JP2009157189A - Light source system, light source control device, light source device, and image display method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light source system capable of improving power efficiency in a light source part at a low cost. <P>SOLUTION: Forward voltages Vf_all between both ends of LEDs are detected in respective division parts of LEDs 1R, 1G, and 1B in a light source part 10. Switching control between two power sources (VCC_LED_max and VCC_LED_min) is performed in accordance with the detected forward voltages Vf_all. Thus, power is appropriately supplied to respective division parts in the light source part 10, so that the power loss in the LEDs is reduced. Automatically switching the power sources in this manner facilitates adjustment of forward voltages in the LEDs in comparison with individually selecting LEDs in a conventional manner. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a light source device used as, for example, a backlight light source of a liquid crystal display device, a light source control device applied to such a light source device, a light source system using such a light source device, and an image display method.

  In recent years, there has been a trend toward thinner displays as represented by LCD TVs and plasma displays (PDP: Plasma Display Panels). Especially, many mobile displays are liquid crystal systems, and faithful color reproducibility is desired. It is rare. In addition, CCFL (Cold Cathode Fluorescent Lamp) type, which uses fluorescent tubes, is the mainstream backlight for liquid crystal panels, but environmentally mercury-free has been required, and a light-emitting diode (LED: Light) is used as a light source instead of CCFL. Emitting Diode) etc. are considered promising.

  As a backlight device using such an LED, for example, those shown in Patent Documents 1 and 2 have been proposed. The LED backlight device disclosed in Patent Document 1 is configured to change the luminance level of the entire backlight device according to the brightness of the surrounding environment by detecting external light. On the other hand, the LED backlight device disclosed in Patent Document 2 is configured by dividing the light source part into a plurality of partial lighting parts and sequentially lighting the plurality of partial lighting parts in order to improve the moving picture response of the liquid crystal panel. By performing the above (partial drive), a so-called black insertion process is performed.

JP 2006-145886 A JP 2006-243283 A

  By the way, in such an LED backlight device, for example, as shown in FIG. 16A, when a rated current If is passed through the LED (Di101), the voltage across the LED is the forward voltage of the LED. Vf. However, for example, as shown in FIG. 16B, even if the same rated current If is applied to a plurality of (in this case, two) LEDs (Di101, Di102), the manufacturing variation of individual LEDs, etc. For this reason, the voltages across the LEDs (forward voltages Vf_1, Vf_2) vary (generally, the variation in the forward voltage Vf when the rated current If flows is about 1-2 V per LED). Degree.) This means that in order to pass the rated current If in FIG. 16B, it is necessary to apply a voltage of (Vf_1 + Vf_2) or more. For example, as shown in FIG. 16C, when a plurality of (in this case, five) LEDs (Di101 to Di105) are connected in series with each other, in order to allow the rated current If to flow, each LED Therefore, it is necessary to apply a voltage equal to or higher than the voltage (Vf_1 + Vf_2 + Vf_3 + Vf_4 + Vf_5) obtained by adding the forward voltage variations.

  Therefore, when a plurality of LEDs are connected in series and the rated current If flows, the voltage across these LEDs (the sum of the forward voltages Vf of the LEDs) is the largest in all LEDs. The forward voltage Vf is the maximum value (Vf_max) ”. Conversely, the voltage across these LEDs (the sum of the forward voltage Vf of each LED) is the smallest when all the LEDs have “the forward voltage Vf is the minimum value (Vf_min)”. It is.

  Here, in the LED backlight device by the partial drive system shown by the said patent document 2, while arranging the light source part containing LED in a some division | segmentation part (partial lighting part), and by these division | segmentation part units Constant current drive is performed. Therefore, the case of dividing into two parts is taken as an example, and in one divided part, the voltage between both ends of the LED is the largest as described above (in all the LEDs, “the forward voltage Vf is the maximum value (Vf_max) In addition, in the other divided portion, the voltage between the both ends of the LED is the smallest as described above (in all the LEDs, “the forward voltage Vf is the minimum value (Vf_min)”). Considering the case, when the rated current If is to be supplied to both, it is necessary to apply the largest voltage (Vf_max × the number of LEDs in series) to each divided portion. Therefore, in the other divided portion, the difference from the largest voltage is a loss of a circuit portion (for example, a transistor) that is controlled to a predetermined rated current If, so that the power efficiency in the light source portion is reduced. Become. Further, when power loss is concentrated on the circuit portion, it may cause heat generation, and when the power loss exceeds the rated value, the circuit portion may be damaged.

  Therefore, conventionally, in order to prevent such a situation, a measure has been taken to align the forward voltage Vf by selecting the forward voltage Vf of each LED. However, since such sorting is time-consuming, it has become one of the factors that increase the cost when manufacturing an LED backlight device.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a light source control device and a light source device capable of realizing an improvement in power efficiency in a light source unit at a low cost, and such a light source device. It is an object to provide a light source system and an image display method used.

  The light source system of the present invention includes a light source unit having a plurality of light sources configured to include a light emitting diode, a power source unit having a plurality of different power sources and supplying power to each light source by these power sources, A forward voltage detection unit for detecting a forward voltage between both ends of each light source, and a light source control means for controlling the light source unit by changing at least one of the lighting period and the emission intensity of each light source, And a switching control means for performing switching control between a plurality of power sources in the power source unit according to the forward voltage between both ends of each light source detected by the forward voltage detecting unit. The light source system may further include a display unit that displays an image based on the video signal.

  The light source control device of the present invention is applied to a light source device including the light source unit, the power source unit, and the forward voltage detection unit, and includes the light source control unit, the switching control unit, and the like. It is equipped with.

  The light source device of the present invention includes the light source unit, the power source unit, the forward voltage detection unit, the light source control unit, and the switching control unit.

  An image display method of the present invention performs image display by modulating light emitted from a light source device in a display unit based on a video signal, and includes a light source including a light emitting diode (LED). Power is supplied to each of the plurality of light sources by a plurality of different power sources, and the light source unit is controlled by changing at least one of the lighting period and light emission intensity of each light source. A forward voltage between both ends is detected, and switching control between a plurality of power sources is performed in accordance with the detected forward voltage between both ends of each light source.

  It should be noted that any combination of the above-described configuration requirements and a representation obtained by converting the expression of the present invention between systems, apparatuses, methods, and the like are also effective as an aspect of the present invention.

