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

Abstract

The present invention can, for example, make it possible to change a division number for a sequential turn signal without the need for a complicated redesign of a circuit. A lighting circuit according to the present invention sequentially lights a plurality of light sources that are connected in series. The lighting circuit comprises: a plurality of switch elements that are provided to correspond to the plurality of light sources and are configured such that the corresponding light source turns on when a switching element is turned off; and a switch control circuit that sequentially outputs a turn-off signal to the plurality of switch elements. The lighting circuit has an on-maintaining unit that can keep at least one of the switch elements of the plurality switch elements excluding an uppermost switch element in an on state regardless of the output of the turn-off signal.

Description

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

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

[0002] An example of a lighting device is a vehicle turn signal lamp (hereinafter referred to as a "turn signal lamp") that uses a so-called sequential technology in which a plurality of light sources each having a light-emitting element are arranged and turned on sequentially. The lighting circuit of a sequential lighting device has a plurality of switch elements provided corresponding to each of the plurality of light sources, and is configured so 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 (see, for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2017-119449

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

[0005] This specification discloses a technique that can solve at least one of the above-mentioned problems.

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

[0007] (1) A lighting circuit disclosed in this specification sequentially lights up a plurality of light sources connected in series. 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 that sequentially outputs a turn-off signal to the plurality of switch elements. The lighting circuit includes an on-maintaining unit that can maintain at least one switch element of the plurality of switch elements, excluding the switch element in the uppermost row, in an on state regardless of the output of the turn-off signal.

[0008] In this lighting circuit, by maintaining at least one switch element, excluding the topmost switch element, in an on state regardless of the output of a turn-off signal, only the lighting control of the switch elements above the switch element maintained in the on state is enabled. As a result, with this lighting circuit, for example, it is possible to change the number of divisions of the sequential turns 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 that output the turn-off signal to the signal input terminal of the corresponding switch element depending on 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 complex design changes to the circuit.

[0010] (3) In the lighting circuit described above, 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 number of divisions of the sequential turns. In this case, this lighting circuit can reduce the number of other switch elements affected by the reference voltage, compared to, for example, a configuration in which 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 plurality of parallel circuits, each having a plurality of resistors connected in parallel to each other, are connected in series. With this lighting circuit, when adjusting 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, finer adjustments to the reference voltage can be made compared to, for example, a configuration in which the reference voltage circuit simply has a plurality of resistors connected in series.

[0012] (5) In the lighting circuit, the on-maintenance unit may include a voltage divider circuit having a first resistor and a second resistor connected in series, the junction of the first resistor and the second resistor being electrically connected to the signal input terminal of the switch element, and a connecting element that is changeable from a connected state to a disconnected state, electrically connecting the output of the switch control circuit to the junction of the voltage divider circuit. According to this lighting circuit, by changing the connecting element from a connected state to a disconnected state, it is possible to change the number of divisions of the sequential turns, for example, without requiring a complex design change of the circuit.

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

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

[0015] A block diagram showing a schematic configuration of a vehicle lamp according to an embodiment. A circuit diagram showing a configuration of a lighting circuit before the number of divisions is changed. A circuit diagram showing a configuration of a lighting circuit after the number of divisions is changed. A circuit diagram showing a configuration of a reference voltage circuit 60 according to a modified example.

[0016] A. Embodiments: A-1. Configuration of the Vehicle Lamp 10: The vehicle lamp 10 according to this embodiment is a so-called sequential turn signal lamp that sequentially lights up a plurality of light sources 22A-22E arranged in a row along a predetermined direction. The vehicle lamp 10 is provided, for example, at the front or rear end of the vehicle body. 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 this embodiment. As shown in FIG. 1, the vehicle lamp 10 includes a light source unit 20 and a lighting circuit 30.

[0018] The light source unit 20 includes multiple (five in this embodiment) light sources 22A-22E connected in series. Each of the light sources 22A-22E includes one or more light-emitting elements (e.g., LEDs). In this embodiment, the first light source 22A includes two light-emitting elements 22a, and the other light sources 22B-22E include 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. The five light sources 22A-22E (six light-emitting elements) are arranged in a row, for example, horizontally, on the vehicle body.

[0019] The lighting circuit 30 of this embodiment sequentially lights up the multiple light sources 22A-22E based on instructions 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 supply 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's 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 turns on the plurality of 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 connected to a power supply line Lv via an input terminal P1 and to 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 each light source of the light source unit 20 via the output power supply line Lv. The DC-DC converter 32 may be, 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 subsequent 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 example, to detect a break in the power supply line Lv and to protect against overcurrent, based on the detection results of the voltage detection circuit 33 and the current detection circuit 34. The lighting circuit 30 also includes an input filter 31 and an output filter 35 as countermeasures against static electricity on 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: Fig. 2 is a circuit diagram showing the configuration of the lighting circuit 30 before the division change. The timer circuit 50 is an example of a switch control circuit.

