U.S. patent application number 16/417270 was filed with the patent office on 2019-09-05 for vehicular lighting device.
This patent application is currently assigned to KOITO MANUFACTURING CO., LTD.. The applicant listed for this patent is KOITO MANUFACTURING CO., LTD.. Invention is credited to Tomoyuki ICHIKAWA, Masayasu ITO, Naoki TATARA, Satoshi Yamamura.
Application Number | 20190274209 16/417270 |
Document ID | / |
Family ID | 56977291 |
Filed Date | 2019-09-05 |
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United States Patent
Application |
20190274209 |
Kind Code |
A1 |
ICHIKAWA; Tomoyuki ; et
al. |
September 5, 2019 |
VEHICULAR LIGHTING DEVICE
Abstract
A first light source illuminates a first region. A second light
source is configured to provide lower luminance than that of the
first light source. The second light source illuminates a second
region that overlaps the first region, and that has a larger area
than that of the first region. A lighting circuit drives the first
light source and the second light source according to a common
lighting instruction. The lighting circuit gradually turns on the
first light source and the second light source with different
gradual changing time periods in response to the lighting
instruction.
Inventors: |
ICHIKAWA; Tomoyuki;
(Shizuoka-shi, JP) ; ITO; Masayasu; (Shizuoka-shi,
JP) ; TATARA; Naoki; (Shizuoka-shi, JP) ;
Yamamura; Satoshi; (Shizuoka-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KOITO MANUFACTURING CO., LTD. |
Tokyo |
|
JP |
|
|
Assignee: |
KOITO MANUFACTURING CO.,
LTD.
Tokyo
JP
|
Family ID: |
56977291 |
Appl. No.: |
16/417270 |
Filed: |
May 20, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15713744 |
Sep 25, 2017 |
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16417270 |
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PCT/JP2016/056854 |
Mar 4, 2016 |
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15713744 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F21S 41/00 20180101;
B60Q 1/18 20130101; B60Q 2300/052 20130101; F21S 41/176 20180101;
H05B 47/16 20200101; F21S 41/16 20180101; B60Q 1/1407 20130101;
H05B 39/02 20130101; B60Q 1/04 20130101; H05B 45/00 20200101; F21S
41/141 20180101; B60Q 1/14 20130101 |
International
Class: |
H05B 37/02 20060101
H05B037/02; B60Q 1/18 20060101 B60Q001/18; F21S 43/00 20060101
F21S043/00; H05B 33/08 20060101 H05B033/08; B60Q 1/14 20060101
B60Q001/14; F21S 41/00 20060101 F21S041/00; B60Q 1/04 20060101
B60Q001/04 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 26, 2015 |
JP |
2015-064377 |
Claims
1.-8. (canceled)
9. A vehicular lighting device comprising: a light source
comprising a laser diode; and a lighting circuit structured to
supply a driving current to the laser diode, wherein the lighting
circuit is structured to be switchable between a normal mode in
which a driving current that exceeds an oscillation threshold value
is supplied to the laser diode and a test mode in which a driving
current that is lower than the oscillation threshold value is
steadily supplied to the laser diode.
10. The vehicular lighting device according to claim 9, further
comprising a processor structured to receive a lighting on/off
instruction for the light source from a vehicular ECU (Electronic
Control Unit) via a bus, wherein the processor is set to the test
mode according to control received via the bus.
11. The vehicular lighting device according to claim 9, wherein the
light source comprises a fluorescent member structured to be
excited by an excitation light output from the laser diode and to
emit a fluorescent light, in addition to the laser diode, and
wherein the light source is structured to generate a white output
light comprising a spectrum of the excitation light and the
fluorescent light.
12. A lighting device system comprising: a vehicular lighting
device comprising a light source comprising a laser diode and a
lighting circuit structured to supply a driving current to the
laser diode; and a vehicular ECU (Electronic Control Unit)
structured to control the vehicular lighting device, wherein the
vehicular lighting device is structured to steadily supply, to the
laser diode, a driving current with a current value that is smaller
than an oscillation threshold value in response to an instruction
from the vehicular ECU, so as to instruct the laser diode to emit
light in a non-oscillation state.
13.-15. (canceled)
16. The vehicular lighting device according to claim 10, wherein
the light source comprises a fluorescent member structured to be
excited by an excitation light output from the laser diode and to
emit a fluorescent light, in addition to the laser diode, and
wherein the light source is structured to generate a white output
light comprising a spectrum of the excitation light and the
fluorescent light.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] The present invention relates to a vehicular lighting device
employed in an automobile or the like.
2. Description of the Related Art
[0002] With conventional techniques, as vehicular lighting devices,
and particularly, as headlamp light sources, halogen lamps or HID
(High Intensity Discharge) lamps have become mainstream. In recent
years, as substitutions for such conventional lamps, the
development of vehicular lighting devices employing a semiconductor
light source such as an LED (light-emitting diode), laser diode
(which will also be referred to as a "semiconductor laser"), or the
like has been advancing.
[0003] A technique has been proposed in which multiple light
sources emit light in an overlapping manner so as to form a desired
light distribution pattern (Japanese Patent Application Laid Open
No. 2005-294166). With conventional techniques, in a case in which
a given region is illuminated by multiple light sources in an
overlapping manner, the on/off operations of such multiple light
sources are controlled at the same time based on a common lighting
on/off instruction. It can be said that such an arrangement is
preferable from the viewpoint of the simplicity of the control
operation.
[0004] However, there is room for further improvement from the
viewpoint of improving the appearance and the impression of high
quality, from the viewpoint of improving the visibility of the
forward area and the driver's comfort based on the improved
visibility, and from the viewpoint of safety.
SUMMARY OF THE INVENTION
[0005] The present invention has been made in view of such a
situation. Accordingly, it is an exemplary purpose of an embodiment
of the present invention to provide a vehicular lighting device
that presents an improved appearance and impression of high quality
and/or provides improved visibility for the forward area.
[0006] An embodiment of the present invention relates to a
vehicular lighting device. The vehicular lighting device comprises:
a first light source structured to illuminate a first region; a
second light source structured to provide a lower luminance than
that of the first light source, and to illuminate a second region
that overlaps the first region and has a larger area than that of
the first region; and a lighting circuit structured to drive the
first light source and the second light source according to a
lighting instruction, and to gradually turn on the first light
source and the second light source with different gradual change
time periods in response to the lighting instruction.
