Light-emitting element driving circuit

Abstract

To detect an abnormality in the luminance of a light-emitting element in local dimming.SOLUTION: A light-emitting element driving circuit 10 is configured to drive a plurality of light-emitting elements 121 to 124 used as a backlight of the display panel 101. The display panel 101 is divided in a plurality of areas 111 to 114 and the light-emitting elements 121 to 124 are divided in each of areas 111 to 114. In that configuration, the light-emitting element driving circuit 10 includes a derivation unit 40 for deriving an actually measured value, an expectation value operation unit 50 for operating an expectation value, and a comparison unit 60 for comparing the actually measured value and the expectation value.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a light-emitting element drive circuit. [Background technology]

[0002] Patent Document 1 describes an LED driver that drives and controls a plurality of LEDs used as a backlight for a liquid crystal display panel. The LED driver is configured to enable local dimming. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-136249 A

[0004] [overview] When multiple light-emitting elements are used as a backlight for a display panel, it may be necessary to suppress luminance abnormalities caused by excessive light emission from the light-emitting elements. In this case, in local dimming, the current flowing through each light-emitting element varies, so there is room for improvement in the method of detecting luminance abnormalities in the light-emitting elements in local dimming.

[0005] A light-emitting element driving circuit according to one aspect of the present disclosure is configured to drive a plurality of light-emitting elements used as a backlight for a display panel, the display panel being divided into a plurality of areas, with the plurality of light-emitting elements being provided for each of the areas, and the light-emitting element driving circuit including: a derivation unit that derives an actual measured value of a current flowing through a target light-emitting element, which is the light-emitting element in at least one of the plurality of areas; an expected value calculation unit that calculates an expected value of the current flowing through the target light-emitting element; a comparison unit that compares the actual measured value with the expected value; and a control unit that controls the target light-emitting element in accordance with the comparison result of the comparison unit. [Brief description of the drawings]

[0006] [Figure 1]FIG. 1 is a schematic diagram showing the configuration of a light-emitting element drive circuit and a display device according to the first embodiment. [Diagram 2] FIG. 2 is a schematic diagram of a display panel. [Diagram 3] FIG. 3 is a waveform diagram of the first and second synchronization signals. [Figure 4] FIG. 4 is a waveform diagram of the first synchronization signal, the first current, the second current, the third current, the fourth current, and the input current. [Diagram 5] FIG. 5 is a time chart showing the timing of A / D conversion of the first synchronization signal, the second synchronization signal, the input current, and the first pattern. [Figure 6] FIG. 6 is a time chart showing the timing of A / D conversion of the first synchronization signal, the second synchronization signal, the input current, and the second pattern. [Figure 7] FIG. 7 is a time chart showing the timing of A / D conversion of the first and second synchronization signals, the input current, and the third pattern. [Figure 8] FIG. 8 is a time chart showing the first synchronization signal, the timing at which the comparison is made by the comparison unit, and the timing at which the abnormality handling process is executed. [Figure 9] FIG. 9 is a schematic diagram showing a light emitting element driving circuit and a display device according to the second embodiment. [Figure 10] FIG. 10 is a schematic diagram showing a light-emitting element drive circuit according to the second embodiment. [Figure 11] FIG. 11 is a diagram showing an image in a normal state. [Figure 12] FIG. 12 is a diagram showing an image in which an abnormal area is present. [Figure 13] FIG. 13 is a time chart showing the first synchronization signal, the timing at which the comparison is made by the comparison unit, the number of errors, and the execution timing of the abnormality response process. [Figure 14] FIG. 14 is a schematic diagram showing another example of a light-emitting element drive circuit. [Figure 15] FIG. 15 is a graph showing the relationship between ambient light and maximum current. [Figure 16]FIG. 16 is a time chart showing the first synchronization signal, the second synchronization signal, the timing of A / D conversion, and the timing of comparison by a comparison section of another example. [Figure 17] FIG. 17 is a time chart showing the first synchronization signal, the second synchronization signal, the timing of A / D conversion, and the timing of comparison by a comparison section of another example. [Figure 18] FIG. 18 is a schematic diagram showing another example of a light-emitting element drive circuit. [Figure 19] FIG. 19 is a schematic diagram showing another example of a light-emitting element drive circuit. [Figure 20] FIG. 20 is a schematic diagram showing another example of a light-emitting element drive circuit. [Figure 21] FIG. 21 is a schematic diagram showing another example of a light-emitting element drive circuit. [Figure 22] FIG. 22 is a schematic diagram showing another example of a light-emitting element drive circuit.

[0007] [Detailed Description] Hereinafter, some embodiments of the light-emitting element driving circuit according to the present disclosure will be described with reference to the accompanying drawings. The accompanying drawings are merely illustrative of the embodiments of the present disclosure and should not be construed as limiting the present disclosure.

[0008] The following detailed description includes devices, systems, and methods embodying exemplary embodiments of the present disclosure. This detailed description is merely illustrative in nature and is not intended to limit the embodiments of the present disclosure or the application and uses of such embodiments.

[0009] First Embodiment First, a light-emitting element drive circuit 10 of the present embodiment and a display device 100 including the light-emitting element drive circuit 10 will be described.

[0010] <Display device 100> 1, the display device 100 is, for example, an in-vehicle display. The display device 100 is configured to receive power from an in-vehicle power supply 200. The in-vehicle power supply 200 includes, for example, a DC / DC converter 201 and a filter circuit 202. The display device 100 may or may not include the in-vehicle power supply 200.

[0011] The display device 100 includes a display panel 101, a plurality of light-emitting elements 121-124 used as a backlight for the display panel 101, and a light-emitting element drive circuit 10 configured to be capable of driving the plurality of light-emitting elements 121-124. The display device 100 of this embodiment may include a display control unit 102 that controls an image to be displayed on the display panel 101. The light-emitting element drive circuit 10 may or may not include the display control unit 102.

[0012] The display panel 101 may be, for example, an LCD (Liquid Crystal Display) panel. As shown in Fig. 2, the display panel 101 is divided into, for example, a plurality of areas 111 to 114. In detail, in this embodiment, the display panel 101 is divided into a first area 111, a second area 112, a third area 113, and a fourth area 114.

[0013] In this embodiment, for convenience of explanation, the display panel 101 is divided into four areas 111 to 114. However, the number of divided areas is not limited to this, and may be any number, such as two, six or more. Furthermore, it is sufficient that a light-emitting element is provided for each area.

[0014] A plurality of light-emitting elements 121-124 are provided in each of the areas 111-114. The plurality of light-emitting elements 121-124 include a first light-emitting element 121 provided in the first area 111, a second light-emitting element 122 provided in the second area 112, a third light-emitting element 123 provided in the third area 113, and a fourth light-emitting element 124 provided in the fourth area 114. The light-emitting elements 121-124 are configured to irradiate the areas 111-114 with light from behind.

[0015] As shown in Fig. 1, the plurality of light-emitting elements 121-124 are, for example, LEDs (Light Emitting Diodes). The plurality of light-emitting elements 121-124 are configured to be electrically connectable to an in-vehicle power supply 200. The plurality of light-emitting elements 121-124 are connected in parallel with each other. An input current Iin input from the DC / DC converter 201 to the plurality of light-emitting elements 121-124 is the sum of currents flowing through all of the light-emitting elements 121-124.

[0016] The number of light-emitting elements 121 to 124 provided in each of the areas 111 to 114 may be any number. For example, as shown in Fig. 1 and Fig. 2, there are two first light-emitting elements 121, which are connected in series with each other. The same is true for the second light-emitting element 122, the third light-emitting element 123, and the fourth light-emitting element 124.

[0017] For ease of explanation, the current flowing through the first area 111 is referred to as a first current I1. The first current I1 is a current flowing through the first light-emitting element 121. Similarly, the current flowing through the second area 112 is referred to as a second current I2, the current flowing through the third area 113 is referred to as a third current I3, and the current flowing through the fourth area 114 is referred to as a fourth current I4.

[0018] <Light-emitting element driving circuit 10> As shown in FIG. 1 and FIG. 2, the light-emitting element drive circuit 10 includes a driver 20 and a control IC 30.

[0019] The driver 20 is operable by receiving power supply from an in-vehicle power source 200. In particular, a power line 21 is provided that electrically connects the in-vehicle power source 200 and the driver 20. Power is supplied from the in-vehicle power source 200 to the driver 20 via the power line 21. Note that a power source dedicated to the driver 20 may be provided separately from the in-vehicle power source 200, and power may be supplied to the driver 20 from the power source dedicated to the driver 20.

[0020] The driver 20 is electrically connected to the plurality of light-emitting elements 121-124. The driver 20 is configured to be able to drive the plurality of light-emitting elements 121-124 individually. Therefore, the driver 20 can individually control the currents I1-I4. In other words, the driver 20 is configured to be able to control the currents I1-I4 flowing in each of the areas 111-114. In this embodiment, one driver 20 is provided corresponding to the plurality of light-emitting elements 121-124. However, this is not limiting, and a driver may be provided corresponding to each of the light-emitting elements 121-124.

