Drive circuit and display device

Abstract

To provide a drive circuit, a display device and the like which improve power consumption.SOLUTION: The drive circuit is a drive circuit for a display device and includes a power supply unit that supplies power to a light emitting unit including a plurality of light emitting units, a current driver that supplies a pulsed drive current whose duty ratio is adjustable to the plurality of light emitting units, and a control unit that controls a current value and a duty ratio of the drive current supplied by the current driver based on an input gradation value corresponding to the plurality of light emitting units. The control unit sets the current value such that the luminance with respect to the maximum input gradation value of the light-emitting unit becomes relatively small when the lighting rate of the plurality of light-emitting units is larger than a first threshold value, and the luminance with respect to the maximum input gradation value becomes relatively large when the lighting rate is equal to or smaller than the first threshold value, and supplies the set current value in common to the plurality of light-emitting units of the light-emitting unit corresponding to the plurality of areas.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a drive circuit, a display device, and the like. [Background technology]

[0002] Conventionally, there have been known drive circuits for driving a display unit (backlight) of a display device. For example, Patent Document 1 discloses a drive circuit that supplies a pulsed drive current with adjustable switching frequency and pulse width. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-233033 Summary of the Invention [Problem to be solved by the invention]

[0004] In conventional methods such as Patent Document 1, when peak luminance is controlled according to the average lighting rate, power consumption is high. For example, in Patent Document 1, voltage is supplied to some light-emitting elements more than necessary, resulting in unnecessary power consumption.

[0005] According to some aspects of the present disclosure, it is possible to provide a drive circuit, a display device, and the like that improve power consumption. [Means for solving the problem]

[0006] One aspect of the present disclosure relates to a drive circuit for a display device, the drive circuit including: a power supply unit that supplies power to a light-emitting section including a plurality of light-emitting units; a current driver that supplies a pulsed drive current with an adjustable duty ratio to the plurality of light-emitting units; and a control unit that controls the current value and the duty ratio of the drive current supplied by the current driver based on an input gradation value corresponding to each of the plurality of light-emitting units, wherein the light-emitting sections are provided in each of a plurality of areas obtained by dividing a display region of the display device into a plurality of areas; and the control unit sets the current value so that when a lighting rate of the plurality of light-emitting units calculated from the input gradation values ​​is greater than a first threshold value, a luminance of the light-emitting section with respect to a maximum input gradation value becomes relatively small, and when the lighting rate is equal to or less than the first threshold value, a luminance of the light-emitting section with respect to the maximum input gradation value becomes relatively large, and the control unit causes the set current value to be supplied in common to the plurality of light-emitting units of the light-emitting section corresponding to the plurality of areas.

[0007] Another aspect of the present disclosure relates to a display device including the above-described drive circuit. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a configuration example of a drive circuit. [Figure 2] 10 is a configuration example of a first control unit. [Figure 3] 10 is a configuration example of a second control unit. [Figure 4A] 10A and 10B are diagrams illustrating control (peak luminance control) according to the average lighting rate of luminance relative to the maximum input gradation value. [Figure 4B] FIG. 10 is a diagram showing the relationship between the input gradation value and the target luminance according to the average lighting rate. [Figure 5A] 10A and 10B are diagrams illustrating the relationship between the input grayscale value, the duty ratio, the current value, and the target brightness when the average lighting rate is low in the present disclosure. [Figure 5B] 10A and 10B are diagrams illustrating the relationship between the input grayscale value, the duty ratio, the current value, and the target brightness when the average lighting rate is high in the present disclosure. [Figure 6A] 10A and 10B are diagrams illustrating drive currents in bright and dark regions when the average lighting rate is low in the present disclosure. [Figure 6B] 10A and 10B are diagrams illustrating drive currents in bright and dark regions when the average lighting rate is high in the present disclosure. [Figure 7A] 10 is a diagram showing the relationship between the input grayscale value and the duty ratio, current value, and target brightness when the average lighting rate is low in the first comparative example. FIG. [Figure 7B] FIG. 10 is a diagram showing the relationship between the input grayscale value, the duty ratio, the current value, and the target brightness when the average lighting rate is high in the first comparative example. [Figure 8A] 10 is a diagram illustrating the drive currents in the bright and dark regions when the average lighting rate is low in the first comparative example. FIG. [Figure 8B] 10 is a diagram illustrating the drive currents in the bright and dark regions when the average lighting rate is high in the first comparative example. FIG. [Figure 9A] FIG. 1 is a diagram showing the current-voltage characteristics of a light-emitting element (LED). [Figure 9B] FIG. 10 is a diagram illustrating an example of a drive current with an average current of 3 mA. [Figure 9C] FIG. 10 is a diagram illustrating an example of a drive current with an average current of 3 mA. [Figure 10A] 10A and 10B are diagrams illustrating the relationship between voltage values ​​in the method of the present disclosure. [Figure 10B] FIG. 10 is a diagram illustrating the relationship between voltage values ​​in a first comparative example. [Figure 11A] FIG. 10 is a diagram showing the relationship between the input grayscale value and each of the duty ratio, current value, and target brightness when the average lighting rate is low in the second comparative example. [Figure 11B] FIG. 10 is a diagram showing the relationship between the input grayscale value and each of the duty ratio, current value, and target brightness when the average lighting rate is high in the second comparative example. [Figure 12A] FIG. 10 is a diagram illustrating the drive currents in the bright and dark regions when the average lighting rate is low in the second comparative example. [Figure 12B]FIG. 10 is a diagram illustrating the drive currents in the bright and dark regions when the average lighting rate is high in the second comparative example. [Figure 13] 1 is an example of the external configuration of a display device including a drive circuit. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, the present embodiment will be described with reference to the drawings. In the drawings, identical or equivalent elements are designated by the same reference numerals, and duplicate explanations will be omitted. Note that the present embodiment described below does not unduly limit the content described in the claims. Furthermore, not all of the configurations described in the present embodiment are necessarily essential components of the present disclosure.

