Abstract:
A lighting device includes: a power conversion unit which converts a direct current (DC) power into a power required by a load; an output current detection unit which detects an output current of the power conversion unit; and a source voltage detection unit which detects a source voltage. Further, the lighting device includes an operation unit which calculates an output current command value so as not to exceed an upper limit of the output current command value set according to a resistance value of an externally connected resistor; and a control unit which controls the power conversion unit such that the output current thereof the power conversion unit becomes the output current command value.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a lighting device, headlamp lighting device, and headlamp unit and vehicle having the same. 
     BACKGROUND OF THE INVENTION 
     Conventionally, there is provided an LED headlamp lighting device for vehicle (see, e.g., Japanese Patent Application Publication No. 2011-113642). The LED headlamp lighting device includes a DC/DC converter which steps up/down a DC voltage supplied from a battery in response to turning on of a LOW beam switch into a DC voltage of a desired voltage value, and a control circuit which controls the on/off of switching elements of the DC/DC converter. The LED headlamp lighting device further includes a power detection circuit to detect a source voltage of the battery and a current detection circuit to detect a current flowing through light emitting diodes (LEDs). The control circuit includes a lamp current command value operation unit and a comparison operation unit. 
     The lamp current command value operation unit selects a lamp current command value stored in a storage unit in advance based on the source voltage, and outputs it as the lamp current command value. The comparison operation unit compares the lamp current command value outputted from the lamp current command value operation unit with an output current value detected by the current detection circuit, and calculates and outputs an output current command value to make these values equal. Thus, in the LED headlamp lighting device, constant current control can be achieved by controlling the output current command value outputted from the comparison operation unit. 
     In the LED headlamp lighting device, if the source voltage of the battery is reduced to, e.g., less than 8 V, it begins to decrease the output current. Then, the reduction of output current is performed depending on a change in the source voltage, and control is performed to maintain a rated current if the source voltage is equal to or greater than 8 V. By this control, it is possible to reduce an increase in circuit loss at a low source voltage, and prevent damage to the lighting device. 
     In the LED headlamp lighting device disclosed in Japanese Patent Application Publication No. 2011-113642, a plurality of LEDs connected in series are used as a load. In this case, there is a variation in luminous flux between the LEDs, and its effect appears prominently when the same forward current flows in each LED. On the other hand, the output current command value is uniquely determined by, e.g., a data table prepared in advance. Accordingly, even if the constant current control is performed using the same output current in multiple lighting devices, the LED brightness is different between the lighting devices or LEDs. 
     Therefore, in order to set the brightness of each LED in the multiple lighting devices to a predetermined range, it is necessary to select an LED having a luminous flux within a predetermined range. In this case, since the selection process of LEDs is needed to be carried out by a manufacturer of the LEDs, the cost of LEDs increases. The LED brightness cannot be finely controlled to the extent that a user desires. 
     In order to solve the above-mentioned problems, multiple data tables can be prepared in advance, and a data table can be selected according to the luminous flux of the LED. This eliminates a need for the selection of the LED, thereby suppressing an increase in cost of LEDs. However, in this case, since it requires a memory with a capacity to store the multiple data tables, it may cause an increase in cost. 
     SUMMARY OF THE INVENTION 
     In view of the above, the present invention provides a lighting device, headlamp lighting device, and headlamp unit and vehicle having the same, which are capable of adjusting an output current while suppressing an increase in cost, with a simple configuration. 
     In accordance with a first aspect of the present invention, there is provided a lighting device including: a power conversion unit which converts a direct current (DC) power supplied from a DC power supply into a power required by a load; an output current detection unit which detects an output current of the power conversion unit; and a source voltage detection unit which detects a source voltage of the DC power supply. Further, the lighting device includes an operation unit which, when calculating an output current command value of the power conversion unit based on a voltage value detected by the source voltage detection unit, calculates the output current command value so as not to exceed an upper limit of the output current command value set according to a resistance value of an externally connected resistor; and a control unit which controls the power conversion unit such that the output current of the power conversion unit detected by the output current detection unit becomes the output current command value calculated by the operation unit. 
