Light emission control device and light emission control method

Abstract

This invention aims to stabilize LED current values ​​and light emission while suppressing the increase in circuit size during LED light emission control. [Solution] This light-emitting control device includes multiple rows of light-emitting elements arranged in parallel and driven by a power supply circuit. The light-emitting control device also includes multiple switching elements corresponding to each of the multiple rows of light-emitting elements, which control the current flowing through each of the multiple rows of light-emitting elements to be on or off. Furthermore, the light-emitting control device includes a single constant current circuit that is commonly connected to one end of the multiple-row circuit including each of the multiple rows of light-emitting elements and each of the multiple switching elements, and controls the current value of each of the multiple switching elements when they are on.

Description

Technical Field

[0001] The present invention relates to a light emission control device and a light emission control method.

Background Art

[0002] In a Light Emitting Diode (LED) backlight of a liquid crystal display, usually, a plurality of LED columns connected in series are connected in parallel in a plurality of rows (for example, Patent Document 1 below). An LED lighting circuit for driving such an LED column is composed of a power supply circuit (boost circuit or buck-boost circuit) for supplying a voltage upstream of the LED, a constant current circuit for driving the LED with a constant current, and the like. In a conventional LED lighting circuit, a constant current circuit is provided for each LED column. Then, the LED lighting circuit controls the LED current by two dimming methods, PWM dimming by a Duty signal from a control unit and Direct Current (DC) dimming for controlling the LED current value by an analog voltage signal or a Duty signal, and adjusts the brightness.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, when a constant current circuit is provided for each LED column, the circuit becomes large. An aspect of the disclosed embodiment is to stabilize the LED current value and light emission while suppressing the increase in the size of the circuit in the light emission control of the LED.

Means for Solving the Problems

[0005] Embodiments of the disclosure are exemplified by a light emission control device. This light emission control device includes a power supply circuit that drives multiple rows of light-emitting elements in parallel. The light emission control device also includes a plurality of switching elements corresponding to each of the multiple rows of light-emitting elements that control the current flowing through each of the multiple rows of light-emitting elements to be on or off. Furthermore, the light emission control device includes a single constant current circuit that is commonly connected to one end of the multi-row circuit including each of the multiple rows of light-emitting elements and each of the plurality of switching elements, and controls the current value of each of the plurality of switching elements when they are on. [Effects of the Invention]

[0006] In this light emission control device, there is a single constant current circuit, which is commonly connected to one end of the multiple rows of circuits, each containing a light-emitting element arranged in multiple rows and each of the multiple switching elements. Therefore, this light emission control device controls the current value of each of the multiple switching elements when they are turned on using this single constant current circuit, thereby stabilizing the LED current value and light emission while suppressing the increase in the size of the circuit in LED light emission control. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a circuit diagram illustrating a comparative example of a light emission control device. [Figure 2] Figure 2 illustrates the duty cycle and current values ​​of the current flowing through each LED row in the light-emitting control device shown in Figure 1. [Figure 3] Figure 3 is a circuit diagram illustrating one embodiment of a light emission control device. [Figure 4] Figure 4 illustrates the duty cycle and current values ​​of the current flowing through each LED in the light-emitting control device shown in Figure 3. [Figure 5] Figure 5 illustrates the duty cycle and current values ​​of the current flowing through each LED row in the light-emitting control device shown in Figure 3. [Figure 6] Figure 6 is an example illustrating the screen brightness state shown in Figure 5. [Figure 7] Figure 7 illustrates the duty cycle and current values ​​of the current flowing through each LED row in the light-emitting control device shown in Figure 3. [Figure 8] Figure 8 illustrates the screen brightness state shown in Figure 7. [Figure 9] Figure 9 is a diagram illustrating the duty cycle and current value of the current flowing through each LED row as an example of the operation of the light emission control device 1. [Figure 10] Figure 10 is a diagram illustrating the duty cycle and current value of the current flowing through each LED row as an example of the operation of the light emission control device 1. [Figure 11] Figure 11 is an example illustrating the screen brightness state shown in Figure 10. [Figure 12] Figure 12 is a diagram illustrating the duty cycle and current value of the current flowing through each LED row as an example of the operation of the light emission control device 1. [Figure 13] Figure 13 is an example illustrating the screen brightness state shown in Figure 12. [Modes for carrying out the invention]

[0008] Hereinafter, with reference to the drawings, a light emission control device 1 and a light emission control method according to one embodiment will be described.

