LED device and liquid crystal display device

Abstract

To provide an LED device and a liquid crystal display device in which power consumption is suppressed.SOLUTION: The LED device 101 includes a plurality of LED light sources 20, an LED driver 12 connected to one end of each of the plurality of LED light sources and controlling a current flowing through each LED light source based on lighting data, a DC power supply 54 having an output terminal connected in parallel to the other end of each of the plurality of LED light sources using a wiring, receiving a control signal, and applying an LED voltage having a value based on the control signal to the output terminal, and a control device 55 receiving display data, generating lighting data and a control signal based on the display data, and outputting the lighting data and the control signal to the LED driver and the DC power supply.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to an LED device and a liquid crystal display device. [Background technology]

[0002] In recent years, light-emitting diodes (hereinafter referred to as LEDs) have been widely used for lighting, backlights for liquid crystal display devices, and display devices. Due to their light-emitting properties, LEDs require a certain voltage to be applied to them to operate, which can lead to the problem of increased power consumption in devices equipped with LEDs. Patent Document 1 discloses a technology that can reduce power consumption generated by a constant current drive circuit in an LED device such as a backlight for a display device. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-14945 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present disclosure is to provide an LED device and a liquid crystal display device with reduced power consumption. [Means for solving the problem]

[0005] An LED device according to an embodiment of the present disclosure includes: a plurality of LED light sources; an LED driver connected to one end of each of the plurality of LED light sources and controlling the current flowing through each LED light source based on lighting data; a DC power supply having output terminals connected in parallel to the other ends of each of the plurality of LED light sources using wiring, receiving control signals and applying an LED voltage of a value based on the control signals to the output terminals; and a control device receiving display data, generating the lighting data and the control signal based on the display data, and outputting them to the LED driver and the DC power supply. [Effects of the Invention]

[0006] According to an embodiment of the present disclosure, it is possible to realize an LED device and a liquid crystal display device with reduced power consumption. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram showing an example of the configuration of a liquid crystal display device according to the first embodiment. [Figure 2] FIG. 2 is a schematic block diagram showing an example of the configuration of the LED device according to the first embodiment. [Figure 3] FIG. 3 is a circuit diagram of the LED device of the first embodiment, which is simplified for the purpose of explanation. [Figure 4] FIG. 4 is a circuit diagram showing an example of an LED voltage correction circuit. [Figure 5] FIG. 5 is a circuit diagram of the LED device of the second embodiment, which is simplified for the purpose of explanation. [Figure 6A] FIG. 6A is a schematic diagram showing the timing of lighting of the LEDs in the LED device of the second embodiment. [Figure 6B] FIG. 6B is a schematic diagram showing the timing of lighting the LEDs in the LED device of the second embodiment. [Figure 6C] FIG. 6C is a schematic diagram showing the timing of lighting the LEDs in the LED device of the second embodiment. [Figure 7]FIG. 7 is a schematic block diagram showing an example of the configuration of an LED device according to the third embodiment. [Figure 8] FIG. 8 is a circuit diagram of the LED device of the third embodiment, which is simplified for the purpose of explanation. [Figure 9] FIG. 9 is a schematic diagram showing the timing of lighting of the LEDs in the LED device of the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] Embodiments of the present disclosure will be described below with reference to the drawings. The present disclosure is not limited to the following embodiments, and appropriate design modifications may be made within the scope of the configuration of the present disclosure. In the following description, the same reference numerals are used in different drawings for identical parts or parts having similar functions, and repeated description of such parts may be omitted. The configurations described in the embodiments and modifications may be combined or modified as appropriate without departing from the spirit of the present disclosure. To facilitate understanding of the description, the drawings referenced below may show simplified or schematic configurations, or may omit some components. Furthermore, the dimensional ratios between components shown in each drawing do not necessarily represent actual dimensional ratios.

[0009] (First embodiment) 1 is a schematic diagram showing the configuration of a liquid crystal display device 501 of this embodiment. The liquid crystal display device 501 includes a liquid crystal panel 201 and an LED device 101 arranged on the back surface of the liquid crystal panel 201. In this embodiment, the LED device 101 is a backlight for the liquid crystal display device 501. The LED device 101 includes an LED substrate 10 and a control substrate 50.

[0010] The LED substrate 10 includes a plurality of light-emitting regions 10a arranged in a matrix on the surface facing the liquid crystal panel 201, and a plurality of LED light sources 20 arranged in each of the light-emitting regions 10a. The LED device 101 can independently light up the LED light sources 20 in each of the light-emitting regions 10a and independently change the brightness of the LED light sources 20. In other words, the LED device 101 can be driven using local dimming.

[0011] 2 is a schematic block diagram showing the configuration of the LED device 101. The LED substrate 10 of the LED device 101 further includes a substrate 11 and a plurality of LED drivers 12, and the plurality of LED light sources 20 and the plurality of LED drivers 12 are mounted on the substrate 11.

[0012] Each LED light source 20 includes one or more LEDs. In FIG. 1, each LED light source 20 is shown as including one LED. When the LED light source 20 includes multiple LEDs, the multiple LEDs may be connected in series or in parallel. Furthermore, the multiple LEDs may be arranged, for example, within a single chip, or may be arranged spaced apart within the light-emitting region 10a.

[0013] The LED driver 12 has a plurality of channel terminals 12a, an input terminal 12b, and an output terminal 12c, and one of two terminals of the LED light source 20, i.e., the cathode of the LED light source 20, is connected to each channel terminal 12a. In the example shown in FIG. 2, for ease of understanding, the plurality of LED drivers 12 are arranged in m rows and n columns, and each LED driver 12 has four channel terminals 12a, but the number of LED drivers 12 and the number of channel terminals 12a are not limited to this example. The other ends, i.e., the anodes, of the plurality of LED light sources 20 are connected in parallel by wiring 30. As will be described later, the wiring 30 is connected to an output terminal 54a of a DC-DC converter 54.

[0014] The LED driver 12 has multiple sink-type current drive circuits that constantly control the current flowing from the load connected to the channel terminal 12a. In this embodiment, the LED driver 12 receives lighting data from the input terminal 12b and independently controls the current flowing through the LED light source 20 connected to the channel terminal 12a. The current value includes zero, and the LED driver 12 controls the on / off and brightness of the LED light source 20 when it is lit based on the lighting data. The output terminal 12c is connected to the input terminal 12b of another LED driver 12.

[0015] The control board 50 includes a board 51, and a control device 55 and a DC-DC converter 54 mounted on the board 51.

[0016] The DC-DC converter 54 is a DC power supply having an output terminal 54a and a control terminal 54b, and controls the LED voltage applied to the output terminal 54a based on a control signal input from the control terminal 54b. In this embodiment, the output terminal 54a is connected to the wiring 30, and the DC-DC converter 54 changes the LED voltage value at the output terminal 54a so as to reduce the difference between the voltage value of the control signal applied to the control terminal 54b and a reference voltage. For example, if the voltage value at the control terminal 54b is greater than the reference voltage, the DC-DC converter 54 reduces the voltage applied to the control terminal 54b, and if the voltage value at the control terminal 54b is less than the reference voltage, the DC-DC converter 54 increases the voltage applied to the control terminal 54b.

[0017] For example, by connecting resistors 54A and 54B in series between output terminal 54a and a reference potential and connecting the connection point between resistors 54A and 54B to control terminal 54b, the voltage at output terminal 54a can be feedback-controlled.

[0018] The control device 55 receives display data from an external device and generates lighting data and a control signal based on the display data. The generated lighting data is output to the input terminal 12b of the LED driver 12, and the control signal is output to the control terminal 54b of the DC-DC converter 54. The lighting data includes information related to the brightness of the LED light source 20. The control signal includes information for changing the value of the LED voltage output by the DC-DC converter 54.

