WO2020013032A1

WO2020013032A1 - Lighting circuit and vehicle light

Info

Publication number: WO2020013032A1
Application number: PCT/JP2019/026304
Authority: WO
Inventors: 知幸市川; 正人原崎
Original assignee: 株式会社小糸製作所
Priority date: 2018-07-13
Filing date: 2019-07-02
Publication date: 2020-01-16
Also published as: JP2020013642A; JP7182925B2

Abstract

In the present invention, a semiconductor light source (502) includes a plurality of light-emitting elements (504_1-504_3) connected in series. A drive circuit (610) receives an input voltage (V_IN) and supplies a drive current (I_LED) to the semiconductor light source (502) according to the input voltage. A bypass circuit (620) is connected to at least one (504_3) of the plurality of light-emitting elements (504_1-504_3) and, according to the relationship between a threshold value (V_TH) and the input voltage (V_IN) having a negative correlation with the temperature of the semiconductor light source (502), turns OFF the light-emitting element (504_3) by bypassing the drive current (I_LED) supplied to the light emitting element (504_3).

Description

Lighting circuit and vehicle lighting

The present disclosure relates to a lighting circuit and a vehicular lamp provided with the lighting circuit.

電球 Light bulbs have been widely used as light sources for vehicle lamps, but in recent years, semiconductor light sources such as LEDs (light emitting diodes) have been widely adopted.

FIG. 1 is a block diagram of a conventional vehicle lamp 1. The vehicle lamp 1 receives a DC voltage (input voltage V _IN ) from the battery 2 via the switch 4. The light source 10 includes a plurality of n LEDs 12 connected in series. The brightness of the light source 10 is controlled according to the drive current I _LED flowing through the light source 10. The lighting circuit 20 includes an LED driver 22 that stabilizes the drive current I _LED to a target amount I _REF according to the target luminance.

The LED 12, when a forward voltage when the driving current _{I REF} stabilized to the target amount _{I REF} flows and Vf _0, the voltage across (referred lowest lighting _{voltage) V MIN} of the light source 10, Vf ₀ × n. Assuming n = 3, V _MIN Ｖ11 V for a white LED and V _MIN ≒ 9 V for a red LED. In other words, when the output voltage V _OUT of the LED driver 22 falls below the minimum lighting voltage V _MIN , the drive current I _LED cannot maintain the target amount I _REF and the plurality of LEDs 12 are turned off.

In the lighting circuit 20 that requires low cost like an LED socket, the LED driver 22 is configured by a constant current series regulator or a constant current output switching converter. In this case, the output voltage V _OUT of the LED driver 22 becomes lower than the input voltage _VIN . The input voltage _VIN is 13 V when the battery is fully charged, but it is not uncommon for the input voltage _VIN to drop to 10 V or less as the discharge proceeds. Therefore, when the battery voltage decreases (hereinafter, referred to as a reduced voltage state), a situation occurs in which the output voltage V _OUT falls below the minimum lighting voltage V _MIN , and the LED 12 may be turned off.

A bypass switch 24 and a bypass control circuit 26 are provided in the lighting circuit 20 to prevent the light source 10 from being turned off in the reduced voltage state. The bypass switch 24 is connected in parallel with one LED 12_n. When the input voltage _VIN becomes lower than a certain threshold value _VTH , the bypass control circuit 26 determines that the voltage is in the reduced voltage state, and turns on the bypass switch 24. In this state, the minimum lighting voltage V _MIN = Vf ₀ × (n−1), and V _IN > V _MIN is maintained. That is, it is possible to maintain the lighting of the remaining LEDs 12_1 to 12_n-1 in exchange for turning off the LED 12_n.