     In accordance with a second aspect of the present invention, there is provided a lighting device including: a power conversion unit which converts a DC power supplied from a DC power supply into a power required by a load; an output current detection unit which detects an output current of the power conversion unit; and a temperature detection unit which detects an ambient temperature. Further, the lighting device includes an operation unit which, when calculating an output current command value of the power conversion unit based on the ambient temperature detected by the temperature detection unit, calculates the output current command value so as not to exceed an upper limit of the output current command value set according to a resistance value of an externally connected resistor; and a control unit which controls the power conversion unit such that the output current of the power conversion unit detected by the output current detection unit becomes the output current command value calculated by the operation unit. 
     In accordance with a third aspect of the present invention, there is provided a lighting device including: a power conversion unit which converts a DC power supplied from a DC power supply into a power required by a load; an output current detection unit which detects an output current of the power conversion unit; and an output voltage detection unit which detects an output voltage of the power conversion unit. Further, the lighting device includes an operation unit which, when calculating an output current command value of the power conversion unit based on the output voltage of the power conversion unit detected by the output voltage detection unit, calculates the output current command value so as not to exceed an upper limit of the output current command value set according to a resistance value of an externally connected resistor; and a control unit which controls the power conversion unit such that the output current of the power conversion unit detected by the output current detection unit becomes the output current command value calculated by the operation unit. 
     Preferably, the lighting device is a headlamp lighting device, and the load is a headlamp for vehicle. 
     In accordance with a fourth aspect of the present invention, there is provided a headlamp unit including any one of the lighting devices described above. 
     In accordance with a fifth aspect of the present invention, there is provided a vehicle including any one of the lighting devices and the headlamp unit which are described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects and features of the present invention will become apparent from the following description of embodiments, given in conjunction with the accompanying drawings, in which: 
         FIGS. 1A and 1B  illustrate a headlamp lighting device in accordance with a first embodiment of the present invention, wherein  FIG. 1A  is a schematic circuit diagram and  FIG. 1B  is a partial circuit diagram; 
         FIGS. 2A to 2C  are graphs for explaining an operation of the headlamp lighting device shown in  FIGS. 1A and 1B ; 
         FIG. 3  is a flowchart for explaining the operation of the headlamp lighting device shown in  FIGS. 1A and 1B ; 
         FIG. 4  is a schematic circuit diagram showing another example of the headlamp lighting device shown in  FIGS. 1A and 1B ; 
         FIG. 5  is a graph for explaining an operation of another example of the headlamp lighting device shown in  FIG. 4 ; 
         FIG. 6  is a schematic circuit diagram showing a headlamp lighting device in accordance with a second embodiment of the present invention; 
         FIGS. 7A to 7C  are graphs for explaining an operation of the headlamp lighting device shown in  FIG. 6 ; 
         FIG. 8  is a schematic circuit diagram illustrating a headlamp lighting device in accordance with a third embodiment of the present invention; 
         FIGS. 9A to 9D  are graphs for explaining an operation of the headlamp lighting device shown in  FIG. 7 ; and 
         FIG. 10  is a diagram showing a partial appearance of a vehicle in accordance with a fourth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, a headlamp lighting device, and headlamp unit and vehicle using the same in accordance with embodiments of the present invention will be described with reference to the accompanying drawings which form a part hereof. In the following description, a headlamp lighting device is described as an example of a lighting device, but the lighting device may be any other lighting device capable of supplying a power to a load without being limited to the headlamp lighting device. 
     First Embodiment 
       FIG. 1A  is a schematic circuit diagram showing an example of a headlamp lighting device  2  in accordance with a first embodiment of the present invention. The headlamp lighting device  2  includes a DC/DC converter  21 , an operation circuit  22 , an output current detection circuit  23 , a source voltage detection circuit  24 , a control power generation circuit  25 , a comparator  26  and a flip-flop  27 . 
