Lighting circuit and vehicle lamp

Abstract

Provided is a lighting circuit that is applied to a vehicle lamp which is provided with n light sources (where n is a plural number) connected in series, said lighting circuit comprising: n switches which are connected in parallel to the n respective light sources; a drive circuit which supplies the n light sources with drive current; and a control circuit which controls the turning on and off of the n switches. The control circuit controls the n switches such that a first state where all the n light sources are lit transitions to a second state where all the n light sources are unlit, after the number of light sources that are lit out of the n light sources sequentially decreases. In each of a plurality of states that have different lighting patterns of the n light sources, including the first and second states, on the basis of the result of detection of the voltages at a plurality of nodes of the n respective light sources on the power supply side, the control circuit determines whether the n light sources are operating as desired.

Description

Lighting circuit and vehicle lighting fixture

[0001] The present invention relates to a lighting circuit and a vehicle lamp.

[0002] For example, a lighting circuit applied to a vehicle lamp that is capable of detecting failures in a plurality of light sources connected in series has been disclosed (for example, Patent Documents 1 and 2).

[0003] JP 2020-087830 A International Publication No. 2021 / 191992

[0004] However, in such lighting circuits, there is a problem in that a plurality of light sources may be erroneously detected as being on or off.

[0005] An object of the present invention is to provide a lighting circuit that suppresses erroneous detection of a fault.

[0006] The main invention for achieving the above-mentioned object is a lighting circuit applied to a vehicle lamp having n (n is plural) light sources connected in series, the lighting circuit comprising: n switches connected in parallel to each of the n light sources; a drive circuit that supplies drive current to the n light sources; and a control circuit that controls the on / off of the n switches, wherein the control circuit controls the n switches so as to transition from a first state in which all of the n light sources are lit to a second state in which the number of lit light sources among the n light sources gradually decreases and all of the n light sources are turned off, and the lighting circuit determines whether the n light sources are operating as desired based on detection results of detecting voltages at a plurality of nodes on the power supply side of each of the n light sources in each of a plurality of states having different lighting patterns of the n light sources, including the first and second states.

[0007] According to the present invention, it is possible to provide a lighting circuit that suppresses erroneous detection of a fault.

[0008] 10 is a diagram showing an example of the configuration of a vehicle lamp 1. FIG. 11 is a diagram showing an example of the configuration of a lighting circuit 40. FIG. 12 is a diagram showing an example of functional blocks realized in a microcomputer 102. FIG. 13 is a flowchart showing an example of processing executed by the microcomputer 102. FIG. 14 is a flowchart showing an example of details of the abnormality determination processing of FIG. 4. FIG. 15 is a diagram showing an example of operation of the lighting circuit 40 in a normal state. FIG. 16 is a diagram showing an example of a lighting pattern of the light source in a normal state. FIG. 17 is a diagram showing an example of operation of the lighting circuit 40 in an abnormal state. FIG. 18 is a diagram showing an example of a lighting pattern of the light source in an abnormal state. FIG. 19 is a flowchart showing an example of processing executed by the microcomputer 102. FIG. 19 is a flowchart showing an example of details of the abnormality determination processing of FIG. 10. FIG. 11 is a diagram showing an example of data stored in a memory unit 220 in a normal state. FIG. 12 is a diagram showing an example of data stored in a memory unit 220 in an abnormal state.

[0009] <Cross-reference to related applications> This application claims priority to Japanese Patent Application No. 2024-066811, filed April 17, 2024, the contents of which are incorporated by reference.

[0010] At least the following matters will become clear from the description of this specification and the accompanying drawings.

[0011] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. The same or equivalent components, members, etc. shown in the drawings will be designated by the same reference numerals, and redundant descriptions will be omitted where appropriate.

[0012] In this embodiment, "connection" refers to an electrically connected state unless otherwise specified. Therefore, "connection" includes not only a case where two components are connected via wiring, but also a case where two components are connected via, for example, a resistor.

[0013] == ...

[0014] <First Light Source 10 and Second Light Source 20> The first light source 10 and the second light source 20 are lighted by receiving a drive current Iout from the lighting circuit 40. In this embodiment, the first light source 10 and the second light source 20 are used as clearance lamps. A clearance lamp is a lamp that indicates the width of a vehicle or its presence, and is also called a sidelight or small lamp.

[0015] The first light source 10 includes a plurality of (e.g., two) light-emitting elements (e.g., light-emitting diodes (LEDs)) 11 and 12. The second light source 20 includes a plurality of (e.g., two) light-emitting elements (e.g., light-emitting diodes (LEDs)) 21 and 22. However, the light-emitting elements are not limited to LEDs, and may be other semiconductor light-emitting elements such as laser diodes (LDs) or organic EL elements.

[0016] In this embodiment, the voltage generated across one light-emitting element when it is lit is, for example, 3±0.1 V. Therefore, the voltage generated across each of the first light source 10 and the second light source 20 when they are lit is, for example, 6±0.2 V. The voltage generated across the first light source 10 when it is lit is referred to as voltage VFa, and the voltage generated across the second light source 20 when it is lit is referred to as voltage VFb. Hereinafter, when the voltages VFa and Vfb are between 5.8 and 6.2 V, they are referred to as being within a predetermined range.