[0019] In this embodiment, LED device 101 is a backlight capable of local dimming, and the display data is, for example, matrix data of brightness values ​​that reflect the brightness of an image displayed by liquid crystal display device 501. For example, the brightness value is indicated by a value obtained by averaging the brightness of each pixel of a frame image displayed by liquid crystal display device 501 for each light-emitting area 10a. This brightness value is updated sequentially, with one frame period being one lighting period.

[0020] The control device 55 includes, for example, a lighting controller 52 and an LED voltage correction circuit 53.

[0021] Based on the display data, the lighting controller 52 generates correction voltage data indicating the difference in voltage drop due to the difference in current flowing through the wiring 30 caused by the difference in brightness between the maximum brightness of the multiple LED light sources 20 during each lighting period and the set brightness. The LED voltage correction circuit 53 generates a correction current Ic, which is a control signal, based on the correction voltage data and inputs it to a control terminal 54b of the DC-DC converter 54.

[0022] Furthermore, the lighting controller 52 generates lighting data based on the display data. The lighting data is input to one of the input terminals 12b of the LED drivers 12 arranged in the column direction, and the output terminal 12c and the other input terminals 12b are cascade-connected, so that the lighting data is also output to the other LED drivers 12 in sequence.

[0023] As described above, the lighting data includes information about the luminance of each LED light source 20, which is updated for each lighting period. In this embodiment, the luminance is adjusted according to the value of the current flowing through the LED light source 20, so the lighting data includes information about the current value corresponding to the luminance of each LED light source 20 for each lighting period.

[0024] When the LED device 101 is driven by local dimming, there are cases where all of the multiple LED light sources 20 light up simultaneously and cases where only some of the multiple LED light sources 20 light up simultaneously. Because the wiring 30 has parasitic resistance, when all of the multiple LED light sources 20 light up simultaneously, the voltage drop ΔV caused by the parasitic resistance of the wiring 30 is ΔV=4×m×n×I×R, where R is the parasitic resistance, I is the current flowing through the LED light sources 20, and 4×m×n is the number of LED light sources 20. For this reason, the LED voltage applied to the output terminal 54a of the DC-DC converter 54 needs to be a voltage that is higher than the voltage sufficient to drive the LED light sources 20 by the voltage drop ΔV.

[0025] On the other hand, when, for example, only one of the multiple LED light sources 20 is turned on, the voltage drop due to the parasitic resistance is ΔV' = I × R. Therefore, ΔV - ΔV' = (4 × m × n - 1) × I × R is applied to the channel terminal 12 a of the LED driver 12 as an excessive voltage and is dissipated as heat.

[0026] The LED device 101 of this embodiment changes the LED voltage value output by the DC power supply based on the display data, so when the number of lit LED light sources is small or the brightness of the LED light sources is low, the LED voltage becomes small, preventing excess voltage from being applied to the channel terminal 12a of the LED driver 12 and reducing unnecessary power consumption.

[0027] Below, we will explain in detail how to control the LED voltage in the LED device 101. Figure 3 is a simplified circuit diagram of the LED device 101 for the purpose of explanation. In Figure 3, the LED light sources 20 are arranged in four rows and four columns, and are hereinafter indicated as L11 to L14, L21 to L24, L31 to L34, and L41 to L44.

[0028] The anodes of these LED light sources 20 are connected to AL1 to AL4, which are wiring 30, and the cathodes are connected to LED drivers 12-1 to 12-4. Specifically, the anodes of L11 to L14 are connected to AL1, and the cathodes are connected to LED driver 12-1. Similarly, the anodes of L21 to L24 are connected to AL2, and the cathodes are connected to LED driver 22-1. The anodes of L31 to L34 are connected to AL3, and the cathodes are connected to LED driver 12-3. The anodes of L41 to L44 are connected to AL4, and the cathodes are connected to LED driver 12-4.

[0029] Each of AL1 to AL4 has a parasitic resistance. Specifically, AL1 has the following parasitic resistance: Between connection point C1 and connection point L11: R1a Between the connection point with L11 and the connection point with L12: R1b Between the connection point with L12 and the connection point with L13: R1c Between the connection point with L13 and the connection point with L14: R1d Similarly, AL2 has the following parasitic resistance: Between connection point C2 and the connection point with L21: R2a Between the connection point with L21 and the connection point with L22: R2b Between the connection point with L22 and the connection point with L23: R2c Between the connection point with L23 and the connection point with L24: R2d Similarly, AL3 has the following parasitic resistance: Between connection point C3 and connection point with L31: R3a Between the connection point with L31 and the connection point with L32: R3b Between the connection point with L32 and the connection point with L33: R3c Between the connection point with L33 and the connection point with L34: R3d Similarly, AL4 has the following parasitic resistance: Between connection point C4 and connection point with L41: R4a Between the connection point with L41 and the connection point with L42: R4b Between the connection point with L42 and the connection point with L43: R4c Between the connection point with L43 and the connection point with L44: R4d Furthermore, the parasitic resistances between connection points C1 and C2, between C2 and C3, and between C3 and C4 are R1, R2, and R3, respectively, and the parasitic resistance between the output terminal 54a of the DC-DC converter 54 and connection point C1 is R0.

[0030] For the sake of explanation, the resistance values ​​of these parasitic resistors are determined as follows. R0=r0(Ω) R1=R2=R3=r1(Ω) R1a=R1b=R1c=R1d =R2a=R2b=R2c=R2d =R3a=R3b=R3c=R3d =R4a=R4b=R4c=R4d =ra(Ω) As described above, the LED voltage Vout applied to the output terminal 54a of the DC-DC converter 54 is controlled by the voltage applied to the control terminal 54b. The LED voltage Vled is the voltage applied when all the LED light sources 20 connected in parallel to the output terminal 54a are lit at maximum brightness.

[0031] The resistance value RA of the resistor 54A and the resistance value RB of the resistor 54B are selected so that the LED voltage Vout becomes Vled (V) when the correction current Ic received from the LED voltage correction circuit 53 is 0 (A). As described above, if the reference voltage for feedback control of the DC-DC converter 54 is Vfb, then Vfb=Vled·RB / (RA+RB) (1) Meet the following.

[0032] The LED drivers 12-1 to 12-4 receive lighting data output from the lighting controller 52 via the input terminal 12b and set the current value of the channel terminal 12a. For this purpose, the input terminal 12b of the LED driver 12-4 is connected to the lighting controller 52 via a data line D1. The output terminal 12c of the LED driver 12-4 is connected to the input terminal 12b of the LED driver 12-3, the output terminal 12c of the LED driver 12-3 is connected to the input terminal 12b of the LED driver 12-2, and the output terminal 12c of the LED driver 12-2 is connected to the input terminal 12b of the LED driver 12-1 via data lines D2, D3, and D4, respectively. As a result, the lighting data output from the lighting controller 52 is transferred via cascade connection to the LED drivers 12-4 to 12-1, which are arranged in the column direction.

[0033] The lighting data is output to LED drivers 12-1 to 12-4 every lighting period, for example, every frame period, and includes lighting data for LED drivers 12-1 to 12-4. The lighting data for LED driver 12-1 includes lighting data for L11, L12, L13, and L14. Similarly, the lighting data for LED driver 12-2 includes lighting data for L21, L22, L23, and L24, the lighting data for LED driver 12-3 includes lighting data for L31, L32, L33, and L34, and the lighting data for LED driver 12-4 includes lighting data for L41, L42, L43, and L44. LED drivers 12-1 to 12-4 control the value of the current flowing through each channel terminal 12a so that the LED light source 20 connected to each channel terminal 12a has the luminance specified by the lighting data.

