Vehicular lamp

A vehicular lamp, including: a plurality of semiconductor light emitting devices connected in parallel; a plurality of current limiting units provided corresponding to the plurality of semiconductor light emitting devices, wherein the plurality of current limiting units connect with the corresponding semiconductor light emitting devices respectively in series, and limit electric current flowing through the corresponding semiconductor light emitting devices respectively; and a current control unit for changing electric current to be supplied to at least one of the plurality of semiconductor light emitting devices. When a wire of one of the plurality of semiconductor light emitting devices is broken, the current control unit increases the electric current to be supplied to at least one of the plurality of semiconductor light emitting devices of which a wire is not broken by causing at least a part of the electric current to flow via a path connected in parallel with corresponding one(s) of the plurality of current limiting units.

The present application claims priority from a Japanese Patent Application No. 2003-123469 filed on Apr. 28, 2003, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vehicular lamp. More particularly, the present invention relates to a headlamp, a stop lamp, a tail lamp, a turn lamp, and the like used for a vehicle including automobiles, motorcycles and trains.

2. Related Art

An apparatus for detecting wire breakage of a vehicular lamp and for warning a driver of the wire breakage is known (e.g., Japanese Patent Laid-Open No. 10-217851 bulletin (page 2–4, FIG. 1-3)), thereby the driver is warned to replace the wire-broken light source.

However, when a wire of a light source of the vehicular lamp is broken, the light source stop emitting light and consequently the quantity of light of the vehicular lamp lowered until the wire-broken light source is replaced.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to provide a vehicular lamp, which is capable of overcoming the above drawbacks accompanying the conventional art. The above and other objects can be achieved by combinations described in the independent claim. The dependent claims define further advantageous and exemplary combinations of the present invention.

According to the aspect of the present invention, there is provided a vehicular lamp, including: a plurality of semiconductor light emitting devices connected in parallel; a plurality of current limiting units provided corresponding to the plurality of semiconductor light emitting devices, wherein the plurality of current limiting units connect with the corresponding semiconductor light emitting devices respectively in series, and limit electric current flowing through the corresponding semiconductor light emitting devices respectively; and a current control unit for changing electric current to be supplied to at least one of the plurality of semiconductor light emitting devices; wherein when a wire of one of the plurality of semiconductor light emitting devices is broken, the current control unit increases the electric current to be supplied to at least one of the plurality of semiconductor light emitting devices of which a wire is not broken by causing at least a part of the electric current to flow via a path connected in parallel with corresponding one(s) of the plurality of current limiting units.

The current control unit may include: a plurality of switches respectively connecting with the plurality of current limiting units in parallel and with the plurality of semiconductor light emitting devices in series, each of the plurality of switches electrically connecting both terminals of corresponding one of the plurality of current limiting units when the switch is turned ON; and a switching unit for detecting wire breakage of at least one of the plurality of semiconductor light emitting devices. When the switching unit detects wire breakage of one of the plurality of semiconductor light emitting devices, the switching unit may turn ON at least one of the plurality of switches corresponding to at least one of the plurality of semiconductor light emitting devices of which a wire is not broken.

Each of the plurality of switches may include a transistor, a collector terminal and an emitter terminal of the transistor connecting with both terminals of corresponding one of the plurality of current limiting units, respectively.

Electric resistance of one of the plurality of switches may be higher than that of corresponding one of the plurality of current limiting units.

The electric resistance of the one of the plurality of switches may be substantially 2.5 times as high as that of corresponding one of the plurality of current limiting units.

The plurality of current limiting units may include a plurality of series resistances respectively connecting with the plurality of semiconductor light emitting devices in series so that at least a part of the electric current to be supplied to each of the plurality of semiconductor light emitting devices flows through corresponding one of the plurality of series resistances, each of the plurality of series resistances may include a terminal located closest to corresponding one of the plurality of semiconductor light emitting devices, the current control unit may include a terminal connecting unit connecting the plurality of terminals with one another.

The vehicular lamp may further include a plurality of lamp bodies accommodating therein the plurality of semiconductor light emitting devices and the plurality of series resistances. Each of the plurality of lamp bodies may accommodate a part of the plurality of semiconductor light emitting devices and corresponding one(s) of the plurality of series resistances, and the terminal connecting unit may include a plurality of connection resistors connected in series, the plurality of connection resistors being accommodated in the plurality of lamp bodies and electrically connecting the plurality of terminals of the plurality of series resistances.

Each of the plurality of lamp bodies may include a circuit unit connecting with at least one of the plurality of semiconductor light emitting devices, the circuit unit including a part of the plurality of series resistances.

The circuit unit may be accommodated inside each one of the plurality of lamp bodies.

The circuit unit may further include the current control unit.

The vehicular lamp may further include a circuit unit connecting with the plurality of semiconductor light emitting devices, the circuit unit including the plurality of series resistances and the current control unit.