     The DC/DC converter (power conversion unit)  21  includes a transformer T 1 , a switching element Q 1  connected to a primary side of the transformer T 1 , a diode D 1  connected to a secondary side of the transformer T 1 , and a primary side current detection circuit  211  which detects a current flowing through the primary side of the transformer T 1 . The DC/DC converter  21  has a function to convert a DC power supplied from a battery (DC power supply)  1  in response to turning on of a LOW beam switch (not shown) into a DC power required by a headlamp (load)  3 . 
     Further, a primary side current I 4  detected by the primary side current detection circuit  211  is inputted to the comparator  26 . The comparator  26  compares the primary side current I 4  with an output current command value I 3  applied from the operation circuit  22  and outputs a reset signal to the flip-flop  27  according to the result of comparison. Between output terminals of the DC/DC converter  21 , a capacitor C 1  for smoothing is connected. If the switching element Q 1  is a field-effect transistor (FET), its on-resistance becomes approximately an ohmic resistance. Therefore, a drain voltage of the switching element Q 1  may be amplified by the primary side current detection circuit  211  consisting of an operation amplifier and the like, thereby detecting the primary side current I 4 . 
     The output current detection circuit (output current detection unit)  23  detects a current (output current of the DC/DC converter  21 ) I 1  flowing through a plurality of (three in  FIG. 1A ) LEDs  31  constituting the headlamp  3  by using a resistor R 2 , and outputs the detected output current I 1  to the operation circuit  22 . 
     The source voltage detection circuit (source voltage detection unit)  24  detects a source voltage (output voltage) of the battery  1 , and outputs the detected source voltage to the operation circuit  22 . 
     The control power generation circuit  25  generates an operating power to the operation circuit  22 , the comparator  26  and the flip-flop  27  from the DC power supplied from the battery  1 . 
     The primary side current I 4  detected by the primary side current detection circuit  211  of the DC/DC converter  21  and the output current command value I 3  applied from the operation circuit  22  are inputted to the comparator  26 , and the comparator  26  outputs a reset signal to the flip-flop  27  according to the result of comparison thereof. Specifically, the comparator  26  does not outputs a reset signal if the primary side current I 4  is smaller than the output current command value I 3 , and outputs a reset signal to reset the flip-flop  27  when the primary side current I 4  reaches the output current command value I 3 . 
     The flip-flop  27  functions as a drive circuit of the switching element Q 1  of the DC/DC converter  21 , and the switching element Q 1  is turned on when the flip-flop  27  is set to a high frequency ON signal HF. When the switching element Q 1  is turned on, the primary side current I 4  flows through a primary winding of the transformer T 1  to store energy in the transformer T 1 . Then, when the primary side current I 4  flowing through the primary winding of the transformer T 1  reaches the output current command value I 3 , the reset signal is outputted from the comparator  26 , and the flip-flop  27  is reset to turn off the switching element Q 1 . When the switching element Q 1  is turned off, a counter electromotive force is generated in a secondary winding by the energy stored in the transformer T 1  and, accordingly, the capacitor C 1  is charged through the diode D 1 . In this embodiment, the comparator  26  and the flip-flop  27  serve as a control unit. 
     The operation circuit (operation unit)  22  is formed of, e.g., a microcomputer and includes a main operation unit  221 , a comparison unit  222 , a limit selection unit  223 , and a storage unit  224 . A conversion table and limit values A to C to be described later are stored in advance in the storage unit  224 . 
     A voltage signal outputted from the limit selection unit  223  is inputted to the main operation unit  221 , and the main operation unit  221  reads from the storage unit  224  one of the limit values A to C according to the voltage signal. Further, the source voltage of the battery  1  detected by the source voltage detection circuit  24  is also inputted to the main operation unit  221 , and the main operation unit  221  reads from the storage unit  224  an output current value corresponding to the source voltage based on the conversion table. Further, the main operation unit  221  calculates an output current command value I 2  based on the limit values A to C and the output current value. In addition, a specific operation will be described later. 