[0010] 1.Configuration example Fig. 1 is a diagram showing an example of the configuration of a drive circuit 100 of this embodiment. The drive circuit 100 is a drive circuit for a display device 200, and includes a power supply unit 130, a current driver 120, and a control unit 140. However, the configuration of the drive circuit 100 is not limited to the example shown in Fig. 1, and various modifications are possible, such as omitting some components or adding other components. Note that the possibility of modifications, such as omitting or adding components, also applies to the figures described below, such as Figs. 2 and 3.

[0011] The power supply unit 130 supplies power to the light-emitting section 110 including a plurality of light-emitting units 111 (light-emitting units 111-1 to 111-n, n is an integer of 2 or more). The current driver 120 supplies a pulsed driving current with an adjustable duty ratio (PWM: Pulse Width Modulation) to the light-emitting units 111. For example, the current driver 120 may be a plurality of current drivers 120-1 to 120-n, each of which supplies a driving current to a corresponding one of the light-emitting units 111. The control section 140 controls the current value and duty ratio of the driving current supplied by the current driver 120 based on the input grayscale value corresponding to each of the plurality of light-emitting units 111-1 to 111-n. Each section of the drive circuit 100 will be described in detail below.

[0012] Each of the plurality of light-emitting units 111-1 to 111-n has one or more light-emitting elements 112. In the following description, when there is no need to distinguish the plurality of light-emitting units 111-1 to 111-n from one another, they will be simply referred to as light-emitting units 111. The light-emitting elements 112 included in the light-emitting units 111 are, for example, semiconductor light-emitting elements, and more specifically, LEDs (Light Emitting Diodes). However, the light-emitting elements 112 may be other light-emitting elements. Furthermore, in the example of FIG. 1, the light-emitting unit 111 includes three light-emitting elements 112 connected in series, but the number of light-emitting elements 112 included in the light-emitting unit 111 is not limited to this.

[0013] Each of the multiple current drivers 120-1 to 120-n drives a corresponding one of the multiple light-emitting units 111-1 to 111-n. In the following description, when there is no need to distinguish between the multiple current drivers 120-1 to 120-n, they will be simply referred to as current drivers 120. For example, the current driver 120 may include a drive element that drives the light-emitting unit 111. The drive element may be a field effect transistor (FET) or another drive element. For example, the current driver 120 according to this embodiment may be configured using a known configuration such as that disclosed in Patent Document 1. The current driver 120 is connected in series with the corresponding light-emitting unit 111. For example, one end of the drive element included in the current driver 120 is connected to the cathode terminal of the light-emitting unit 111, and the other end of the drive element is connected to a low-potential power supply (for example, ground). Furthermore, another element such as a resistor may be disposed between the drive element and ground.

[0014] A power supply unit 130 (PSU) supplies power to the light-emitting unit 111. As shown in FIG. 1, the power supply unit 130 may supply a common voltage Vout to the plurality of light-emitting units 111-1 to 111-n included in the light-emitting section 110. Specifically, the power supply unit 130 is connected to the anode terminals of each of the plurality of light-emitting units 111-1 to 111-n, and supplies the voltage Vout to the anode terminals. In the example of FIG. 1, the light-emitting unit 111 and the current driver 120 are connected in series between the power supply unit 130 and ground. The power supply unit 130 may control the voltage Vout under the control of the control unit 140.

[0015] The control unit 140 may include a first control unit 141 and a second control unit 142. The first control unit 141 performs feedback control of Vout output by the power supply unit 130 based on a feedback voltage VLED (see FIG. 2 described later). The feedback voltage VLED is, for example, a voltage between the cathode terminal of the light-emitting unit 111 and the current driver 120. The second control unit 142 controls the current value and duty ratio of the drive current supplied by the current driver 120 based on an input grayscale value.

[0016] The control unit 140 of this embodiment is configured by the following hardware. The hardware can include at least one of a circuit for processing digital signals and a circuit for processing analog signals. For example, the hardware can be configured by one or more circuit devices or one or more circuit elements mounted on a circuit board. The one or more circuit devices are, for example, an integrated circuit (IC), a field-programmable gate array (FPGA), etc. The one or more circuit elements are, for example, a resistor, a capacitor, etc.

