Light-emitting element drive circuit and lighting device using same, display device, and electronic apparatus

Abstract

This light-emitting element drive circuit comprises a plurality of current drivers respectively connected to light-emitting elements of a plurality of channels, and a controller configured to control the plurality of current drivers. The controller is configured to perform ON / OFF switching of the current drivers of one channel and to set the on-duty of the current drivers of the remaining channels to 100% if the light control ratio is a first light control ratio greater than 100×(N-1) / N% and less than 100%, where N is the number of channels in the plurality of channels.

Description

Light-emitting element drive circuit, and lighting device, display device, and electronic device using the same

[0001] The invention disclosed in this specification relates to a drive circuit for a light-emitting element.

[0002] White light-emitting diodes (hereinafter abbreviated as LEDs), which have excellent characteristics in terms of longer life, lower power consumption, and a wider color gamut, are being used as backlights for liquid crystal display (LCD) panels, instead of conventional cold cathode fluorescent lamps (CCFLs) and external electrode fluorescent lamps (EEFLs).

[0003] An example of the related prior art is disclosed in Japanese Patent Application Laid-Open No. 2003-222299.

[0004] Japanese Patent Application Laid-Open No. 2014-207204

[0005] Known methods for controlling the brightness of LEDs for backlighting include current dimming (analog dimming) and PWM dimming. Current dimming adjusts the amount of drive current flowing to the light-emitting element according to the target brightness. PWM dimming switches the drive current to adjust the time ratio (duty ratio) between the on period when the drive current flows and the off period when the drive current is cut off, thereby controlling the effective brightness of the light-emitting element.

[0006] In recent years, the contrast ratio required for lighting devices has been increasing. For example, by current dimming, the driving current I LED When the duty ratio is changed from the maximum current corresponding to maximum brightness to the minimum current, which is 0.1% of that, the contrast ratio becomes 1000:1. When the duty ratio is changed in the range of 100% to 0.1% by PWM dimming, the contrast ratio becomes 1000:1.

[0007] Therefore, the contrast ratio of a lighting device is limited by the minimum amount of current that can be generated by the current driver in current dimming, and by the minimum pulse width in PWM dimming. Alternatively, the contrast ratio can be increased by combining analog dimming and PWM dimming, but even in this case, there is an upper limit to the contrast ratio.

[0008] Furthermore, when driving LEDs for dimming, there is a method of simultaneously dimming all LEDs using PWM dimming. When dimming all LEDs simultaneously, the load fluctuations associated with PWM dimming become large, causing audible noise. To reduce the output voltage ripple and improve this noise, the capacitor capacity must be increased, which increases costs.

[0009] By dimming the LEDs at different times using Phase Shift rather than dimming all of them simultaneously, load fluctuations can be suppressed to some extent. Therefore, noise can be suppressed even if the capacity of the output capacitor is reduced, leading to cost reduction. However, since the number of switching events itself does not decrease even when Phase Shift is implemented, a reduction in switching noise cannot be expected.

[0010] The light-emitting element drive circuit disclosed in this specification comprises a plurality of current drivers connected to respective light-emitting elements of a plurality of channels, and a controller configured to control the plurality of current drivers, wherein the number of channels of the plurality of channels is N, and the controller is configured to switch the current driver of one channel ON / OFF when the dimming rate is a first dimming rate that is greater than 100×(N−1) / N% and less than 100%, and to set the on-duty of the current drivers of the remaining channels to 100%.

[0011] The lighting device disclosed in this specification includes light emitting elements of multiple channels and a light emitting element drive circuit configured as described above that drives the light emitting elements of the multiple channels.

[0012] The electronic device disclosed in this specification includes a display panel and an illumination device having the above-described configuration.

[0013] The display device disclosed in this specification includes a display panel and an illumination device having the above-described configuration.

[0014] The light-emitting element drive circuit, lighting device, electronic device, and display device disclosed in this specification can reduce audible noise, costs, and switching noise.