       FIG. 1B  shows an example of circuit diagram of the limit selection unit  223 , which has a resistor R 3  connected to an output terminal of the control power generation circuit  25 . A voltage (partial voltage) of a connection point of the resistor R 3  and the resistor R 1  externally connected to a cathode terminal of the headlamp  3  is inputted as the voltage signal to the main operation unit  221 . For example, when the output voltage of the control power generation circuit  25  is 5 V and a resistance value of the resistor R 3  is 10 kΩ and when the resistor R 1  having a resistance value of 10 kΩ is connected, the voltage signal outputted from the limit selection unit  223  becomes 2.5 V. 
     Further, if both terminals of the resistor R 1  are shorted (i.e., corresponding to the resistance value 0 of the resistor R 1 ), the voltage signal outputted from the limit selection unit  223  becomes 0 V. If the connection point between the resistor R 1  and the resistor R 3  is opened (i.e., corresponding to the resistance value ∞), the voltage signal outputted from the limit selection unit  223  becomes 5 V. Then, the main operation unit  221  reads, from the storage unit  224 , the limit value A if the voltage signal inputted from the limit selection unit  223  is 0 V, the limit value B if the voltage signal is 2.5 V, and the limit value C if the voltage signal is 5 V. 
     Here, it is assumed that a rated current of the LEDs  31  included in the headlamp  3  is 0.7 A, and 0.7 A, 0.69 A and 0.68 A are set as the limit values A to C, respectively. For example, if the LEDs  31  having a luminous flux of high rank are installed to the headlamp lighting device  2 , the connection point between the resistor R 1  and the resistor R 3  is opened in order to suppress the output current of the headlamp lighting device  2  to a low level. Accordingly, the main operation unit  221  reads the limit value C from the storage unit  224 . 
     Further, if the LEDs  31  having a luminous flux of low rank are installed to the headlamp lighting device  2 , both terminals of the resistor R 1  are shorted in order to increase the output current. The main operation unit  221  reads the limit value A from the storage unit  224 . Further, if the LEDs  31  having a luminous flux of middle rank are installed to the headlamp lighting device  2 , the resistor R 1  having a resistance value of 10 kΩ is connected, and the main operation unit  221  reads the limit value B from the storage unit  224 . By selecting one of the limit values A to C according to the rank of the LEDs  31  used in this way, the brightness of each of the LEDs  31  can be set to a predetermined range regardless of the rank of the luminous flux of the LEDs  31 . 
     The output current command value I 2  is inputted to the comparison unit  222  from the main operation unit  221  and the output current I 1  detected by the output current detection circuit  23  is also inputted to the comparison unit  222 . The comparison unit  222  changes the output current command value I 3  to make these values equal, and outputs it to the comparator  26 . 
       FIG. 2A  is a graph showing an example of the conversion table stored in the storage unit  224 . As represented by the solid line b in the figure, the output current value is set according to the source voltage of the battery  1 . Also in this embodiment, one of the limit values A to C is selected according to the resistance value of the externally connected resistor R 1 , and the limit value is indicated by the solid line c in  FIG. 2B  ( FIG. 2B  shows a case where the limit value is 0.68 A). Then, the main operation unit  221  compares the output current value read from the storage unit  224  based on the conversion table with the selected limit value, and outputs the smaller value as the output current command value I 2  to the comparison unit  222  (see the solid line d in  FIG. 2C ). 
     In this embodiment, by PWM controlling the ON time of the switching element Q 1  of the DC/DC converter  21  using the above circuit configuration, the constant current control of the LEDs  31  can be achieved. 
     Next, an operation of the headlamp lighting device  2  will be described with reference to a flowchart shown in  FIG. 3 . When the operating power is supplied from the control power generation circuit  25  to the operation circuit  22 , the operation circuit  22  is released from the reset and starts the operation (step S 1 ). At first, various initialization processes of the program are performed (step S 2 ). Subsequently, the operation circuit  22  determines whether the LOW beam switch (not shown) is ON or not (step S 3 ). 