[0017] The control unit 140 may also be implemented by the following processor. The drive circuit 100 of this embodiment includes a memory that stores information and a processor that operates based on the information stored in the memory. The information may be, for example, a program and various data. The processor includes hardware. Various types of processors may be used, such as a central processing unit (CPU), a graphics processing unit (GPU), or a digital signal processor (DSP). The memory may be a semiconductor memory such as a static random access memory (SRAM), a dynamic random access memory (DRAM), or a flash memory, or may be a register, a magnetic storage device such as a hard disk drive (HDD), or an optical storage device such as an optical disk drive. For example, the memory stores computer-readable instructions, and the processor executes the instructions to realize the functions of the control unit 140 as processing. The instructions may be instructions from an instruction set that constitutes a program, or instructions that instruct the hardware circuitry of the processor to operate.

[0018] 2 is a diagram showing an example of the configuration of the first control unit 141. The first control unit 141 may include a voltage acquisition unit 1411 and a control signal output unit 1412.

[0019] The voltage acquisition unit 1411 acquires (detects) the feedback voltage VLED. The feedback voltage VLED is expressed, for example, as in the following equation (1) using the voltage Vout supplied by the power supply unit 130 and the voltage Vf applied to the light-emitting unit 111. VLED=Vout-Vf (1)

[0020] Here, since a plurality of light-emitting units 111-1 to 111-n are considered, voltages VLED1 to VLEDn are obtained as candidates for the feedback voltage VLED. When the voltage applied to the light-emitting unit 111-i (i is an integer between 1 and n) is Vfi, VLEDi is expressed by the following equation (2): VLEDi=Vout-Vfi (2)

[0021] The control signal output unit 1412 outputs a signal to the power supply unit 130 to determine a voltage value required to drive the light-emitting unit 111, based on the voltages VLED1 to VLEDn acquired by the voltage acquisition unit 1411. Here, the power supply unit 130 needs to supply the voltage Vout so that sufficient voltages Vf1 to Vfn are applied to all of the light-emitting units 111-1 to 111-n included in the light-emitting unit 110. In other words, the power supply unit 130 needs to supply a Vout that can realize the maximum value of the voltages Vf1 to Vfn. Therefore, the control signal output unit 1412 outputs a control signal based on the feedback voltage VLED, which is the minimum value of the voltages VLED1 to VLEDn, to the power supply unit 130. The power supply unit 130 determines the voltage Vout to be supplied to the light-emitting unit 111 based on the output of the control signal output unit 1412. Note that the configurations of the voltage acquisition unit 1411 and the control signal output unit 1412 can be configured using known techniques such as those described in Patent Document 1, and therefore detailed description thereof will be omitted. Further, a known method such as that disclosed in Patent Document 1 can be applied to the configuration for determining the voltage Vout based on the output of the control signal output unit 1412, and therefore detailed description thereof will be omitted.

[0022] In this way, the first control unit 141 may control, based on the feedback voltage VLED, the voltage Vout that the power supply unit 130 supplies to one end (anode end) of the light-emitting unit 111. Through such feedback control, the power supply unit 130 can supply, as the voltage Vout, a voltage that can appropriately drive the multiple light-emitting units 111-1 to 111-n included in the light-emitting section 110.

[0023] 3 is a diagram showing an example of the configuration of the second control unit 142. The second control unit 142 includes a lighting rate determination unit 1421, a current value setting unit 1422, and a duty ratio setting unit 1423.

[0024] The lighting rate determination unit 1421 determines the lighting rate of the light-emitting unit 110 based on the input gradation value of each light-emitting unit 111. The lighting rate here is, for example, the average lighting rate (APL: Average Picture Level). The input gradation value is the signal value of an image signal to be displayed on the display 210 of the display device 200, and more specifically, may be the pixel value of each pixel. The input gradation value is, for example, a value between 0 and 255, but other numerical ranges may also be used. Note that methods for determining the APL from the input gradation value are well known, so detailed description will be omitted. Furthermore, although an example in which the lighting rate is the APL will be described below, other lighting rates may also be used.

[0025] The current value setting unit 1422 sets the current value of the drive current to be supplied to the plurality of light-emitting units 111 based on the APL determined by the lighting rate determination unit 1421. When the APL is low, the current value setting unit 1422 sets a higher current value than when the APL is high. The current value set here is determined according to the APL and is common to the plurality of light-emitting units 111-1 to 111-n regardless of the individual input gradation values.

[0026] The duty ratio setting unit 1423 sets the duty ratio of the drive current supplied to each of the plurality of light-emitting units 111-1 to 111-n based on the input gradation value corresponding to each of the light-emitting units 111. The duty ratio setting unit 1423 sets the duty ratio for each light-emitting unit 111 so that when the input gradation value is small, the duty ratio is lower than when the input gradation value is large.

[0027] The current value setting section 1422 and the duty ratio setting section 1423 control the current drivers 120-1 to 120-n, respectively, so that drive currents of the set current value and duty ratio are supplied to the plurality of light-emitting units 111-1 to 111-n.

