LIGHTING CONTROL DEVICE

Abstract

A lighting control device (10) operates a plurality of semiconductor light sources (20) including a headlight and a signal light connected in series. A lighting control circuit (12) of the lighting control device (10) drives the plurality of semiconductor light sources (20) through pulse width modulation (PWM) control, supplying an output voltage of a switching power supply (11) in switching mode to the plurality of semiconductor light sources (20) in one cycle, and controls a width of a period in which the output voltage of the switching power supply (11) in switching mode is supplied to each of the plurality of semiconductor light sources (20) in each cycle of the PWM control to control a light emission amount of 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 a cycle of the PWM control into a plurality of sub-sections each associated with the plurality of groups to divide a period in which the output voltage of the switching power supply (11) is provided to each group.

Description

TECHNICAL FIELDThe present invention relates to an illumination control device that performs illumination control for a plurality of semiconductor light sources.BACKGROUNDA vehicle in which a semiconductor light source formed of a semiconductor light emitting element such as a light emitting diode (LED) and a semiconductor laser (LD) is used for an apparatus for lighting such as a headlight and a signal lamp is widely used. For example, Patent Document 1 described below discloses an illumination control device for a vehicle that controls a plurality of semiconductor light sources.In a technique of Patent Document 1, the plurality of semiconductor light sources are connected in series and are controlled by pulse width modulation (PWM) in which the voltage is supplied in one cycle. In the PWM control, a width of a period in which the voltage is supplied to each of the semiconductor light sources in each cycle (a so-called "duty ratio") is controlled to control a light emission amount of each semiconductor light source.Although a voltage drop occurs in the illumination in the semiconductor light source, when the plurality of semiconductor light sources are connected in series as in Patent Document 1 to perform constant current control using a switched-mode power supply, the plurality of semiconductor light sources can be turned on at the same time by a single switched-mode power supply. That is, in the PWM control, a period in which each semiconductor light source is supplied with voltage may be overlapped with each other.DOCUMENTS RELATED TO PRIOR ART PATENT DOCUMENT(S)Patent Document 1: Japanese Patent No. 6916668SUMMARYOBJECT OF THE INVENTIONThe number of semiconductor light sources mounted on a vehicle increases as the application of the semiconductor light source in the lighting device of the vehicle progresses. Meanwhile, heat generation of the device increases, and downsizing of the lighting control device is also required to achieve a headlamp design that cannot be achieved in a halogen headlamp. In the technique in Patent Document 1, the period in which the voltage is applied to each semiconductor light source may overlap each other; therefore, even if the number of semiconductor light sources is increased, the period in which the voltage is applied to each semiconductor light source is secured, and a required light emission amount can be detected. However, when the number of semiconductor light sources turned on simultaneously increases, the voltage drop becomes large; therefore, a switching power supply with a high maximum output voltage needs to be prepared or the number of switching power supplies needs to be increased, and such a configuration results in an increase in the heat generation amount and an increase in the illumination control device.The present invention is intended to solve the above problems, and an object of the present invention is to ensure a required light emission amount while suppressing a voltage drop occurring in a plurality of semiconductor light sources in a light source illumination device that drives the plurality of semiconductor light sources connected in series.MEANS FOR ACHIEVING THE OBJECTAn illumination control device according to the present invention includes: a switching power supply that supplies voltage to a plurality of semiconductor light sources connected in series including a headlight and a signal lamp; and an illumination control circuit that controls the plurality of semiconductor light sources by a pulse width modulation (PWM) control that supplies the output voltage of the switching power supply to the plurality of semiconductor light sources in one cycle and controls a width of a period in 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 to control a light emission amount of each of the plurality of semiconductor light sources, wherein the illumination control circuit divides the plurality of semiconductor light sources into a plurality of groups and divides a cycle of the PWM control into a plurality of sections respectively allocated to the plurality of groups to divide a period in which the output voltage is supplied to the power supply for each group.EFFECTS OF THE INVENTIONAccording to the illumination control device in the present invention, the illumination periods of the plurality of semiconductor light sources are divided for each group; thereby, the number of semiconductor light sources turned on simultaneously can be reduced, and the voltage drop is suppressed. In the subsection, the illumination period of each semiconductor light source can be overlapped with each other; thus, a length of the illumination period of each semiconductor light source can be secured, and a required light emission amount can be detected.These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGS[FIG. 1 ] is a diagram showing a configuration of a lighting control device according to Embodiment 1.