Display device and display method

Abstract

To provide a display device and a method for display that can suppress reduction of the display quality of an image.SOLUTION: In the display device, a voltage adjusting unit for adjusting the voltage value of a driving voltage supplied from a power source unit includes: a first adjusting unit for adjusting a current value measured by a measurement unit to a first voltage value as a desired value; and a second adjusting unit for adjusting the voltage value of a driving voltage supplied by the power source unit to a second voltage value as a predetermined fixed value when a non-emission period of time of a plurality of light emitting elements is provided immediately before a PWM processing period of time. The second voltage value is higher than the first voltage value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a display device and a display method. [Background technology]

[0002] Patent Document 1 discloses an LED driver that controls the brightness of an LED (Light Emitting Diode) by controlling a PWM (Pulse Width Modulation) switch. The LED driver disclosed in Patent Document 1 has a feedback loop circuit that measures the level of current actually flowing through the LED and adjusts the voltage supplied to the anode of the LED according to the measured current level in order to maintain the current flowing through the LED at a desired current level. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Patent Publication US2013 / 0127344 Summary of the Invention [Problem to be solved by the invention]

[0004] According to the LED driver of Patent Document 1, the voltage supplied to the LED anode is adjusted simply by feeding back the current level actually flowing through the LED. Therefore, when the duty cycle of the PWM signal is zero, no current flows through the LED, and feedback is not possible. Furthermore, if a period in which the duty cycle of the PWM signal is zero is followed by a period in which the duty cycle of the PWM signal is greater than zero (i.e., a period in which current flows through the LED), time is required for the current level flowing through the LED to be adjusted to the desired current level. This may result in a degradation of image display quality. The present disclosure provides a display device and a display method that can quickly adjust the voltage value of the drive voltage supplied to multiple light-emitting elements to a voltage value that allows a desired current value to flow through the multiple light-emitting elements, thereby suppressing a degradation of image display quality. [Means for solving the problem]

[0005] A display device according to one embodiment of the present disclosure includes a display panel, a backlight having a plurality of light-emitting elements, a power supply unit that supplies a driving voltage to the plurality of light-emitting elements, a measurement unit that measures a current value flowing through the plurality of light-emitting elements, and a voltage adjustment unit that adjusts the voltage value of the driving voltage supplied by the power supply unit, wherein the voltage adjustment unit has a first adjustment unit that adjusts the voltage value of the driving voltage supplied by the power supply unit to a first voltage value at which the current value measured by the measurement unit becomes a desired value during a PWM processing period in which the plurality of light-emitting elements are PWM processed, and a second adjustment unit that adjusts the voltage value of the driving voltage supplied by the power supply unit to a second voltage value that is a predetermined fixed voltage when a non-light-emitting period in which the plurality of light-emitting elements are in a non-light-emitting state for a predetermined period is provided immediately before the PWM processing period, and the second voltage value is higher than the first voltage value.

[0006] A display method according to one embodiment of the present disclosure includes the steps of supplying a driving voltage to a plurality of light-emitting elements of a backlight that illuminates a display panel, measuring a current value flowing through the plurality of light-emitting elements, and adjusting a voltage value of the driving voltage supplied to the plurality of light-emitting elements, wherein the step of adjusting the voltage value of the driving voltage includes the steps of: adjusting, during a PWM processing period in which the plurality of light-emitting elements are PWM-processed, the voltage value of the driving voltage supplied to the plurality of light-emitting elements to a first voltage value at which the current value measured in the step of measuring the current value becomes a desired value; and, when a non-light-emitting period in which the plurality of light-emitting elements are in a non-light-emitting state for a predetermined period is provided immediately before the PWM processing period, adjusting the voltage value of the driving voltage supplied to the plurality of light-emitting elements to a second voltage value that is a predetermined fixed voltage, wherein the second voltage value is higher than the first voltage value. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a block diagram showing an outline of a display device according to an embodiment. [Figure 2] FIG. 2 is a diagram showing the PWM processing. [Figure 3] FIG. 3 is a diagram showing an example of a control pattern relating to a combination of a current value and a duty ratio to be applied to an LED for each period. [Figure 4] FIG. 4 is a block diagram illustrating an outline of a display device according to a comparative example. [Figure 5] FIG. 10 is a diagram illustrating a state of LED control in a display device according to a comparative example. [Figure 6] FIG. 6 is a flowchart illustrating a processing flow of the display device according to the embodiment. [Figure 7] FIG. 7 is a diagram illustrating the LED control of the display device according to the embodiment. [Figure 8] FIG. 8 is a diagram showing the operation of the display device according to the embodiment during a period in which the duty ratio of the LED is not zero. [Figure 9]FIG. 9 is a diagram showing the operation of the display device according to the embodiment during a period when the duty ratio of the LED is zero. DETAILED DESCRIPTION OF THE INVENTION

[0008] The embodiments described below are merely examples of the present disclosure, and the present disclosure is not limited to these embodiments. Various modifications other than these embodiments are possible depending on the design, etc., as long as they do not deviate from the technical concept of the present disclosure.

[0009] [Embodiment] 1 is a block diagram showing an outline of a display device 1 according to an embodiment. The display device 1 is a device capable of displaying various images including still images and moving images. For example, the display device 1 may be a television receiver.

[0010] The display device 1 includes a display panel 10, a backlight 20, a display panel control unit 30, a backlight control unit 40, an LED driver 50, a power supply unit 60, and a storage unit 70. The backlight control unit 40 includes a switching determination unit 41, a current setting unit 42, and a duty ratio setting unit 43. The LED driver 50 includes a plurality of switching elements 51, a voltage adjustment unit 52, an LED drive unit (drive unit) 53, and a measurement unit 54. The voltage adjustment unit 52 includes a switching unit 521, a first adjustment unit 522, and a second adjustment unit 523. The switching unit 521, the first adjustment unit 522, and the second adjustment unit 523 may be configured by hardware or software.

[0011] The display panel 10 is, for example, a liquid crystal display panel. The display panel 10 has a display area in which a plurality of pixels are arranged in a matrix, for displaying various images. The display panel control unit 30 controls the driving of the display panel 10. That is, the display panel control unit 30 displays images in the display area of ​​the display panel 10.

[0012] The backlight 20 is an illumination device that is disposed so as to overlap the rear surface of the display panel 10 and that provides planar illumination to the display panel 10. The backlight 20 controls the brightness of the illumination light that illuminates the display area of ​​the display panel 10 from behind, and the display panel 10 controls the transmittance of each of the multiple pixels arranged in the display area, thereby controlling the brightness of the image displayed in the display area of ​​the display panel 10.

[0013] The backlight 20 has a plurality of LEDs (light-emitting elements) 21 arranged in an array. In the example shown in FIG. 1, the plurality of LEDs 21 are arranged in parallel to each other in a plurality of LED groups, and each of the plurality of LED groups has a plurality of LEDs 21 connected in series to each other. The arrangement of the plurality of LEDs 21 is not limited to the example shown in FIG. 1. Each of the plurality of LEDs 21 has an anode and a cathode. When a drive voltage is supplied from the power supply unit 60 to each of the plurality of LEDs 21, a current corresponding to the potential difference between the anode and the cathode flows, and the LEDs 21 emit light with a brightness corresponding to the current flowing.

