Lighting circuit and lighting device

Abstract

To provide a lighting circuit capable of simultaneously lighting a first light source and a second light source connected in series with each other by applying different currents to the sources.SOLUTION: A lighting circuit lights a first light source and a second light source connected in series with each other. The lighting circuit comprises: a drive circuit which outputs a drive current to a connection line in which the first and second light sources are connected in series; a bypass switch which is connected in parallel with the second light source and switches from an ON state to an OFF state on the basis of the input of a lighting control signal instructing the lighting of the second light source; a parallel line connected in parallel with either the first light source or the second light source; and a current-diverting circuit which diverts a part of the drive current output from the drive circuit to the parallel line on the condition that the bypass switch is in the OFF state.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Conventionally, there has been known a lighting circuit that lights a low beam and a high beam that are connected in series with each other. This lighting circuit is a so-called bypass type lighting circuit, and includes one drive circuit and a bypass switch. The drive circuit outputs a drive current to a connection line that connects the low beam and the high beam in series. The bypass switch is connected in parallel with the high beam, and is switched from an on (closed) state to an off (open) state based on an input of a lighting control signal that instructs lighting of the high beam. With this configuration, the lighting circuit can selectively perform single lighting, in which only the low beam is turned on when the bypass switch is in an on state, and simultaneous lighting, in which both the low beam and the high beam are turned on when the bypass switch is in an off state (for example, see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-156913 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in a conventional bypass lighting circuit, the low beam and the high beam are connected in series to a common connection line, which means that the conventional bypass lighting circuit has a problem in that it cannot handle lighting patterns in which currents of different magnitudes flow through the low beam and the high beam, respectively.

[0005] Note that this problem is not limited to low beam and high beam, but is a common problem to any lighting circuit that lights a first light source and a second light source that are connected in series to a common connection line in a bypass manner.

[0006] This specification discloses a technique that can solve at least one of the above-mentioned problems. [Means for solving the problem]

[0007] The technology disclosed in this specification can be realized, for example, in the following forms.

[0008] (1) A lighting circuit disclosed in the present specification is a lighting circuit that lights a first light source and a second light source connected in series to each other, and includes: a drive circuit that outputs a drive current to a connection line connecting the first light source and the second light source in series; a bypass switch that is connected in parallel to the second light source and changes from an on state to an off state based on an input of a lighting control signal that instructs the second light source to be turned on; a parallel line that is connected in parallel to the first light source or the second light source; and a shunt circuit that flows a portion of the drive current output from the drive circuit to the parallel line on condition that the bypass switch is in the off state.

[0009] In this configuration, a part of the drive current output from the drive circuit flows to the parallel line on condition that the bypass switch is in an off state. As a result, it is possible to reduce the current flowing through the light source (the first light source or the second light source) connected in parallel to the parallel line. In other words, according to this configuration, it is possible to simultaneously light up the first light source and the second light source connected in series by passing different currents through them.

[0010] (2) In the lighting circuit, the second light source may be arranged on a lower potential side with respect to the first light source, and the parallel line may be connected in parallel to the first light source. With this configuration, the first light source and the second light source can be simultaneously turned on while reducing the current flowing through the first light source arranged on the higher potential side relative to the current flowing through the second light source arranged on the lower potential side.

[0011] (3) In the lighting circuit, the second light source may be arranged on a lower potential side relative to the first light source, and the parallel line may be connected in parallel to the second light source. With this arrangement, the first light source and the second light source can be simultaneously turned on while reducing the current flowing through the second light source arranged on the lower potential side relative to the current flowing through the first light source arranged on the higher potential side.

[0012] (4) In the above lighting circuit, the shunt circuit may be configured to stop shunting current to the parallel line when the voltage of the connection line is equal to or lower than a first threshold value that correlates to a total value of voltage drops between the first light source and the second light source, and to shunt current to the parallel line when the voltage of the connection line is greater than the first threshold value.

[0013] The voltage of the connection line is different between when the bypass switch is turned off and both the first light source and the second light source are turned on, and when the bypass switch is turned on and only one of the first light source and the second light source is turned on. That is, the on / off state of the bypass switch can be detected based on the voltage of the connection line (or a voltage correlated to the voltage). In this configuration, the current dividing circuit is configured to divide the current into the parallel line according to the magnitude relationship between the voltage of the connection line and the first threshold value. As a result, according to this configuration, it is possible to simultaneously light up the first light source and the second light source connected in series with each other by passing different currents to each other, without the need to separately provide a detection means for detecting the presence or absence of an input of a lighting control signal to the bypass switch.

[0014] (5) In the above lighting circuit, the parallel line may be connected in parallel to one of the first light source and the second light source that is arranged on the higher potential side, and may further include a protection circuit that prohibits the shunt circuit from shunting current to the parallel line on condition that the voltage of the connection line is equal to or higher than a second threshold for overvoltage protection that is higher than the first threshold.