Japanese Patent Application Laid-Open No. 2016-197711 JP 2014-148253 A

The present inventors have studied the lighting circuit 20 of FIG. 1 and have come to recognize the following problem. The forward voltage Vf ₀ when the drive current I _LED stabilized to the target amount I _REF flows has a negative temperature coefficient, and the forward voltage Vf ₀ increases as the temperature decreases. When the threshold value V _TH is constant, the forward voltage Vf ₀ (−40) at the lowest temperature (−40 ° C.) in an assumed temperature range (operation guarantee temperature range as a lamp, for example, −40 ° C. to 125 ° C.) C), it is necessary to determine the threshold value V _TH .

When the threshold value V _TH is defined based on the minimum temperature, at room temperature or high temperature, the LEDs are bypassed and the brightness is reduced although all the LEDs can be turned on without bypass.

In reality, since the LED 12 generates heat, its temperature is rarely maintained at the lowest temperature (-40 ° C.) of the operation guarantee temperature range. From this point of view, it can be said that the design of the threshold value V _TH based on the minimum temperature lowers the performance of the lamp more than necessary.

The present disclosure has been made in view of such a problem, and one of exemplary purposes of one embodiment thereof is to suppress unnecessary reduction in luminance of a semiconductor light source.

One embodiment of the present invention relates to a lighting circuit. The lighting circuit lights a first semiconductor light source including a plurality of light emitting elements connected in series. The lighting circuit is connected to a first driving circuit that receives an input voltage and supplies a driving current to the first semiconductor light source, and is connected to at least one of the plurality of light emitting elements, is enabled in a reduced voltage state, and bypasses the driving current. And a circuit. The determination threshold value of the reduced voltage state has a negative correlation with the temperature of the first semiconductor light source.

In addition, any combination of the above-described components, and any replacement of the components and expressions of the present invention between methods, apparatuses, systems, and the like are also effective as embodiments of the present invention.

According to an embodiment of the present disclosure, it is possible to suppress an unnecessary decrease in the luminance of the semiconductor light source.

It is a block diagram of the conventional vehicle lamp. It is a block diagram of a vehicular lamp provided with a lighting circuit according to an embodiment. FIG. 3A shows a temperature characteristic of the threshold value V _TH in the lighting circuit of FIG. 2, and FIG. 3B shows a threshold value V _TH ′ based on a conventional design method. FIG. It is a block diagram of a vehicular lamp provided with a lighting circuit according to a first embodiment. FIG. 3 is a circuit diagram illustrating a specific configuration example of a lighting circuit. It is a block diagram of a vehicular lamp provided with a lighting circuit according to a second embodiment. It is a figure showing the layout of the vehicular lamp. FIGS. 8A to 8D are views showing an LED socket which is an example of a vehicular lamp.

One embodiment disclosed in the present specification provides a lighting circuit configured to light a first semiconductor light source including a plurality of light emitting elements connected in series.
The lighting circuit,
A first drive circuit configured to receive an input voltage and to supply a drive current to the first semiconductor light source according to the input voltage;
The at least one light emitting device is connected to at least one of the plurality of light emitting elements and according to a relationship between a threshold value having a negative correlation with a temperature of the first semiconductor light source and the input voltage. A bypass circuit configured to turn off the at least one light emitting element by diverting the drive current supplied to the element,
Is provided.

Further, the bypass circuit includes:
Receiving the input voltage;
According to a detection voltage obtained by multiplying the input voltage by a coefficient having a positive correlation with the temperature of the first semiconductor light source, the driving current supplied to the at least one light emitting element is bypassed. You may.

Further, the bypass circuit includes:
A first resistor and a second resistor provided in series between an input line where the input voltage appears and a ground line;
A thermistor having a negative temperature coefficient provided in parallel with the first resistor;
May be included.
The detection voltage may appear at a connection node between the first resistor and the second resistor.