[0014] For example, the backlight 20 may have a so-called local dimming function in which the brightness of each of a plurality of regions is controlled according to the image to be displayed. Furthermore, the light emission of each of the plurality of LEDs 21 is controlled by PWM processing by the backlight control unit 40, the LED driver 50, and the power supply unit 60 so as to obtain the required brightness for each predetermined period.

[0015] Here, an overview of PWM processing will be explained using Figure 2. Figure 2 is a diagram showing the state of PWM processing. The horizontal axis in Figure 2 represents time, and the vertical axis represents the current flowing through the LED 21. The LED 21 emits light with a brightness that corresponds to the current that flows.

[0016] To achieve the brightness required for a predetermined period T (e.g., one frame period), the LED 21 undergoes a so-called PWM process, in which an off period TL during which a relatively low current AL flows through the LED 21 and an on period TH during which a current AH (AH>AL) relatively higher than the current AL flows through the LED 21 are alternately repeated. The off period TL is a non-light-emitting period during which the LED 21 does not emit light, and the on period TH is a light-emitting period during which the LED 21 emits light. The ratio of the on period TH to the predetermined period T is the duty ratio.

[0017] The PWM processing of the LED 21 is mainly controlled by two elements: the duty ratio during a predetermined period T, and the value AH of the current flowing through the LED 21 during the on-period TH. In this way, the LED 21 achieves the required brightness during the predetermined period T by repeatedly emitting and not emitting light during the predetermined period T.

[0018] 2, a period during which the LED 21 is subjected to PWM processing to achieve a predetermined brightness is referred to as a PWM processing period, and a period during which the LED 21 is not subjected to PWM processing and does not emit light for a predetermined period is sometimes referred to as a non-light-emitting period or non-PWM processing period. In other words, a PWM processing period is a period during which the duty ratio of the LED 21 is not zero, and a non-light-emitting period (non-PWM processing period) is a period during which the duty ratio of the LED 21 is substantially zero. In further words, a PWM processing period is a period during which the LED 21 is controlled to emit light or not emit light by inputting a PWM signal, for example, a square wave, to the switching element 51 during the predetermined period T, and a non-light-emitting period (non-PWM processing period) is a period during which the LED 21 is controlled to be in a non-light-emitting state by inputting a non-PWM signal, which turns the switching element 51 off (non-conducting state), to the switching element 51 during the predetermined period T. Furthermore, the non-light emitting period (non-PWM processing period) is a period during which, for example, a PWM signal, which is a rectangular wave, is not input to the switching element 51 and is kept off (non-conducting state) for a predetermined period T, so that no current flows through the LED 21 and the LED 21 is kept in a non-light emitting state for the predetermined period T, and is therefore sometimes referred to as a period during which PWM processing is not performed.

[0019] 1 and 2, the backlight control unit 40 controls the brightness of the backlight 20 in synchronization with the image that the display panel control unit 30 displays on the display panel 10. That is, the backlight control unit 40 controls the driving of the backlight 20 via the LED driver 50 and the power supply unit 60. The backlight control unit 40 controls each of the plurality of LEDs 21 via the LED driver 50 to perform PWM processing, thereby controlling whether to emit light or not so as to obtain the required brightness in a predetermined period T.

[0020] The backlight control unit 40 sets the two elements mainly used to control the above-mentioned PWM processing, namely, the duty ratio of the LED 21 and the current value AH to be passed through the LED 21 during the on period TH, for each predetermined period T according to the brightness required for the image to be displayed on the display panel 10.

[0021] The switching determination unit 41 switches the voltage value of the drive voltage output by the power supply unit 60 via the voltage adjustment unit 52 in the LED driver 50, depending on the duty ratio of the LED 21 in a predetermined period T and the current value AH to be passed through the LED 21 during the on-period TH of the LED 21. For example, when a non-light-emitting period is provided immediately before a PWM processing period, the switching determination unit 41 determines to switch the adjustment of the voltage value of the drive voltage supplied by the power supply unit 60 during the non-light-emitting period from the first adjustment unit 522 to the second adjustment unit 523. The detailed contents of the processing performed by the switching determination unit 41 will be described later with reference to FIGS. 6 to 9.

[0022] Of the two elements mainly used to control the PWM processing described above, the current setting unit 42 sets the current value AH to be passed through the LEDs 21 during the on-period TH of the LEDs 21. The current setting unit 42 sets the current value AH to be passed through the LEDs 21 during the on-period TH of the LEDs 21 so as to obtain the brightness required for an image to be displayed on the display panel 10 during a predetermined period T. The current setting unit 42 then outputs set current value information including the set current value AH as information to the voltage adjustment unit 52 of the LED driver 50.

[0023] Of the two elements primarily used to control the PWM process described above, the duty ratio setting unit 43 sets the duty ratio of the LEDs 21. The duty ratio setting unit 43 sets the duty ratio of the LEDs 21 during a predetermined period T so as to obtain the brightness required for an image to be displayed on the display panel 10 during the predetermined period T. The duty ratio setting unit 43 then outputs set duty ratio information including the set duty ratio as information to the LED driving unit 53 of the LED driver 50.

[0024] The LED driver 50 controls the driving of the backlight 20 in accordance with various instruction information (such as set current value information and set duty ratio information) from the backlight control unit 40. That is, the LED driver 50 controls the drive voltage supplied to the plurality of LEDs 21 via the power supply unit 60 and the duty ratio of each of the plurality of LEDs 21 in accordance with the various instruction information from the backlight control unit 40. For example, the LED driver 50 controls the light emission state of each of the plurality of LEDs 21 by performing PWM processing.

[0025] The multiple switching elements 51 are elements that switch on and off a current flowing through the LEDs 21 to which a drive voltage is supplied from the power supply unit 60. Each switching element 51 is connected to one of the multiple LEDs 21. In the example shown in FIG. 1, for example, each of the multiple switching elements 51 is provided for each individual LED group in the multiple LED groups. Note that each of the multiple switching elements 51 may be provided for each of the multiple LEDs 21.

[0026] For example, the switching element 51 can be configured by a MOSFET (metal-oxide-semiconductor field-effect transistor), but is not limited to this, and may be any element that can switch on and off the current flowing through the switching element 51. For example, in the switching element 51, the gate is connected to the LED driving unit 53, the source is connected to the cathode of the LED 21, and the drain is connected to the measuring unit 54 and is also grounded.

[0027] The voltage adjustment unit 52 adjusts the drive voltage supplied from the power supply unit 60 to the anodes of each of the LEDs 21. The switching unit 521 is, for example, a selector circuit, which switches the adjustment unit that supplies the drive voltage to the anodes of each of the LEDs 21 between the first adjustment unit 522 and the second adjustment unit 523 based on an instruction from the switching determination unit 41 of the backlight control unit 40. The switching operation performed by the switching unit 521 will be described in detail later.