[0009] <Comparative Example> Figure 1 is a circuit diagram illustrating a comparative example of a light emission control device 501. The light emission control device 501 drives LEDs, which are light-emitting elements arranged in multiple rows (for example, four rows from L1 to L4), in parallel. The light emission control device 501 includes a power supply circuit 511, a control unit 512, switches S1 to S4, and constant current sources I1 to I4. In Figure 1, the constant current sources I1 to I4 are assumed to supply constant currents with current values ​​I1 to I4.

[0010] The LED columns (L1 to L4) may each be a single LED or a plurality of LEDs connected in series. In the LED columns (L1 to L4), the input terminal AN to which a high voltage (or a positive voltage) is supplied is connected to the same terminal of the power supply circuit 511 and is supplied with the power supply voltage VH. Note that the input terminal AN may sometimes be called an anode.

[0011] On the other hand, in the LED columns (L1 to L4), the output terminals CT (CT1 to CT4) of the other ends with respect to the input terminal AN may sometimes be called cathodes. The power supply circuit 511 is supplied with the input voltage VIN and the reference voltage VREF in order to generate the power supply voltage VH.

[0012] That is, the power supply circuit 511 is supplied with the voltage VIN from the external power supply 502 and supplies the power supply voltage VH to each input terminal AN of the LED columns (L1 to L4). Here, when each input terminal AN of the LED columns (L1 to L4) is distinguishable, they are called AN1 to AN4.

[0013] Also, the power supply circuit 511 has an error amplifier circuit inside, and voltages VL1 to VL4 are input from the output terminals CT1 to CT4 of each of the LED columns (L1 to L4). Since the input of the error amplifier circuit is a high impedance when viewed from the output terminals CT1 to CT4, almost no current flows from the output terminals CT1 to CT4 into the power supply circuit 511.

[0014] Also, the output terminals CT of each of the LED columns (L1 to L4) are connected to the constant current sources I1 to I4 respectively via the switches S1 to S4 respectively. As described above, since almost no current flows from the output terminals CT1 to CT4 into the power supply circuit 511, each of the LED columns (L1 to L4) and the corresponding switches S1 to S4 form a series circuit. And the switches S1 to S4 are turned on or off Then, the current flowing through each of the LED columns (L1 to L4) is controlled to be on or off. Therefore, the switches S1 to S4 control the period during which the current flows through each of the LED columns (L1 to L4). The switches S1 to S4 are semiconductor elements such as transistors, for example.

[0015] On the other hand, the constant current sources I1 to I4 control the constant current (I1 to I4) to flow through the LED columns (L1 to L4) corresponding to the on switches S1 to S4 among the LED columns (L1 to L4). Therefore, the constant current sources I1 to I4 control the peak value of the current flowing through each of the LED columns (L1 to L4).

[0016] The control unit 512 executes the on / off control of the switches S1 to S4 and the designation of the current values of the constant current sources I1 to I4. The control unit 512 controls the duty ratio of the current flowing through each of the LED columns (L1 to L4) by controlling the on / off of the switches S1 to S4.

[0017] In the example of FIG. 1, the control unit 512 controls the on / off of the switches S1 to S4 by a single, that is, the same control signal (Duty). The control unit 512 controls the light emission amount or luminance of each of the LED columns (L1 to L4) by controlling the duty ratio of the current flowing through each of the LED columns (L1 to L4). The control of the light emission amount or luminance by controlling the duty ratio is called Pulse Width Modulation (PWM) dimming.