[FIG. 2 ] is a timing chart illustrating, for example, an operation of the lighting control device according to Embodiment 1.[FIG. 3 ] is a timing chart showing a comparative example of the operation of a lighting control device.[FIG. 4 ] is a diagram showing a modification example of the configuration of the illumination control device according to Embodiment 1.[FIG. 5 ] is a timing chart showing a variation example of the operation of the lighting control device according to Embodiment 1.[FIG. 6 ] is a timing chart showing an example of the operation of a lighting control device according to an embodiment 2.DESCRIPTION OF THE EMBODIMENT(S)< 1>FIG. 1 is a diagram showing a configuration of a lighting control device 10 according to Embodiment 1. The illumination control device 10 according to Embodiment 1 is mounted on a vehicle to drive a plurality of semiconductor light sources 20 including a headlight and a signal light of the vehicle. The plurality of semiconductor light sources 20 driven by the illumination control device 10 are connected in series. A semiconductor light element forming the semiconductor light source 20 is an LED, but may also be another semiconductor light element, for example an LD.For example, the present embodiment indicates that the illumination control device 10 drives three semiconductor light sources 20 a, 20 b, and 20 c. Here, it is particularly assumed that a semiconductor light source 20 ais a low beam of the headlamp, a semiconductor light source 20 bis a high beam of the headlamp, and a semiconductor light source 20 cis a signal light. Examples of the signal light include a daytime running light (hereinafter also referred to as "daylight"), a position light (hereinafter also referred to as "small light" or "street light"), and a flasher lamp (hereinafter also referred to as "flasher").As illustrated in FIG. 1, lighting control device 10 includes switching power supply 11, lighting control circuit 12, switching elements 13 a, 13 b, and 13 c, smoothing capacitor 14, and discharge circuit 15.The switching power supply 11 supplies power to the plurality of semiconductor light sources 20 (a low beam 20 a, a high beam 20 b, and a signal light 20 c) connected in series. The power supply of the switching power supply 11 is performed via a battery 30, and the smoothing capacitor 14 that smoothes the output voltage and the discharge circuit 15 for discharging the electric charge stored in the smoothing capacitor 14 are connected to an output terminal of the switching power supply 11.The illumination control circuit 12 performs PWM control of supplying the output voltage of the switching power supply 11 to the plurality of semiconductor light sources 20 in one cycle to drive the plurality of semiconductor light sources 20. The illumination control circuit 12 controls a width of a period in which the output voltage of the switching power supply 11 is supplied to each of the plurality of semiconductor light sources 20 in each cycle of the PWM control to control a light emission amount of each of the plurality of semiconductor light sources 20.The switching elements 13 a, 13 band 13 cconsists of, for example, a metal oxide semiconductor field effect transistor (MOSFET), and are connected in series between the output terminal of the switching power supply 11 and a ground terminal. The switching elements 13 a, 13 b, and 13 care connected in parallel to the low beam 20 a, the high beam 20 b, and the signal light 20 c, respectively. The lighting control device 10 turns on and off the switching elements 13 a, 13 band 13 c, thereby controlling the timing at which the output voltage of the switching power supplies 11 is supplied to the low beam 20 a, the high beam 20 band the signal lamp 20 c, respectively. That is, the lighting control device 10 turns off the switch control member 13 awhen the voltage is supplied to the low beam 20 a, turns off the switch control member 13 bwhen the voltage is supplied to the high beam 20 b, and turns off the switch control member 13 cwhen the voltage is supplied to the signal light 20 c.The switching power supply 11 performs constant current control to keep the current flow in the low beam 20 a, the high beam 20 b, and the signal lamp 20 c constant. Thus, a period in which the control unit 12 supplies the voltage to each of the low beam 20 a, the high beam 20 b, and the signal lamp 20 c, that is, an illumination period of each of the low beam 20 a, the high beam 20 b, and the signal lamp 20 cmay be overlapped with each other. In this way, the length of the period in which the voltage is supplied to the low beam 20 a, the high beam 20 b, and the signal light 20 cmay be easily secured, and the light emission amount required by each light source may be detected.The illumination control