[0015] FIG. 1 is a diagram showing the configuration of a display device including a backlight device according to an embodiment. FIG. 2A is a diagram showing an example of an arrangement layout of light-emitting elements of an illumination device. FIG. 2B is a diagram showing a substrate on which the light-emitting elements are mounted. FIG. 3 is a diagram showing another example of an arrangement layout of light-emitting elements of an illumination device. FIG. 4 is a diagram showing an example of dimming control when the dimming rate is 90%. FIG. 5 is a diagram showing an example of dimming control when the dimming rate is 50%. FIG. 6 is a diagram showing an example of dimming control when the dimming rate is 0.25%. FIG. 7 is a diagram showing load fluctuations when the dimming rate is 20%. FIG. 8 is a diagram showing a comparison with conventional technology. FIG. 9A is a diagram showing an example of an electronic device including an illumination device. FIG. 9B is a diagram showing an example of an electronic device including an illumination device.

[0016] FIG. 1 is a diagram showing the configuration of a display device including an illumination device according to an embodiment.

[0017] The display device 100 includes an LCD (Liquid Crystal Display) panel 101 and an illumination device 1. The illumination device 1 is configured to irradiate the LCD panel 101 from the rear surface with backlight.

[0018] The lighting device 1 is configured as a multi-channel device and includes N (N is an integer of 2 or more) channel light-emitting element strings 10_1 to 10_N, a light-emitting element drive circuit 2, a capacitor C1, and a light guide plate (not shown in FIG. 1).

[0019] Each of the N light-emitting element strings 10_1 to 10_N includes M (M is an integer of 2 or more) light-emitting units 11 connected in series. For example, each light-emitting unit 11 includes one or multiple light-emitting elements connected in series. The light-emitting elements are, for example, LEDs.

[0020] The M light emitting units 11 included in the same light emitting element string 10 (channel) are configured to have substantially the same size (light emitting area) so as to emit light with the same luminance.

[0021] Hereinafter, the i-th light-emitting unit 11 of the light-emitting element string 10_j of the j-th (1≦j≦N) channel CHj will be referred to as light-emitting unit (11_j,i). In this embodiment, for the purpose of simplifying the explanation and facilitating understanding, a case will be described in which all of the light-emitting units (11_1,1) to (11_N,M) have the same size (light-emitting area).

[0022] The LCD panel 101 is divided into a plurality of M regions 102_1 to 102_M along one side (in the present embodiment, the X direction in the drawing). Here, division does not mean that the LCD panel 101 is physically divided, but rather that it is divided into virtual regions.

[0023] The LCD panel 101 has an i-th light-emitting unit (11_1, i) to (11_N, i) included in each of the N light-emitting element strings 10_1 to 10_N on one side thereof (in this embodiment), which is assigned to the i-th region 102_i and is arranged to illuminate the corresponding region 102_i. The light-emitting units (11_1, i) to (11_N, i) of each of the multiple channels CH1 to CHN assigned to the i-th region 102_i are referred to as light-emitting modules 12_i.

[0024] A dimming signal PWMCLK that indicates the brightness of the backlight is externally input to the light-emitting element drive circuit 2. The light-emitting element drive circuit 2 is configured to be able to independently turn on and off the light emission of each of the N light-emitting element strings 10_1 to 10_N in response to the dimming signal PWMCLK.

[0025] The light-emitting element driving circuit 2 includes a plurality of current drivers 3_1 to 3_N connected to the light-emitting elements of the plurality of channels, a DC / DC converter 4 configured to supply voltage to the light-emitting elements of the plurality of channels, and a controller 5 configured to control the plurality of current drivers and the DC / DC converter.

[0026] N current drivers 3_1 to 3_N are provided for each of the light-emitting element strings 10_1 to 10_N. The j-th (1≦j≦N) current driver 3_j is provided in series with the corresponding light-emitting element string 10_j. Specifically, the current driver 3_j is provided between the cathode of the corresponding light-emitting element string 10_j and the ground line. Alternatively, the current driver 3_j may be provided between the light-emitting element string 10_j and the output line of the DC / DC converter 4. The current driver 3_j supplies a drive current I LEDj The current driver 3 may be configured using known technology, and there are no limitations on its configuration.

[0027] The controller 5 controls the current drivers 3_1 to 3_N in response to the dimming signal PWMCLK to perform PWM (pulse width modulation) dimming. LED The time ratio during which the current flows is controlled.

[0028] The controller 5 can independently turn on and off each of the current drivers 3_1 to 3_N in response to the dimming signal PWMCLK for the purpose of adjusting brightness.

[0029] The DC / DC converter 4 supplies a driving voltage V between both ends of the pair of the light emitting element string 10 and the current driver 3 of each channel CH1 to CHN, that is, between the output line and the ground line. CC The capacitor C1 supplies the drive voltage V CC Suppresses ripple.