[0018] Further, the control unit 512 controls the peak value of the current flowing through each of the LED columns (L1 to L4) by changing the current values of the constant current sources I1 to I4. The control unit 512 controls the light emission amount or luminance of each of the LED columns (L1 to L4) by controlling the peak value of the current. The control of the light emission amount or luminance by controlling the peak value is called DC dimming or analog dimming (ADIM). Hereinafter, in the present embodiment, the control signal for DC dimming is called the LED current control signal ADIM. For the sake of, the control signal is called the LED current control signal ADIM.

[0019] Figure 2 illustrates the duty cycle and current values ​​of the current flowing through each LED row (L1 to L4) in Figure 1. In the example in Figure 2, switches S1 to S4 are all controlled with the same duty cycle (see Duty). The peak values ​​of the currents (IL1 to IL4) flowing through each LED row (L1 to L4) are I1 to I4. However, the peak values ​​of the currents (IL1 to IL4) flowing through each LED row (L1 to L4) may be the same.

[0020] As shown in Figure 1, if the output terminals CT1 to CT4 of each LED row (L1 to L4) are connected to constant current sources I1 to I4 via switches S1 to S4 respectively, there is a problem that the circuit size of the light emission control device 501 becomes large. In the following embodiment, a light emission control device 1 that can reduce the circuit size compared to the example in Figure 1 is illustrated.

[0021] <First Embodiment> (Configuration) Figure 3 is a circuit diagram illustrating the light emission control device 1 of this embodiment. Similar to Figure 1, the light emission control device 1 drives LEDs, which are light-emitting elements arranged in multiple rows (for example, four rows from L1 to L4), in parallel. The light emission control device 1 includes a power supply circuit 11, a control unit 12, switches S1 to S4, and a constant current source I0. In Figure 3, the constant current source I0 is assumed to supply a constant current with a current value I0. That is, the configuration of the light emission control device 1 differs from the light emission control device 501 in Figure 1, which has constant current sources I1 to I4, in that the constant current source I0 is a single unit.

[0022] The LED array (L1 to L4) in Figure 3 is an example of multiple light-emitting elements arranged in parallel and driven by the power supply circuit 11. Each LED array (L1 to L4) may be a single LED or multiple LEDs connected in series. In Figure 3, as in Figure 1, a high voltage (or positive voltage) is provided to the LED array (L1 to L4). The input terminal AN is connected to the same terminal of the power supply circuit 11 and supplied with the power supply voltage VH. The power supply circuit 11 is supplied with the input voltage VIN and the reference voltage VREF in order to generate the power supply voltage VH.

[0023] In other words, the power supply circuit 11 is supplied with a voltage VIN from an external power supply 2 and supplies the power supply voltage VH to each input terminal AN (AN1 to AN4) of the LED row (L1 to L4). Also, like the power supply circuit 511 in Figure 1, the power supply circuit 11 has an internal error amplifier circuit and receives voltages VL1 to VL4 from each output terminal CT1 to CT4 of the LED row (L1 to L4). Since the input to the error amplifier circuit is high impedance when viewed from the output terminals CT1 to CT4, almost no current flows from the output terminals CT1 to CT4 to the power supply circuit 11.

[0024] In Figure 3, the output terminals CT1 to CT4 of each LED row (L1 to L4) are connected to a single, identical constant current source I0 via switches S1 to S4. As described above, since almost no current flows from the output terminals CT1 to CT4 to the power supply circuit 11, each LED row (L1 to L4) and its corresponding switch S1 to S4 form a series circuit of multiple rows. The single constant current source I0 is then connected to one end of this series circuit of multiple rows.