[0034] Next, the value of Vled is estimated. A constant current circuit is provided at each channel terminal 12a of LED drivers 12-1 to 12-4, and the constant current circuit is composed of components such as resistors and transistors. Therefore, unless a voltage Vh (headroom voltage) equal to or greater than a certain value is applied to channel terminal 12a, no current will flow through the constant current circuit.

[0035] Furthermore, in order for the LED light sources 20 such as L11 and L12 to emit light, it is necessary to apply a voltage equal to or greater than the forward voltage Vf.

[0036] When the LED light sources 20 such as L11 and L12 are lit at maximum brightness, the current flowing through the LED light sources 20 is defined as Imax. Since the wiring 30 has the parasitic resistance described above, Vled is a value that takes into account the total value of Vf and Vh as well as the voltage drop due to the current flowing through the parasitic resistance.

[0037] When a current Imax flows through all of L11-L14, L21-L24, L31-L34, and L41-L44, the current path that lights L44 has the largest voltage drop due to the parasitic resistance of wiring 30. Therefore, Vled is defined as the potential difference between output terminal 54c of DC-DC converter 54 and channel terminal 12a of LED driver 12-4 that is connected to L44. Vled is the voltage required to light all LED light sources 20 at maximum brightness, and in this case, Vled is expressed by the following equation:

[0038] Vled=16×Imax×R0+12×Imax×R1+8×Imax×R2 +4×Imax×R3+4×Imax×R4a+3×Imax×R4b +2×Imax×R4c+1×Imax×R4d +Vf+Vh If the values ​​of the parasitic resistances are denoted by r0, r1, and ra as described above, then Vled=16×Imax×r0+12×Imax×r1+8×Imax×r1 +4×Imax×r1+4×Imax×ra+3×Imax×ra +2×Imax×ra+1×Imax×ra +Vf+Vh =(16·r0+24·r1+10·ra)·Imax+Vf+Vh (2) At this time, the correction current Ic, which is the control signal, becomes 0 (A). For example, the actual Ic is on the order of microamperes.

[0039] If the LED light source 20 other than L44 is not turned on and the LED voltage required to turn on L44 at maximum brightness is Vled', then: Vled'=(R0+R1+R2+R3+R4a+R4b+R4c+R4d)×Imax +Vf+Vh =(r0+3·r1+4·ra)·Imax+Vf+Vh And Vled-Vled'=(15·r0+21·r1+6·ra)·Imax··(3) In other words, the voltage shown in equation (3) is excessively applied to the channel terminal 12a to which L44 of the LED driver 12-4 is connected, and the energy obtained by multiplying this voltage by the current value Imax is consumed as heat.

[0040] In this way, the presence of parasitic resistance in the wiring 30 causes a voltage drop due to the parasitic resistance in the wiring 30, and as a result, the magnitude of the voltage drop varies depending on the number and brightness of the LED light sources 20 that are turned on.

[0041] For this reason, in this embodiment, the lighting controller 52 estimates the number and brightness of the LED light sources 20 to be turned on in each lighting period, that is, the total driving current of the LED light sources 20 in each lighting period, based on the display data, and generates correction voltage data.

[0042] For example, the lighting data of the LED light sources 20 are respectively set as L11:d11, L12:d12, ..., L43:d43, and L44:d44 in order from L11. The current flowing through each LED light source 20 is 0 to Imax (A) and is associated with the lighting data. When the lighting data is expressed in 12 bits, the lighting data value LD is any value from 0 to 4095, and if the current value determined by the lighting data is id, then id=LD / 4095×Imax For example, the current value id11 of L11 is expressed as follows: id11=d11 / 4095×Imax It is shown as follows.

[0043] The voltage drop in the wiring 30 is greatest when any of L14, L24, L34, or L44, which is located farthest from the output terminal 54a among AL1 to AL4, is lit. Because the magnitude of the current flowing through L14, L24, L34, and L44 is not the same, the voltage drop is not necessarily greatest when L44 is lit. Furthermore, if the lighting data for any of L14, L24, L34, or L44 is 0, no voltage drop occurs in the current path of that LED light source 20. When the lighting data for L14, L24, L34, and L44 is not zero, the voltage drop values ​​at the respective anodes, Vad14, Vad24, Vad34, and Vad44, are expressed as follows:

[0044] Vad14=r0×(d11+d12+···+d44) / 4095×Imax +ra×(d11+d12+d13+d14) / 4095×Imax +ra× (d12+d13+d14) / 4095×Imax +ra× (d13+d14) / 4095×Imax +ra× (d14) / 4095×Imax Vad24=r0×(d11+d12+···+d44) / 4095×Imax +r1×(d21+d22+···+d44) / 4095×Imax +ra×(d21+d22+d23+d24) / 4095×Imax +ra× (d22+d23+d24) / 4095×Imax +ra× (d23+d24) / 4095×Imax +ra× (d24) / 4095×Imax Vad34=r0×(d11+d12+···+d44) / 4095×Imax +r1×(d21+d22+···+d44) / 4095×Imax +r1×(d31+d32+···+d44) / 4095×Imax +ra×(d31+d32+d33+d34) / 4095×Imax +ra× (d32+d33+d34) / 4095×Imax +ra× (d33+d34) / 4095×Imax +ra× (d34) / 4095×Imax Vad44=r0×(d11+d12+···+d44) / 4095×Imax +r1×(d21+d22+···+d44) / 4095×Imax +r1×(d31+d32+···+d44) / 4095×Imax +r1×(d41+d42+d43+d44) / 4095×Imax +ra×(d41+d42+d43+d44) / 4095×Imax +ra× (d42+d43+d44) / 4095×Imax +ra× (d43+d44) / 4095×Imax +ra× (d44) / 4095×Imax

[0045] The largest value among Vad14 to Vad44 is defined as Vcom. If the substrate 11 on which the wiring 30 is formed is designed so that the resistance values ​​r0, r1, and ra are an integer ratio, the size of the calculation circuit for the correction voltage data calculated as described above during each lighting period can be significantly reduced. Vcom is the maximum value of the voltage drop due to the wiring 30 estimated during each lighting period.

[0046] At this time, the LED voltage Vout required to properly light the LED light source 20 based on the lighting data d11 to d44 is expressed by the following formula. Vout=Vf+Vh+Vcom (4) Meanwhile, during each lighting period, the correction current Ic, which is a control signal, flows through the control terminal 54b of the DC-DC converter 54, thereby adjusting the LED voltage Vout at the output terminal 54c of the DC-DC converter 54. At this time, the LED voltage Vout at the output terminal 54c is expressed by the following equation.

[0047] Vout=Vled-RA×Ic (5) Therefore, from equations (4) and (5), Vf+Vh+Vcom=Vled-RA×Ic When the correction current Ic is calculated using the relationship in equation (2), Ic=(Vled-Vf-Vh-Vcom) / RA ={(16·r0+24·r1+10·ra)·Imax-Vcom} / RA (6) The lighting controller 52 outputs correction voltage data to the LED voltage correction circuit 53 so that this correction current Ic is output.

[0048] The value of Vcom is between 0 (V) and {16·r0+24·r1+10·ra}·Imax(V). The correction voltage data may be a digital value converted to an appropriate number of gradations. For example, if the correction voltage data is represented by Vcd and is expressed as an 8-bit value (0 to 255), Vcd is expressed by the following formula. Here, int() means the integer conversion process. The correction voltage data Vcd is not limited to 8 bits. Vcd=int(Vcom / [{16·r0+24·r1+10·ra}·Imax] ×255) (7)

[0049] 4 is a circuit diagram showing an example of the LED voltage correction circuit 53. The LED voltage correction circuit 53 receives correction voltage data Vcd from the lighting controller 52, generates a correction current Ic, and outputs it to the DC-DC converter 54. For example, the LED voltage correction circuit 53 includes a data conversion table 53a, a D / A converter 53b, an operational amplifier 53c, a resistor 53d, and a transistor 53e. The LED voltage correction circuit 53 is not limited to the circuit shown in FIG. 4, and may have other circuit configurations as long as it is configured to receive the correction voltage data Vcd and output the correction current Ic.