One embodiment disclosed in the present specification provides a lighting circuit configured to light a first semiconductor light source including a plurality of light emitting elements connected in series.
The lighting circuit,
A first drive circuit configured to receive an input voltage and to supply a drive current to the first semiconductor light source according to the input voltage;
While being connected in parallel with at least one of the plurality of light emitting elements, it is configured to turn off the at least one light emitting element by bypassing the drive current supplied to the at least one light emitting element. A bypass circuit;
Is provided.
The bypass circuit bypasses the drive current supplied to the at least one light emitting element according to a comparison between a detection voltage that changes according to a temperature of the first semiconductor light source and a predetermined reference voltage. Is configured.

One embodiment disclosed in the present specification provides a vehicular lamp including a first semiconductor light source including a plurality of light emitting elements connected in series, and a lighting circuit that drives the first semiconductor light source. You may.

The bypass circuit of the lighting circuit may be connected to two light emitting elements of the plurality of light emitting elements. When the bypass circuit turns off the two light emitting elements, symmetry of a light emitting pattern output from the first semiconductor light source may be maintained.

The vehicle lighting device may further include a second semiconductor light source that can be turned on and off independently of the first semiconductor light source. The plurality of light emitting elements of the first semiconductor light source may be arranged to surround the second semiconductor light source. The two light emitting elements may be provided symmetrically with respect to the second semiconductor light source.

The lighting circuit may further include a second driving circuit configured to supply a driving current to the second semiconductor light source. The second driving circuit may include a third resistor provided in series with the second semiconductor light source.

(Embodiment)
Hereinafter, the present disclosure will be described based on preferred embodiments with reference to the drawings. The same or equivalent components, members, and processes shown in each drawing are denoted by the same reference numerals, and the repeated description will be omitted as appropriate. In addition, the embodiments do not limit the invention but are exemplifications, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

In this specification, “the state in which the member A is connected to the member B” refers to the case where the member A and the member B are physically directly connected to each other. Indirect connection via another member that does not substantially affect the basic connection state or impair the function or effect provided by the combination thereof.

Similarly, “the state in which the member C is provided between the member A and the member B” means that the member A and the member C or the member B and the member C are directly connected, Indirect connection via another member that does not substantially affect the basic connection state or impair the function or effect provided by the combination thereof.

In this specification, electric signals such as voltage signals and current signals, or symbols attached to circuit elements such as resistors and capacitors denote the respective voltage values, current values, or resistance values and capacitance values as necessary. Shall be represented.

FIG. 2 is a block diagram of a vehicle lamp 500 including a lighting circuit 600 according to the embodiment. The DC voltage (input voltage) _VIN from the battery 2 is supplied to the vehicle lamp 500 via the switch 4. The vehicle lamp 500 includes a semiconductor light source 502 and a lighting circuit 600. The semiconductor light source 502 includes a plurality of n (n ≧ 2) light emitting elements 504_1, 504_2,... 504_n connected in series. FIG. 2 shows a case where n = 3. The light emitting element 504 is preferably, for example, an LED, but is not limited thereto, and an LD (laser diode), an organic EL element, or the like may be employed. The vehicle lamp 500 is, for example, a stop lamp or a tail lamp, and the semiconductor light source 502 may be a red LED. One preferred embodiment of the vehicle lamp 500 is an LED socket in which the semiconductor light source 502 and the lighting circuit 600 are housed in one package, and has a shape that can be attached to and detached from a lamp body (not shown). The LED socket is not only required to have a long service life, but is also a consumable item, so that a low cost is strongly required.

The lighting circuit 600 includes a drive circuit 610 and a bypass circuit 620. Driving circuit 610 receives an input voltage _{V IN,} and supplies the stabilized drive current _{I LED} to the target amount _{I REF} to the semiconductor light source 502 in response to the input voltage _{V IN.} The drive circuit 610 may be configured by any one of (i) a constant current linear regulator, (ii) a step-down switching converter with a constant current output, or (iii) a combination of a step-down switching converter with a constant voltage output and a constant current circuit. it can.