[0030] The controller 5 calculates the voltage drops of the N current drivers 3_1 to 3_N, that is, the cathode voltages V LED1 ~V LEDN The DC / DC converter 4 is controlled so that the lowest voltage among these approaches a predetermined reference voltage.

[0031] FIG. 2A is a diagram showing an example of the layout of light-emitting elements in a lighting device. FIG. 2A is a diagram showing an example of the layout when the number of channels is four. The lighting device 1 includes light-emitting element strings 10_1 to 10_4, each of which is provided for each of multiple channels CH1 to CH4, a light-emitting element drive circuit 2 that drives the light-emitting element strings 10_1 to 10_4, and a light guide plate 103. In the layout example shown in FIG. 2A, the light-emitting module 12_i is arranged to illuminate the corresponding region 102_i (see FIG. 1) and includes light-emitting elements that are part of the light-emitting element strings 10_1 to 10_4 (all light-emitting elements connected to the light-emitting element drive circuit 2) and that are included in all channels. In the layout example shown in FIG. 2A, the light-emitting elements are illustrated arranged in four rows for each of multiple channels CH1 to CH4 to make it easier to understand the electrical connection state of the light-emitting element strings 10_1 to 10_4. However, in practice, it is desirable for the light-emitting elements of multiple channels CH1 to CH4 (all light-emitting elements connected to the light-emitting element drive circuit 2) to be arranged in a single row, as shown in FIG. 2B. This makes it possible to reduce the area of ​​the substrate 6 on which the light-emitting elements of the multiple channels CH1 to CH4 (all the light-emitting elements connected to the light-emitting element drive circuit 2) are mounted. The substrate 6 is preferably a flexible circuit board. If the substrate 6 is a flexible circuit board, the process of attaching the substrate 6 to the housing of the display device 100 becomes easier.

[0032] 2A illustrates the light guide plate 103, which was omitted from FIG. 1. Each of the light emitting element strings 10_1 to 10_4 includes a plurality of LEDs connected in series, and light from the light emitting element strings 10_1 to 10_4 driven by the light emitting element drive circuit 2 is introduced from the side of the light guide plate 103, thereby making the LCD panel 101 (see FIG. 1) uniformly illuminate. The LCD panel 101 is disposed in front of the light guide plate 103 and facing the light guide plate 103. The light emitting element drive circuit 2 is housed in the semiconductor package 7. A light emitting element drive circuit 2 is exposed from the semiconductor package 7 and supplies a driving current I LED1 ~I LED4The four terminals T1 to T4 that output the drive currents are adjacent to each other. The arrangement of the terminals that output the drive currents is not limited to the example shown in FIG. 2A, but it is desirable that at least two of the terminals that output the drive currents be adjacent to each other. This makes it easier to wire between the light-emitting element drive circuit 2 and the light-emitting elements.

[0033] Even if an abnormality occurs in channel CH1 and it goes out, the remaining channels CH2 to CH4 can light up all of the divided areas. By arranging the light-emitting elements as shown in Figure 2A, even if an abnormality occurs in a channel, the entire LCD panel 101 can be illuminated, although the dimming will be darker than the target dimming.

[0034] On the other hand, if the layout of the light-emitting elements is as shown in Figure 3, when an abnormality occurs in a certain channel and the channel is turned off, a specific area will become dark. As a result, the brightness will vary depending on the location on the LCD panel 101. In view of this disadvantage, the lighting device according to the embodiment does not adopt the layout of the light-emitting elements as shown in Figure 3.

[0035] 4 is a diagram showing an example of dimming control when the dimming ratio is 90%. A dimming signal PWMCLK adjusted so that the on-duty is 90% is input to the controller 5.

[0036] The left side of Figure 4 shows the case of the conventional technology, in which the controller 5 switches the current drivers 3_1 to 3_4 ON / OFF at the same duty ratio as the dimming signal PWMCLK for all channels CH1 to CH4, with the on-duty to off-duty ratio of the duty cycle being the same as that of the dimming signal PWMCLK.

[0037] The right side of Figure 4 shows the case of a method controlled by the configuration of this embodiment, in which the ratio of on-duty to off-duty of the duty cycle is different from that of the prior art, and the dimming signal PWMCLK is different. For channels CH1 to CH3, the controller 5 turns on the current drivers 3_1 to 3_3 with an on-duty of 100%, and for channel CH4 only, it switches on / off the current driver 3_4 with an on-duty of 60%. In this case, the total on-duty of the four channels is 360%, and if the total on-duty is divided by the number of channels, 4, the dimming rate is 90%.