[0050] The LED voltage correction circuit 53 refers to the data conversion table 53a and converts the correction voltage data Vcd into digital data Vcdd of 8 bits or more. For example, Vcdd is expressed by the following formula.

[0051] Vcdd=int[VCC-RC / RA×{Vcd×(Vled-Vh-Vf) / 255}] (8) Here, VCC is the power supply voltage of the LED voltage correction circuit 53, and RC is the resistance value of the resistor 53d shown in FIG.

[0052] The converted Vcdd is converted into an analog voltage indicated by Vc by the D / A converter 53b.

[0053] The voltage Vc is input to an operational amplifier 53c, the output of which is connected to a transistor 53e, which generates a correction current Ic according to the value of the voltage Vc.

[0054] The voltage Vc generated when the correction voltage data Vcd is input is expressed by the following formula. Vc=VCC-Ic×RC =VCC-{(16·r0+24·r1+10·ra)·Imax}-Vcom}· RC / RA (9) where: Vcom=Vcd / 255×{(16·r0+24·r1+10·ra)·Imax} (10) The data conversion table 53a and the D / A converter 53b are configured to generate this voltage Vc.

[0055] When Vcd=255, all the LED light sources 20 are lit at maximum brightness, so the correction current Ic=0. In this case, Vc=VCC. on the other hand, When Vcd=0, Ic={(16·r0+24·r1+10·ra)·Imax} / RA that's why, Vc=VCC-Ic×RC =VCC-{(16·r0+24·r1+6·ra)·Imax}·RC / RA This becomes:

[0056] As described above, according to this embodiment, the LED voltage output by the DC-DC converter 54 is adjusted based on the display data. Therefore, when the number of lit LED light sources 20 is small or when the brightness of the LED light sources 20 is low, the LED voltage is reduced, thereby suppressing heat generation and unnecessary power consumption due to application of excess voltage to the channel terminal 12a of the LED driver 12.

[0057] (Second embodiment) 5 is a simplified circuit diagram of the LED device 102 of this embodiment for the purpose of explanation. In the LED device 101 of the first embodiment, the brightness was adjusted by changing the value of the current flowing through the LED light sources 20, but in the LED device 102 of this embodiment, the brightness of each LED light source 20 in one lighting period is adjusted by changing the lighting duty ratio, that is, the ratio between the ON period (time) and the OFF period (time). In other words, the lighting data includes information regarding the duty ratio between the lighting period and the non-lighting period of each LED light source, which corresponds to the brightness set for each lighting period.

[0058] When driving the LED device 102 with local dimming, lighting data is updated in each lighting period, and the duty ratio of the LED light source 20 is determined. For ease of understanding, each lighting period is referred to as "one lighting period," and the period during which the LED light source 20 is turned on based on the duty ratio within one lighting period is referred to as the LED lighting period.

[0059] When the lighting data is represented by 12 bits, it is preferable to control the lighting of the LED light source 20 in units of sub-lighting periods, which are obtained by dividing one lighting period by 4096. It is also preferable that the duty ratio is determined in units of sub-lighting periods. In this case, it is preferable that the DC-DC converter 54 has a duty ratio of the same order. In other words, it is preferable to divide one lighting period in accordance with the response speed of the DC-DC converter 54. For example, one lighting period may be divided into 16 to 128 parts, taking into account the response speed of the DC-DC converter 54. In this case, the lighting data is represented by 4 to 10 bits.

[0060] The timing at which the LED light source 20 is turned on can be set to various timings, such as the beginning, middle, or end of one lighting period. Also, the lighting timing may be different for each LED light source 20. In this embodiment, an example will be described in which each LED light source 20 is turned on at the beginning of one lighting period.

[0061] As in the first embodiment, the resistance values ​​RA and RB of the resistors 54A and 54B are set so that the LED voltage Vout at the output terminal 54a becomes the voltage Vled when the correction current Ic is zero and all the LED light sources 20 (L11 to L44) are turned on at maximum brightness. Also, as in the first embodiment, the largest voltage drop due to the wiring 30 occurs in L44, and the voltage Vled taking the voltage drop into consideration satisfies the relationship between the formulas (1) and (2) shown in the first embodiment.

[0062] The driving of the LED device 102 will now be described in detail with reference to Figures 6A, 6B and 6C.

[0063] 6A, 6B, and 6C schematically show the lighting timing of L11 to L44 when one lighting period is divided into 16. In each figure, a rectangular block represents one sub-lighting period, with open circles representing lighting and shaded circles representing extinguishing.

[0064] In the LED device 102, the lighting controller 52 generates lighting data and control signals based on the display data for each sub-lighting period. In other words, the sub-lighting period corresponds to the lighting period (one frame period) in the first embodiment. However, in this embodiment, the same current value is passed through L11 to L44 during the sub-lighting period, and the value of the voltage drop in the wiring 30 is determined only by the number of LED light sources 20 (L11 to L44) that are turned on during the sub-lighting period.

[0065] As shown in FIG. 6A, when all of L11 to L44 are lit, the LED with the largest voltage drop is L44 as described in the first embodiment, and the LED voltage Vout is set to Vled in all sub-lighting periods.

[0066] Therefore, at this time, the correction current Ic=0 and Vcd=255.

[0067] As shown in FIG. 6B, when all of L11 to L44 are turned off, no current flows through the wiring 30, so there is no voltage drop due to the wiring 30, and Vcom=0 and Vcd=0.

[0068] 6C, the LED light sources 20 other than L32 are turned on. However, the lengths (number) of the sub-lighting periods during which the LED light sources 20 are turned on are different.

[0069] In this case, the largest voltage drop in the wiring 30 is L44, and Vad44 is expressed by the following formula because L32 is not lit. Vad44=(15·r0+11·r1+7r1+4·r1+4·ra+3·ra +2·ra+ra)×Imax =(15·r0+22·r1+10·ra)×Imax (11)

[0070] In the LED device 102 of this embodiment, in each sub-lighting period, L11 to L44 are either lit or extinguished (the current value is either Imax or 0), so if the condition r1>(4+3+2+1)×ra is met, the voltage drop value in each LED light source 20 is greatest at L44 and decreases as it approaches the output terminal 54a of the DC-DC converter 54 from L44.

[0071] Vad44>Vad43>Vad42>Vad41>Vad34>... >Vad13>Vad12>Vad11

[0072] Therefore, assuming that this condition is met, the magnitude of the voltage drop at each part of the wiring 30 is not compared, but only the on / off of L11 to L44 is considered, and the voltage drop to be referenced is determined in order from L44 onwards, by referring to L43 if the current of L44 is 0, and then referring to L42 if the current of L43 is 0.