[0028] 2. Control details Next, the drive current control according to this embodiment will be described in detail.

[0029] 4A and 4B are diagrams illustrating peak luminance control (APL Limit control). Conventionally, peak luminance control is known in which, when the APL is high, the luminance relative to the maximum input gradation value is lower than when the APL is low. The maximum input gradation value here is the maximum value of the input gradation value, for example, 255.

[0030] The vertical axis of Fig. 4A represents the luminance relative to the maximum input gradation value, and the horizontal axis represents the APL. The rectangles shown along the horizontal axis of Fig. 4A are diagrams that schematically represent the light-emitting states of display 210, with the shaded areas corresponding to low luminance and the white areas corresponding to high luminance. In other words, the rectangle on the left, with a relatively wide shaded area, represents a low APL state, and the rectangle on the right, with a relatively wide white area, represents a high APL state.

[0031] As shown in FIG. 4A, when the APL is relatively low, the luminance for the maximum input gradation value is not limited but is set to a high value. In this case, the luminance for the maximum input gradation value is, in a narrow sense, the luminance achieved when the light-emitting unit 111 (light-emitting element 112) exhibits its maximum performance, but a luminance lower than this may also be used. In contrast, when the APL is high, the luminance for the maximum input gradation value is limited to a low value. By performing such peak luminance control, it is possible to reduce power consumption even when the APL is high.

[0032] 4B is a diagram showing the relationship between input gradation values ​​and target luminance. The target luminance here is the target luminance of the light-emitting units 111, and the control unit 140 controls the current driver 120 so that each of the multiple light-emitting units 111 emits light at the target luminance corresponding to the input gradation value.

[0033] The vertical axis of FIG. 4B represents the target luminance value, and the horizontal axis represents the input gradation value. As shown in FIG. 4B, when the input gradation value is 0, the corresponding pixel (light-emitting unit 111) expresses black, and therefore the target luminance is set to 0. Furthermore, the larger the input gradation value, the higher the luminance value of the corresponding pixel is set. In this case, as described with reference to FIG. 4A, the luminance value relative to the maximum input gradation value changes according to the APL. As shown in FIG. 4B, when the APL is low, the luminance relative to the maximum input gradation value is high, and therefore the degree of increase in target luminance when the input gradation value increases is relatively large. FIG. 4B shows an example in which the target luminance and input gradation value are linear, and therefore the slope is relatively large. On the other hand, when the APL is high, the luminance relative to the maximum input gradation value is limited to a low value, and therefore the degree of increase in target luminance when the input gradation value increases is relatively small, and therefore the slope is shallow.

[0034] As described above, the peak brightness control is realized by changing the relationship between the input gradation value and the target brightness according to the APL. Specifically, the control unit 140 realizes the peak brightness control by controlling the current value and duty ratio of the drive current of each light-emitting unit 111.

[0035] 5A and 5B are diagrams illustrating drive current control according to input gradation values ​​in this embodiment. FIG. 5A illustrates a case where the APL is low and the luminance relative to the maximum input gradation value is high. FIG. 5B illustrates a case where the APL is high and the luminance relative to the maximum input gradation value is limited to a low level. The two graphs on the left side of FIGS. 5A and 5B respectively show the relationship between the input gradation value and the duty ratio, and the relationship between the input gradation value and the current value. Since the luminance of the light-emitting unit 111 is determined by multiplying the current value and the duty ratio, the relationship between the input gradation value and the target luminance shown in FIG. 4B is determined based on these two relationships.

[0036] As can be seen from a comparison between FIGS. 5A and 5B, the control unit 140 (or, more specifically, the current value setting unit 1422 of the second control unit 142) of this embodiment sets the current value so that the luminance of the light-emitting unit 110 relative to the maximum input gradation value is relatively low when the lighting rate (APL) of the multiple light-emitting units 111 calculated from the input gradation value is greater than a first threshold, and the luminance of the light-emitting unit 110 relative to the maximum input gradation value is relatively high when the lighting rate is equal to or less than the first threshold. Specifically, the control unit 140 sets the current value high when the APL is low (FIG. 5A) and low when the APL is high (FIG. 5B). Note that the current value in this embodiment may be changed in at least two stages depending on the lighting rate. For example, the current value is not limited to being changed in two stages with the first threshold as a boundary, and may be continuously controlled as described above with reference to FIG. 4A.

[0037] The control unit 140 then supplies a common current value set based on the APL to the plurality of light-emitting units 111 of the light-emitting unit 110. For example, if the display region (display 210, display panel) of the display device 200 is divided into a plurality of areas and a light-emitting unit 110 is provided in each of the plurality of areas, the control unit 140 supplies a common current value set to the light-emitting units 111 of the light-emitting units 110 corresponding to the plurality of areas (all of the light-emitting units 111 included in all of the light-emitting units 100). Specifically, as shown in FIG. 5A , when the APL is low, a relatively large current value is set, and the current value is a constant value for all of the light-emitting units 111, regardless of the input grayscale value for each of the light-emitting units 111. Similarly, as shown in FIG. 5B , when the APL is high, a relatively small current value is set, and the current value is a constant value for all of the light-emitting units 111, regardless of the input grayscale value for each of the light-emitting units 111. In other words, the current values ​​of the plurality of light-emitting units 111-1 to 111-n are determined by the lighting rate (APL) of the light-emitting section 110 as a whole, and are constant regardless of the individual input grayscale values ​​of each light-emitting unit 111.