     If it is determined that the LOW beam switch is not ON, the operation does not proceed to step S 4  (No of step S 3 ). If it is determined that the LOW beam switch is ON (Yes of step S 3 ), the operation circuit  22  performs A/D conversion on and reads the source voltage of the battery  1  detected by the source voltage detection circuit  24 , and inputs it to the main operation unit  221  (step S 4 ). At this time, the main operation unit  221  reads from the storage unit  224  one of the limit values A to C according to the voltage signal inputted from the limit selection unit  223  (step S 4 ). 
     In addition, the main operation unit  221  calculates the output current value corresponding to the source voltage of the battery  1  based on the conversion table stored in the storage unit  224  (step S 5 ). Then, the main operation unit  221  compares the output current value with the selected limit value, and outputs the smaller value as the output current command value I 2  to the comparison unit  222  (step S 6 ). Further, the operation circuit  22  reads the output current I 1  detected by the output current detection circuit  23 , after performing A/D conversion thereon, and inputs it to the comparison unit  222  (step S 7 ). 
     The comparison unit  222  compares the output current command value I 2  inputted from the main operation unit  221  with the output current I 1  (step S 8 ), and changes the output current command value I 3  to make these values equal. Then, the comparison unit  222  outputs it to the comparator  26  (step S 9 ). Thus, based on the primary side current I 4  and the output current command value I 3 , on/off control of the switching element Q 1  of the DC/DC converter  21  is performed by the comparator  26  and the flip-flop  27  (step S 10 ), thereby executing the constant current control. 
       FIG. 4  is a schematic circuit diagram showing another example of the headlamp lighting device  2  of this embodiment, which is different from the example of  FIG. 1A  in that a limit operation unit  225  is provided instead of the limit values A to C. In addition, since the other configuration is the same as that of  FIG. 1A , the same reference numerals are assigned to the same components, and a description thereof will be omitted. Also, the conversion table is stored in advance in the storage unit  224  as in  FIG. 1A . 
     The operation circuit  22  has the limit operation unit  225 , and the voltage signal according to the resistance value of the resistor R 1  is inputted to the limit operation unit  225  from the limit selection unit  223 . Then, the limit value corresponding to the voltage signal is outputted to the main operation unit  221 .  FIG. 5  is a graph showing the relationship between the resistance value of the resistor R 1  and the limit value, and the limit operation unit  225  sets the limit value according to this graph. 
     Specifically, as represented by the solid line e in  FIG. 5 , the limit value increase linearly up to 0.7 A from 0.68 A until the resistance value of the resistor R 1  reaches a predetermined value greater than 10 kΩ from the state where the both terminals across the resistor R 1  are shorted (i.e., resistance value 0). Further, when the resistance value of the resistor R 1  is equal to or greater than the predetermined value, the limit value becomes constant to be 0.7 A. 
     Thus, in the headlamp lighting device  2  in which the output current I 1  of the DC/DC converter  21  is limited according to the source voltage of the battery  1 , when a change occurs in the number or luminous flux of the LEDs  31 , the output current I 1  can be adjusted according to the change only by replacing the resistor R 1 . Therefore, it is possible to simply adjust the output current I 1  while reducing the cost. Further, by adjusting the output current I 1  of the DC/DC converter  21  for each headlamp lighting device  2 , it is possible to reduce a variation in light output between headlamp lighting devices  2 . In particular, as shown in  FIG. 5 , by continuously changing the limit value according to the resistance value of the resistor R 1 , it is possible to further reduce the variation in light output between headlamp lighting devices. 
     In addition, a method of determining the limit value described in this embodiment is merely exemplary. For example, if the LEDs  31  delivered from parts manufacturers are divided into ranks in advance according to the luminous flux, limit values are prepared according to the number of ranks, and the limit value may be selected according to the rank of the LEDs  31  to be used. Further,  FIG. 5  showing the relationship between the resistance value of the resistor R 1  and the limit value which is used in the limit operation unit  225  is merely exemplary, and is preferred in that the limit value can be further finely set. For example, a data table in which the resistance value of the resistor R 1  is associated with the limit value may be used. In addition, the relationship of the limit value and the resistance value is not limited to linear characteristics as shown in  FIG. 5 , and may have characteristics of a curve. 