The bypass circuit 620 is connected to at least one of the light emitting elements 504 504_3. The bypass circuit 620 includes a warming element 622 provided so that the electrical state changes according to the temperature of the semiconductor light source 502. The electrical state refers to the impedance of the warming element, its voltage drop, the current flowing through it, the voltage at one end thereof, and the like. The warming element 622 can directly or indirectly monitor the temperature of the semiconductor light source 502. For example, the warming element 622 may be directly attached to the semiconductor light source 502 or may be mounted on the same substrate as the semiconductor light source 502. The semiconductor light source 502 may be mounted adjacent or close to the heat sink. The bypass circuit 620 is enabled based on the relationship between the threshold voltage V _TH having a negative correlation with the temperature T of the semiconductor light source 502 and the input voltage _VIN, and bypasses the drive current I _LED . Thus, the bypass circuit 620 can turn off the light emitting element 504_3.

The above is the configuration of the lighting circuit 600. Next, the operation of the dot equalization circuit 600 will be described. FIG. 3A is a diagram illustrating a temperature characteristic of the threshold value V _TH in the lighting circuit 600 of FIG. V _MIN is the lowest lighting voltage of the light source 502, has a negative correlation with the temperature T, and decreases as the temperature T increases. The threshold value V _TH is defined to be slightly higher than the minimum lighting voltage V _MIN , and is represented by the following equation (1), for example.

V _TH = V _MIN + ΔV (1)

ΔV is the sum of the voltage drop of the drive circuit 610 and the design margin. In FIG. 3A, the threshold value V _TH and the minimum lighting voltage V _MIN are drawn in parallel while ΔV is kept constant, but this is not the only option, and ΔV may have temperature dependence. The threshold value V _TH and the minimum lighting voltage V _MIN may be non-parallel.

FIG. 3B shows a threshold value V _TH ′ based on a conventional design method, and is a constant value independent of temperature. Conventionally, the bypass switch is off in the region of _VIN > _VTH '(hatched), and all the LEDs 12 can be turned on. In the region of V _IN <V _TH ′, the bypass switch is turned on and one LED 12 is turned off, so that the light amount of the light source 10 decreases.

Returning to FIG. In this embodiment mode, the bypass circuit 620 is in a disabled state in a range satisfying V _IN > V _TH (indicated by hatching), and all the light-emitting elements 504_1 to 504_3 can be turned on. As can be seen from the comparison with FIG. 3B, according to the lighting circuit 600 according to the embodiment, the voltage range in which the lighting of all the light emitting elements 504 can be maintained can be widened.

The present invention extends to various devices and methods grasped as the block diagram or circuit diagram of FIG. 2 or derived from the above description, and is not limited to a specific configuration. Hereinafter, more specific configuration examples and embodiments will be described not to narrow the scope of the present invention but to help understand the essence and operation of the present invention and to clarify them.

(First embodiment)
FIG. 4 is a block diagram of a vehicle lamp 500A including a lighting circuit 600A according to the first embodiment. The bypass circuit 620A includes a thermistor 622a corresponding to the warming element 622 in FIG. The state of the bypass circuit 620A is such that the detection voltage Vd is generated by multiplying the input voltage _VIN by a coefficient K (T) having a positive correlation with the temperature T of the semiconductor light source 502 (refer to the following equation (2)).

Vd = V _IN × K (T) (2)

For example, bypass circuit 620A may switch between an enable state and a disable state based on the relationship between detection voltage Vd and predetermined reference voltage V _REF . Specifically, when Vd = V _IN × K (T) <V _REF , in other words, when V _IN <V _REF / K (T), the bypass circuit 620A is enabled. Therefore, in the first embodiment, V _REF / K (T) can be associated with the threshold value V _TH shown in FIG.

The bypass circuit 620A includes a voltage dividing circuit 621 that generates the detection voltage Vd. The voltage dividing circuit 621 includes a first resistor R1 and a second resistor R2 provided in series between an input line 624 where an input voltage _VIN appears and a ground line 626, and a negative temperature coefficient provided in parallel with the first resistor R1. And a thermistor Ra. The detection voltage Vd appears at a connection node between the first resistor R1 and the second resistor R2. In this case, the coefficient K (T) is represented by the following equation (3).