[0073] The first to sixteenth correction voltage data Vcd(1) to Vcd(16) in each sub-lighting period are expressed as follows: Vcd(1) =int[{( r0+ 2·r1 )×Imax} / (Vled-Vh-Vf)×255 Vcd(2) =int[{( r0+ 2·r1 )×Imax} / (Vled-Vh-Vf)×255 Vcd(3) =int[{( r0+ 2·r1 )×Imax} / (Vled-Vh-Vf)×255 Vcd(4) =int[{( 4·r0+ 6·r1 )×Imax} / (Vled-Vh-Vf)×255 Vcd(5) =int[{( 4·r0+ 6·r1 )×Imax} / (Vled-Vh-Vf)×255 Vcd(6) =int[{( 4·r0+ 6·r1 )×Imax} / (Vled-Vh-Vf)×255 Vcd(7) =int[{( 6·r0+ 7·r1 )×Imax} / (Vled-Vh-Vf)×255 Vcd(8) =int[{( 6·r0+ 7·r1 )×Imax} / (Vled-Vh-Vf)×255 Vcd(9) =int[{( 6·r0+ 7·r1 )×Imax} / (Vled-Vh-Vf)×255 Vcd(10)=int[{( 8·r0+ 8·r1 )×Imax} / (Vled-Vh-Vf)×255 Vcd(11)=int[{( 8·r0+ 8·r1 )×Imax} / (Vled-Vh-Vf)×255 Vcd(12)=int[{( 8·r0+ 8·r1 )×Imax} / (Vled-Vh-Vf)×255 Vcd(13)=int[{(10·r0+ 8·r1 )×Imax} / (Vled-Vh-Vf)×255 Vcd(14)=int[{(11·r0+11·r1+2·ra)×Imax} / (Vled-Vh-Vf)×255 Vcd(15)=int[{(12·r0+14·r1+5·ra)×Imax} / (Vled-Vh-Vf)×255 Vcd(16)=int[{(13·r0+17·r1+6·ra)×Imax} / (Vled-Vh-Vf)×255 In this way, the lighting controller 52 generates the correction voltage data Vcd(1) to Vcd(16) based on the display data for each sub-lighting period, and the LED voltage correction circuit 53 generates the correction current Ic. As a result, similar to the first embodiment, heat generation and unnecessary power consumption caused by application of excess voltage to the channel terminal 12a of the LED driver 12 are suppressed.

[0074] (Third embodiment) 7 is a schematic block diagram showing the configuration of an LED device 103 of this embodiment. The LED device 103 differs from the LED device 102 of the second embodiment in that a plurality of LED light sources 20 are divided into a plurality of groups, and the LED light sources 20 of each group are driven in a time-division manner.

[0075] For this purpose, the LED device 103 includes an LED light source 20 including at least a plurality of first LED light sources 20-1 and a plurality of second LED light sources 20-2, and wiring 30 including at least a first wiring 30-1 and a second wiring 30-2. The LED device 103 also includes a plurality of switching elements 13 including at least a first switching element 13-1 and a second switching element 13-2. In the example shown in FIG. 7, the LED device 103 includes the first LED light source 20-1 through the m-th LED light source 20-m, the first wiring 30-1 through the m-th wiring 30-m, and the first switching element 13-1 through the m-th switching element 13-m, where m is a natural number greater than or equal to 2.

[0076] One ends of the first LED light source 20-1 to the m-th LED light source 20-m are connected to the channel terminals 12a of the LED drivers 12'-1 to 12'-n. More specifically, among the first LED light source 20-1 to the m-th LED light source 20-m, the LED light sources located in the same column are connected to the same channel terminal 12a of the LED driver 12'.

[0077] Meanwhile, the other ends of the first LED light source 20-1 to the m-th LED light source 20-m are connected to the first wiring 30-1 to the m-th wiring 30-m, respectively. The first wiring 30-1 to the m-th wiring 30-m are connected to an output terminal 54a of a DC-DC converter 54 via the first switching element 13-1 to the m-th switching element 13-m.

[0078] The LED driver 12'-1 also has a scanning terminal 12d, which is connected to the control terminals of the first switching element 13-1 to the m-th switching element 13-m.

[0079] The lighting controller 52 receives display data from the outside and generates lighting data. The lighting data is output to the LED driver 12-1 for each lighting period via a data line D1, and is further transferred to the LED drivers 12-2 to 12-n arranged in the row direction via a data line D2.

[0080] The LED drivers 12-1 to 12-n drive the first LED light source 20-1 to the m-th LED light source 20-m in a time-division manner based on the lighting data. In this embodiment, one lighting period is divided into m parts, and the first LED light source 20-1 to the m-th LED light source 20-m are driven in each of the divided parts. A period divided into m parts is called one time-division lighting period.

[0081] The LED driver 12-1 outputs a scanning signal from the scanning terminal 12d to sequentially turn on the first switching element 13-1 through the m-th switching element 13-m during each time-division lighting period. The LED driver 12-1 also controls the current flowing through the channel terminal 12a so that the LED light source 20 connected to the switching element that is turned on achieves the brightness of the lighting data. The brightness of the LED light source 20 is achieved by driving it according to the duty of the lighting period described in the second embodiment. As a result, the LED drivers 12-1 through 12-n selectively connect the first wiring 30-1 through the m-th wiring 30-m to the output terminal 54a of the DC-DC converter 54 in a time-division manner, thereby driving the first LED light source 20-1 through the m-th LED light source 20-m, respectively.

[0082] Next, the control of the voltage at the output terminal of the DC-DC converter 54 will be described. The values ​​of the resistors 54A and 54B connected to the control terminal 54b of the DC-DC converter 54 are set so that the LED voltage Vout at the control terminal 54b becomes the voltage Vled, which is the maximum voltage required to drive the LED device 103. In this embodiment, all of the LED light sources 20 do not light up at the same time, but are driven in groups. Therefore, when the LED light sources of each group, the first LED light source 20-1 to the m-th LED light source 20-m, are driven at maximum brightness, Vled is determined based on the largest voltage drop value.

[0083] When the first LED light source 20-1 to the m-th LED light source 20-m connected to each of the first wiring 30-1 to the m-th wiring 30-m are turned on at maximum brightness, if the largest voltage drop value among the first wiring 30-1 to the m-th wiring 30-m is Vadmax, Vled is expressed by the following equation. Vled=Vadmax+Vh+Vf (11)

[0084] Since the resistance value RA of the resistor 54A and the resistance value RB of the resistor 54B satisfy the relationship of equation (1), the resistance values ​​RA and the resistor 54B satisfy the following relationship: At this time, the correction current Ic is zero. RB / (RA+RB)=(Vadmax+Vh+Vf) / Vfb (12) As in the first and second embodiments, a method for adjusting the LED voltage will be described with reference to Fig. 8, which shows a simplified circuit diagram of the LED device 103 for the purpose of explanation. In Fig. 8, the LED light sources 20 are arranged in four rows and four columns, and will be hereinafter designated as L11 to L14, L21 to L24, L31 to L34, and L41 to L44.

[0085] Unlike the first and second embodiments, in the LED device 103, the first LED light source 20-1, the second LED light source 20-2, ..., the m-th LED light source 20-m are each driven independently in a time-division manner. In the example shown in Fig. 8, the first LED light sources L11 to L14, the second LED light sources L21 to L24, the third LED light sources L31 to L34, and the fourth LED light sources L41 to L44, which are connected to the first wiring 30-1, the second wiring 30-2, the third wiring 30-3, and the fourth wiring 30-4, respectively, are driven at different timings in a time-division manner.

[0086] The brightness of each LED light source 20 may be controlled by the current value as described in the first embodiment, or may be controlled by the duty ratio, which is the ratio between the ON and OFF periods of the LED light source 20, as described in the second embodiment. In this embodiment, an example will be described in which the brightness of the LED light source 20 is adjusted by the duty ratio, as in the second embodiment.

[0087] As described above, one lighting period is divided into the same number of parts as the number of groups of LED light sources 20, and one time-division period, which is one divided period, is further divided into a plurality of sub-lighting periods. As in the second embodiment, the following describes an example in which the LED light sources 20 are turned on at the beginning of each time-division period.