[0007] With this embodiment, after the brightness of a given region
is changed, the brightness of another region is changed with a time
lag between them. This presents an improved appearance and feeling
of high quality and/or provides improved visibility for the forward
area as compared with an arrangement in which the brightness levels
of these regions are changed at the same time.
[0008] Also, the gradual change time period set for the first light
source may be longer than the gradual change time period set for
the second light source.
[0009] With such an arrangement, after the wide region is
illuminated beforehand in order to allow the driver to grasp the
overall situation, the spot to which attention is to be directed
along the driving axis is intensively illuminated, thereby
facilitating driving the vehicle.
[0010] Also, the gradual change time period set for the second
light source may be longer than the gradual change time period set
for the first light source.
[0011] With such an arrangement, after the spot to which attention
is to be directed along the driving axis is illuminated so as to
direct the driver's attention, the surrounding region is
illuminated over a wide area, thereby providing improved
safety.
[0012] Also, the difference in the gradual change time period
between the first light source and the second light source may be
included in a range from 0.2 to 5 seconds.
[0013] In a case in which the time difference is excessively small,
the effect is hard to recognize. Conversely, if the time difference
is excessively large, a long time is required before sufficient
brightness is obtained, and accordingly, a long time is required
before securing visibility for the driver. This degrades the
primary function of the vehicular lighting device. By designing the
time difference in a range of 0.2 to 5 seconds, such an arrangement
provides both the effect according to the present invention and the
primary function of the vehicular lighting device.
[0014] Also, the first light source and the second light source may
each be a light source for providing an additional high beam.
[0015] Also, the first light source may be structured as a laser
diode. Also, the second light source may be structured as a
light-emitting diode.
[0016] By employing a combination of two kinds of light sources
having different characteristics, such an arrangement is capable of
emitting light over a long distance by means of the laser diode
having high directionality and of illuminating a wide region with
high brightness by means of the light-emitting diode.
[0017] Also, the first light source and the second light source may
be coupled in series. Also, the lighting circuit may comprise: a
driving circuit structured to supply a driving current that
corresponds to a dimming signal to a series connection circuit of
the first light source and the second light source; a bypass switch
arranged in parallel with one light source from among the first
light source and the second light source set for a longer gradual
change time period; and a gradual change controller structured to
generate the dimming signal that corresponds to gradually turning
on/off the other light source set for a shorter gradual change time
period, and to control a state of the bypass switch so as to
gradually turn on/off the aforementioned one light source.
[0018] This allows a common driving circuit to turn on the two
light sources with different gradual change time periods. Thus,
such an arrangement allows costs to be reduced as compared with an
arrangement including a pair of driving circuits.
[0019] Also, the gradual change controller may comprise: a
transistor structured as the bypass switch; a signal generating
unit structured to generate a gradual change signal that indicates
a waveform for gradually turning on the other light source; and an
error amplifier structured to amplify a difference between a signal
that indicates a driving current that flows through the other light
source and the gradual change signal, and to output the difference
thus amplified to a control terminal of the transistor.
[0020] Also, the gradual change controller may comprise: a
transistor structured as the bypass switch; a signal generating
unit structured to generate a gradual change signal that indicates
a waveform for gradually turning on the other light source; and a
pulse modulator structured to perform switching of the transistor
according to the gradual change signal.
[0021] Another embodiment of the present invention also relates to
a vehicular lighting device. The vehicular lighting device
comprises: a light source comprising a laser diode; and a lighting
circuit structured to supply a driving current to the laser diode.
The lighting circuit is structured to be switchable between a
normal mode in which a driving current that exceeds an oscillation
threshold value is supplied to the laser diode and a test mode in
which a driving current that is lower than the oscillation
threshold value is steadily supplied to the laser diode.
[0022] During maintenance, the vehicle is stationary, and it can be
assumed that there are workers around the vehicle. In this state,
in a case in which the laser diode emits light in the same way as
when the vehicle is driven, this disturbs the workers in the
vicinity of the lighting device. Also, a malfunction can occur in
the lighting device, and in such a case, it is conceivable that the
output light of the laser diode would be directly emitted without
being scattered.
[0023] With such an embodiment, in the maintenance mode, the laser
diode emits very weak light without oscillation of the laser diode,
thereby providing improved safety.
[0024] Also, the vehicular lighting device may further comprise a
processor structured to receive a lighting on/off instruction for
the light source from a vehicular ECU (Electronic Control Unit) via
a bus. Also, the processor may be set to the test mode according to
control received via the bus. In this case, after a maintenance
tool is coupled to the vehicular ECU, such an arrangement is
capable of transmitting an instruction to emit light in the test
mode to the vehicular lighting device via the vehicular ECU.
[0025] Also, the light source may comprise a fluorescent member
structured to be excited by an excitation light output from the
laser diode and to emit a fluorescent light, in addition to the
laser diode. Also, the light source may be structured to generate a
white output light comprising a spectrum of the excitation light
and the fluorescent light.
[0026] With such a light source, if a malfunction occurs in the
fluorescent member, the output light of the laser diode is directly
emitted without being scattered. Thus, this is a particularly
effectively usage of such a light source.
[0027] Yet another embodiment of the present invention also relates
to a vehicular lighting device. The vehicular lighting device
comprises: a semiconductor light source; a driving circuit
structured to supply, to the semiconductor light source, a driving
current that corresponds to a dimming signal; a processor
structured to generate a lighting on/off instruction signal that
instructs the semiconductor light source to turn on and off
according to an instruction from a vehicle and driving information
that indicates a driving situation; a gradual change controller
structured to generate the dimming signal that gradually changes
with time in response to the lighting on/off instruction signal;
and a switch arranged on a power supply path that extends from a
battery to the driving circuit, and structured such that an on/off
state thereof is controlled by the processor. When the laser diode
is to be gradually turned off, the processor turns off the switch
after a predetermined time period elapses after the lighting on/off
instruction signal is set to the lighting off level.
[0028] This supports the gradual lighting off function. In
addition, this prevents the semiconductor light source from being
driven by an out-of-control current even if a short-circuit fault
has occurred in the switching element on the current path of the
driving circuit.
[0029] Also, when the semiconductor light source is to be instantly
turned off, the processor may immediately turn off the switch.
