Light source lighting control device

Abstract

The objective of the present invention is to provide a technology capable of suppressing an inrush current into a semiconductor light source when switching the lighting state, without having to provide a discharge circuit. This light source lighting control device comprises a controller that controls the lighting of a plurality of light source units by controlling a switching circuit. When turning off all of a plurality of semiconductor light sources, the controller selects, from among the plurality of light source units, a subset of light source units with fewer semiconductor light sources than the entirety of the one or more light source units that are currently on, turns on the subset of light source units or leaves the subset of light source units on, and then turns off the subset of light source units.

Description

Light source lighting control device

[0001] The present disclosure relates to a light source lighting control device.

[0002] In recent years, the adoption of semiconductor light sources such as light-emitting diodes (LEDs) for automotive lighting has been increasing due to their energy-saving features, long life, and high design flexibility. Automotive lighting includes low beams that illuminate the area near the vehicle, high beams that illuminate areas farther away from the vehicle, turn signals, and daytime running lamps (DRLs) that notify surrounding areas of the vehicle's location during daytime driving. To provide a reasonable solution for these various lighting needs, a technology has been proposed that shares a single DC-DC converter with multiple LEDs and adjusts the brightness of the LEDs using pulse width modulation (PWM) or by varying the number of LED elements.

[0003] However, for example, in a lighting control device that selectively supplies current output from a single DC-DC converter to multiple LEDs, when switching between lighting modes, an inrush current may flow through the LEDs due to the discharge of the smoothing capacitor, damaging the LEDs. As a countermeasure, a technology has been proposed that provides a discharge circuit (also called a short circuit) that includes a discharge resistor to suppress the inrush current to the LEDs (see, for example, Patent Document 1).

[0004] JP 2013-47047 A

[0005] However, the conventional technology has a problem in that the cost for the discharge circuit is high.

[0006] Therefore, the present disclosure has been made in consideration of the above-mentioned problems, and aims to provide a technology that can suppress inrush current to a semiconductor light source when switching between lighting modes without providing a discharge circuit.

[0007] The light source lighting control device according to the present disclosure is a light source lighting control device that controls the lighting of a plurality of semiconductor light sources connected in series, and includes a DC-DC converter that generates current, a smoothing circuit that smooths the output of the DC-DC converter, a switching circuit that switches the lighting and extinguishing of each of the plurality of light source units by controlling the current supplied to the plurality of light source units having different combinations of semiconductor light sources, and a control unit that controls the lighting of the plurality of light source units by controlling the switching circuit, and when turning off all of the plurality of semiconductor light sources, the control unit selects from the plurality of light source units some light source units that have fewer semiconductor light sources than all of the one or more light source units that are turned on, and turns them on from off or leaves them on, and then turns off some of the light source units.

[0008] According to the present disclosure, when turning off all of the plurality of semiconductor light sources, the control unit selects some of the light source units from the plurality of light source units that have fewer semiconductor light sources than all of the one or more light source units that are turned on, and turns them on or leaves them on, and then turns off the some of the light source units. With this configuration, it is possible to suppress inrush current to the semiconductor light sources when switching on and off without providing a discharge circuit.

[0009] The objects, features, aspects and advantages of the present disclosure will become more apparent from the following detailed description and the accompanying drawings.

[0010] Fig. 1 is a block diagram showing a configuration of a light source lighting control device according to embodiment 1. Fig. 2 is a timing chart showing an example of an operation of a light source lighting control device according to embodiment 1. Fig. 3 is a timing chart showing an example of an operation of a light source lighting control device according to embodiment 2. Fig. 4 is a block diagram showing a configuration of a light source lighting control device according to embodiment 3.

[0011] <First Embodiment> Fig. 1 is a circuit diagram showing the configuration of a light source lighting control device according to the first embodiment. The light source lighting control device of Fig. 1 controls the lighting of a plurality of semiconductor light sources connected in series. The following description will be given taking as an example a configuration in which the plurality of semiconductor light sources connected in series are a plurality of light emitting diodes (LEDs), but the present invention is not limited to this.

[0012] The plurality of LEDs 1 are included in light source units 1A and 1B (i.e., the plurality of light source units), and the combination of LEDs 1 included in light source unit 1A is different from the combination of LEDs 1 included in light source unit 1B. As an example, the following describes a configuration in which light source unit 1A includes two LEDs 1 and light source unit 1B includes four LEDs 1, which is more than the number of LEDs 1 in light source unit 1A. However, the number of LEDs 1 in light source units 1A and 1B is not limited to this, and for example, the same LED may be shared by different light source units as in embodiment 3.