[0088] As shown in FIG. 8, the first wiring 30-1, the second wiring 30-2, the third wiring 30-3, and the fourth wiring 30-4 have parasitic resistances as described below. The output terminal 54a of the DC-DC converter 54 Between the first switching element 13-1 to the fourth switching element 13-4: R0 Between the first switching element 13-1 and the connection point C1: R1 Between connection point C1 and connection point L11: R1a Between the connection point with L11 and the connection point with L12: R1b Between the connection point with L12 and the connection point with L13: R1c Between the connection point with L13 and the connection point with L14: R1d Between the second switching element 13-2 and the connection point C2: R2 Between connection point C2 and the connection point with L21: R2a Between the connection point with L21 and the connection point with L22: R2b Between the connection point with L22 and the connection point with L23: R2c Between the connection point with L23 and the connection point with L24: R2d Between the third switching element 13-3 and the connection point C3: R3 Between connection point C3 and connection point with L31: R3a Between the connection point with L31 and the connection point with L32: R3b Between the connection point with L32 and the connection point with L33: R3c Between the connection point with L33 and the connection point with L34: R3d Between the fourth switching element 13-4 and the connection point C4: R4 Between connection point C4 and connection point with L41: R4a Between the connection point with L41 and the connection point with L42: R4b Between the connection point with L42 and the connection point with L43: R4c Between the connection point with L43 and the connection point with L44: R4d

[0089] For the sake of explanation, the resistance values ​​of these parasitic resistors are determined as follows. R0=r0(Ω) R1=r1(Ω) R2=r2(Ω) R3=r3(Ω) R4=r4(Ω) r1>r2>r3>r4 R1a=R1b=R1c=R1d =R2a=R2b=R2c=R2d =R3a=R3b=R3c=R3d =R4a=R4b=R4c=R4d =ra(Ω) Also, the current flowing through each of the LED light sources (L11 to L44) is Imax.

[0090] As in the first and second embodiments, the voltage drop due to the parasitic resistance is greatest when a current Imax flows through L14, and the voltage drop at this time is expressed by the following equation, where Vad14 is the voltage drop at this time. Vad14=(4·r0+4·r1+4·ra+3·ra+2·ra+1·ra) ×Imax (13) Therefore, Vled is given by the following formula: Vled=Vh+Vf+Vad14 =Vh+Vf+(4·r0+4·r1+10·ra)×Imax (14)

[0091] Furthermore, from equation (13) and equation (1), RB / (RA+RB)={Vh+Vf+(4·r0+4·r1+10·ra) ×Imax} / Vfb (15) where Vfb is the reference voltage of the DC-DC converter 54. The resistance value RA of the resistor 54A and the resistance value RB of the resistor 54B are determined so as to satisfy the relationship of equation (14). At this time, the correction current Ic is zero.

[0092] Fig. 8 shows a schematic diagram of the lighting timing of each LED light source 20 in one lighting period. In Fig. 8, one lighting period is divided into four time-divided lighting periods (first to fourth), and each time-divided lighting period is further divided into 16 sub-lighting periods. The number of divisions into the sub-lighting periods is preferably determined according to the response speed of the DC-DC converter 54, and may be, for example, approximately 16 to 128.

[0093] In four one-time-division lighting periods, the first LED light source 20-1 (L11 to L14) connected to the first wiring 30-1, the second LED light source 20-2 (L21 to L24) connected to the second wiring 30-2, the third LED light source 20-3 (L31 to L34) connected to the third wiring 30-3, and the fourth LED light source 20-4 (L41 to L44) connected to the fourth wiring 30-4 are each driven. In each one-time-division lighting period, the upper part shows (1) a case where the four LED light sources are lit at maximum brightness, the center part shows (2) a case where the four LED light sources are turned off, and the lower part shows (3) a case where the four LED light sources are lit at their respective brightnesses.

[0094] As shown in Figure 8, a blank period may be provided at the end of each time-division lighting period. In this case, the sub-lighting period can be determined by equally dividing the time excluding the blank period. During the blank period, none of the LED light sources 20 are lit.

[0095] As in the second embodiment, the lighting controller 52 generates the correction voltage data Vcd for each sub-lighting period.

[0096] The correction voltage data is Vcd=int[{(Vled-Vcom-Vh-Vf) / (Vled-Vh-Vf)} ×255] (14) Here, Vcom is the maximum value of the voltage drop on the wiring 30 during the sub-lighting period.

[0097] When all the LED light sources 20 are turned on at maximum brightness in each time-division lighting period, the parasitic resistance value of the wiring 30 connected to the power supply for the LEDs to be turned on differs, and therefore the correction voltage data Vcd also differs for each time-division lighting period.

[0098] In the first time-division lighting period, the anode voltage drop of L14 is maximum. Vcom at this time is expressed by the following formula in all sub-lighting periods.

[0099] Vcom=(4·r0+4·r1+10·ra)×Imax (16) This Vcom is the same as Vad14 shown in equation (13). Ic=0[A] is.

[0100] Similarly, in the second time-division lighting period, the anode voltage drop of L24 reaches its maximum. Vcom at this time is expressed by the following formula in all sub-lighting periods. Vcom=(4·r0+4·r2+10·ra)×Imax (17) The correction current Ic is expressed by the following formula: Ic≒{4(r1-r2)·Imax} / RA (18) Here, since the right-hand side is converted to an integer during the calculation, a rounding error may occur in equation (18).

[0101] Similarly, in the third time-division lighting period, the anode voltage drop of L34 reaches its maximum. Vcom at this time is expressed by the following formula in all sub-lighting periods. Vcom=(4·r0+4·r3+10·ra)×Imax (19) The correction current Ic is expressed by the following formula: Ic≒{4(r1-r3)·Imax} / RA (20) Here, since the right-hand side is converted to an integer during the calculation, a rounding error may occur in equation (20).

[0102] Similarly, in the fourth time-division lighting period, the drop in the anode voltage of L44 reaches its maximum. Vcom at this time is expressed by the following formula in all sub-lighting periods. Vcom=(4·r0+4·r4+10·ra)×Imax (21) The correction current Ic is expressed by the following formula: Ic≒{4(r1-r4)·Imax} / RA (22) Here, since the right-hand side is converted to an integer during the calculation, a rounding error may occur in equation (22).

[0103] When all of the LED light sources 20 are turned off in each time-division lighting period, no current flows through the wiring 30. Vcom=0 Also, Ic≒{(4·r0 + 4·r1 + 10·ra)×Imax} / RA (23) This becomes:

[0104] Next, an example of calculating the correction current Ic when lighting each of the LED light sources 20 at a predetermined brightness is shown. Vcom in each sub-lighting period is represented as Vcom(n_m). Here, n indicates the nth time-division lighting period, and m indicates the mth sub-lighting period. n is a natural number from 1 to 4, and m is a natural number from 1 to 16. The correction current Ic at this time is similarly represented as Ic(n_m).