[0015] For example, if the connection line is in an overvoltage state due to a disconnection of the light source, even if no drive current is being output from the drive circuit, the shunt circuit will start based on the voltage of the connection line and pass a current to the parallel line, which may cause the light source at the lower potential to erroneously light up. In contrast, in this configuration, when the connection line is in an overvoltage state, the protection circuit prohibits shunting to the parallel line. This makes it possible to suppress erroneous lighting of the light source when the connection line is overvoltage.

[0016] (6) The lighting device may include the first light source, the second light source, and the lighting circuit. With this configuration, the first light source and the second light source connected in series can be simultaneously lit by passing different currents through them.

[0017] (7) In the lighting device, the lighting device may be mounted on a vehicle, and of the first light source and the second light source, the light source connected in parallel to the bypass switch may be a light source for high beam, and the light source not connected in parallel to the bypass switch may be a light source for low beam. According to this configuration, different currents may be passed through the high beam and the low beam connected in series to light them simultaneously.

[0018] 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 bypass lighting method for multiple light sources, etc. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a block diagram showing a schematic configuration of a vehicle lamp according to a first embodiment; [Diagram 2] Circuit diagram showing the configuration of a constant voltage circuit [Diagram 3] Circuit diagram showing the configuration of a clamp circuit [Figure 4] Circuit diagram showing the configuration of the protection circuit [Diagram 5] FIG. 11 is a block diagram showing a schematic configuration of a vehicle lamp according to a second embodiment. [Figure 6] Circuit diagram showing the configuration of a constant voltage circuit [Figure 7] Circuit diagram showing the configuration of a clamp circuit DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] A. First embodiment: A-1. Configuration of the vehicle lamp 10: The vehicle lamp 10 according to this embodiment is a headlight device including a low beam 22L and a high beam 22H arranged adjacent to each other. The low beam 22L is a passing headlight, and emits light with an amount of light for illuminating, for example, 40 m ahead. The high beam 22H is a driving headlight, and emits light with an amount of light for illuminating, for example, 100 m ahead. The vehicle lamp 10 is provided, for example, at the front end of the vehicle body. The vehicle lamp 10 is a headlamp and an example of a lighting device, the low beam 22L is an example of a first light source, and the high beam 22H is an example of a second light source.

[0021] 1 is a block diagram showing a schematic configuration of a vehicle lamp 10 according to the first embodiment. As shown in FIG.

[0022] The light source unit 20 includes a low beam 22L and a high beam 22H. The low beam 22L and the high beam 22H are connected in series to each other via a first power supply line L1. The low beam 22L and the high beam 22H each have one or more light emitting elements (e.g., LEDs). The first power supply line L1 is an example of a connection line. In addition, the low beam 22L and the high beam 22H are disposed adjacent to each other on the vehicle body.

[0023] The lighting circuit 30 of this embodiment is configured to selectively perform single lighting, in which only the low beam 22L is turned on, and simultaneous lighting, in which both the low beam 22L and the high beam 22H are turned on, based on instructions from the vehicle's ECU (Electronic Control Unit) 80.

[0024] The lighting circuit 30 is a bypass type lighting circuit that lights the low beam 22L and the high beam 22H with a drive current I from a common drive circuit (a DC-DC converter 32 described below). Specifically, the lighting circuit 30 includes a DC-DC converter 32, a voltage detection circuit 34, a current detection circuit 36, an LED driver 38, a switching interface 40, and a bypass switch 42.

[0025] In the lighting circuit 30, the first power supply line L1 is introduced into the lighting circuit 30 through the input terminal P1, the second power supply line L2 is introduced into the lighting circuit 30 through the input terminal P2, and the ground line Lg is introduced into the lighting circuit 30 through the input terminal P3. In the lighting circuit 30, the first power supply line L1 is led out of the lighting circuit 30 through the output terminal P4, and the ground line Lg is led out of the lighting circuit 30 through the output terminal P6. In the vehicle lamp 10, a bypass line L3 is formed that branches out from a branch point B between the low beam 22L and the high beam 22H. In the lighting circuit 30, the bypass line L3 is led into the lighting circuit 30 through the branch terminal P5. The tip of the bypass line L3 is electrically connected to the ground line Lg.

[0026] The DC-DC converter 32 is electrically connected to the first power supply line L1. When a first power supply voltage Vt1 is applied to the first power supply line L1, the DC-DC converter 32 generates a drive current I and supplies the drive current I to each light source of the light source unit 20 via the first power supply line L1 on the output side. Note that, for example, a step-up / step-down converter is used as the DC-DC converter 32.