[0013] The light source lighting control device of FIG. 1 includes a DC-DC converter 11, a smoothing circuit 12, a switching circuit 13, and a control unit .

[0014] The DC-DC converter 11 generates a current (for example, a constant current) from a battery voltage (not shown).

[0015] The smoothing circuit 12 smoothes the output (voltage) of the DC-DC converter 11. The smoothing circuit 12 includes a capacitor connected in parallel to the DC-DC converter 11, for example.

[0016] The switching circuit 13 controls the current supplied from the DC-DC converter 11 to the light source units 1A and 1B, thereby switching on and off each of the light source units 1A and 1B. The switching circuit 13 in FIG. 1 includes switches 13a and 13b connected in parallel to the light source units 1A and 1B, respectively, and the switches 13a and 13b include semiconductor switching elements such as MOSFETs (Metal Oxide Semiconductor Field Effect Transistors). When the switch 13a is off, the light source unit 1A is turned on, and when the switch 13a is on, the light source unit 1A is turned off. Similarly, when the switch 13b is off, the light source unit 1B is turned on, and when the switch 13b is on, the light source unit 1B is turned off.

[0017] In the first embodiment, the lighting of the light source units 1A and 1B is not PWM (Pulse Width Modulation) lighting, in which the lighting is intermittent during lighting control, but DC lighting, in which the lighting is continued during lighting control. Because DC lighting does not require the rapid switching between on and off as in PWM lighting, a circuit with a slower switching speed than a circuit used for PWM lighting can be used for the switching circuit 13 according to the first embodiment.

[0018] The control unit 14 controls the lighting of the light source units 1A and 1B by controlling the on / off of the switching circuit 13. The control unit 14 may include a microcontroller or a logic circuit having a similar function. The control unit 14 may also be realized by cooperation between hardware such as a central processing unit (CPU) and memory (not shown) and software such as a control program for controlling the operation of the light source lighting control device.

[0019] When turning off all of the LEDs 1, the control unit 14 selects from the light source units 1A and 1B a portion of the light source units that has fewer LEDs 1 than all of the one or more lit light source units. In the first embodiment, the one or more lit light source units are the light source units 1A and 1B, and the portion of the light source units is the light source unit 1A that has the fewest LEDs 1 among the light source units 1A and 1B. However, the one or more lit light source units and the portion of the light source units are not limited to those described above, as will be described later.

[0020] The control unit 14 turns on the selected light source unit 1A from off, or leaves it on if it is already on, and turns off the remaining light source units 1B, and then turns off the light source unit 1A, thereby turning off all of the plurality of LEDs 1.

[0021] As described above, in the first embodiment, the light source units 1A and 1B are DC lit. Therefore, when turning off all of the LEDs 1, the control unit 14 does not increase the number of lit LEDs 1, but instead selects light source unit 1A from the DC lit light source units 1A and 1B, leaves it lit, turns off the remaining light source unit 1B, and then turns off light source unit 1A. The control unit 14 may also be configured to be able to control the DC-DC converter 11. This will be described later.

[0022] Fig. 2 is a timing chart showing an example of the operation of the light source lighting control device according to the first embodiment. Fig. 2 shows an example in which the control unit 14 controls the on / off of the light source units 1A and 1B in accordance with an instruction to turn on both light source units 1A and 1B, an instruction to turn off both light source units 1A and 1B, and an instruction to turn on only light source unit 1A. For convenience, in Fig. 2, the light source unit 1A is abbreviated as light source 1A, and the light source unit 1B is abbreviated as light source 1B.

[0023] Before time t1, the control unit 14 lights up both light source units 1A and 1B with DC. At time t1, when the control unit 14 receives an instruction to turn off both light source units 1A and 1B, it selects light source unit 1A and leaves it turned on without increasing the number of lit LEDs 1, and turns off light source unit 1B. At time t2, the control unit 14 turns off light source unit 1A. At time t3, when the control unit 14 receives an instruction to turn on only light source unit 1A, it lights up light source unit 1A with DC.

[0024] 2 indicates the voltage applied to light source units 1A and 1B. In the present embodiment, the number of LEDs 1 in light source unit 1B is greater than the number of LEDs 1 in light source unit 1A, and therefore the decrease in applied voltage (=V1-V2) when light source unit 1B is turned off is greater than the decrease in applied voltage (=V2-V3) when light source unit 1A is turned off.

