be turned on. Similarly, the anode common terminals of the LED arrays 110 and 111 are connected to the switch 21. When the switch 21 is set to ON by the control of the control circuit 80, the LED arrays 110 and 111 are turned on, and those LEDs can be turned on.

The switch 30 is connected between the green and blue power supply circuit 40 and the red power supply circuit 50 and the

switches

20 and 21. This switch 30 is controlled by the control circuit 80 so that the green and blue power supply circuit 40 and the red power supply circuit 50 are supplied with one type of voltage (anode common terminal of the LED array to be lit) from a plurality of types of voltages Vgb and Vr. The voltage to be supplied is selected, and the one kind of voltage is supplied to the anode common terminal of the LED array to be lit.

The constant current circuit block 60 includes a constant current circuit 61R for the first row red, a constant current circuit 61G for the first row green, a constant current circuit 61B for the first row blue, and a constant current circuit for the second row red. A current circuit 62R, a second row green constant current circuit 62G, and a second row blue constant current circuit 62B are provided. The constant current circuit 61R is electrically connected to the cathodes of the

red LEDs

100R and 110R of the

LED arrays

100 and 110, and the constant current circuit 61G is electrically connected to the cathodes of the

green LEDs

100G and 110G of the

LED arrays

100 and 110. The constant current circuit 61B is electrically connected to the cathodes of the

blue LEDs

100B and 110B of the

LED arrays

100 and 110. Similarly, the constant

current circuits

62R, 62G, and 62B are electrically connected to the cathodes of the red, green, and blue LEDs of the LED arrays 101 and 111.

The ON / OFF circuit block 70 includes ON /

OFF circuits

71R, 71G, 71B, 72R, 72G, 72B. The on and off circuit 71R is electrically connected to the cathodes of the

LEDs

100R and 110R via the constant current circuit 61R, and the on and off circuit 71G is electrically connected to the cathodes of the

LEDs

100G and 110G via the constant current circuit 61G. The on / off circuit 71B is electrically connected to the cathodes of the

LEDs

100B and 110B via the constant current circuit 61B. Similarly to these, the ON /

OFF circuits

72R, 72G, 72B are electrically connected to the cathodes of the red, green, and blue LEDs via the constant

current circuits

62R, 62G, 62B. The on and off

circuits

71R, 71G, 71B, 72R, 72G, and 72B described above turn on or off the electrical connection under the control of the control circuit 80.

The control circuit 80 controls switching of the switch 30 by time division control. In addition, the control circuit 80 individually controls on and off of the on and off

circuits

71R, 71G, 71B, 72R, 72G, and 72B in synchronization with the switching, thereby turning on and off the current flowing through the LEDs. As a result, lighting and extinguishing of the LED are individually controlled.

In the first embodiment, the control circuit 80 performs LED lighting control by PWM (Pulse Width Modulation) control using a duty ratio (ratio of on period per pulse period). For this reason, the LED lighting control performed by the control circuit 80 is strictly LED blinking control, but since the pulse cycle is very short, it is perceived as lighting by human eyes. In such PWM control, as the duty ratio increases, the ratio of the on-period increases, so that the brightness of the LED felt by human eyes increases.

The control circuit 80 not only performs the above control but also controls the switching of the

switches

20 and 21.

The drive unit 5 configured as described above performs time-sharing control of switching of the switch 30, so that a voltage (a voltage to be supplied to the anode common terminal of the LED array to be lit out of a plurality of types of voltages Vgb and Vr) One type of voltage) is switched by time-sharing control.

And the drive part 5 synchronizes some LED which should be lighted with the voltage (one type of voltage) which should be supplied to the said LED array among several LED contained in the LED array of lighting object to switching of a voltage. And turn it on. When the voltage to be supplied to the LED array is the voltage Vr of the red power supply circuit 50, the drive unit 5 according to the first embodiment replaces the red LED in the LED array with the part of the LEDs. Turn on as. Further, when the voltage to be supplied to the LED array is the voltage Vgb of the green and blue power supply circuit 40, the driving unit 5 according to the first embodiment selects the green and blue LEDs in the LED array. The LED is turned on as the partial LED. The LED lighting control will be described in detail later.