[0105] Each Vcom(n_m) in the first time-division lighting period is expressed as follows: Vcom(1_ 1)=(4·r0+4·r1+10·ra)×Imax Vcom(1_ 2)=(4·r0+4·r1+10·ra)×Imax Vcom(1_ 3)=(4·r0+4·r1+10·ra)×Imax Vcom(1_ 4)=(4·r0+4·r1+10·ra)×Imax Vcom(1_ 5)=(3·r0+3·r1+ 9·ra)×Imax Vcom(1_ 6)=(3·r0+3·r1+ 9·ra)×Imax Vcom(1_ 7)=(3·r0+3·r1+ 9·ra)×Imax Vcom(1_ 8)=(2·r0+2·r1+ 7·ra)×Imax Vcom(1_ 9)=(2·r0+2·r1+ 7·ra)×Imax Vcom(1_10)=(2·r0+2·r1+ 7·ra)×Imax Vcom(1_11)=(1·r0+1·r1+ 4·ra)×Imax Vcom(1_12)=(1·r0+1·r1+ 4·ra)×Imax Vcom(1_13)=(1·r0+1·r1+ 4·ra)×Imax Vcom(1_14)=0 Vcom(1_15)=0 Vcom(1_16)=0

[0106] Furthermore, each Ic(n_m) in the first time-division lighting period is expressed as follows: Ic(1_1)=Ic(1_2) =Ic(1_3) =Ic(1_4) =0 Ic(1_5)=Ic(1_6) =Ic(1_7) ≒{(r0+r1+ra)·Imax} / RA Ic(1_8)=Ic(1_9) =Ic(1_10) ≒{(2·r0+2·r1+3·ra)·Imax} / RA Ic(1_11)=Ic(1_12) =Ic(1_13) ≒{(3·r0+3·r1+6·ra)×Imax} / RA Ic(1_14)=Ic(1_15) =Ic(1_16) ≒{(4·r0+4·r1+10·ra)·Imax} / RA

[0107] Each Vcom(n_m) in the second time-division lighting period is expressed as follows: Vcom(2_ 1)=(4·r0+4·r2+10·ra)·Imax Vcom(2_ 2)=(4·r0+4·r2+10·ra)·Imax Vcom(2_ 3)=(4·r0+4·r2+10·ra)·Imax Vcom(2_ 4)=(4·r0+4·r2+10·ra)·Imax Vcom(2_ 5)=(3·r0+3·r2+ 6·ra)·Imax Vcom(2_ 6)=(3·r0+3·r2+ 6·ra)·Imax Vcom(2_ 7)=(3·r0+3·r2+ 6·ra)·Imax Vcom(2_ 8)=(2·r0+2·r2+ 3·ra)·Imax Vcom(2_ 9)=(2·r0+2·r2+ 3·ra)·Imax Vcom(2_10)=(2·r0+2·r2+ 3·ra)·Imax Vcom(2_11)=(1·r0+1·r2+ 1·ra)·Imax Vcom(2_12)=(1·r0+1·r2+ 1·ra)·Imax Vcom(2_13)=(1·r0+1·r2+ 1·ra)·Imax Vcom(2_14)=0 Vcom(2_15)=0 Vcom(2_16)=0

[0108] Furthermore, each Ic(n_m) in the second time-division lighting period is expressed as follows: Ic(2_1)=Ic(2_2) =Ic(2_3) =Ic(2_4) ={4·(r1-r2)·Imax} / RA Ic(2_5)=Ic(2_6) =Ic(2_7) ≒{(1·r0+4·r1-3·r2+4·ra)·Imax} / RA Ic(2_8)=Ic(2_9) =Ic(2_10) ≒{(2·r0+4·r1-2·r2+7·ra)·Imax} / RA Ic(2_11)=Ic(2_12) =Ic(2_13) ≒{(3·r0+4·r1-1·r2+9·ra)·Imax} / RA Ic(2_14)=Ic(2_15) =Ic(2_16) ≒{(4·r0+4·r1+10·ra)·Imax} / RA

[0109] Each Vcom(n_m) in the third time-division lighting period is expressed as follows: Vcom(3_ 1)=(4·r0+4·r3+10·ra)·Imax Vcom(3_ 2)=(4·r0+4·r3+10·ra)·Imax Vcom(3_ 3)=(4·r0+4·r3+10·ra)·Imax Vcom(3_ 4)=(4·r0+4·r3+10·ra)·Imax Vcom(3_ 5)=(3·r0+3·r3+ 6·ra)·Imax Vcom(3_ 6)=(3·r0+3·r3+ 6·ra)·Imax Vcom(3_ 7)=(3·r0+3·r3+ 6·ra)·Imax Vcom(3_ 8)=(2·r0+2·r3+ 5·ra)·Imax Vcom(3_ 9)=(2·r0+2·r3+ 5·ra)·Imax Vcom(3_10)=(2·r0+2·r3+ 5·ra)·Imax Vcom(3_11)=(1·r0+1·r3+ 2·ra)·Imax Vcom(3_12)=(1·r0+1·r3+ 2·ra)·Imax Vcom(3_13)=(1·r0+1·r3+ 2·ra)·Imax Vcom(3_14)=0 Vcom(3_15)=0 Vcom(3_16)=0

[0110] Moreover, each Ic(n_m) in the third time-division lighting period is expressed as follows: Ic(3_1)=Ic(3_2) =Ic(3_3) =Ic(3_4) ={4·(r1-r3)·Imax} / RA Ic(3_5)=Ic(3_6) =Ic(3_7) ≒{(1·r0+4·r1-3·r3+4·ra)·Imax} / RA Ic(3_8) = Ic(3_9) = Ic(3_10) ≈{(2·r0 + 4·r1 - 2·r3 + 5·ra)·Imax} / RA Ic(3_11) = Ic(3_12) = Ic(3_13) ≈{(3·r0 + 4·r1 - 1·r3 + 8·ra)·Imax} / RA Ic(3_14) = Ic(3_15) = Ic(3_16) ≈{(4·r0 + 4·r1 + 10·ra)·Imax} / RA

[0111] Each Vcom(n_m) in the fourth divided lighting period is shown as follows. Vcom(4_1) = (4·r0 + 4·r4 + 10·ra)·Imax Vcom(4_2) = (4·r0 + 4·r4 + 10·ra)·Imax Vcom(4_3) = (4·r0 + 4·r4 + 10·ra)·Imax Vcom(4_4) = (4·r0 + 4·r4 + 10·ra)·Imax Vcom(4_5) = (3·r0 + 3·r4 + 9·ra)·Imax Vcom(4_6) = (3·r0 + 3·r4 + 9·ra)·Imax Vcom(4_7) = (3·r0 + 3·r4 + 9·ra)·Imax Vcom(4_8) = (3·r0 + 3·r4 + 9·ra)·Imax Vcom(4_9) = (3·r0 + 3·r4 + 9·ra)·Imax Vcom(4_10) = (3·r0 + 3·r4 + 9·ra)·Imax Vcom(4_11) = (2·r0 + 2·r4 + 7·ra)·Imax Vcom(4_12) = (2·r0 + 2·r4 + 7·ra)·Imax Vcom(4_13) = (2·r0 + 2·r4 + 7·ra)·Imax Vcom(4_14) = (1·r0 + 1·r4 + 3·ra)·Imax Vcom(4_15)=(1·r0+1·r4+ 3·ra)·Imax Vcom(4_16)=(1·r0+1·r4+ 3·ra)·Imax

[0112] Furthermore, each Ic(n_m) in the fourth time-division lighting period is expressed as follows: Ic(4_1)=Ic(4_2) =Ic(4_3) =Ic(4_4) ={4·(r1-r4)·Imax} / RA Ic(4_5)=Ic(4_6) =Ic(4_7) =Ic(4_8) =Ic(4_9) =Ic(4_10) ≒{(1·r0+4·r1-3·r4+1·ra)×Imax} / RA Ic(4_11)=Ic(4_12) =Ic(4_13) ≒{(2·r0+4·r1-2·r4+3·ra)×Imax} / RA Ic(4_14)=Ic(4_15) =Ic(4_16) ≒{(3·r0+4·r1-1·r4+7·ra)×Imax} / RA

[0113] In this way, the lighting controller calculates Vcom for each sub-lighting period based on the display data, and generates the correction voltage data Vcd using the relationship in equation (14). Furthermore, the LED voltage correction circuit 53 receives the correction voltage data Vcd, generates a correction current Ic, and supplies the correction current Ic to the control terminal 54b of the DC-DC converter 54. This allows the LED voltage output by the DC-DC converter 54 to be adjusted. Therefore, when the number of lit LED light sources 20 is small or the brightness of the LED light sources 20 is low, the LED voltage decreases, suppressing heat generation and unnecessary power consumption due to excess voltage being applied to the channel terminal 12a of the LED driver 12.