[0038] 4 shows a case where the number of channels is 4, but when the number of channels is N, the controller 5 is configured to switch the current driver of one channel ON / OFF in the duty cycle of the multiple current drivers and set the on-duty of the current drivers of the remaining channels to 100% when the dimming rate is a first dimming rate greater than 100×(N−1) / N% (where N is the number of channels). For example, when the number of channels is 4, the first dimming rate is greater than 75% and less than 100%.

[0039] Fig. 5 is a diagram showing an example of dimming control when the dimming ratio is 50%. The left side of Fig. 5 shows the case of the conventional technology, in which the controller 5 switches on / off the current drivers 3_1 to 3_4 of the channels CH1 to CH4 with the duty cycle having the same on-duty / off-duty ratio as the dimming signal PWMCLK, as in Fig. 4.

[0040] The right side of Figure 5 shows the case of a method controlled by the configuration of this embodiment, in which the controller 5 turns on the current drivers 3_1 to 3_2 for channels CH1 to CH2 with an on-duty of 100%, and turns off the current drivers 3_3 to 3_4 for channels CH3 to CH4 with an on-duty of 0%.

[0041] In this case, the total on-duty of the four channels is 200%, and dividing the total on-duty by the number of channels (4) results in a dimming ratio of 50%. In Figure 5, the controller is configured to control multiple current drivers so that, at the third dimming ratio, there are both channels with an on-duty of 0% and channels with an on-duty of 100%. For example, if the number of channels is four, the third dimming ratio will be 75%, 50%, 25%, etc. The third dimming ratio is a dimming ratio that is smaller than the first dimming ratio, greater than or equal to 100 / N%, and divisible by 100 / N%.

[0042] Fig. 6 is a diagram showing an example of dimming control when the dimming ratio is 0.25%. The left side of Fig. 6 shows the case of the conventional technology, in which the controller 5 switches on / off the current drivers 3_1 to 3_4 of the channels CH1 to CH4 with the duty cycle having the same ratio of on-duty to off-duty as the dimming signal PWMCLK, as in Fig. 4.

[0043] 6 shows the case of a method controlled by the configuration of this embodiment, in which the controller 5 switches the current driver 3_1 ON / OFF with a duty of 1% for the ON time of only channel CH1, and turns OFF the current drivers 3_2 to 3_4 for channels CH2 to CH4 because the ON duty is 0%. The total ON time duty of the four channels is 1%, and when the total ON time duty is divided by the number of channels, the dimming ratio is 0.25%.

[0044] 6 shows a case where the number of channels is 4, but when the minimum value of the on-duty of the dimming signal PWMCLK is 1% and the number of channels is N, the dimming ratio is 1% for the total on-time duty of the N channels, and by dividing the total on-time duty by the number of channels, the dimming ratio can be 1 / N%. In this way, the dimming ratio can be narrowed down to the value obtained by dividing the minimum value of the duty setting range for the on-time of the duty cycle by the number of channels.

[0045] 6, the controller is configured to control the current drivers so that, when the dimming ratio is a fourth dimming ratio less than 100 / N%, the current driver of one channel is switched on / off and the on-duty of the current drivers of the remaining channels is set to 0%. For example, when the number of channels is four, the fourth dimming ratio is less than 25%. The fourth dimming ratio is a dimming ratio less than 100 / N%.

[0046] Although not illustrated herein, the controller is configured to control the multiple current drivers so that, at the second dimming rate, there is a channel with a 0% on-duty, a channel with a 100% on-duty, and one channel that switches between ON and OFF. For example, if the number of channels is four, the second dimming rate is greater than 50% and less than 75%. The second dimming rate is a dimming rate that is less than the first dimming rate and greater than 100 / N% and leaves a remainder when divided by 100 / N%.

[0047] At the same dimming rate, the channel for switching the current driver ON / OFF may be fixed. In this configuration, the controller receives an abnormality detection signal output from the abnormality detection unit, determines which channel's light-emitting element has an abnormality based on the abnormality detection signal, and removes the current driver connected to the light-emitting element in which the abnormality has occurred from the candidates for lighting.