[0025] Therefore, switches S1 to S4 control the current flowing through each of the LED rows (L1 to L4) by being turned on or off. In other words, as in the case of Figure 1, switches S1 to S4 control the duration for which current flows through each of the LED rows (L1 to L4). That is, as an example of a switching element, switches S1 to S4 control the current flowing through each of the multiple rows of LEDs (L1 to L4) by turning them on or off. It can also be said that switches S1 to S4 are provided in correspondence to each of the multiple rows of LEDs (L1 to L4).

[0026] On the other hand, the first terminal on the upstream side of the constant current source I0 is commonly connected to the downstream terminals of multiple switches S1 to S4. Also, the second terminal on the downstream side of the constant current source I0 is grounded. The constant current source I0 controls the LED array (L1 to L4) so ​​that a constant current (I0) flows through the LED array (L1 to L4) whose corresponding switches S1 to S4 are turned on. In other words, as an example of a single constant current circuit, the constant current source I0 controls the current value of each LED array (L1 to L4) when it is turned on. Therefore, the constant current source I0 controls the peak value of the current flowing through each LED array (L1 to L4) to a constant current (I0). The control unit 12 controls the on / off state of switches S1 to S4 and specifies the current value of the constant current source I0.

[0027] However, in the example shown in Figure 3, the control unit 12, as an example of a control circuit, independently and individually controls the on / off state of each switch S1 to S4 using separate DUTY control signals D1 to D4. That is, the control unit 12 individually controls the duty cycle of the current flowing through each LED row (L1 to L4) by controlling the on / off state of switches S1 to S4.

[0028] Therefore, the control unit 12 controls the amount of light emitted or brightness of each LED row (L1 to L4) individually by controlling the duty cycle of the current flowing through each LED row (L1 to L4).

[0029] Furthermore, the control unit 12 controls the peak value of the current flowing through each LED string (L1 to L4) by changing the current value of the constant current source I0. That is, as in Figure 1, the control unit 12 controls the peak value of the current to control the amount of light emitted or brightness of each LED string (L1 to L4). Control the degree.

[0030] (Example of operation 1) Figure 4 illustrates the duty cycle and current values ​​of the current flowing through each LED sequence (L1 to L4) as an example of the operation of the light emission control device 1. In Figure 4, the horizontal axis represents time, and the vertical axis represents the control signal value or the current values ​​flowing through each LED sequence (L1 to L4).

[0031] In the example shown in Figure 4, during periods T1 to T4, switches S1 to S4 operate according to the duty cycles specified by the duty signals D1 to D4, respectively. Here, D1 to D4 are merely illustrative examples of their duty cycles. Period T5 is the same as period T1.

[0032] Then, during each period T1 to T4, a current flows at peak value I0 in the LED strings (L1 to L4) corresponding to each period. Comparing Figure 4 with Figure 2, in Figure 4, the LED strings (L1 to L4) do not all light up simultaneously, but each lights up individually during periods T1 to T5.

[0033] Therefore, if the current values ​​I1 to I4 in Figure 2 are the same as I0, the amount of light emitted in Figure 4 will be 1 / 4 of that in Figure 2. Conversely, if I0 in Figure 4 is four times the current values ​​I1 to I4 in Figure 2, the amount of light emitted will be the same as in Figure 2. However, since the constant current source I0 is alone in Figure 4, the light emission control device 1 can have a smaller circuit size than the light emission control device 501.

[0034] (Example of operation 2) Figure 5 illustrates the duty cycle and current values ​​of the current flowing through each LED sequence (L1 to L4) as an example of the operation of the light emission control device 1. In Figure 5, the horizontal axis represents time, and the vertical axis represents the control signal value or the current values ​​flowing through each LED sequence (L1 to L4).