[0028] The first adjustment unit 522 outputs to the power supply unit 60 a drive voltage such that the current value flowing through the LEDs 21 is the current value AH set by the current setting unit 42 during an emission period in which the LEDs 21 are PWM-processed and emit light. When the first adjustment unit 522 receives feedback information from the measurement unit 54 indicating the current values ​​flowing through the LEDs 21 measured by the measurement unit 54, the first adjustment unit 522 controls the power supply unit 60 to adjust the voltage value of the drive voltage to be output in accordance with the fed-back current value. For example, if the current value indicated by the feedback information acquired from the measurement unit 54 is insufficient relative to the current value AH set by the current setting unit 42, the first adjustment unit 522 controls the power supply unit 60 to increase the voltage value of the drive voltage to be output. Alternatively, if the current value indicated by the feedback information acquired from the measurement unit 54 is excessive relative to the current value AH set by the current setting unit 42, the first adjustment unit 522 controls the power supply unit 60 to decrease the voltage value of the drive voltage to be output. In this way, during the PWM processing period of the LEDs 21, the first adjustment unit 522 adjusts the voltage value of the drive voltage supplied by the power supply unit 60 to a first voltage value at which the current value flowing through each of the plurality of LEDs 21 measured by the measurement unit 54 becomes the desired current value AH. The first voltage value is the voltage value of the drive voltage supplied by the power supply unit 60 that is adjusted by the first adjustment unit 522.

[0029] Unlike the first adjustment unit 522, which adjusts the drive voltage output from the power supply unit 60 in response to feedback information from the measurement unit 54, the second adjustment unit 523 adjusts the drive voltage output from the power supply unit 60 to a second voltage value, which is a predetermined fixed voltage, regardless of the feedback information from the measurement unit 54. The second voltage value is a voltage value adjusted by the second adjustment unit 523 out of the drive voltages supplied by the power supply unit 60. Furthermore, the second voltage value can be set to, for example, the maximum voltage value among the voltage values ​​that the power supply unit 60 can output. This makes it possible to easily set in advance the fixed voltage adjusted by the second adjustment unit 523.

[0030] The predetermined fixed voltage may be the maximum value among the variations in the forward voltages of the LEDs, which prevents an excessively high fixed voltage from being supplied to each of the LEDs when the predetermined fixed voltage is supplied to each of the LEDs, and also prevents an insufficient voltage from being supplied to each of the LEDs.

[0031] Furthermore, the storage unit 70 or another storage unit may store information indicating the correspondence between the current value flowing through each of the plurality of LEDs 21 and the voltage value required to supply that current value. The second adjustment unit 523 may then set a predetermined fixed voltage based on the voltage value based on the information stored in the storage unit 70 or another storage unit. This also prevents an excessively high fixed voltage from being supplied to each of the plurality of LEDs, and also prevents an insufficient voltage from being supplied to each of the plurality of LEDs. Note that the information indicating the correspondence between the current value flowing through each of the plurality of LEDs 21 and the voltage value required to supply that current value may be created by measuring the correspondence between the current value and the voltage value during calibration, which is performed when the display device 1 is started up, for example.

[0032] The period during which the second adjustment unit 523 adjusts the voltage value of the drive voltage supplied by the power supply unit 60 to the second voltage value, which is a predetermined fixed voltage, is a non-light-emitting period during which the multiple LEDs 21 are not subjected to PWM processing (i.e., a period during which no PWM signal, for example a rectangular wave, is input to the switching element 51, and the switching element 51 is maintained in a non-light-emitting state for a predetermined period T, thereby maintaining the LEDs 21 in a non-light-emitting state), as will be described in detail later, when it is necessary to increase the current value flowing through the LEDs 21 in the PWM processing period immediately after the non-light-emitting period compared to the current value flowing through the LEDs 21 in the PWM processing period immediately before the non-light-emitting period.

[0033] The LED driving unit 53 generates a PWM signal, for example, a square wave, in response to the duty ratio setting signal acquired from the duty ratio setting unit 43. Then, based on the generated PWM signal, the LED driving unit 53 repeatedly turns on (conducting state) and off (non-conducting state) the switching element 51 so that each of the plurality of LEDs 21 to which the driving voltage is supplied repeatedly emits and does not emit light.

[0034] The PWM signal is a signal that defines a gate voltage at which the switching element 51 is turned on (conductive state) and a gate voltage at which the switching element 51 is turned off (non-conductive state). For example, in the PWM signal, during an off period TL in which the LED 21 is not emitting light, a voltage value of the gate voltage at which the switching element 51 is turned off (non-conductive state) is defined. When the switching element 51 is turned off (non-conductive state), no current flows through the LED 21 connected in series with the switching element 51, and the LED 21 is in a non-emitting state. Also, for example, during an on period TH in which the LED 21 is emitting light, a voltage value of the gate voltage at which the switching element 51 is turned on (conductive state) is defined. When the switching element 51 is turned on (conductive state), a current flows through the LED 21 connected in series with the switching element 51, and the LED 21 emits light.

[0035] In this way, the LED driving unit 53 controls the on / off of the switching element 51 during a predetermined period T so that the duty ratio is equal to the duty ratio indicated by the PWM signal, thereby controlling the light emission of the LED 21 so that the duty ratio is equal to the predetermined duty ratio during the predetermined period T.

[0036] During the period when the LED 21 is not subjected to PWM processing (i.e., the period when a PWM signal is not input to the gate of the switching element 51), the LED drive unit 53 inputs a non-PWM signal to the gate of the switching element 51, the non-PWM signal defining a constant gate voltage at which the switching element 51 is turned off (non-conductive state). As a result, the switching element 51 and the LED 21 are turned off (non-conductive state) throughout the period when the non-PWM processing is performed. In other words, during the period when the non-PWM processing is performed, the backlight 20 is in a non-emitting state.

[0037] The measuring unit 54 is connected to the cathode of the LED 21, measures the current value of the current flowing from the anode to the cathode of the LED 21, and outputs feedback information indicating the measured current value to the first adjusting unit 522.

[0038] The power supply unit 60 is a power supply circuit that supplies voltage to the backlight 20. The power supply unit 60 is connected to the anodes of the plurality of LEDs 21. In the example shown in Fig. 1, the power supply unit 60 is connected to the anodes of each of the plurality of light-emitting element groups, and controls the anode voltage (drive voltage) supplied to the anodes.

[0039] For example, the power supply unit 60 supplies a drive voltage to each of the plurality of LEDs 21 to cause the LEDs 21 to emit light at a desired brightness, based on a voltage value specified by the voltage adjustment unit 52 of the LED driver 50. When the power supply unit 60 receives instruction information from the first adjustment unit 522, which has received feedback information from the measurement unit 54, the power supply unit 60 adjusts the drive voltage supplied to the anode of the LED 21 to a first voltage in accordance with the voltage instruction information received from the first adjustment unit 522 so that a predetermined current value AH flows through the LED 21. When the power supply unit 60 receives voltage instruction information from the second adjustment unit 523, the power supply unit 60 adjusts the drive voltage supplied to the anode of the LED 21 to a second voltage, which is a predetermined fixed voltage.

[0040] The storage unit 70 stores a control program 71 installed from a recording medium external to the display device 1 or from a server capable of communicating with the display device 1. The control program 71 causes the backlight control unit 40 to function as a switching determination unit 41, a current setting unit 42, and a duty ratio setting unit 43. The control program 71 may also cause the voltage adjustment unit 52 to function as a switching unit 521, a first adjustment unit 522, and a second adjustment unit 523.

[0041] The backlight control unit 40 includes a computer as a hardware configuration. The computer includes a processor that functions as a switching determination unit 41, a current setting unit 42, and a duty ratio setting unit 43 by executing a control program 71. The voltage adjustment unit 52 includes a computer as a hardware configuration. The computer includes a processor that functions as a switching unit 521, a first adjustment unit 522, and a second adjustment unit 523 by executing the control program 71.

