Lighting circuit, lighting device, and method for manufacturing lighting circuit

Abstract

To change the number of divisions of a sequential turn, for example, without requiring complex design changes to a circuit.SOLUTION: A lighting circuit sequentially lights up a plurality of light sources connected in series with each other. The lighting circuit includes a plurality of switch elements provided corresponding to the plurality of light sources, each of which is configured to light up a corresponding light source when turned off, and a switch control circuit which sequentially outputs a turn-off signal to the plurality of switch elements. The lighting circuit includes an on-maintaining unit capable of maintaining at least one switch element, excluding the topmost switch element, of the plurality of switch elements in an on state regardless of the output of a turn-off signal.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The technology disclosed in this specification relates to a lighting circuit, a lighting device, and a method for manufacturing a lighting circuit. [Background technology]

[0002] As an example of a lighting device, there is a vehicular direction indicator lamp (hereinafter referred to as a "turn signal lamp") that uses a so-called sequential method technology in which a plurality of light sources each having a light-emitting element are arranged and sequentially lit. The lighting circuit of a lighting device using the sequential method includes a plurality of switch elements provided corresponding to each of the plurality of light sources, and is configured such that when each switch element is turned off, a drive current flows through the light source corresponding to the switch element, causing the light source to light up (for example, see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-119449 A Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, the number of divisions of the sequential turn required in a lighting device of the sequential type may differ depending on, for example, the type of product (vehicle model) in which the lighting device is mounted. The number of divisions of the sequential turn is the number of switches that are turned on sequentially with a time difference within a predetermined time. For this reason, in the past, for example, when the number of divisions of the sequential turn required for a lighting device having five switch elements is four, there was a problem that it was necessary to change the design of the wiring pattern or circuit configuration of the lighting device, or to prepare a separate lighting device having five switch elements. Note that this problem is not limited to vehicle turn signal lamps, but is a common problem for any lighting device of the sequential type.

[0005] This specification discloses a technique that can solve at least one of the above problems. [Means for solving the problem]

[0006] The technology disclosed in this specification can be realized, for example, in the following forms.

[0007] (1) The lighting circuit disclosed in this specification sequentially lights up a plurality of light sources connected in series with each other. The lighting circuit includes a plurality of switch elements provided corresponding to the plurality of light sources, each of which is configured to light up the corresponding light source when turned off, and a switch control circuit which sequentially outputs a turn-off signal to the plurality of switch elements. The lighting circuit includes an on-maintaining unit capable of maintaining at least one switch element, excluding the switch element in the uppermost stage, of the plurality of switch elements in an on state regardless of the output of the turn-off signal.

[0008] In this lighting circuit, at least one switch element, except for the topmost switch element, is maintained in the on state regardless of the output of the turn-off signal, so that only the lighting control of the switch elements above the switch element maintained in the on state is enabled. As a result, according to this lighting circuit, for example, it is possible to change the division number of the sequential turn without requiring complex design changes to the circuit.

[0009] (2) In the lighting circuit, the switch control circuit may have a CR timer circuit including a capacitor, a reference voltage circuit that generates a plurality of reference voltages having different levels corresponding to the plurality of switch elements, and a plurality of comparators that are provided corresponding to the plurality of switch elements, and output the turn-off signal to the signal input terminal of the corresponding switch element according to the magnitude relationship between the level of a signal corresponding to the voltage of the capacitor and the level of the reference voltage. With this configuration, the number of divisions of the sequential turns can be changed in the CR timer circuit, for example, without requiring a complex design change of the circuit.

[0010] (3) In the above lighting circuit, the reference voltage circuit may include a plurality of individual reference voltage circuits provided corresponding to a plurality of groups formed by dividing the plurality of switch elements, and each of the individual reference voltage circuits may generate the reference voltage corresponding to the switch elements belonging to each group. In this lighting circuit, the corresponding reference voltage may be changed in order to adjust the turn-off timing of a specific switch element (the light emission timing of a specific light source) in accordance with a change in the division number of the sequential turn. In this case, according to this lighting circuit, the number of other switch elements affected by the reference voltage can be reduced, compared to a configuration in which, for example, one reference voltage circuit is provided for all switch elements included in the lighting circuit.