[0030] Also, when the lighting on/off instruction signal is to be
set to a lighting on level, the processor may turn on the switch at
the same time as or otherwise before the setting of the lighting
on/off instruction signal to the lighting on level.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] Embodiments will now be described, by way of example only,
with reference to the accompanying drawings which are meant to be
exemplary, not limiting, and wherein like elements are numbered
alike in several Figures, in which:
[0032] FIG. 1A is a diagram showing light distribution patterns in
a low-beam mode and a high-beam mode formed on a virtual vertical
screen arranged at a predetermined forward position of the lighting
device, and FIG. 1B is a diagram showing a light distribution
pattern supported by the additional high-beam lamp;
[0033] FIG. 2 is a block diagram showing a lighting device system
including a vehicular lighting device according to a first
embodiment;
[0034] FIGS. 3A and 3B are operation waveform diagrams each showing
the operation of the vehicular lighting device shown in FIG. 2;
[0035] FIG. 4 is a block diagram showing a lighting circuit
according to a first example configuration;
[0036] FIG. 5 is an operation waveform diagram showing the
operation of the lighting circuit shown in FIG. 4;
[0037] FIG. 6 is a circuit diagram showing a specific example
configuration of a gradually-change controller shown in FIG. 4;
[0038] FIG. 7 is a circuit diagram showing an another example
configuration of the gradually-change controller shown in FIG.
4;
[0039] FIG. 8 is a block diagram showing a lighting circuit
according to a second example configuration;
[0040] FIG. 9 is a block diagram showing a lighting device system
including a vehicular lighting device according to a second
embodiment;
[0041] FIG. 10 is a cross-sectional view of a high-beam light
source including a laser diode;
[0042] FIG. 11 is a block diagram showing a lighting device system
according to a third embodiment;
[0043] FIG. 12 is a circuit diagram showing a constant current
converter configured as a driving circuit;
[0044] FIG. 13 is a first operation waveform diagram showing the
operation of the vehicular lighting device shown in FIG. 11;
and
[0045] FIG. 14 is a second operation waveform diagram showing the
operation of the vehicular lighting device shown in FIG. 11.
DETAILED DESCRIPTION OF THE INVENTION
[0046] Description will be made below regarding the present
invention based on preferred embodiments with reference to the
drawings. The same or similar components, members, and processes
are denoted by the same reference numerals, and redundant
description thereof will be omitted as appropriate. The embodiments
have been described for exemplary purposes only, and are by no
means intended to restrict the present invention. Also, it is not
necessarily essential for the present invention that all the
features or a combination thereof be provided as described in the
embodiments.
[0047] In the present specification, the state represented by the
phrase "the member A is coupled to the member B" includes a state
in which the member A is indirectly coupled to the member B via
another member that does not substantially affect the electric
connection therebetween, or that does not damage the functions or
effects of the connection therebetween, in addition to a state in
which the member A is physically and directly coupled to the member
B.
[0048] Similarly, the state represented by the phrase "the member C
is provided between the member A and the member B" includes a state
in which the member A is indirectly coupled to the member C, or the
member B is indirectly coupled to the member C via another member
that does not substantially affect the electric connection
therebetween, or that does not damage the functions or effects of
the connection therebetween, in addition to a state in which the
member A is directly coupled to the member C, or the member B is
directly coupled to the member C.
First Embodiment
[0049] FIG. 1A shows light distribution patterns in a low-beam mode
and a high-beam mode formed on a virtual vertical screen arranged
at a predetermined position forward of the lighting device. Here,
"PL" indicates a region illuminated by a low-beam lamp, and "PH"
indicates a region illuminated by an ordinary high-beam lamp.
Furthermore, "PAH" indicates a region illuminated by an additional
high-beam lamp that differs from the ordinary high-beam lamp, so as
to illuminate a more distant region. FIG. 1B is a diagram showing a
light distribution pattern PAH of the additional high-beam lamp.
The light distribution pattern PAH of the additional high-beam lamp
is formed by a first light source and a second light source. The
first light source illuminates a first region PN defined as a
central narrow region. The first light source is preferably
configured as a laser diode having high directionality. The second
light source illuminates a second region PB overlapping the first
region PN and having an area that is larger than the first region
PN. As the second light source, an LED is employed, for
example.
[0050] FIG. 2 is a block diagram showing a lighting device system
100 including a vehicular lighting device 200 according to a first
embodiment.
[0051] The vehicular lighting device 200 forms the additional
high-beam distribution pattern shown in FIG. 1. In actuality, in
addition to the additional high-beam lamp, the vehicular lighting
device 200 further includes an ordinary high-beam lamp, a low-beam
lamp, and a clearance lamp, which are not shown.
[0052] A vehicular ECU (electronic control unit) 104 is coupled to
the vehicular lighting device 200 via a control line such as a CAN
(controller area network) bus 106 or the like, and integrally
controls the vehicular lighting device 200.
[0053] As viewed from the vehicular ECU 104, the additional
high-beam lamp of the vehicular lighting device 200 is a single
lamp. Accordingly, the vehicular ECU 104 generates a single
lighting instruction S1 which instructs the additional high-beam
lamp to turn on and off. In some cases, the lighting instruction S1
is also used as an instruction to turn on the high-beam lamp.
[0054] Furthermore, in addition to the lighting instruction S1, the
vehicular ECU 104 transmits, to the vehicular lighting device 200,
information (driving information) S2 which indicates a driving
situation.
[0055] Next, description will be made regarding a configuration of
the vehicular lighting device 200. The vehicular lighting device
200 includes a first light source 202A, a second light source 202B,
a lighting circuit 300 for such light sources, and a lighting
device ECU 400. The first light source 202A is configured as a
laser diode. The second light source 202B is configured as an LED.
In actuality, the lighting device system 100 is provided with a
pair of left and right vehicular light sources. However, only one
of the vehicular lighting devices 200 is shown.
[0056] The lighting circuit 300 drives the first light source 202A
and the second light source 202B according to a lighting on/off
instruction signal S4 received from the lighting device ECU 400.
The lighting on/off instruction signal S4 is shared between the
first light source 202A and the second light source 202B. The
lighting circuit 300 is configured to turn on the first light
source 202A and the second light source 202B with different gradual
change time periods TA and TB according to the lighting on/off
instruction signal S4.
[0057] When the lighting on/off instruction signal S4 transits to a
lighting on level (e.g., high level), the lighting circuit 300
raises a driving current I.sub.LD to be supplied to the first light
source 202A with a first transition time period (gradual change
time period). Furthermore, when the lighting on/off instruction
signal S4 transits to the lighting on level, the lighting circuit
300 raises a driving current I.sub.LD to be supplied to the second
light source 202B with a second transition time period .tau..sub.B
(gradual change time period). Detailed description thereof will be
made later.
