JP2020013642A - Lighting circuit and vehicle lighting fixture - Google Patents

Abstract

To suppress an unnecessary reduction in brightness of a semiconductor light source.SOLUTION: 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 Vand supplies a drive current Ito the semiconductor light source 502. A bypass circuit 620 is connected to at least one light emitting element (504_3) of the plurality of light emitting elements 504_1-504_3, and is brought into an enable state based on the relationship between the input voltage Vand a threshold Vhaving a negative correlation with the temperature of the semiconductor light source 502 thereby to bypass the drive current I.SELECTED DRAWING: Figure 2

Description

  The present invention relates to lamps used for automobiles and the like.

  Conventionally, light bulbs have been widely used as light sources for vehicle lamps, but recently, 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 it. 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, if the battery voltage is lowered (that reduced voltage condition), the output voltage _{V OUT} is generated a situation that below the minimum operating voltage _{V MIN,} LED 12 is turned off.

A bypass switch 24 and a bypass control circuit 26 are provided 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 _VIN > V _MIN is maintained. That is, the lighting of the remaining LEDs 12_1 to 12_n-1 can be maintained in exchange for turning off the LED 12_n.

JP-A-2006-197711 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 assurance 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, it is rare that the temperature is maintained at the lowest temperature (-40 ° C.) in 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 invention has been made in view of such a problem, and one of exemplary purposes of one embodiment of the present invention 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 low 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.

  It should be noted that 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 invention, it is possible to suppress an unnecessary decrease in luminance of a semiconductor light source.

It is a block diagram of the conventional vehicle lamp. It is a block diagram of a vehicle lamp provided with a lighting circuit according to an embodiment. FIG. 3A is a diagram showing a temperature characteristic of a threshold value V _TH in the lighting circuit of FIG. 2, and FIG. 3B is a diagram showing a threshold value V _TH ′ based on a conventional design method. is there. 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 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 a threshold having a negative correlation with a temperature of the first semiconductor light source. A bypass circuit that is enabled based on the relationship between the value and the input voltage and bypasses the drive current.

  The state of the bypass circuit may be controlled based on 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 bypass circuit may include a first resistor and a second resistor provided in series between the input line where the input voltage appears and the ground line, and a thermistor having a negative temperature coefficient provided in parallel with the first resistor.

  The vehicle lamp may include a first semiconductor light source and a lighting circuit. The number of light emitting elements to be bypassed in the reduced voltage state may be two. The two light emitting elements may be laid out such that the symmetry of the light emitting pattern of the first semiconductor light source is maintained when the bypass circuit is enabled. Thereby, when the lamp is viewed from the front, the difference between the strong direction and the weak direction of the emitted light can be suppressed.

  The vehicle lamp may further include a first semiconductor light source and another second semiconductor light source. The plurality of light emitting elements of the first semiconductor light source may be arranged so as to surround the second semiconductor light source, and the two light emitting elements to be bypassed in the reduced voltage state may be provided at symmetric positions with respect to the second semiconductor light source.

  The lighting circuit may further include a third resistor provided in series with the second semiconductor light source. By driving the second semiconductor light source only with a simple resistor, the lighting circuit can be simplified.

(Embodiment)
Hereinafter, the present invention 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” means that the member A and the member B are physically directly connected, and that the member A and the member B It does not substantially affect the actual connection state, or does not impair the function or effect exerted by the combination thereof, and also includes the case where the connection is made indirectly via another member.

  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, It does not substantially affect the actual connection state, or does not impair the function or effect exerted by the combination thereof, and also includes the case where the connection is made indirectly via another member.

  In this specification, electric signals such as voltage signals and current signals, or reference numerals 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 the case where n = 3. The light emitting element 504 is preferably, for example, an LED, but is not limited thereto, and may be an LD (laser diode), an organic EL element, or the like. 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). LED sockets are not only required to have a long service life, but are also consumables, so that cost reduction is strongly required.

The lighting circuit 600 includes a driving circuit 610 and a bypass circuit 620. The drive circuit 610 receives the input voltage V _IN and supplies the semiconductor light source 502 with a drive current I _LED stabilized to the target amount I _REF . The drive circuit 610 may be configured by any one of (i) a constant current linear regulator, (ii) a step-down switching converter having a constant current output, or (iii) a combination of a step-down switching converter having 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 adjacent to or adjacent to the same substrate. Alternatively, it may be attached to a heat sink to which the semiconductor light source 502 is attached. 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 .