The plurality of series resistances may respectively include: a plurality of first series resistances, each of the plurality of first series resistances includes a first terminal located closest to high voltage side of corresponding one of the plurality of semiconductor light emitting devices; and a plurality of second series resistances, each of the plurality of second series resistances includes a second terminal located closest to low voltage side corresponding one of the plurality of semiconductor light emitting devices. The current control unit may include: a first terminal connecting unit electrically connecting the plurality of first terminals of the plurality of first series resistances with one another; and a second terminal connecting unit electrically connecting the plurality of second terminals of the plurality of second series resistances with one another, the vehicular lamp may act as at least one of a stop lamp and a tail lamp depending on an instruction from outside, the plurality of light emitting devices may receive electric power from outside of the vehicular lamp via either of the first series resistances or the second series resistances when the vehicular lamp acts as a stop lamp, and the plurality of light emitting devices may receive electric power from outside of the vehicular lamp via both of the first series resistances and the second series resistances when the vehicular lamp acts as a tail lamp.

Electric resistance of the first terminal connecting unit may be higher than that of one of the plurality of first series resistances, and electric resistance of the second terminal connecting unit may be higher than that of one of the plurality of second series resistances.

The electric resistance of the first terminal connecting unit may be substantially 1.5 times as high as that of the one of the plurality of first series resistance, and the electric resistance of the second terminal connecting unit may be substantially 1.5 times as high as that of the one of the plurality of second series resistance.

Each of the plurality of current limiting units may connect with corresponding one of the plurality of semiconductor light emitting devices in series, each of the plurality of current limiting units may include a first series resistance and a second series resistance connected in series, at least a part of the electric current, which is to be supplied to the corresponding one of the plurality of semiconductor light emitting devices, flowing through at least one of the first series resistance and the second series resistance, the vehicular lamp may act as at least one of a stop lamp and a tail lamp depending on an instruction from outside, the plurality of light emitting devices may receive electric power from outside of the vehicular lamp via either of the first series resistances or the second series resistances when the vehicular lamp acts as a stop lamp, and the plurality of light emitting devices may receive electric power from outside of the vehicular lamp via both of the first series resistances and the second series resistances when the vehicular lamp acts as a tail lamp.

The current control unit may include: a first switch connecting with the first series resistance in parallel and with the corresponding one of the plurality of semiconductor light emitting devices in series, the first switch electrically connecting both terminals of the first series resistance when the first switch is turned ON; a second switch connecting with the second series resistance in parallel and with the corresponding one of the plurality of semiconductor light emitting devices in series, the second switch electrically connecting both terminals of the second series resistance when the second switch is turned ON; and a switching unit for detecting wire breakage of at least one of the plurality of semiconductor light emitting devices, and when the switching unit detects wire breakage of one of the plurality of semiconductor light emitting devices, the switching unit may turn ON at least one of the first switch and the second switch corresponding to one of the plurality of semiconductor light emitting devices of which a wire is not broken.

Electric current flowing through each of the plurality semiconductor light emitting devices, when no wire of the plurality of semiconductor light emitting devices is broken, may be lower than rated electric current of each of the plurality of semiconductor light emitting devices.

The electric current flowing through each of the plurality semiconductor light emitting devices, when no wire of the plurality of semiconductor light emitting devices is broken, may be 60–70 percent of the rated electric current of each of the plurality of semiconductor light emitting devices.

The summary of the invention does not necessarily describe all necessary features of the present invention. The present invention may also be a sub-combination of the features described above. The above and other features and advantages of the present invention will become more apparent from the following description of the embodiments taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a schematic diagram of a vehicular lamp10with a power supply unit50according to one embodiment of the present invention. The purpose of the present embodiment is to provide the vehicular lamp10which emits sufficient quantity of light. For example, the vehicular lamp10is a part of a rear combination lamp (RCL) which is employed to a motor vehicle, the RCL including a plurality of marker lamps12aand12bwhich are adjoined mutually. For example, each of the marker lamps12aand12bis a stop lamp, a tail lamp, or the like, and it includes a circuit unit18, a plurality of light emitting diodes20, a support member24, a reflecting mirror26, a cover16, and a lamp body14.

For examples, the circuit unit18is a module including the lighting circuit which causes the plurality of light emitting diodes20to emit light, and supplies electric power received from the power supply unit50to the plurality of light emitting diodes20. The light emitting diodes20are examples of semiconductor light emitting devices, and they receive the electric power from the circuit unit18and emit red or amber light to comply with a requirement of the vehicular lamp10.

The support member24supports the plurality of light emitting diodes20so that the plurality of light emitting diodes20is oriented to a predetermined direction. The support member24may also act as a radiator to radiate heat generated by the light emitting diodes20. The reflecting mirror26reflects the light generated by the light emitting diodes20opposite to a traveling direction of the vehicle.