[0017] <Third Light Source 30> The third light source is illuminated by receiving a drive current Iout from the lighting circuit 40. In this embodiment, the third light source is used as a turn signal lamp. A turn signal lamp is a vehicular direction indicator lamp that is illuminated when a driver of the vehicle operates a turn signal (not shown). Furthermore, if a turn signal lamp fails, it is required by law to rapidly flash the turn signal lamp located opposite the failed lamp in the forward / reverse direction to notify those around that the turn signal lamp has failed.

[0018] The third light source 30 includes a plurality of (for example, six) light-emitting elements (for example, light-emitting diodes (LEDs)) 31 to 36. However, the light-emitting elements are not limited to LEDs, and may be other semiconductor light-emitting elements such as laser diodes (LDs) or organic EL elements.

[0019] Furthermore, the voltage generated across both ends of the third light source 30 when it is turned on is, for example, 18±0.6 V. The voltage generated across both ends of the third light source 30 when it is turned on is referred to as voltage VFc. Hereinafter, when voltage VFc indicates a voltage between 17.4 and 18.6 V, it is described as voltage VFc being within a predetermined range. Furthermore, the first light source 10, the second light source 20, and the third light source 30 are connected in series within the lighting circuit 40. Note that the first light source 10, the second light source 20, and the third light source 30 correspond to "n light sources" (n = 3 in this embodiment). Furthermore, the minimum voltage of voltages VFa, VFb, and VFc corresponds to a "first value," and the maximum voltage corresponds to a "second value."

[0020] <Lighting Circuit 40> The lighting circuit 40 is applied to the vehicle lamp 1, and is a circuit that controls the turning on and off of the first light source 10, the second light source 20, and the third light source 30 in accordance with instructions from a control device (not shown: hereinafter also referred to as an ECU) provided on the vehicle side. Specifically, a voltage Vbat from a battery 50 is supplied to the lighting circuit 40 via a switch SW, and the lighting circuit 40 supplies a drive current Iout to the first light source 10, the second light source 20, and the third light source 30.

[0021] The lighting circuit 40 includes terminals Tbat, Tgnd, Tr, Ts, Ta0, Ta1, Tb0, Tb1, Tc0, and Tc1. A first light source 10 is provided between the terminals Ta0 and Ta1, a second light source 20 is provided between the terminals Tb0 and Tb1, and a third light source 30 is provided between the terminals Tc0 and Tc1. The positive electrode of the battery 50 is connected to the terminal Tbat via a switch SW, and the negative electrode of the battery 50 is connected to the terminal Tgnd and is also grounded. The lighting circuit 40 is connected to an ECU (not shown) at the terminals Tr and Ts.

[0022] 2 is a diagram showing an example of the configuration of the lighting circuit 40. The lighting circuit 40 includes a boost circuit 100, a drive circuit 101, a microcomputer 102, switch circuits 110 and 111, voltage divider circuits 120, 121 and 122, switches SW0, SW1 and SW2, and terminals Tbat, Tgnd, Tr, Ts, Ta0, Ta1, Tb0, Tb1, Tc0 and Tc1.

[0023] The switch SW0 is provided between the terminal Ta0 and the terminal Ta1 (in other words, so as to be connected in parallel to the first light source 10). When the switch SW0 is on (conducting), a path is formed through which current is supplied to the second light source 20, bypassing the first light source 10. As a result, no current is supplied to the first light source 10, so the first light source 10 is not lit and is in an extinguished state. On the other hand, when the switch SW1 is off (non-conducting), current is supplied to the first light source 10, so that the first light source 10 is in an lit state.

[0024] The switch SW1 is provided between the terminal Tb0 and the terminal Tb1 (in other words, so as to be connected in parallel to the second light source 20). When the switch SW1 is on, a path is formed that bypasses the second light source 20. As a result, no current is supplied to the second light source 20, so that the second light source 20 is not lit and is in an extinguished state. On the other hand, when the switch SW2 is off, a current is supplied to the second light source 20, so that the second light source 20 is in an lit state.

[0025] The switch SW2 is a switch provided between the terminal Tc0 and the terminal Tc1 (in other words, so as to be connected in parallel to the third light source 30). When the switch SW2 is on, a path is formed that bypasses the third light source 30. As a result, no current is supplied to the third light source 30, so that the third light source 30 is not lit and is in an extinguished state. On the other hand, when the switch SW2 is off, current is supplied to the third light source 30, so that the third light source 30 is in an lit state. The switches SW0 to SW2 correspond to "n switches" (n=3 in this embodiment).

[0026] The boost circuit 100 is a circuit that boosts the voltage V1 (i.e., the voltage Vbat of the battery 50) and outputs a voltage V2, and is provided between the terminal Tbat and the drive circuit 101. The boost circuit 100 normally outputs the voltage V2, and when the switch SW is turned off, it outputs the voltage V2 at the ground level.