  In the light source system, the light source control device, the light source device, and the image display method of the present invention, power is supplied from the power supply unit to the plurality of light sources in the light source unit including the light emitting diode. Then, the light source unit is controlled by changing at least one of the lighting period and the emission intensity of each light source. Here, the forward voltage between both ends of each light source is detected, and switching control between a plurality of power sources in the power supply unit is performed according to the detected forward voltage between both ends of each light source. Thus, as compared with the case where such power supply switching control is not performed, appropriate power supply is performed to each light source. In addition, since the power supply is automatically switched, the forward voltage of the light emitting diode can be easily adjusted as compared with the case where the light emitting diodes are individually selected as in the prior art.

  According to the light source system, the light source control device, the light source device, or the image display method of the present invention, the forward voltage between both ends of each light source is detected, and the detected forward voltage between both ends of each light source is detected. Thus, switching control between a plurality of power supplies is performed, so that an appropriate power supply can be supplied to each light source, and power loss in the light emitting diodes (for example, the order of individual light emitting diodes connected in series) It is possible to reduce the power loss in the circuit portion that absorbs the voltage difference generated by the accumulation of the directional voltage differences. In addition, since the power supply is automatically switched, the power loss can be reduced at any time, and the forward voltage of the light emitting diode can be easily adjusted. Therefore, it is possible to realize an improvement in power efficiency in the light source unit at a low cost by making the parts for performing the switching control between the power supplies inexpensive.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows the overall configuration of an image display system (liquid crystal display device 3) according to an embodiment of the present invention. The liquid crystal display device 3 is a so-called transmissive liquid crystal display device that emits transmitted light as display light Dout. The backlight device 1 as a light source device according to an embodiment of the present invention and a transmissive liquid crystal display. The panel 2 is included. The image display method according to the embodiment of the present invention is embodied by the image display system according to the present embodiment, and will be described below.

  The liquid crystal display panel 2 includes a transmissive liquid crystal layer 20 and a pair of substrates sandwiching the liquid crystal layer 20, that is, a TFT (Thin Film Transistor) substrate 211 which is a substrate on the backlight device 1 side, and a substrate opposed thereto. And the polarizing plate 210 and 220 laminated on the TFT substrate 211 and the counter electrode substrate 221 on the opposite side of the liquid crystal layer 20 respectively.

  Further, the TFT substrate 211 is formed with a matrix of pixels, and each pixel is formed with a pixel electrode 212 including a driving element such as a TFT.

  The backlight device 1 is of a mixed color system that obtains illumination light Lout that is specific color light by mixing a plurality of color lights (in this case, red light, green light, and blue light). The backlight device 1 includes a light source unit (a light source unit 10 to be described later) including a plurality of red LEDs 1R, green LEDs 1G, and blue LEDs 1B as three types of light sources that emit different color lights.

  2 and 3 show an example of an arrangement configuration of each color LED in the backlight device 1.

  As shown in FIG. 2A, in this backlight device 1, unit cells 41 and 42 of the light emitting unit are formed by two sets of red LED 1R, green LED 1G and blue LED 1B, respectively, and these two unit cells 41, The partial lighting part 4 which is a unit unit of the light emission part is formed by 42. In addition, each color LED is connected in series in each unit cell and between the unit cells 41 and 42. Specifically, as shown in FIG. 2B, the anode and cathode of each color LED are connected.

  The partial lighting units 4 configured in this way are arranged in a matrix in the light source unit 10 as shown in FIG. 3, for example, and can be controlled independently of each other as will be described later. Further, on the light source unit 10, one illumination light sensor 13 is arranged for four partial lighting units 4 (for example, partial lighting units 4A to 4D). The illumination light sensor 13 receives light from the partial lighting unit 4 (illumination light Lout described later), and receives light from a region (detection region 40) corresponding to the arrangement region of the four partial lighting units 4. It can receive light.

  Next, with reference to FIG. 4, the structure of the drive and control part of the liquid crystal display panel 2 and the light source unit 10 described above will be described in detail. FIG. 4 shows a block configuration of the liquid crystal display device 3. In FIG. 4 (and FIG. 5 described later), the illumination light sensor 13 is shown as being disposed in the vicinity of the light source unit 10 for convenience.

  As shown in FIG. 4, the driving circuit for driving the liquid crystal display panel 2 to display an image displays an X driver (data) that supplies a driving voltage based on the video signal to each pixel electrode 212 in the liquid crystal display panel 2. Driver) 51, a Y driver (gate driver) 52 that drives each pixel electrode 212 in the liquid display panel 2 along a scanning line (not shown), and timing control for controlling the X driver 51 and the Y driver 52. Unit (timing generator) 61, an RGB process processing unit 60 (signal generator) for processing an external video signal to generate an RGB signal, and a frame memory for storing the RGB signal from the RGB process processing unit 60 And a video memory 62.

  On the other hand, the part which performs the drive and control for the light source part 10 of the backlight apparatus 1 to perform lighting operation is the backlight drive part 11, the backlight control part 12, the illumination light sensor 13, and the I / V conversion part. 14 and an A / D converter 15.

  The illumination light sensor 13 receives the illumination light Lout from the light source unit 10 (specifically, the partial lighting unit 4 in each detection region 40 as described above) and obtains a light reception signal. (In this case, the red light sensor 13R that extracts red light from the mixed color light obtained by mixing red light, green light, and blue light and selectively receives the light, and extracts the green light and selectively receives the light. And a blue light sensor 13B that extracts blue light and selectively receives it.

  The I / V conversion unit 14 performs I / V (current / voltage) conversion on the light reception signal for each color obtained by the illumination light sensor 13, and outputs light reception data that is an analog voltage signal for each color. Is.

  The A / D conversion unit 15 samples the light reception data for each color output from the I / V conversion unit 14 at a predetermined timing according to the sampling gate signal SG supplied from the timing control unit 61, and also performs A / D (analog) / Digital) conversion is performed, and the received light data D1, which is a digital voltage signal, is output to the backlight control unit 12 for each color.

  The backlight control unit 12 is supplied from the light reception data D 1 for each color supplied from the A / D conversion unit 15, a control signal (control data) D 0 supplied from the timing control unit 61, and the backlight drive unit 11. Based on a control signal (a control signal D6 described later), control signals D3 and D4 described later and a selection signal SEL are generated and output, and the drive operation of the backlight drive unit 11 is controlled. The detailed configuration of the backlight control unit 12 will be described later (FIGS. 5 and 6).