circuit 12 divides the plurality of semiconductor light sources 20 into a plurality of groups and divides a cycle of PWM control into a plurality of sections respectively assigned to the plurality of groups to divide a period in which the output voltage of the power supply 11 is provided for each group.FIG. 2, for example, shows a timing chart of an operation of the illumination control device 10 in a case where the illumination control circuit 12 divides the plurality of semiconductor light sources 20 into a group of the low beam 20 aand the high beam 20 band a group of the signal light 20 c. A vertical axis in FIG. 2 indicates the output voltage of the switching power supply 11 (corresponding to the voltage drop occurring in the low beam 20 a, the high beam 20 b, and the signal light 20 c), and a lateral axis indicates time. FIG. 2 shows the maximum output voltage Vmax of the switching power supply 11. FIG. 2 illustrates the operation of the lighting control circuit 12 that turns on the entire low beam 20 a, the high beam 20 b, and the signal lamp 20 c.As illustrated in FIG. 2, the cycle of PWM control (hereinafter referred to as "PWM cycle") is divided into a section associated with the group of signal light 20 cand a section associated with the group of low beam 20 aand high beam 20 b. In the section associated with the group of the signal lamp 20 c, the lighting control circuit 12 performs lighting control for the signal lamp 20 ccorresponding to this group, and does not turn on the low beam 20 aand the high beam 20 bnot corresponding to this group. On the other hand, in the section associated with the group of the low beam 20 aand the high beam 20 b, the light control circuit 12 performs light control of the low beam 20 aand the high beam 20 bbelong to the group, and does not turn on the signal lamp 20 cnot belonging to the group. Thus, the low beam 20a, the high beam 20b and the signal lamp 20c are not all turned on simultaneously.FIG. 3 is a timing chart showing an operation in a case where the lighting control circuit 12 does not divide the low beam 20 a, the high beam 20 b, and the signal lamp 20 cin groups as a comparative example. In this case, the low beam 20 a, the high beam 20 b, and the signal lamp 20 cmay be turned on at the same time in the PWM cycle. At this time, as illustrated in FIG. 3, when the voltage required for simultaneously turning on the low beam 20 a, the high beam 20 b, and the signal lamp 20 c(which is a total of the voltage drops in the low beam 20 a, the high beam 20 b, and the signal lamp 20 c) is larger than the maximum output voltage Vmax of the power supply 11, the low beam 20 a, the high beam 20 b, and the signal lamp 20 care not normally turned on. In this case, the switching power supply 11 needs to be prepared with a high maximum output voltage, or two switching power supplies 11 need to be prepared, and such a configuration results in an increase in the heat generation amount and an increase in the lighting control device.In contrast, according to the lighting control device 10 in Embodiment 1, not all of the low beams 20 a, the high beams 20 b, and the signal beams 20 care turned on simultaneously, and the voltage drop occurring therein is prevented from exceeding the maximum output voltage Vmax of the switching power supplies 11; thus, the occurrence of the above-described problem of the increase in the heat generation amount and the increase in the size of the lighting control device can be prevented.When the plurality of semiconductor light sources 20 connected in series are driven by the PWM control, as illustrated in FIG. 2, the output voltage of the switching power supply 11 fluctuates, and the voltage having the highest output voltage is held in the smoothing capacitor 14 at the time of termination of the PWM cycle or termination of the subsection. When the process proceeds to a next PWM cycle or section while maintaining such a state, an overcurrent flows in the semiconductor light source 20 that was first turned on, and the semiconductor light source 20 may be interrupted. Thus, the lighting control circuit 12 causes the discharge circuit 15 to transition to a conduction state before the start of the PWM cycle or before the start of the subsection, and to discharge the remaining electric charge in the output terminal of the switching power supply 11, i.e., the electric charge stored in the smoothing capacitor 14. For example, the electric charge in the smoothing capacitor 14 may be discharged at a time when the illumination period of the semiconductor light source 20 is completed in the divided portion (a time Td illustrated in FIG. 2 )In Embodiment 1, the division of the plurality of semiconductor light sources 20 into the group of the low beam 20 aand the high beam 20 band the group of the signal light 20 c,i.e., the division of the headlight and the signal light into the different groups, will be described by way of example; however, any division into groups may be made. Since the headlamp requires a large amount of light and the lighting time for the headlamp alone must be long, it is effective to divide the headlamp and the signal light into the various groups.Although it is exemplarily described in Embodiment 1 that the illumination control device 10 drives three semiconductor light sources 20, the illumination control device 10 may drive