[0027] The drive circuit 101 is a circuit (constant current circuit) that outputs a predetermined drive current Iout for lighting the first light source 10, the second light source 20, and the third light source 30 based on the voltage V2, and is provided between the boost circuit 100 and the terminal Ta0. The drive circuit 101 is configured to include, for example, a step-down switching regulator (DC-DC converter). Note that the drive circuit 101 is not limited to a switching regulator, and may be configured using, for example, a linear regulator.

[0028] The microcomputer 102 is a circuit that controls the operation of the vehicle lamp 1. The microcomputer 102 turns on and off the switches SW0 to SW2 to turn on or off the first light source 10, the second light source 20, and the third light source 30.

[0029] The microcomputer 102 is realized as a hardware configuration including circuits such as a CPU and memory (not shown). The CPU executes a predetermined program, thereby realizing various functions in the microcomputer 102. The microcomputer 102 corresponds to a "control circuit," as will be described in detail later.

[0030] The switch circuit 110 is an integrated circuit that outputs a signal Ssw0 that turns on or off the switch SW0 based on a signal S0 from the microcomputer 102. Similarly, the switch circuit 111 is an integrated circuit that outputs a signal Ssw1 that turns on or off the switch SW1 based on a signal S1 from the microcomputer 102. The switch SW2 is turned on or off based on a signal S2 from the microcomputer 102.

[0031] The voltage divider circuit 120 divides the voltage Va generated at the terminal Ta0. Specifically, the voltage divider circuit 120 divides the voltage Va, which may be up to 40 V, by a factor of 10, and outputs the divided voltage Vad. In this way, the voltage divider circuit 120 converts the voltage Va to a voltage level that can be handled by the microcomputer 102.

[0032] The voltage divider circuit 121 divides the voltage Vb generated at the terminal Tb0. Specifically, the voltage divider circuit 121 divides the voltage Vb by, for example, 1 / 10, and outputs the divided voltage Vbd. In this way, the voltage divider circuit 121 converts the voltage Vb to a voltage level that can be handled by the microcomputer 102.

[0033] The voltage divider circuit 122 divides the voltage Vc generated at the terminal Tc0. Specifically, the voltage divider circuit 122 divides the voltage Vc, for example, by a factor of 10, and outputs the divided voltage Vcd. In this way, the voltage divider circuit 122 converts the voltage Vc to a voltage level that can be handled by the microcomputer 102. The terminals Ta0, Tb0, and Tc0 correspond to "multiple nodes on the power supply side."

[0034] In this way, the voltage divider circuits 120 to 122 divide the voltages Va, Vb, and Vc into divided voltages Vad, Vbd, and Vcd, respectively, which can be handled by the microcomputer 102. Therefore, the microcomputer 102 can calculate the differential voltage Va-Vb between the voltages Va and Vb and the differential voltage Vb-Vc between the voltages Vb and Vc based on the divided voltages Vad, Vbd, and Vcd. Furthermore, the microcomputer 102 can calculate the differential voltage Vc-0 between the voltage Vc and the ground voltage (0 V) based on the voltage Vcd.

[0035] 3 is a diagram showing an example of functional blocks realized in the microcomputer 102. When the CPU of the microcomputer 102 executes a predetermined program, a control unit 200, a determination unit 210, a storage unit 220, and a transmission unit 230 are realized in the microcomputer 102.

[0036] <<Control Unit 200>> The control unit 200 outputs signals for controlling the on / off of each of the switches SW0 to SW2 based on the signal Sr from the ECU. In other words, the control unit 200 outputs a signal S0 to control the on / off of the switch SW0, thereby turning on or off the first light source 10. The control unit 200 also outputs a signal S1 to control the on / off of the switch SW1, thereby turning on or off the second light source 20. The control unit 200 also outputs a signal S2 to control the on / off of the switch SW2, thereby turning on or off the third light source 30.

[0037] Specifically, the control unit 200 first outputs signals S0 to S2 to turn off all of the switches SW0 to SW2 so that the first light source 10, the second light source 20, and the third light source 30 are all turned on (hereinafter referred to as state A). In this embodiment, the control unit 200 then outputs signals S0 to S2 to turn on the switches SW0, SW1, and SW2 in sequence so that the first light source 10 and the second light source 20 are turned off in that order, thereby sequentially reducing the number of turned-on light sources. The control unit 200 then outputs signals S0 to S2 to turn on all of the switches SW0 to SW2 so that the first light source 10, the second light source 20, and the third light source 30 are all turned off (hereinafter referred to as state D). Note that, hereinafter, the state in which only the first light source 10 is turned off will be referred to as state B, and the state in which the first light source 10 and the second light source 20 are turned off will be referred to as state C. Moreover, state A corresponds to the "first state," and state D corresponds to the "second state."

[0038] <<Determination Unit 210>> The determination unit 210 detects divided voltages Vad, Vbd, and Vcd, calculates differential voltages Va-Vb, Vb-Vc, and Vc-0, and determines whether or not the switches SW0 to SW2, the first light source 10, the second light source 20, and the third light source 30 are malfunctioning. Specifically, the determination unit 210 detects the voltages Va, Vb, and Vc in each of a plurality of states (e.g., states B and C) including states A and D and having different lighting patterns for the first light source 10, the second light source 20, and the third light source 30, and determines whether or not the first light source 10, the second light source 20, and the third light source 30 are operating as desired, based on the detection results. The differential voltages Va-Vb (hereinafter referred to as Vab), Vb-Vc (hereinafter referred to as Vbc), and Vc-0 (hereinafter referred to as Vc0) correspond to "plural voltages."