  The backlight driving unit 11 performs lighting operation in units of the partial lighting unit 4 based on the control signals D3 and D4 and the selection signal SEL supplied from the backlight control unit 12 and the control signal D0 supplied from the timing control unit 61. The light source unit 10 is driven in a time division manner so as to perform the above. The detailed configuration of the backlight drive unit 11 will also be described later (FIGS. 5 and 6).

  Next, with reference to FIGS. 5-7, the detailed structure of the backlight drive part 11 and the backlight control part 12 mentioned above is demonstrated. FIG. 5 is a block diagram illustrating the detailed configuration of the backlight driving unit 11 and the backlight control unit 12 and the configuration of the light source unit 10, the illumination light sensor 13, the I / V conversion unit 14, and the A / D conversion unit 15. Is. 6 shows a power supply unit (a power supply unit 110 described later), a light source unit 10, a PWM driver (a PWM driver 113 described later), a resistor unit (a resistor unit 114 described later), and a Vf detection unit shown in FIG. A detailed configuration of (a Vf detection unit described later) is shown in a circuit diagram only for the blue LED 1B in particular. 7 shows the detailed configuration of the power supply unit 110 with respect to the power supply unit 110, the light source unit 10, the PWM driver 113, the resistor unit 114, the Vf detection unit 115B, and the power supply switching control unit 123 shown in FIGS. In particular, only the circuit relating to the blue LED 1B is shown in a circuit diagram. The light reception data D1 includes red light reception data D1R, green light reception data D1G, and blue light reception data D1B, and the control signal D3 includes a red control signal D3R, a green control signal D3G, and a blue control. It is assumed that the detection data D6 includes red detection data D6R, green detection data D6G, and blue detection data D6B. For convenience, the red LED 1R, the green LED 1G, and the blue LED 1B are all shown as being connected in series in the light source unit 10 here.

  As shown in FIG. 5, the backlight driving unit 11 includes a power supply unit 110 that switches power according to a selection signal SEL supplied from a power supply switching control unit 123 described later, and a control signal supplied from the backlight control unit 12. In accordance with D3 (red control signal D3R, green control signal D3G, and blue control signal D3B), current IR is supplied to the anode side of red LED 1R, green LED 1G, and blue LED 1B in light source unit 10 by power supply from power supply unit 110, respectively. Constant current drivers 111R, 111G, and 111B that supply IG and IB, resistor units 114R, 114G, and 114B having a plurality of resistors to be described later, and forward voltages of LEDs 1R, 1G, and 1B in the light source unit 10 (described later) Vf_all) is detected, and detection data D6 (red detection data D6R, green detection data D6) G and blue detection data D6B) are generated and output between Vf detection units 115R, 115G, and 115B, and cathodes of red LED 1R, green LED 1G, and blue LED 1B and resistor units 114R, 114G, and 114B. A control signal D5 (pulse signal) for the switching elements 112R, 112G, and 112B based on the switching elements 112R, 112G, and 112B, the control signal D4 supplied from the backlight control unit 12, and the control signal D0 supplied from the timing control unit 61. ) And a PWM driver 113 that performs PWM control of each of the switching elements 112R, 112G, and 112B. The switching elements 112R, 112G, and 112B are configured by transistors such as MOS-FETs (Metal Oxide Semiconductor-Field Emission Transistors), as will be described later.

  Further, the backlight control unit 12 includes a light amount balance control unit 121, a light amount control unit 122, and a power supply switching control unit 123.

  The light quantity balance control unit 121 is based on the light reception data D1 (red light reception data D1R, green light reception data D1G, and blue light reception data D1B) supplied from the A / D conversion unit 15, and the control signal D0 supplied from the timing control unit. By generating and outputting control signals D3 (red control signal D3R, green control signal D3G, and blue control signal D3B) for the constant current drivers 111R, 111G, and 111B, respectively, red LED 1R, green LED 1G, and blue LED 1B The currents (light emission currents) IR, IG, and IB flowing through the light source are changed for each color temperature to change the light emission intensity, and thereby the color balance (color temperature) of the illumination light Lout from the light source unit 10 according to the set value. ).

  The light quantity control unit 122 generates a control signal D4 for the PWM driver 113 based on the green light reception data D1G of the light reception data D1 supplied from the A / D conversion unit 15 and the control signal D0 supplied from the timing control unit. By generating and outputting, the light emission periods (lighting periods) of the red LED 1R, the green LED 1G, and the blue LED 1B are changed, and thereby the light emission amount (light emission luminance) of the illumination light Lout from the light source unit 10 is controlled. . In this case, only D1G of the control signals D1R, D1G, and D1B is input. This is because human visibility is the highest for green light, and other control signals D1R and D1B are input. You may make it do.

  The power supply switching control unit 123 detects detection data D6 (red detection data D6R, green detection data D6G, and blue detection data D6B supplied from the Vf detection units 115R, 115G, and 115B; both ends of each LED 1R, 1G, and 1B in the light source unit 10 A selection signal SEL for performing switching control between two power sources (power sources VCC_LED_max and VCC_LED_min described later) in the power source unit 110 is generated and output in accordance with the forward voltage Vf_all between them. Details of such switching control between power sources will be described later.

  Next, as shown in FIG. 6, the power supply unit 110 is configured to include a power supply VCC_LED_max (and a power supply VCC_LED_min described later) for generating a light emission current If1 described later. These power supplies are connected to the anode side of the blue LED 1B. Further, the switching element 112B related to the blue LED 1B is configured by an N-channel MOS-FET, and a drain is connected to the cathode side of the blue LED 1B.

  As for the blue LED 1B, the PWM driver 113 includes, for example, an operational amplifier OP1B whose upper limit of the dynamic range is 3.3 (V) and a switching element SW1B. Specifically, the operational amplifier OP1B inputs the control voltage V2 of the switching element 112B to the positive input terminal, and the negative input terminal is connected to the source of the switching element 112B. Therefore, the value of the operational voltage OP1B functions as a voltage follower. The switching element SW1B is configured to connect one of the output terminal of the operational amplifier OP1B and the ground (ground) to the gate of the switching element 112B in accordance with the control signals D0 and D4. Note that the switching element SW1B is also configured by a transistor such as a MOS-FET, for example. Note that the red LED 1R and the green LED 1G (not shown) in the PWM driver 113 have the same configuration.