[0035] In the example in Figure 5, during periods T1 to T5, switches S1 to S4 and S1 operate with duty cycles of 100%, 50%, 50%, 25%, and 100%, respectively. During each of periods T1 to T5, a current with peak value I0 flows through the corresponding LED arrays (L1 to L4). Therefore, the amount of light emitted from LED array L1 during period T1 is halved from LED array L2 or L3 during period T2 or T3. Similarly, the amount of light emitted from LED array L4 during period T4 is 1 / 4 of the amount of light emitted from LED array L1 during period T1. The process in Figure 5 is an example of controlling the ratio of the periods when each of multiple switching elements is individually on and off.

[0036] Figure 6 illustrates the screen brightness state due to the LED array (L1 to L4). Figure 6 illustrates the regions AR1 to AR4 illuminated by the light emitted by the LED array (L1 to L4). There are no limitations to regions AR1 to AR4. Regions AR1 to AR4 may also be regions of the liquid crystal illuminated by the backlight. In Figure 6, regions AR1 to AR4 correspond, for example, to the current values ​​IL1 to IL4 of the LED array (L1 to L4) in Figure 5, and to duty cycles of 100%, 50%, 50%, and 25%. Therefore, the light emission control device 1 can supply light at different brightness levels for each time period and region by controlling switches S1 to S4 and the constant current source I0 as shown in Figure 5.

[0037] (Example of operation 3) Figure 7 illustrates the duty cycle and current values ​​of the current flowing through each LED row (L1 to L4) as an example of the operation of the light emission control device 1. In Figure 7 as well, the horizontal axis is time. The vertical axis illustrates the value of the control signal or the current flowing through each LED row (L1 to L4).

[0038] In the example shown in Figure 7, during periods T1 to T5, switches S1 to S4 and S1 operate with duty cycles of 100%, 50%, 50%, 25%, and 100%, respectively. Also, during periods T1 to T5, currents IL1 to IL4 and IL1 flow through the LED rows (L1 to L4), with peak values ​​of 100%, 100%, 50%, and 25% of I0, respectively. Therefore, the light emission of LED row L1 during period T1 is 50% of that of LED row L2 during period T2, 25% of that of LED row L3 during period T3, and 6.25% of that of LED row L4 during period T4.

[0039] Figure 8 illustrates the screen brightness state due to the LED array (L1 to L4). Figure 8 illustrates regions AR1 to AR4 illuminated by the light emitted by the LED array (L1 to L4). There are no limitations to regions AR1 to AR4. Regions AR1 to AR4 may also be regions of the liquid crystal illuminated by the backlight. In Figure 8, regions AR1 to AR4 correspond, for example, to the current values ​​IL1 to IL4 of the LED array (L1 to L4) in Figure 7, and the brightness corresponds to 100%, 50%, 25%, and 6.25%. Therefore, the light emission control device 1 can supply light at different brightness levels for each time period and region by controlling switches S1 to S4 and the constant current source I0 as shown in Figure 7.

[0040] (Effects of the first embodiment) As described above, in this embodiment, the light emission control device 1 has a power supply circuit 11 that drives multiple rows of LEDs (L1 to L4) in parallel and controls the light emission of the LEDs (L1 to L4). That is, the light emission control device 1 has multiple switches S1 to S4 corresponding to each of the multiple rows of LEDs (L1 to L4). The light emission control device 1 controls the current flowing through each of the multiple rows of LEDs (L1 to L4) to turn on or off.

[0041] In this configuration, the light emission control device 1 is equipped with a single constant current source I0 that is commonly connected to one end of the multiple rows of circuits, each of which includes multiple rows of LEDs (L1 to L4) and multiple switches S1 to S4. The constant current source I0 controls the current value of each of the multiple switches S1 to S4 when they are turned on. As a result, the light emission control device 1 can have a smaller circuit size compared to the light emission control device 501 in Figure 1.