[0039] <<Storage Unit 220>> The storage unit 220 stores the digital values ​​of the voltages Vad, Vbd, and Vcd detected by the determination unit 210, along with the on / off states of the switches SW0 to SW2.

[0040] <<Transmitting Unit 230>> When the determining unit 210 determines that an abnormality has occurred, the transmitting unit 230 transmits information indicating the abnormality to the ECU. Details of each functional block will be described below along with the processing executed in the lighting circuit 40.

[0041] <<Operation of Microcomputer 102 in Normal Operation>> Fig. 4 is a flowchart showing an example of processing executed by the microcomputer 102. Fig. 5 is a flowchart showing an example of details of the abnormality determination processing in Fig. 4. Fig. 6 is a diagram showing an example of operation of the lighting circuit 40 in normal operation. Fig. 7 is a diagram showing an example of a lighting pattern of the light source in normal operation.

[0042] First, at time t0 in Fig. 6, the control unit 200 turns off the switches SW0 to SW2 and turns on all the light sources (S10 in Fig. 4). Then, at time t1, the determination unit 210 performs an abnormality determination process (S11 in Fig. 4). Specifically, as shown in Fig. 5, the determination unit 210 detects the voltages Va, Vb, and Vc (S20 in Fig. 5). Note that, in reality, the determination unit 210 detects divided voltages Vad, Vbd, and Vcd, but for convenience, these will be referred to as voltages Va, Vb, and Vc.

[0043] The determination unit 210 then calculates the differential voltages Vab, Vbc, and Vc0 (S21). The determination unit 210 then determines that the switches SW0 to SW2 have been correctly turned off and all light sources are lighting normally, based on the fact that the differential voltages Vab, Vbc, and Vc0 corresponding to the switches SW0 to SW2 that are off are voltages VFa, VFb, and VFc, respectively, within a predetermined range (YES in S22). Specifically, when the control unit 200 turns off the switch SW0 and the voltage across the first light source 10 is between 5.8 V and 6.2 V, for example, the determination unit 210 determines that the switch SW0 has been correctly turned off and that the first light source 10 is lighting normally.

[0044] Then, none of the switches SW0 to SW2 are turned on (YES in S25). The determination unit 210 determines that there is no abnormality because the switches SW0 to SW2 are correctly turned off and all the light sources are lit normally (S27). The lighting pattern at this time is state A in FIG. 7.

[0045] At time t2 in Fig. 6, the control unit 200 turns on the switch SW0 to turn off the first light source 10 (S12 in Fig. 4). At this time, the control unit 200 has not turned off all the light sources (NO in S13).

[0046] At time t3, the determination unit 210 performs an abnormality determination process (S11 in FIG. 4). Specifically, the determination unit 210 detects the voltages Va, Vb, and Vc (S20 in FIG. 5).

[0047] The determination unit 210 then calculates the differential voltages Vab, Vbc, and Vc0 (S21). Thereafter, the determination unit 210 determines that the switches SW1 and SW2 are correctly turned off and that the second light source 20 and the third light source 30 are properly lit, based on the fact that the differential voltages Vbc and Vc0 corresponding to the switches SW1 and SW2 that are turned off among the switches SW0 to SW2 are voltages VFb and VFc, respectively, within a predetermined range (YES in S22).

[0048] The determination unit 210 then determines that the switch SW0 is correctly turned on based on the fact that the differential voltage Vab corresponding to the switch SW0 that is turned on among the switches SW0 to SW2 is lower than a predetermined range (YES in S25). Specifically, when the control unit 200 turns on the switch SW0 and the voltage across the first light source 10 is 0 V, for example, the determination unit 210 determines that the switch SW0 is correctly turned on because it has been confirmed that the first light source 10 is lighting normally. The determination unit 210 determines that there is no abnormality because the switches SW0 to SW2 are correctly turned on and off and the second light source 20 and the third light source 30 are lighting normally (S27). The lighting pattern at this time is state B in FIG. 7 .

[0049] 6, the switches SW0 and SW1 are turned on to turn off the first light source 10 and the second light source 20 (S12 in FIG. 4). At this time, the control unit 200 has not turned off all the light sources (NO in S13).

[0050] At time t5, the determination unit 210 performs an abnormality determination process (S11). Specifically, the determination unit 210 detects the voltages Va, Vb, and Vc (S20 in FIG. 5).

[0051] The determination unit 210 then calculates the differential voltages Vab, Vbc, and Vc0 (S21). Thereafter, the determination unit 210 determines that the switch SW2 is correctly turned off and the third light source 30 is lit normally, based on the fact that the differential voltage Vc0 corresponding to the switch SW2 that is turned off among the switches SW0 to SW2 is the voltage VFc within a predetermined range (YES in S22).