  The resistor section 114B related to the blue LED 1B has a resistor R1 for detecting a main current (light emission current If1 in the figure) that flows when the blue LED 1B emits light. Specifically, one end of the resistor R1 is connected to the source of the switching element 112B, and the other end of the resistor R1 is grounded. The detailed configuration (not shown) of the resistor portion 114R related to the red LED 1R and the resistor portion 114G related to the green LED 1G is also the same configuration as the resistor portion 114B.

  The Vf detection unit 115B related to the blue LED 1B includes a power supply VCC_det for generating a detection current If2 described later, and a diode 115B1 and a resistor used to detect a forward voltage Vf_all between both ends of the LED 1B in the light source unit 10. A / D (analog / digital) conversion is performed on the voltage ΔV_FET_R (analog voltage) between R2 and the anode of the diode 115B1 detected by R2 and the ground to generate detection data D6B (digital voltage data). And an A / D converter 115B2 for output. Specifically, one end of the resistor R2 is connected to the power supply VCC_det, and the other end of the resistor R2 is connected to the anode of the diode 115B1 and the input terminal of the A / D converter 115B2. The cathode of the diode 115B1 is connected to the drain of the switching element 112B and the cathode side of the LED 1B. The voltage of the power supply VCC_det is set to be larger than the voltage ΔV_FET_R so that the current If2 flows through the diode 115B1. The resistance value of the resistor R2 is set so that the value of the detection current If2 (for example, about several μA) is significantly smaller than the value of the light emission current If (for example, about several tens of mA). (The resistance value of the resistor R2 is set to be very large). The detailed configurations (not shown) of the Vf detection unit 115R related to the red LED 1R and the Vf detection unit 115G related to the green LED 1G are also the same as the Vf detection unit 115B.

  Next, as shown in FIG. 7, the power supply unit 110 is related to the blue LED 1 </ b> B. The power supply VCC_LED_max and the power supply VCC_LED_min (voltage values are set so that VCC_LED_max> power supply VCC_LED_min). A power supply VCC_LOGIC which is a logic power supply for control, resistors R01, R11 to R13, R21 to R23, diodes Di1 and Di2, and bipolar transistors Tp0 to Tp2 and Tn0 to Tn2.

  Specifically, one end of the resistor R02 is connected to the power supply VCC_LOGIC, and the other end of the resistor R02 is connected to the collector of the NPN transistor Tn0 and one end of the resistor R11. The other end of the resistor R11 is connected to the base of the NPN transistor Tn1. The selection signal SEL is input to one end of the resistor R01 together with one end of the resistor R02. The other end of the resistor R01 is connected to the base of the NPN transistor Tn0. The end is connected to the base of the NPN transistor Tn2. The emitters of the NPN transistors Tn0, Tn1, and Tn2 are all grounded. The emitter of the PNP transistor Tp1 is connected to the power supply VCC_LED_min and one end of the resistor R12, the base of the PNP transistor Tp1 is connected to one end of the resistor R13, and the collector of the PNP transistor Tp1 is connected to the anode of the diode Di1. Yes. The other ends of the resistors R12 and R13 are both connected to the collector of the NPN transistor Tn1. The emitter of the PNP transistor Tp2 is connected to the power supply VCC_LED_max and one end of the resistor R22, the base of the PNP transistor Tp2 is connected to one end of the resistor R23, and the collector of the PNP transistor Tp2 is connected to the anode of the diode Di2. Yes. The other ends of the resistors R22 and R23 are both connected to the collector of the NPN transistor Tn2. Further, the cathodes of the diodes Di 1 and Di 2 are connected to the anode side of the LED 1 B in the light source unit 10.

  Although the details will be described later in the power supply unit 110 with such a configuration, one of the two power supplies VCC_LED_max and VCC_LED_min, which are different from each other, according to the selection signal SEL supplied from the power supply switching control unit 123. Is selected so that power is supplied from the selected power source to the LED 1B.

  Note that the detailed configuration (not shown) of the portion related to the red LED 1R and the green LED 1G in the power supply unit 110 has the same configuration as the portion related to the blue LED 1B shown in FIG.

  Here, the backlight control unit 12 corresponds to a specific example of “light source control device” in the present invention. The liquid crystal display panel 2 corresponds to a specific example of “display unit” in the invention. Further, the light quantity balance control unit 121 and the light quantity control unit 122 correspond to a specific example of “light source control unit” in the present invention, and the power supply switching control unit 123 corresponds to a specific example of “switch control unit” in the present invention. . The Vf detectors 115R, 115G, and 115B correspond to a specific example of “forward voltage detector” in the present invention.

  Next, operations of the backlight device 1 and the liquid crystal display device 3 of the present embodiment having the above-described configuration will be described in detail.

  First, basic operations of the backlight device 1 and the liquid crystal display device 3 according to the present embodiment will be described with reference to FIGS. FIG. 8 is a timing waveform diagram showing the lighting operation in the light source unit 10 of the backlight device 1. FIG. 8A shows a current (light emission current) IR flowing through the red LED 1R, and FIG. 8B shows a flow through the green LED 1G. The current IG and (C) represent the current IB flowing through the blue LED 1B, respectively. FIG. 9 is a timing waveform diagram showing an outline of the operation of the entire liquid crystal display device 3. FIG. 9A shows a voltage (X) applied from the X driver 51 to a certain pixel electrode 212 in the liquid crystal display panel 2. (B) is applied to the response of liquid crystal molecules (actual potential state at the pixel electrode 212), and (C) is applied from the Y driver 52 to the gate of the TFT element in the liquid crystal display panel 2. The applied voltages (pixel gate pulses) are respectively shown.

  In the backlight device 1, when the switching elements 112 R, 112 G, and 112 B are turned on in the backlight driving unit 11, currents (light emitting currents) are supplied from the constant current drivers 111 R, 111 G, and 111 B by power supply from the power supply unit 110. ) IR, IG, and IB flow to the red LED 1R, the green LED 1G, and the blue LED 1B in the light source unit 10, thereby emitting red light, green light, and blue light, respectively, and emitting illumination light Lout that is mixed color light.