For example, the cover16is transparent and covers the plurality of light emitting diodes20at the rear of the vehicle. The lamp body14faces the cover16across the plurality of light emitting diodes20, so that the plurality of light emitting diodes20are covered with the lamp body14and the cover16. Thereby, the lamp body14accommodates the plurality of light emitting diodes20and the circuit unit18so that they are protected from water, debris and the like. The lamp body14may be integrated with the body of the vehicles. According to the present embodiment, the vehicular lamp10operates properly.

In addition, the power supply unit50supplies electric power received from a battery of the vehicle to the vehicular lamp10when the vehicular lamp10is ON. The plurality of marker lamps12aand12bmay include the same or similar configuration as/to each other. That is, the plurality of marker lamps have identical design. Moreover, a plurality of vehicular lamps10may be provided on the right side and left side of a rear panel of the vehicle. In this case, the vehicle include four marker lamps, which have the same or similar function as/to one another, wherein two of them is provided on the right side while the others on the left. Alternatively, the vehicular lamp10includes single marker lamp. Alternatively, the vehicular lamp10is used for lighting equipment for a vehicle such as a headlamp.

FIG. 2is a circuit diagram illustrating a part of a circuit configuration of the vehicular lamp10according to a first embodiment of the present invention. In the present embodiment, the vehicular lamp10includes a plurality of marker lamps12aand12bwhich act as a stop lamp. The marker lamp12ahas the same or similar configuration as/to the marker lamp12b, each of which includes a light source unit100, a diode108, a current limiting unit116, and an electric current control unit112.

The light source unit100includes a plurality of light emitting diodes20connected in series. The plurality of light emitting diodes20emit light according to electric current supplied from the power supply unit50through diode108so that the marker lamp12operates properly. Alternatively, the light source unit100includes single light emitting diode20, or includes a plurality of light emitting diodes20connected in parallel.

In addition, in the present embodiment, the light source units100in the plurality of marker lamps12aand12are connected in parallel with each other and in series with the power supply unit50. Therefore, the vehicular lamp10includes a plurality of light emitting diodes20connected in parallel. Moreover, the diode108and the light source unit100are connected in series and in the same direction to protect the light source unit100against reverse connection of the power supply.

The current limiting unit116is provided corresponding to the light source unit100in each of the marker lamps12aand12b, and connects with the light emitting diodes20of the corresponding light source unit100in series. In the present embodiment, the current limiting unit116includes a resistor102. The resistor102is an example of a series resistance connected in series with the light source unit100, and limits electric current flowing through the light source unit100by grounding a terminal of the resistor102opposite to the other terminal connecting with the light source unit100. Thereby, the current limiting unit116limits the electric current flowing through the light emitting diodes20. Alternatively, a plurality of current limiting units116is provided corresponding to a plurality of light emitting diodes20connected in parallel, respectively.

The current control unit112includes a switching unit106and a bypass unit104. The switching unit of the marker lamp12aconnects with the bypass unit104of the marker lamp12b, and the switching unit of the marker lamp12bconnects with the bypass unit104of the marker lamp12athrough terminals provided in the marker lamps12aand12b. The switching unit106includes an NPN transistor210and a resistor. The base terminal of the NPN transistor210connects with a node between the light source unit100and the current limiting unit116via the resistor. Therefore, when the electric current flowing through the light source unit100decreases, the voltage of this node also decreases and the NPN transistor210is turned OFF. Thereby, the NPN transistor210detects wire breakage of the light source unit100.

Moreover, the collect or terminal of the NPN transistor210of the marker lamp12aor12bconnects with the bypass unit104of the other marker lamp12bor12a. In the present embodiment, the NPN transistor210opens the collector terminal when wire breakage is detected, and it sinks the collector current when wire breakage is not detected. Thereby, the NPN transistor210of the marker lamp12aor12binforms the bypass unit104in the other marker lamp12bor12aabout the existence of the wire breakage of the light source unit100in the marker lamp12aor12b.

Consequently, the switching unit106in the marker lamp12aor12bdetects the wire breakage of the light source unit100in the marker lamp12aor12b. Then, the switching unit106controls the bypass unit104in the other marker lamp12bor12abased on the result of the detection. For example, the switching unit106in the marker lamp12acontrols the bypass unit104in the marker lamp12b.

In the present embodiment, the switching units106are provided in the marker lamps12aand12brespectively, the switching units106corresponding to the plurality of light source units100connected in parallel, respectively. Thereby, the switching units106detect the wire breakage in each of the plurality of light emitting diodes20connected in parallel.

The bypass unit104includes a capacitor114, an NPN transistor206, and a plurality of resistors. The input to the bypass unit is smoothed by the capacitor114and is supplied to the NPN transistor206through the resistor208.

The NPN transistor206is an example of a switch connected in series with the light emitting diodes20, and in parallel with the resistor102. The collector terminal of the NPN transistor206connects with the non-grounded terminal of the current limiting unit116via the resistor212, and the emitter terminal of the NPN transistor206connects with the grounded terminal of the current limiting unit116. Moreover, the base terminal of the NPN transistor206in the marker lamp12aor12bconnects with the switching unit106in the other marker lamp12bor12avia the resistor208.