[0025] As shown in FIG. 2, the bypass switch circuit 40 includes multiple switch elements 41B to 41E. Each switch element 41B to 41E is provided corresponding to one of the multiple light sources 22B to 22E. Each switch element 41B to 41E is electrically connected to a branch line Lb that branches off from a connection point on the high-potential side of the corresponding light source 22B to 22E. When each switch element 41B to 41E is in the on state (closed state), a drive current Ia flows through the branch line Lb, turning off the corresponding light source 22B to 22E. When each switch element 41B to 41E is turned off (open state), a drive current Ia flows through the corresponding light source 22B to 22E, turning it 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, with the drain of the NMOS transistor electrically connected to the connection point (power supply line Lv) and the source electrically connected to the ground line Lg. Therefore, the on / off control of each of the switch elements 41B-41E can be performed using the same voltage. In this embodiment, no switch element is provided for the light source 22A, which is located at the highest potential among the light sources 22A-22E included in each of the vehicle lamps 10. Therefore, when the turn voltage Vt is applied to the power supply line Lv, the light source 22A always lights up, regardless of the on / off control by the timer circuit 50 (described later).

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

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

[0029] The RC circuit 56 includes a capacitor 58, and the voltage of the capacitor 58 changes over time depending on the length of the period during which the turn voltage Vt is applied to the power supply line Lv (high-level period). Specifically, the RC circuit 56 includes a resistor 57 and a capacitor 58 connected in series. The resistor 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 turned on when the power supply line Lv is at a high level, and charges the capacitor 58 in accordance with the constant voltage Vcc generated by the constant voltage circuit 37, thereby increasing the voltage level of the capacitor 58 over time. Note that FIG. 2 shows only the resistor 57 and the capacitor 58 connected in series to simplify the RC circuit 56.

[0030] The reference voltage circuit 52 generates a plurality of reference voltages VhB to VhE, each of which corresponds to a respective one of the plurality of switch elements 41B to 41E and has a different level. The second reference voltage VhB is the lowest, and the fifth reference voltage VhE is the highest. Specifically, the reference voltage circuit 52 is configured with five resistors 52a to 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 plurality of comparators 54B to 54E are provided corresponding to the plurality of 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 depending on 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 terminal of each comparator 54B-54E is electrically connected to the signal input terminal (the connection point of the voltage divider circuits 42B-42E) of the corresponding switch element 41B-41E via the connection element 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 comparator 54B-54E switches from high to low, turning off the corresponding switch element 41B-41E.

[0033] A-3. Manufacturing method of the lighting circuit 30: First, a preparation step is carried out 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 connecting elements 43B to 43E, respectively. In other words, the number of divisions 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 turn signal is not operated and the turn voltage Vt is not applied to the power line Lv, all comparators 54B-54E are not activated, and all switch elements 41B-41E are in the OFF state. Next, when the turn signal is operated and the turn voltage Vt is applied to the power line Lv, power supply voltages for the comparators 54B-54E are generated, and the constant voltage circuit 37 generates a constant voltage Vcc, turning all switch elements 41B-41E into the ON state. After that (e.g., several milliseconds to several tens of milliseconds), the drive current Ia from the DC-DC converter 32 flows to the first light source 22A and then to the ground line Lg via the second switch element 41B. As a result, only the first light source 22A is turned on, and the other light sources 22B-22E are turned off.

[0035] Furthermore, when the turn voltage Vt is applied to the power supply line Lv, charging of the capacitor 58 begins, and the level of a signal corresponding to the voltage of the capacitor 58 rises. 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 the second switch element 41B turns off. This causes the drive current Ia to flow through the first light source 22A and the second light source 22B and then to the ground line Lg via the third switch element 41C. As a result, the second light source 22B turns on following the first light source 22A, while the other light sources 22C to 22E remain 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 turns off. This causes the drive current Ia to flow to the third light source 22C and 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 turns off accordingly. Then, the drive 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 also lights up, 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 turns off accordingly. Then, the drive current Ia also flows to the fifth light source 22E and flows to the ground line Lg. Therefore, all of the light sources 22A to 22E are turned on.

[0038] Next, a division number changing process is performed on the lighting circuit 30 shown in FIG. 2 to change the division number. FIG. 3 is a circuit diagram showing the configuration of the lighting circuit 30 after the division number change. For example, when changing the division number of the sequential turn from "5" to "3," as shown in FIG. 3, the fourth connection element 43D corresponding to the fourth switch element 41D is removed. This changes the output terminal of the fourth comparator 54D and the signal input terminal of the fourth switch element 41D 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 switches to a low level, the fourth switch element 41D remains on. 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 sequentially lit, while the remaining light sources 22D and 22E are always off. If you want to change the number of divisions of the sequential turn to "4", you can simply remove the fifth connecting element 43E, and if you want to change the number of divisions of the sequential turn to "2", you can simply remove the third connecting element 43C.

[0039] In this way, the number of divisions of the sequential turns is appropriately changed depending on the specifications of the vehicle in which the lighting circuit 30 is to be installed, and then the manufacturing 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 of the second switch element 41B to the fifth switch element 41E in the on state regardless of the output of a 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 number of divisions of the sequential turns without requiring complex design changes to the circuit.