[0038] Furthermore, the control unit 140 (or, more narrowly, the duty ratio setting unit 1423 of the second control unit 142) determines the duty ratio of the drive current supplied to each light-emitting unit 111 based on the input gradation value corresponding to that light-emitting unit 111. As shown in FIGS. 5A and 5B, the relationship between the input gradation value and the duty ratio may be fixed regardless of the APL. For example, the duty ratio is set for each light-emitting unit 111 so that it is minimum (0%) when the input gradation value is minimum (0) and maximum (100%) when the input gradation value is maximum (255).

[0039] In this way, it is possible to realize peak brightness control by changing the value of the current according to the APL. Therefore, it is possible to reduce power consumption while performing peak brightness control, compared to, for example, the first and second comparative examples described below. Details of the comparative examples will be described later. Note that "supplying a common current value to a plurality of light-emitting units" here means that a common target current value is used in the control of the control unit 140, and errors in the supplied current due to individual differences between the current driver 120 and the light-emitting unit 111 are allowed.

[0040] 6A and 6B are diagrams illustrating the drive current in a bright region of the light-emitting unit 110 where the input grayscale value (target brightness value) is relatively large, and the drive current in a dark region where the input grayscale value (target brightness value) is relatively small. Specifically, FIG. 6A shows an example of the drive current in a bright region and the drive current in a dark region when the APL is low. FIG. 6B shows an example of the drive current in a bright region and the drive current in a dark region when the APL is high. Note that the rectangles on the left in FIGS. 6A and 6B are diagrams that schematically represent the light-emitting state of the display 210, similar to the example shown in FIG. 4A. In addition, the vertical axis of the graph showing the drive current represents the current value, and the horizontal axis represents time.

[0041] As shown in FIGS. 6A and 6B, the control unit 140 supplies a common current value to the light-emitting units 111-1 to 111-n corresponding to bright regions where the input grayscale value is equal to or greater than a predetermined value and the light-emitting units 111 corresponding to dark regions where the input grayscale value is less than the predetermined value. The control unit 140 also sets the duty ratio of the light-emitting units corresponding to the bright regions higher than that of the light-emitting units corresponding to the dark regions. For example, when comparing the drive currents for the bright and dark regions in the example of FIG. 6A, a relatively high current value is set in common, and the duty ratio is high in the bright regions and low in the dark regions. When comparing the drive currents for the bright and dark regions in the example of FIG. 6B, a relatively low current value is set in common, and the duty ratio is high in the bright regions and low in the dark regions. This allows peak luminance control according to the APL while appropriately representing the bright and dark regions in each APL.

[0042] In this case, the control unit 140 may set the duty ratio of the first light-emitting unit among the plurality of light-emitting units, whose input gradation value is the maximum input gradation value (e.g., 255), to a value corresponding to the maximum value, and may also set the current value to a value according to the lighting rate (APL).

[0043] As will be described later with reference to Figures 9A-9C, when considering the characteristics of LEDs, even if the average brightness (the product of the current value and the duty ratio) is the same, power consumption can be reduced by setting the current value low and the duty ratio high. Therefore, power consumption can be reduced by setting the duty ratio of the drive current of the light-emitting unit 111 that maximizes the input grayscale value to the maximum value and setting the current value so that the product of the duty ratio and the current value is the desired brightness (the brightness for the maximum input grayscale value shown in Figure 4A). Note that the maximum value of the duty ratio is, for example, 100%, but other values ​​may also be used.

[0044] 3. Comparative Example Next, a comparative example will be described.

[0045] <First Comparative Example> 7A and 7B are diagrams illustrating drive current control according to input gradation values ​​in a first comparative example. The first comparative example corresponds to, for example, the technique of Patent Document 1. FIG. 7A shows a case where the APL is low and the luminance relative to the maximum input gradation value is high. FIG. 7B shows a case where the APL is high and the luminance relative to the maximum input gradation value is limited to a low value. The two graphs on the left side of FIGS. 7A and 7B, like FIGS. 5A and 5B, respectively show the relationship between the input gradation value and the duty ratio, and the relationship between the input gradation value and the current value, and the relationship between the input gradation value and the target luminance is determined based on these two relationships.

[0046] As can be seen from the relationship between input gradation value and target brightness in Figures 7A and 7B (the graphs on the far right), even in the first comparative example, when the APL is high, the brightness relative to the maximum input gradation value is limited, thereby achieving peak brightness control.

[0047] However, in the first comparative example, as shown in Figures 7A and 7B, both the duty ratio and the current value change depending on the input gradation value. For example, when the APL is low, as shown in Figure 7A, within the input gradation value range of 0 to x1, the duty ratio increases as the input gradation value increases, and the current value is constant regardless of the input gradation value. Furthermore, within the input gradation value range of x1 to 255, the duty ratio is constant regardless of the input gradation value, and the current value increases as the input gradation value increases. x1 is a given number between 0 and 255.