four or more semiconductor light sources 20. FIG. 4 shows a configuration example in the case where the illumination control device 10 drives four semiconductor light sources 20 a, 20 b, 20 c, and 20 d. The switching element controlled by the lighting control unit 12 includes the switching elements 13 a, 13 b, and 13 cand a switching element 13 dconnected in parallel with the semiconductor light sources 20 a, 20 b, 20 c, and 20 d.Specifically, in FIG. 4, it is assumed that the semiconductor light source 20 ais the low beam of the headlight, the semiconductor light source 20 bis the high beam of the headlight, the semiconductor light source 20 cis a position light as one of the signal lights, and the blinking light 20 dis a blinking light as the other of the signal lights. FIG. 5 is a timing chart showing an operation of the illumination control device 10 in a case where the control circuit 12 divides the plurality of semiconductor light sources 20 into the group of the low beam 20 aand the high beam 20 band a group of the position light 20 cand the flashing light 20 d. A similar effect as described above can be detected even when the number of semiconductor light sources 20 is four or more.< 2>Daylight has an effect of improving the visibility of a pedestrian and a vehicle seen from another vehicle during the day, and demand for this has recently increased. However, a light emission amount required by the semiconductor light source such as daylight turned on during the day is relatively large; therefore, it is considered difficult to ensure the light emission amount required by the daylight when the PWM cycle is divided into a plurality of sections as in Embodiment 1. In particular, when the headlamp and the daylight are divided into different groups to suppress the voltage drop, such a problem becomes significant because the long section of the group of the headlamp needs to be secured.Since the headlamp does not need to be turned on during the day, the daylight is hardly used together with the headlamp. Therefore, in Embodiment 2, the control circuit 12 does not divide the plurality of semiconductor light sources 20 into groups when the headlamp is not turned on. FIG. 6 is a timing chart illustrating the operation of the illumination control device 10 in a case where the illumination control circuit 12 turns on the daylight and the flasher without dividing the plurality of semiconductor light sources 20 into the groups. Since the plurality of semiconductor light sources 20 are not divided into the groups, the PWM cycle is not divided. An operation of the lighting control circuit 12 in a case where the headlamp is turned on is similar to Embodiment 1.According to the illumination control device 10 in Embodiment 2, the plurality of semiconductor light sources 20 are not divided into the groups when the headlamp is not turned on; thus, a long illumination period of the semiconductor light source, for example, daylight turned on during the day, can be ensured. Such a configuration is effective because a relatively large amount of light emission is required from the semiconductor light source turned on in the day.Each embodiment may be combined arbitrarily, or each embodiment may be appropriately varied or omitted.The foregoing description is illustrative in all respects and it is therefore to be understood that numerous modification examples, not shown by way of example, may be devised.EXPLANATION OF THE REFERENCE NUMERALS10 Lighting control device, 11 Switching power supply, 12 Lighting control circuit, 13 ato 13 dSwitching element, 14 Smoothing capacitor, 15 Discharging circuit, 20 ato 20 d Halbleiter light source.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedJP 6916668

[0005]

Claims

An illumination control device, comprising: a switching power supply that supplies voltage to a plurality of semiconductor light sources including a headlight and a signal light connected in series; An illumination control circuit that drives the plurality of semiconductor light sources by a pulse width modulation (PWM) control that supplies an output voltage of the switching power supply to the plurality of semiconductor light sources in one cycle and controls a width of a period in 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 to control a light emission amount of each of the plurality of semiconductor light sources, wherein the illumination control circuit divides the plurality of semiconductor light sources into a plurality of groups and divides a cycle of the PWM control into a plurality of sections respectively allocated to the plurality of groups to divide a period in which the output voltage of the switching power supply is supplied for each group.The lighting control device according to claim 1, wherein the lighting control circuit divides the headlight and the signal light into groups different from each other.The lighting control device according to claim 1, wherein when the headlamp is not turned on, the plurality of semiconductor light sources are not divided into groups.The lighting control device according to claim 1, further comprising a discharge circuit that discharges residual electric charge in an output terminal of the switching power supply before the cycle of the PWM control is started or before the subsection is started.

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