[0048] If the channel for which the current driver is switched ON / OFF is fixed at the same dimming rate, only the same channel is switched, which may result in element degradation in only a specific channel. Therefore, for example, the channel for which the current driver is switched ON / OFF may be switched each time the device is started, or at specific intervals using a counter. Alternatively, if the controller receives a frame switching signal from the display panel, the switching may be synchronized with the frame period of the display panel. If the channel for which the current driver is switched ON / OFF is switched at the same dimming rate, element degradation in only a specific channel can be reduced.

[0049] Furthermore, if an abnormality occurs, the controller may receive an abnormality detection signal output from the abnormality detection unit, as in the case of fixing the channel that switches the current driver on and off at the same dimming rate, and determine which channel's light-emitting element has an abnormality based on the abnormality detection signal, and the controller may remove the current driver connected to the light-emitting element in which the abnormality occurred from the candidates for lighting.

[0050] Figure 7 shows the load fluctuation when the dimming ratio is 20%. When the current driver is switched on, a load fluctuation of 100 mA occurs per channel. The left side of Figure 7 shows the case of conventional technology. When there are four channels, all four channels switch at the same time, so the total load is 400 mA. As shown above, with conventional technology, the larger the load fluctuation, the larger the input / output ripple voltage. This causes audible noise.

[0051] The center of Figure 7 shows the case of conventional technology (Phase Shift), which differs from the conventional technology on the left side of Figure 7 in that instead of switching all channels at the same timing, each channel is switched at a different timing. By switching each channel in this way, the total load is 100 mA, and load fluctuations are reduced. The reduced load fluctuations reduce input and output ripple voltages, reducing audible noise. However, because the number of switching operations is not reduced, a reduction in switching noise cannot be expected.

[0052] The right side of Figure 7 shows the case of a method controlled by the configuration of this embodiment, in which only one channel is switched, and the remaining channels are turned off because their on-duty is 0%. In the case of a method controlled by the configuration of this embodiment, since only one channel is switched, the total load is 100 mA. The number of switching operations can be significantly reduced compared to the case of the conventional technology (Phase Shift). As a result, audible noise can be reduced and the generation of switching noise can also be suppressed. Furthermore, if a capacitor is used to suppress ripple, the capacitance of the capacitor can be reduced, resulting in lower costs.

[0053] Figure 8 is a diagram showing a comparison with the conventional technology. To summarize the contents explained in Figure 7, in the case of the method controlled by the configuration of this embodiment, since switching is limited to one channel, load fluctuations are small and input / output ripple voltages are small. Therefore, audible noise can be suppressed and the capacitor size can be reduced. Furthermore, since the number of switching operations is small, the generation of switching noise can also be suppressed. It can be seen that there are advantages compared to the conventional technology and the conventional technology (Phase Shift). Furthermore, it is possible to expand the range of dimming ratio compared to the conventional technology.

[0054] <Other Modifications> While the above description uses PWM dimming, it is not limited to PWM dimming, and pulse modulation dimming other than PWM dimming is also acceptable. Examples of pulse modulation dimming other than PWM dimming include PFM (pulse frequency modulation) dimming and PDM (pulse density modulation) dimming. Furthermore, by combining PWM dimming and analog dimming, it is possible to further increase the contrast ratio. Taking a four-channel example, when a current of X mA flows and the on-duty of all four channels becomes the same value (e.g., 100%) as the maximum on-duty of the dimming signal PWMCLK, the current can be changed from X mA to Y mA using analog dimming to achieve even greater brightness. Note that Y can be any value greater than X.

[0055] In addition, in the case of four channels, for example, when a current of X mA flows and the total on-duty of the four channels becomes the same value as the minimum value of the on-duty of the dimming signal PWMCLK (for example, 1%), the current can be changed from X mA to Z mA by analog dimming, making it possible to make the light even darker. Note that Z can be any value smaller than X.

[0056] Next, applications of the lighting device 1 will be described. Figures 9A and 9B are diagrams showing an example of an electronic device equipped with the lighting device 1. The electronic device 200 in Figure 9A is a display device such as a television, a car navigation system, or a PC. In Figure 9B, the electronic device 200 is a tablet PC, a PDA (Personal Digital Assistant), a mobile phone terminal, or the like. The electronic device 200 includes a housing 201 and an LCD panel 101. The light-emitting element strings 10 are arranged on the back surface of the LCD panel 101 as a backlight.