[0042] The type of processor is not limited as long as it can realize functions by executing the control program 71. Various types of processors can be used, such as a CPU (Central Processing Unit), GPU (Graphics Processing Unit), DSP (Digital Signal Processor), ASIC (Application Specific Integrated Circuit), etc. The processor may also include peripheral circuit devices in addition to the CPU, GPU, DSP, etc. The peripheral circuit devices may be ICs (Integrated Circuits) and may include resistors, capacitors, etc.

[0043] The storage unit 70 is a computer-readable recording medium that non-temporarily stores the control program 71. The storage unit 70 may be a semiconductor memory such as a static random access memory (SRAM), a dynamic random access memory (DRAM), a read only memory (ROM), 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. The control program 71 may be stored in the storage unit 70 in advance, or may be supplied to the storage unit 70 via a wide area communication network including the Internet.

[0044] Next, an example of a control pattern for the backlight 20 of the display device 1 will be described with reference to Fig. 3. Fig. 3 is a diagram showing an example of a control pattern relating to a combination of a current value and a duty ratio to be passed through an LED for each period. The display device 1 and a display device according to a comparative example described later (a display device 100 shown in Fig. 4) may control the light emission of an LED by, for example, a combination of a current value and a duty ratio to be passed through the LED, as shown in Fig. 3.

[0045] Periods T1 to T3 shown in Figure 3 are consecutive periods in this order in chronological order. Of periods T1 to T3, period T1 is the first period, period T2 is the period immediately after period T1, and period T3 is the period immediately after period T2. For example, periods T1 to T3 may each be three consecutive frame periods. Then, for example, at the transition from period T1 to period T2, the backlight control unit makes an increase determination to increase the current value flowing through the LEDs in period T3, which follows period T2, compared to period T1 (in other words, an increase determination to increase the luminance in period T3 compared to period T1).

[0046] An example of the control pattern from period T1 to period T3 is to display an image with a relatively low brightness in period T1, and before increasing the brightness of the backlight to display an image with a relatively high brightness in period T3 after period T1, to prevent an afterimage of the displayed image from being visible, a black image (an image in which the backlight is not emitting light) is inserted in period T2 between periods T1 and T3. Note that the control pattern from period T1 to period T3 is not limited to the above example.

[0047] Period T1 is a period during which the current flowing through the LED is relatively low, i.e., the voltage value of the drive voltage (anode voltage) supplied to the LED is relatively low. Period T1 is also a period during which the duty ratio of the LED is not zero (duty ratio ≠ 0). In other words, period T1 can also be expressed as a period during which the duty ratio of the PWM signal supplied to the switching element is not zero. In other words, period T1 is a PWM processing period during which the LED is PWM-processed so as to obtain a brightness that is relatively lower than that of period T3.

[0048] Period T2 is a period during which a drive voltage (anode voltage) is supplied to the LED, but the duty ratio of the LED is zero (duty ratio = 0). In other words, during period T2, the duty ratio of the PWM signal supplied to the switching element is zero, so no current flows through the LED or the switching element, and the LED does not emit light. That is, period T2 is a non-light-emitting period during which no PWM processing is performed on the LED. In other words, during period T2, no PWM signal, for example a square wave, is input to the switching element 51, and the switching element 51 is maintained in a non-conducting state for a predetermined period T. As a result, no current flows through the LED 21, and the LED 21 is maintained in a non-light-emitting state for the period T2.

[0049] Period T3 is a period during which the current value flowing through the LED is relatively higher than that of period T1, i.e., the voltage value of the drive voltage (anode voltage) supplied to the LED is relatively higher than that of period T1. Period T3 is also a period during which the duty ratio of the LED is not zero (duty ratio ≠ 0). In other words, period T3 can also be expressed as a period during which the duty ratio of the PWM signal supplied to the switching element is not zero. In other words, period T3 is a PWM processing period during which the LED is PWM-processed so as to obtain a brightness relatively higher than that of period T1.

[0050] Next, before explaining the case where the display device 1 of the embodiment displays an image using the control pattern shown in Figure 3, we will use Figures 4 and 5 to explain the case where the display device of the comparative example displays an image using the control pattern shown in Figure 3.

[0051] 4 is a block diagram showing an outline of a display device 100 according to a comparative example. The display device 100 has a configuration in which the switching determination unit 41 of the backlight control unit 40, the switching unit 521 and the second adjustment unit 523 of the voltage adjustment unit 52, and the storage unit 70 are omitted from the display device 1 shown in FIG.

[0052] In display device 100, display panel 110, LEDs 121 in backlight 120, display panel control unit 130, current setting unit 142 and duty ratio setting unit 143 of backlight control unit 140, and power supply unit 160 correspond to display panel 10, LEDs 21 in backlight 20, display panel control unit 30, current setting unit 42 and duty ratio setting unit 43 of backlight control unit 40, and power supply unit 60, respectively, in display device 1 shown in Fig. 1. Also, in display device 100, switching element 151, voltage adjustment unit 152, LED driving unit 153, and measurement unit 154 of LED driver 150 correspond to switching element 51, voltage adjustment unit 52 including first adjustment unit 522 of LED driver 50, LED driving unit 53, and measurement unit 54, respectively, in display device 1 shown in Fig. 1.

[0053] Fig. 5 is a diagram illustrating LED control by the display device 100 according to the comparative example. Fig. 5 illustrates how the display device 100 according to the comparative example, which performs the control pattern shown in Fig. 3, controls the drive voltage (anode voltage) supplied to the LEDs and the value of the current flowing through the LEDs for each of the periods T1 to T3.

[0054] In order to obtain the brightness required for an image to be displayed on the display panel 110 during the period T1, the current setting unit 142 sets a current value AHa to be passed through the LED 121 during the on-period TH of the LED 121, and outputs the set information to the voltage adjustment unit 52. In addition, the duty ratio setting unit 143 sets a duty ratio of the LED 121 during the period T1, and outputs the set information to the LED drive unit 153.

[0055] Then, based on the information acquired from the current setting unit 142, the voltage adjustment unit 152 outputs voltage adjustment information v100 to the power supply unit 160, which includes information on the voltage value at which the desired current value AHa to be passed through the LED 121 is assumed to flow through the LED 21. As a result, the power supply unit 160 supplies a driving voltage V120 to the anode of the LED 121, the driving voltage V120 being the voltage value indicated by the voltage adjustment information v100.

[0056] Furthermore, the LED driving unit 153 performs PWM processing to control the on (light emitting) and off (non-light emitting) of the LED 121 by continuously switching the switching element 151 between on (conducting state) and off (non-conducting state) based on information acquired from the duty ratio setting unit 143. Furthermore, the measurement unit 154 measures the current value of the current output from the LED 121 and feeds back the measured current value to the voltage adjustment unit 152. Then, the voltage adjustment unit 152 outputs voltage adjustment information v100 to the power supply unit 60, which adjusts the voltage value of the driving voltage V120 output from the power supply unit 160 to a voltage value V1a so that the fed-back current value becomes the desired current value AHa. Then, the power supply unit 160 adjusts the voltage value of the driving voltage V120 to the voltage value V1a. As a result, during the period T1, the current value AL flows when the LED 121 is in the off period TL, and the current value AHa flows when the LED 121 is in the on period TH, and the LED 121 is PWM-processed according to the set duty ratio.

[0057] Then, at the timing of transition to the next period T2, the duty ratio setting unit 143 sets the duty ratio of the LED 121 in period T2 to zero and outputs the set information to the LED drive unit 53. Furthermore, because the duty ratio of the LED 121 in period T2 is zero, the current setting unit 142 continues to output information including the current value AHa set in period T1 to the voltage adjustment unit 52.