K (T) = (Ra // R1) / (Ra // R1 + R2) (3)

“//” is an operator representing a combined resistance of two resistors connected in parallel.

The bypass circuit 620A further includes a bypass transistor M1 and a current bypass control unit 628. The bypass transistor M1 is connected in parallel with the light emitting element 504_3. The current bypass circuit 628 controls the bypass transistor M1 based on the detection voltage Vd.

FIG. 5 is a circuit diagram showing a specific configuration example of the lighting circuit 600A. Current bypass control section 628 includes a voltage comparator 630 that compares detected voltage Vd with a predetermined reference voltage _VREF . When vd _{<V REF,} the output of the voltage comparator 630 becomes high, the bypass transistor M1 is turned on, the bypass circuit 620B becomes the enable state.

As shown in FIG. 5, when the current bypass control unit 628 is configured by the voltage comparator 630, the bypass transistor M1 functions as a switch controlled in two states, ON and OFF. Note that the configuration of the current bypass control unit 628 is not limited to the voltage comparator, and the current of the drive current I _LED is partially changed while the bypass transistor M1 is switched from the off state to the on state or from the on state to the off state. A state may be provided in which the detour is performed. That is, the enabled state of the bypass circuit 620B may include not only a state in which the entire drive current I _LED is bypassed, but also a state in which a part thereof is bypassed.

(Second embodiment)
FIG. 6 is a block diagram of a vehicle lamp 500B including a lighting circuit 600B according to the second embodiment. The vehicle lamp 500B includes a first semiconductor light source 502A, a second semiconductor light source 502B, and a lighting circuit 600B.

The turning on and off of the second semiconductor light source 502B can be controlled independently of the first semiconductor light source 502A. When the first input voltage V _IN1 is supplied, the lighting circuit 600B supplies the driving current I _LED1 to the first semiconductor light source 502A to turn on the first semiconductor light source 502A. When the second input voltage V _IN2 is supplied, the lighting circuit 600B supplies the driving current I _LED2 to the second semiconductor light source 502B to turn on the second semiconductor light source 502B.

{For example, the first semiconductor light source 502A is a lamp that should emit light with relatively high luminance, for example, a stop lamp. The second semiconductor light source 502B is a lamp that should emit light with relatively low luminance, for example, a tail lamp. The vehicular lamp 500B may be a socket LED serving as both a stop lamp and a tail lamp.

Regarding the first semiconductor light source 502A, it is necessary to supply a drive current I _LED1 of several hundred mA in order to obtain a required light amount, and includes a relatively large number of light emitting elements 504. Therefore, the combination of the first drive circuit 610A and the bypass circuit 620 is suitable for driving the first semiconductor light source 502A. The first drive circuit 610A and the bypass circuit 620 may employ the configuration described in the first embodiment.

In this embodiment, the first semiconductor light source 502A includes four light emitting elements 504_1 to 504_4. The bypass circuit 620 is connected in parallel with the two light emitting elements 504_3 and 504_4. When the bypass circuit 620 is enabled, the light emitting elements 504_3 and 504_4 are bypassed and turned off. The bypass circuit 620 may be configured similarly to the first embodiment. The first drive circuit 610A preferably has a temperature derating function of reducing the drive current I _LED1 when the temperature of the first semiconductor light source 502A exceeds a certain threshold.

On the other hand, with respect to the second semiconductor light source 502B, it is sufficient to supply a driving current I _LED2 of several tens mA in order to obtain a required light amount, and the second semiconductor light source 502B can be composed of a relatively small number of light emitting elements 508. Therefore, the power consumption of the second semiconductor light source 502B is relatively small, so that the temperature derating function is not required. Further, since the number of the light emitting elements 508 is small (one in FIG. 6), the minimum lighting voltage is sufficiently lower than the input voltage _VIN2 , so that the bypass control in the reduced voltage state is unnecessary. For this reason, the second driving circuit 640 that drives the second semiconductor light source 502B can be configured more simply than the first driving circuit 610A, and in the present embodiment, the second driving circuit 640 A third resistor (current limiting resistor) R3 provided in series with the light source 502B is included.