[0025] 2 indicates the charging voltage of the capacitor of the smoothing circuit 12 when both light source units 1A and 1B are turned off at the same time without turning on light source unit 1A and turning off light source unit 1B at time t1. In this case, the charging voltage of the capacitor of the smoothing circuit 12 is maintained at approximately voltage V1 after time t1. In a configuration in which the circuit impedance is high and the period from time t2 to time t3 is short, when only light source unit 1A is turned on at time t3, an inrush current corresponding to the voltage difference between voltage V2 and voltage V3 (=V2-V3) flows through light source unit 1A.

[0026] The dashed-dotted line shown in the applied voltage in Fig. 2 indicates the charging voltage of the capacitor of the smoothing circuit 12 when light source unit 1A is turned on and light source unit 1B is turned off at time t1, that is, when control is performed by the light source lighting control device according to the first embodiment. In this case, the charging voltage of the capacitor of the smoothing circuit 12 drops to voltage V2 during the period from time t1 to time t2. During this period, the switching circuit 13 turns off the light source unit 1A over a certain amount of time, so that the charging voltage of the smoothing circuit 12 is consumed as heat and becomes voltage V2. After time t2, the charging voltage of the capacitor of the smoothing circuit 12 is maintained at approximately voltage V2.

[0027] When only light source unit 1A is turned on at time t3, there is substantially no voltage difference between the voltage at times before time t3 and the voltage at time t3, so substantially no inrush current flows through light source unit 1A.

[0028] Summary of First Embodiment In the light source lighting control device according to the first embodiment described above, when turning off all of the plurality of LEDs 1, some of the light source units 1A, 1B that have fewer LEDs 1 than all of the one or more light source units 1A, 1B that are turned on are selected from the light source units 1A, 1B, and are turned on or left on, and then some of the light source units 1A are turned off. With this configuration, it is possible to suppress the inrush current to the LEDs 1 when the lighting is switched on (time t3 in FIG. 2 ) without providing a discharge circuit.

[0029] In the first embodiment, some of the light source units are light source unit 1A, which has the fewest LEDs 1 among light source units 1A and 1B. With this configuration, it is possible to suppress the inrush current (inrush current at time t3 in FIG. 2 ) to light source unit 1A, which is turned on after both light source units 1A and 1B are turned off.

[0030] Furthermore, in the first embodiment, when turning off all of the LEDs 1, the control unit 14 selects some of the light source units 1A from the light source units 1A and 1B that are DC-lit, keeps them lit, and then turns off some of the light source units 1A, without increasing the number of lit LEDs 1. This configuration allows a circuit with a slower switching speed than a circuit used for PWM lighting to be used in the switching circuit 13. Furthermore, when a circuit with a slower switching speed is used in the switching circuit 13, the inrush current to the switches 13a and 13b (described later) can be reduced whether the light source units 1A and 1B are turned off sequentially or simultaneously. Furthermore, because the operation of the control unit 14 is simpler than that of the control unit 14 according to the second embodiment, simplification of the control unit 14 and reduction in development costs can be expected.

[0031] <Modification 1> In the first embodiment, some of the light source units are light source unit 1A, which has the fewest LEDs 1 among light source units 1A and 1B, but they may also be light source unit 1B. In this case, the inrush current (inrush current at time t3) to the light source unit that is turned on after both light source units 1A and 1B are turned off is larger than in the first embodiment, but is smaller than the inrush current corresponding to the voltage difference (= V2 - V3). Therefore, even if some of the light source units are light source unit 1B, the inrush current to LED 1 at the time of lighting switching can be suppressed as in the first embodiment.

[0032] <Modification 2> In the first embodiment, the plurality of light source units are two light source units (light source units 1A and 1B), but may be three light source units (light source units 1A, 1B, and 1C). For example, when turning off the DC-lit light source units 1A, 1B, and 1C, the control unit 14 may select one or two of the light source units, leave them lit, and then turn off the selected light source units. Furthermore, when turning off the DC-lit light source units 1A and 1C, the control unit 14 may select one of the light source units, leave it lit, and then turn off the selected light source unit. Expanding on the above, the plurality of light source units may be two or more light source units.

[0033] <Embodiment 2> A circuit diagram showing the configuration of a light source lighting control device according to Embodiment 2 is the same as that shown in Fig. 1. Hereinafter, among the components according to Embodiment 2, components that are the same as or similar to the components described above will be assigned the same or similar reference numerals, and different components will be mainly described.