     In this embodiment, the output current of the DC/DC converter  21  is reduced, but an average current may be reduced by PWM dimming, and similarly, it is possible to simply adjust the output current while suppressing an increase in cost. In this case, for example, when the LEDs  31  are turned on at a frequency of 100 Hz and its duty is 100% at a normal source voltage, the duty may be reduced down to the limit value at a rate of 2% per minute in case of a low source voltage. 
     Further, the LEDs  31  and the resistor R 1  may be included in the same package. In this case, the resistance value of the resistor R 1  is determined according to the rank of the luminous flux of the LEDs  31  included in the same package. In addition, the graphs and the source voltage and output current command value in the graphs that have been described in this embodiment are merely exemplary, and the present invention is not limited thereto. 
     In this embodiment, a case where the resistance value of the resistor R 1  is of three types, i.e., 0, 10 kΩ and ∞ has been described as an example. However, the resistance value of the resistor R 1  is not limited to the above and may be selected according to the number of limit values. Further, although the DC/DC converter  21  is used as a power conversion unit in this embodiment, for example, a chopper circuit or the like may be used without being limited to this. 
     Second Embodiment 
     A second embodiment of the headlamp lighting device  2  will be described with reference to  FIGS. 6 and 7 . Although the output current command value of the DC/DC converter  21  is calculated based on the source voltage of the battery  1  in the first embodiment, the output current command value is calculated based on the ambient temperature detected by a temperature detection circuit  28  in the second embodiment. Further, since the other configuration is the same as that of  FIG. 1A  of the first embodiment, the same reference numerals are assigned to the same components, and a description thereof will be omitted. 
     The headlamp lighting device  2  of this embodiment includes the DC/DC converter  21 , the operation circuit  22 , the output current detection circuit  23 , the control power generation circuit  25 , the comparator  26 , the flip-flop  27  and the temperature detection circuit  28  which detects the ambient temperature. 
     The ambient temperature detected by the temperature detection circuit (temperature detection unit)  28  is inputted to the main operation unit  221  of the operation circuit  22 , and the main operation unit  221  calculates the output current command value I 2  of the DC/DC converter  21  based on the detected ambient temperature. 
       FIG. 7A  is a graph showing an example of the conversion table stored in the storage unit  224 . As represented by the solid line f in the figure, the output current command value is set according to the ambient temperature. Further, one of the limit values A to C is selected according to the resistance value of the externally connected resistor R 1 , and the solid line g in  FIG. 7B  indicates the limit value (the limit value is 0.68 A in  FIG. 7B ). 
     Then, the main operation unit  221  compares the output current value read from the storage unit  224  based on the conversion table with the selected limit value, and outputs the smaller value as the output current command value I 2  to the comparison unit  222  (see the solid line h in  FIG. 7C ). Since the operation of obtaining the output current command value is similar to that of the first embodiment, its description is omitted. 
     Thus, in the headlamp lighting device  2  in which the output current I 1  of the DC/DC converter  21  is limited according to the ambient temperature, the output current I 1  can be adjusted according to a change in the number or luminous flux of the LEDs  31  only by replacing the resistor R 1 . Therefore, it is possible to simply adjust the output current I 1  while reducing the cost. In addition, by adjusting the output current I 1  of the DC/DC converter  21  for each headlamp lighting device  2 , it is possible to reduce a variation in light output between headlamp lighting devices  2 . 
     Also in this embodiment, the limit operation unit may be provided instead of the limit values A to C stored in the storage unit  224 . Similarly, it is possible to simply adjust the output current I 1  while suppressing an increase in cost. 
     Third Embodiment 
     A third embodiment of the headlamp lighting device  2  will be described with reference to  FIGS. 8 and 9 . Although the output current command value of the DC/DC converter  21  is calculated based on the source voltage of the battery  1  in the first embodiment, the output current command value is calculated based on an output voltage of the DC/DC converter  21  in the third embodiment. Since the other configuration is the same as that of  FIG. 1A  of the first embodiment, the same reference numerals are assigned to the same components, and a description thereof will be omitted. 
