DE-112022007761-B4 - LIGHTING CONTROL DEVICE

Abstract

A lighting control device (10), comprising: a switching power supply (11) which supplies voltage to a plurality of semiconductor light sources (20) comprising a headlight (20a, 20b) and a signal light (20c) connected in series; a lighting control circuit (12) that controls the plurality of semiconductor light sources (20) by means of a pulse width modulation (PWM) control, which supplies an output voltage of the switching power supply (11) to the plurality of semiconductor light sources (20) in a cycle and 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 in order to control a quantity of light emission from each of the plurality of semiconductor light sources (20); a smoothing capacitor (14) connected to an output terminal of the switching power supply, which smooths the output voltage of the switching power supply; and a discharge circuit (15) which discharges a residual electrical charge stored in the smoothing capacitor (14) into an output terminal of the switching power supply (11), wherein the lighting 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 sub-sections, each assigned to the plurality of groups, in order to subdivide a period in which the output voltage of the switching power supply (11) is supplied to each group; and the discharge circuit (15) discharges the remaining electrical charge in the output terminal of the switching power supply (11) at a time when the illumination time of the semiconductor light source (20) ends in the several subsections in each cycle of the PWM control.

Inventors

• Takashi Hiratsuka
• Hiroshi Ishizaki
• Yasuhiro Nukisato

Assignees

• MITSUBISHI ELECTRIC MOBILITY CORPORATION

Dates

Publication Date

20260513

Application Date

20221213

Claims (3)

1. A lighting control device (10) comprising: a switching power supply (11) that supplies voltage to a plurality of semiconductor light sources (20), comprising a headlight (20a, 20b) and a signal light (20c) connected in series; a lighting control circuit (12) that controls the plurality of semiconductor light sources (20) by means of pulse-width modulation (PWM) control, which supplies an output voltage of the switching power supply (11) to the plurality of semiconductor light sources (20) in one cycle and controls a period width 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 quantity of light emission from each of the plurality of semiconductor light sources (20); a smoothing capacitor (14) connected to an output terminal of the switching power supply and smoothing the output voltage of the switching power supply; and a discharge circuit (15) that discharges a residual electrical charge stored in the smoothing capacitor (14) into an output terminal of the switching power supply (11), wherein the lighting 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 sub-sections, each assigned to the plurality of groups, in order to subdivide a period in which the output voltage of the switching power supply (11) is supplied to each group; and the discharge circuit (15) discharges the remaining electrical charge in the output terminal of the switching power supply (11) at a time when the illumination duration of the semiconductor light source (20) in the multiple sub-sections in each cycle of PWM control ends.
2. Lighting control device (10) according Claim 1 , wherein the lighting control circuit (12) divides the headlight (20a, 20b) and the signal light (20c) into separate groups.
3. Lighting control device (10) according Claim 1 , wherein when the headlight (20a, 20b) is not switched on, the plurality of semiconductor light sources (20) is not divided into groups.

Description

TECHNICAL AREA The present invention relates to a lighting control device that performs lighting control for a plurality of semiconductor light sources. BACKGROUND Vehicles in which a semiconductor light source, consisting of a light-emitting semiconductor element such as a light-emitting diode (LED) and a semiconductor laser (LD), is used for a lighting device such as a headlight and a signal light, are widely used. For example, patent document 1 described below discloses a lighting control device for a vehicle that controls a plurality of semiconductor light sources. In one technique described in patent document 1, a multitude of semiconductor light sources are connected in series and controlled by pulse-width modulation (PWM), in which the voltage is applied in a cycle. With PWM control, the width of one period in which the voltage is supplied to each of the semiconductor light sources in each cycle (a so-called "duty cycle") is controlled in order to regulate the amount of light emission from each semiconductor light source. Although a voltage drop occurs in the semiconductor light source during illumination, if the multiple semiconductor light sources are connected in series, as in patent document 1, to perform constant current control using a switching power supply, the multiple semiconductor light sources can be switched on simultaneously by a single switching power supply. That is, with PWM control, the periods during which each semiconductor light source is supplied with voltage can overlap. DOCUMENTS ON THE STATE OF THE TECHNOLOGY PATENT DOCUMENT(S) Patent document 1: Japanese patent no. 6916668Patent document 2: DE 20 2012 004 747 U1Patent document 3: JP 2020 - 59 430 APatent document 4: DE 11 2012 002 240 T5Patent document 5: JP 2011 - 84 141 A SUMMARY TASK STATEMENT OF THE INVENTION The number of semiconductor light sources mounted on a vehicle increases with the increasing use of semiconductor light sources in the vehicle's lighting system. Meanwhile, the heat generated by the system increases, and a miniaturization of the lighting control device is also necessary to achieve a headlight design that is not possible with a halogen headlight. In the technology described in Patent Document 1, the time periods during which voltage is applied to each semiconductor light source can overlap; therefore, even with an increase in the number of semiconductor light sources, the time period during which voltage is applied to each semiconductor light source is ensured, and the required amount of light emission can be achieved. However, if the number of simultaneously switched-on semiconductor light sources increases, the voltage drop becomes large; therefore, a switching power supply with a high maximum output voltage must be provided, or the number of switching power supplies must be increased. Such a configuration leads to an increase in the amount of heat generated and a larger lighting control device. The present invention is intended to solve the above problems, and one object of the present invention is to ensure a required amount of light emission while suppressing a voltage drop that occurs in a plurality of semiconductor light sources in a lighting control device that controls the plurality of series-connected semiconductor light sources. MEANS OF SOLVING THE TASK A lighting control device according to the present invention comprises: a switched-mode power supply that supplies voltage to a plurality of series-connected semiconductor light sources, including a headlight and a signal lamp, and a lighting control circuit that controls the plurality of semiconductor light sources by means of pulse-width modulation (PWM) control, which supplies the output voltage of the switched-mode power supply to the plurality of semiconductor light sources in a cycle and controls a period width in which the output voltage of the switched-mode power supply is supplied to each of the plurality of semiconductor light sources in each cycle of the PWM control in order to control a quantity of light emission from each of the plurality of semiconductor light sources, wherein the lighting control circuit controls the plurality of semiconductor light Sources are divided into a multitude of groups, and a cycle of PWM control is divided into a multitude of sub-sections, each assigned to the multitude of groups, in order to subdivide a period in which the output voltage of the power supply is supplied to each group. EFFECTS OF INVENTION According to the lighting control device in the present invention, the illumination periods of the plurality of semiconductor light sources are divided for each group; this allows the number of simultaneously switched-on semiconductor light sources to be reduced, and the voltage drop is suppressed. In this subsection, the illumination period of each semiconductor light source can be overlapped; thus, a specific illumination period length for each semiconductor light source can be ensured, and a r