[0021] The control IC 30 controls the driver 20. The control IC 30 is electrically connected to the driver 20 and is configured to be able to communicate with the driver 20 via a communication line 22.

[0022] The control IC 30 includes a signal unit 31, a memory unit 32, and a control unit 33. The signal unit 31 is configured to be able to output the first synchronization signal SG1 and the second synchronization signal SG2. As shown in FIG. 3, the second period T2, which is the period of the second synchronization signal SG2, is shorter than the first period T1, which is the period of the first synchronization signal SG1. The rising edge of the first synchronization signal SG1 coincides with the rising edge of the second synchronization signal SG2. The first synchronization signal SG1 may be, for example, a vertical synchronization signal VSYNC, and the second synchronization signal SG2 may be, for example, a horizontal synchronization signal HSYNC. The signal unit 31 may be configured to generate both synchronization signals SG1 and SG2, or may be configured to obtain both synchronization signals SG1 and SG2 from the outside (for example, the display control unit 102). The signal unit 31 outputs both synchronization signals SG1 and SG2 to the control IC and the driver 20. The driver 20 is configured to operate in synchronization with both synchronization signals SG1 and SG2.

[0023] The storage unit 32 stores luminance setting data that is set in association with the luminance of each of the areas 111 to 114. As the storage unit 32, for example, a register circuit or the like can be used.

[0024] The luminance setting data is, for example, duty ratios D1 to D4 indicating a period during which a current flows through the light emitting elements 121 to 124 in the first period T1. In detail, the luminance of the areas 111 to 114 depends on the currents I1 to I4 flowing through the light emitting elements 121 to 124. The currents I1 to I4 can be adjusted by the duty ratios D1 to D4, which are the ratios of the period during which a current flows through the light emitting elements 121 to 124 to the first period T1. In this embodiment, the duty ratios D1 to D4 are set for each of the areas 111 to 114. Therefore, by controlling the duty ratios D1 to D4, the luminance of each of the areas 111 to 114 can be controlled. Note that the luminance setting data is not limited to the duty ratios D1 to D4, and may be any data as long as it can specify the luminance of each of the areas 111 to 114.

[0025] The configuration for storing the luminance setting data in the storage unit 32 is arbitrary, but for example, the display control unit 102 may generate the luminance setting data corresponding to the image to be displayed for each first synchronization signal SG1. In this case, the display control unit 102 outputs the luminance setting data to the control IC 30 of the light-emitting element drive circuit 10. The control IC 30 stores the luminance setting data in the storage unit 32 based on the luminance setting data input from the display control unit 102. The luminance setting data stored in the storage unit 32 is updated periodically. For example, the luminance setting data is updated in synchronization with the first synchronization signal SG1.

[0026] The display control unit 102 may be built into the control IC 30. In other words, the control IC 30 may include the display control unit 102. In this case, the display control unit 102 causes the storage unit 32 to store the luminance setting data.

[0027] The control unit 33 outputs commands related to the currents I1-I4 to the driver 20 using the communication line 22. The driver 20 controls the light-emitting elements 121-124 based on the commands. This controls the currents I1-I4. In other words, it can be said that the control IC 30 controls the driver 20 to control the light-emitting elements 121-124.

[0028] The control unit 33 controls the ON / OFF of the light-emitting elements 121-124 based on the second synchronization signal SG2 so that the periods during which the currents I1-I4 flow in the first cycle T1 correspond to the duty ratios D1-D4 stored in the storage unit 32. In other words, the control unit 33 controls the light-emitting elements 121-124 so that the currents I1-I4 flow over the periods corresponding to the duty ratios D1-D4 set for each of the areas 111-114.

[0029] In detail, the control unit 33 outputs the duty ratios D1 to D4 to the driver 20. The driver 20 controls the light emitting elements 121 to 124 based on the second synchronization signal SG2 so that the waveforms of the currents I1 to I4 in the first period T1 correspond to the duty ratios D1 to D4. In this case, the driver 20 counts the second synchronization signal SG2 to count the periods corresponding to the duty ratios D1 to D4.

[0030] An example of the currents I1 to I4 in the areas 111 to 114 will be described with reference to Fig. 4. Fig. 4 is a waveform diagram of the first synchronization signal SG1, the first current I1, the second current I2, the third current I3, the fourth current I4, and the input current Iin. For ease of explanation, an example will be taken in which the first duty ratio D1 is 50%, the second duty ratio D2 is 100%, the third duty ratio D3 is 0%, and the fourth duty ratio D4 is 25%.

[0031] As shown in Fig. 4, the first current I1 flows for 1 / 2 the first period T1. The second current I2 flows for the entire first period T1. The third current I3 does not flow during the first period T1. The fourth current I4 flows for 1 / 4 the first period T1. By controlling the duty ratios D1-D4 of the currents I1-I4 in this way, it is possible to adjust the brightness of each of the areas 111-114, i.e., local dimming.

[0032] Here, as shown in Fig. 4, the input current Iin is the sum of the currents flowing through all the light-emitting elements 121-124. The input current Iin changes in accordance with the changes in the currents I1-I4 within the first period T1. That is, the input current Iin is not a simple two-level waveform, but a waveform with three or more levels. In other words, the peak value of the input current Iin can take multiple values ​​within the first period T1.

[0033] As shown in FIG. 1, the light-emitting element driving circuit 10 includes a derivation section 40, an expected value calculation section 50, and a comparison section 60. The derivation unit 40 derives an actual measurement value Ix of a current flowing through a target light-emitting element, which is a light-emitting element in at least one of the multiple areas 111-114. In this embodiment, the derivation unit 40 derives actual measurement values ​​Ix of currents I1-I4 flowing through the light-emitting elements 121-124 in all of the areas 111-114. That is, in this embodiment, all of the areas 111-114 correspond to the "target area", and the multiple light-emitting elements 121-124 correspond to the "target light-emitting elements".

[0034] The derivation unit 40 of this embodiment includes a current detection circuit 41 that detects the total current flowing through the light emitting elements 121 to 124, an A / D conversion circuit 42 and a current value calculation unit 43 provided in the control IC 30.

[0035] The current detection circuit 41 is provided, for example, on the input side of the light emitting elements 121-124, specifically between the light emitting elements 121-124 and the in-vehicle power supply 200. The current detection circuit 41 detects the input current Iin output from the in-vehicle power supply 200 and input to the light emitting elements 121-124 as an analog signal, and outputs the analog signal that is the detection result to the A / D conversion circuit 42. As an example, the current detection circuit 41 includes, for example, a resistor 41a through which the input current Iin flows, and an amplifier 41b connected to the resistor 41a. However, the specific configuration of the current detection circuit 41 is not limited to this and is arbitrary, and may be, for example, a circuit using a Hall element.

[0036] 1, the A / D conversion circuit 42 is electrically connected to the current detection circuit 41. The A / D conversion circuit 42 is electrically connected to the signal section 31. Both synchronization signals SG1 and SG2 are input to the A / D conversion circuit 42 from the signal section 31. The A / D conversion circuit 42 periodically performs A / D conversion of the detection signal input from the current detection circuit 41 in synchronization with at least one of the synchronization signals SG1 and SG2. This allows the control IC 30 to periodically grasp the input current Iin.

[0037] The current value calculation unit 43 is electrically connected to, for example, the signal unit 31. The current value calculation unit 43 receives both synchronization signals SG1 and SG2 from the signal unit 31. The current value calculation unit 43 of this embodiment calculates an average current value Ixa, which is the average value of the currents I1-I4 flowing through the areas 111-114 in the first period T1, as the actual measurement value Ix. Then, the current value calculation unit 43 outputs the calculated average current value Ixa to the comparison unit 60.

[0038] As already described, the input current Iin is the sum of the currents I1 to I4 and is a value that changes within the first period T1. Therefore, the average current value Ixa in this embodiment is a value obtained by dividing the average value of the input current Iin in the first period T1 by the number of areas (for example, "4").

[0039] Here, a configuration for calculating the average value of the input current Iin in the first period T1 will be described. In this embodiment, three patterns are shown using Fig. 5 to Fig. 7. For convenience of illustration, Fig. 5 to Fig. 7 show the second period T2 and A / D conversion larger than they actually are.

[0040] <First pattern> FIG. 5 is a time chart showing a first pattern for calculating the average value of the input current Iin in the first period T1. As shown in FIG. 5, the A / D conversion circuit 42 performs A / D conversion in synchronization with the second synchronization signal SG2. In detail, the A / D conversion circuit 42 A / D converts the input current Iin detected by the current detection circuit 41 for each second synchronization signal SG2. The current value calculation unit 43 stores the input current Iin every time A / D conversion is performed. That is, the sampling period of the input current Iin is the second period T2. Then, the current value calculation unit 43 calculates the average value of the input current Iin in the first period T1 based on the multiple input currents Iin sampled within the first period T1.