[0052] The determination unit 210 then determines that the switches SW0 and SW1 are correctly turned on based on the fact that the differential voltages Vab and Vbc corresponding to the switches SW0 and SW1 that are turned on are lower than a predetermined range (YES in S25). The determination unit 210 determines that there is no abnormality because the switches SW0 to SW2 are correctly turned on and off and the first light source 10, second light source 20, and third light source 30 are lighting normally (S27). The lighting pattern at this time is state C in FIG. 7.

[0053] 6, the control unit 200 turns on the switches SW0 to SW2 to turn off the first light source 10, the second light source 20, and the third light source 30 (S12 in FIG. 4). At this time, the control unit 200 turns off all the light sources (YES in S13).

[0054] At time t7, the determination unit 210 performs an abnormality determination process (S14). Note that step S14 is the same as step S11. Specifically, the determination unit 210 detects the voltages Va, Vb, and Vc (S20 in FIG. 5).

[0055] Then, the determination unit 210 calculates the differential voltages Vab, Vbc, and Vc0 (S21).Then, the determination unit 210 determines that none of the switches SW0 to SW2 are turned off (YES in S22).

[0056] Then, the determination unit 210 determines that the switches SW0 to SW2 are correctly turned on based on the fact that the differential voltages Vab, Vbc, and Vc0 corresponding to the switches SW0 to SW2 that are turned on are lower than a predetermined range (YES in S25). The determination unit 210 determines that there is no abnormality because the switches SW0 to SW2 are correctly turned on (S27). The lighting pattern at this time is state D in FIG. 7. Note that the same operation is repeated from t8 onwards.

[0057] The above describes a case where there is no abnormality in the switches SW0 to SW2, the first light source 10, the second light source 20, and the third light source 30. Below, a case where a fault occurs in the switch SW1, causing it to be in an open state will be described.

[0058] <<Operation of Microcomputer 102 in the Event of Abnormality>> Fig. 4 is a flowchart showing an example of processing executed by the microcomputer 102. Fig. 5 is a flowchart showing an example of details of the abnormality determination processing of Fig. 4. Fig. 8 is a diagram showing an example of operation of the lighting circuit 40 in the event of an abnormality. Fig. 9 is a diagram showing an example of a lighting pattern of the light source in the event of an abnormality.

[0059] First, at time t10 in Fig. 8, the control unit 200 turns off the switches SW0 to SW2 and turns on all the light sources (S10 in Fig. 4). Then, at time t11, the determination unit 210 performs an abnormality determination process (S11 in Fig. 4). Specifically, the determination unit 210 detects the voltages Va, Vb, and Vc (S20 in Fig. 5). Note that, in reality, the determination unit 210 detects divided voltages Vad, Vbd, and Vcd, but for convenience, these will be referred to as voltages Va, Vb, and Vc.

[0060] The determination unit 210 then calculates the differential voltages Vab, Vbc, and Vc0 (S21). Thereafter, the determination unit 210 determines that the switches SW0 to SW2 are correctly turned off and all the light sources are properly lit, based on the fact that the differential voltages Vab, Vbc, and Vc0 corresponding to the switches SW0 to SW2 that are turned off are voltages VFa, VFb, and VFc, respectively, within a predetermined range (YES in S22).

[0061] Then, none of the switches SW0 to SW2 are turned on (YES in S25). The determination unit 210 determines that there is no abnormality because the switches SW0 to SW2 are correctly turned off and all the light sources are lit normally (S27). The lighting pattern at this time is state A in FIG. 9.

[0062] At time t12 in Fig. 8, the control unit 200 turns on the switch SW0 to turn off the first light source 10 (S12 in Fig. 4). At this time, the control unit 200 has not turned off all the light sources (NO in S13).

[0063] At time t13, the determination unit 210 performs an abnormality determination process (S11 in FIG. 4). Specifically, the determination unit 210 detects the voltages Va, Vb, and Vc (S20 in FIG. 5).

[0064] The determination unit 210 then calculates the differential voltages Vab, Vbc, and Vc0 (S21). Thereafter, the determination unit 210 determines that the switches SW1 and SW2 are correctly turned off and that the second light source 20 and the third light source 30 are properly lit, based on the fact that the differential voltages Vbc and Vc0 corresponding to the switches SW1 and SW2 that are turned off among the switches SW0 to SW2 are voltages VFb and VFc, respectively, within a predetermined range (YES in S22).

[0065] The determination unit 210 then determines that the switch SW0 is correctly turned on based on the fact that the differential voltage Vab corresponding to the switch SW0 that is turned on among the switches SW0 to SW2 is lower than a predetermined range (YES in S25). The determination unit 210 determines that there is no abnormality because the switches SW0 to SW2 are correctly turned on and off and the second light source 20 and the third light source 30 are lighting normally (S27). The lighting pattern at this time is state B in FIG. 9 .

[0066] 8, the switches SW0 and SW1 are turned on to turn off the first light source 10 and the second light source 20 (S12 in FIG. 4). At this time, the control unit 200 has not turned off all the light sources (NO in S13).

[0067] At time t15, the determination unit 210 performs an abnormality determination process (S11). Specifically, the determination unit 210 detects the voltages Va, Vb, and Vc (S20 in FIG. 5).