[0058] Human eyes have logarithmical sensitivity characteristics
with respect to the surrounding brightness. Accordingly, as the
surrounding brightness level becomes lower, the sensitivity of
human eyes becomes higher. In the case of gradually raising the
luminance of a lamp (gradually turning on), during a range in which
the luminance of the lamp is low, the luminance is raised with a
low rate of change. Subsequently, the rate of change in luminance
is raised according to an increase in the luminance of the lamp.
With such an arrangement, the lamp can be turned on in a manner
that is natural for human eyes. Similarly, in a case of gradually
lowering the luminance of the lamp (gradually turning off), during
a range in which the luminance of the lamp is high, the luminance
is lowered with a high rate of change. Subsequently, the rate of
change in luminance is lowered according to a reduction in the
luminance of the lamp.
[0059] The lighting device ECU 400 includes a CPU (central
processing unit) 402 and a semiconductor switch 404. The CPU 402
generates the lighting on/off instruction signal S4 which instructs
the additional high-beam light source 202 to turn on or off
according to the lighting instruction S1 and the driving
information S2 received from the vehicular ECU 104.
[0060] For example, the driving information S2 includes the
presence or absence of a forward vehicle (S2a), the vehicle speed
(S2b), and the steering angle (S2c). When the lighting instruction
S1 is an instruction to turn on the lamp, and when the presence or
absence of a forward vehicle, the vehicle speed, and the steering
angle satisfy predetermined conditions, the lighting device ECU 400
sets the lighting on/off instruction signal S4 to the lighting on
level.
[0061] As an example, when the lighting on/off instruction signal
S4 is an instruction to turn on the lamp, and when the conditions
(i) no forward vehicle is detected, (ii) the vehicle speed is equal
to or higher than a predetermined value (80 km/h), and (iii) the
steering angle is equal to or lower than a predetermined value
(e.g., 5 degrees) are satisfied, the lighting on/off instruction
signal S4 is set to the lighting on level.
[0062] Furthermore, when the lighting on/off instruction signal S4
is set to the lighting on level, and when at least one condition is
satisfied from among (i) a forward vehicle is detected, (ii) the
vehicle speed is equal to or lower than a predetermined value (60
km/h), and (iii) the steering angle is equal to or higher than a
predetermined value (e.g., 10 degrees), the lighting on/off
instruction signal S4 is set to the lighting off level.
[0063] The semiconductor switch 404 is arranged on a power supply
path via which power is supplied from the battery 102 to a driving
circuit 302. The on/off operation of the semiconductor switch 404
is controlled according to a control signal S5 received from the
processor 402. In the lighting on state of the additional high-beam
light source 202, the semiconductor switch 404 is turned on.
[0064] The above is the configuration of the lighting device system
100. Next, description will be made regarding the operation
thereof.
[0065] FIGS. 3A and 3B are operation waveform diagrams each showing
the operation of the vehicular lighting device 200 shown in FIG.
2.
[0066] FIG. 3A shows an example in which the first gradual change
time period .tau..sub.A is longer than the second gradual change
time period .tau..sub.B. In this control operation, first, the LED
illuminates a relatively wide range over a long distance. After the
driver has grasped the overall situation, the laser diode gradually
illuminates a spot to which attention is be directed along the
driving axis, thereby facilitating driving the vehicle.
[0067] FIG. 3B shows an example in which the first gradual change
time period .tau..sub.A is shorter than the second gradual change
time period .tau..sub.B. In this control operation, first, the spot
to which attention is to be directed along the driving axis is
illuminated. After directing the driver's attention to the spot,
the surrounding region is illuminated over a wide range, thereby
providing improved safety.
[0068] That is to say, with the vehicular lighting device 200, by
providing a time difference in the change of the luminance between
the two light sources, this provides improved visibility for a
forward area as compared to an arrangement in which the luminance
is changed at the same time for the two light sources. The control
operation shown in FIG. 3A or 3B may be set for the vehicular
lighting device 200 beforehand. Also, the CPU 402 may adaptively
select the control operation.
[0069] In addition, this provides effects of improving the
appearance and impression of high quality.
[0070] The difference between the first gradual change time period
.tau..sub.A and the second gradual change time period .tau..sub.B
is preferably set to a value on the order of 0.2 seconds to 5
seconds. Furthermore, each of the first gradual change time period
.tau..sub.A and the second gradual change time period .tau..sub.B
is preferably set to a value on the order of 0.2 seconds to 5
seconds.
[0071] In a case in which the time difference is excessively small,
the effect is hard to recognize. Conversely, if the time difference
is excessively large, a long time is required before sufficient
brightness is obtained, and accordingly, a long time is required
before securing visibility for the driver. This degrades the
primary function of the vehicular lighting device. By designing the
time difference in a range of 0.2 to 5 seconds, such an arrangement
provides both the effect according to the present invention and the
primary function of the vehicular lighting device.
[0072] Next, description will be made regarding example
configurations of the lighting circuit 300.
First Example Configuration
[0073] FIG. 4 is a block diagram showing a lighting circuit 300a
according to a first example configuration. In this example, an
arrangement in which .tau..sub.A<.tau..sub.B will be described.
The first light source 202A and the second light source 202B are
coupled in series. The lighting circuit 300a includes a driving
circuit 302, a gradual change controller 304, and a bypass switch
310. The driving circuit 302 supplies a driving current I.sub.LD
that corresponds to a dimming signal S3A to a series connection
circuit 202 comprising the first light source 202A and the second
light source 202B.
[0074] The driving circuit 302 is preferably configured as a
constant current converter that stabilizes the driving current
I.sub.LED to a target current that corresponds to the dimming
signal S3. It should be noted that the topology of the constant
current converter is not restricted in particular. The driving
circuit 302 may employ both an analog dimming operation in which
the amount of the driving current I.sub.LD is adjusted and a PWM
(pulse width modulation) dimming operation in which high-speed
switching is performed for the driving current I.sub.LD so as to
adjust the duty ratio thereof. Also, the driving circuit 302 may
employ only one from among the analog dimming operation and the PWM
dimming operation.
[0075] The bypass switch 310 may be configured as a transistor. The
bypass switch 310 is arranged in parallel with the light source
202B, i.e., the light source to be provided with a longer gradual
change time period from among the first light source 202A and the
second light source 202B. The gradual change controller 304
generates the dimming signal S3A that corresponds to gradually
turning on and off the light source 202A with a shorter gradual
change time period. Furthermore, the gradual change controller 304
controls the state of the bypass switch 310 so as to gradually turn
on and off the other light source 202B.