[0041] A-5. Modification of this embodiment: Figure 4 is a circuit diagram showing the configuration of a reference voltage circuit 60 in a modification. This modification differs from the lighting circuit 30 of the above embodiment in the configuration of the reference voltage circuit 60, but the other configurations are the same. Note that in Figure 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 one another, are connected in series in multiple 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 one another. 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 the parallel circuits 64a to 64c may be the same or different from one another.

[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 parallel circuit 68c is shown in FIG. 4) each having a plurality of resistors 63 connected in parallel with one another are connected in series in multiple stages.

[0046] For example, when the number of divisions of the sequential turn is changed, the corresponding reference voltage may be changed to adjust the turn-off timing of a specific switch element (the light emission timing of a specific light source). 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 a single reference voltage circuit is provided for all switch elements included in the lighting circuit 30 (see FIG. 2 of the above embodiment). For example, changing the resistance value of the resistor 63 in the first parallel circuit 64a to adjust the second reference voltage VhB does not affect the second individual reference voltage circuit 66, which generates a reference voltage independently of the first individual reference voltage circuit 62. 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 (the light emission timing of a specific light source) in accordance with a change in the division number of the sequential turns, finer adjustments to the reference voltage can be made compared to, for example, a reference voltage circuit configured simply with multiple resistors connected in series (see FIG. 2 of the above embodiment). For example, when adjusting the second reference voltage VhB, fine adjustments to the second reference voltage VhB can be made by changing the resistance value of only one of the two resistors 63 that make up the first parallel circuit 64a.

[0048] B. Modifications: The technology disclosed in this specification is not limited to the above-described embodiment, 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 vehicular lamp 10 in the above embodiment is merely an example and can be modified in various ways. For example, in the above embodiment, the vehicular lamp 10 is used as an example of a lighting device, but the lighting device may be a device installed on a moving body other than a vehicle or a fixed device. Furthermore, the light source is not limited to an LED, and may be configured to include other light-emitting elements, such as a halogen lamp. Multiple light-emitting elements may be connected in parallel to one light source. In short, in this specification, multiple light-emitting elements that are simultaneously turned on by turning off a common switch element constitute one light source. Furthermore, the number of light-emitting elements and the connection method may differ for each light source. Furthermore, the number of light sources included in the light source unit 20 is not limited to five, as long as there are at least two or more. For example, there may be six or more light sources.

[0050] In the above embodiment, the switch element may be another type of switch element, such as a PMOS transistor or a bipolar transistor. Furthermore, the switch element may be connected in parallel to the corresponding light source. Furthermore, in the above embodiment, the switch elements 22B to 22E are provided for some of the light sources 22A to 22E included in the vehicle lamp 10, respectively. However, the vehicle lamp 10 may be configured such that a switch element is provided for each of the light sources 22A to 22E.

[0051] In the above embodiment, detachable connection elements 43B to 43E are used as an example of the on-maintenance unit, but this is not limited to this. For example, a configuration in which a switch element or the like is provided instead of the connection element may be used, 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, but 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.

[0053] This international application claims priority based on Japanese Patent Application No. 2023-171056, filed on October 2, 2023, the entire contents of which are incorporated herein by reference.

[0054] The above descriptions of specific embodiments of the present invention have been presented for purposes of illustration. They are not intended to be exhaustive or to limit the invention to the precise forms described. Numerous modifications and variations will be apparent to those skilled in the art in light of the above description.

[0055] 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 circuits 64a to 64c: Parallel circuit

Claims

1. A lighting circuit that sequentially lights up a number of light sources connected in series with each other, comprising: a number of switch elements provided corresponding to each of the plurality of light sources, the switch elements being configured to light up 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 the lighting circuit has an on-maintaining unit that is capable of maintaining at least one switch element among the plurality of switch elements, excluding the switch element in the topmost stage, in an on state regardless of the output of the turn-off signal.

2. A lighting circuit as claimed in claim 1, wherein the switch control circuit has a CR timer circuit including: a capacitor; a reference voltage circuit which generates a plurality of reference voltages having different levels corresponding to the respective switch elements; and a plurality of comparators provided corresponding to the respective switch elements, and which output the turn-off signal to the signal input terminal of the corresponding switch element depending on the magnitude relationship between the level of a signal corresponding to the voltage of the capacitor and the level of the reference voltage.

3. A lighting circuit as claimed in claim 2, wherein 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, and each of the individual reference voltage circuits generates the reference voltage corresponding to the switch element belonging to each group.

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

5. A lighting circuit as claimed in claim 1, wherein the on-maintaining section comprises: 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 the signal input terminal of the switch element; and a connection element which is capable of changing from a connected state electrically connecting the output of the switch control circuit to the connection point of the voltage divider circuit to a disconnected state.

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

7. A manufacturing method for a lighting circuit which sequentially lights up a number of light sources connected in series with each other, the manufacturing method including: a preparation step of preparing a lighting circuit including a number of switch elements provided corresponding to each of the plurality of light sources, the switch elements being 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; and a division number changing step of maintaining at least one switch element of the plurality of switch elements, excluding the switch element in the uppermost stage, in an on state regardless of the output of the turn-off signal.

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