[0041] <Second pattern> 6 is a time chart showing a second pattern for calculating the average value of the input current Iin in the first period T1. As shown in FIG. 6, the A / D conversion circuit 42 performs A / D conversion at a period multiple times (e.g., four times) the second period T2. That is, the sampling period of the input current Iin is multiple times the second period T2. The current value calculation unit 43 calculates the average value of the input current Iin in the first period T1 based on the multiple input currents Iin sampled within the first period T1. Note that the sampling period of the input current Iin may be shorter than the first period T1, and may be, for example, two times, or may be five times or more as long as it is shorter than the first period T1.

[0042] <Third pattern> 7 is a time chart showing a third pattern for calculating the average value of the input current Iin in the first period T1. As shown in FIG. 7, the A / D conversion circuit 42 performs A / D conversion at a timing not synchronized with the second synchronization signal SG2. That is, the timing at which the input current Iin is sampled is not synchronized with the second synchronization signal SG2. In detail, the sampling period of the input current Iin may be a period different from the second period T2 and a multiple of the second period T2. In this case, the sampling period of the input current Iin may be set to correspond to the minimum period in which the A / D conversion circuit 42 can operate.

[0043] The current value calculation unit 43 calculates the average value of the input current Iin in the first period T1 by using one of the patterns. Then, the current value calculation unit 43 divides the average value of the input current Iin by the number of target areas ("4" in this embodiment) to calculate the average current value Ixa as the actual measurement value Ix. Then, the current value calculation unit 43 outputs the average current value Ixa to the comparison unit 60.

[0044] The expected value calculation unit 50 of this embodiment calculates an average expected value Iea, which is, for example, the average of expected values ​​set for each of the areas 111-114. In detail, the expected value calculation unit 50 calculates an average duty ratio Da based on the duty ratios D1-D4. The average duty ratio Da is a value obtained by dividing the sum of the duty ratios D1-D4 by the number of areas. Then, the expected value calculation unit 50 calculates a current corresponding to the average duty ratio Da as the average expected value Iea. The expected value calculation unit 50 outputs the average expected value Iea to the comparison unit 60.

[0045] <Comparison of actual values ​​and expected values> The comparison unit 60 compares the actual measurement value Ix calculated by the current value calculation unit 43 with the expected value Ie calculated by the expected value calculation unit 50. In this embodiment, the comparison unit 60 compares the average current value Ixa as the actual measurement value Ix with the average expected value Iea as the expected value Ie. For example, the comparison unit 60 performs a comparison to determine whether the average current value Ixa is higher than the average expected value Iea by a predetermined threshold value Th or more (in other words, an abnormality determination). The threshold value Th is arbitrary, and may be, for example, a value of a predetermined percentage of the average expected value Iea (for example, several % to several tens of % of the average expected value Iea), or may be a predetermined fixed value regardless of the average expected value Iea.

[0046] The current value calculation unit 43 may derive a duty ratio corresponding to the average current value Ixa as the actual measurement value Ix. In this case, the comparison unit 60 may compare the duty ratio with the average duty ratio Da. In short, the actual measurement value Ix and the expected value Ie are not limited to the current value itself, but include parameters associated with the current value.

[0047] The comparison unit 60 outputs to the control unit 33 a comparison result (in other words, a determination result) of whether or not the average current value Ixa is higher than the average expected value Iea by a predetermined threshold value Th or more. Here, the timing of comparison by the comparing section 60 will be described with reference to FIG.

[0048] 8, in this embodiment, the comparison unit 60 performs the comparison (in other words, the abnormality determination) in synchronization with the first synchronization signal SG1. Accordingly, the derivation of the actual value Ix by the derivation unit 40 and the calculation of the expected value Ie by the expected value calculation unit 50 are performed in synchronization with the first synchronization signal SG1.

[0049] In detail, at the timing of t1, the expected value calculation section 50 calculates the average expected value Iea in the first synchronization period T11 based on the luminance setting data stored in the storage section 32. Note that the timing at which the average expected value Iea is calculated is arbitrary, and may be, for example, the timing of t2 or between the timings of t1 and t2.

[0050] The current value calculation unit 43 calculates an average current value Ixa in the first synchronization period T11 from time t1 to time t2 at time t2. Time t1 is the rising edge of a predetermined first synchronization signal SG11. Time t2 is the rising edge of the next first synchronization signal SG12 relative to the predetermined first synchronization signal SG11. In other words, the derivation unit 40 derives the actual current value Ix in the first synchronization period T11 at time t2.

[0051] The comparing unit 60 compares the average current value Ixa as the actual value Ix in the first synchronization period T11 with the average expected value Iea as the expected value Ie in the first synchronization period T11 based on the next rising edge of the first synchronization signal SG12. Note that the comparison by the comparing unit 60 only needs to be synchronized with the first synchronization signal SG1, and for example, the comparing unit 60 may perform the comparison based on the next falling edge of the first synchronization signal SG12.

[0052] The control unit 33 controls the light-emitting elements 121-124 based on the comparison result of the comparison unit 60. In detail, when the comparison result shows that the average current value Ixa is higher than the average expected value Iea by the threshold value Th or more, the control unit 33 may determine that a luminance abnormality has occurred and execute an abnormality response process at timing t2.

[0053] <An example of abnormality handling processing> The abnormality handling process may include a process of stopping the emission of the plurality of light-emitting elements 121 to 124. For example, the abnormality handling process includes a process of stopping the power supply from the in-vehicle power source 200 to the driver 20. In detail, as shown in FIG. 1, as already described, a power supply line 21 for supplying power from the in-vehicle power source 200 to the driver 20 is provided as a connection between the control IC 30 and the driver 20, in addition to the communication line 22 for transmitting commands. The light-emitting element drive circuit 10 includes a switching element Q0 connected to the power supply line 21 and ground. The switching element Q0 is configured to connect the power supply line 21 to ground by being turned on.

[0054] The process of stopping the light emitting elements 121 to 124 is not limited to this. For example, the driver 20 may be configured to be able to input a start-up signal and configured to be started when the start-up signal is input. In this case, the abnormality handling process may be a process of stopping the power supply so that the start-up signal is not input to the driver 20.

[0055] The control unit 33 is configured to be able to control the switching element Q0. As an abnormality response process, the control unit 33 turns the switching element Q0 to the ON state. This forces the operation of the driver 20 to stop regardless of the command output via the communication line 22. As a result, the multiple light-emitting elements 121 to 124 stop operating.

[0056] The abnormality handling process may include a process of outputting an abnormality signal to the outside. For example, the control unit 33 may output the abnormality signal to the display control unit 102. This allows the display control unit 102 to know that an abnormality has occurred in the backlight. Note that the abnormality handling process is not limited to this, and may include, for example, a process of reducing the currents I1 to I4 flowing through the light emitting elements 121 to 124.

[0057] <Action of this embodiment> The operation of this embodiment will be described. The control unit 33 can change the luminance of each of the areas 111-114 by varying the duty ratios D1-D4 for each of the areas 111-114. In this case, the average current value Ixa, which is the average value of the currents I1-I4 flowing through the light emitting elements 121-124 as the target light emitting elements, is compared with the average expected value Iea calculated based on each of the duty ratios D1-D4. As a result, even if the currents I1-I4 flowing through the areas 111-114 due to local dimming are different, a luminance abnormality is detected.

[0058] <Effects of this embodiment> According to the present embodiment described above in detail, the following effects are achieved. (1-1) The light-emitting element drive circuit 10 is configured to be capable of driving a plurality of light-emitting elements 121-124 used as a backlight of the display panel 101. The display panel 101 is partitioned into a plurality of areas 111-114, and the light-emitting elements 121-124 are provided for each of the areas 111-114.

[0059] In this configuration, the light-emitting element drive circuit 10 includes a derivation section 40, an expected value calculation section 50, a comparison section 60, and a control section 33. The derivation unit 40 derives actual measurement values ​​Ix of currents I1-I4 flowing through target light-emitting elements (light-emitting elements 121-124 in this embodiment) which are light-emitting elements in at least one of the areas 111-114. The expected value calculation unit 50 calculates expected values ​​Ie of currents I1-I4 flowing through the light-emitting elements 121-124 as the target light-emitting elements. The comparison unit 60 compares the actual measurement values ​​Ix with the expected value Ie. The control unit 33 controls the light-emitting elements 121-124 as the target light-emitting elements based on the comparison result of the comparison unit 60.

[0060] According to this configuration, by deriving the actual measurement value Ix and calculating the expected value Ie for each target light-emitting element (in other words, for each target area) and comparing the two, it is possible to detect luminance abnormalities even in local dimming.