[0076] FIG. 5 is an operation waveform diagram showing the
operation of the lighting circuit 300a shown in FIG. 4. When the
lighting on/off instruction signal S4 becomes the lighting on level
at the time point t0, the gradual change controller 304 changes the
dimming signal S3A with the first gradual change time period
.tau..sub.A, which gradually increases the driving current
I.sub.LD. As a result, the luminance of the first light source 202A
rises with the first gradual change time period .tau..sub.A.
[0077] On the other hand, a current I.sub.LD that flows through the
second light source 202B is proportional to the difference between
the current I.sub.LD supplied to the first light source 202A and
the current I.sub.BP that flows through the bypass switch 310.
I.sub.LED=I.sub.LD-I.sub.BP
[0078] In other words, by controlling the waveform of the current
I.sub.BP so as to obtain a desired gradual change profile of the
driving current I.sub.LED, such an arrangement is capable of
gradually turning on the second light source 202B with a desired
gradual change time period .tau..sub.B independently of the
waveform of the dimming signal S3A.
[0079] By providing a control operation that is the reverse of the
lighting on control operation, such an arrangement provides a
gradual change in turning off the lighting. When the lighting
on/off instruction signal S4 transits to the lighting off level at
the time point t2, the gradual change controller 304 raises the
current I.sub.LD that flows through the bypass switch 310. As a
result, first, the current I.sub.LED supplied to the second light
source 202B starts to decrease. Furthermore, at the time point t2,
the output current I.sub.LD of the driving circuit 302 starts to
decrease with the first gradual change time period .tau..sub.A
based on the dimming signal S3A. The current I.sub.BP that flows
through the bypass switch 310 is generated such that the current
I.sub.LED to be supplied to the second light source 202B decreases
with a desired profile.
[0080] As described above, with the lighting circuit 300a shown in
FIG. 4, such an arrangement allows the two light sources 202A and
202B to be turned on with different gradual change periods
.tau..sub.A and .tau..sub.B by means of a common driving circuit.
This allows the cost to be reduced as compared with an arrangement
including a pair of driving circuits. It should be noted that the
waveform in FIG. 5 is shown for exemplary purposes only. That is to
say, a desired waveform may be designed.
[0081] FIG. 6 is a circuit diagram showing a specific example
configuration of the gradual change controller 304 shown in FIG. 4.
The bypass switch 310 is a transistor. Here, the bypass switch 310
is configured as an N-channel MOSFET. Also, an NPN bipolar
transistor may be employed. Alternatively, a P-channel MOSFET or a
PNP bipolar transistor may be employed.
[0082] A signal generating unit 330 generates a gradual change
signal S3B for representing the waveform to be provided by the
second light source 202B. It can also be said that the gradual
change signal S3B corresponds to S3B shown in FIG. 4. The signal
generating unit 330 may be configured as a capacitor 332 and a
current source 334, for example. The current source 334 is
configured such that, when the lighting is gradually turned on, the
current I.sub.C is supplied to the capacitor 332 so as to charge
the capacitor 332, and such that, when the lighting is gradually
turned off, the capacitor 332 is discharged. The voltage across the
capacitor 332 is used as the gradual change signal S3B.
[0083] In a case of design giving consideration to the sensitivity
of human eyes, when the lighting is gradually turned on, as shown
in FIG. 5, the slope of the driving current I.sub.LED is preferably
designed such that it becomes larger with the passage of time. In
this case, the current source 334 may preferably be configured to
change the charging current I.sub.C according to the voltage across
the capacitor 332.
[0084] The signal generating unit 330 may be configured as a
combination of a processor that generates digital waveform data and
a D/A converter that converts the waveform data into an analog
gradual change signal S3B.
[0085] An error amplifier 320 amplifies the difference between the
gradual change signal S3B and a current detection signal V.sub.IS
that indicates the driving current I.sub.LED that flows through the
second light source 202B, and outputs the difference signal thus
amplified to a control terminal (gate) of the transistor 310. The
generating method for the current detection signal V.sub.IS is not
restricted in particular. For example, a sensing resistor R.sub.S
may be arranged on a path of the driving current I.sub.LED, and a
voltage drop across the sensing resistor R.sub.S may be used.
[0086] With the gradual change controller 304 shown in FIG. 6, such
an arrangement is capable of feedback controlling the on resistance
(i.e., the amount of current I.sub.BP) of the transistor 310 such
that the current waveform of the driving current I.sub.LED matches
the waveform of the gradual change signal S3B.
[0087] With the gradual change controller 304 shown in FIG. 6, the
bypass switch 310 is feedback controlled in a closed loop manner so
as to obtain a desired waveform of the driving current I.sub.LED.
However, the present invention is not restricted to such an
arrangement. Also, the bypass switch 310 may be controlled in an
open loop manner.
[0088] FIG. 7 is a circuit diagram showing another example
configuration of the gradual change controller 304 shown in FIG. 4.
The gradual change controller 304 includes a pulse modulator 322.
The pulse modulator 322 performs switching of the transistor 310
according to a gradual change signal S3b.
[0089] The current detection signal V.sub.IS may be a signal
obtained by smoothing the voltage drop across the sensing resistor
R.sub.S by means of a low-pass filter 324. In the example shown in
FIG. 7, the pulse modulator 322 generates a pulse signal S.sub.PWM
having a duty ratio that corresponds to an output V.sub.ERR of the
error amplifier 320. The configuration of the pulse generator 322
is not restricted in particular. Known techniques may be employed.
For example, by comparing the output V.sub.ERR of the error
amplifier 320 with a triangle wave or a sawtooth wave, such an
arrangement is capable of generating the pulse signal
S.sub.PWM.
[0090] With the gradual change controller 304 shown in FIG. 7, this
allows the duty ratio of the switching of the transistor 310 to be
feedback controlled such that the time average waveform of the
driving current I.sub.LED matches the waveform of the gradual
change signal S3B.
[0091] By controlling the bypass switch 310 using the pulse
modulation, the following additional advantages can be obtained.
First, such an arrangement is capable of providing chromaticity
matching of the illumination color between a steady lighting state
and a dimming state.
[0092] When the supplied current is equal to or lower than a
threshold current, a laser diode is not able to perform laser
oscillation. Accordingly, in a case of controlling the LED and the
laser diode at the same timing according to a common gradual change
signal that rises from zero, this leads to a problem of a delay in
the lighting on timing of the laser diode. By performing a control
operation using the pulse modulation, such an arrangement is
capable of providing lighting on timing matching between the LED
and the laser diode.
