lighting control device

Abstract

This lighting control device (10) drives a plurality of semiconductor light sources (20) connected in series, including a headlight and a signal light. A lighting control circuit (12) of a lighting control device (10) drives a plurality of semiconductor light sources (20) via pulse width modulation (PWM) control for periodically supplying the output voltage of a switching power source (11) to the plurality of semiconductor light sources (20), and controls the width of the period during which the output voltage of the switching power source (11) is supplied to each of the plurality of semiconductor light sources (20) in each cycle of PWM control, thereby controlling the amount of light emitted from each of the plurality of semiconductor light sources (20). The lighting control circuit (12) divides the plurality of semiconductor light sources (20) into a plurality of groups and divides the period of PWM control into a plurality of partial intervals assigned to each of the plurality of groups, thereby dividing the period in which the output voltage of the switching power source (11) is supplied among the groups.

Description

[Technical Field]

[0001] The present disclosure relates to a lighting control device that controls the lighting of a plurality of semiconductor light sources. [Background technology]

[0002] Vehicles that use semiconductor light sources configured with semiconductor light emitting elements such as LEDs (light emitting diodes) and LDs (semiconductor lasers) in lighting devices such as headlights and signal lights are becoming widespread. For example, Patent Document 1 listed below discloses a lighting control device for vehicles that controls multiple semiconductor light sources.

[0003] In the technology of Patent Document 1, multiple semiconductor light sources are connected in series and driven by PWM (Pulse Width Modulation) control, in which voltage is supplied periodically. In PWM control, the light emission amount of each semiconductor light source is controlled by controlling the width of the period during which voltage is supplied to each semiconductor light source in each period (so-called "duty ratio").

[0004] Here, a voltage drop occurs in the semiconductor light source when it is turned on, but by connecting multiple semiconductor light sources in series and performing constant current control using a switching power supply as in Patent Document 1, it is possible to simultaneously turn on multiple semiconductor light sources with one switching power supply. In other words, under PWM control, the periods during which voltage is supplied to each semiconductor light source can be made to overlap with each other. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6916668 Summary of the Invention [Problem to be solved by the invention]

[0006] As vehicle lighting systems increasingly use semiconductor light sources, the number of semiconductor light sources installed in vehicles is increasing. Meanwhile, the amount of heat generated by lighting systems is also increasing. This has led to a demand for smaller lighting control devices to enable headlight designs that were previously unavailable with halogen headlights. The technology described in Patent Document 1 allows the periods during which voltage is supplied to each semiconductor light source to overlap, ensuring a period during which voltage is supplied to each semiconductor light source, even if the number of semiconductor light sources increases, thereby achieving the required light output. However, as the number of semiconductor light sources that are turned on simultaneously increases, the voltage drop increases. This necessitates either preparing a switching power supply with a higher maximum output voltage or increasing the number of switching power supplies, which increases the heat generated by the lighting control device and increases its size.

[0007] The present disclosure has been made to solve the above-mentioned problems, and aims to ensure the necessary amount of light emission while suppressing voltage drops that occur in the multiple semiconductor light sources in a light source lighting device that drives multiple semiconductor light sources connected in series. [Means for solving the problem]

[0008] A lighting control device according to the present disclosure includes a switching power supply that supplies voltage to a plurality of semiconductor light sources connected in series, including headlights and signal lights; a lighting control circuit that drives the plurality of semiconductor light sources by PWM (Pulse Width Modulation) control, which periodically supplies the output voltage of the switching power supply to the plurality of semiconductor light sources, and controls the width of the period during which the output voltage of the switching power supply is supplied to each of the plurality of semiconductor light sources in each cycle of the PWM control, thereby controlling the amount of light emitted by each of the plurality of semiconductor light sources; a smoothing capacitor that is connected to an output terminal of the switching power supply and smooths the output voltage of the switching power supply; and a discharge circuit that discharges residual charge stored in the smoothing capacitor at the output terminal of the switching power supply, wherein the lighting control circuit divides the plurality of semiconductor light sources into a plurality of groups and divides the cycle of the PWM control into a plurality of partial sections assigned to each of the plurality of groups, thereby dividing the period during which the output voltage of the switching power supply is supplied for each group; Multiple PWM control periods subinterval eachWhen the lighting period of the semiconductor light source ends, the residual charge in the output terminal of the switching power supply is discharged. [Effects of the Invention]

[0009] According to the lighting control device of the present disclosure, the lighting periods of multiple semiconductor light sources are divided into groups, which reduces the number of semiconductor light sources that are turned on simultaneously and suppresses voltage drops. Furthermore, within a partial section, the lighting periods of each semiconductor light source can overlap with each other, ensuring the length of the lighting period of each semiconductor light source and achieving the required light emission amount.