     The headlamp lighting device  2  of this embodiment includes the DC/DC converter  21 , the operation circuit  22 , the output current detection circuit  23 , the control power generation circuit  25 , the comparator  26 , the flip-flop  27  and an output voltage detection circuit  29  which detects the output voltage of the DC/DC converter  21 . 
     The output voltage of the DC/DC converter  21  detected by the output voltage detection circuit (output voltage detection unit)  29  is inputted to the main operation unit  221  of the operation circuit  22 , and the main operation unit  221  calculates the output current command value I 2  of the DC/DC converter  21  based on the detected output voltage. In this embodiment, a voltage (partial voltage) of a connection point of resistors R 4  and R 5  connected between the output terminals of the DC/DC converter  21  is detected as the output voltage. 
       FIG. 9A  is a graph showing an example of the conversion table stored in the storage unit  224 . As represented by the solid line j in the figure, a reduction width of the output current command value is set according to a change width in the output voltage of the DC/DC converter  21 . Also in this embodiment, one of the limit values A to C of the current reduction width is selected according to the resistance value of the externally connected resistor R 1 , and the solid line k in  FIG. 9B  indicates the limit value of the current reduction width (e.g., 0.02 A in  FIG. 9B ). The limit values A to C are set, for example, such that the reduction width increases as the luminous flux increases. 
     Then, the main operation unit  221  compares the reduction width of the output current value read from the storage unit  224  based on the conversion table with the selected limit value of the current reduction width, and selects the larger value as the reduction width of the output current command value (see solid line m in  FIG. 9C ). As a result, the main operation unit  221  calculates the output current command value I 2  according to the solid line n in  FIG. 9D . In addition, since the other operation is similar to that of the first embodiment, its description is omitted. 
     Thus, in the headlamp lighting device  2  in which the output current I 1  of the DC/DC converter  21  is limited according to the output voltage of the DC/DC converter  21 , the output current I 1  can be adjusted according to a change in the number or luminous flux of the LEDs  31  only by replacing the resistor R 1 . Therefore, it is possible to simply adjust the output current I 1  while reducing the cost. In addition, by adjusting the output current I 1  of the DC/DC converter  21  for each headlamp lighting device  2 , it is possible to reduce a variation in light output between headlamp lighting devices  2 . 
     Also in this embodiment, the limit operation unit may be provided instead of the limit values A to C stored in the storage unit  224 . Similarly, it is possible to simply adjust the output current I 1  while suppressing an increase in cost. 
     Fourth Embodiment 
     An embodiment of a headlamp and vehicle using the headlamp lighting device  2  described in the first to third embodiments will be described with reference to  FIG. 10 . 
       FIG. 10  partially shows an appearance of vehicle A in accordance with this embodiment. The vehicle A includes a pair of headlamps  3  arranged on both sides of the vehicle in its width direction, and a pair of headlamp lighting devices  2  each supplying a predetermined lighting power to each of the headlamps  3 . 
     In this embodiment, by using the headlamp lighting device  2  described in the first to third embodiments, for example, even if there is a difference in the luminous flux of the LEDs  31  constituting the headlamps  3  on the right and left, the light output of the headlamps  3  on both sides can be set to a predetermined range by adjusting the resistance value of the externally connected resistor R 1 . That is, according to this embodiment, by using the headlamp lighting device  2  described in the first to third embodiments, it is possible to provide a headlamp unit and the vehicle A capable of simply adjusting the output current of the DC/DC converter  21  while reducing the cost. Further, in case of using the headlamp lighting device  2  of the second embodiment, the circuit can be prevented from being broken due to temperature rise, and the vehicle A capable of stably turning on the headlamps  3  can be achieved. 
     While the invention has been shown and described with respect to the embodiments, it will be understood by those skilled in the art that various changes and modification may be made without departing from the scope of the invention as defined in the following claims.