[0093] It should be noted that, in a case of performing PWM control
of the bypass switch 310, the pulse signal S.sub.PWM may be
generated in an open loop manner. Also, other modulation methods
such as pulse density modulation, pulse frequency modulation, or
the like may be employed instead of the PWM modulation.
Second Example Configuration
[0094] FIG. 8 is a block diagram showing a lighting circuit 300b
according to a second example configuration. The lighting circuit
300b includes individual driving circuits 302A and 302B for the
first light source 202A and the second light source 202B,
respectively. Such a configuration requires a pair of driving
circuits 302, i.e., involves a larger circuit scale than the
lighting circuit 300a shown in FIG. 4. However, such a
configuration allows the waveforms for gradually turning on and
gradually turning off the first light source 202A and the second
light source 202B to be individually designed as desired. Also, in
a case in which there is a difference in the rated current between
the first light source 202A and the second light source 202B, such
a configuration can be effectively employed.
Second Embodiment
[0095] FIG. 9 is a block diagram showing a lighting device system
100b including a vehicular lighting device 200b according to a
second embodiment. The vehicular lighting device 200b includes a
light source 202 including a laser diode 206 and a lighting circuit
300 that supplies the driving current I.sub.LD to the laser diode
206. As a stage upstream from the lighting circuit 300, a lighting
device ECU 400 is provided. The lighting circuit 300 is also
referred to as the "LDDM (laser diode driver module)."
[0096] For example, the lighting device system 100b is configured
as the first light source 202A that supports the additional high
beam described in the first embodiment and a circuit that relates
to a lighting circuit thereof.
[0097] The lighting circuit 300 is configured to be switchable
between a normal mode in which the driving current I.sub.LD that is
higher than an oscillation threshold value I.sub.TH is supplied to
the laser diode 206, and a test mode (which will also be referred
to as the "maintenance mode" or "diagnostic mode") in which the
driving current I.sub.LD that is lower than the oscillation
threshold value I.sub.TH is steadily supplied to the laser diode
206.
[0098] As shown in FIG. 2 or the like, the lighting device ECU 400
includes a CPU 402. The CPU 402 is set to the test mode according
to control received via the bus 106. For example, the vehicular ECU
104 outputs a mode control signal S6 in addition to the lighting
instruction S1 and the driving information S2. The mode control
signal S6 is data that provides an instruction for selection of one
from among the normal mode and the test mode. When the mode control
signal S6 indicates the normal mode, the lighting device ECU 400
controls the laser diode 206 to emit light in an oscillation state.
When the mode control signal S6 indicates the test mode, the
lighting device ECU 400 controls the laser diode 206 to emit light
in a non-oscillation state.
[0099] In addition to the lighting on/off instruction signal S4,
current control data S7 which indicates the amount of driving
current may be output from the lighting device ECU 400 to the
lighting circuit 300. When the lighting on/off instruction signal
S4 becomes the lighting on level, the lighting circuit 300
generates the driving current I.sub.LD with an amount of current
that corresponds to the current control data S7.
[0100] The above is the basic configuration of the lighting device
system 100b. Next, description will be made regarding the operation
thereof.
[0101] During maintenance, the vehicle is stationary, and it can be
assumed that there are workers around the vehicle. In this state,
in a case in which the laser diode 206 emits light in the same way
as when the vehicle is driven, this disturbs the workers in the
vicinity of the lighting device.
[0102] With the lighting device system 100b shown in FIG. 9, during
maintenance of the vehicle, a maintenance tool 108 is coupled to
the vehicular ECU 104 as indicated by the broken line in FIG. 9.
This instructs the vehicular ECU 104 to transmit the mode control
signal S6 that is an instruction to set the test mode to the
lighting device ECU 400.
[0103] In this case, the laser diode 206 operates in a
non-oscillation state, and accordingly, the laser diode 206 emits
only a weak light. This prevents the workers from being subjected
to disturbance even if they are in the vicinity of the vehicle.
Also, such an arrangement allows the optical axis alignment or the
like to be performed for the laser diode 206 using such a weak
light.
[0104] In particular, in a case in which the high-beam light source
202 is configured as follows, the lighting device system 100b
provides marked advantages.
[0105] FIG. 10 is a cross-sectional view of the high-beam light
source 202 including the laser diode 206. The light source 202
mainly includes the laser diode 206, a fluorescent member 14, an
optical system 16, and a housing 18.
[0106] The laser diode 206 shown in FIG. 10 generates blue
excitation light 20. The excitation light 20 is focused on the
fluorescent member 14 by means of the optical system 16. The
optical system 16 is configured as a lens, reflecting mirror,
optical fiber, or a combination thereof. Upon reception of the blue
excitation light 20, the fluorescent member 14 generates
fluorescent light 22 having a spectrum distribution over a
wavelength region including wavelengths (green to red) that are
longer than the excitation light 20. The excitation light 20
emitted to the fluorescent member 14 is scattered by the
fluorescent member 14. As a result, after the excitation light 20
passes through the fluorescent member 14, the excitation light 20
has only negligible coherence. The fluorescent member 14 is fitted
to and held by an opening formed in the housing 18, for example.
The output light 24 of the light source 202 includes green to red
fluorescent light 22 emitted from the fluorescent member 14, and
the blue excitation light 20a remaining after it passes through the
fluorescent member 14. As a result, the output light 24 has a
spectrum distribution of white light.
[0107] With such a high-beam light source 202, if an abnormal state
(which will be referred to as the "fluorescent member abnormal
state" hereafter) has occurred, e.g., if there is a crack in the
fluorescent member 14 or if the fluorescent member 14 has fallen
away from the housing 18, the excitation light 20 generated by the
laser diode 206 is directly output with strong coherence without
being scattered by the fluorescent member 14, and is emitted to the
area forward of the vehicle.
[0108] By operating the vehicular lighting device 200b including
the high-beam light source 202 shown in FIG. 10 in the test mode
during maintenance, the output light becomes very weak.
Accordingly, such an arrangement provides improved safety even if a
situation has occurred in which the output light of the laser diode
206 is directly emitted without being scattered.
[0109] Also, after the maintenance tool 108 is inserted such that
it is arranged between the lighting device ECU 400 and the
vehicular ECU 104, the mode control signal S6, which is an
instruction to set the test mode, may be directly input from the
maintenance tool 108 to the lighting device ECU 400.
Third Embodiment
[0110] FIG. 11 is a block diagram showing a lighting device system
100c according to a third embodiment.
[0111] The lighting device system 100c includes a battery 102, a
vehicular ECU 104, a CAN bus 106, and a vehicular lighting device
200c. Each block has the same functions as those described in the
first and second embodiments.