The output of the switching unit106is pulled up by a resistor in the bypass unit104, and the base terminal of the NPN transistor206receives the pulled-up output via the resistor208. Moreover, the base terminal is pulled down by a resistor. Therefore, when the switching unit106in the marker lamp12aor12bdetects wire breakage of the light source unit100in the other marker lamp12bor12a, the NPN transistor206is turned ON, whereby the NPN transistor206electrically connects the both terminals of the current limiting unit116through the resistor212. In this case, the NPN transistor206increases electric current to be supplied to the light source unit100by supplying a part of the electric current supplied to the corresponding light source unit100via a path connected in parallel with the current limiting unit116. Thereby, the bypass unit104of the marker lamp12aor12bbypasses a part of the electric current in response to the wire breakage of the light source unit100in the other marker lamp12bor12a.

In addition, the wire of each of the light source units100is considered to be broken when the wire of at least one of the plurality of light emitting diodes20in the light source unit100connected in series is broken. Therefore, when the wire of at least one of the light emitting diodes20is broken, at least a part of the electric current to be supplied to the light emitting diodes20of which the wire are not broken flows through the path connected in parallel with the current limiting unit116. Thereby, the current control unit112increases the electric current to be supplied to the light emitting diodes20.

According to the vehicular lamp10explained hereinbefore, when the light source unit100in either the marker lamp12aor12bis broken, the current control unit112increases the electric current to be supplied to the light source unit100in the other marker lamp12bor12a, and increases quantity of light of the light source unit100in the other marker lamp12bor12a. In this case, even if the light source unit100in either the marker lamp12aor12bis broken, the total quantity of light of the vehicular lamp10can be maintained properly, and visibility of the vehicular lamp10can be maintained properly. According to the present embodiment, the safety requirement of the vehicular lamp10can be appropriately satisfied. Moreover, according to the present embodiment, the vehicular lamp10can be operated appropriately.

In addition, resistance of the resistor212is 2.5 times as high as that of the resistor102in the present embodiment. In this case, when one of the light emitting diodes20in the other marker lamp12bor12ais broken, the current control unit112increases the electric current to be supplied to the light source unit100in the marker lamp12aor12bby about 1.4 times of the normal condition. It is preferable that the current control unit112changes the electric current to be supplied to the light source unit100within the rated current of the light emitting diodes20. During the normal condition, the current limiting unit116may limit the electric current to be supplied to the light source unit100to about 60 to 70 percents of the rating of the light emitting diodes20.

Moreover, in the present embodiment, the switching unit106opens the output when wire breakage is detected. Therefore, according to the present embodiment, when there is a poor connection at an input terminal of either the marker lamp12aor12b, the bypass unit104in the other marker lamp12bor12areceives information as is the case with the wire breakage, and increases the electric current to be supplied to the light source unit100of the marker lamp12aor12b. Therefore, according to the present embodiment, even in the case that there occurs a poor connection at the input terminal, the quantity of light of the vehicular lamp10can be maintained properly.

For example, the diode108, the current limiting unit116, and the current control unit112are provided in the circuit unit18(refer toFIG. 1). The circuit unit18to be included in the marker lamp12ais identical to that of the marker lamp12b. In this case, substrate assembly on which electronic parts of the marker lamp are mounted can be commonized.

FIG. 3is a circuit diagram illustrating a part of a circuit configuration of the vehicular lamp10according to a second embodiment of the present invention. In the present embodiment, the marker lamp12aincludes a diode108, a light source unit100, a plurality of current limiting units116aand116band a plurality of current control units112aand112b. The marker lamp12bincludes a light source unit100. Since like reference numbers are used to denote like parts inFIG. 2andFIG. 3, the explanation of those parts will be omitted to avoid redundancy except otherwise described below.

In the present embodiment, the current control unit112aand the current limiting unit116acorrespond to the light source unit100in the marker lamp12a, and the current control unit112band the current limiting unit116bcorresponds to the light source unit100in the marker lamp12b. Functions of the current control unit112aand the current limiting unit116aare the same or similar as/to those of the current control unit112and the current limiting unit116in the marker lamp12adescribed in reference toFIG. 2, respectively. Moreover, functions of the current control unit112band the current limiting unit116bare the same or similar as/to those of the current control unit112and the current limiting unit116in the marker lamp12bdescribed in reference toFIG. 2, respectively, expect that the current control unit112band the current limiting unit116bare located in the marker lamp12aalthough they correspond to the light source100in the marker lamp12b.