[0042] Furthermore, in Figure 3, the first terminal on the upstream side of the single constant current source I0 is commonly connected to the downstream terminals of multiple switches S1 to S4. Also, the second terminal on the downstream side of the constant current source I0 is grounded. Each of the multiple switches S1 to S4 is provided between the downstream terminals (CT1 to CT4) of each of the multiple rows of LEDs (L1 to L4) and the first terminal on the upstream side of the single constant current source I0. As a result, the light emission control device 1 can stably control the single constant current source I0 at a potential close to ground.

[0043] Furthermore, the light emission control device 1 includes a control unit 12 that individually controls each of the multiple rows of LEDs (L1 to L4) using DUTY control signals D1 to D4 and an LED current control signal ADIM. Therefore, as illustrated in Figures 4, 5, and 7, the light emission control device 1 can individually control the duty cycle and peak value of each of the multiple rows of LEDs (L1 to L4) in separate periods T1 to T4 on the time axis.

[0044] Furthermore, the control unit 12 individually turns on each of the multiple rows of LEDs (L1 to L4) to power each of the LED rows (L1 to L4) in a time-division manner to create a single constant current source I It connects to 0. Therefore, the light emission control device 1 can flexibly control each of the LED rows (L1 to L4) with respect to time.

[0045] Furthermore, the control unit 12 controls the brightness of each LED row (L1 to L4) by individually controlling the current (IL1 to IL4) of each of the multiple rows of LEDs (L1 to L4) using the DUTY control signals D1 to D4 and the LED current control signal ADIM. Therefore, the light emission control device 1 can flexibly control the brightness of each LED row (L1 to L4) over time.

[0046] <Second Embodiment> The second embodiment will now be described with reference to Figures 9 to 13. In the second embodiment, the configuration of the light emission control device 1 is the same as in Figure 3. However, in the second embodiment, in addition to the operation examples 1 to 3 in the first embodiment, operation examples 4 to 6 are added below.

[0047] (Example of operation 4) Figure 9 illustrates the duty cycle and current values ​​of the current flowing through each LED row (L1 to L4) as an example of the operation of the light emission control device 1. In Figure 9, the horizontal axis represents time, and the vertical axis represents the values ​​of the control signals (D1 to D4) or the current values ​​flowing through each LED row (L1 to L4).

[0048] In the examples shown in Figures 4, 5, and 7 illustrating operation examples 1 to 3 of the first embodiment described above, switches S1 to S4 switch according to the duty cycles determined by the DUTY control signals D1 to D4 during periods T1 to T4, respectively. That is, during periods T1 to T4, the control unit 12 repeatedly generates pulse signals multiple times, inputs them to switches S1 to S4, and switches them on and off repeatedly.

[0049] On the other hand, in operation example 4 of this embodiment, the control unit 12 assigns one control signal (D1 to D4) to each of the periods T1 to T4. The control unit 12 then turns on one of each of the control signals (D1 to D4) in sequence, only once for a period of time Ton from the start of each corresponding period T1 to T4. As shown in Figure 9, the length of each period T1 to T4 is T. Therefore, in each of the periods T1 to T4, after the time Ton has elapsed, the control signals (D1 to D4) are turned off. Then, the same operation is repeated in the periods T5 to T8.

[0050] In the example in Figure 9, the duration Ton for which the control signals (D1 to D4) are ON is common, and the current values ​​flowing through the LED array (L1 to L4) when switches S1 to S4 by the constant current source I0 are ON are common, for example, in terms of peak value I0. Therefore, in the operation example in Figure 9, as in Figure 4, the brightness of the light emitted by the LED array (L1 to L4) is common, and the brightness (screen brightness) in the area illuminated by the LED array (L1 to L4) (for example, AR1 to AR4 in Figures 6, 8, and 11) is also common. Compared to Figure 2, in the example in Figure 9, one of the control signals (D1 to D4) is ON in each of the periods T1 to T4. For this reason, even if the peak values ​​(e.g. I0) of each current IL1 to IL4 in Figure 9 are the same as in Figure 2, and the duty cycle is the same, the brightness of the light emitted by the LED array (L1 to L4) in Figure 9 is 1 / 4 of that in Figure 2.