[0058] Then, based on the information obtained from the current setting unit 142, the LED driving unit 153 outputs to the power supply unit 160 voltage adjustment information v100 that has been adjusted so that the same current value AHa continues to flow from the period T1, and as a result, the power supply unit 160 continues to supply to the anode of the LED 121 a driving voltage V120 that is the voltage value indicated by the voltage adjustment information v100.

[0059] Furthermore, the LED driving unit 153 turns off (non-conducting state) the switching element 151 so that the duty ratio becomes zero based on the information acquired from the duty ratio setting unit 143. As a result, the driving voltage V120 is supplied to the LED 121, but no current flows. Therefore, the measuring unit 154 does not measure the current, and does not output feedback to the voltage adjusting unit 152.

[0060] Then, at the timing of transition to the next period T3, the current setting unit 142 sets the current value AHb to be passed through the LED 121 during the on period TH of the LED 121 so that the brightness required for the image to be displayed on the display panel 110 during the period T3 is obtained, and outputs the set information to the voltage adjustment unit 52. In addition, the duty ratio setting unit 143 sets the duty ratio of the LED 121 during the period T3, and outputs the set information to the LED drive unit 153.

[0061] Here, the brightness required in period T3 is higher than the brightness required in period T1, and in period T3, it is necessary to flow a current value AHb to LED 121 that is higher than the current value AHa that flowed during the on period TH of LED 121 in period T1.

[0062] Based on the information acquired from the current setting unit 142, the voltage adjustment unit 152 outputs voltage adjustment information v100 to the power supply unit 160, the voltage information v100 including information on a voltage value at which a desired current value AHb to be passed through the LED 121 is assumed to flow through the LED 121. As a result, the power supply unit 160 supplies a drive voltage V120 having the voltage value indicated by the voltage adjustment information v100 to the anode of the LED 121. Furthermore, the LED drive unit 153 performs PWM processing on the LED 121 by continuously switching the switching element 151 between on (conductive state) and off (non-conductive state) so as to achieve the duty ratio set for period T3 based on the information acquired from the duty ratio setting unit 143.

[0063] Furthermore, the measurement unit 154 measures the current value of the current output from the LED 121 and feeds back the measured current value to the voltage adjustment unit 152. Then, the voltage adjustment unit 152 outputs voltage adjustment information v100 to the power supply unit 160 to adjust the voltage value of the drive voltage V120 output from the power supply unit 160 to a voltage value V1a so that the fed-back current value becomes a desired current value AHb.

[0064] Here, during period T2, no current was flowing through LED 121, and therefore measurement unit 154 was unable to feed back the current value to voltage adjustment unit 152. For this reason, after transition from period T2, which was a non-light-emitting period, to period T3, which is a PWM processing period, the voltage value of drive voltage V120 supplied to LED 121 falls short of voltage value V1b required to cause current value AHb to flow through LED 121. For this reason, immediately after transition from period T2 to period T3, a current value lower than the required current value AHb flows through LED 121, and LED 121 emits light at a brightness lower than the required brightness.

[0065] Then, after the transition to period T3, the voltage adjustment unit 152 gradually increases the voltage value of the drive voltage V120 output from the power supply unit 60 for each on-period TH for which feedback is obtained, from voltage value V1a to voltage value V1b higher than voltage value V1a, so that the current value flowing through the LED 121 becomes the desired current value AHb. As a result, after the transition to period T3, the current is adjusted to gradually increase from a value lower than the current value AHb that should flow through the LED 121 to the desired current value AHb.

[0066] Thus, in the display device 100 according to the comparative example, when the non-emission period T2 transitions to the PWM processing period T3, time is required immediately after the transition to the period T3 to adjust the current value AHb to flow through the LED 121. This may result in a degradation of the display quality of the image.

[0067] Next, a case where the display device 1 controls the backlight 20 based on the control pattern shown in FIG. 3 will be described with reference to FIGS. 6 to 9 along with a flowchart of the display device 1. FIG.

[0068] Fig. 6 is a flowchart showing the processing flow of the display device 1 according to the embodiment. Fig. 7 is a diagram showing LED control of the display device 1 according to the embodiment. Fig. 7 shows how the display device 1 according to the embodiment, which performs control using the control pattern shown in Fig. 3, controls the drive voltage (anode voltage) supplied to the LED 21 and the value of the current flowing through the LED 21 for each of periods T1 to T3.

[0069] Fig. 8 is a diagram showing the operation of the display device 1 according to the embodiment during a period when the duty ratio of the LED 21 is not zero. Fig. 9 is a diagram showing the operation of the display device 1 according to the embodiment during a period when the duty ratio of the LED 21 is zero. For example, Fig. 8 shows the operation of the display device 1 during periods T1 to T3 in Fig. 3, and Fig. 9 shows the operation of the display device 1 during period T2 in Fig. 3.

[0070] First, a processing flow of the display device 1 for the period T1 will be described with reference to FIGS. 6 to 8. As shown in FIGS. 6 to 8, for example, based on a video signal acquired by the display device 1 from an external device, the current setting unit 42 sets a current value (current value AHa in the example shown in FIG. 7) to be applied to the LED 21 during the on-period of the LED 21 (on-period TH in the example shown in FIG. 7) so as to obtain the brightness required for an image to be displayed on the display panel 10 during a predetermined period (period T1 in the example shown in FIG. 7) in step S11, and outputs set current value information including the set current value to the voltage adjustment unit 52. Furthermore, in step S12, the duty ratio setting unit 43 sets a duty ratio for the LED 21 during the predetermined period (period T1 in the example shown in FIG. 7) and outputs set duty ratio information including the set duty ratio to the LED drive unit 53. Note that the order of steps S11 and S12 may be reversed.

[0071] Next, in step S13, the switching determination unit 41 determines whether the duty ratio set by the duty ratio setting unit 43 is zero. Here, as shown in FIG. 7, the duty ratio during period T1 is not zero, so the switching determination unit 41 determines that the duty ratio set by the duty ratio setting unit 43 is not zero (No in step S13). In step S14, the switching determination unit 41 determines to switch the adjustment unit that adjusts the drive voltage from the power supply unit 60 during a predetermined period (period T1 here) from the second adjustment unit 523 to the first adjustment unit 522, and outputs determination information to the voltage adjustment unit 52. As a result, the switching unit 521 switches the configuration so that the adjustment unit that adjusts the drive voltage from the power supply unit 60 during the predetermined period (period T1 here) is changed from the second adjustment unit 523 to the first adjustment unit 522. If the switching unit 521 is already configured so that the adjustment unit that adjusts the drive voltage from the power supply unit 60 is the first adjustment unit 522, step S14 may be omitted.

[0072] Next, in step S15, the first adjustment unit 522 outputs voltage adjustment information v1 (see Figure 8) to the power supply unit 60 via the switching unit 521, the voltage value being the voltage at which the desired current value to be passed through the LED 21 (current value AHa in the example shown in Figure 7) indicated by the set current value information acquired from the current setting unit 42 is assumed to flow through the LED 21. As a result, the power supply unit 60 supplies a drive voltage V having the voltage value indicated by the voltage adjustment information to the anode of the LED 21.