[0057] In addition to the above-described embodiments, various modifications can be made to the configuration of the present invention without departing from the spirit of the invention. The above-described embodiments are illustrative in all respects and should be considered not to be limiting. The technical scope of the present invention is defined by the claims, not by the description of the above-described embodiments, and should be understood to include all modifications that fall within the meaning and scope of the claims.

[0058] The light-emitting element drive circuit described above includes a plurality of current drivers connected to the light-emitting elements of the plurality of channels, respectively, and a controller configured to control the plurality of current drivers. The controller is configured to switch the current driver of one channel ON / OFF and set the on-duty of the current drivers of the remaining channels to 100% when the dimming rate is a first dimming rate that is greater than 100×(N−1) / N% and less than 100%, where N is the number of channels of the plurality of channels (first configuration).

[0059] In addition, the light-emitting element drive circuit of the first configuration is configured such that, at a second dimming rate that is smaller than the first dimming rate but larger than 100 / N% and that produces a remainder when divided by 100 / N%, the controller controls the multiple current drivers so that there is one channel with an on-duty of 0%, one channel with an on-duty of 100%, and one channel that performs ON / OFF switching (second configuration).

[0060] In addition, in the light-emitting element drive circuit of the first or second configuration, the controller is configured to control the multiple current drivers so that, at a third dimming rate that is smaller than the first dimming rate, is equal to or greater than 100 / N%, and is divisible by 100 / N%, both a channel with an on-duty of 0% and a channel with an on-duty of 100% exist (third configuration).

[0061] In addition, in a light-emitting element drive circuit having any of the first to third configurations described above, the controller is configured to switch the current driver of one channel ON / OFF when the fourth dimming ratio is smaller than 100 / N%, and to set the on-duty of the current drivers of the remaining channels to 0% (fourth configuration).

[0062] In addition, in a light-emitting element driving circuit having any of the first to fourth configurations described above, when an abnormality occurs in a light-emitting element, the controller is configured to remove the current driver connected to the light-emitting element in which the abnormality occurred from the candidates for lighting (fifth configuration).

[0063] In addition, in the same dimming rate of any of the first to fifth configurations, the channel for switching the current driver ON / OFF is fixed (sixth configuration).

[0064] Furthermore, in the same dimming rate of any of the first to fifth configurations, the channel for switching ON / OFF of the current driver is switched (seventh configuration).

[0065] Furthermore, the light-emitting element driving circuit of the seventh configuration is configured to switch the channel that switches the current driver ON / OFF each time it is started or at specific intervals using a counter (eighth configuration).

[0066] In addition, the light-emitting element driving circuit of the seventh configuration is configured to switch the channel that switches the current driver ON / OFF in synchronization with the frame period of the display panel when the controller receives a frame switching signal from the display panel (ninth configuration).

[0067] Furthermore, the light-emitting element driving circuit having any of the first to ninth configurations is configured such that the light-emitting element driving circuit is housed in a semiconductor package, is exposed from the semiconductor package, and at least two of the multiple terminals that output each of the multiple driving currents generated by each of the multiple current drivers are adjacent to each other (tenth configuration).

[0068] The lighting device described above has a configuration (eleventh configuration) including a light-emitting element drive circuit having any one of the first to tenth configurations and the light-emitting elements of the multiple channels.

[0069] The electronic device described above has a configuration (twelfth configuration) including a display panel and the lighting device of the eleventh configuration.

[0070] Furthermore, the electronic device of the twelfth configuration is provided with a plurality of light-emitting units, the display panel is divided into a plurality of virtual areas, and each of the plurality of light-emitting units is arranged to illuminate the corresponding area, and is configured to be a part of the light-emitting elements of the plurality of channels and to have light-emitting elements of all channels (thirteenth configuration).

[0071] In addition, the electronic device having the thirteenth configuration is configured so that the light emitting elements of the plurality of channels are arranged in a row (fourteenth configuration).

[0072] The display device described above has a configuration (fifteenth configuration) including a display panel and the lighting device of the eleventh configuration.

[0073] Furthermore, the display device of the fifteenth configuration above includes a plurality of light-emitting units, the display panel is divided into a plurality of virtual areas, and each of the plurality of light-emitting units is arranged to illuminate the corresponding area, and is configured to be a part of the light-emitting elements of the plurality of channels and to have light-emitting elements of all channels (sixteenth configuration).