  At this time, the control signal D0 is supplied from the timing control unit 61 to the backlight driving unit 11, and the control signal D5 based on the control signal D0 is transmitted from the PWM driver 113 in the backlight driving unit 11 to the switching elements 112R, 112G, and 112B. Therefore, the switching elements 112R, 112G, and 112B are turned on at a timing according to the control signal D0, and the lighting periods of the red LED 1R, the green LED 1G, and the blue LED 1B are also synchronized with this. . In other words, the red LED 1R, the green LED 1G, and the blue LED 1B are PWM-driven by time-division driving using the control signal D5 that is a pulse signal.

  At this time, the illumination light sensor 13 receives the irradiation light Lout from the light source unit 10. Specifically, in the red light sensor 13R, the green light sensor 13G, and the blue light sensor 13B in the illumination light sensor 13, each color light of the irradiation light Lout from the light source unit 10 is extracted by a photodiode for each color. As a result, a current corresponding to the amount of light of each color is generated, and the received light data of the current value is supplied to the I / V conversion unit 14. Further, the received light data of the current value for each color is converted into the received light data of the analog voltage value by the I / V conversion unit 14 respectively. The light reception data of the analog voltage value for each color is sampled at a predetermined timing according to the sampling gate signal SG supplied from the timing control unit 61 in the A / D conversion unit 15, and the light reception of the digital voltage value is performed. Data D1R, D1G, and D1B are converted.

  Here, in the backlight control unit 12, based on the light reception data D1R, D1G, D1B for each color supplied from the A / D conversion unit 15, a control signal is sent from the light amount balance control unit 121 to the constant current drivers 111R, 111G, 111B. D3R, D3G, and D3B are respectively supplied, and thereby the magnitudes of the currents IR, IG, and IB ΔIR, ΔIG, and ΔIB so that the chromaticity (color temperature and color balance) of the irradiation light Lout is kept constant, that is, The light emission intensity of the LEDs 1R, 1G, and 1B is adjusted (see FIGS. 8A to 8C).

  The light quantity control unit 122 generates a control signal D4 based on the light reception data D1G among the light reception data D1R, D1G, and D1B for each color supplied from the A / D conversion unit 15 and supplies the control signal D4 to the PWM driver 113. Thus, the on / off operation of the switching element SW1B and the like is controlled, so that the on period of the switching elements 112R, 112G, and 112B, that is, the lighting period ΔT of each color LED 1R, 1G, and 1B is adjusted (FIG. 8 ( A) to (C)).

  In this way, based on the illumination light Lout from the light source unit 10, the magnitudes ΔIR, ΔIG, ΔIB of the currents IR, IG, IB (light emission intensity of the LEDs 1R, 1G, 1B) and the lighting period are controlled. The light emission amount (light emission luminance) of the light Lout is controlled by the partial lighting unit 4 unit.

  On the other hand, in the entire liquid crystal display device 3 of the present embodiment, the light source of the backlight device 1 is driven by the drive voltage (pixel applied voltage) to the pixel electrode 212 output from the X driver 51 and the Y driver 52 based on the video signal. The illumination light Lout from the unit 10 is modulated by the liquid crystal layer 20 and output from the liquid crystal display panel 2 as display light Dout. In this manner, the backlight device 1 functions as a backlight (liquid crystal light source device) of the liquid crystal display device 3, thereby displaying an image with the display light Dout.

  Specifically, for example, as shown in FIG. 9C, a pixel gate pulse is applied from the Y driver 52 to the gates of TFT elements for one horizontal line in the liquid crystal display panel 2, and at the same time, FIG. As shown in (), the pixel application voltage based on the video signal is applied from the X driver 51 to the pixel electrode 212 for one horizontal line. At this time, as shown in FIG. 9B, the response of the actual potential of the pixel electrode 212 (response of the liquid crystal) is delayed with respect to the pixel applied voltage (the pixel applied voltage rises at timing t21). The actual potential rises at timing t12). In the backlight device 1, the backlight device 1 is turned on during the period from the timing t22 to t23 when the actual potential is equal to the pixel applied voltage (FIG. 9D). As a result, the liquid crystal display device 3 performs video display based on the video signal. In FIG. 9, the period from timing t21 to t23 corresponds to one horizontal period (one frame period), and the pixel applied voltage is common in one horizontal period from timing t23 to t25 to prevent liquid crystal burn-in and the like. The operation is the same as that in one horizontal period from timing t21 to t23 except that it is inverted with respect to the (common) potential Vcom.

  In the liquid crystal display device 3, the control signal D 0 is sent from the timing control unit 61 to the PWM driver 113 in the backlight drive unit 11 using a signal (a signal based on the video signal) supplied from the RGB process processing unit 60. For example, as shown in FIG. 10, in the light source unit 10, a video display area (area in which the display video Pa is displayed) having a predetermined luminance or higher in the video display area in the liquid crystal display panel 2. It is possible to perform an operation in which only the partial lighting part 4 in the region corresponding to is turned on to form the partial lighting region Pb.

  Next, referring to FIGS. 11 to 13 in addition to FIGS. 1 to 10, the control operation of the characteristic part of the present invention will be described in detail in comparison with a comparative example. FIG. 11 is a circuit diagram showing the detailed configuration of the conventional power supply unit 110, light source unit 10, PWM driver 113, and resistor unit 114B according to the comparative example, and FIG. 12 shows a decrease in power efficiency in the comparative example. It is a circuit diagram for demonstrating this problem. FIG. 13 is a flowchart showing the power source switching control process according to the present embodiment.

  First, in the backlight device according to the comparative example shown in FIG. 11, unlike the backlight device 1 of the present embodiment shown in FIG. 6, the voltage across the blue LEDs 1B in the light source unit 10 (the order of each LED). The Vf detector 115B for detecting the sum of the directional voltages Vf) is not provided. Further, the power source switching control based on the voltage across the blue LED 1B is not performed. Therefore, in this comparative example, as shown in FIG. 12, for example, the light source unit 10 is divided into two divided parts (partial lighting parts) and a constant current drive is performed in units of these divided parts. .