[0073] Next, in step S16, the LED drive unit 53 generates a PWM signal to achieve the set duty ratio for a predetermined period (here, period T1) indicated by the set duty ratio information acquired from the duty ratio setting unit 43, and controls the gate voltage of the switching element 51 based on the PWM signal to continuously switch the switching element 51 between on (conducting state) and off (non-conducting state). In this way, the LED drive unit 53 controls the light-emitting state of the LED 21 to achieve the set duty ratio, i.e., performs PWM processing.

[0074] Next, in step S17, the measurement unit 54 measures the current value of the current I flowing through the LED 21 and output via the cathode of the LED 21 and the switching element 51, and outputs feedback information a1 including the measured current value as information to the first adjustment unit 522.

[0075] Next, in step SS18, the first adjustment unit 522 adjusts the voltage value of the driving voltage V output from the power supply unit 60 to a first voltage value (voltage value V1a in the example shown in FIG. 7) so that the measured current value indicated by the feedback information becomes the desired current value to be passed through the LED 21 (current value AHa in the example shown in FIG. 7). That is, the first adjustment unit 522 outputs voltage adjustment information v1 to the power supply unit 60 via the switching unit 521, for adjusting the voltage value of the driving voltage V output from the power supply unit 60 to become the first voltage value (voltage value V1a in the example shown in FIG. 7).

[0076] Then, in step S19, the power supply unit 60 supplies the drive voltage V, adjusted to a first voltage value (voltage value V1a in the example of FIG. 7), to the anode of the LED 21. As a result, the current value during the off period TL of the LED 21 (current value AL in the example of FIG. 7) and the current value during the on period TH (current value AHa in the example of FIG. 7) are adjusted to the desired current value to be passed, and the LED 21 is PWM-processed for a predetermined period (e.g., period T1) using the set duty ratio. As a result, the LED 21 emits light to achieve the required brightness for the predetermined period (e.g., period T1).

[0077] Next, in step S20, the backlight control unit 40 determines whether it is time to transition to the next period (for example, period T2). The timing to transition to the next period (for example, period T2) is, for example, a predetermined period before the start of the next period (for example, period T2).

[0078] In step S20, if it is not time to transition to the next period (for example, period T2) (if No in step S20), the backlight control unit 40 waits until it is time to transition to the next period (for example, period T2). In step S20, if the backlight control unit 40 determines that it is time to transition to the next period (for example, period T2) (if Yes in step S20), the process returns to step S11.

[0079] Next, the processing flow of the display device 1 for the period T2 will be described with reference to Figures 6, 7, and 9. After the "Yes" in step S20 described above, based on the video signal acquired by the display device 1 from the outside, in step S11, the current setting unit 42 sets a current value (current value AHa in the example shown in Figure 7) to be passed through the LED 21 during the on-period of the LED 21 (on-period TH in the example shown in Figure 7) so that the brightness required for the image to be displayed on the display panel 10 during a predetermined period (period T2 in the example shown in Figure 7) is obtained, and outputs set current value information including the set current value to the voltage adjustment unit 52. In addition, in step S12, the duty ratio setting unit 43 sets a duty ratio for the LED 21 during a predetermined period (period T2 in the example shown in Figure 7) and outputs set duty ratio information including the set duty ratio to the LED drive unit 53.

[0080] Next, in step S13, the switching determination unit 41 determines whether or not the duty ratio set by the duty ratio setting unit 43 is zero. Here, as shown in Fig. 7, the duty ratio in the period T2 is zero, so the switching determination unit 41 determines that the duty ratio set by the duty ratio setting unit 43 is zero (if Yes in step S13).

[0081] Next, in step S21, the switching determination unit 41 determines whether or not it is necessary to increase the value of the current to be passed through the LED 21 in the period (here, period T3) following the period when the duty ratio is zero (here, period T2). For example, the switching determination unit 41 may compare the luminance in the period (e.g., period T1) immediately before the period when the duty ratio is zero (here, period T2) with the luminance in the period (e.g., period T3) immediately after the period when the duty ratio is zero (here, period T2) based on a video signal obtained from the outside, and determine that it is necessary to increase the value of the current to be passed through the LED 21 in the period (here, period T3) immediately after the period when the duty ratio is zero (here, period T2) if the luminance in the immediately after period (e.g., period T3) is higher.

[0082] In step S21, if the switching determination unit 41 determines that there is no need to increase the current value to be passed through the LED 21 in the period (here, period T3) following the period when the duty ratio is zero (here, period T2) (if the answer is No in step S21), the switching determination unit 41 performs the above-mentioned processes from step S14 to step S18 in the period when the duty ratio is zero (here, period T2).

[0083] In step S21, when the switching determination unit 41 determines that it is necessary to increase the value of the current to be passed through the LED 21 in the period (here, period T3) following the period in which the duty ratio is zero (here, period T2) (if Yes in step S21), then in step S22, the switching determination unit 41 determines to switch the adjustment unit that adjusts the drive voltage from the power supply unit 60 for a predetermined period (here, period T2) from the first adjustment unit 522 to the second adjustment unit 523, and outputs determination information to the voltage adjustment unit 52. As a result, the switching unit 521 switches the configuration so that the adjustment unit that adjusts the drive voltage from the power supply unit 60 for the predetermined period (here, period T2) is the second adjustment unit 523 from the first adjustment unit 522. Note that if the switching unit 521 is already configured so that the adjustment unit that adjusts the drive voltage from the power supply unit 60 is the second adjustment unit 523, step S22 may be omitted.

[0084] Next, in step S23, the second adjustment unit 523 outputs voltage adjustment information v2 (see FIG. 9 ), which is information for adjusting the voltage to a second voltage value that is a fixed voltage higher than the first voltage, such as the maximum voltage value among the voltage values ​​that the power supply unit 60 can output, to the power supply unit 60 via the switching unit 521. As a result, the power supply unit 60 supplies the driving voltage V, which is the fixed voltage indicated by the voltage adjustment information, to the anode of the LED 21. That is, the power supply unit 60 supplies the driving voltage V, which has been adjusted to a second voltage value (voltage value V2 in the example of FIG. 7 ), to the anode of the LED 21. As a result, the driving voltage V, which has been adjusted to a second voltage value higher than the first voltage value supplied to the LED 21 during the next period (e.g., period T3), is supplied to the anode of the LED 21 for a predetermined period (here, period T2).

[0085] Next, in step S24, the LED drive unit 53 generates a non-PWM signal with a duty ratio of zero because the set duty ratio for a predetermined period (here, period T2) indicated by the set duty ratio information acquired from the duty ratio setting unit 43 is zero. Based on the non-PWM signal, the LED drive unit 53 controls the gate voltage of the switching element 51 to maintain the switching element 51 in an off (non-conducting) state. This causes the LED drive unit 53 to place the LED 21 in a non-light-emitting state so that the duty ratio is zero. That is, the LED drive unit 53 controls the LED 21 so that the predetermined period (here, period T2) is a non-light-emitting period (performs non-PWM processing). That is, although the drive voltage V, which is the second voltage value, is supplied to the anode of the LED 21, no current flows through the LED 21, and therefore the LED 21 is in a non-light-emitting state. Furthermore, because no current flows through the LED 21, the measurement unit 54 neither measures the current nor outputs feedback information a1 (see FIG. 8 ) to the voltage adjustment unit 52.