[0051] (Example of operation 5) Figure 10 illustrates the duty cycle and current value of the current flowing through each LED string (L1 to L4) as an example of the operation of the light emission control device 1. In Figure 10, the horizontal axis is time, and the vertical axis is the value of the control signals (D1 to D4) or the current flowing through each LED string (L1 to L4). Let's look at an example of current values. In Figure 10, the current values ​​flowing through the LED array (L1 to L4) with switches S1 to S4 turned on by the constant current source I0 are common, for example, at the peak value (e.g., I0).

[0052] However, in Figure 10, the duration for which the control signals (D1 to D4) are turned on differs for each period T1 to T4, as shown by lengths Ton1 to Ton4. Let the total duration of each period T1 to T4 be length T. We will call the ratio of the duration for which the control signals (D1 to D4) are turned on (lengths Ton1 to Ton4) to the total duration T the duty cycle. For example, the duty cycles for periods T1 to T4 are Ton1 / T (=20%), Ton2 / T (=40%), Ton3 / T (=60%), and Ton4 / T (=100%). Then, the same operation is repeated for periods T5 to T8.

[0053] Figure 11, similar to Figure 6 of the first embodiment, illustrates the screen brightness state due to the LED array (L1 to L4). Specifically, Figure 11 illustrates regions AR1 to AR4 illuminated by the light emitted by the LED array (L1 to L4). In Figure 11, regions AR1 to AR4 correspond to, for example, the current values ​​IL1 to IL4 of the LED array (L1 to L4) in Figure 10, and the screen brightness corresponds to duty cycles of 20%, 40%, 60%, and 100%. Therefore, the light emission control device 1 can supply light with different brightness levels for each time period and region by controlling switches S1 to S4 and the constant current source I0 as shown in Figure 10, similar to Figure 6 of the first embodiment.

[0054] (Example of operation 6) Figure 12 illustrates the duty cycle and current values ​​of the current flowing through each LED row (L1 to L4) as an example of the operation of the light emission control device 1. In Figure 11 as well, the horizontal axis represents time, and the vertical axis illustrates the value of the control signal or the current values ​​flowing through each LED row (L1 to L4).

[0055] In the example shown in Figure 12, during periods T1 through T4, switches S1 through S4 are turned on with duty cycles Tn1 / T (=20%), Tn2 / T (=40%), Tn3 / T (=60%), and Tn4 / T (=100%), respectively. Also, during periods T1 through T4, currents IL1 through IL4 flow through the LED trains (L1 through L4) with peak values ​​of, for example, 25%, 50%, 75%, and 100% of I0. Therefore, the light emission of LED train L1 in period T1 is 5% of the light emission of LED train L4 in period T4, the light emission of LED train L2 in period T2 is 20%, and the light emission of LED train L3 in period T3 is 45%. Then, the same operation is repeated during periods T5 through T8.

[0056] Figure 13, similar to Figure 8 of the first embodiment, illustrates the screen brightness state due to the LED array (L1 to L4). That is, Figure 13 illustrates regions AR1 to AR4 illuminated by the light emitted by the LED array (L1 to L4). There are no limitations to regions AR1 to AR4. Regions AR1 to AR4 may also be regions of liquid crystal illuminated by the backlight. In Figure 13, regions AR1 to AR4 correspond, for example, to the current values ​​IL1 to IL4 of the LED array (L1 to L4) in Figure 12, and the screen brightness corresponds to 5%, 20%, 45%, and 100%. Therefore, the light emission control device 1 can supply light at different brightness levels for each time period and region by controlling switches S1 to S4 and a constant current source I0 (see Figure 3) as shown in Figure 12. (Effects of the second embodiment) As described above, in this embodiment, the control unit 12 of the light emission control device 1 assigns one control signal (D1 to D4) to each of the periods T1 to T4, as shown in Figures 9, 10, and 12. The control unit 12 then turns on one of each of the control signals (D1 to D4) in sequence, once for a predetermined time from the start of each corresponding period T1 to T4. Through this operation, the light emission control device 1 operates in the same way as in the first embodiment, for each time period and region. Light can be supplied at different brightness levels. However, in operations 4 to 6 of this embodiment, compared to the switching operation of the first embodiment, the number of times switches S1 to S4 are turned on and off in each period (T1 to T8, etc.) is limited to one. As a result, if the total control period (T1+T2+T3+T4) for all rows is the same, operations 4 to 6 are different from operations 1 to 3 in terms of each control signal Because the frequency of the signal is low, the minimum duty cycle can be reduced, which means that the range of screen brightness adjustment can be widened.