  Here, in one divided portion (the divided portion including the blue LED 1B-1, the switching element 112B-1 and the resistor R1-1), the voltage between both ends of the blue LED 1B-1 is the largest (all LEDs , The forward voltage Vf is the maximum value (Vf_max)), and in the other divided portion (the divided portion including the blue LED 1B-2, the switching element 112B-2 and the resistor R1-2), the blue LED 1B- 2 is the smallest (in all LEDs, the forward voltage Vf is the minimum value (Vf_min)), when the rated current If101 is attempted to flow through both, It is necessary to apply the largest voltage (Vf_max × voltage corresponding to the number of LEDs = VCC_LED_max) to the divided portion. Therefore, in the other divided portion, the voltage between both ends of the blue LED 1B-2 is (Vf_min × voltage for the number of LEDs = VCC_LED_min), so that, for example, the MOS-FET configuring the switching element 112B-2 , A power loss corresponding to the difference (ΔVCC) from the largest voltage VCC_LED_max occurs, and the power efficiency in the light source unit 10 decreases. Further, when power loss concentrates on the switching element 112B-2, it may cause heat generation, and when the power loss exceeds the rated value, it may cause damage to the switching element 112B-1.

  In order to avoid such a situation, the forward voltage Vf of each LED is selected to make the forward voltage Vf uniform, or the total value of the forward voltages Vf of all the LEDs connected in series is made uniform. Measures are required. However, such sorting is time-consuming and increases the cost for manufacturing the backlight device.

  Therefore, in the backlight device 1 according to the present embodiment, the Vf detection unit 115B is provided as shown in FIG. 6, and the power source switching is performed in the control unit 12 as shown in FIGS. A control unit 123 is provided. Thereby, the voltage Vf_all between both ends of the blue LED 1B in the light source unit 10 (the sum of the forward voltage Vf of each LED) is detected, and the forward voltage Vf_all between the both ends of the detected light source (specifically, The switching control between the two power supplies (VCC_LED_max and VCC_LED_min) in the power supply unit 110 is possible in accordance with the detection data D6B based on the forward voltage Vf_all. Therefore, as compared with the comparative example in which such power supply switching control is not performed, appropriate power supply is performed to each LED in the light source unit 10.

Specifically, as shown in FIG. 6, first, VCC_LED_max that is the maximum value is selected as the power supply in the power supply unit 110, and power is supplied to the blue LED 1 </ b> B in the light source unit 10. Then, the voltage V_R between both ends of the resistor R1 becomes a fixed value by the constant current circuit including the operational amplifier OP1B in the PWM driver 113. Here, in the Vf detector 115B, the power supply VCC_det is set to be larger than the voltage ΔV_FET_R in the figure, so that the diode 115B1 is turned on (the detection current If2 flows through the diode 115B1). ). At this time, the voltage Vf_all between the both ends of the blue LED 1B in the light source unit 10 (the sum of the forward voltage Vf of each LED) is calculated by the following equation (1). In other words, the detection data D6B based on the voltage ΔV_FET_R detected by the A / D conversion unit 115B2 is supplied to the power supply switching control unit 123, so that the power supply unit 123 causes the blue LED 1B in the light source unit 10 to be expressed by the equation (1). Thus, the voltage Vf_all between the two terminals is calculated.
Vf_all≈VCC_LED_max−ΔV_FET_R (1)

  Strictly speaking, in the equation (1), the forward voltage V_D of the diode 115B1 is excessively added, but if a Schottky barrier diode is used as the diode 115B1, the forward voltage V_D = Since it is about 0.6V, it is a negligible value compared to the voltage Vf_all across the blue LED 1B. Further, if the value of the detection current If2 is too large, the voltage generated across the resistor R1 increases, which causes an error in detecting Vf_all. Therefore, as described above, the resistance value of the resistor R2 is set to be as large as possible so that the value of the detection current If2 is significantly smaller than the light emission current If1 (for example, about several μA). Is desirable.

  More specifically, such power supply switching control processing is performed as follows. That is, first, the detection data D6B is generated and output by detecting and A / D converting the voltage ΔV_FET_R by the A / D conversion unit 115B2 in the Vf detection unit 115B, and the power supply switching control unit 123 in the control unit 12 Based on the detection data D6B, the voltage Vf_all across the blue LED 1B is calculated (step S11 in FIG. 13). Next, the power supply switching control unit 123 determines which one of VCC_LED_max and VCC_LED_min is connected to this divided portion (step S12). Specifically, as the voltage Vf_all across the blue LED 1B increases, the power source is switched to a power source having a higher power source voltage. That is, in this case, the power supply VCC_LED_max is connected when the voltage Vf_all between both ends of the blue LED 1B is larger than a predetermined threshold (for example, VCC_LED_min which is the smallest voltage), while the power supply VCC_LED_min when it is VCC_LED_min. To connect. Next, the power source switching control unit 123 performs switching control between two power sources (VCC_LED_max and VCC_LED_min) in the power source unit 110 by determining the logic of the selection signal SEL (step S13). Specifically, as can be seen from FIG. 7, when the power supply VCC_LED_min is connected, the selection signal SEL = “L (low)”, while when the source VCC_LED_max is connected, the selection signal SEL = “H”. (High) ”. Then, by repeating the processes of steps S11 to S13 as many times as the number of divisions (step S14), the entire process is completed.

  As described above, in the present embodiment, the forward voltage Vf_all between both ends of the LED is detected in each divided portion of the LEDs 1R, 1G, and 1B in the light source unit 10, and the detected forward voltage Vf_all is detected. Accordingly, switching control between the two power sources (VCC_LED_max and VCC_LED_min) is performed, so that appropriate power can be supplied to each divided portion in the light source unit 10 and power loss in the LEDs can be reduced. Is possible. In addition, since such power supply switching is automatically performed, the forward voltage of the LED can be easily adjusted as compared with the case of individually selecting the LED as in the prior art. Therefore, it is possible to improve the power efficiency of the light source unit 10 at a low cost.

  Moreover, since it is possible to reduce the power loss in the LED that occurs due to the accumulation of the forward voltage differences of the individual LEDs connected in series, heat generation in the switching elements 112R, 112G, 112B, etc., for example. Can also be suppressed.

  In addition, since it is possible to perform power source switching control using inexpensive parts (for example, the transistor described in this embodiment), the manufacturing cost is reduced as compared with the case where parts such as a relay are used. It becomes possible to do.

  In addition, since the switching control is automatically performed by software, even when the efficiency of the LED changes due to aging deterioration, it is possible to dynamically change the power supply, and the individual LEDs connected in series can be changed. It becomes possible to always reduce the power loss caused by the accumulation of the forward voltage differences.

  Furthermore, since such a backlight device 1 is used as a backlight (light source device for liquid crystal) of the liquid crystal display device 3, the entire liquid crystal display device 3 can realize improvement in power efficiency at a low cost. It becomes possible.