<Voltage of voltage supply unit>
The voltages Vgb and Vr of the voltage supply unit (green and blue power supply circuit 40 and red power supply circuit 50) will be described. Table 1 shows an example of materials of R, G, and B LEDs according to the first embodiment and forward voltages.

As shown in Table 1, the forward voltage of the green (G) LED and the blue (B) LED are substantially the same, but the forward voltage of the red (R) LED is green (G). There is a voltage difference of approximately 1.0 V between the forward voltage of the blue LED and the blue (B) LED. This voltage difference causes power loss when the anode common is connected. In view of this, in the first embodiment, when the R LED is lit, the control circuit 80 switches the switch 30 to the red power supply circuit 50 and supplies the voltage to the R LED. On the other hand, when the G and B LEDs are lit, the control circuit 80 switches the switch 30 to the green and blue power supply circuit 40 and supplies the voltage to the G and B LEDs.

FIG. 5 is a diagram showing an example of the relationship between the applied voltage and the output current in the constant

current circuits

61R and 62R. The constant

current circuits

61R and 62R have a function of flowing a specified current (a specified current) regardless of the applied voltage. However, in order to make this function effective, as shown in FIG. 5, the voltage applied to the constant

current circuits

61R and 62R is a voltage called knee voltage depending on the constant

current circuits

61R and 62R (in the case of FIG. 5). 0.5V) or more is necessary. For this reason, in the configuration in which a current of 10 mA is supplied to the R LED, for example, a voltage of 2.9 V or more obtained by adding a knee voltage to a forward voltage of 2.4 V is applied as the voltage Vr of the power supply circuit 50 for red. However, in consideration of variations, for example, a voltage slightly higher than 2.9 V is preferably applied as the voltage Vr.

For the same reason, in the configuration in which a current of 10 mA is supplied to the G and B LEDs, for example, a voltage of 3.9 V or more obtained by adding a knee voltage of 0.5 V to a forward voltage of 3.4 V is a green and blue power supply circuit. It is applied as a voltage Vgb of 40. However, in consideration of variations, for example, a voltage slightly higher than 3.9 V is preferably applied as the voltage Vgb.

As described above, in the first embodiment, the plurality of types of voltages that can be supplied by the voltage supply unit include the voltage Vgh that is the second voltage and the voltage Vr that is the first voltage smaller than the second voltage. .

<LED lighting control>
FIG. 6 is a timing chart showing switch switching and LED lighting control according to the first embodiment. FIG. 6 shows the supply voltage supplied to the LEDs from the voltage supply unit via the switch 30, the on and off of the

switches

20 and 21, and the LEDs that are lit.

First, in the period t1 to t2, the switch 30 is switched to the red power supply circuit 50 so that the supply voltage becomes the voltage Vr. The switch 20 is turned on and the switch 21 is turned off, so that the red power supply circuit 50 and the

LED arrays

100 and 101 are electrically connected. In such setting of the

switches

20, 21, and 30, the control circuit 80 performs PWM control of the on and off

circuits

71R and 72R and PWM control of the constant

current circuits

61R and 62R. As a result, the LED 100R of the LED array 100 in the first row and the LED 101R of the LED array 101 in the second row are turned on.

That is, when the supply voltage (one type of voltage) is the voltage Vr, the control circuit 80 (drive unit 5) lights the

red LEDs

100R and 101R included in the

LED arrays

100 and 101 to be lit. At this time, the control circuit 80 (drive unit 5) turns off the on / off

circuits

71G, 71B, 72G, 72B, thereby turning on the

LEDs

100G, 100B other than the LED 100R in the LED array 100 to be lit and the LEDs to be lit. The

LEDs

101G and 101B other than the LED 101R in the array 101 are turned off.