[0086] Next, in step S20, the backlight control unit 40 determines whether it is time to transition to the next period (for example, period T3). The timing to transition to the next period (for example, period T3) is, for example, a preset period from the timing of transition to a predetermined period (for example, period T2) to the start of the next period (for example, period T3).

[0087] In step S20, if it is not time to transition to the next period (for example, period T3) (No in step S20), the backlight control unit 40 waits until it is time to transition to the next period (for example, period T3). In step S20, if the backlight control unit 40 determines that it is time to transition to the next period (for example, period T3) (Yes in step S20), the process returns to step S11.

[0088] Next, a processing flow of the display device 1 for the period T3 will be described with reference to Figures 6 to 8. After the "Yes" in step S20 described above, in step S11, the current setting unit 42 sets a current value (current value AHb in the example shown in Figure 7) to be passed through the LED 21 during the on-period of the LED 21 (on-period TH in the example shown in Figure 7) so as to obtain the brightness required for the image to be displayed on the display panel 10 during a predetermined period (period T3 in the example shown in Figure 7) based on the video signal acquired by the display device 1 from the outside, and outputs set current value information including the set current value to the voltage adjustment unit 52. In addition, in step S12, the duty ratio setting unit 43 sets a duty ratio for the LED 21 during a predetermined period (period T3 in the example shown in Figure 7) and outputs set duty ratio information including the set duty ratio to the LED drive unit 53.

[0089] Next, in step S13, the switching determination unit 41 determines whether the duty ratio set by the duty ratio setting unit 43 is zero. Here, as shown in FIG. 7, the duty ratio during period T3 is not zero, so the switching determination unit 41 determines that the duty ratio set by the duty ratio setting unit 43 is not zero (No in step S13). In step S14, the switching determination unit 41 determines to switch the adjustment unit that adjusts the drive voltage from the power supply unit 60 during a predetermined period (period T3 in this case) from the second adjustment unit 523 to the first adjustment unit 522, and outputs determination information to the voltage adjustment unit 52. As a result, the switching unit 521 switches the configuration so that the adjustment unit that adjusts the drive voltage from the power supply unit 60 during the predetermined period (period T3 in this case) is changed from the second adjustment unit 523 to the first adjustment unit 522. If the switching unit 521 is already configured so that the adjustment unit that adjusts the drive voltage from the power supply unit 60 is the first adjustment unit 522, step S14 may be omitted.

[0090] Next, in step S15, the first adjustment unit 522 outputs voltage adjustment information v1 (see Figure 8) to the power supply unit 60 via the switching unit 521, the voltage value being the voltage at which the desired current value to be passed through the LED 21 (current value AHb in the example shown in Figure 7) is assumed to flow through the LED 21, as indicated by the set current value information acquired from the current setting unit 42. As a result, the power supply unit 60 supplies a drive voltage V having the voltage value indicated by the voltage adjustment information to the anode of the LED 21.

[0091] Next, in step S16, the LED drive unit 53 generates a PWM signal to achieve the set duty ratio for a predetermined period (here, period T3) indicated by the set duty ratio information acquired from the duty ratio setting unit 43, and controls the gate voltage of the switching element 51 based on the PWM signal to continuously switch the switching element 51 between on (conducting state) and off (non-conducting state). In this way, the LED drive unit 53 controls the light-emitting state of the LED 21 to achieve the set duty ratio, i.e., performs PWM processing.

[0092] Next, in step S17, the measurement unit 54 measures the current value of the current I (see Figure 8) flowing through the LED 21 and output via the cathode of the LED 21 and the switching element 51, and outputs feedback information a1 (see Figure 8) including the measured current value as information to the first adjustment unit 522.

[0093] Next, in step S18, the first adjustment unit 522 adjusts the voltage value of the driving voltage V output from the power supply unit 60 in stages for each on-period TH during which feedback information a1 is obtained, from a second voltage value (voltage value V2 in the example of FIG. 7) higher than the first voltage value to the first voltage value (voltage value V1b in the example of FIG. 7) so that the measured current value indicated by the feedback information a1 becomes the desired current value to be passed through the LED 21 (current value AHb in the example shown in FIG. 7). That is, the first adjustment unit 522 outputs voltage adjustment information v1 to the power supply unit 60 via the switching unit 521 for each on-period TH during which feedback information a1 is obtained, for adjusting the voltage value of the driving voltage V output from the power supply unit 60 to become the first voltage value (voltage value V1b in the example of FIG. 7).

[0094] Then, in step S19, the power supply unit 60 supplies the drive voltage V, adjusted to a first voltage value (voltage value V1b in the example of FIG. 7), to the anode of the LED 21. As a result, the current value during the off period TL of the LED 21 (current value AL in the example of FIG. 7) and the current value during the on period TH (current value AHb in the example of FIG. 7) are adjusted to the desired current value to be passed, and the LED 21 is PWM-processed for a predetermined period (e.g., period T3) using the set duty ratio. As a result, the LED 21 emits light to achieve the required brightness for the predetermined period (e.g., period T3).

[0095] Here, the voltage value V1b of the drive voltage V supplied to the LED 21 during the period T3 is higher than the voltage value V1a of the drive voltage V during the period T1 and lower than the voltage value V2, which is a fixed voltage during the period T2. Furthermore, the current value AHb flowing during the ON period TH of the LED 21 during the period T3 is higher than the current value AHa flowing during the ON period TH of the LED 21 during the period T1.

[0096] As described above, the second voltage value (voltage value V2 in FIG. 7 ) during period T2, which is the non-light-emitting period, is higher than the first voltage value (voltage value V1b in FIG. 7 ) supplied during period T3, which is the PWM processing period immediately following period T2, and adjusted in accordance with the feedback information a1. Therefore, when the non-light-emitting period T2 transitions to period T3, which is the PWM processing period, it is possible to prevent the drive voltage V supplied to the LEDs 21 from being insufficient for the first voltage value (voltage value V1b in FIG. 7 ) required to cause the current value AHb to flow through the LEDs 21. This prevents the current value flowing through each of the LEDs 21 from being insufficient for the desired current value AHb after the transition from period T2, which is the non-light-emitting period, to period T3, which is the PWM processing period. As a result, it is possible to quickly adjust the current value flowing through each of the LEDs 21 to the desired current value AHb after the transition from period T2, which is the non-light-emitting period, to period T3, which is the PWM processing period. This allows each of the multiple LEDs 21 to emit light at the required brightness immediately after the transition from period T2, which is a non-light-emitting period, to period T3, which is a PWM processing period, thereby preventing a decrease in the display quality of the image.

[0097] In addition, it is preferable that the LED driving unit 53 has a constant current function that adjusts the potential difference between the anode and cathode of the LED 21 to which the driving voltage V is supplied to be the first voltage value (voltage value V1b) even when the voltage value of the driving voltage V supplied to the LED 21 is higher than the first voltage value (voltage value V1b).

[0098] This makes it possible to prevent a current exceeding the desired current value AHb from flowing through the LEDs 21, even when the voltage value of the drive voltage V supplied to the LEDs 21 is higher than the first voltage value (voltage value V1b). Therefore, even when switching from period T2, which is a non-light-emitting period, to period T3, which is a PWM processing period, the current value flowing through each of the plurality of LEDs 21 can be quickly adjusted to the desired current value AHb to be flowed.