(4) Between the input terminal of the first drive circuit 610A and the first input terminal IN1 of the vehicle lamp 500B, a diode D1 for power supply reverse connection protection and a zener diode D2 for load dump protection may be provided.

On the other hand, a diode D3 for power supply reverse connection protection is provided between the input terminal of the second drive circuit 640 and the second input terminal IN2 of the vehicle lamp 500B. However, since the third resistor R3 itself has surge resistance, a Zener diode for load dump protection can be omitted. This contributes to downsizing and cost reduction of the vehicle lamp 500B.

FIG. 7 is a diagram showing a layout of the vehicle lamp 500B. The two light emitting elements 504_3 and 504_4 to be bypassed in the reduced voltage state have the symmetry of the light emitting pattern of the first semiconductor light source 502 when the bypass circuit 620 is enabled, that is, when they are turned off. It is laid out to be maintained.

{For example, the plurality of light emitting elements 504_1 to 504_4 of the first semiconductor light source 502A are arranged so as to surround the light emitting element 508 of the second semiconductor light source 502. The two light emitting elements 504_3 and 504_4 to be turned off in the reduced voltage state are provided at symmetrical positions with respect to the light emitting element 508. By adopting such a layout, when the lamp is viewed from the front, a difference between a strong direction and a weak direction of the emitted light can be suppressed. From another viewpoint, the two light emitting elements to be turned off in the reduced voltage state may be arranged so as not to be adjacent to each other.

FIGS. 8A to 8D are views showing an LED socket 700 which is an example of the vehicle lamp 500B. FIG. 8A is a perspective view of the appearance of the LED socket 700. 8B is a front view of the LED socket 700, FIG. 8C is a plan view of the LED socket 700, and FIG. 8C is a bottom view of the LED socket 700.

The housing 702 has a shape that can be attached to and detached from a lamp body (not shown). A plurality of light emitting elements 504 are mounted at the center of the housing 702, and the light emitting elements 504 are covered with a transparent cover 704. The components of the lighting circuit 600 are mounted on the substrate 710. The plurality of light emitting elements 504 are, for example, red LED chips and are used as stop lamps.

In the LED socket serving as both a stop lamp and a tail lamp, as shown in FIG. 7, a light emitting element 508 for the tail lamp is mounted in the center of the plurality of light emitting elements 504, and a lighting circuit for the tail lamp is provided on the substrate 710. Implemented.

Three

pins

721, 722, 723 are exposed on the bottom side of the housing 702. The pin 721 is supplied with a first input voltage V _IN1 via a switch, and the pin 722 is supplied with a ground voltage. The pin 723 is supplied with the second input voltage V _IN2 which becomes high when the tail lamp is turned on. The pins 721 to 723 pass through the inside of the housing 702, and one ends of the pins 721 to 723 are connected to the wiring pattern of the substrate 710.

The present invention has been described based on the embodiments. This embodiment is an exemplification, and it is understood by those skilled in the art that various modifications can be made to the combination of each component and each processing process, and that such modifications are also within the scope of the present invention. is there. Hereinafter, such modified examples will be described.

(Modification 1)
In the first embodiment, the detection voltage Vd is generated by multiplying the input voltage _VIN by a coefficient K (T) having temperature dependency, and based on the relationship between the detection voltage Vd and a predetermined reference voltage _VREF , Although the state of the bypass circuit 620A is controlled, the present embodiment is not limited to this. For example, a threshold V _TH is generated by multiplying a predetermined reference voltage V _REF by a coefficient having a negative correlation with temperature, and then the threshold V _TH and the input voltage _VIN (or a predetermined threshold V _TH). The state of the bypass circuit may be controlled based on the relationship with the voltage multiplied by the coefficient.