[0027] The voltage detection circuit 34 and the current detection circuit 36 ​​are electrically connected to the first power supply line L1 at the rear stage of the DC-DC converter 32. The LED driver 38 controls the operation of the DC-DC converter 32. Based on the detection results of the voltage detection circuit 34 and the current detection circuit 36, the LED driver 38 also executes processing for, for example, disconnection detection of the first power supply line L1, overvoltage protection, and overcurrent protection.

[0028] The bypass switch 42 is connected in parallel to the high beam 22H. Specifically, the bypass switch 42 is electrically connected to the bypass line L3. The bypass switch 42 changes between an on (closed) state in which the branch point B of the first power supply line L1 is electrically connected to the ground line Lg, and an off (open) state in which the branch point B is electrically disconnected from the ground line Lg. The switching interface 40 controls the on and off of the bypass switch 42. Specifically, the switching interface 40 is electrically connected to the second power supply line L2. When the second power supply voltage Vt2 is applied to the second power supply line L2, the switching interface 40 changes the bypass switch 42 from the on state to the off state.

[0029] With the above configuration, for example, when the driver of the vehicle performs a low beam operation to turn on the low beam 22L, the ECU 80 applies the first power supply voltage Vt1 to the first power supply line L1 to operate the DC-DC converter 32, but does not apply the second power supply voltage Vt2 to the second power supply line L2. Therefore, the branch point B of the first power supply line L1 is electrically connected (shorted) to the ground line Lg via the bypass switch 42. Therefore, the drive current I from the DC-DC converter 32 flows through the low beam 22L, but does not flow through the high beam 22H, and flows into the bypass line L3 (see the arrow Ia in FIG. 1). As a result, the low beam 22L is turned on alone.

[0030] Next, when the driver of the vehicle performs a high beam operation to turn on the high beam 22H, the ECU 80 outputs a lighting control signal to apply the second power supply voltage Vt2 to the second power supply line L2 while applying the first power supply voltage Vt1 to the first power supply line L1 to operate the DC-DC converter 32. Therefore, the branch point B of the first power supply line L1 and the ground line Lg are electrically disconnected by the bypass switch 42. Therefore, the driving current I from the DC-DC converter 32 flows through the low beam 22L, does not flow through the bypass line L3, and flows through the high beam 22H (see the arrow Ib in FIG. 1). As a result, the low beam 22L and the high beam 22H are simultaneously turned on.

[0031] A-2. Configuration for reducing the current flowing through the low beam 22L: The lighting circuit 30 is configured to reduce the current flowing through the low beam 22L to be less than the current flowing through the high beam 22H during simultaneous lighting. The lighting circuit 30 is also configured to reduce the current flowing through the low beam 22L during simultaneous lighting to be less than the current flowing through the low beam 22L during single lighting.

[0032] Specifically, the lighting circuit 30 is formed with a parallel line L4 connected in parallel to the low beam 22L. The parallel line L4 is connected between a connection point D of the first power supply line L1 subsequent to the DC-DC converter 32 (on the output terminal P4 side of the lighting circuit 30) and a branch point B. The lighting circuit 30 also includes a current dividing circuit. The current dividing circuit is configured to flow a part of the drive current I output from the DC-DC converter 32 to the parallel line L4 (see the arrow Ic in FIG. 1) on the condition that the bypass switch 42 is in the off state (simultaneous lighting).

[0033] In this embodiment, the current dividing circuit includes a constant voltage circuit 50 and two clamp circuits 60a, 60b (see FIG. 3 described later). The constant voltage circuit 50 and the two clamp circuits 60a, 60b are electrically connected to a parallel line L4.

[0034] (Constant voltage circuit 50): 2 is a circuit diagram showing the configuration of the constant voltage circuit 50. The constant voltage circuit 50 generates a power supply voltage VCC for operational amplifiers 65a and 65b (to be described later) included in each of the clamp circuits 60a and 60b.

[0035] As shown in Fig. 2, the constant voltage circuit 50 has a first Zener diode 55 and two transistors 51a and 51b, and is configured to output a first Zener voltage Vz1 of the first Zener diode 55 after buffering it with the transistors 51a and 51b. The first Zener voltage Vz1 is a value (e.g., 24V) larger than the total value (e.g., 20V) of the voltage drop (=Vfl+Vfh, see Fig. 3) between the low beam 22L and the high beam 22H when they are simultaneously turned on. In addition, the first Zener voltage Vz1 is preferably equal to or lower than the rated voltage of the operational amplifiers 65a and 65b.

[0036] Specifically, the collectors of the transistors 51a and 51b are electrically connected to the connection point D of the first power supply line L1, and the emitters of the transistors 51a and 51b are electrically connected to the clamp circuits 60a and 60b. The first Zener diode 55 is electrically connected between the bases of the transistors 51a and 51b and the ground line Lg. Two base resistors 54a and 54b are electrically connected between the bases and collectors of the transistors 51a and 51b. With this configuration, the constant voltage circuit 50 generates a power supply voltage VCC according to the voltage Vd (the voltage on the anode side of the low beam 22L) on the output side (connection point D) of the first power supply line L1. In addition, the constant voltage circuit 50 can pass a relatively large current through the transistors 51a and 51b.