[0061] (1-2) The derivation unit 40 includes a current value calculation unit 43 that calculates an average current value Ixa, which is the average value of currents I1 to I4 flowing in each target area (all areas 111 to 114 in this embodiment) in which the target light-emitting elements exist. The derivation unit 40 derives the average current value Ixa as the actual measurement value Ix. The expected value calculation unit 50 calculates an average expected value Iea, which is the average value of expected values ​​(in other words, currents corresponding to duty ratios D1 to D4) set for each target area. The comparison unit 60 compares the average current value Ixa with the average expected value Iea.

[0062] According to this configuration, even if there are multiple target areas, it is possible to detect luminance abnormalities. In particular, according to this configuration, it is sufficient to provide a configuration for detecting current (such as a current detection circuit) for each target area, and there is no need to provide a configuration for each of the areas 111 to 114, which can simplify the configuration.

[0063] (1-3) The derivation unit 40 includes a current detection circuit 41 that detects an input current Iin, which is the sum of the currents I1 to I4 flowing through all of the light-emitting elements 121 to 124, and an A / D conversion circuit 42 that is electrically connected to the current detection circuit 41. The current value calculation unit 43 calculates an average current value Ixa based on the digital signal converted by the A / D conversion circuit 42. This makes it possible to detect luminance abnormalities in all of the light-emitting elements 121 to 124 by using the single current detection circuit 41 and A / D conversion circuit 42.

[0064] (1-4) Duty ratios D1 to D4 in one period of the first synchronization signal SG1 are set for each of the areas 111 to 114. Based on the second synchronization signal SG2 that is shorter than the first synchronization signal SG1, the control unit 33 controls the light emitting elements 121 to 124 corresponding to the duty ratios D1 to D4 so that currents I1 to I4 flow over periods corresponding to the respective duty ratios D1 to D4.

[0065] According to this configuration, the light emitting elements 121-124 are controlled in accordance with the duty ratios D1-D4, thereby controlling the currents I1-I4 flowing through the areas 111-114. This makes it possible to adjust the luminance in each of the areas 111-114. Furthermore, by using the second synchronization signal SG2, the periods corresponding to the duty ratios D1-D4 can be counted.

[0066] (1-5) The derivation unit 40 derives an actual measurement value Ix (average current value Ixa in this embodiment) in a first synchronization period T11 from the rising edge of a given first synchronization signal SG11 to the rising edge of the next first synchronization signal SG12. The expected value calculation unit 50 calculates an expected value Ie (average expected value Iea in this embodiment) in the first synchronization period T11. The comparison unit 60 compares the actual measurement value Ix in the first synchronization period T11 with the expected value Ie based on the rising or falling edge of the next first synchronization signal SG12.

[0067] According to this configuration, the comparison by the comparator 60 is performed in synchronization with the first synchronization signal SG1. As a result, even if a momentary change in the currents I1 to I4 occurs that is shorter than the first synchronization signal SG1, erroneous determination is unlikely to occur. Therefore, erroneous determination caused by the momentary change can be suppressed.

[0068] (1-6) The derivation unit 40 may detect the input current Iin every one or more periods of the second synchronization signal SG2 (Patterns 1 and 2). The derivation unit 40 (specifically, the current value calculation unit 43) derives an average value of the input current Iin in the first synchronization period T11 based on the detection result. This makes it possible to derive the actual measured value Ix corresponding to the change even if the input current Iin changes within the first period T1.

[0069] (1-7) The derivation unit 40 may detect the input current Iin in a period different from the second period T2 or a multiple thereof (Pattern 3). The derivation unit 40 (specifically, the current value calculation unit 43) derives the average value of the input current Iin in the first synchronization period T11 based on the detection result. This makes it possible to derive the actual measured value Ix corresponding to the change even if the input current Iin changes within the first period T1. In addition, since it is not necessary to set the specifications of the A / D conversion circuit 42 so as to synchronize with the second synchronization signal SG2, the degree of freedom in designing the A / D conversion circuit 42 can be improved.

[0070] (1-8) When the comparison result of the comparator 60 indicates that the average current value Ixa is higher than the average expected value Iea by a predetermined threshold value Th or more, the controller 33 executes an abnormality handling process to stop the target light-emitting elements 121 to 124. This makes it possible to prevent the display from continuing in the state where a luminance abnormality occurs.

[0071] (1-9) The light-emitting element drive circuit 10 includes a driver 20 configured to be capable of driving a plurality of light-emitting elements 121 to 124. The driver 20 operates by receiving power supply. The abnormality handling process includes a process of stopping the power supply to the driver 20. This makes it possible to forcibly stop the light-emitting elements 121 to 124.

[0072] (1-10) The abnormality handling process includes a process of outputting an abnormality signal to the outside (to the display control unit 102 in this embodiment), thereby making it possible to notify the outside that a luminance abnormality has occurred.

[0073] <Second embodiment> A light-emitting element drive circuit 10 according to the second embodiment will be described with reference to FIGS. The light-emitting element driving circuit 10 includes a plurality of drivers 301-304 provided corresponding to the plurality of areas 111-114, and power supply lines 311-314 electrically connecting the in-vehicle power supply 200 to each of the drivers 301-304 individually.

[0074] The drivers 301 to 304 are configured to be able to drive the corresponding light-emitting elements 121 to 124 among the multiple areas 111 to 114. In particular, the first driver 301 is configured to be able to drive the first light-emitting element 121, and operates by receiving power supply from the in-vehicle power source 200 via a first power source line 311. The second driver 302 is configured to be able to drive the second light-emitting element 122, and operates by receiving power supply from the in-vehicle power source 200 via a second power source line 312. The third driver 303 is configured to be able to drive the third light-emitting element 123, and operates by receiving power supply from the in-vehicle power source 200 via a third power source line 313. The fourth driver 304 is configured to be able to drive the fourth light-emitting element 124, and operates by receiving power supply from the in-vehicle power source 200 via a fourth power source line 314.

[0075] 10, the control IC 30 is electrically connected to the drivers 301-304 individually via communication lines 321-324. The control IC 30 outputs commands (specifically, duty ratios D1-D4) to the drivers 301-304 individually via the communication lines 321-324, thereby controlling the drivers 301-304 individually.

[0076] 9, a plurality of (for example, four) first light emitting elements 121 in this embodiment are provided and connected in parallel to each other. Therefore, the plurality of first light emitting elements 121 can be made to emit light individually. The same applies to the second light emitting element 122, the third light emitting element 123, and the fourth light emitting element 124. The number of light emitting elements 121 to 124 can be any number.

[0077] The light-emitting element drive circuit 10 (specifically, the derivation section 40) of this embodiment is configured to be able to detect the currents I1 to I4 of the areas 111 to 114 individually. In detail, the derivation section 40 includes a plurality of current detection circuits 331 to 334 that detect the currents I1 to I4 of the plurality of areas 111 to 114. That is, the derivation section 40 includes a first current detection circuit 331 that detects the first current I1 flowing through the first light-emitting element 121 (specifically, the first area 111). The derivation section 40 includes a second current detection circuit 332 that detects the second current I2 flowing through the second light-emitting element 122 (specifically, the second area 112). The derivation section 40 includes a third current detection circuit 333 that detects the third current I3 flowing through the third light-emitting element 123 (specifically, the third area 113). The lead-out portion 40 includes a fourth current detection circuit 334 that detects a fourth current I4 flowing through the fourth light-emitting element 124 (specifically, the fourth area 114).

[0078] The current detection circuits 331 to 334 include resistors 331a to 334a and amplifiers 331b to 334b. The resistors 331a to 334a are provided on paths through which the currents I1 to I4 flow. The amplifiers 331b to 334b ​​are electrically connected to the resistors 331a to 334a.

[0079] The derivation unit 40 includes A / D conversion circuits 341-344. In this embodiment, the A / D conversion circuits 341-344 are provided in the same number as the current detection circuits 331-334. That is, in this embodiment, a plurality of current detection circuits 331-334 and A / D conversion circuits 341-344 are provided in correspondence with the number of areas 111-114.

[0080] The voltages detected by the resistors 331a to 334a are amplified by the amplifiers 331b to 334b ​​and input to the A / D conversion circuits 341 to 344. That is, the analog signals detected by the resistors 331a to 334a and the amplifiers 331b to 334b ​​are input to the A / D conversion circuits 341 to 344.

[0081] The A / D conversion circuits 341 to 344 are electrically connected to the control IC 30 and are electrically connected to corresponding ones of the plurality of current detection circuits 331 to 334. In particular, the first A / D conversion circuit 341 is connected to the first current detection circuit 331. The second A / D conversion circuit 342 is connected to the second current detection circuit 332. The third A / D conversion circuit 343 is connected to the third current detection circuit 333. The fourth A / D conversion circuit 344 is connected to the fourth current detection circuit 334. The A / D conversion circuits 341 to 344 convert analog signals as detection results of the current detection circuits 331 to 334 into digital signals and output them to the control IC 30. This allows the control IC 30 to grasp the respective currents I1 to I4. Note that the plurality of A / D conversion circuits 341 to 344 are provided outside the control IC 30, but this is not limiting and they may be provided inside the control IC 30.