The above is the configuration of the lighting circuit 600. Subsequently, the operation 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, for example.
V _TH = V _MIN + ΔV
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 with ΔV kept constant, but this is not a limitation, and ΔV may have a temperature dependency, and thus the threshold value is set. The 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 _VIN < _VTH ', the bypass switch is turned on, one LED 12 is turned off, and the light amount of the light source 10 is reduced.

Returning to FIG. In this embodiment, 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 a comparison with FIG. 3B, according to the lighting circuit 600 according to the embodiment, the voltage range in which all the light-emitting elements 504 can maintain lighting 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 generates a detection voltage Vd 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.
Vd = V _IN × K (T)

For example, bypass circuit 620A may switch between an enabled state and a disabled state based on the relationship between detection voltage Vd and predetermined reference voltage V _REF . Specifically, when Vd = _VIN × K (T) < _VREF , in other words, when _VIN < _VREF / 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 the input line 624 where the input voltage _VIN appears and the 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.
K (T) = (Ra // R1) / (Ra // R1 + R2)
“//” 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. The current bypass control unit 628 includes a voltage comparator 630 that compares the detection 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 of 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 a part of the drive current I _LED may be 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. May be provided in a state in which is bypassed. That is, the enable state of the bypass circuit 620B, not only the state in which all of the drive current I _LED to bypass may also include a state where 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 a 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 _VIN2 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, 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 vehicle lamp 500 </ b> B 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 adopt 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 drive circuit 610 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, for the second semiconductor light source 502B, it is sufficient to supply a drive current I _LED2 of several tens of 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. In the present embodiment, the second driving circuit 640 includes the second semiconductor light source 502B. A third resistor (current limiting resistor) R3 provided in series with the light source 502B is included.

  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, between the input terminal of the second drive circuit 640 and the second input terminal IN2 of the vehicular lamp 500B, a diode D3 for power supply reverse connection protection is provided. However, since the third resistor R3 itself has surge resistance, the 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 a 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 detachable from a lamp body (not shown). A plurality of light emitting elements 504 are mounted in the center, and 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 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 thereof are connected to a 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 modifications will be described.

(Modification 1)
In the first embodiment, by multiplying the coefficient K (T) having a temperature dependence to generate a detection voltage Vd to the input voltage V _IN, based on the relationship between the predetermined reference voltage V _REF, the state of the bypass circuit 620A Controlled, but not limited. A predetermined reference voltage V _REF is multiplied by a coefficient having a negative correlation with temperature to generate a threshold value V _TH , based on a relationship between the threshold voltage V _TH and an input voltage V _IN (or a voltage obtained by multiplying the input voltage V _IN by a predetermined coefficient). Alternatively, the state of the bypass circuit may be controlled.

(Modification 2)
In the second embodiment, the socket LED serving as both the stop lamp and the tail lamp has been described. However, the present invention is not limited to this, and a layout of light emitting elements in consideration of symmetry may be introduced in the socket LED of the stop lamp alone. It can be understood that the layout in this case is such that 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.

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 (7)

A lighting circuit for lighting a first semiconductor light source including a plurality of light emitting elements connected in series,
A first drive circuit that receives an input voltage and supplies a drive current to the first semiconductor light source;
A bypass circuit that is connected to at least one of the plurality of light emitting elements and that is enabled based on a relationship between a threshold value having a negative correlation with the temperature of the first semiconductor light source and the input voltage, and bypasses the drive current; When,
A lighting circuit, comprising:   2. The lighting according to claim 1, wherein the state of the bypass circuit is controlled based on 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. circuit.   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, and a thermistor having a negative temperature coefficient provided in parallel with the first resistor. The lighting circuit according to claim 2, wherein the detection voltage appears at a connection node between the first resistor and the second resistor. A first semiconductor light source including a plurality of light emitting elements;
The lighting circuit according to any one of claims 1 to 3, 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,
5. The layout according to claim 4, wherein the two light emitting elements are laid out such that the symmetry of the light emitting pattern of the first semiconductor light source is maintained when the bypass circuit is enabled. Vehicle lighting fixtures. Further comprising a second semiconductor light source different from 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 vehicular lamp according to claim 5, wherein the two light emitting elements are provided at symmetric positions with respect to the second semiconductor light source. The lighting circuit further includes a second drive circuit that supplies a drive current to the second semiconductor light source,
The vehicular lamp according to claim 6, wherein the second drive circuit includes a third resistor provided in series with the second semiconductor light source.

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