[0037] In this embodiment, the constant voltage circuit 50 includes two transistors 51a and 51b, so that the branch current Ic flowing through the parallel line L4 is distributed into a first branch current Ica flowing through the transistor 51a and a first branch current Icb flowing through the transistor 51b. This allows the heat generated by the current flowing through the transistors to be distributed more effectively than when the constant voltage circuit 50 includes only one transistor. Furthermore, by providing two base resistors 54a and 54b for each of the transistors 51a and 51b, the heat generated by the base resistors can be distributed. The input side of the constant voltage circuit 50 includes a capacitor 53 connected in parallel to the first Zener diode 55, and the output side of the constant voltage circuit 50 includes a capacitor 56 connected between the emitters of the transistors 51a and 51b and the ground line Lg. This allows the fluctuation of the power supply voltage VCC generated by the constant voltage circuit 50 to be suppressed.

[0038] With this configuration, the power supply voltage VCC generated by the constant voltage circuit 50 changes according to the output voltage Vd as follows: When the light is turned on alone, the output voltage Vd becomes a voltage value (e.g., 12V) equal to the voltage drop (=Vfl) of only the low beam 22L, and when the light is turned on simultaneously, it becomes a voltage value (e.g., 20V) equal to the voltage drop (=Vfl+Vfh) of both the low beam 22L and the high beam 22H. (1) When "output voltage Vd"<"first Zener voltage Vz1 of first Zener diode 55" (when one is turned on, when two are turned on simultaneously): "power supply voltage VCC"="output voltage Vd". (2) When the “output voltage Vd” ​​is greater than or equal to the “first Zener voltage Vz1” (for example, in the event of an overvoltage abnormality due to a wire breakage or the like, as described below): “Power supply voltage VCC” = “first Zener voltage Vz1” - “base-emitter voltage Vbe of transistors 51a and 51b.”

[0039] (Clamp circuits 60a, 60b): 3 is a circuit diagram showing the configuration of the clamp circuits 60a, 60b. Each of the clamp circuits 60a, 60b absorbs a branch current Ic of a predetermined amount from the first power supply line L1 to the parallel line L4. As shown in FIG. 3, each of the clamp circuits 60a, 60b has an operational amplifier 65a, 65b, a reference voltage generating unit 68, a current setting unit 61a, 61b, and a transistor 67a, 67b. The two operational amplifiers 65a, 65b are mounted on the same substrate 65 and packaged.

[0040] A power supply voltage VCC generated by the constant voltage circuit 50 is applied to the power supply terminals of the operational amplifiers 65a and 65b. The power supply voltage VCC of the constant voltage circuit 50 is limited to the first Zener voltage Vz1 (24V) of the first Zener diode 55, so that a voltage exceeding the first Zener voltage Vz1 is prevented from being applied to the power supply terminals of the operational amplifiers 65a and 65b. The output terminals of the operational amplifiers 65a and 65b are electrically connected to the bases of the transistors 67a and 67b via base resistors 66a and 66b. The emitters of the transistors 67a and 67b are electrically connected to the inverting input terminals of the operational amplifiers 65a and 65b, and the collectors of the transistors 67a and 67b are electrically connected to the branch point B of the first power supply line L1. The transistors 67a and 67b are P-type bipolar transistors, but are not limited thereto and may be, for example, P-type FETs (field effect transistors).

[0041] The reference voltage generating unit 68 generates a reference voltage Vh that triggers the operation of each of the clamp circuits 60a and 60b. The reference voltage generating unit 68 has a second Zener diode 68b, and generates a reference voltage Vh according to a second Zener voltage Vz2 of the second Zener diode 68b. Specifically, the cathode of the second Zener diode 68b is electrically connected to the output terminal of the constant voltage circuit 50 via a resistor 68a, and the anode of the second Zener diode 68b is electrically connected to the ground line Lg. The connection point between the resistor 68a and the second Zener diode 68b is electrically connected to the non-inverting input terminal of each of the operational amplifiers 65a and 65b. The second Zener voltage Vz2 is lower than the first Zener voltage Vz1 (the output voltage Vd of the first power supply line L1 when both are turned on simultaneously (a voltage equivalent to the voltage drop (=Vfl+Vfh) of the low beam 22L and the high beam 22H, e.g., 20V)) and is higher (e.g., 16V) than the output voltage Vd of the first power supply line L1 when both are turned on individually (a voltage equivalent to the voltage drop (=Vfl) of the low beam 22L, e.g., 12V).