[0112] The vehicular lighting device 200c includes a semiconductor
light source 208 configured as the high-beam light source 202.
Examples of the semiconductor light source 208 include laser
diodes, light-emitting diodes, organic EL, and the like.
Description will be made in the present embodiment regarding an
arrangement in which the semiconductor light source 208 is
configured as a laser diode. Also, the high-beam light source 202
may be an additional high-beam light source which is provided in
addition to an ordinary high-beam light source.
[0113] The lighting circuit 300 includes a driving circuit 302 and
a gradual change controller 304. The driving circuit 302 supplies
the driving current I.sub.LD that corresponds to the dimming signal
S3 to the high-beam light source 202. As the driving circuit 302, a
constant current converter is preferably employed, configured to
step up or otherwise step down the power supply voltage V.sub.DD
and to supply the power supply voltage thus stepped up or down to
the high-beam light source 202, and to stabilize the driving
current I.sub.LED that flows through the high-beam light source 202
to a target current that corresponds to the dimming signal S3. It
should be noted that the topology of the constant current converter
is not restricted in particular. The driving circuit 302 may employ
both an analog dimming operation in which the amount of the driving
current I.sub.LD is adjusted and a PWM (pulse width modulation)
dimming operation in which high-speed switching is performed for
the driving current I.sub.LD so as to adjust the duty ratio
thereof. Also, the driving circuit 302 may employ only one from
among the analog dimming operation and the PWM dimming
operation.
[0114] The gradual change controller 304 generates the dimming
signal S3 that gradually changes with time according to the
lighting on/off instruction signal S4 received from the lighting
device ECU 400. Specifically, when the lighting on/off instruction
signal S4 transits to the lighting on level (e.g., high level), the
gradual change controller 304 gradually changes (gradually raises,
for example) the dimming signal S3 with time so as to increase the
driving current I.sub.LD. Conversely, when the lighting on/off
instruction signal S4 transits to the lighting off level (e.g., low
level), the gradual change controller 304 gradually changes
(gradually lowers, for example) the dimming signal S3 with time so
as to reduce the driving current I.sub.LD. In a second mode
described later, the time (gradual change time period) .tau.
required for the dimming signal S3 to transit is preferably
designed in a range between 0.2 and 5 seconds.
[0115] Human eyes have logarithmical sensitivity characteristics
with respect to the surrounding brightness. Accordingly, as the
surrounding brightness level becomes lower, the sensitivity of
human eyes becomes higher. In the case of gradually raising the
luminance of a lamp (gradually turning on), during a range in which
the luminance of the lamp is low, the luminance is raised with a
low rate of change. Subsequently, the rate of change in luminance
is raised according to an increase in the luminance of the lamp.
With such an arrangement, the lamp can be turned on in a manner
that is natural for human eyes. Similarly, in a case of gradually
lowering the luminance of the lamp (gradually turning off), during
a range in which the luminance of the lamp is high, the luminance
is lowered with a high rate of change. Subsequently, the rate of
change in luminance is lowered according to a reduction in the
luminance of the lamp.
[0116] The configuration of the gradual change controller 304 is
not restricted in particular. In a case in which the driving
circuit 302 receives a voltage signal as the dimming signal S3, the
gradual change controller 304 may include a capacitor and a
charging/discharging circuit that charges or otherwise discharges
the capacitor. With such an arrangement, the voltage across the
capacitor may be employed as the dimming signal S3.
[0117] The lighting device ECU 400 includes a CPU (central
processing unit) 402 and a semiconductor switch 404. The CPU 402
generates the lighting on/off instruction signal S4 that is an
instruction to turn on and off the high-beam light source 202
according to the lighting instruction S1 and the driving
information S2 received from the vehicular ECU 104.
[0118] For example, the driving information S2 includes the
presence or absence of a forward vehicle (S2a), the vehicle speed
(S2b), and the steering angle (S2c). When the lighting instruction
S1 is an instruction to turn on the lamp, and when the presence or
absence of a forward vehicle, the vehicle speed, and the steering
angle satisfy predetermined conditions, the lighting device ECU 400
sets the lighting on/off instruction signal S4 to the lighting on
level.
[0119] As an example, when the lighting on/off instruction signal
S4 is an instruction to turn on the lamp, and when the conditions
(i) no forward vehicle is detected, (ii) the vehicle speed is equal
to or higher than a predetermined value (80 km/h), and (iii) the
steering angle is equal to or lower than a predetermined value
(e.g., 5 degrees) are satisfied, the lighting on/off instruction
signal S4 is set to the lighting on level.
[0120] Furthermore, when the lighting on/off instruction signal S4
is set to the lighting on level, and when at least one condition is
satisfied from among (i) a forward vehicle is detected, (ii) the
vehicle speed is equal to or lower than a predetermined value (60
km/h), and (iii) the steering angle is equal to or higher than a
predetermined value (e.g., 10 degrees), the lighting on/off
instruction signal S4 is set to the lighting off level.
[0121] The semiconductor switch 404 is arranged on a power supply
path via which power is supplied from the battery 102 to a driving
circuit 302. The on/off operation of the semiconductor switch 404
is controlled according to a control signal S5 received from the
processor 402. In the lighting on state of the high-beam light
source 202, the semiconductor switch 404 is turned on.
[0122] With a lighting device employing a high-luminance laser
diode or the like as the semiconductor light source 208, there is a
demand for a failsafe function for suppressing risk around it to a
minimum.
[0123] Relating to such a failsafe function, description will be
made regarding the configuration of the driving circuit 302.
[0124] FIG. 12 is a circuit diagram showing a constant current
converter that functions as the driving circuit 302. The constant
current converter is a buck converter including a switching
transistor M1, a rectifier element D1, an inductor L1, and a
capacitor C1. A converter controller 312 performs switching of the
switching transistor M1 such that a detection signal I.sub.S of the
driving current I.sub.LD matches a predetermined target value. The
converter controller 312 feedback controls the duty ratio of the
switching transistor M1 using a PWM method or bang-bang method
(hysteresis control). It should be noted that the topology of the
converter is being described for exemplary purposes only. Also,
other known configurations may be employed.
[0125] Description will be made regarding a case in which a
short-circuit fault has occurred in the switching transistor M1 in
such a converter. In this case, the driving current I.sub.LD to be
supplied to the high-beam light source 202 cannot be controlled. In
some cases, a large amount of current flows through the high-beam
light source 202, leading to undesired illumination by the beam.