[0074] In addition, the display device having the sixteenth configuration is configured so that the light emitting elements of the plurality of channels are arranged in a row (seventeenth configuration).

[0075] REFERENCE SIGNS LIST 1 Lighting device 2 Light-emitting element drive circuit 3_1 to 3_N Current driver 4 DC / DC converter 5 Controller 6 Substrate 7 Semiconductor package 10_1 to 10_N Light-emitting element string 11 Light-emitting unit 12_1 to 12_M Light-emitting module 100 Display device 101 LCD panel 102_1 to 102_M Area 103 Light guide plate 200 Electronic device 201 Housing C1 Capacitor T1 to T4 Terminal

Claims

1. A plurality of current drivers connected to the light emitting elements of the plurality of channels, respectively; a controller configured to control the plurality of current drivers; Preparation, The light-emitting element drive circuit is configured such that the number of channels of the multiple channels is N, and when the dimming rate is a first dimming rate that is greater than 100×(N-1) / N% and less than 100%, the controller switches the current driver of one channel ON / OFF and sets the on-duty of the current driver of the remaining channels to 100%.

2. 2. The light-emitting element driving circuit according to claim 1, wherein the controller is configured to control the plurality of current drivers so that, at a second dimming ratio that is smaller than the first dimming ratio and larger than 100 / N%, and that produces a remainder when divided by 100 / N%, there is one channel with an on-duty of 0%, one channel with an on-duty of 100%, and one channel that performs ON / OFF switching.

3. 2. The light-emitting element driving circuit according to claim 1, wherein the controller is configured to control the plurality of current drivers so that, at a third dimming ratio that is smaller than the first dimming ratio, is equal to or greater than 100 / N%, and is divisible by 100 / N%, the on-duty of the current driver of at least one channel is set to 0% and the on-duty of the current driver of the remaining channels is set to 100%.

4. 2. The light-emitting element driving circuit according to claim 1, wherein the controller is configured to switch the current driver of one channel ON / OFF and set the on-duty of the current driver of the remaining channels to 0% when the fourth dimming ratio is smaller than 100 / N%.

5. The light-emitting element drive circuit according to claim 1 , wherein, when an abnormality occurs in the light-emitting element, the controller is configured to exclude the current driver connected to the light-emitting element in which the abnormality occurs from candidates for lighting.

6. The light-emitting element driving circuit according to claim 1 , wherein the light-emitting element driving circuit is configured to fix a channel for switching the current driver ON / OFF at the same dimming rate.

7. The light-emitting element driving circuit according to claim 1 , configured to switch a channel for switching ON / OFF of the current driver at the same dimming rate.

8. 8. The light-emitting element drive circuit according to claim 7, configured to switch a channel for switching the current driver ON / OFF every time the circuit is started or every specific period by using a counter.

9. 8. The light-emitting element driving circuit according to claim 7, configured to switch a channel for switching ON / OFF of the current driver in synchronization with a frame period of the display panel when the controller receives a frame switching signal from the display panel.

10. The light emitting element driving circuit is accommodated in a semiconductor package, 2 . The light-emitting element drive circuit according to claim 1 , wherein at least two of a plurality of terminals exposed from the semiconductor package and outputting a plurality of drive currents generated by each of the plurality of current drivers are adjacent to each other.

11. A light emitting element drive circuit according to any one of claims 1 to 10; The multi-channel light-emitting element; A lighting device comprising:

12. A display panel; A lighting device according to claim 11; An electronic device comprising:

13. Equipped with a plurality of light emitting units, The display panel is divided into a plurality of virtual regions; The electronic device according to claim 12 , wherein each of the plurality of light-emitting units is arranged to illuminate the corresponding area, and includes light-emitting elements that are a part of the light-emitting elements of the plurality of channels and include light-emitting elements of all the channels.

14. The electronic device according to claim 13 , wherein the light emitting elements of the multiple channels are arranged in a row.

15. A display panel; A lighting device according to claim 11; A display device comprising:

16. Equipped with a plurality of light emitting units, The display panel is divided into a plurality of virtual regions; The display device according to claim 15 , wherein each of the plurality of light-emitting units is arranged to illuminate the corresponding area, and includes light-emitting elements that are a part of the light-emitting elements of the plurality of channels and include light-emitting elements of all the channels.

17. 17. The display device of claim 16, wherein the multi-channel light emitting elements are aligned in a row.