[0042] Each current setting unit 61a, 61b has a third Zener diode 63a, 63b and a limiting resistor 64a, 64b, and sets a predetermined amount of current determined by the third Zener voltage Vz3 of each third Zener diode 63a, 63b and each limiting resistor 64a, 64b. Each limiting resistor 64a, 64b is configured by connecting multiple resistors (two in FIG. 3) in parallel. Specifically, the cathodes of each third Zener diode 63a, 63b are electrically connected to the output terminal of the constant voltage circuit 50 via parallel circuits 62a, 62b, and the anodes of each third Zener diode 63a, 63b are electrically connected to the ground line Lg.

[0043] Each of the parallel circuits 62a, 62b has a configuration in which a plurality of resistors (four in FIG. 3) are connected in parallel. A connection point between each of the parallel circuits 62a, 62b and each of the third Zener diodes 63a, 63b is electrically connected to an inverting input terminal of each of the operational amplifiers 65a, 65b via each of the limiting resistors 64a, 64b. The third Zener voltage Vz3 is lower than the output side voltage Vd (=Vfl+Vfh) of the first power supply line L1 during simultaneous lighting and is higher than the second Zener voltage Vz2 (e.g., 18V).

[0044] With this configuration, each of the clamp circuits 60a and 60b operates in the following manner in response to the power supply voltage VCC generated by the constant voltage circuit 50. (1) When "power supply voltage VCC"≦"second Zener voltage Vz2" (when alone illuminated): the clamp circuits 60a and 60b do not output a branch current. (2) When "power supply voltage VCC" > "second Zener voltage Vz2" (simultaneous lighting): the clamp circuits 60a, 60b output branch currents Ica, Icb. Each branch current Ica, Icb is a constant current determined by the voltage difference between the third Zener voltage Vz3 and the second Zener voltage Vz2 and the resistance value of each limiting resistor 64a, 64b. The branch currents Ica, Icb output by each clamp circuit 60a, 60b join together and flow as the branch current Ic in the high beam 22H.

[0045] With the above configuration, the shunt circuit switches the operation of passing the branch current Ic to the parallel line L4 on and off based on the output voltage Vd of the first power supply line L1. That is, the shunt circuit is configured to stop shunting to the parallel line L4 when the output voltage Vd is equal to or lower than the second Zener voltage Vz2, and to shunt to the parallel line L4 when the output voltage Vd is greater than the second Zener voltage Vz2. The output voltage Vd is an example of a voltage of a connection line, and the second Zener voltage Vz2 is an example of a first threshold value.

[0046] (protection circuit 70): Fig. 4 is a circuit diagram showing the configuration of the protection circuit 70. As shown in Fig. 1 and Fig. 4, the lighting circuit 30 further includes a protection circuit 70. The protection circuit 70 stops the shunt circuit when an overvoltage occurs due to, for example, a break in the light sources 22L, 22H or the first power line L1.

[0047] The protection circuit 70 has a switch element 74 connected in parallel to the first Zener diode 55 of the constant voltage circuit 50. The protection circuit 70 stops the generation of the power supply voltage VCC by the constant voltage circuit 50 by changing the switch element 74 from an off (open) state to an on (closed) state, assuming that the first power supply line L1 has reached an overvoltage protection threshold value (e.g., 30 V) or higher as a necessary condition.

[0048] Specifically, the protection circuit 70 includes a switch element 74, a fourth Zener diode 71, a resistor 72, and a capacitor 73. The cathode of the fourth Zener diode 71 is electrically connected to the first power supply line L1, and the anode is electrically connected to the ground line Lg via the resistor 72 and the capacitor 73. The fourth Zener voltage Vz4 of the fourth Zener diode 71 is a value (e.g., 30 V) greater than the first Zener voltage Vz1. The switch element 74 is, for example, a bipolar transistor. The collector of the switch element 74 is electrically connected to a connection point between the bases of the transistors 51a and 51b in the constant voltage circuit 50 and the first Zener diode 55. The emitter of the switch element 74 is electrically connected to the ground line Lg, and the base is electrically connected to a connection point between the resistor 72 and the capacitor 73 via a base resistor 75. A resistor 76 is electrically connected between the base and emitter of the switch element 74. The fourth Zener voltage Vz4 is an example of a second threshold.

[0049] With this configuration, when the output voltage Vd of the first power line L1 is in a normal state where it is less than the fourth Zener voltage Vz4, the switch element 74 is in an off state, and the constant voltage circuit 50 can generate the power supply voltage VCC by the operation of each of the transistors 51a and 51b. On the other hand, when an abnormal state occurs where the output voltage Vd is equal to or greater than the fourth Zener voltage Vz4 due to, for example, a break in the light sources 22L and 22H, the switch element 74 is in an on state, and the base voltages of the transistors 51a and 51b become zero, so that the constant voltage circuit 50 cannot generate the power supply voltage VCC, and accordingly, the clamp circuits 60a and 60b stop absorbing the branch current Ic.