[0010] The objects, features, aspects, and advantages of the present disclosure will become more apparent from the following detailed description and the accompanying drawings. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a diagram showing a configuration of a lighting control device according to a first embodiment. [Figure 2] 4 is a timing diagram showing an example of the operation of the lighting control device according to the first embodiment. FIG. [Figure 3] FIG. 10 is a timing diagram showing a comparative example of the operation of the lighting control device. [Figure 4] FIG. 4 is a diagram showing a modified example of the configuration of the lighting control device according to the first embodiment. [Figure 5] FIG. 6 is a timing diagram showing a modified example of the operation of the lighting control device according to the first embodiment. [Figure 6] 10 is a timing diagram showing an example of the operation of the lighting control device according to the second embodiment. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] <First Embodiment> 1 is a diagram showing the configuration of a lighting control device 10 according to the first embodiment. The lighting control device 10 according to the first embodiment is mounted on a vehicle and drives a plurality of semiconductor light sources 20 including headlights and signal lights of the vehicle. The plurality of semiconductor light sources 20 driven by the lighting control device 10 are connected in series. Here, the semiconductor light emitting elements constituting the semiconductor light sources 20 are assumed to be LEDs, but other semiconductor light emitting elements such as LDs may also be used.

[0013] In this embodiment, an example is shown in which the lighting control device 10 drives three semiconductor light sources 20a, 20b, and 20c. Specifically, it is assumed here that the semiconductor light source 20a is a low beam headlight, the semiconductor light source 20b is a high beam headlight, and the semiconductor light source 20c is a signal light. Examples of signal lights include daytime running lights (hereinafter referred to as "daytime running lights"), position lights (also called "low beam lights" or "side light"), and turn signal lamps (hereinafter referred to as "turn signals").

[0014] As shown in FIG. 1, the lighting control device 10 includes a switching power supply 11, a lighting control circuit 12, switch elements 13a, 13b, and 13c, a smoothing capacitor 14, and a discharge circuit 15.

[0015] The switching power supply 11 supplies voltage to a plurality of semiconductor light sources 20 (low beam 20a, high beam 20b, signal light 20c) connected in series. Power is supplied to the switching power supply 11 from a battery 30. The output terminal of the switching power supply 11 is connected to a smoothing capacitor 14 that smoothes the output voltage and a discharge circuit 15 that discharges the charge accumulated in the smoothing capacitor 14.

[0016] The lighting control circuit 12 drives the semiconductor light sources 20 by PWM control, which periodically supplies the output voltage of the switching power supply 11 to the semiconductor light sources 20. The lighting control circuit 12 also controls the amount of light emitted by each of the semiconductor light sources 20 by controlling the width of the period during which the output voltage of the switching power supply 11 is supplied to each of the semiconductor light sources 20 in each cycle of the PWM control.

[0017] Switching elements 13a, 13b, and 13c are configured, for example, by MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) or the like, and are connected in series between the output terminal and the ground terminal of switching power supply 11. Switching elements 13a, 13b, and 13c are connected in parallel with low beam 20a, high beam 20b, and signal light 20c, respectively. Lighting control device 10 controls the timing at which the output voltage of switching power supply 11 is supplied to low beam 20a, high beam 20b, and signal light 20c by switching switching elements 13a, 13b, and 13c on and off. That is, lighting control device 10 turns off switching element 13a when supplying voltage to low beam 20a, turns off switching element 13b when supplying voltage to high beam 20b, and turns off switching element 13c when supplying voltage to signal light 20c.

[0018] The switching power supply 11 performs constant current control to keep the current flowing through the low beam 20a, the high beam 20b, and the signal light 20c constant. Therefore, the periods during which the lighting control circuit 12 supplies voltage to each of the low beam 20a, the high beam 20b, and the signal light 20c, i.e., the lighting periods of the low beam 20a, the high beam 20b, and the signal light 20c, may overlap. This makes it easy to ensure the length of the period during which voltage is supplied to each of the low beam 20a, the high beam 20b, and the signal light 20c, and to obtain the required amount of light emission for each.