[0034] In the first embodiment, the light source units 1A and 1B are lit by DC lighting, but in the second embodiment, the light source units 1A and 1B are lit by PWM lighting (also called PWM dimming). Here, it is assumed that the operation described in the first embodiment is performed as is in a light source lighting control device that performs PWM lighting. In this case, for example, at time t1 in FIG. 2 , when the light source unit 1A is strictly turned off by PWM lighting, there is a possibility that the light source unit 1B will be turned off due to a control error in actual operation.

[0035] 1 are turned on simultaneously, the entire switches 13a and 13b are short-circuited, and an inrush current flows through the switches 13a and 13b, which may cause malfunctions. In particular, unlike DC lighting, PWM lighting uses a circuit with a high switching speed for the switching circuit 13 so that the switches are turned off for, for example, several microseconds. Therefore, the inrush current to the switches 13a and 13b is larger than the inrush current to the switches 13a and 13b during DC lighting, which increases the possibility of malfunctions in the switches 13a and 13b.

[0036] The light source lighting control device according to the second embodiment is configured to eliminate this problem. Specifically, when turning off all of the plurality of LEDs 1, the control unit 14 turns on the light source units 1A and 1B that are PWM-lit in an overlapping manner, then selects some of the light source units 1A from the overlapping light source units 1A and 1B that are turned on, leaves them on, and then turns off some of the light source units 1A. Note that in the second embodiment, the case will be described in which some of the light source units are light source units 1A, as in the first embodiment. However, some of the light source units may also be light source units 1B, as in the first modification.

[0037] Fig. 3 is a diagram showing an example of the operation of the light source lighting control device according to the embodiment 2. Fig. 3 shows an example in which the control unit 14 controls the on / off of the light source units 1A and 1B in accordance with an instruction to turn on both the light source units 1A and 1B, an instruction to turn off both the light source units 1A and 1B, and an instruction to turn on only the light source unit 1A.

[0038] Before time t12, the control unit 14 PWM lights both light source units 1A and 1B. The duty ratio of PWM lighting of light source unit 1A is greater than 0% and less than 100%, and light source unit 1A is turned off from time t11 to time t12. On the other hand, the duty ratio of PWM lighting of light source unit 1B is 100%, and light source unit 1A is turned on from time t11 to time t12. Note that the duty ratio of PWM lighting of light source unit 1B during this period does not have to be 100%.

[0039] At time t12, when the control unit 14 receives an instruction to turn off both light source units 1A and 1B, it turns on both light source units 1A and 1B simultaneously. At time t13, the control unit 14 selects light source unit 1A and leaves it turned on, and turns off light source unit 1B. At time t14, the control unit 14 turns off light source unit 1A. At time t15, when the control unit 14 receives an instruction to turn on only light source unit 1A, it PWM-lights light source unit 1A. Note that in the example of FIG. 3, after time t15, light source unit 1A is PWM-lit with a duty ratio of 100%, but this is not limited to this.

[0040] Summary of Second Embodiment In the light source lighting control device according to the second embodiment described above, when turning off all of the plurality of LEDs 1, the light source units 1A and 1B that are PWM-lit are turned on in an overlapping manner, and then some of the light source units 1A are selected from the overlapping light source units 1A and 1B that are turned on and kept on, and then some of the light source units 1A are turned off. With this configuration, as in the first embodiment, it is possible to suppress the inrush current to the LEDs 1 at the time of lighting switching (time t15 in FIG. 3 ) without providing a discharge circuit.

[0041] Furthermore, with this configuration, the overlapping lighting of the light source units 1A and 1B allows the control of the switches 13a and 13b to be synchronized. This prevents short circuits across the switches 13a and 13b during PWM lighting, and prevents problems caused by inrush currents to the switches 13a and 13b. Furthermore, PWM lighting makes it possible to adjust the average current values ​​of the light source units 1A and 1B, making it possible to accommodate a variety of automotive lighting specifications.

[0042] <Modifications> In the second embodiment, the plurality of light source units are two light source units (light source units 1A and 1B), but may be three light source units (light source units 1A, 1B, and 1C). For example, when turning off the light source units 1A, 1B, and 1C that are PWM-lit, the control unit 14 may turn on the light source units 1A, 1B, and 1C in duplicate, select one or two of them, leave them on, and then turn off the light source units. Furthermore, when turning off the light source units 1A and 1C that are PWM-lit, the control unit 14 may turn on the light source units 1A and 1C in duplicate, select one of them, leave it on, and then turn off the light source unit. Expanding on the above, the plurality of light source units may be two or more light source units.