[0050] A-3. Advantages of this embodiment: As described above, in the lighting circuit 30 according to the present embodiment, a part of the driving current I output from the DC-DC converter 32 flows to the parallel line L4 on condition that the bypass switch 42 is in the off state. The branch current Ic that flows into the parallel line L4 is returned to the first power supply line L1 via the branch point B and flows to the high beam 22H. That is, during simultaneous lighting, the current value of the current flowing through the low beam 22L is the current value obtained by subtracting the branch current Ic from the driving current I, and the current value of the current flowing through the high beam 22H is the same current value as the driving current I. Therefore, according to the present embodiment, during simultaneous lighting, the current flowing through the low beam 22L can be reduced to be smaller than the current flowing through the high beam 22H.

[0051] As described above, the output voltage Vd of the first power supply line L1 is different between the simultaneous lighting and the single lighting. That is, the on / off state of the bypass switch 42 can be detected based on the output voltage Vd (or a voltage correlated with the output voltage Vd). In this embodiment, the current dividing circuit is configured to divide the current to the parallel line L4 according to the magnitude relationship between the voltage Vd of the first power supply line L1 and the second Zener voltage Vz2. As a result, according to this embodiment, it is possible to simultaneously light the low beam 22L and the high beam 22H by passing different currents to each other without the need to separately provide a detection means for detecting the presence or absence of an input of a lighting control signal to the bypass switch 42.

[0052] For example, if the voltage of the first power supply line L1 (output side voltage Vd) becomes an overvoltage state due to a break in the light sources 22L, 22H, even if the drive current I is not output from the DC-DC converter 32, the shunt circuit starts based on the voltage of the first power supply line L1 and flows a current to the parallel line L4, which may cause the high beam 22H to be erroneously turned on. In contrast, in this embodiment, when the voltage of the first power supply line L1 becomes an overvoltage state, the protection circuit 70 prohibits shunting to the parallel line L4. As a result, according to this embodiment, it is possible to suppress erroneous lighting of the high beam 22H when the first power supply line L1 is overvoltage.

[0053] B. Second embodiment: 5 is a block diagram showing a schematic configuration of a vehicular lamp 10A according to the second embodiment. In the following, the same components of the vehicular lamp 10A according to the second embodiment as those of the vehicular lamp 10 according to the first embodiment are denoted by the same reference numerals and will not be described again.

[0054] B-1. Configuration for reducing the current flowing through high beam 22H: The lighting circuit 30A of the vehicle lamp 10A is configured to reduce the current flowing through the high beam 22H to less than the current flowing through the low beam 22L when both are turned on simultaneously. The lighting circuit 30A is also configured to make the current flowing through the low beam 22L when both are turned on simultaneously the same as the current flowing through the low beam 22L when both are turned on alone.

[0055] Specifically, the lighting circuit 30A is formed with a parallel line L4A connected in parallel to the high beam 22H. The parallel line L4A is connected between the branch point B of the first power supply line L1 and the ground line Lg. The lighting circuit 30A also includes a current shunt circuit. The current shunt circuit is configured to flow a part of the drive current I output from the DC-DC converter 32 to the parallel line L4A, with the bypass switch 42 being in the off state (simultaneous lighting) as a necessary condition (see the arrow IcA in FIG. 5).

[0056] In this embodiment, the current dividing circuit includes a constant voltage circuit 50A and two clamp circuits 60aA, 60bA (see FIG. 7 described later). The two clamp circuits 60aA, 60bA are electrically connected to the parallel line L4A.

[0057] (Constant voltage circuit 50A): 6 is a circuit diagram showing the configuration of the constant voltage circuit 50 A. The constant voltage circuit 50 A generates a power supply voltage VCC for the operational amplifiers 65 a and 65 b, which are described below, included in each of the clamp circuits 60 aA and 60 bA.

[0058] The constant voltage circuit 50A of this embodiment differs from the constant voltage circuit 50 of the first embodiment in that it generates a power supply voltage VCC according to the input side (connection point E on the upstream side of the DC-DC converter 32) of the first power supply line L1. The constant voltage circuit 50A also differs from the constant voltage circuit 50 in that it does not have a transistor 51b and a base resistor 54b.

[0059] As shown in Fig. 6, the constant voltage circuit 50A has a first Zener diode 55A and a transistor 51a, and is configured to buffer and output a first Zener voltage Vz1A of the first Zener diode 55A by the transistor 51a. The first Zener voltage Vz1A is a value (e.g., 9.1V) that is equal to or greater than the voltage (e.g., 9V) at which each of the clamp circuits 60aA and 60bA can operate. With this configuration, the constant voltage circuit 50A generates a power supply voltage VCC that corresponds to the input side voltage Ve. The input side voltage Ve has a value that corresponds to the first power supply voltage Vt1 applied to the first power supply line L1.