[0011] (4) In the lighting circuit, the reference voltage circuit may include a configuration in which a parallel circuit having a plurality of resistors connected in parallel to each other is connected in series in multiple stages. According to this lighting circuit, when adjusting the turn-off timing of a specific switch element (light emission timing of a specific light source) in accordance with a change in the division number of the sequential turn, it is possible to make finer adjustments to the reference voltage than, for example, a reference voltage circuit having a configuration in which a plurality of resistors are simply connected in series.

[0012] (5) In the above lighting circuit, the on-maintenance unit may include a voltage divider circuit having a first resistor and a second resistor connected in series with each other, the connection point between the first resistor and the second resistor being electrically connected to a signal input terminal of the switch element, and a connection element that can be changed from a connected state that electrically connects the output of the switch control circuit and the connection point of the voltage divider circuit to a cut-off state. According to this lighting circuit, by changing the connection element from a connected state to a cut-off state, it is possible to change the division number of the sequential turn without, for example, requiring a complex design change of the circuit.

[0013] (6) The method of manufacturing a lighting circuit disclosed in this specification is a method of manufacturing a lighting circuit that sequentially lights up a plurality of light sources connected in series with each other, and includes a preparation step of preparing a lighting circuit including a plurality of switch elements provided corresponding to each of the plurality of light sources, the plurality of switch elements being configured to light the corresponding light source when turned off, and a switch control circuit that sequentially outputs a turn-off signal to the plurality of switch elements, and a division number changing step of maintaining at least one of the plurality of switch elements, except for the switch element in the uppermost stage, in an on state regardless of the output of the turn-off signal. According to this method of manufacturing a lighting circuit, for example, a lighting device in which the division number of a sequential turn is changed can be manufactured without requiring a complex design change of the circuit.

[0014] The technology disclosed in this specification can be realized in various forms, for example, in the form of a lighting circuit, a lighting device including the lighting circuit and a plurality of light sources, a manufacturing method for a lighting circuit, etc. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a block diagram showing a schematic configuration of a vehicle lamp according to an embodiment; [Diagram 2] Circuit diagram showing the configuration of the lighting circuit before changing the number of divisions [Diagram 3] Circuit diagram showing the configuration of the lighting circuit after changing the number of divisions [Figure 4] A circuit diagram showing a configuration of a reference voltage circuit 60 according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] A. Embodiment: A-1. Configuration of the vehicle lamp 10: The vehicle lamp 10 according to this embodiment is a so-called sequential type turn signal lamp that sequentially lights up a plurality of light sources 22A-22E arranged in a line along a predetermined direction. The vehicle lamp 10 is provided, for example, at the front end or rear end of the body of the vehicle. The vehicle lamp 10 is an example of a lighting device.

[0017] 1 is a block diagram showing a schematic configuration of a vehicle lamp 10 according to the present embodiment. As shown in FIG.

[0018] The light source unit 20 includes a plurality of light sources 22A-22E (five in this embodiment) connected in series to each other. Each of the light sources 22A-22E has one or more light emitting elements (e.g., LEDs). In this embodiment, the first light source 22A has two light emitting elements 22a, and the other light sources 22B-22E have one light emitting element. The five light sources 22A-22E (six light emitting elements) are connected in series between the power supply line Lv and the ground line Lg. In addition, the five light sources 22A-22E (six light emitting elements) are arranged in the vehicle body, for example, aligned along the horizontal direction.

[0019] The lighting circuit 30 of this embodiment sequentially lights up the multiple light sources 22A to 22E based on an instruction from an ECU (Electronic Control Unit, not shown) on the vehicle side. For example, when a driver of the vehicle operates a turn signal (not shown) to turn on the vehicle lamp 10, the ECU applies a turn voltage Vt to the power line Lv at a predetermined cycle. The turn voltage Vt is an on-off voltage that includes, for example, a low-level period during which the vehicle power supply voltage is not applied and a high-level period during which the power supply voltage is applied.