[0068] The determination unit 210 then calculates the differential voltages Vab, Vbc, and Vc0 (S21). Thereafter, the determination unit 210 determines that the switch SW2 is correctly turned off and the third light source 30 is lit normally, based on the fact that the differential voltage Vc0 corresponding to the switch SW2 that is turned off among the switches SW0 to SW2 is the voltage VFc within a predetermined range (YES in S22).

[0069] The determination unit 210 then determines that the switch SW0 is correctly turned on based on the fact that the differential voltage Vab corresponding to the switch SW0 that is turned on among the switches SW0 to SW2 is lower than a predetermined range. On the other hand, the determination unit 210 determines that the switch SW1 is not correctly turned on based on the fact that the differential voltage Vbc corresponding to the switch SW1 that is turned on among the switches SW0 to SW2 is a voltage VFb within a predetermined range (NO in S25). Specifically, for example, when the control unit 200 turns on the switch SW1 and the voltage across the first light source 10 is 5.8 V to 6.2 V, the determination unit 210 determines that the switch SW1 is not correctly turned on, that is, that an open circuit fault has occurred in the switch SW1, because it has been confirmed that the second light source 20 is lit normally. Therefore, the determination unit 210 determines that the switch SW1 is in an open state (S26). The transmission unit 230 then transmits information indicating an abnormality, that the switch SW1 is in an open state, to the ECU. The illumination pattern at this time is state C in FIG. 9 .

[0070] 8, the control unit 200 turns on the switches SW0 to SW2 to turn off the first light source 10, the second light source 20, and the third light source 30 (S12). At this time, the control unit 200 turns off all the light sources (YES in S13).

[0071] At time t17, the determination unit 210 performs an abnormality determination process (S14 in FIG. 4). Note that step S14 and step S11 are the same process. Specifically, the determination unit 210 detects the voltages Va, Vb, and Vc (S20 in FIG. 5).

[0072] Then, the determination unit 210 calculates the differential voltages Vab, Vbc, and Vc0 (S21).Then, the determination unit 210 determines that none of the switches SW0 to SW2 are turned off (YES in S22).

[0073] The determination unit 210 then determines that the switches SW0 and SW2 are properly turned on based on the fact that the differential voltages Vab and Vc0 corresponding to the switches SW0 and SW2 that are turned on are lower than a predetermined range. On the other hand, the determination unit 210 determines that the switch SW1 is not properly turned on based on the fact that the differential voltage Vbc corresponding to the switch SW1 that is turned on is a voltage VFb within a predetermined range (NO in S25). The determination unit 210 then determines that the switch SW1 is in an open state (S26). The transmission unit 230 then transmits information indicating an abnormality that the switch SW1 is in an open state to the ECU. The illumination pattern at this time is state D in FIG. 9 . Note that the same operation is repeated from time t18 onwards.

[0074] In this way, by performing fault detection every time the lighting patterns of the first light source 10, the second light source 20, and the third light source 30 change, it is possible to suppress erroneous fault detection.

[0075] The above description deals with the case where switch SW1 is in an open state as an abnormality. However, for example, when switch SW0 is controlled to be turned off, if the differential voltage Vab of first light source 10 is lower than voltage VFa, determination unit 210 can determine that switch SW0 or first light source 10 is in a short-circuit state.

[0076] Furthermore, for example, when the switch SW0 is controlled to be turned on, if the differential voltage Vab of the first light source 10 is higher than the voltage VFa, the judgment unit 210 can determine that the switch SW0 and the first light source 10 are each in an open state.

[0077] Second Embodiment The first embodiment described an embodiment in which abnormality determination processing is performed each time the lighting patterns of the first light source 10, the second light source 20, and the third light source 30 change. As a second embodiment, an embodiment in which the voltages Va, Vb, and Vc are detected each time the lighting pattern changes, and then the abnormality determination processing is performed when all lighting patterns have ended will be described below.

[0078] <<Operation of the microcomputer 102 under normal conditions>> Fig. 10 is a flowchart showing an example of processing executed by the microcomputer 102. Fig. 11 is a flowchart showing an example of details of the abnormality determination processing. Fig. 12 is a diagram showing an example of data stored in the storage unit 220 under normal conditions, and will be described below together with Fig. 6.

[0079] First, at time t0 in FIG. 6 , the control unit 200 turns off the switches SW0 to SW2 and turns on all the light sources (S10 in FIG. 10 ). Then, at time t1, the determination unit 210 detects the voltages Va, Vb, and Vc (S20). Note that, in reality, the determination unit 210 detects the voltages Vad, Vbd, and Vcd, but for convenience, these will be referred to as voltages Va, Vb, and Vc. Thereafter, each time the determination unit 210 detects the voltages Va, Vb, and Vc, it writes the detected voltages Va, Vb, and Vc data along with the on / off data of the switches SW0 to SW2 to the storage unit 220, as shown, for example, in No. 1 in FIG. 12 .

[0080] At time t2, the control unit 200 turns on the switch SW0 to turn off the first light source 10 (S12). At this time, the control unit 200 has not turned off all the light sources (NO in S13).