[0082] <Comparison of actual values ​​and expected values> The control IC 30 of this embodiment is configured to compare the actual measurement values ​​Ix1 to Ix4 with the expected values ​​Ie1 to Ie4 for each of the areas 111 to 114.

[0083] In detail, the current value calculation section 43 of the present embodiment calculates average values ​​of the currents I1 to I4 in the first period T1 based on the digital signals input from the A / D conversion circuits 341 to 344, as actual measurement values ​​Ix1 to Ix4, respectively.

[0084] For example, the current value calculation unit 43 calculates the first measured value Ix1, which is the average value of the first current I1 in the first period T1, based on the digital signal periodically input from the first A / D conversion circuit 341. The calculation method is as described in the first embodiment.

[0085] Similarly, the current value calculation unit 43 calculates a second measured value Ix2 corresponding to the second current I2, a third measured value Ix3 corresponding to the third current I3, and a fourth measured value Ix4 corresponding to the fourth current I4. Then, the current value calculation unit 43 outputs these measured values ​​Ix1 to Ix4 to the comparison unit 60.

[0086] The expected value calculation section 50 of the present embodiment calculates expected values ​​Ie1 to Ie4 for the areas 111 to 114, based on the luminance setting data (for example, duty ratios D1 to D4) stored in the storage section 32, respectively.

[0087] For example, the expected value calculation unit 50 calculates a first expected value Ie1, which is an average value of a current corresponding to a first duty ratio D1 in a first period T1. Similarly, the expected value calculation unit 50 calculates a second expected value Ie2 corresponding to a second duty ratio D2, a third expected value Ie3 corresponding to a third duty ratio D3, and a fourth expected value Ie4 corresponding to a fourth duty ratio D4. The expected value calculation unit 50 then outputs these expected values ​​Ie1 to Ie4 to the comparison unit 60.

[0088] The comparison unit 60 compares the corresponding actual measured values ​​Ix1-Ix4 with the corresponding expected values ​​Ie1-Ie4 to determine whether or not a luminance abnormality occurs in each of the areas 111-114. In detail, the comparison unit 60 compares the first actual measured value Ix1 with the first expected value Ie1. For example, the comparison unit 60 determines whether or not the first actual measured value Ix1 is higher than the first expected value Ie1 by the threshold value Th or more. Similarly, the comparison unit 60 compares the second actual measured value Ix2 with the second expected value Ie2. The comparison unit 60 compares the third actual measured value Ix3 with the third expected value Ie3. The comparison unit 60 compares the fourth actual measured value Ix4 with the fourth expected value Ie4. The comparison unit 60 outputs the determination result of each of the areas 111-114 to the control unit 33 as a comparison result.

[0089] In this case, when focusing on the comparison of each area 111-114, the target light-emitting element and the target area can be said to be one. For example, when focusing on the comparison between the first actual measurement value Ix1 and the first expected value Ie1, the first light-emitting element 121 and the first area 111 can be said to correspond to the target light-emitting element and the target area. On the other hand, when focusing on the comparisons in each area 111-114 as a single comparison, the target light-emitting element and the target area can be said to be all the light-emitting elements 121-124 and the areas 111-114.

[0090] The control unit 33 determines that a luminance abnormality has occurred and executes an abnormality handling process when the comparison results in each of the areas 111 to 114 include a result corresponding to a luminance abnormality. For example, when the comparison result shows that the second actual measurement value Ix2 is higher than the second expected value Ie2 by the threshold value Th or more, the control unit 33 determines that a luminance abnormality has occurred and executes an abnormality handling process.

[0091] The abnormality handling process executed by the control unit 33 includes a process of stopping the light emitting elements of the areas 111 to 114 that have been determined to have a luminance abnormality. 10, the light-emitting element drive circuit 10 includes switching elements Q1 to Q4 that are connected to corresponding ones of the multiple power supply lines 311 to 314 and are also connected to ground. The switching elements Q1 to Q4 are configured to connect the power supply lines 311 to 314 to ground when they are turned on.

[0092] The control unit 33 is configured to be able to control each of the switching elements Q1 to Q4 individually. The control unit 33 stops the power supply to the driver corresponding to the area determined to have a luminance abnormality (hereinafter also referred to as an "abnormal area") by controlling each of the switching elements Q1 to Q4. In detail, for example, when a luminance abnormality occurs in the second area 112, the control unit 33 turns the second switching element Q2 to the ON state. This stops the power supply to the second driver 302. Therefore, regardless of a command from the second communication line 322, the second light-emitting element 122 is stopped.

[0093] Moreover, the abnormality handling process of this embodiment includes a process of outputting an abnormality signal to the display control unit 102. In this case, the abnormality signal includes information indicating that a luminance abnormality has occurred in the second area 112. This allows the display control unit 102 to grasp that a luminance abnormality has occurred in the second area 112.

[0094] Here, for example, the display control unit 102 may change the display image in accordance with the abnormal area. 11, when no luminance abnormality occurs in any of the areas 111 to 114, the display control unit 102 displays the image GP0 using all of the areas 111 to 114. In this case, the image GP0 is displayed across the areas 111 to 114.

[0095] On the other hand, when an abnormal area occurs, the display control unit 102 may display an image using only normal areas. In this case, as shown in Fig. 12, the display control unit 102 may display a reduced image GP1 obtained by reducing and displaying the image GP0. The image displayed using only normal areas is not limited to the reduced image GP1, and may be a simplified image whose display content is simpler than that of the image GP0.

[0096] As an example, the abnormality handling process may include a process of executing a test mode. In detail, the control IC 30 (for example, the control unit 33) may perform a process of sequentially causing a plurality of light-emitting elements corresponding to the abnormal area to emit light one by one in the test mode. Then, the control IC 30 (for example, the comparison unit 60) may compare the actual measurement value and the expected value of the light-emitting element to be emitted. For example, when the second area 112 is the abnormal area, the control IC 30 causes one of the plurality of second light-emitting elements 122 to emit light, and performs a process of comparing the actual measurement value and the expected value in that state. If this series of processes is considered as a unit determination process, the control IC 30 may perform the unit determination process for each of the plurality of second light-emitting elements 122. This makes it possible to identify which of the plurality of light-emitting elements 122 has a luminance abnormality. However, this is not limited to this, and the control IC 30 may perform the unit determination process for each of all the light-emitting elements 121 to 124 including the light-emitting elements other than the light-emitting elements in the abnormal area.

[0097] According to the present embodiment described above in detail, the following advantageous effects are achieved. (2-1) The derivation unit 40 derives actual measurement values ​​Ix1-Ix4 for each of the multiple areas 111-114. The expected value calculation unit 50 calculates expected values ​​Ie1-Ie4 for each of the multiple areas 111-114. The comparison unit 60 compares the actual measurement values ​​Ix1-Ix4 with the expected values ​​Ie1-Ie4 for each of the multiple areas 111-114. With this configuration, it is possible to determine whether or not a luminance abnormality has occurred for each of the areas 111-114. This makes it easier to identify the location where the luminance abnormality has occurred.

[0098] (2-2) The derivation unit 40 includes a plurality of current detection circuits 331-334 for detecting currents I1-I4 corresponding to the plurality of areas 111-114, and a plurality of A / D conversion circuits 341-344 electrically connected to the plurality of current detection circuits 331-334. The A / D conversion circuits 341-344 are provided in a plurality of circuits corresponding to the plurality of current detection circuits 331-334. The A / D conversion circuits 341-344 and the plurality of current detection circuits 331-334 are electrically connected to each other. This allows the derivation unit 40 to grasp each of the currents I1-I4, and therefore allows the derivation unit 40 to derive the actual measured values ​​Ix1-Ix4. Furthermore, according to this configuration, the derivation unit 40 can grasp each of the currents I1-I4 simultaneously. This makes it possible to shorten the period required to derive each of the actual measured values ​​Ix1 to Ix4, as compared to a configuration in which each of the currents I1 to I4 is grasped sequentially by sequentially connecting one A / D conversion circuit to the multiple current detection circuits 331 to 334.

[0099] <Example of change> The above-described embodiments can be modified as follows: The following modified examples can be combined with each other as long as no technical contradiction occurs.

[0100] The target light emitting element may be a part of the plurality of light emitting elements 121-124, and the target area may be a part of the plurality of areas 111-114. For example, in the first embodiment, the current value calculation unit 43 may derive an average current value Ixa of the first current I1 and the second current I2. The expected value calculation unit 50 may derive an average expected value Iea based on the first duty ratio D1 and the second duty ratio D2. The comparison unit 60 may then compare the two. In this case, the target light-emitting element is the first light-emitting element 121 and the second light-emitting element 122, and the target area is the first area 111 and the second area 112.