[0020] The lighting circuit 30 is a sequential turn circuit that sequentially lights up the multiple light sources 22A to 22E. Specifically, the lighting circuit 30 includes a DC-DC converter 32, a voltage detection circuit 33, a current detection circuit 34, a control circuit 36, a constant voltage circuit 37, a bypass switch circuit 40, and a timer circuit 50.

[0021] The lighting circuit 30 is introduced with a power supply line Lv via an input terminal P1, and with a ground line Lg via an input terminal P2. The DC-DC converter 32 is electrically connected to the power supply line Lv and the ground line Lg. The DC-DC converter 32 generates a drive current Ia (see Figs. 2 and 3 described below) based on a turn voltage Vt applied to the power supply line Lv, and supplies the drive current Ia to the light-emitting elements of the light source of the light source unit 20 via the output power supply line Lv. The DC-DC converter 32 is, for example, a step-up / step-down converter.

[0022] The voltage detection circuit 33 and the current detection circuit 34 are electrically connected to the power supply line Lv at the rear stage of the DC-DC converter 32. The control circuit 36 ​​controls the operation of the DC-DC converter 32. The control circuit 36 ​​also executes processing for, for example, detecting a break in the power supply line Lv and protecting against overcurrent, based on the detection results of the voltage detection circuit 33 and the current detection circuit 34. The lighting circuit 30 includes an input filter 31 and an output filter 35 for static electricity countermeasures against the power supply line Lv.

[0023] The constant voltage circuit 37 is electrically connected to the power supply line Lv, and generates a constant voltage to be supplied to the timer circuit 50. The configurations of the bypass switch circuit 40 and the timer circuit 50 will be described next.

[0024] A-2. Configuration of the bypass switch circuit 40 and the timer circuit 50: 2 is a circuit diagram showing the configuration of the lighting circuit 30 before division is changed. The timer circuit 50 is an example of a switch control circuit.

[0025] As shown in FIG. 2, the bypass switch circuit 40 has a plurality of switch elements 41B-41E. Each of the switch elements 41B-41E is provided corresponding to each of the plurality of light sources 22B-22E. Each of the switch elements 41B-41E is electrically connected to a branch line Lb branching from a connection point on the high potential side of the corresponding light source 22B-22E. When each of the switch elements 41B-41E is in an on state (closed state), a drive current Ia flows through the branch line Lb, and the corresponding light source 22B-22E is turned off. When each of the switch elements 41B-41E is turned off (open state), a drive current Ia flows through the corresponding light source 22B-22E, and the corresponding light source 22B-22E is turned on.

[0026] Specifically, in this embodiment, the branch line Lb is electrically connected between the connection point of the corresponding light source 22B-22E and the ground line Lg. Each of the switch elements 41B-41E is, for example, an NMOS transistor, and the drain of the NMOS transistor is electrically connected to the connection point (power supply line Lv) and the source is electrically connected to the ground line Lg. Therefore, the multiple switch elements 41B-41E can be controlled to be turned on and off by the same voltage. In this embodiment, no switch element is provided for the light source 22A located on the highest potential side among the multiple light sources 22A-22E provided in the multiple vehicle lamps 10. Therefore, when the turn voltage Vt is applied to the power supply line Lv, the light source 22A is always turned on regardless of the on / off control by the timer circuit 50 described later.

[0027] Voltage-dividing circuits 42B-42E constituting a gate drive circuit are electrically connected to the signal input terminals (gates of NMOS transistors) of the respective switch elements 41B-41E. Each of the voltage-dividing circuits 42B-42E is electrically connected between the output of the constant voltage circuit 37 and the ground line Lg, and a constant voltage Vcc generated by the constant voltage circuit 37 is applied to each of the voltage-dividing circuits 42B-42E. Each of the voltage-dividing circuits 42B-42E has a first resistor 42a and a second resistor 42b connected in series with each other, and a connection point (division point) between the first resistor 42a and the second resistor 42b is electrically connected to the signal input terminal of each of the switch elements 41B-41E.