[0081] At time t3, the determination unit 210 detects the voltages Va, Vb, and Vc (S20).

[0082] At time t4, the switches SW0 and SW1 are turned on to turn off the first light source 10 and the second light source 20 (S12). At this time, the control unit 200 has not turned off all the light sources (NO in S13).

[0083] At time t5, the determination unit 210 detects the voltages Va, Vb, and Vc (S20).

[0084] At time t6, the control unit 200 turns on the switches SW0 to SW2 to turn off the first light source 10, the second light source 20, and the third light source 30 (S12). At this time, the control unit 200 turns off all the light sources (YES in S13).

[0085] At time t7, the determination unit 210 detects the voltages Va, Vb, and Vc (S20).

[0086] Thereafter, the determination unit 210 performs an abnormality determination process (S30) based on the data stored in the storage unit 220, as shown in Fig. 12. Specifically, the determination unit 210 reads all data (e.g., No. 1 to No. 4 in Fig. 12) from the storage unit 220, and calculates the differential voltages Vab, Vbc, and Vc0 at all detection timings (S40 in Fig. 11).

[0087] Thereafter, the determination unit 210 determines that the switches SW0 to SW2 have been correctly turned off and that the first light source 10, the second light source 20, and the third light source 30 are properly lit, based on the fact that the differential voltages Vab, Vbc, and Vc0 corresponding to the switches SW0 to SW2 that are turned off are voltages VFa, VFb, and VFc within a predetermined range, respectively (YES in S22). Specifically, when the control unit 200 turns off the switch SW0 and the voltage across the first light source 10 is 5.8 V to 6.2 V, for example, the determination unit 210 determines that the switch SW0 has been correctly turned off and that the first light source 10 is properly lit.

[0088] The determination unit 210 then determines that the switches SW0 to SW2 are correctly turned on based on whether the differential voltages Vab, Vbc, and Vc0 corresponding to the switches SW0 to SW2 that are turned on are lower than a predetermined range (YES in S25). Specifically, when the control unit 200 turns on the switch SW0 and the voltage across the first light source 10 is 0 V, for example, the determination unit 210 determines that the switch SW0 is correctly turned on because it has been confirmed that the first light source 10 is lighting normally. The determination unit 210 determines that there is no abnormality because the switches SW0 to SW2 are correctly turned on and off and the first light source 10, the second light source 20, and the third light source 30 are correctly lighting (S27). Note that the same operation is repeated from t8 onwards.

[0089] The above describes a case where there is no abnormality in the switches SW0 to SW2, the first light source 10, the second light source 20, and the third light source 30. Below, a case where a fault occurs in the switch SW1, causing it to be in an open state will be described.

[0090] <<Operation of Microcomputer 102 in Abnormal Conditions>> FIG. 10 is a flowchart showing an example of processing executed by the microcomputer 102. FIG. 11 is a flowchart showing a detailed example of the abnormality determination processing. FIG. 13 is a diagram showing an example of data stored in the storage unit 220 in the event of an abnormality, and will be described below in conjunction with FIG. 8. In the second embodiment, the operation of the microcomputer 102 in the event of an abnormality from time t10 to time t17 is the same as the operation of the microcomputer 102 in the normal condition from time t0 to time t7, and therefore will not be described again. Furthermore, each time the determination unit 210 detects the voltages Va, Vb, and Vc, the determination unit 210 writes the detected voltages Va, Vb, and Vc data along with the on / off data of the switches SW0 to SW2 to the storage unit 220, as shown in, for example, No. 1 in FIG. 13.

[0091] After time t17 in Fig. 8, the determination unit 210 performs an abnormality determination process (S30 in Fig. 10) based on the data stored in the storage unit 220, as shown in Fig. 13. Specifically, the determination unit 210 reads all data (e.g., No. 1 to No. 4 in Fig. 13) from the storage unit 220 and calculates the differential voltages Vab, Vbc, and Vc0 at all detection timings (S40 in Fig. 11).

[0092] Thereafter, the determination unit 210 determines that the switches SW0 to SW2 have been correctly turned off and all the light sources are lighting normally, based on the fact that the differential voltages Vab, Vbc, and Vc0 corresponding to the switches SW0 to SW2 that are turned off are voltages VFa, VFb, and VFc within a predetermined range, respectively (YES in S22). Specifically, when the control unit 200 turns off the switch SW0 and the voltage across the first light source 10 is 5.8 V to 6.2 V, for example, the determination unit 210 determines that the switch SW0 has been correctly turned off and the first light source 10 is lighting normally.

[0093] The determination unit 210 then determines that the switches SW0 and SW2 are correctly turned on based on the fact that the differential voltages Vab and Vc0 corresponding to the on switches SW0 and SW2 are lower than a predetermined range. On the other hand, the determination unit 210 determines that the switch SW1 is not correctly turned on based on the fact that the differential voltage Vb-Vc corresponding to the on switch SW1 is within a predetermined range (NO in S25). Specifically, for example, when the control unit 200 turns on the switch SW1 and the voltage across the first light source 10 is 5.8 V to 6.2 V, the determination unit 210 determines that the switch SW1 is not correctly turned on, that is, that an open circuit fault has occurred in the switch SW1, because it has been confirmed that the second light source 20 is lit normally. Therefore, the determination unit 210 determines that the switch SW1 is in an open state (S26). The transmission unit 230 then transmits information indicating an abnormality that the switch SW1 is in an open state to the ECU. The same operation is repeated from time t18 onwards. This makes it possible to provide a lighting circuit that simplifies the procedure for detecting a fault.