The light source unit100in the marker lamp12bconnects with the power supply unit50via the diode108in the marker lamp12a. Moreover, the light source unit100is grounded via the current limiting unit116bin the marker lamp12a. Also in this case, when the wire of either of the light source units100is broken, the current control unit112aor112bincreases the electric current to be supplied to the corresponding light source unit100of which the wire is not broken. Thereby, even if the wire of either of the light source units100is broken, the quantity of light of the vehicular lamp10can be maintained properly. Therefore, according to the present embodiment, the vehicular lamp10can be operated appropriately. Moreover, according to the present embodiment, man-hour of inspection of the marker lamp12bbefore shipping is reducible by simplifying the configuration of the marker lamp12b. Alternatively, a part of the current control unit112band/or the current limiting unit116bis located in the marker lamp12b.

FIG. 4is a circuit diagram illustrating a part of a circuit configuration of the vehicular lamp10according to a third embodiment of the present invention. In the present embodiment, the function and configuration of the marker lamp12ais the same or similar as/to those of the marker lamps12b, and the plurality of the marker lamps12aand12bact as at least one of a stop lamp and a tail lamp and are operated depending on an instruction from outside. Since like reference numbers are used to denote like parts inFIG. 2andFIG. 4, the explanation of those parts will be omitted to avoid redundancy except otherwise described below.

Each of the marker lamps12aand12bincludes a light source unit100, a plurality of diodes108aand108b, a current limiting unit116, and a current control unit112. When the vehicular lamp10acts as a tail lamp, each of the marker lamps12aand12breceives positive voltage from the power supply unit50provided in the exterior of the marker lamps12aand12bvia the respective diode108a. Moreover, when the vehicular lamp10acts as a stop lamp, each of the marker lamps12aand12breceives positive voltage from the power supply unit50via the respective diode108b.

The current limiting unit116in each of the marker lamps12aand12bincludes a plurality of resistors102aand102blocated upstream of the light source unit100with respect to the current flow direction and corresponding to the light source unit100in the respective marker lamp12aor12b. The resistors102aand102bare examples of a first series resistance and a second series resistance, respectively. In the present embodiment, a high voltage side of the resistor102aconnects with the diode108a, and a low voltage side of the resistor102aconnects with a high-voltage side of the resistor102b. Moreover, the high voltage side of the resistor102bconnects with the diode108b, and a low voltage side of the resistor102bconnects with the light source unit100. Thereby, the plurality of resistors102aand102bare connected in series, and they also connect with the light source unit100in series.

Therefore, when the marker lamps12aand12bact as a stop lamp, each of the light source units100receives electric power from the power supply unit50via the resistor102band the diode108b. In this case, at least a part of the electric current to be supplied to the light source unit100flows through the resistor102b. Moreover, when the marker lamps12aand12bact as a tail lamp, each of the light source units100receives electric power from the power supply unit50via the resistors102aand102band the diode108a. In this case, at least a part of the electric current to be supplied to the light source unit100flows through the resistors102aand102b.

The current control unit112includes a switching unit106, a diode110and a plurality of bypass units104aand104b. The switching unit106in each of the marker lamp12aand12bincludes a PNP transistor204and a resistor, detects wire breakage of the light source unit100based on a voltage of a low voltage side of the current limiting unit116, and informs the bypass units104aand104bin the other marker lamp12bor12aabout the existence of the wire breakage of the light source unit100in the marker lamp12aor12b.

In the present embodiment, the emitter terminal of the PNP transistor204receives a positive voltage output from the power supply unit50via the diode108awhen the vehicular lamp10acts as a tail lamp, and via the diode110and the diode108bwhen the vehicular lamp10acts as a stop lamp. When the wire breakage of the corresponding light source unit100is not detected, the collector current does not flow through the PNP transistor204, and when the wire breakage of the corresponding light source unit100is detected, the PNP transistor sources the collector current to the bypass units104aand104bof the other marker lamp12bor12aaccording to the positive voltage. Thereby, the PNP transistor204informs the bypass units104aand104bin the other marker lamps12bor12aabout the existence of the wire breakage of the corresponding light source unit100in the marker lamp12aor12b.

The diode110is directed so that electric current flows from a cathode of the diode108bto a cathode of the diode108a. Thereby, the diode110prevents to connect the diode108adirectly with the high voltage side of the resistor102bwithout the resistor102a.

The plurality of bypass units104aand104bare provided corresponding to the plurality of resistors102aand102b, respectively, each of which includes a PNP transistor202and a plurality of resistors. The collector terminals of the PNP transistors202connect with low voltage side of the resistors102aand102b, respectively, via the respective resistor212, and the emitter terminals of the PNP transistors202connect with the high voltage side of the resistors102aand102b, respectively. Therefore, each of the PNP transistors202electrically connects the both terminals of the respective resistor102aor102bthrough the respective resistor212when it is turned ON, thereby each of the PNP transistors202increases the electric current to be supplied to the light source unit100. For example, resistance of the resistor212is substantially 2.5 times as high as that of the corresponding current control unit112.