[0028] The timer circuit 50 is configured to sequentially output turn-off signals to the multiple switch elements 41B to 41E in response to the passage of time. Specifically, the timer circuit 50 is a CR timer circuit, and includes a reference voltage circuit 52, multiple comparators 54B to 54E, and an RC circuit 56.

[0029] The RC circuit 56 has a capacitor 58, and is configured so that the voltage of the capacitor 58 changes over time according to the length of the period (high level period) during which the turn voltage Vt is applied to the power supply line Lv. Specifically, the RC circuit 56 has a resistive element 57 and a capacitor 58 connected in series with each other. The resistive element 57 and the capacitor 58 are electrically connected between the output of the constant voltage circuit 37 and the ground line Lg, and the constant voltage Vcc generated by the constant voltage circuit 37 is applied to them. The RC circuit 56 is configured to turn on when the power supply line Lv is at a high level, charge the capacitor 58 according to the constant voltage Vcc generated by the constant voltage circuit 37, and increase the voltage level of the capacitor 58 over time. Note that in FIG. 2, the RC circuit 56 is simply shown as the resistive element 57 and the capacitor 58 connected in series with each other.

[0030] The reference voltage circuit 52 generates a plurality of reference voltages VhB-VhE corresponding to the plurality of switch elements 41B-41E, respectively, and having different levels. The second reference voltage VhB is the lowest, and the fifth reference voltage VhE is the highest. Specifically, the reference voltage circuit 52 has five resistors 52a-52e connected in series. The reference voltage circuit 52 is electrically connected between the output of the constant voltage circuit 37 and the ground line Lg, and the constant voltage Vcc generated by the constant voltage circuit 37 is applied to the reference voltage circuit 52.

[0031] The multiple comparators 54B to 54E are provided corresponding to the multiple switch elements 41B to 41E, respectively. Each of the comparators 54B to 54E provides a turn-off signal to the signal input terminal of the corresponding switch element 41B to 41E according to the magnitude relationship between the level of a signal corresponding to the voltage of the capacitor 58 and the level of the corresponding reference voltage. Specifically, a signal corresponding to the reference voltage is provided to the positive input terminal of each of the comparators 54B to 54E, and a signal corresponding to the voltage of the capacitor 58 is provided to the negative input terminal. The second comparator 54B and the third comparator 54C are disposed on the same substrate 54 and packaged, and the fourth comparator 54D and the fifth comparator 54E are disposed on the same substrate 54 and packaged.

[0032] The lighting circuit 30 is provided with a plurality of connection elements 43B-43E corresponding to the plurality of switch elements 41B-41E, respectively. The output terminals of the comparators 54B-54E are electrically connected to the signal input terminals (connection points of the voltage dividing circuits 42B-42E) of the corresponding switch elements 41B-41E via the connection elements 43B-43E. With this configuration, when the level of the signal corresponding to the voltage of the capacitor 58 exceeds the level of the signal corresponding to the reference voltage, the output level of each of the comparators 54B-54E switches from high to low, and the corresponding switch element 41B-41E is turned off.

[0033] A-3. Manufacturing method of the lighting circuit 30: First, a preparation step is performed to prepare the lighting circuit 30 shown in Fig. 2. As described above, in the lighting circuit 30 shown in Fig. 2, the output terminals of the four comparators 54B to 54E and the signal input terminals of the four switch elements 41B to 41E are all electrically connected via the connection elements 43B to 43E, respectively. That is, the division number of the sequential turns in the lighting circuit 30 shown in Fig. 2 is "5".

[0034] Next, the lighting operation of the lighting circuit 30 shown in FIG. 2 will be described. When the direction indicator is not operated and the turn voltage Vt is not applied to the power line Lv, all the comparators 54B to 54E are not activated and all the switch elements 41B to 41E are in the OFF state. Next, when the direction indicator is operated and the turn voltage Vt is applied to the power line Lv, the power supply voltage of the comparators 54B to 54E is generated, and the constant voltage circuit 37 generates the constant voltage Vcc, so that all the switch elements 41B to 41E are in the ON state. After that (for example, after several ms to several tens of ms), the drive current Ia from the DC-DC converter 32 flows to the first light source 22A and flows to the ground line Lg via the second switch element 41B. Therefore, only the first light source 22A is turned on, and the other light sources 22B to 22E are turned off.