[0101] For example, in the second embodiment, the derivation unit 40 may derive only the first actual measurement value Ix1, and the expected value calculation unit 50 may calculate only the first expected value Ie1. In this case, the comparison unit 60 may only compare the first actual measurement value Ix1 with the first expected value Ie1. In this case, the target light-emitting element is the first light-emitting element 121, and the target area is the first area 111. In other words, the target light-emitting element and the target area for which a comparison regarding a luminance abnormality is performed may be at least a part of each other.

[0102] As shown in FIG. 13, the control unit 33 may be configured to execute an abnormality response process based on a comparison result in which the actual measurement value Ix is higher than the expected value Ie by a threshold Th or more consecutively occurring for a specified number of times Cx or more. Specifically, the control unit 33 is configured to count the comparison results in which the actual measurement value Ix is higher than the expected value Ie by a threshold Th or more (hereinafter referred to as the "number of errors"). If the number of errors is less than the specified number of times Cx, the control unit 33 maintains the emission of the target light-emitting element. On the other hand, the control unit 33 executes an abnormality response process based on the number of errors reaching the specified number of times Cx. This can suppress erroneous determination of a luminance abnormality caused by an instantaneous change in current. The specified number of times Cx is, for example, three times, but the specific number of times is arbitrary.

[0103] The first synchronization period T11 may be a period from a falling edge of a given first synchronization signal SG11 to a falling edge of the next first synchronization signal SG12. In this case, the comparison by the comparator 60 may be performed based on the falling edge of the next first synchronization signal SG12.

[0104] In the first embodiment, the expected value Ie is the average value of the current corresponding to the average duty ratio Da, but is not limited to this. 14, the display device 100 may include an illuminance sensor 350 that detects ambient light. In this case, the control IC 30 may include an acquisition unit 351 that acquires a detection result from the illuminance sensor 350. The acquisition unit 351 is, for example, a connector that is provided in the control IC 30 and is for electrically connecting to the illuminance sensor 350. In this configuration, the expected value calculation unit 50 may calculate the maximum value of a current that can be passed through the target light-emitting element (hereinafter referred to as "maximum current Imax") as the expected value Ie.

[0105] In this case, the expected value Ie may be a value according to the detection result of the illuminance sensor 350. In detail, as shown in Fig. 15, the maximum current Imax may be set to be larger as the ambient light becomes stronger. The maximum current Imax is, for example, a current value when white color is displayed. The expected value calculation unit 50 may have data in which the intensity of the ambient light is associated with the maximum current Imax, and may calculate the maximum current Imax corresponding to the detection result of the illuminance sensor 350 as the expected value Ie by referring to the data.

[0106] The expected value Ie may be a constant value regardless of the intensity of the ambient light. For example, the expected value Ie may be a maximum current Imax in a situation where the ambient light is at its maximum (100%). In this case, the expected value Ie will not be exceeded under normal operating conditions. Therefore, a luminance abnormality can also be detected by comparing the expected value Ie with the actual measured value Ix. The illuminance sensor 350 may be included in the light-emitting element drive circuit 10, or may not be included in the light-emitting element drive circuit 10.

[0107] In both embodiments, the comparison by the comparing section 60 is performed in synchronization with the first synchronization signal SG1, but this is not limiting, and the timing at which the comparison by the comparing section 60 is performed may be arbitrary. For example, as shown in Fig. 16, the comparison by the comparison unit 60 may be configured to be performed in synchronization with the second synchronization signal SG2. That is, the derivation unit 40 may derive the actual measurement value Ix in synchronization with the second synchronization signal SG2. In particular, the A / D conversion circuit 42 performs A / D conversion every time the second synchronization signal SG2 rises. The derivation unit 40 (current value calculation unit 43) may derive the actual measurement value Ix based on the A / D converted digital signal.

[0108] Furthermore, the expected value calculation section 50 may calculate the expected value Ie in the same cycle as the cycle in which the derivation section 40 derives the actual measurement value Ix. For example, the expected value calculation section 50 may calculate the expected value Ie every time the second synchronization signal SG2 rises.

[0109] For example, when the comparison is performed using the input current Iin as in the first embodiment, the expected value calculation unit 50 may calculate the peak value of the input current Iin at that timing or the average value obtained by dividing the peak value by the number of areas as the expected value Ie based on each duty ratio D1 to D4 every time the second synchronization signal SG2 rises. For example, when the comparison is performed in units of areas 111 to 114 as in the second embodiment, the expected value calculation unit 50 may calculate the peak value of the current of the target light-emitting element at that timing or the average value obtained by dividing the peak value by the number of areas as the expected value Ie every time the second synchronization signal SG2 rises, based on the duty ratio of the target area. In this way, even if the peak value of the input current Iin or the current of the target light-emitting element changes within the first period T1, it is possible to calculate the expected value Ie corresponding to the change.

[0110] The comparator 60 may compare the actual measurement value Ix with the expected value Ie each time the actual measurement value Ix is derived and the expected value Ie is calculated. This allows the abnormality handling process to be performed when a luminance abnormality occurs without waiting for the next rise of the first synchronization signal SG12. This reduces the time lag between the occurrence of a luminance abnormality and the execution of the abnormality handling process.

[0111] Further, the comparison by the comparison unit 60 is not limited to being performed in the same cycle as the second synchronization signal SG2. For example, as shown in Fig. 17, the derivation by the derivation unit 40 and the comparison by the comparison unit 60 may be performed every several cycles of the second synchronization signal SG2.

[0112] In a configuration in which the expected value Ie does not fluctuate, for example, when the maximum current Imax when the ambient light is at its maximum and white color is displayed is calculated as the expected value Ie, the expected value calculation section 50 does not need to synchronize with the second synchronization signal SG2.

[0113] In the second embodiment, a plurality of A / D conversion circuits are provided corresponding to the plurality of current detection circuits 331 to 334, but this is not limited thereto. For example, as shown in FIG. 18, a single A / D conversion circuit 42 may be provided. In this case, the light-emitting element drive circuit 10 may include a plurality of switches 361 to 364 used to electrically connect the A / D conversion circuit 42 to the plurality of current detection circuits 331 to 334 individually. The current value calculation unit 43 may be configured to grasp the currents I1 to I4 for each of the plurality of areas 111 to 114 by controlling the plurality of switches 361 to 364. That is, the derivation unit 40 may be configured to grasp each of the currents I1 to I4 by sequentially switching the connection destination of the A / D conversion circuit 42 to one of the plurality of current detection circuits 331 to 334. This makes it possible to reduce the number of A / D conversion circuits.

[0114] In the second embodiment, the switching elements Q1 to Q4 used to stop the power supply are provided for each of the drivers 301 to 304, but this is not limited thereto. For example, as shown in FIG. 19, one switching element may be provided corresponding to the plurality of drivers 301 to 304. For example, the second power line 312 may be connected to the first power line 311. The first switching element Q1 may be provided at a position closer to the in-vehicle power source 200 than the connection point of the first power line 311 with the second power line 312. In this case, for example, when a luminance abnormality occurs in the first area 111, the power supply to the first driver 301 and the second driver 302 is stopped. This stops the first light emitting element 121 and the second light emitting element 122. The same applies to the third power line 313, the fourth power line 314, and the third switching element Q3.

[0115] 20, the A / D conversion circuit 42 may be provided separately from the control IC 30. In this case, it is preferable that the A / D conversion circuit 42 and the control IC 30 are electrically connected to each other.

[0116] 21 , in the first embodiment, the driver 20 may include an A / D conversion circuit 42, a current value calculation unit 43, an expected value calculation unit 50, a comparison unit 60, and a control unit 33. In this case, the control IC 30 may include a signal unit 31 and a storage unit 32, and output both synchronization signals SG1, SG2 and brightness setting data to the driver 20.

[0117] The same applies to the second embodiment. In this case, each of the drivers 301 to 304 may include a current value calculation section 43, an expected value calculation section 50, a comparison section 60, and a control section 33. In addition, the control section 33 and the comparison section 60 may be provided separately, or the current value calculation section 43 and the comparison section 60 may be provided separately.

[0118] 22, the light-emitting element driving circuit 10 may include a microcomputer 370 provided separately from the control IC 30. The microcomputer 370 may include an A / D conversion circuit 42, a current value calculation unit 43, an expected value calculation unit 50, and a comparison unit 60. The control IC 30 may include a signal unit 31, a storage unit 32, and a control unit 33. In this case, the current detection circuit 41 outputs the detection result to the microcomputer 370. The control IC 30 outputs the luminance setting data to the microcomputer 370. The comparison unit 60 of the microcomputer 370 compares the actual measurement value Ix with the expected value Ie based on the detection result of the current detection circuit 41 and the luminance setting data, and outputs the comparison result to the control IC 30. The control unit 33 of the control IC 30 controls the light-emitting elements 121 to 124 by outputting a command to the driver 20 based on the comparison result. Note that the microcomputer 370 may include the control unit 33.