[0048] Similarly, when the APL is high, as shown in Fig. 7B, within the input gradation value range of 0 to x2 (x2 is a value greater than x1), the duty ratio increases as the input gradation value increases, and the current value is constant regardless of the input gradation value. Furthermore, within the input gradation value range of x2 to 255, the duty ratio is constant regardless of the input gradation value, and the current value increases as the input gradation value increases.

[0049] In this way, in the first comparative example, even if the APL is determined to a certain value, the current value of the drive current supplied to the light-emitting unit varies depending on the input gradation value of the light-emitting unit. As shown in Figure 7A, when the APL is low, the variation in the current value depending on the input gradation value is significant.

[0050] 8A and 8B are diagrams illustrating the drive current in the bright region and the drive current in the dark region of the light-emitting section. Specifically, FIG. 8A is an example of the drive current in the bright region and the drive current in the dark region when the APL is low. FIG. 8B is an example of the drive current in the bright region and the drive current in the dark region when the APL is high. As with FIGS. 6A and 6B, the rectangles represent the light-emitting state of the display, the vertical axis of the graph represents the current value, and the horizontal axis represents time.

[0051] As shown in Figure 8A, in the first comparative example, when the APL is low, both the current value and duty ratio change depending on the input gradation value. Specifically, the drive current corresponding to the bright region has a large current value and duty ratio, while the drive current corresponding to the dark region has a small current value and duty ratio. On the other hand, as shown in Figure 8B, in the first comparative example, when the APL is high, the duty ratio mainly changes depending on the input gradation value. Note that, as shown in Figure 7B, in the first comparative example, even when the APL is high, the current value may change depending on the input gradation value, but the degree of change is smaller than when the APL is low, so Figure 8B shows an example in which only the duty ratio changes.

[0052] Here, we will consider the power consumption of the method of this embodiment and the first comparative example. Fig. 9A is a diagram showing the current-voltage characteristics of an LED, which is an example of a light-emitting element. The vertical axis of Fig. 9A represents the magnitude of the forward current, and the horizontal axis represents the magnitude of the forward voltage. As can be seen from Fig. 9A, the greater the current value flowing through the LED, the greater the forward voltage of the LED.

[0053] As shown in Figures 1 and 2, the light-emitting unit 111 of this embodiment is configured so that multiple light-emitting elements 112 are connected in series, and therefore the voltage Vf applied to the light-emitting unit 111 increases as the current value of the driving current supplied to the light-emitting unit 111 increases.

[0054] 9B and 9C are diagrams showing examples of the current value and duty ratio of the drive current. FIG. 9B shows an example where the current value is 10 mA and the duty ratio is 30%. FIG. 9C shows an example where the current value is 3 mA and the duty ratio is 100%. In this case, regardless of which drive current is used, the average current is the same at 3 mA, and therefore the brightness of the LED (light-emitting unit 111) is the same. On the other hand, because the current value of the drive current shown in FIG. 9C is smaller than that of the drive current shown in FIG. 9B, the voltage Vf applied to the light-emitting unit 111 is also smaller when the drive current shown in FIG. 9C is used, resulting in reduced power consumption.

[0055] Thus, considering the characteristics of LEDs, reducing the current value and increasing the duty ratio contributes to reducing power consumption, and so the method of the first comparative example appears at first glance to be effective in reducing power consumption (see the drive current corresponding to the dark area in FIG. 8A). In fact, if it is possible to supply an individual voltage Vout to each of the multiple light-emitting units 111-1 to 111-n, the method of the comparative example may be effective in reducing power consumption.

[0056] However, in a display device 200 having a large number of light-emitting units 111, switching the voltage Vout for each light-emitting unit 111 requires providing a power supply unit 130 for each light-emitting unit 111, or providing a power supply unit 130 with multiple output terminals capable of supplying different voltages. Therefore, switching the voltage Vout for each light-emitting unit 111 is not practical. Furthermore, in recent display devices, a technique has been known in which the backlight of a display (display panel) is divided into multiple local dimming areas and the brightness of the backlight is adjusted for each local dimming area. This allows for flexible control of the brightness of the light-emitting units 111 in each local dimming area. For example, the light-emitting unit 110 in this embodiment may be provided for each of the multiple local dimming areas. However, even when local dimming is used, the voltage supplied to the multiple light-emitting units 111 is the same unless the power supply units 130 are provided individually.

[0057] FIG. 10A is a diagram illustrating voltages for the light-emitting unit 111-a (where a is an integer between 1 and n) corresponding to the bright region and the light-emitting unit 111-b (where b is an integer between 1 and n, but different from a) corresponding to the dark region, in the method of this embodiment. In this embodiment, as described above, a current value is determined according to the APL, and the determined current value is supplied in common to the light-emitting units 111-a and 111-b, regardless of whether the region is a bright region or a dark region (FIGS. 5A to 6B). If the current values ​​are common, the forward voltages of the light-emitting elements 112 are also common, as shown in FIG. 9A, and therefore the voltage Vfa applied to the light-emitting unit 111-a and the voltage Vfb applied to the light-emitting unit 111-b become equal.