[0094] Summary The above describes the lighting circuit 40 of this embodiment. The lighting circuit 40 includes switches SW0 to SW2, a drive circuit 101, and a microcomputer 102. The microcomputer 102 controls the switches SW0 to SW2 so that, starting from a state in which the first light source 10, the second light source 20, and the third light source 30 are all on, the number of light sources that are on is sequentially reduced until all of the light sources are turned off. The microcomputer 102 then detects the voltages Va, Vb, and Vc each time the lighting pattern changes. The microcomputer 102 then determines whether the first light source 10, the second light source 20, and the third light source 30 are operating as desired. This makes it possible to provide a lighting circuit that suppresses erroneous detection of a fault.

[0095] Furthermore, the microcomputer 102 calculates differential voltages Vab, Vbc, and Vc0 generated in the first light source 10, the second light source 20, and the third light source 30, respectively, based on the voltages Va, Vb, and Vc at the terminals Ta0, Tb0, and Tc0. Then, the microcomputer 102 determines whether the first light source 10, the second light source 20, and the third light source 30 are operating as desired, based on the differential voltages Vab, Vbc, and Vc0, respectively. This makes it possible to reliably determine whether the first light source 10, the second light source 20, and the third light source 30 are operating as desired.

[0096] Furthermore, when the differential voltage (e.g., differential voltage Vab) of a light source (e.g., first light source 10) connected in parallel to a switch (e.g., switch SW0) that is controlled to be turned off is lower than voltage VFa, the microcomputer 102 determines that either the switch SW0 or the first light source 10 is short-circuited. This allows the lighting circuit 40 to determine whether the vehicular lamp 1 has failed.

[0097] Furthermore, when the differential voltage (e.g., differential voltage Vab) of a light source (e.g., first light source 10) connected in parallel to a switch (e.g., switch SW0) that is controlled to be turned on is higher than voltage VFa, the microcomputer 102 determines that the switch SW0 and the first light source 10 are both in an open state. This allows the lighting circuit 40 to determine whether the vehicular lamp 1 has failed.

[0098] Furthermore, the microcomputer 102 determines that the switch SW0 is in an open state when the differential voltage (e.g., differential voltage Vab) of the light source (e.g., the first light source 10) connected in parallel to the switch (e.g., switch SW0) that is being controlled to be turned on is a voltage VFa within a predetermined range. This allows the lighting circuit 40 to determine whether the vehicle lamp 1 has a malfunction.

[0099] The above-described embodiments are intended to facilitate understanding of the present invention and are not intended to limit the present invention. Furthermore, the present invention may be modified or improved without departing from the spirit thereof, and the present invention includes equivalents thereof.

[0100] REFERENCE SIGNS LIST 1 vehicular lamp 10 first light source 20 second light source 30 third light source 40 lighting circuit 50 battery 100 boost circuit 101 drive circuit 102 microcomputer 110, 111 switch circuit 120, 121, 122 voltage dividing circuit 200 control unit 210 determination unit 220 storage unit 230 transmission unit

Claims

1. A lighting circuit applied to a vehicle lamp having n (n is plural) light sources connected in series, comprising: n switches connected in parallel to each of the n light sources; a drive circuit that supplies drive current to the n light sources; and a control circuit that controls the on / off of the n switches, wherein the control circuit controls the n switches to transition from a first state in which all of the n light sources are lit to a second state in which the number of lit light sources among the n light sources gradually decreases until all of the n light sources are turned off, and determines whether the n light sources are operating as desired based on detection results of voltages detected at multiple nodes on the power supply side of each of the n light sources in each of a plurality of states having different lighting patterns of the n light sources, including the first and second states.

2. A lighting circuit according to claim 1, wherein the control circuit calculates a plurality of voltages generated in each of the n light sources based on the voltages of the plurality of nodes in each of the plurality of states, and determines whether or not each of the n light sources is operating as desired based on each of the calculated plurality of voltages.

3. A lighting circuit as claimed in claim 2, wherein the control circuit, when controlling a specified switch among the n switches so that the specified switch is turned off, determines that either the specified switch or the specified light source is in a short-circuit state if the voltage of a specified light source connected in parallel to the specified switch is lower than a first value.

4. A lighting circuit according to claim 3, wherein the control circuit determines that the predetermined switch and the predetermined light source are both in an open state if the voltage of the predetermined light source is higher than a second value when the control circuit controls the predetermined switch so that the predetermined switch is turned on.

5. A lighting circuit according to claim 4, wherein the control circuit determines that the specified switch is in an open state when the voltage of the specified light source falls within a range from the first value to the second value while controlling the specified switch to turn it on.

6. A vehicle lamp comprising: n (n is a plural number) light sources connected in series; and a lighting circuit according to any one of claims 1 to 5.

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