[0035] Moreover, by applying the turn voltage Vt to the power supply line Lv, charging of the capacitor 58 starts, and the level of the signal corresponding to the voltage of the capacitor 58 rises. Then, when the level of the signal corresponding to the voltage of the capacitor 58 exceeds the second reference voltage VhB, the output level of the second comparator 54B switches from high to low, and accordingly, the second switch element 41B turns off. Then, the drive current Ia flows through the first light source 22A and the second light source 22B, and flows to the ground line Lg via the third switch element 41C. Therefore, the second light source 22B turns on following the first light source 22A, and the other light sources 22C to 22E are turned off.

[0036] When the level of the signal corresponding to the voltage of the capacitor 58 exceeds the third reference voltage VhC, the output level of the third comparator 54C switches from high to low, and the third switch element 41C is turned off. Then, the drive current Ia also flows to the third light source 22C, and flows to the ground line Lg via the fourth switch element 41D. Therefore, the third light source 22C is also turned on, and the other light sources 22D to 22E are turned off.

[0037] Next, when the level of the signal corresponding to the voltage of the capacitor 58 exceeds the fourth reference voltage VhD, the output level of the fourth comparator 54D switches from high to low, and the fourth switch element 41D is turned off accordingly. Then, the driving current Ia also flows to the fourth light source 22D, and flows to the ground line Lg via the fifth switch element 41E. Therefore, the fourth light source 22D is also turned on, and only the fifth light source 22E is turned off. Next, when the level of the signal corresponding to the voltage of the capacitor 58 exceeds the fifth reference voltage VhE, the output level of the fifth comparator 54E switches from high to low, and the fifth switch element 41E is turned off accordingly. Then, the driving current Ia also flows to the fifth light source 22E, and flows to the ground line Lg. Therefore, all the light sources 22A to 22E are turned on.

[0038] Next, a division number changing step for changing the division number is performed on the lighting circuit 30 shown in FIG. 2. FIG. 3 is a circuit diagram showing the configuration of the lighting circuit 30 after the division number is changed. For example, when the division number of the sequential turn is changed from "5" to "3", the fourth connection element 43D corresponding to the fourth switch element 41D is removed as shown in FIG. 3. As a result, the output terminal of the fourth comparator 54D and the signal input terminal of the fourth switch element 41D are switched from a connected state to a disconnected state. Therefore, even if the level of the signal corresponding to the voltage of the capacitor 58 exceeds the fourth reference voltage VhD and the output level of the fourth comparator 54D is switched to a low level, the fourth switch element 41D maintains the on state. Therefore, in the lighting circuit 30 after the division change shown in FIG. 3, the first light source 22A to the third light source 22C are turned on in a sequential manner, and the remaining light sources 22D and 22E are always turned off. If the number of divisions of the sequential turns is to be changed to "4", the fifth connecting element 43E can be removed, and if the number of divisions of the sequential turns is to be changed to "2", the third connecting element 43C can be removed.

[0039] In this manner, the number of divisions of the sequential turns is appropriately changed according to the specifications of the vehicle in which the lighting circuit 30 is mounted, and then the manufacture of the lighting circuit 30 is completed.

[0040] A-4. Advantages of this embodiment: As described above, in the lighting circuit 30 of the vehicle lamp 10 according to this embodiment, by maintaining any one of the second switch element 41B to the fifth switch element 41E in the on state regardless of the output of the turn-off signal, only the lighting control of the switch element above the switch element maintained in the on state is enabled (see FIG. 3). As a result, according to this embodiment, for example, it is possible to change the division number of the sequential turn without requiring a complex design change of the circuit.

[0041] A-5. Modifications of this embodiment: Fig. 4 is a circuit diagram showing the configuration of a reference voltage circuit 60 in a modified example. This modified example differs from the lighting circuit 30 in the above embodiment in the configuration of the reference voltage circuit 60, but the other configurations are the same. Note that in Fig. 4, the configuration of the bypass switch circuit 40 is simplified.