[0057] (Variation 1) In the first and second embodiments described above, light emission from four rows of LEDs (L1 to L4) was illustrated. However, the number of LED rows is not limited to four. In other words, the light emission control device 1 only needs to drive two or more rows of LEDs.

[0058] (Modification 2) In the first and second embodiments described above, as shown in Figure 3, the control unit 12 of the light emission control device 1 controlled the current value (peak value) of the constant current source I0 using the LED current control signal ADIM. Here, the LED current control signal ADIM may be a normal DC analog signal. However, the LED current control signal ADIM may also be a PWM signal. The control unit 12 may also input a digital signal to the constant current source I0 to generate the LED current control signal ADIM. Then, the LED current control signal ADIM may be generated from the input digital signal in the constant current source I0, and the constant current source I0 may be controlled. [Explanation of Symbols]

[0059] 1,501 Light emission control device 2, 502 power supply 11, 511 Power supply circuit 12, 512 Control Unit

Claims

1. A power supply circuit that drives multiple rows of light-emitting elements in parallel, A plurality of switching elements corresponding to each of the multiple rows of light-emitting elements that control the current flowing through each of the multiple rows of light-emitting elements to be turned on or off, The system comprises a single constant current circuit that is commonly connected to one end of the multi-row circuit including each of the multiple light-emitting elements arranged in the multi-row and each of the multiple switching elements, and controls the current value of each of the multiple switching elements when they are turned on. Light emission control device.

2. The first terminal of the constant current circuit is connected in common to the downstream terminals of the plurality of switching elements, and the second terminal of the constant current circuit is grounded. Each of the plurality of switching elements is provided between each of the plurality of light-emitting elements arranged in multiple rows and the first terminal, according to claim 1. Light emission control device.

3. The claim 1 further comprises a control circuit for individually controlling each of the plurality of switching elements. Light emission control device.

4. The control circuit connects each of the light-emitting elements to the constant current circuit in a time-division manner by individually turning on each of the plurality of switching elements, as described in claim 3. Light emission control device.

5. The control circuit controls the brightness of each of the light-emitting elements by controlling the ratio of the period during which each of the plurality of switching elements is individually turned on to the period during which each of them is turned off, as described in claim 3. Light emission control device.

6. A single constant current circuit, commonly connected to one end of a multi-row circuit including multiple switching elements corresponding to each of the multiple rows of light-emitting elements arranged in multiple rows and each of the multiple rows of light-emitting elements, controls the current flowing through each of the multiple rows of light-emitting elements, which are driven in parallel by a power supply circuit, thereby controlling the current value of each of the multiple switching elements when they are on. To individually control each of the aforementioned multiple switching elements and to perform the following: Light emission control method.

7. The claim in claim 6, which connects each of the light-emitting elements to the constant current circuit in a time-division manner by individually turning on each of the plurality of switching elements. Light emission control method.

8. The brightness of each of the light-emitting elements is controlled by controlling the ratio of the period during which each of the plurality of switching elements is individually turned on to the period during which each of them is turned off, as described in claim 6. Light emission control method.

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