The base terminal of the PNP transistor202in the marker lamp12aor12breceives the output of the switching unit106in the other marker lamp12bor12athrough a resistor. Moreover, the output of the switching unit106is pulled down by the resistor in the current control unit112, and the base terminal of the PNP transistor202is pulled up by connecting with the cathode of the respective diode108aor108bvia a resistor. Therefore, the PNP transistor202in the marker lamp12aor12bis turned ON when the switching unit106in the other marker lamp12bor12adetects wire breakage. Thereby, when the wire of one of the light source units100is broken, the current control unit112increases the electric current to be supplied to the light source unit100of which the wire is not broken. Therefore, also in the present embodiment, the quantity of light of the vehicular lamp10can be maintained properly. According to the present embodiment, the vehicular lamp10can be operated appropriately.

In addition, the PNP transistor202in the bypass unit104ais an example of a first switch connected with the light source unit100in series and with the resistor102ain parallel. Moreover, the PNP transistor202in the bypass unit104bis an example of a second switch connected with the light source unit100in series and with the resistor102bin parallel. When the wire breakage of either of the light source units100is detected, the plurality of switching units106, which are provided corresponding to the plurality of marker lamps12aand12b, may turn ON the PNP transistor202in either the bypass unit104aor104bcorresponding to the light source units100of which the wire is not broken. Unless otherwise described above, the function of the PNP transistor202described in reference toFIG. 4is the same or similar as/to that of the NPN transistor206described in reference toFIG. 2.

FIG. 5is a circuit diagram illustrating a part of a circuit configuration of the vehicular lamp10according to a fourth embodiment of the present invention. The marker lamp12aincludes a plurality of diodes108aand108b, a light source unit100, a plurality of current limiting units116aand116b, and a plurality of current control units112aand112b. The marker lamp12bincludes a light source unit100. Since like reference numbers are used to denote like parts inFIG. 3,FIG. 4, andFIG. 5, the explanation of those parts will be omitted to avoid redundancy except otherwise described below.

In the present embodiment, the current control unit112band the current limiting unit116b, which correspond to the light source unit100in the marker lamp12b, are provided in the marker lamp12a. A high voltage side of the light source unit100of the marker lamp12bconnects with the current limiting unit116bthrough a terminal provided in the marker lamp12a, and a low voltage side of the light source unit100is grounded. The vehicular lamp10can be operated appropriately also in the present embodiment. Moreover, according to the present embodiment, as described in the embodiment described in reference toFIG. 3, man-hour of inspection of the marker lamp12bbefore shipping is reducible by simplifying the configuration of the marker lamp12b.

FIG. 6is a circuit diagram illustrating a part of a circuit configuration of the vehicular lamp10according to a fifth embodiment of the present invention. In the present embodiment, a plurality of marker lamps12aand12bact as at least one of a stop lamp and a tail lamp depending on an instruction from outside. The marker lamp12aincludes a light source unit100, a plurality of diodes108aand108b, a current limiting unit116, and a current control unit112. The marker lamp12bincludes a light source unit100, a plurality of diodes108aand108b, and a current limiting unit116. Since like reference numbers are used to denote like parts inFIG. 4andFIG. 6, the explanation of those parts will be omitted to avoid redundancy except otherwise described below.

The current limiting unit116includes a plurality of resistors102aand102b. In the present embodiment, the resistor102aconnects with a high voltage side of the light source unit100and the diode108a. Moreover, a low voltage side of the light source unit100is grounded via the resistor102b. The resistors102aand102bbare examples of a first series resistance and a second series resistance, respectively, which are connected in series. The series resistances connect with the light emitting diodes20(refer toFIG. 2) in the corresponding light source unit100in series, so that at least a part of the electric current to be supplied to the light emitting diodes20flows through the series resistances.

When the vehicular lamp10acts as a stop lamp, a positive voltage from the power supply unit50is supplied to an anode of the light emitting diodes20via the diode108b, and a cathode of the light emitting diodes20is grounded via the resistor102b. Thereby, the electric power from the power supply unit50is supplied to the light emitting diodes20via the resistor102b, which is one of the series resistances. When the vehicular lamp10acts as a tail lamp, the electric power from the power supply unit50is supplied to the light emitting diodes20via the resistors102aand102b, which are both of the series resistances.

The current control unit112includes a plurality of resistors118aand118b. The plurality of resistors118aand118bare examples of a first and a second terminal connecting units respectively, where the first and second terminal connecting units are provided corresponding to the resistors102aand102b, respectively. The resistor118aelectrically connects a node between the resistor102aand the light source unit100in the marker lamp12aand a node between the resistor102aand the light source unit100in the marker lamp12b. The resistor118belectrically connects a node between the resistor102band the light source unit100in the marker lamp12aand a node between the resistor102band the light source unit100in the marker lamp12b. That is, each of the plurality of resistors118aand118bconnects nodes between the light emitting diodes20and the respective resistors102aor102bin the marker lamps12aand12b.