[0060] (Clamp circuits 60aA, 60bA): 7 is a circuit diagram showing the configuration of the clamp circuits 60aA and 60bA. Each of the clamp circuits 60aA and 60bA absorbs a predetermined amount of branch current IcA from the first power supply line L1 to the parallel line L4A, with the prerequisite that the anode voltage Vb (voltage at branch point B) of the high beam 22H is a predetermined value (a voltage drop of the high beam 22H (=voltage Vfh or more).

[0061] 7, each of the clamp circuits 60aA and 60bA includes an operational amplifier 65a, 65b, a reference voltage generating unit 68A, a current setting unit 61aA, 61bA, and an N-type FET 67aA, 67bA. The FET 67aA, 67bA may be an N-type transistor, for example.

[0062] The output terminals of the operational amplifiers 65a and 65b are electrically connected to the gates of the FETs 67aA and 67bA via the gate resistors 66aA and 66bA. The drains of the FETs 67aA and 67bA are electrically connected to the branch point B of the first power supply line L1, and the sources of the FETs 67aA and 67bA are electrically connected to the ground line Lg via the parallel circuits 62aA and 62bA of the current setting units 61aA and 61bA. The parallel circuits 62aA and 62bA are configured with a plurality of resistors connected in parallel. The sources of the FETs 67aA and 67bA are electrically connected to the inverting input terminals of the operational amplifiers 65a and 65b.

[0063] The reference voltage generating unit 68A generates a reference voltage VhA that is a reference for the clamp voltages generated by the clamp circuits 60a and 60b. The reference voltage generating unit 68A differs from the reference voltage generating unit 68 of the first embodiment in that it has a resistor 69a instead of a second Zener diode 68b. A capacitor 69b is connected in parallel to the resistor 69a. The connection point between the resistor 68a and the resistor 69a is electrically connected to the non-inverting input terminals of the operational amplifiers 65a and 65b. The reference voltage generating unit 68A may be configured to generate a divided voltage between a Zener diode and a resistor as the reference voltage VhA, similar to the reference voltage generating unit 68.

[0064] With this configuration, each of the clamp circuits 60aA, 60bA operates as follows in response to the anode voltage Vb (voltage at the branch point B) of the high beam 22H. (1) When “anode voltage Vb of high beam 22H” is smaller than “high beam threshold value corresponding to voltage drop of high beam 22H” (when only the high beam is lit): When only the high beam is lit, the anode voltage Vb of high beam 22H is approximately zero, so that the clamp circuits 60aA, 60bA are stopped and no absorption of branch current from the first power supply line L1 is performed. (2) When "anode voltage Vb of high beam 22H" ≧ "high beam threshold" (when simultaneously illuminated): When simultaneously illuminated, the anode voltage Vb becomes equal to or greater than the high beam threshold due to the illumination of high beam 22H, and the clamp circuits 60aA, 60bA absorb the branch currents IcaA, IcbA from the first power supply line L1. The current values ​​of the branch currents IcaA, IcbA are determined by the reference voltage VhA (clamp voltage) generated by the reference voltage generator 68A and the combined resistance value of the parallel circuits 62aA, 62bA. The anode voltage Vb of high beam 22H is an example of the voltage of the connection line, and the high beam threshold is an example of the first threshold.

[0065] In this embodiment, the lighting circuit 30A is provided with a dummy circuit 78 on the parallel line L4A. Specifically, the dummy circuit 78 has an element (e.g., a dummy resistor) having a resistance component, and is connected to the high potential side of each of the FETs 67aA, 67bA. With this configuration, during simultaneous lighting, a voltage obtained by subtracting the reference voltage VhA from the voltage drop of the high beam 22H (=Vfh) is distributed to each of the FETs 67aA, 67bA and the dummy circuit 78. This makes it possible to suppress the occurrence of thermal destruction of the devices (FETs 67aA, 67bA) that constitute the clamp circuits 60aA, 60bA.

[0066] As described above, in the lighting circuit 30A according to the present embodiment, a part of the driving current I output from the DC-DC converter 32 flows to the parallel line L4A on condition that the bypass switch 42 is in the off state. That is, during simultaneous lighting, the current value of the current flowing through the low beam 22L is the same as the driving current I, and the current value of the current flowing through the high beam 22H is the current value obtained by subtracting the branch current IcA from the driving current I. Therefore, according to the present embodiment, during simultaneous lighting, the current flowing through the high beam 22H can be reduced to be less than the current flowing through the low beam 22L.

[0067] C. 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.

[0068] The configuration of the vehicle lamp 10, 10A in each of the above embodiments is merely an example, and various modifications are possible. For example, in each of the above embodiments, the vehicle lamp 10, 10A 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. In addition, in each of the above embodiments, the low beam 22L and the high beam 22H are exemplified as the first light source and the second light source, but the present invention is not limited to this, and other types of light sources may be used as long as they are multiple light sources connected in series with each other. In addition, 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 single light source may have multiple light-emitting elements connected in series or in parallel. In addition, the number of light-emitting elements and the connection method may be different for each light source.