[0099] Even if the LED drive unit 53 has a constant current function, if the drive voltage V supplied to the LEDs 21 is a second voltage value (voltage value V2) higher than the desired first voltage value (voltage value V1b in FIG. 7) during the period T3, it is preferable to adjust the drive voltage V to the desired first voltage value (voltage value V1b in FIG. 7). As a result, if the switching element 51 is configured by a MOSFET, the drain-source voltage increases due to the continuous supply of a high second voltage value (voltage value V2), and malfunction of the switching element 51 caused by heat loss of the MOSFET can be suppressed.

[0100] Next, in step S20, the backlight control unit 40 determines whether it is time to transition to the next period (for example, the period following period T3). The timing to transition to the next period (for example, the period following period T3) is, for example, a preset period from the timing of transition to a predetermined period (for example, period T3) to the start of the next period (for example, the period following period T3).

[0101] In step S20, if it is not time to transition to the next period (for example, the period following period T3) (No in step S20), the backlight control unit 40 waits until it is time to transition to the next period (for example, the period following period T3). In step S20, if the backlight control unit 40 determines that it is time to transition to the next period (for example, the period following period T3) (Yes in step S20), the process returns to step S11.

[0102] As described above, in the display device 1, the voltage adjustment unit 52 includes a first adjustment unit 522 and a second adjustment unit 523. During a PWM processing period (e.g., period T3 in FIG. 7 ) in which the LEDs 21 are PWM-processed, the first adjustment unit 522 adjusts the value of the drive voltage V supplied by the power supply unit 60 to a first voltage value (e.g., voltage value V1b in FIG. 7 ) at which the current value measured by the measurement unit 54 becomes a desired value (e.g., current value AHb in FIG. 7 ). Furthermore, when a non-emission period (e.g., period T2 in FIG. 7 ) in which the LEDs 21 are in a non-emission state for a predetermined period (e.g., period T2 in FIG. 7 ) is provided immediately before the PWM processing period (e.g., period T3 in FIG. 7 ), the second adjustment unit 523 adjusts the value of the drive voltage V supplied by the power supply unit 60 to a second voltage value (e.g., voltage value V2 in FIG. 7 ), which is a predetermined fixed voltage. Furthermore, the second voltage value (e.g., voltage value V2 in FIG. 7) is higher than the first voltage value (e.g., voltage value V1b in FIG. 7). This prevents the current value flowing through each of the LEDs 21 from being insufficient with respect to the desired current value (e.g., current value AHb in FIG. 7) even when switching from a non-light-emitting period (e.g., period T2 in FIG. 7) to a PWM processing period (e.g., period T3 in FIG. 7). As a result, even when switching from a non-light-emitting period (e.g., period T2 in FIG. 7) to a PWM processing period (e.g., period T3 in FIG. 7), the current value flowing through each of the LEDs 21 can be quickly adjusted to the desired current value (e.g., current value AHb in FIG. 7).

[0103] The present invention is not limited to the above-described embodiments, and may be replaced with a configuration that is substantially the same as the configuration shown in the above-described embodiments, a configuration that has the same action and effect, or a configuration that can achieve the same purpose. [Explanation of symbols]

[0104] 1: display device, 10: display panel, 20: backlight, 30: display panel control unit, 40: backlight control unit, 41: switching determination unit, 42: current setting unit, 43: duty ratio setting unit, 51: switching element, 52: voltage adjustment unit, 53: LED drive unit (drive unit), 54: measurement unit, 60: power supply unit, 70: storage unit

Claims

1. A display panel; a backlight having a plurality of light-emitting elements; a power supply unit that supplies a driving voltage to the plurality of light-emitting elements; a measurement unit for measuring a current value flowing through the plurality of light-emitting elements; a voltage adjusting unit that adjusts the voltage value of the driving voltage supplied by the power supply unit; a switching element connected to one of the plurality of light-emitting elements; a drive unit that switches the switching element on and off, the voltage adjusting unit has a first adjusting unit and a second adjusting unit, The first adjustment unit is During a PWM processing period in which the plurality of light-emitting elements are PWM-processed, a voltage value of the driving voltage supplied by the power supply unit is adjusted to a first voltage value at which a current value measured by the measurement unit becomes a desired value; during a non-light emitting period in which the plurality of light emitting elements are in a non-light emitting state for a predetermined period immediately after a first PWM processing period, if a current value to be passed through the plurality of light emitting elements in a second PWM processing period immediately after the non-light emitting period is greater than a current value to be passed through the plurality of light emitting elements in the first PWM processing period, switching the first adjustment unit to the second adjustment unit; the second adjustment unit adjusts, during the non-light-emitting period, a voltage value of the drive voltage supplied by the power supply unit to a second voltage value that is a predetermined fixed voltage higher than the first voltage value at which a current value required to obtain image brightness during the second PWM processing period becomes a desired value; The driving unit has a constant current function of adjusting a potential difference between the anode and the cathode of the light-emitting element to the first voltage value even when the driving voltage supplied to the light-emitting element is higher than the first voltage value. , display device.

2. The display device according to claim 1 , wherein the non-light emitting period is a period during which the duty ratio during which the plurality of light emitting elements emit light is zero.

3. 3. The display device according to claim 1, further comprising a switching determination unit that determines to switch the adjustment of the voltage value of the driving voltage supplied by the power supply unit from the first adjustment unit to the second adjustment unit during the non-light-emitting period when the current value to be passed through the plurality of light-emitting elements during the second PWM processing period is greater than the current value to be passed through the plurality of light-emitting elements during the first PWM processing period.

4. 4. The display device according to claim 1, wherein the predetermined fixed voltage is a maximum voltage value that the power supply unit can output.

5. 4. The display device according to claim 1, wherein the predetermined fixed voltage is a maximum value among variations in forward voltages of the plurality of light-emitting elements.

6. a storage unit that stores a correspondence relationship between a current value flowing through the plurality of light-emitting elements and a voltage value for causing the current value to flow; 4. The display device according to claim 1, wherein the second adjustment section sets the predetermined fixed voltage based on the voltage value stored in the storage section.

7. supplying a driving voltage to a plurality of light-emitting elements included in a backlight that illuminates a display panel; measuring current values ​​flowing through the plurality of light-emitting elements; adjusting a voltage value of the driving voltage supplied to the plurality of light-emitting elements; switching on and off a switching element connected to one of the plurality of light-emitting elements, the step of adjusting the voltage value of the driving voltage includes a first step and a second step; The first step comprises: During a PWM processing period in which the plurality of light-emitting elements are PWM-processed, a voltage value of the driving voltage supplied to the plurality of light-emitting elements is adjusted to a first voltage value at which the current value measured in the step of measuring the current value becomes a desired value; during a non-light-emitting period in which the plurality of light-emitting elements are in a non-light-emitting state for a predetermined period immediately after a first PWM processing period, if a current value to be passed through the plurality of light-emitting elements in a second PWM processing period immediately after the non-light-emitting period is greater than a current value to be passed through the plurality of light-emitting elements in the first PWM processing period, switching from the first step to the second step; the second step adjusts the voltage value of the drive voltage supplied to the plurality of light-emitting elements during the non-light-emitting period to a second voltage value that is a predetermined fixed voltage higher than the first voltage value at which a current value required to obtain an image brightness during the second PWM processing period becomes a desired value; A display method, wherein the step of switching the switching element on and off has a constant current function of adjusting the potential difference between the anode and cathode of the one light-emitting element to be the first voltage value even when the driving voltage supplied to the one light-emitting element is higher than the first voltage value.

Images