[0119] The display device 100 is not limited to being mounted on a vehicle and may be used in any manner. The light emitting elements 121 to 124 are not limited to LEDs and may be any other elements, for example, organic EL (Electro Luminescence) elements.

[0120] In the first embodiment, the comparison unit 60 may compare the average current value Ixa with "0" and determine that a disconnection abnormality has occurred if the average current value Ixa is "0" or close to "0". In this case, the comparison unit 60 may output a determination result of a disconnection abnormality to the control unit 33 as a comparison result. The same applies to the second embodiment.

[0121] For example, in the first embodiment, the anomaly handling process may include a process of executing a determination mode for identifying an abnormal area. In this way, when it is determined that a luminance abnormality has occurred by comparing the average current value Ixa with the average expected value Iea, the determination mode is executed, thereby making it possible to identify the abnormal area where the luminance abnormality has occurred.

[0122] In the identification mode, the control unit 33 causes each of the areas 111-114 to emit light one by one, and the currents I1-I4 can be detected using the current detection circuit 41. For example, when the control IC 30 causes only the first light-emitting element 121 in the first area 111 to emit light, the first current I1 can be detected by the current detection circuit 41. Therefore, the comparison unit 60 can compare the first actual measurement value Ix1 with the first expected value Ie1. Therefore, the abnormal area can be identified without providing the current detection circuits 331-334 for each of the areas 111-114. However, this is not limiting, and the current detection circuits 331-334 may be provided as in the second embodiment.

[0123] In the first embodiment, the multiple first light-emitting elements 121 are not limited to being connected in series with each other, but may be connected in parallel with each other. In this case, the driver 20 may be configured to be able to cause the multiple first light-emitting elements 121 to emit light individually. The same applies to the second light-emitting element 122, the third light-emitting element 123, and the fourth light-emitting element 124.

[0124] In such a configuration, the control IC 30 may include a process of executing a test mode in the abnormality handling process. In this case, the control IC 30 may execute the unit determination process for each of all the light-emitting elements 121 to 124. Alternatively, the control IC 30 may execute the unit determination process for each of the plurality of light-emitting elements corresponding to the abnormal area after identifying the abnormal area in the identification mode.

[0125] The control IC 30 is not limited to a configuration in which the test mode is executed in the abnormality handling process, and may execute the test mode, for example, at the time of startup. This makes it possible to prevent the display device 100 from performing display when a luminance abnormality occurs.

[0126] In the second embodiment, the first light emitting elements 121 may be connected in series to each other. The same applies to the second light emitting elements 122, the third light emitting elements 123, and the fourth light emitting elements .

[0127] The terms "first", "second", "third", etc. in this disclosure are used merely to distinguish objects and do not rank the objects. <Additional Notes> The technical ideas that can be understood from the present disclosure are described below. Note that, for the purpose of aiding understanding, not for the purpose of limitation, the components described in the appendices are given the reference symbols of the corresponding components in the embodiments. The reference symbols are shown as examples for the purpose of aiding understanding, and the components described in each appendix should not be limited to the components indicated by the reference symbols.

[0128] [Appendix 1] A light-emitting element drive circuit (10) configured to be capable of driving a plurality of light-emitting elements (121-124) used as a backlight of a display panel (101), The display panel is divided into a plurality of areas (111 to 114), and the plurality of light-emitting elements are provided for each of the areas, The light emitting element driving circuit includes: a derivation unit (40) that derives an actual measured value (Ix) of a current flowing through a target light-emitting element that is the light-emitting element in at least one of the plurality of areas; an expected value calculation unit (50) that calculates an expected value (Ie) of a current flowing through the target light-emitting element; A comparison unit (60) that compares the actual measurement value with the expected value; A control unit (33) that controls the target light-emitting element in response to a comparison result of the comparison unit; A light emitting element driving circuit including:

[0129] [Appendix 2] the target light emitting element includes the light emitting element in two or more target areas among the plurality of areas; the derivation unit includes a current value calculation unit (43) that calculates an average current value (Ixa) that is an average value of a current flowing in each of the target areas in which the target light-emitting element is present, and derives the average current value as the actual measurement value; The expected value calculation unit calculates an average expected value (Iea) which is an average of the expected values ​​set for each of the target areas as one type of the expected value, The comparison unit compares the average current value with the average expected value. 2. A light-emitting element drive circuit as described in claim 1.

[0130] [Appendix 3] the target light-emitting element is all of the plurality of light-emitting elements, 3. The light-emitting element driving circuit according to claim 2, wherein the target area is all of the plurality of areas.

[0131] [Appendix 4] The lead-out portion is a current detection circuit (41) for detecting a total current flowing through the plurality of light-emitting elements and outputting an analog signal as a detection result; an A / D conversion circuit (42) electrically connected to the current detection circuit; Equipped with 4. The light-emitting element drive circuit according to claim 3, wherein the current value calculation unit calculates the average current value based on the signal converted by the A / D conversion circuit.

[0132] [Appendix 5] An acquisition unit (351) that acquires a detection result of an illuminance sensor (350), The light-emitting element driving circuit according to claim 1, wherein the expected value calculation unit calculates as the expected value a maximum value of current that can be passed through the target light-emitting element, the maximum value being a value corresponding to the detection result of the illuminance sensor.

[0133] [Appendix 6] The derivation unit derives the actual measurement value for each of the plurality of areas, the expected value calculation unit calculates the expected value for each of the plurality of areas, 2. The light-emitting element drive circuit according to claim 1, wherein the comparison unit compares the actual measurement value with the expected value for each of the plurality of areas.

[0134] [Appendix 7] The lead-out portion is A plurality of current detection circuits (331 to 334) for detecting currents in the plurality of areas and outputting analog signals as detection results; one or more A / D conversion circuits (42, 341 to 344) electrically connected to the plurality of current detection circuits; 7. The light-emitting element driving circuit according to claim 6,

[0135] [Appendix 8] a plurality of the A / D conversion circuits are provided corresponding to the plurality of current detection circuits; The plurality of A / D conversion circuits are electrically connected to the corresponding current detection circuits. 8. The light-emitting element drive circuit according to claim 7.

[0136] [Appendix 9] The A / D conversion circuit is one. The derivation unit includes a plurality of switches (361 to 364) used to electrically connect the A / D conversion circuit and the plurality of current detection circuits individually, and grasps the current for each of the plurality of areas by controlling the plurality of switches. 8. The light-emitting element drive circuit according to claim 7.

[0137] [Appendix 10] A duty ratio (D1 to D4) in one period of a first synchronization signal (SG1) is set for each of the plurality of areas, The control unit controls the plurality of light-emitting elements so that a current (I1 to I4) flows over a period corresponding to the duty ratio set for each of the plurality of areas, based on a second synchronization signal (SG2) having a period shorter than that of the first synchronization signal. 10. A light-emitting element drive circuit according to any one of claims 1 to 9.

[0138] [Appendix 11] The derivation unit derives an actual measurement value of a current flowing through the target light-emitting element during a first synchronization period (T11) from a rising or falling edge of a predetermined first synchronization signal to a rising or falling edge of the next first synchronization signal with respect to the predetermined first synchronization signal, the expected value calculation unit calculates an expected value of a current flowing through the target light emitting element during the first synchronization period; The comparison unit compares the actual measurement value and the expected value during the first synchronization period based on a rising edge or a falling edge of the next first synchronization signal. 11. The light-emitting element drive circuit according to claim 10.

[0139] [Appendix 12] The derivation unit detects a current flowing through the target light-emitting element for each one or more periods of the second synchronization signal, and derives an average value of the current flowing through the target light-emitting element during the first synchronization period. 12. The light-emitting element drive circuit according to claim 11.

[0140] [Appendix 13] The derivation unit detects a current flowing through the target light-emitting element at a period different from a period of the second synchronization signal or a multiple thereof, and derives an average value of the current flowing through the target light-emitting element during the first synchronization period based on the detection result. 12. The light-emitting element drive circuit according to claim 11.

[0141] [Appendix 14] The derivation unit derives the actual measurement value for each one or a plurality of periods of the second synchronization signal, the comparison unit compares the actual measurement value with the expected value every time the derivation unit derives the actual measurement value; 11. The light-emitting element drive circuit according to claim 10.

[0142] [Appendix 15] the expected value calculation unit calculates the expected value in the same cycle as the cycle in which the derivation unit derives the actual measurement value, the comparison unit compares the actual measurement value with the expected value every time the actual measurement value is derived and the expected value is calculated. 15. The light-emitting element drive circuit according to claim 14.