[0069] In each of the above embodiments, the bypass switch 42 may be another switching element, such as a PMOS transistor or a bipolar transistor. Also, in each of the above embodiments, the bypass switch 42 is connected in parallel to the light source on the low potential side (high beam 22H), but the bypass switch 42 may be connected in parallel to the light source on the high potential side (low beam 22L).

[0070] In the first embodiment, the constant voltage circuit 50 may have one transistor or three or more. In the first embodiment, the constant voltage circuit 50 may have one base resistor or three or more. In the first embodiment, the clamp circuit constituting the current divider circuit may have one clamp circuit or three or more. In the first embodiment, the voltage of the first power supply line L1 (output side voltage Vd) may not be used, and for example, a detection means for detecting the presence or absence of an input of a lighting control signal to the bypass switch 42 may be provided, and the operation of the clamp circuits 60a, 60b may be turned on and off based on the detection result.

[0071] In the second embodiment, the constant voltage circuit 50A is electrically connected to the input side of the first power supply line L1 (connection point E on the upper end side of the DC-DC converter 32) and generates the power supply voltage VCC according to the input side voltage Ve, but may be electrically connected to the output side of the first power supply line L1 (connection point D on the rear side of the DC-DC converter 32) and generate the power supply voltage VCC according to the output side voltage Vd. In the second embodiment, the constant voltage circuit 50A may have a plurality of transistors and base resistors. In the second embodiment, the constant voltage circuit 50A may include a detection means for detecting the presence or absence of an input of a lighting control signal to the bypass switch 42, for example, without using the voltage of the first power supply line L1 (anode voltage Vb of the high beam 22H), and may turn on and off the operation of the clamp circuits 60aA, 60bA based on the detection result. [Explanation of symbols]

[0072] 10, 10A: Vehicle lamp 20: Light source unit 22H: High beam 22L: Low beam 30, 30A: Lighting circuit 32: DC-DC converter 34: Voltage detection circuit 36: Current detection circuit 38: LED driver 40: Switching interface 42: Bypass switch 50, 50A: Constant voltage circuit 51a, 51b, 67a, 67b: Transistor 55, 55A: First Zener diode 60a, 60b, 60aA, 60bA: Clamp circuit 61a, 61b, 61aA, 61bA: Current setting unit 62a, 62b, 62aA, 62bA: Parallel circuit 63a, 63b: Third Zener diode 64a, 64b: Limiting resistor 65a, 65b: Operational amplifier 66aA, 66bA: Gate resistor 67aA, 67bA: FET 68, 68A: Reference voltage generating unit 68b: Second Zener diode 70: Protection circuit 71: Fourth Zener diode 74: Switch element 78: Dummy circuit 80: ECU L1: First power supply line L2: Second power supply line L3: Bypass line L4, L4A: Parallel lines Lg: Ground line

Claims

1. A lighting circuit for lighting a first light source and a second light source connected in series to each other, comprising: a drive circuit that outputs a drive current to a connection line through which the first light source and the second light source are connected in series; a bypass switch connected in parallel to the second light source and turned from an on state to an off state based on an input of a lighting control signal that instructs lighting of the second light source; a parallel line connected in parallel to the first light source or the second light source; a shunt circuit that causes a portion of the drive current output from the drive circuit to flow to the parallel line on condition that the bypass switch is in the off state.

2. 2. The lighting circuit according to claim 1, The second light source is disposed on a lower potential side with respect to the first light source, The parallel line is connected in parallel to the first light source.

3. 2. The lighting circuit according to claim 1, The second light source is disposed on a lower potential side with respect to the first light source, The parallel line is connected in parallel to the second light source.

4. A lighting circuit according to any one of claims 1 to 3, The lighting circuit is configured so that the shunt circuit stops shunting current to the parallel line when the voltage of the connection line is equal to or lower than a first threshold value that correlates to the sum of voltage drops between the first light source and the second light source, and shunts current to the parallel line when the voltage of the connection line is greater than the first threshold value.

5. The lighting circuit according to claim 4, the parallel line is connected in parallel to a light source arranged on a higher potential side out of the first light source and the second light source, The lighting circuit further includes a protection circuit that prohibits the shunt circuit from shunting current to the parallel line, on condition that the voltage of the connection line is equal to or greater than a second threshold for overvoltage protection that is higher than the first threshold.

6. The first light source; the second light source; A lighting device comprising: a lighting circuit according to any one of claims 1 to 3.

7. 7. The lighting device according to claim 6, The lighting device is mounted on a vehicle, A lighting device, wherein, of the first light source and the second light source, a light source connected in parallel to the bypass switch is a high beam, and a light source not connected in parallel to the bypass switch is a low beam.

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