[0042] 4, the reference voltage circuit 60 has two individual reference voltage circuits 62 and 66. The first individual reference voltage circuit 62 corresponds to the group to which the second switch element 41B and the third switch element 41C belong, and the first individual reference voltage circuit 62 generates the second reference voltage VhB and the third reference voltage VhC.

[0043] The first individual reference voltage circuit 62 has a configuration in which parallel circuits 64a to 64c, each having a plurality of resistors 63 connected in parallel to each other, are connected in series in a plurality of stages. Specifically, the first individual reference voltage circuit 62 has a configuration in which a first parallel circuit 64a, a second parallel circuit 64b, and a third parallel circuit 64c are connected in series to each other. Each of the parallel circuits 64a to 64c has a configuration in which two resistors 63 are connected in parallel. The resistance values ​​of the resistors in each of the parallel circuits 64a to 64c may be the same as each other or may be different.

[0044] The voltage at the connection point between the first parallel circuit 64a and the second parallel circuit 64b is set to a second reference voltage VhB, and the voltage at the connection point between the second parallel circuit 64b and the third parallel circuit 64c is set to a third reference voltage VhC.

[0045] The second individual reference voltage circuit 66 corresponds to the group to which the fourth switch element 41D and the fifth switch element 41E belong, and the second individual reference voltage circuit 66 generates the fourth reference voltage VhD and the fifth reference voltage VhE. Similar to the first individual reference voltage circuit 62, the second individual reference voltage circuit 66 has a configuration in which parallel circuits (only the parallel circuit 68c is shown in FIG. 4) each having a plurality of resistors 63 connected in parallel with each other are connected in series in multiple stages.

[0046] For example, in order to adjust the turn-off timing of a specific switch element (light emission timing of a specific light source) in accordance with a change in the number of divisions of the sequential turn, the corresponding reference voltage may be changed. In this case, according to this modification, the number of other switch elements affected by the reference voltage can be reduced, compared to a configuration in which one reference voltage circuit is provided for all switch elements included in the lighting circuit 30 (see FIG. 2 of the above embodiment). For example, even if the resistance value of the resistor 63 of the first parallel circuit 64a is changed to adjust the second reference voltage VhB, the second individual reference voltage circuit 66 that generates a reference voltage independently of the first individual reference voltage circuit 62 is not affected. That is, the fourth reference voltage VhD and the fifth reference voltage VhE do not fluctuate.

[0047] Furthermore, according to this modification, when adjusting the turn-off timing of a specific switch element (light emission timing of a specific light source) in accordance with a change in the division number of the sequential turn, it is possible to make fine adjustments to the reference voltage, compared to, for example, a reference voltage circuit having a configuration in which multiple resistors are simply connected in series (see FIG. 2 of the above embodiment). For example, when adjusting the second reference voltage VhB, it is possible to make fine adjustments to the second reference voltage VhB by changing the resistance value of only one of the two resistors 63 that make up the first parallel circuit 64a.

[0048] B. Variations: The technology disclosed in this specification is not limited to the above-described embodiments, and can be modified in various forms without departing from the spirit of the invention. For example, the following modifications are also possible.

[0049] The configuration of the vehicle lamp 10 in the above embodiment is merely an example, and various modifications are possible. For example, in the above embodiment, the vehicle lamp 10 is exemplified as a lighting device, but the lighting device may be a device disposed on a moving body other than a vehicle or a fixed device. The light source is not limited to an LED, and may be configured to include other light-emitting elements, such as a halogen lamp. A plurality of light-emitting elements may be connected in parallel to one light source. In short, in this specification, a plurality of light-emitting elements that are simultaneously turned on by turning off a common switch element constitute one light source. In addition, the number of light-emitting elements and the connection method may differ for each light source. In addition, the number of light sources provided in the light source unit 20 is not limited to five, but may be at least two or more. For example, six or more may be used.