[0058] As shown in the above formula (1), the feedback voltage VLED is determined based on the difference between Vout supplied from the power supply unit 130 and the voltage Vf applied to the light-emitting unit 111. As described above, it is not easy to switch the voltage Vout for each light-emitting unit 111, so the voltage Vout is considered to be common to multiple light-emitting units 111. Furthermore, in the method of this embodiment, since the voltages Vfa and Vfb are equal as described above, the voltages VLEDa and VLEDb, which are the differences from the voltage Vout, are also equal. Similarly, when multiple light-emitting units 111-1 to 111-n are considered, the values ​​of the voltages VLED1 to VLEDn are equal, so this voltage value is used as the value of the feedback voltage VLED. Therefore, in the method of this embodiment, all of the voltages VLED1 to VLEDn do not become excessively large relative to the feedback voltage VLED, thereby suppressing power loss.

[0059] FIG. 10B illustrates the voltages for the light-emitting unit 111-a corresponding to the bright region and the light-emitting unit 111-b corresponding to the dark region when the APL is low in the method of the first comparative example. As described above with reference to FIGS. 7A and 8A, when the APL is low in the first comparative example, control of the bright and dark regions is achieved by significantly changing both the current value and the duty ratio according to the input gradation value. Therefore, the current value is set lower in the dark region than in the bright region. Therefore, the forward voltage of the LED corresponding to the dark region is lower than the forward voltage of the LED corresponding to the bright region. As a result, as shown in FIG. 10B, the voltage Vfb applied to the light-emitting unit 111-b is lower than the voltage Vfa applied to the light-emitting unit 111-a.

[0060] On the other hand, as described above, it is not realistic to switch the voltage Vout supplied from the power supply unit 130 for each light-emitting unit 111 within the screen. Therefore, the voltage Vout is common to the light-emitting units 111-a and 111-b. Therefore, as shown in FIG. 10B , when considering the voltage that is the difference between Vout and Vf, the voltage VLEDb of the light-emitting unit 111-b becomes larger than the voltage VLEDa of the light-emitting unit 111-a.

[0061] Here, in consideration of supplying a voltage Vout large enough to cause each of the light-emitting units 111-1 to 111-n to emit light at a target brightness, a relatively small voltage VLEDa is used as the feedback voltage VLED. In other words, the voltage VLoss, which is the difference between the voltages VLEDb and VLEDa, does not contribute to either the light emission of the light-emitting elements or feedback control, and is an excessive voltage that increases power consumption.

[0062] As described above, when compared with the first comparative example, the method of this embodiment differs in that a current value determined from the average lighting rate is supplied in common to the plurality of light-emitting units 111-1 to 111-n (FIGS. 5A to 6B). More specifically, once a current value is set based on the APL, the current value is supplied in common to the plurality of light-emitting units 111, including the light-emitting unit 111-b corresponding to the dark region. Therefore, even in a configuration in which the display region of the display device 200 is divided into a plurality of areas and the power supply unit 130 supplies a common voltage Vout to the plurality of light-emitting units 111-1 to 111-n of the light-emitting section 110 corresponding to the plurality of areas (in a narrow sense, all the light-emitting units 111 corresponding to the entire display 210), it is possible to suppress an increase in power consumption due to the generation of an excessive voltage VLoss (FIG. 10A).

[0063] <Second Comparative Example> 11A and 11B are diagrams illustrating drive current control according to input gradation values ​​in a second comparative example. FIG. 11A shows a case where the APL is low and the luminance relative to the maximum input gradation value is high. FIG. 11B shows a case where the APL is high and the luminance relative to the maximum input gradation value is limited to a low value. The two graphs on the left side of FIGS. 11A and 11B, similar to FIGS. 5A and 5B, respectively show the relationship between input gradation value and duty ratio, and the relationship between input gradation value and current value, and the relationship between input gradation value and target luminance is determined based on these two relationships.

[0064] As can be seen from the relationship between input gradation value and target brightness in Figures 11A and 11B (the graphs on the far right), even in the second comparative example, when the APL is high, the brightness for the maximum input gradation value is limited, thereby achieving peak brightness control.

[0065] However, in the second comparative example, as shown in Figures 11A and 11B, only the duty ratio changes, and the current value does not change. Specifically, the current value is constant regardless of the APL and the input gradation value. The maximum value of the duty ratio is determined by the APL, and the specific value is determined according to the input gradation value. In other words, the slope representing the change in the duty ratio relative to the input gradation value is set small when the APL is high.

[0066] 12A and 12B are diagrams illustrating the drive current in the bright region and the drive current in the dark region of the light-emitting unit 110. Specifically, FIG. 12A is an example of the drive current in the bright region and the drive current in the dark region when the APL is low. FIG. 12B is an example of the drive current in the bright region and the drive current in the dark region when the APL is high. As with FIGS. 6A and 6B, the rectangles represent the light-emitting state of the display, and the vertical axis of the graph represents the current value and the horizontal axis represents time.