Also, this leads to the potential to involve adverse effects on the
high-beam light source 202 or other circuit elements.
[0126] The vehicular lighting device 200 is preferably designed
giving consideration to a failsafe function for handling such a
fault. From this viewpoint, the CPU 402 controls the semiconductor
switch 404 as follows.
[0127] When the semiconductor light source 208 is to be gradually
turned off, the CPU 402 turns off the switch after a predetermined
time period T.sub.OFF elapses after the CPU 402 sets the lighting
on/off instruction signal S4 to the lighting off level. The
predetermined time period T.sub.OFF is designed to be substantially
equal to or to be slightly longer than the gradual change time
period .tau. of the dimming signal S3.
[0128] FIG. 13 is a first operation waveform diagram showing the
operation of the vehicular lighting device 200c shown in FIG. 11.
At the time point t0, the lighting instruction S1 transits to the
lighting on level. The lighting instruction S1 may be configured as
a common instruction shared by an instruction to turn on the
ordinary high-beam lamp. Also, the lighting instruction S1 may be
input via a manual control operation of the driver. Also, the
lighting instruction S1 may be configured as an automatic high-beam
control instruction automatically provided by the vehicle in order
to control the lighting on/off of the lamp.
[0129] In response to a transition of the lighting instruction S1,
the CPU 402 sets a control signal S5 to the high level so as to
turn on the semiconductor switch 404.
[0130] In this stage, the vehicle speed indicated by the driving
information S2b is lower than a threshold value (80 km/h), and
accordingly, the lighting on/off instruction signal S4 is set to
the low level. When the vehicle speed indicated by the driving
information S2b exceeds the threshold value (80 km/h) at the time
point t1, the lighting on/off instruction signal S4 is switched to
the high level. The gradual change controller 304 raises the
dimming signal S3 with time, according to the lighting on/off
instruction signal S4 set to the high level. As a result, the
driving circuit 302 raises the driving current I.sub.LD with time,
thereby gradually turning on the high-beam light source 202.
[0131] At the time point t2, the vehicle speed is reduced and
becomes lower than 60 km/h. The CPU 402 switches the lighting
on/off instruction signal S4 to the lighting off level while
maintaining the on state of the semiconductor switch 404. The
gradual change controller 304 raises the dimming signal S3 with
time according to the lighting on/off instruction signal S4 set to
the lighting off level. As a result, the driving circuit 302
reduces the driving current I.sub.LD with time, thereby gradually
turning off the high-beam light source 202. Subsequently, at the
time point t3 after a predetermined time period T.sub.OFF elapses
from the time point t2, the CPU 402 turns off the semiconductor
switch 404.
[0132] It should be noted that the timing at which the
semiconductor switch 404 is to be turned on is not restricted in
particular. In the example shown in FIG. 13, the control signal S5
is set to the high level at the same time as the transition of the
lighting instruction to the high level. Also, the control signal S5
may be set to the high level at the same time as or otherwise
immediately before the lighting on/off instruction signal S4 is
switched to the lighting on level. Alternatively, the semiconductor
switch 404 may be turned on before the transition of the lighting
instruction S1 to the lighting on level.
[0133] The above is the operation of the vehicular lighting device
200. Next, description will be made regarding the advantages
thereof.
[0134] As a comparison technique, let us consider a control
operation in which the semiconductor switch 404 is fixed to the
normally on state regardless of whether the high-beam light source
202 is set to the lighting on state or the lighting off state. With
such a control operation, in a case in which a short-circuit fault
has occurred in the switching transistor M1, the high-beam light
source 202 emits light even when the lighting instruction S1 or
otherwise the lighting on/off instruction signal S4 is set to the
lighting off level.
[0135] Furthermore, in such a comparison technique, let us consider
an arrangement configured to detect a fault in the switching
transistor M1, and that is provided with a protection function of
switching off the lighting on/off instruction signal S4 so as to
control the high-beam light source 202 to turn off when there is
such a fault. Even with such an arrangement, in a case in which a
short circuit-fault has occurred in the switching transistor M1,
when the power supply voltage V.sub.DD is supplied to the driving
circuit 302, the power is supplied to the high-beam light source
202, which is a problem.
[0136] Furthermore, in some cases, the high-beam light source 202
may be configured as a combination of a blue light laser diode and
a fluorescent member that can be excited by the laser diode as
shown in FIG. 10. If an abnormal state of the fluorescent member
has occurred, the output light of the laser diode is directly
emitted without being scattered by the fluorescent member, which
becomes a problem. With such a comparison technique, a problem
remains even in a case in which a protection function is provided
for turning off the high-beam light source 202 upon detecting an
abnormal state of the fluorescent light source. That is to say, in
a case in which a short-circuit fault has occurred in the switching
transistor M1, when the power supply voltage V.sub.DD is supplied
to the driving circuit 302, the power is supplied to the high-beam
light source 202, which is a problem.
[0137] In contrast, with the vehicular lighting device 200
according to the third embodiment, the semiconductor switch 404 is
turned on during only a minimum necessary period. After
transmitting an instruction to turn off the high-beam light source
202, such an arrangement turns off the semiconductor switch 404,
thereby allowing the power supply to the high-beam light source 202
to be stopped in a sure manner. Thus, such an arrangement resolves
the problems that can occur in the comparison techniques.
[0138] FIG. 14 is a second operation waveform diagram showing the
operation of the vehicular lighting device 200c shown in FIG. 11.
When the ordinary high-beam lamp is instructed to turn on at the
time point t0, the CPU 402 sets the control signal S5 to the high
level so as to turn on the semiconductor switch 404. At the time
point t3, the driving information S2a indicates detection of a
forward vehicle. In this case, the CPU 402 immediately switches the
control signal S5 to the low level. This turns off the
semiconductor switch 404, which stops the supply of the power
supply voltage V.sub.DD to the driving circuit 302. As a result,
the driving current I.sub.LD falls to zero in a short period of
time, thereby turning off the vehicular lighting device. At the
time point t3, the CPU 402 sets the lighting on/off instruction
signal S4 to the lighting off level. However, after the supply of
the power supply voltage V.sub.DD is stopped, the operation of the
gradual change controller 304 for gradually turning off the lamp
has no effect.
[0139] Description has been made regarding the present invention
with reference to the embodiments using specific terms. However,
the above-described embodiments show only the mechanisms and
applications of the present invention for exemplary purposes only,
and are by no means intended to be interpreted restrictively.
Rather, various modifications and various changes in the layout can
be made without departing from the spirit and scope of the present
invention defined in appended claims.
* * * * *