[0050] In the above embodiment, the switch element may be another switch element such as a PMOS transistor or a bipolar transistor. Also, the switch element may be connected in parallel to the corresponding light source. Also, in the above embodiment, the switch elements 22B-22E are provided for some of the light sources 22A-22E included in the vehicle lamp 10, but the switch elements may be provided for all of the light sources 22A-22E included in the vehicle lamp 10.

[0051] In the above embodiment, detachable connection elements 43B to 43E are used as an example of the on-maintaining unit. However, this is not limited to this, and for example, a configuration in which a switch element is provided instead of the connection element, or a configuration in which the output level of comparators 54B to 54E is maintained at a high level, may be used.

[0052] In the above modification, the number of individual reference voltage circuits constituting the reference voltage circuit 60 is not limited to two, and may be three or more. Furthermore, the individual reference voltage circuits may be configured with a plurality of resistors connected in series, or may be configured with three or more resistors connected in parallel. [Explanation of symbols]

[0053] 10: Vehicle lamp 20: Light source unit 22A to 22E: Light source 22B: Second light source 22C: Third light source 22a: Light-emitting element 30: Lighting circuit 31: Input filter 32: DC-DC converter 33: Voltage detection circuit 34: Current detection circuit 35: Output filter 36: Control circuit 37: Constant voltage circuit 40: Bypass switch circuit 41B to 41E: Switch element 42B to 42E: Voltage divider circuit 42a: First resistor 42b: Second resistor 43B to 43E: Connection element 50: Timer circuit 52: Reference voltage circuit 54B to 54E: Comparator 56: RC circuit 57: Resistance element 58: Capacitor 60: Reference voltage circuit 62, 66: Individual reference voltage circuit 64a to 64c: Parallel circuit

Claims

1. A lighting circuit for sequentially lighting a plurality of light sources connected in series with each other, a plurality of switch elements provided corresponding to the plurality of light sources, the plurality of switch elements being configured to light the corresponding light sources when turned off; a switch control circuit that sequentially outputs a turn-off signal to the plurality of switch elements; a lighting circuit having an on-maintaining unit capable of maintaining at least one switch element, among the plurality of switch elements, except for the switch element in an uppermost stage, in an on state regardless of the output of the turn-off signal.

2. 2. The lighting circuit according to claim 1, The switch control circuit includes: A capacitor; a reference voltage circuit that generates a plurality of reference voltages having different levels corresponding to the plurality of switch elements; a plurality of comparators provided corresponding to each of the plurality of switch elements, the comparators outputting the turn-off signal to a signal input terminal of the corresponding switch element in accordance with a magnitude relationship between a level of a signal corresponding to a voltage of the capacitor and a level of the reference voltage.

3. 3. The lighting circuit according to claim 2, the reference voltage circuit includes a plurality of individual reference voltage circuits provided corresponding to a plurality of groups formed by dividing the plurality of switch elements, A lighting circuit, wherein each of the individual reference voltage circuits generates the reference voltage corresponding to the switch elements belonging to each group.

4. 4. The lighting circuit according to claim 3, The lighting circuit, wherein the reference voltage circuit includes a configuration in which parallel circuits, each having a plurality of resistors connected in parallel to each other, are connected in series in a plurality of stages.

5. 2. The lighting circuit according to claim 1, The on-maintenance unit is a voltage divider circuit including a first resistor and a second resistor connected in series with each other, the connection point between the first resistor and the second resistor being electrically connected to a signal input terminal of the switch element; a connection element that is changeable from a connected state to a cut-off state, electrically connecting an output of the switch control circuit and the connection point of the voltage divider circuit;

6. The plurality of light sources; A lighting device comprising: a lighting circuit according to any one of claims 1 to 5.

7. A method for manufacturing a lighting circuit for sequentially lighting a plurality of light sources connected in series with each other, comprising the steps of: a preparation step of preparing a lighting circuit including a plurality of switch elements provided corresponding to a plurality of light sources, the plurality of switch elements being configured to light the corresponding light sources when turned off, and a switch control circuit that sequentially outputs a turn-off signal to the plurality of switch elements; and a division number changing step of maintaining at least one switch element, among the plurality of switch elements, except for the switch element in the uppermost stage, in an on state regardless of the output of the turn-off signal.

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