[0043] 4 is a circuit diagram showing the configuration of a light source lighting control device according to Embodiment 3. Hereinafter, among the components according to Embodiment 3, components that are the same as or similar to the components described above will be assigned the same or similar reference numerals, and different components will be mainly described.

[0044] In the third embodiment, the plurality of LEDs 1 include a first semiconductor light source LED 1f, a second semiconductor light source LED 1g, and a third semiconductor light source LED 1h. Light source unit 1A, which is the first light source unit, includes LED 1f and LED 1g connected in series to LED 1f. Light source unit 1B, which is the second light source unit, includes LED 1f and LED 1h connected in series to LED 1f and in parallel to LED 1g.

[0045] Furthermore, the number of LEDs in light source unit 1A, which includes one LED 1f and one LED 1g, is smaller than the number of LEDs in light source unit 1B, which includes one LED 1f and two LEDs 1h. However, the number of LEDs in light source units 1A and 1B is not limited to this.

[0046] The control unit 14 according to the third embodiment turns off the light source unit 1B, which is turned on, while selecting and turning on the light source unit 1A as one of the light source units. That is, the control unit 14 turns on the light source units 1A as one of the light source units while turning on the light source units 1A and 1B substantially exclusively. Thereafter, the control unit 14 turns off the light source unit 1A.

[0047] Summary of Embodiment 3 In the light source lighting control device according to the third embodiment, the light source unit 1A is selected as one of the light source units described above and turned on while the light source unit 1B that is turned on is turned off. With this configuration, as in the first embodiment, when turning off all of the multiple LEDs 1, the light source unit 1A having fewer LEDs 1 than the light source unit 1B is selected from the light source units 1A and 1B and turned on, and then the light source unit 1A is turned off. This allows the charging voltage of the capacitor of the smoothing circuit 12 to be gradually reduced, thereby suppressing the inrush current to the LEDs 1 when switching the lighting, even without providing a discharge circuit.

[0048] It should be noted that the embodiments and modifications may be freely combined, and the embodiments and modifications may be modified or omitted as appropriate.

[0049] The above description is illustrative in all respects and is not restrictive. It is understood that countless variations not illustrated can be envisioned.

[0050] 1, 1f, 1g, 1h LEDs, 1A, 1B light source unit, 11 DC-DC converter, 12 smoothing circuit, 13 switching circuit, 14 control unit.

Claims

1. A light source lighting control device that controls the lighting of multiple semiconductor light sources connected in series, comprising: a DC-DC converter that generates a current; a smoothing circuit that smoothes the output of the DC-DC converter; a switching circuit that switches between on and off each of the multiple light source units by controlling the current supplied to multiple light source units with different combinations of the multiple semiconductor light sources; and a control unit that controls the lighting of the multiple light source units by controlling the switching circuit, wherein when turning off all of the multiple semiconductor light sources, the control unit selects from the multiple light source units a part of the light source units which have fewer semiconductor light sources than all of the one or more light source units that are lit, changes them from off to on or leaves them lit, and then turns off the part of the light source units.

2. A light source lighting control device according to claim 1, wherein the part of the light source units is a light source unit having the smallest number of semiconductor light sources among the plurality of light source units.

3. A light source lighting control device as described in claim 1, wherein the lighting of the plurality of light source units includes PWM lighting, and when turning off all of the plurality of semiconductor light sources, the control unit turns on the plurality of light source units that are PWM lit in an overlapping manner, then selects some of the light source units from the plurality of light source units that are overlappingly lit, keeps them lit, and then turns off the some of the light source units.

4. A light source lighting control device as described in claim 1, wherein the lighting of the plurality of light source units includes DC lighting, and when turning off all of the plurality of semiconductor light sources, the control unit selects some of the light source units from the plurality of light source units that are DC lit, leaves them lit, and then turns off the some of the light source units, without increasing the number of the semiconductor light sources that are lit.

5. A light source lighting control device as described in claim 1, wherein the plurality of light source units include: a first light source unit including a first semiconductor light source which is the semiconductor light source, and a second semiconductor light source which is the semiconductor light source connected in series to the first semiconductor light source; and a second light source unit including the first semiconductor light source and a third semiconductor light source which is the semiconductor light source connected in series to the first semiconductor light source and connected in parallel to the second semiconductor light source, wherein the number of the semiconductor light sources of the first light source unit is smaller than the number of the semiconductor light sources of the second light source unit, and the control unit selects and lights up the first light source unit as one of the part of the light source units while turning off the second light source unit which is turned on.

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