Therefore, when all wires of both of the light source units100are connected properly, voltage of one terminal of each of the resistors118aand118bis substantially the same as voltage of the other terminal of each of the resistors118aand118b, respectively, because the voltage of the corresponding nodes in the marker lamps12aand12bare substantially the same as each other (e.g., the voltage of the node between the resistance102aand the light source unit100in the marker lamp12ais substantially the same as the voltage of the node between the resistance102aand the light source unit100in the marker lamp12b). Therefore, electric current does not flow through the resistor118aor118b. In this case, the electric current to be supplied to the light source unit100is determined by the resistance of the plurality of resistors102aand102b, and the light source unit100emits light according to the supplied electric current.

On the other hand, when the vehicular lamp10acts as a tail lamp, and when the wire of the light source unit100in one of the marker lamps12aand12bis broken, since electric current does not flow through the light source unit100of which the wire is broken, the electric current does not flow through the resistors102aor102bcorresponding to the wire-broken light source unit100. Thereby, the voltage of the node between the resistance102aand the light source unit100increases while the voltage of the node between the resistance102band the light source unit100decreases. Therefore, electric current flows from the node between the resistance102aand the light source unit100of which the wire is broken to the node between the resistance102aand the other light source unit100of which the wire is not broken, and electric current flows from the node between the resistance102band the other light source unit100of which the wire is not broken to the node between the resistance102band the light source unit100of which the wire is broken. In this case, the electric current flows through the light source unit100of which the wire is not broken via not only the corresponding current limiting unit116but also via the resistors118aand118b.

Thereby, when the wire of one of the light source units100is broken, the current control unit112increases the electric current to be supplied to the light source unit100of which the wire is not broken. Therefore, also in the present embodiment, the quantity of light of the vehicular lamp10can be maintained properly. According to the present embodiment, the vehicular lamp10can be operated appropriately.

Moreover, when the vehicular lamp10acts as a stop lamp, since each of the light source units100receives electric current from the respective diode108b, and the voltage of a node between the diode108band the light source unit100in the marker lamp12ais substantially the same as the voltage of a node between the diode108band the light source unit100in the marker lamp12b, electric current does not flow through the resistor118aregardless whether the wire of the light source unit100is broken or not. In this case, when the wire of one of the light source units100is broken, the current control unit112increases the electric current to be supplied to the light source unit100of which the wire is not broken via the resistor118b. Also in this case, the vehicular lamp10can be operated appropriately.

In addition, in the present embodiment, resistance of the resistor118ais substantially 1.5 times as high as that of the resistor102a, and resistance of the resistor118bis substantially 1.5 times as high as that of the resistor102b. In this case, when the wire of one of the light source units100is broken, the current control unit112increases the electric current to be supplied to the light source unit100of which the wire is not broken by about 1.4 times of the normal condition. Alternatively, each of the marker lamps12aand12bomits the diode108aand the resistor102a. In this case, the marker lamps12aand12bact as a stop lamp.

FIG. 7is a circuit diagram illustrating a part of a circuit configuration of the vehicular lamp10according to a sixth embodiment of the present invention. Since like reference numbers are used to denote like parts inFIG. 6andFIG. 7, the explanation of those parts will be omitted to avoid redundancy except otherwise described below.

In the present embodiment, the current limiting unit116includes a plurality of resistors102aand102blocated upstream of the light source unit100with respect to the current flow direction. The resistor102aconnects the diode108aand a high voltage side of the resistor102b, and the resistor102bconnects the diode108band a high voltage side of the light source unit100. Also in this case, when the wire of the one of the light source units100is broken, the current control unit112increases the electric current to be supplied to the light source unit100of which the wire is not broken according to the electric current flowing through the resistor118aand/or the resistor118b. Therefore, also in the present embodiment, the quantity of light of the vehicular lamp10can be maintained properly. According to the present embodiment, the vehicular lamp10can be operated appropriately.

FIG. 8is a circuit diagram illustrating a part of a circuit configuration of the vehicular lamp10according to a seventh embodiment of the present invention. Since like reference numbers are used to denote like parts inFIG. 6andFIG. 8, the explanation of those parts will be omitted to avoid redundancy except otherwise described below.

In the present embodiment, the vehicular lamp10includes a plurality of resistors118cand118einstead of the resistor118aexplained in reference toFIG. 6, and includes a plurality of resistors118dand118finstead of the resistor118bexplained in reference toFIG. 6. In the present embodiment, the plurality of resistors118c–118fconstitutes a current control unit112. The resistors118cand118dare provided in the marker lamp12a, and the resistors118eand118fare provided in the marker lamp12b.