Next, in the period t2 to t3, the switch 30 is switched to the green and blue power supply circuits 40 so that the supply voltage becomes the voltage Vgb. The

switches

20 and 21 are maintained in a state, and the green and blue power supply circuit 40 and the

LED arrays

100 and 101 are electrically connected. In such setting of the

switches

20, 21, and 30, the control circuit 80 performs PWM control of the on and off

circuits

71G, 71B, 72G, and 72B, and performs PWM control of the constant

current circuits

61G, 61B, 62G, and 62B. As a result, the

LEDs

100G and 100B of the LED array 100 in the first row and the

LEDs

101G and 101B of the LED array 101 in the second row are turned on.

That is, when the supply voltage (one type of voltage) is the voltage Vgb, the control circuit 80 (drive unit 5) causes the

green LEDs

100G and 101G and the

blue LEDs

100B and 101B included in the

LED arrays

100 and 101 to be lit. Lights up. At this time, the control circuit 80 (drive unit 5) turns off the on and off

circuits

71R and 72R, thereby turning on the LED 100R other than the

LEDs

100G and 100B in the LED array 100 to be lit and the LED array 101 to be lit. The LEDs 101R other than the

LEDs

101G and 101B are turned off.

Next, in the period t3 to t4, the switch 30 is switched to the red power supply circuit 50 so that the supply voltage becomes the voltage Vr. The switch 20 is turned off and the switch 21 is turned on, and the red power supply circuit 50 and the LED arrays 110 and 111 are electrically connected. In such setting of the

switches

20, 21, and 30, the control circuit 80 performs PWM control of the on and off

circuits

71R and 72R and PWM control of the constant

current circuits

61R and 62R. As a result, the LED 110R of the first row LED array 110 and the LED 111R of the second row LED array 111 are lit.

red LEDs

110R and 111R included in the LED arrays 110 and 111 to be lit. At this time, the control circuit 80 (drive unit 5) turns off the

LEDs

110G and 110B other than the LED 110R in the LED array 110 to be lit and the

LEDs

111G and 111B other than the LED 111R in the LED array 111 to be lit.

Next, in the period t4 to t5, the switch 30 is switched to the green and blue power supply circuits 40 so that the supply voltage becomes the voltage Vgb. The

switches

20 and 21 are maintained in a state, and the green and blue power supply circuit 40 and the LED arrays 110 and 111 are electrically connected. In such setting of the

switches

20, 21, and 30, the control circuit 80 performs PWM control of the on and off

circuits

71G, 71B, 72G, and 72B, and performs PWM control of the constant

current circuits

61G, 61B, 62G, and 62B. As a result, the

LEDs

110G and 110B of the LED array 110 in the first row and the

LEDs

111G and 111B of the LED array 111 in the second row are turned on.

green LEDs

110G and 111G and the

blue LEDs

110B and 111B included in the LED arrays 110 and 111 to be lit. Lights up. At this time, the control circuit 80 (drive unit 5) turns off the LED 110R other than the

LEDs

110G and 110B in the LED array 110 to be turned on and the LED 111R other than the

LEDs

111G and 111B in the LED array 111 to be turned on.

After the period t5, the same control as described above is repeatedly performed. Accordingly, the lighting of the

LEDs

100R, 101R, the lighting of the

LEDs

100G, 100B, 101G, 101B, the lighting of the

LEDs

110R, 111R, and the lighting of the

LEDs

110G, 110B, 111G, 111B are sequentially repeated. The brightness at the time of lighting is controlled by PWM control, and a desired image is displayed on the LED display unit 1.

Here, the power consumption is compared between the conventional anode common LED display device and the LED display device according to the first embodiment. The LED display device according to the present embodiment 1 has a power supply voltage difference of 1 (V) × 10 (mA) × PWM control duty ratio × the number of pixels, which is higher than the conventional LED display device. Power consumption is reduced. Here, assuming that the duty ratio is 0.25, the number of pixels is 2 million or more assuming full high-definition, and these are substituted into the above equation, according to the LED display device according to the first embodiment, 5 kW It can be seen that power consumption can be reduced to a certain extent.