[0143] [Appendix 16] The control unit executes an abnormality response process to reduce a current flowing through the target light-emitting element or stop the target light-emitting element based on a comparison result in which the actual measurement value is higher than the expected value by a predetermined threshold value (Th) or more. 16. A light-emitting element drive circuit according to any one of claims 1 to 15.

[0144] [Appendix 17] When the comparison result in which the actual measurement value is higher than the expected value by a predetermined threshold value or more continues for a specified number of times (Cx) or more, the control unit executes an abnormality response process to reduce the current flowing through the target light-emitting element or stop the target light-emitting element. 16. A light-emitting element drive circuit according to any one of claims 1 to 15.

[0145] [Appendix 18] A plurality of drivers (301 to 304) configured to be capable of driving the plurality of light-emitting elements and provided corresponding to each of the plurality of areas, The abnormality response process includes a process of stopping power supply to a target driver configured to drive the target light-emitting element among the plurality of drivers. 18. The light-emitting element drive circuit according to claim 16 or 17.

[0146] [Appendix 19] The abnormality response process includes a process of outputting an abnormality signal to the outside. 19. The light-emitting element drive circuit according to any one of claims 16 to 18.

[0147] [Appendix 20] A driver (20) configured to be able to drive the plurality of light-emitting elements; A control IC (30) configured to be able to control the driver; Equipped with The control IC includes the expected value calculation unit. 20. A light-emitting element drive circuit according to any one of claims 1 to 19.

[0148] [Appendix 21] A driver (20) configured to be able to drive the plurality of light-emitting elements; A control IC (30) configured to be able to control the driver; A microcomputer (370) provided separately from the control IC; Equipped with The microcomputer includes the expected value calculation unit. 20. A light-emitting element drive circuit according to any one of claims 1 to 19.

[0149] [Appendix 22] A driver (20) configured to be able to drive the plurality of light-emitting elements, The driver includes the expected value calculation unit. 20. A light-emitting element drive circuit according to any one of claims 1 to 19.

[0150] [Appendix 23] A storage unit (32) in which luminance setting data for each of the plurality of areas is stored, The expected value calculation unit calculates the expected value based on the luminance setting data stored in the storage unit. 23. A light-emitting element drive circuit according to any one of claims 1 to 22. [Explanation of symbols]

[0151] 10...Light emitting element drive circuit 20,301~304...Driver 30...Control IC 33...Control section 40…Derivation part 41, 331 to 334: Current detection circuit 42,341~344...A / D conversion circuit 43...Current value calculation section 50...Expected value calculation section 60…Comparison section 100...Display device 101...Display panel 102...Display control unit 111~114...Area 121 to 124: Light emitting element 200…Vehicle power supply 350…Illuminance sensor 351…Acquisition Department 361~364…Switch 370…Microcomputer SG1,SG11,SG12…1st synchronization signal SG2…Second synchronization signal D1~D4…Duty ratio Ix: Actual measurement value Ixa: Average current value Ie…Expected value Iea: average expected value T1…1st period T11: First synchronization period

Claims

1. A light-emitting element drive circuit configured to drive a plurality of light-emitting elements used as a backlight of a display panel, the display panel is divided into a plurality of areas, and the plurality of light-emitting elements are provided for each of the areas; The light emitting element driving circuit includes: a derivation unit that derives an actual measurement value of a current flowing through a target light-emitting element that is the light-emitting element in at least one of the plurality of areas; an expected value calculation unit that calculates an expected value of a current flowing through the target light emitting element; a comparison unit that compares the actual measurement value with the expected value; A control unit that controls the target light emitting element in response to a comparison result of the comparison unit; A light-emitting element driving circuit including:

2. The target light emitting element includes the light emitting element in two or more target areas among the plurality of areas, the derivation unit includes a current value calculation unit that calculates an average current value that is an average value of a current flowing in each of the target areas in which the target light-emitting element is present, and derives the average current value as the actual measurement value; the expected value calculation unit calculates, as one type of the expected value, an average expected value that is an average of the expected values ​​set for each of the target areas; The comparison unit compares the average current value with the average expected value. The light emitting element drive circuit according to claim 1 .

3. An acquisition unit that acquires a detection result of the illuminance sensor, The light-emitting element drive circuit according to claim 1 , wherein the expected value calculation unit calculates, as the expected value, a maximum value of a current that can be passed through the target light-emitting element, which is a value according to a detection result of the illuminance sensor.

4. The derivation unit derives the actual measurement value for each of the plurality of areas, the expected value calculation unit calculates the expected value for each of the plurality of areas, 2 . The light-emitting element drive circuit according to claim 1 , wherein the comparison section compares the actual measurement value with the expected value for each of the plurality of areas.

5. The lead-out portion is a plurality of current detection circuits for detecting current in each of the plurality of areas and outputting analog signals as detection results; one or more A / D conversion circuits electrically connected to the plurality of current detection circuits; The light emitting element driving circuit according to claim 4 , comprising:

6. a plurality of the A / D conversion circuits are provided corresponding to the plurality of current detection circuits; The plurality of A / D conversion circuits are electrically connected to the corresponding current detection circuits.

6. The light emitting element drive circuit according to claim 5.

7. The A / D conversion circuit is one. the derivation unit includes a plurality of switches used to electrically connect the A / D conversion circuit and the plurality of current detection circuits individually, and grasps the current for each of the plurality of areas by controlling the plurality of switches; 6. The light emitting element drive circuit according to claim 5.

8. a duty ratio in one period of the first synchronization signal is set for each of the plurality of areas; the control unit controls the plurality of light-emitting elements based on a second synchronization signal having a shorter period than the first synchronization signal so that a current flows for a period corresponding to the duty ratio set for each of the plurality of areas. The light emitting element drive circuit according to any one of claims 1 to 7.

9. The derivation unit derives an actual measurement value of a current flowing through the target light-emitting element during a first synchronization period from a rising or falling edge of a predetermined first synchronization signal to a rising or falling edge of a next first synchronization signal with respect to the predetermined first synchronization signal, the expected value calculation unit calculates an expected value of a current flowing through the target light emitting element in the first synchronization period; the comparison unit compares the actual measurement value and the expected value during the first synchronization period based on a rising edge or a falling edge of the next first synchronization signal; The light emitting element drive circuit according to claim 8.

10. The derivation unit detects a current flowing through the target light-emitting element for each one or more periods of the second synchronization signal, and derives an average value of the current flowing through the target light-emitting element during the first synchronization period. The light emitting element drive circuit according to claim 9.

11. The derivation unit detects a current flowing through the target light-emitting element at a period different from a period of the second synchronization signal or a multiple thereof, and derives an average value of the current flowing through the target light-emitting element during the first synchronization period based on the detection result. The light emitting element drive circuit according to claim 9.

12. The derivation unit derives the actual measurement value for each one or a plurality of periods of the second synchronization signal, the comparison unit compares the actual measurement value with the expected value every time the derivation unit derives the actual measurement value; The light emitting element drive circuit according to claim 8.

13. the expected value calculation unit calculates the expected value in the same cycle as the cycle in which the derivation unit derives the actual measurement value, the comparison unit compares the actual measurement value with the expected value every time the actual measurement value is derived and the expected value is calculated. The light emitting element drive circuit according to claim 12.

14. The control unit executes an abnormality response process to reduce a current flowing through the target light-emitting element or stop the target light-emitting element based on a comparison result in which the actual measurement value is higher than the expected value by a predetermined threshold value or more. The light emitting element drive circuit according to claim 1 .

15. When the comparison result that the actual measurement value is higher than the expected value by a predetermined threshold value or more continues for a specified number of times or more, the control unit executes an abnormality response process to reduce a current flowing through the target light-emitting element or stop the target light-emitting element. The light emitting element drive circuit according to claim 1 .

16. A plurality of drivers are provided corresponding to each of the plurality of areas and configured to be capable of driving the plurality of light emitting elements, The abnormality response process includes a process of stopping power supply to a target driver configured to drive the target light-emitting element among the plurality of drivers. The light emitting element drive circuit according to claim 14.

17. The abnormality response process includes a process of outputting an abnormality signal to the outside. The light emitting element drive circuit according to claim 14.

18. A driver configured to be able to drive the plurality of light emitting elements; A control IC configured to be able to control the driver; Equipped with The control IC includes the expected value calculation unit. The light emitting element drive circuit according to claim 1 .

19. A driver configured to be able to drive the plurality of light emitting elements; A control IC configured to be able to control the driver; A microcomputer provided separately from the control IC; Equipped with The microcomputer includes the expected value calculation unit. The light emitting element drive circuit according to claim 1 .

20. A driver configured to drive the plurality of light-emitting elements, The driver includes the expected value calculation unit. The light emitting element drive circuit according to claim 1 .

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