(Modification)
FIG. 14 is a circuit diagram and a block diagram showing detailed configurations of the power supply unit 110A, the light source unit 10, the PWM driver 13, the resistor unit 114B, the Vf detection unit 115B, and the power supply switching control unit 123A according to the modification of the present invention. Is. In this modification, a power supply unit 110A and a power supply switching control unit 123A are provided instead of the power supply unit 110 and the power supply switching control unit 123 in the above embodiment. In addition, the same code | symbol is attached | subjected to the same thing as the component in the said embodiment, and description is abbreviate | omitted suitably.

  The power supply switching control unit 123A is configured to detect detection data D6 (red detection data D6R, green detection data D6G, and blue detection data D6B; both ends of each LED 1R, 1G, 1B in the light source unit 10 supplied from the Vf detection units 115R, 115G, 115B. The selection signals SEL1 to SEL4 for performing switching control between four power sources (power sources VCC_LED_Low1, VCC_LED_Low2, VCC_LED_Hi1, VCC_LED_Hi2 described later) in the power source unit 110 are generated and output in accordance with the forward voltage Vf_all detection data therebetween. To do. Specifically, for example, as shown in FIG. 15, the selection signals SEL1 to SEL4 are generated and output.

  As for the blue LED 1B, the power supply unit 110A has power supplies VCC_LED_Low1, VCC_LED_Low2, VCC_LED_Hi, and VCC_LED_Hi2 (voltage values are set such that VCC_LED_Low2 <VCC_LED_Low1 <VCC_LED_Hi2 <VCC_LED_Hi1). RH11-RH13, RH21-RH23, RL11-RL13, RL21-RL23, diodes DiH1, DiH2, DiL1, DiL2, bipolar transistors TpH1-TpH2, TpL1-TpL2, TnH1-TnH2, TnL1-TnL2 Yes.

  With this configuration, in the power supply unit 110A, one of the four power supplies VCC_LED_Low1, VCC_LED_Low2, VCC_LED_Hi, and VCC_LED_Hi2 that are different from each other is selected according to the selection signals SEL1 to SEL4 supplied from the power supply switching control unit 123A. Switching control is performed so as to be selected, and power is supplied from the selected power source to the LED 1B.

  In this way, in this modified example, it is possible to obtain the same effect by the same operation as in the above embodiment, and the switching control between the power sources that are four different power sources is performed. Compared with the embodiment, it is possible to further reduce power loss and improve power efficiency.

  While the present invention has been described with reference to the embodiment, the present invention is not limited to this embodiment, and various modifications can be made.

  For example, in the above embodiment, the case where four partial lighting units 4 are provided in one detection region 40 has been described, but the number of partial lighting units 4 is not limited thereto. In the above-described embodiment, the case where all the four partial lighting units 4 are lit in the total lighting period Δt4 and only one partial lighting unit 1 is lit in the partial lighting period Δt1 has been described. The number of the partial lighting parts 4 to perform should just be larger than the number of the partial lighting parts 4 which light in a partial lighting period, and is not restricted to this case.

  In the above embodiment, the case where the luminance and color temperature of the light source unit are controlled by changing at least one of the lighting period and the emission intensity of each LED has been described. You may make it control at least one of the brightness | luminance and color temperature of a light source part by changing at least one of a period and luminescence intensity, respectively.

  In the above-described embodiment, the backlight drive unit 11 is controlled using light reception data from one illumination light sensor 13. However, for example, a plurality of illumination lights at different positions with respect to the light source unit 10. A sensor may be provided, and the backlight drive unit 11 may be controlled by taking an average value of received light data from the plurality of illumination light sensors.

  Moreover, in the said embodiment, while the light source part 10 is comprised by the some partial lighting part 4 which can be controlled mutually independently, in this partial lighting part 4 unit, the brightness | luminance and color temperature of the light source part 10, and Although the case where the power source switching control is performed in the power source unit 110 (in the case of partial driving of the backlight device) has been described, the present invention is not limited to such partial driving, and the entire light source unit is collectively processed. It can also be applied to drive and control.

  Moreover, although the said embodiment demonstrated the case where red LED1R, green LED1G, and blue LED1B were each accommodated in the separate package, for example, these several color LED is accommodated in one package. You may make it.

  Moreover, in the said embodiment, although the case where the light source part 10 was comprised from red LED1R, green LED1G, and blue LED1B was demonstrated, in addition to these (or instead of these), LED which emits another color light was used. You may make it comprise. When configured with four or more color lights, it is possible to expand the color reproduction range and express more diverse colors.

  In the above embodiment, the case where the liquid crystal display device 3 is a transmissive liquid crystal display device including the backlight device 1 has been described. However, the front light device is configured by the light source device of the present invention, and the reflection type liquid crystal device is used. A display device may be used.

  In the above embodiment, the liquid crystal display panel is described as an example of the display unit. However, a display unit other than the liquid crystal display panel may be used.

  Furthermore, the light source device of the present invention can be applied not only to a light source device for a liquid crystal display device but also to other light source devices such as lighting equipment.

1 is a perspective view illustrating an overall configuration of an image display system (liquid crystal display device) according to an embodiment of the present invention. It is a plane schematic diagram showing the structural example of the unit unit (partial lighting part) of the light source part in the backlight apparatus shown in FIG. FIG. 3 is a schematic plan view illustrating an arrangement configuration example of a partial lighting unit and an illumination light sensor in a light source unit in FIG. 2. It is a block diagram showing the whole structure of the liquid crystal display device shown in FIG. FIG. 5 is a block diagram illustrating in detail a configuration of a drive and control part of the light source unit illustrated in FIG. 4. FIG. 6 is a circuit diagram illustrating in detail the configuration of a power supply unit, a light source unit, a PWM driver, a resistor unit, and a Vf detection unit illustrated in FIG. 5. It is the circuit diagram and block diagram showing in detail the structure of a power supply part, a light source part, a PWM driver, a resistor part, a Vf detection part, and a power supply switching control part. It is a timing waveform diagram for demonstrating the drive pulse signal of a light source part. FIG. 3 is a timing waveform diagram for explaining an example of a method for driving the liquid crystal display panel and the backlight device shown in FIG. 1. It is a perspective view for demonstrating an example of arrangement | positioning relationship between a video display area | region and a partial lighting area | region. It is a circuit diagram showing in detail the composition of the power supply part, light source part, PWM driver, and resistor part concerning a comparative example. It is a circuit diagram for demonstrating the problem of the power efficiency fall in a comparative example. It is a flowchart showing the switching control process of the power supply which concerns on this Embodiment. It is the circuit diagram and block diagram showing in detail the structure of the power supply part which concerns on the modification of this invention, a light source part, a PWM driver, a resistor part, a Vf detection part, and a power supply switching control part. It is a figure showing the relationship between the selection signal in the modification shown in FIG. 14, and the power supply switched and set. It is a circuit diagram for demonstrating the dispersion | variation in the forward voltage of a light emitting diode (LED).