[0114] (Other forms) The LED device and liquid crystal display device of the present disclosure are not limited to the above-described embodiments and may be modified in various ways. In the above-described embodiments, the LED device is a backlight for the liquid crystal display device, but the LED device may also be a self-luminous display device itself. In this case, the display data may be information regarding the brightness of each pixel.

[0115] Furthermore, in the above embodiment, the LD light source device is provided with a DC-DC converter having a feedback terminal as a DC power supply, but may be provided with other DC power supplies such as a variable voltage power supply circuit that can change the output voltage.

[0116] The LED device and liquid crystal display device of the present disclosure can also be explained as follows.

[0117] The LED device according to the first configuration is Multiple LED light sources and an LED driver connected to one end of each of the plurality of LED light sources, the LED driver controlling a current flowing through each of the LED light sources based on lighting data; a DC power supply having an output terminal connected in parallel to the other end of each of the plurality of LED light sources using wiring, receiving a control signal, and applying an LED voltage of a value based on the control signal to the output terminal; a control device that receives display data, generates the lighting data and the control signal based on the display data, and outputs the lighting data and the control signal to the LED driver and the DC power supply; Equipped with.

[0118] According to the first configuration, the DC power supply changes the LED voltage applied to the output terminal in response to a control signal based on display data. Therefore, when the number of LED light sources that are lit is small or when the brightness of the LED light sources is low, the LED voltage is reduced, preventing excess voltage from being applied to the LED driver and reducing unnecessary power consumption.

[0119] In the LED device according to the second configuration, in addition to the first configuration, the display data may include information about luminance set for each lighting period of the plurality of LED light sources.

[0120] In the LED device according to the third configuration, in addition to the second configuration, the lighting data may include information on a current value flowing through each LED light source corresponding to a luminance set for each lighting period.

[0121] In the LED device according to the fourth configuration, in the second configuration, the lighting data may include information on a duty ratio between a lighting period and a non-lighting period of each LED light source, which corresponds to a luminance set for each lighting period.

[0122] In the LED device according to a fifth configuration, in addition to the fourth configuration, the lighting period may include a plurality of sub-lighting periods, and the duty ratio may be determined based on the sub-lighting periods.

[0123] In the LED device of the sixth configuration, in the first configuration, the control signal may include information regarding a difference in voltage drop value due to a difference in the amount of current flowing through the wiring caused by a difference in luminance between the maximum luminance of the plurality of LED light sources in each lighting period and a set luminance.

[0124] An LED device according to a seventh configuration may be the first configuration, wherein the plurality of LED light sources include a plurality of first LED light sources and a plurality of second LED light sources, the wiring includes a first wiring and a second wiring, one end of each of the plurality of first LED light sources is connected to the LED driver, the other end of each of the plurality of first LED light sources is connected in parallel to the first wiring, one end of each of the plurality of second LED light sources is connected to the LED driver, and the other end of each of the plurality of second LED light sources is connected in parallel to the second wiring, and the LED driver selectively connects the first wiring and the second wiring to the output terminal in a time-division manner.

[0125] An LED device according to an eighth aspect is the LED device of the first aspect, wherein the control device includes a lighting controller and an LED voltage correction circuit, the lighting controller generates correction voltage data based on the display data, which indicates a difference in voltage drop caused by a difference in current flowing through the wiring resulting from a difference in luminance between a maximum luminance of the plurality of LED light sources in each lighting period and a set luminance, and the LED voltage correction circuit generates a correction current based on the correction voltage data; The DC power supply may control the LED voltage based on the correction current.

[0126] A liquid crystal display device according to a ninth configuration includes a liquid crystal display panel and an LED device according to any one of the first to eighth configurations, which is disposed on the back surface of the liquid crystal display panel. [Explanation of symbols]

[0127] 10...LED board, 11...board, 12, 12', 12-1 to 12-4...LED driver, 12a...channel terminal, 12b...input terminal, 12c...output terminal, 12d...scanning terminal, 13...switching element, 13-1...first switching element, 13-2...second switching element, 13-3...third switching element, 13-4...fourth switching element, 13-m...mth switching element, 20...LED light source, 20 -1...first LED light source, 20-2...second LED light source, 20-3...third LED light source, 20-4...fourth LED light source, 20-m...mth LED light source, 30...wiring, 30-1...first wiring, 30-2...second wiring, 30-3...third wiring, 30-4...fourth wiring, 30-m...mth wiring, 40...wiring, 50...control board, 51...board, 52...lighting controller, 53...LED voltage compensation circuit, 53a...data conversion table 53b...D / A converter, 53c...op-amp, 53d...resistor, 53e...transistor 54... DC-DC converter, 54A, 54B... resistors, 55... control device, 101 to 103... LED devices, 201... liquid crystal panel, 501... liquid crystal display device

Claims

1. A plurality of LED light sources; an LED driver connected to one end of each of the plurality of LED light sources, the LED driver controlling a current flowing through each of the LED light sources based on lighting data; a DC power supply having an output terminal connected in parallel to the other end of each of the plurality of LED light sources using wiring, receiving a control signal, and applying an LED voltage of a value based on the control signal to the output terminal; a control device that receives display data, generates the lighting data and the control signal based on the display data, and outputs the lighting data and the control signal to the LED driver and the DC power supply; An LED device comprising:

2. The LED device according to claim 1 , wherein the display data includes information about luminance set for each lighting period of the plurality of LED light sources.

3. The LED device according to claim 2 , wherein the lighting data includes information about a current value flowing through each LED light source, the current value corresponding to a luminance set for each lighting period.

4. The LED device according to claim 2 , wherein the lighting data includes information regarding a duty ratio between a lighting period and a non-lighting period of each LED light source, the duty ratio corresponding to a luminance set for each lighting period.

5. The LED device according to claim 4 , wherein the lighting period includes a plurality of sub-lighting periods, and the duty ratio is determined based on the sub-lighting periods.

6. 2. The LED device according to claim 1, wherein the control signal includes information regarding a difference in voltage drop caused by a difference in the amount of current flowing through the wiring due to a difference in luminance between a maximum luminance of the plurality of LED light sources during each lighting period and a set luminance.

7. the plurality of LED light sources include a plurality of first LED light sources and a plurality of second LED light sources; the wiring includes a first wiring and a second wiring, one end of each of the plurality of first LED light sources is connected to the LED driver, and the other end of each of the plurality of first LED light sources is connected in parallel to a first wiring; one end of each of the plurality of second LED light sources is connected to the LED driver, and the other end of each of the plurality of second LED light sources is connected in parallel to a second wiring; The LED device according to claim 1 , wherein the LED driver selectively connects the first wiring and the second wiring to the output terminal in a time-division manner.

8. The control device includes a lighting controller and an LED voltage correction circuit, the lighting controller generates, based on the display data, correction voltage data indicating a difference in voltage drop due to a difference in current flowing through the wiring caused by a difference in luminance between a maximum luminance of the plurality of LED light sources in each lighting period and a set luminance; the LED voltage correction circuit generates a correction current based on the correction voltage data; The LED device according to claim 1 , wherein the DC power supply controls the LED voltage based on the correction current.

9. A liquid crystal display panel; The LED device according to claim 1 , which is disposed on a rear surface of the liquid crystal display panel; and A liquid crystal display device comprising:

Images