(Modification 2)
In the second embodiment, the stop LED and the socket LED serving as the tail lamp have been described, but the present embodiment is not limited to this. For example, a layout of light emitting elements in consideration of symmetry may be introduced in a socket LED of a stop lamp alone. The layout of the light-emitting elements in this case corresponds to the layout of the light-emitting elements in which the light-emitting element 508 is omitted in FIG.

Although the present invention has been described using specific words and phrases based on the embodiments, the embodiments are merely illustrative of the principles and applications of the present invention, and the embodiments are defined in the appended claims. Many modifications and changes in arrangement may be made without departing from the spirit of the present invention.

In this application, the contents disclosed in Japanese Patent Application No. 2018-133095 filed on July 13, 2018 are appropriately incorporated.

500 vehicle lamp 502 semiconductor light source 504 light emitting element 502A first semiconductor light source 502B second semiconductor light source 600 lighting circuit 610 drive circuit 610A first drive circuit 620 bypass circuit 622 warming element 628 current bypass control unit 630 voltage comparator 640 second drive Circuit 700 LED socket 702 Housing 704 Cover 710

Board

721, 722, 723 pins

Claims

A lighting circuit configured to light a first semiconductor light source including a plurality of light emitting elements connected in series,
A first drive circuit configured to receive an input voltage and to supply a drive current to the first semiconductor light source according to the input voltage;
The at least one light emitting device is connected to at least one of the plurality of light emitting elements and according to a relationship between a threshold value having a negative correlation with a temperature of the first semiconductor light source and the input voltage. A bypass circuit configured to turn off the at least one light emitting element by diverting the drive current supplied to the element,
A lighting circuit comprising:
The bypass circuit,
Receiving the input voltage;
According to a detection voltage obtained by multiplying the input voltage by a coefficient having a positive correlation with the temperature of the first semiconductor light source, the driving current supplied to the at least one light emitting element is bypassed.
Is configured as
The lighting circuit according to claim 1.
The bypass circuit,
A first resistor and a second resistor provided in series between an input line where the input voltage appears and a ground line;
A thermistor having a negative temperature coefficient provided in parallel with the first resistor;
Including
The detection voltage appears at a connection node between the first resistor and the second resistor.
The lighting circuit according to claim 2.
A lighting circuit configured to light a first semiconductor light source including a plurality of light emitting elements connected in series,
A first drive circuit configured to receive an input voltage and to supply a drive current to the first semiconductor light source according to the input voltage;
While being connected in parallel with at least one of the plurality of light emitting elements, it is configured to turn off the at least one light emitting element by bypassing the drive current supplied to the at least one light emitting element. A bypass circuit;
With
The bypass circuit bypasses the drive current supplied to the at least one light emitting element according to a comparison between a detection voltage that changes according to a temperature of the first semiconductor light source and a predetermined reference voltage. Is configured to
Lighting circuit.
A first semiconductor light source including a plurality of light emitting elements connected in series;
The lighting circuit according to any one of claims 1 to 4, which drives the first semiconductor light source;
A vehicle lighting device comprising:
The bypass circuit of the lighting circuit is connected to two light emitting elements of the plurality of light emitting elements,
When the bypass circuit turns off the two light emitting elements, symmetry of a light emitting pattern output from the first semiconductor light source is maintained.
The vehicular lamp according to claim 5.
A second semiconductor light source that can be turned on and off independently of the first semiconductor light source;
The plurality of light emitting elements of the first semiconductor light source are arranged to surround the second semiconductor light source,
The two light emitting elements are provided to be symmetric with respect to the second semiconductor light source.
The vehicular lamp according to claim 6.
The lighting circuit further includes a second drive circuit configured to supply a drive current to the second semiconductor light source,
The second drive circuit includes a third resistor provided in series with the second semiconductor light source.
The vehicular lamp according to claim 6.