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Backlight apparatus, 1R ... Red LED, 1G ... Green LED, 1B ... Blue LED, 10 ... Light source part, 11 ... Backlight drive part, 110, 110A ... Power supply part, 111R, 111G, 111B ... Constant current driver, 112R, 112G, 112B ... switching element, 113 ... PWM driver, 114R, 114G, 114B ... resistor unit, 115R, 115G, 115B ... Vf detection unit, 115B1 ... diode, 115B2 ... A / D conversion unit, 12 ... backlight Control unit 121: Light amount control unit 122 ... Light amount balance control unit 123, 123A ... Power supply switching control unit 13 ... Illumination light sensor 13R ... Red light sensor 13G ... Green light sensor 13B ... Blue light sensor 14 ... I / V converter, 15 ... A / D converter, 2 ... liquid crystal display panel, 20 ... liquid crystal layer, 210 220 ... Polarizing plate, 211 ... TFT substrate, 212 ... Pixel electrode, 221 ... Counter electrode substrate, 3 ... Liquid crystal display device, 4, 4A, 4B, 4C, 4D ... Unit unit (partial lighting part), 40 ... Detection region, 41, 42 ... unit cells, 51 ... X driver, 52 ... Y driver, 60 ... RGB process processing unit, 61 ... timing control unit, 62 ... video memory, Lout ... illumination light, Dout ... display light, Ls ... external light ( Ambient light), CFR, CFG, CFB ... color filter, D0, D3, D4, D5 ... control data (control signal), D6 ... detection data, SEL, SEL1-SEL4 ... selection signal, D1 ... light reception data, IR, IG , IB, If1, If2 ... current, Vcom ... common potential, V1 (V_R), V2, V_FET, Vf_all, V_D, ΔV_FET_R, Vf_max, Vf_min ... voltage, VCC_LED, CC_LED_max, VCC_LED_min, VCC_LED_Low1, VCC_LED_Low2, VCC_LED_Hi1, VCC_LED_Hi2, VCC_LOGIC, VCC_det ... power supply, ΔVCC ... potential difference, OP1B ... operational amplifier, SW1B, SW2B ... switching element, R01, R02, R1, R11, R11 R22, R23, RL11, RL12, RL13, RL21, RL22, RL23, RH11, RH12, RH13, RH21, RH22, RH23 ... resistors, Di1, Di2, DiL1, DiL2, DiH1, DiH2 ... diodes, Tp1, Tp2, TpL1 , TpL2, TpH1, TpH2, Tn0, Tn1, Tn2, TnL1, TnL2, TnH1, TnH2 ... transistors, t1-t3, t21-t 5 ... timing, Pa ... display image, Pb ... partial lighting region, SG ... sampling gate signal, [Delta] T ... pulse width, ΔIR, ΔIG, ΔIB ... current value (pulse height).

Claims (10)

A light source unit having a plurality of light sources configured to include a light emitting diode;
A power supply unit having a plurality of different power supplies and supplying power to each light source by these power supplies,
A forward voltage detector for detecting the forward voltage between both ends of each light source;
Light source control means for controlling the light source unit by changing at least one of the lighting period and emission intensity of each light source;
And a switching control means for performing switching control between a plurality of power sources in the power source in accordance with a forward voltage between both ends of each light source detected by the forward voltage detector. 2. The light source system according to claim 1, wherein the switching control unit performs switching control so that a power source having a larger power source voltage is switched as a forward voltage between both ends of each light source increases. Each light source is comprised including the some light emitting diode connected in series by the mutually same direction. The light source system of Claim 1 or Claim 2 characterized by the above-mentioned. When detecting the forward voltage, the forward voltage detector is set so that the value of the current flowing in the forward voltage detector is significantly smaller than the value of the light emission current flowing in each light source. The light source system according to claim 1, wherein the light source system is a light source system. The light source unit is composed of a plurality of partial lighting units that can be controlled independently of each other,
The light source control unit and the switching control unit perform control of the light source unit and switching control between a plurality of power sources in the power source unit in units of the partial lighting units. The light source system according to any one of the above. The light source control means controls at least one of luminance and color temperature of the light source unit by changing at least one of a lighting period and light emission intensity of each light source. The light source system according to claim 5. The light source system according to any one of claims 1 to 6, further comprising a display unit configured to modulate light emitted from the light source system based on a video signal. A light source unit having a plurality of light sources configured to include light emitting diodes, a power source unit having a plurality of different power sources and supplying power to each light source by these power sources, and the order between both ends of each light source A light source control device applied to a light source device including a forward voltage detection unit that detects a directional voltage,
A light source control means for controlling the light source unit by changing at least one of the lighting period and emission intensity of each light source;
A light source control, comprising: a switching control unit that performs switching control between a plurality of power sources in the power source unit according to a forward voltage between both ends of each light source detected by the forward voltage detecting unit. apparatus. A light source unit having a plurality of light sources configured to include a light emitting diode;
A power supply unit having a plurality of different power supplies and supplying power to each light source by these power supplies,
A forward voltage detector for detecting the forward voltage between both ends of each light source;
A light source control means for controlling the light source unit by changing at least one of the lighting period and emission intensity of each light source;
A light source apparatus comprising: a switching control unit configured to perform switching control between a plurality of power sources in the power source unit according to a forward voltage between both ends of each light source detected by the forward voltage detecting unit. . An image display method for displaying an image by modulating light emitted from a light source device in a display unit based on a video signal,
For each of a plurality of light sources in a light source section configured to include a light emitting diode, power is supplied by a plurality of different power sources, and at least one of a lighting period and a light emission intensity of each light source is changed. Control the light source,
Detect the forward voltage across each light source,
Switching control between the plurality of power sources is performed according to a forward voltage between both ends of each detected light source.

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