[0019] In addition, the lighting control circuit 12 divides the semiconductor light sources 20 into multiple groups and divides the PWM control cycle into multiple subintervals assigned to each of the multiple groups, thereby dividing the period during which the output voltage of the switching power supply 11 is supplied for each group.

[0020] For example, the operation of the lighting control device 10 when the lighting control circuit 12 divides the multiple semiconductor light sources 20 into a group of low beams 20a and high beams 20b and a group of signal lights 20c is shown in the timing diagram of Figure 2. The vertical axis of Figure 2 represents the output voltage of the switching power supply 11 (corresponding to the voltage drops that occur in the low beams 20a, high beams 20b, and signal lights 20c), and the horizontal axis represents time. Figure 2 also shows the maximum output voltage Vmax of the switching power supply 11. Note that Figure 2 shows the operation when the lighting control circuit 12 turns on all of the low beams 20a, high beams 20b, and signal lights 20c.

[0021] As shown in FIG. 2 , the PWM control cycle (hereinafter referred to as the "PWM cycle") is divided into a partial interval assigned to the group of signal lights 20c and a partial interval assigned to the group of low beams 20a and high beams 20b. In the partial interval assigned to the group of signal lights 20c, the lighting control circuit 12 controls the lighting of the signal lights 20c that belong to that group, and does not turn on the low beams 20a and high beams 20b that do not belong to that group. Conversely, in the partial interval assigned to the group of low beams 20a and high beams 20b, the lighting control circuit 12 controls the lighting of the low beams 20a and high beams 20b that belong to that group, and does not turn on the signal lights 20c that do not belong to that group. Therefore, the low beams 20a, high beams 20b, and signal lights 20c are not all turned on at the same time.

[0022] As a comparative example, the timing diagram in FIG. 3 shows the operation when the lighting control circuit 12 does not group the low beams 20a, high beams 20b, and signal lights 20c. In this case, it is possible that the low beams 20a, high beams 20b, and signal lights 20c are all turned on simultaneously within a PWM period. In this case, if the voltage required to simultaneously turn on the low beams 20a, high beams 20b, and signal lights 20c (corresponding to the sum of the voltage drops occurring in the low beams 20a, high beams 20b, and signal lights 20c) is greater than the maximum output voltage Vmax of the switching power supply 11, the low beams 20a, high beams 20b, and signal lights 20c will not light up properly. In this case, it becomes necessary to provide a switching power supply 11 with a higher maximum output voltage or to provide two switching power supplies 11, which increases the heat generation and size of the lighting control device.

[0023] In contrast, according to the lighting control device 10 of embodiment 1, the low beam 20a, the high beam 20b, and the signal light 20c are not all turned on at the same time, and the voltage drop that occurs therein is prevented from exceeding the maximum output voltage Vmax of the switching power supply 11, thereby avoiding the problems of increased heat generation and size increase of the lighting control device described above.

[0024] When multiple semiconductor light sources 20 connected in series are driven by PWM control, the output voltage of switching power supply 11 fluctuates as shown in FIG. 2, and at the end of a PWM period or a partial interval, the voltage at which the output voltage reached its highest level is held in smoothing capacitor 14. If the next PWM period or partial interval is started in this state, an overcurrent may flow through semiconductor light source 20 that is to be turned on first, potentially damaging semiconductor light source 20. Therefore, lighting control circuit 12 turns on discharge circuit 15 before the start of a PWM period or a partial interval to discharge the residual charge at the output terminal of switching power supply 11, i.e., the charge accumulated in smoothing capacitor 14. For example, smoothing capacitor 14 may be discharged at the end of the lighting period of semiconductor light source 20 in the partial interval (timing Td shown in FIG. 2).

[0025] In the first embodiment, an example is shown in which the semiconductor light sources 20 are divided into a group of low beams 20a and high beams 20b and a group of signal lights 20c, i.e., an example in which the headlights and signal lights are divided into separate groups, but any other grouping may be used. However, because the headlights require a large amount of light emission and a long lighting period is required for just the headlights, it is effective to divide the headlights and signal lights into separate groups.