Resistance of each of the resistors118cand118eis about half of the resistance of the resistor118a, and the resistors118cand118eare connected in series and connect a terminal of the resistor102ain the marker lamp12aand a terminal of the resistor102ain the marker lamp12bin a similar manner to what the resistor118aconnects the two terminals according to other embodiments. Resistance of each of the resistors118dand118fis about half of the resistance of the resistor118b, and the resistors118dand118fconnect with each other in series and connect a terminal of the resistor102bin the marker lamp12aand a terminal of the resistor102bin the marker lamp12bin a similar manner to what the resistor118bconnects the two terminals according to other embodiments.

Also in this case, when the wire of the light source unit100in one of the marker lamps12aand12bis broken, the current control unit112increases the electric current to be supplied to the light source unit100of which the wire is not broken. Therefore, also in the present embodiment, the quantity of light of the vehicular lamp10can be maintained properly. According to the present embodiment, the vehicular lamp10can be operated appropriately. Moreover, in the present embodiment, the circuit configuration of the marker lamp12ais the same as that of the marker lamp12b. Therefore, according to the present embodiment, the cost of the vehicular lamp10is reducible by commonizing the substrate assembly of the marker lamps12aand12b, for example.

In addition, in the present embodiment, the resistors118c–118fare examples of connection resistors. In this case, the resistors118cand118econstitute a first terminal connecting unit, and the resistors118dand118fconstitute a second terminal connecting unit, for example.

Moreover, the resistors118cand118dare accommodated in the lamp body14(refer toFIG. 1) of the marker lamp12a, and the resistors118eandfare accommodated in the lamp body14of the marker lamp12b. Moreover, the resistors118cand118eare connected in series and electrically connects the terminals of the resistors102aaccommodated in the different lamp bodies14. Moreover, the resistors118dand118fare connected in series and electrically connects the terminals of the resistors102baccommodated in the different lamp bodies14. Each of the lamp bodies14may accommodate a set of the light emitting diodes20(refer toFIG. 1) and the resistors102aand102bcorresponding to the set of the light emitting diodes20to protect them from water.

FIG. 9is a circuit diagram illustrating a configuration of a marker lamp12. In the present embodiment, the marker lamp12includes a plurality of diodes108a–108c, a plurality of light source units100aand100b, a plurality of resistors102a–102d, and a current control unit112.

In the present embodiment, a plurality of light source units100aand100b, which are connected in parallel, are provided in single marker lamp12. In this case, the vehicular lamp10(refer toFIG. 1) includes the single marker lamp12. Moreover, the resistors102aand102bare examples of series resistances connected with the light source unit100ain series, and the resistors102cand102dare examples of series resistances connected with the light source unit100bin series. A high voltage side of the light source unit100aconnects with the diode108avia the resistor102a, and a low voltage side of the light source unit100ais grounded via the resistor102b. A high voltage side of the light source unit100bconnects with the diode108avia the resistor102c, and a low voltage side of the light source unit100bis grounded via the resistor102d. Moreover, the high voltage side of the light source units100aand100bconnect with the diodes108band108c, respectively, wherein the diodes108band108care connected in parallel.

Therefore, when the vehicular lamp10acts as a tail lamp, the light source unit100areceives a positive voltage output from the power supply unit50via the resistor102aand the diode108a, and the light source unit100breceives the positive voltage via the resistor102cand the diode108a. On the other hand, when the vehicular lamp10acts as a stop lamp, the light source units100aand100breceive a positive voltage output from the power supply unit50via the diodes108band108c, respectively.

The current control unit112includes resistors118aand118b. The resistor118aconnects a high voltage side of the light source unit100aand a high voltage side of the light source unit100b. The resistor118bconnects a low voltage side of the light source unit100band a low voltage side of the light source unit100b.

Therefore, when the wire of one of the light source units100aand100bis broken, electric current flows from the high voltage side of the light source unit100aor100bof which the wire is broken to the high voltage side of the light source unit100bor100aof which the wire is not broken via the resistor118a. Moreover, the electric current flows from the low voltage side of the light source unit100bor100aof which the wire is not broken to the lower voltage side of the light source unit100aor100bof which the wire is broken via the resistor118b. Thereby, the current control unit112increases the electric current to be supplied to the light source unit100bor100aof which the wire is not broken. Therefore, according to the present embodiment, even if the wire of one of the light source units100aor100bis broken, the quantity of light of the vehicular lamp10can be maintained properly. According to the present embodiment, the vehicular lamp10can be operated appropriately.

The vehicular lamp to which the present invention may be applied to includes, but not limited to, headlamp, tail lamp, back-up lamp and turn-signal lamp of automobiles, motorcycles and trains, and the headlamp includes but not limited to regular headlamp, fog lamp and cornering lamp.

Although the present invention has been described by way of an exemplary embodiment, it should be understood that those skilled in the art might make many changes and substitutions without departing from the spirit and the scope of the present invention. It is obvious from the definition of the appended claims that embodiments with such modifications also belong to the scope of the present invention.

As is obvious from the description above, according to the present invention, the quantity of light of the vehicular lamp can always be maintained properly and also the vehicular lamp can be operated appropriately.