[0067] As shown in Fig. 12A, in the second comparative example, when the APL is low, bright and dark regions are realized by changing the duty ratio according to the input gradation value. On the other hand, as shown in Fig. 12B, in the second comparative example, even when the APL is high, the current value is maintained high, and bright and dark regions are realized by lowering the duty ratio compared to when the APL is low.

[0068] As is clear from FIG. 12B, in the second comparative example, even in bright regions (pixels with the highest input gradation value and the highest target luminance, in the narrow sense), the duty ratio is limited to a value lower than the maximum value. In contrast, with the method of this embodiment, as shown in FIGS. 6A and 6B, the duty ratio of bright regions can be set to a high value (the maximum value, in the narrow sense) regardless of whether the APL is high or low. As a result, with the method of this embodiment, the voltage value can be reduced when the APL is high compared to the second comparative example, making it possible to reduce power consumption (see FIGS. 9A to 9C).

[0069] 4.Display device The technique of this embodiment may be applied to a display device 200 including the above-described drive circuit 100. FIG. 13 is a diagram showing an example of the external configuration of the display device 200. As shown in FIG. 13, the display device 200 includes a display 210, and the light-emitting unit 110 constitutes the display 210. For example, the display device 200 may be a television device or the like equipped with a liquid crystal display, and the light-emitting unit 110 may be a backlight for the liquid crystal display. According to the technique of this embodiment, it is possible to reduce the power consumption of the display device 200.

[0070] Furthermore, the above-described light-emitting unit 110 may be provided in each of a plurality of areas obtained by dividing the display 210, and each of the plurality of areas may be a local dimming area. In this way, even when local dimming control is performed, it is possible to reduce the power consumption of the display device 200 (display 210).

[0071] Although the present embodiment has been described in detail above, it will be readily apparent to those skilled in the art that many modifications are possible without substantially departing from the novel features and advantages of the present embodiment. Therefore, all such modifications are intended to be included within the scope of the present disclosure. For example, a term described at least once in the specification or drawings together with a different term having a broader or equivalent meaning may be replaced with that different term anywhere in the specification or drawings. Furthermore, all combinations of the present embodiment and modifications are also included within the scope of the present disclosure. Furthermore, the configurations and operations of the driving circuits, display devices, etc. are not limited to those described in the present embodiment, and various modifications are possible. [Explanation of symbols]

[0072] 100: drive circuit, 110: light emitting section, 111, 111-1 to 111-n: light emitting units, 112: light emitting element, 120, 120-1 to 120-n: current drivers, 130: power supply unit, 140: control section, 141: first control section, 1411: voltage acquisition section, 1412: control signal output section, 142: second control section, 1421: lighting rate determination section, 1422: Current value setting unit; 1423: Duty ratio setting unit; 200: Display device; 210: Display; Vf, Vfa, Vfb: Voltage applied to light emitting unit; VLED: Feedback voltage; VLEDa, VLEDb: Voltages that are candidates for feedback voltage; VLoss: Voltage that becomes loss; Vout: Voltage supplied from power supply unit

Claims

1. A drive circuit for a display device, a power supply unit for supplying power to a light-emitting section including a plurality of light-emitting units; a current driver that supplies a pulsed driving current with an adjustable duty ratio to the plurality of light-emitting units; a control unit that controls the current value of the driving current supplied by the current driver and the duty ratio based on an input grayscale value corresponding to each of the plurality of light-emitting units; Including, the light-emitting units are provided in a plurality of areas obtained by dividing a display area of ​​the display device into a plurality of areas, The control unit setting the current value so that, when a lighting rate of the plurality of light-emitting units calculated from the input gradation value is greater than a first threshold value, the luminance of the light-emitting unit with respect to the maximum input gradation value becomes relatively small, and when the lighting rate is equal to or less than the first threshold value, the luminance of the light-emitting unit with respect to the maximum input gradation value becomes relatively large; a drive circuit that supplies the set current value in common to the plurality of light-emitting units of the light-emitting section corresponding to the plurality of areas;

2. 2. The drive circuit according to claim 1, The power supply unit comprises: a drive circuit for supplying a common voltage to the plurality of light-emitting units of the light-emitting section corresponding to the plurality of areas;

3. 3. The drive circuit according to claim 1, The control unit a drive circuit that sets the duty ratio of a first light-emitting unit among the plurality of light-emitting units, the first light-emitting unit having the input gradation value that is the maximum input gradation value, to a value corresponding to the maximum value, and sets the current value to a value according to the lighting rate.

4. 3. The drive circuit according to claim 1, The control unit A drive circuit that supplies a common current value to light-emitting units corresponding to bright areas where the input gradation value is equal to or greater than a predetermined value and light-emitting units corresponding to dark areas where the input gradation value is less than a predetermined value, and that sets the duty ratio of the light-emitting units corresponding to the bright areas to be higher than the duty ratio of the light-emitting units corresponding to the dark areas.

5. A display device comprising the drive circuit according to claim 1 or 2.

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