[0026] Furthermore, although the first embodiment has shown an example in which lighting control device 10 drives three semiconductor light sources 20, it may also drive four or more semiconductor light sources 20. Fig. 4 shows a configuration example in which lighting control device 10 drives four semiconductor light sources 20a, 20b, 20c, and 20d. There are four switch elements controlled by lighting control circuit 12: switch elements 13a, 13b, 13c, and 13d, which are connected in parallel to semiconductor light sources 20a, 20b, 20c, and 20d, respectively.

[0027] 4, it is specifically assumed that the semiconductor light source 20a is a low beam headlight, the semiconductor light source 20b is a high beam headlight, the semiconductor light source 20c is a position light, which is one type of signal light, and the turn signal light 20d is a turn signal light, which is another type of signal light. The timing diagram of FIG. 5 shows the operation of the lighting control device 10 when the lighting control circuit 12 divides the multiple semiconductor light sources 20 into a group of low beams 20a and high beams 20b and a group of position lights 20c and turn signals 20d. The same effect as above can be obtained when the number of semiconductor light sources 20 is four or more.

[0028] <Embodiment 2> Daytime running lights (DSLs) improve the visibility of vehicles from pedestrians and other vehicles during the day, and demand for them has been increasing in recent years. However, because the light output required for semiconductor light sources that are turned on during the day, such as daytime running lights, is relatively large, it may be difficult to ensure the required light output for daytime running lights if the PWM cycle is divided into multiple subintervals as in the first embodiment. In particular, if headlights and daytime running lights are divided into separate groups to suppress voltage drops, the subinterval for the headlight group must be long, making this problem more pronounced.

[0029] On the other hand, since there is no need to turn on the headlights during the day, it is unlikely that daytime running lights will be used in combination with the headlights. Therefore, in the second embodiment, the lighting control circuit 12 does not group the multiple semiconductor light sources 20 when the headlights are not turned on. FIG. 6 is a timing diagram showing the operation of the lighting control device 10 when the lighting control circuit 12 turns on the daytime running lights and turn signals without grouping the multiple semiconductor light sources 20. Because the multiple semiconductor light sources 20 are not grouped, the PWM period is not divided. The operation of the lighting control circuit 12 when the headlights are turned on is the same as in the first embodiment.

[0030] According to the lighting control device 10 of the second embodiment, when the headlights are not turned on, the semiconductor light sources 20 are not grouped, so that the lighting period of the semiconductor light sources that are turned on during the day, such as daylights, can be secured for a long time. This is effective because a relatively large amount of light is required for the semiconductor light sources that are turned on during the day.

[0031] It is possible to freely combine the embodiments, and to modify or omit the embodiments as appropriate.

[0032] The above description is illustrative in all respects, and it is understood that countless variations not illustrated can be envisioned. [Explanation of symbols]

[0033] 10 lighting control device, 11 switching power supply, 12 lighting control circuit, 13a to 13d switch elements, 14 smoothing capacitor, 15 discharge circuit, 20a to 20d semiconductor light sources.

Claims

1. a switching power supply that supplies voltage to a plurality of semiconductor light sources connected in series, including headlights and signal lights; a lighting control circuit that drives the semiconductor light sources by PWM (Pulse Width Modulation) control, which periodically supplies the output voltage of the switching power supply to the semiconductor light sources, and controls the width of a period during which the output voltage of the switching power supply is supplied to each of the semiconductor light sources in each cycle of the PWM control, thereby controlling the light emission amount of each of the semiconductor light sources; a smoothing capacitor connected to an output terminal of the switching power supply to smooth the output voltage of the switching power supply; a discharge circuit that discharges residual charge stored in the smoothing capacitor at the output terminal of the switching power supply; Equipped with the lighting control circuit divides the semiconductor light sources into a plurality of groups, and divides a period of the PWM control into a plurality of partial sections assigned to each of the plurality of groups, thereby dividing a period during which the output voltage of the switching power supply is supplied for each of the groups; the discharge circuit discharges residual charges at the output terminal of the switching power supply at a timing when a lighting period of the semiconductor light source ends in each of the plurality of partial sections within each cycle of the PWM control. Lighting control device.

2. The lighting control circuit divides the headlights and the signal lights into separate groups. The lighting control device according to claim 1 .

3. When the headlight is not turned on, the plurality of semiconductor light sources are not grouped. The lighting control device according to claim 1 .

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