<Summary of Embodiment 1>
According to the LED display device according to the first embodiment as described above, among the plurality of LEDs included in the LED array to be lit, some of the LEDs that should be lit are lit by the voltage to be supplied to the LED array. Let As a result, a suitable voltage can be applied to each of the R, G, and B LEDs, so that wasteful power consumption can be suppressed and power consumption can be reduced. Moreover, since heat generation of the drive circuit 80 (drive unit 5) and the like can be suppressed, the life of the LED can be extended and the reliability is improved.

Further, as described above, since it can be applied to an anode common type LED drive circuit commercialized by many manufacturers, it is advantageous in terms of availability and cost. However, even if the same configuration as described above is applied to the cathode common type LED drive circuit in which the cathodes of the R, G, and B LEDs are electrically connected to each other, the same effect as described above can be obtained.

In the first embodiment, two types of power supply circuits (green and blue power supply circuit 40 and red power supply circuit 50) are applied to the voltage supply unit. However, there are not necessarily two types, and three types of power supply circuits may be applied to the voltage supply unit so that three types of voltages can be independently supplied corresponding to R, G, and B. In FIG. 4, the combination of the number of LED arrays is 2 × 2, but the present invention is not limited to this, and an arbitrary number of combinations may be applied. Moreover, in FIG. 4, it was comprised so that the time division control (time division process) of light emission of LED might be performed per 2 lines. However, the present invention is not limited to this, and time division control (time division processing) may be performed in arbitrary line units (for example, 32 line units) in correspondence with the number of LEDs constituting the LED panel.

In the present invention, the embodiments can be appropriately modified or omitted within the scope of the invention.

Although the present invention has been described in detail, the above description is illustrative in all aspects, and the present invention is not limited thereto. It is understood that countless variations that are not illustrated can be envisaged without departing from the scope of the present invention.

1 LED display section, 5 drive section, 40 power supply circuit for green and blue, 50 power supply circuit for red, 100, 101, 110, 111 LED array, 100R-100B, 101R-101B, 110R-110B, 111R-111B LED.

Claims

An LED display section <1> including a plurality of LED arrays <100, 101, 102, 103>;
A voltage supply unit <40, 50> capable of supplying a plurality of different types of voltages;
A drive unit <5> for driving the LED display unit using the plurality of types of voltages that can be supplied by the voltage supply unit;
With
Each said LED array
A plurality of LEDs <100R to 100B, 101R to 101B, 110R to 110B, 111R to 111B> having different emission wavelengths, the anodes or cathodes of which are electrically connected to each other;
The drive unit is
From among the plurality of types of voltage, the voltage to be supplied to the LED array to be lit is switched by time division control, and
An LED display device, wherein among the plurality of LEDs included in the LED array to be lit, a part of the LEDs to be lit by the voltage to be supplied to the LED array is lit in synchronization with the switching.
The LED display device according to claim 1,
The plurality of LEDs include an LED display device including red, green and blue LEDs <100R to 100B, 101R to 101B, 110R to 110B, 111R to 111B>.
The LED display device according to claim 2,
The plurality of types of voltages include a first voltage and a second voltage different from each other,
The drive unit <5>
When the voltage to be supplied to the LED array <100, 101, 102, 103> is the first voltage, the red LEDs included in the LED array are turned on as the partial LEDs, and the LEDs An LED display device that, when the voltage to be supplied to the array is the second voltage, lights the green and blue LEDs included in the LED array as the partial LEDs.
The LED display device according to any one of claims 1 to 3,
The drive unit <5>
An LED display device that turns off LEDs other than the part of the plurality of LEDs included in the LED array <100, 101, 102, 103> to be turned on.
A driving device <5> for driving an LED display unit including a plurality of LED arrays <100, 101, 102, 103> using a plurality of different voltages;
Each said LED array
A plurality of LEDs <100R to 100B, 101R to 101B, 110R to 110B, 111R to 111B> having different emission wavelengths, the anodes or cathodes of which are electrically connected to each other;
The driving device includes:
From among the plurality of types of voltage, the voltage to be supplied to the LED array to be lit is switched by time division control, and
A drive device that causes some of the LEDs to be lit by the voltage to be supplied to the LED array to be lit in synchronization with the switching among the plurality of LEDs included in the LED array to be lit.