Abstract:
A lighting controller for a lighting device for a vehicle includes a semiconductor light source; a power source for supplying electric power; and control circuitry for controlling a supply of a current to the semiconductor light source. The control circuitry selectively supplies the current to the semiconductor light source through a resistance element or through a bypass circuit for bypassing the resistance element based on a determination of a state of the current. A method for controlling a lighting device for a vehicle includes receiving electric power from a power source; supplying a current to a semiconductor light source; determining a state of the current supplied to the semiconductor light source; and selectively supplying the current to the semiconductor light source through a resistance element or through a bypass circuit for bypassing the resistance element based on the determination of the state of the current.

Description:
BACKGROUND OF INVENTION 
   1. Field of the Invention 
   The present invention relates to a lighting controller for a lighting device for a vehicle, and more particularly to a lighting controller for a lighting device for a vehicle constructed so as to control a semiconductor light source composed of a semiconductor light emitting element to be turned on. 
   2. Background Art 
   As the lighting device for a vehicle, a lighting device for a vehicle using a semiconductor light emitting element such as an LED (Light Emitting Diode) as a light source has been known. Mounted on such a lighting device for a vehicle is a lighting control circuit for controlling the LED to be turned on. 
   As the lighting control circuit, for instance, a lighting control circuit has been proposed in which the battery voltage of a vehicle is boosted and the boosted voltage is applied to LEDs to drive a light source having a plurality of LEDs connected in series (see Patent Document 1). 
   In such a lighting control circuit, a structure is employed in which a voltage not higher than the forward voltage (a voltage drop) of the LED is applied to the LED to supply a prescribed current to the LED. Thus, when a supply voltage is constant, a prescribed electric current can be always supplied to the LED. 
   However, during a transient time, for instance, at the time of starting by turning on a power switch, when the lighting control circuit performs a control for allowing a supply current to the LED to come close to a set value, if a control delay arises, the supply current to the LED exceeds the set value to overshoot so that an over-current may be supplied to the LED. Further, when a load suddenly changes, for instance, when a chattering phenomenon arises that, when a lead wire for connecting the lighting control circuit to the LED is disconnected from a contactor and then connected to the contactor again, because the load is open and accordingly a detected current is zero, the lighting control circuit carries out a control for increasing an output voltage as much as possible to maintain the detected current to the set value. When the output voltage of the lighting control circuit reaches a maximum value, if the LED as the load is connected to the lighting control circuit, the over-current may be possibly supplied to the LED. When the over-current is supplied to the LED, a bonding wire is disconnected or a chip is deteriorated due to a current concentration. Thus, the LED fails. 
   [Patent Document 1] JP-A-2004-51014. 
   To prevent the over-current from being supplied to the LED during the transient time, a method may be devised that a resistance element is inserted into a circuit for connecting the lighting control circuit to the LED to consume the current supplied during the transient time by the resistance element and prevent the over-current from being supplied to the LED. However, in this method, because the current is consumed by the resistance element even in a steady state, a power loss is increased. 
   SUMMARY OF INVENTION 
   One or more embodiments of the present invention suppress a current supplied to a semiconductor light source during a transient time and suppress a power loss during a steady state. 
   In one or more embodiments, a lighting controller for a lighting device for a vehicle comprises: a current supply control unit for receiving the supply of an electric power from a power source and controlling the supply of a current to a semiconductor light source; a current detecting unit for detecting the current of the semiconductor light source; a resistance element that consumes the current when the semiconductor light source is turned on; a switch unit for forming a turning on circuit including the resistance element in a current supply path for connecting the current supply control unit to the semiconductor light source during an off operation and forming a bypass circuit for bypassing the resistance element in the current supply path during an on operation; and a switch control unit for deciding whether or not the detected current of the current detecting unit is a current showing a transient state and turning off the switch unit when an affirmative decided result is obtained, and turning on the switch unit when a negative decided result is obtained. 
   When a power is turned on, during a process that the current is supplied to the semiconductor light source from the current supply control unit, it is decided whether or not the current supplied to the semiconductor light source is a current showing a transient state. When the affirmative decided result is obtained, that is, the current supplied to the semiconductor light source is the current showing the transient state, the switch unit is turned off, the turning on circuit including the resistance element is formed in the current supply path for connecting the current supply control unit to the semiconductor light source and the current is consumed by the resistance element. Thus, during a transient time, an over-current can be restrained from being supplied to the semiconductor light source. On the other hand, when the turning on circuit including the resistance element is formed in the current supply path for connecting the semiconductor light source to the current supply control unit, if it is decided that the current of the semiconductor light source is not the current showing the transient state, the transient state is decided to shift to a steady state. Then, the switch unit is turned on, the bypass circuit for by-passing the resistance element is formed in the current supply path for connecting the current supply control unit to the semiconductor light source. Thus, the current can be supplied to the semiconductor light source from the current supply control unit without consuming the current in the resistance element and a power loss during the steady state can be suppressed. 
   In one or more embodiments, before the detected current of the current detecting unit begins to flow or when the detected current of the current detecting unit shows the transient state accompanied by an over-current, the switch control unit turns off the switch unit, and when the detected current of the current detecting unit is a current showing a steady state, the switch control unit turns on the switch unit in the lighting controller for a lighting device for a vehicle. 
   Before the current of the semiconductor light source begins to flow or when the current of the semiconductor light source shows the transient state accompanied by an over-current, the switch unit is turned off so that the over-current can be restrained from being supplied to the semiconductor light source during the transient time. Further, when the current of the semiconductor light source is a current showing a steady state, the switch unit is turned on so that a prescribed current is supplied to the semiconductor light source without consuming the current by the resistance element and the power loss during the steady state can be suppressed. 
   In one or more embodiments, when the switch control unit decides that the detected current of the current detecting unit is the current showing the steady state, then, after a setting time elapses, the switch control unit turns on the switch unit in the lighting controller for a lighting device for a vehicle. 
   When the current showing the steady state is supplied to the semiconductor light source, and then, the setting time elapses, the switch unit is turned on. Thus, even when the rise of the current supplied to the semiconductor light source is steep, even when the time of the transient state has a certain range, or even when a chattering phenomenon arises that a turned on state and a turned off state are continuously alternately generated, the bypass circuit is formed with a delay of the setting time, so that the over-current can be assuredly restrained from being supplied to the semiconductor light source. 
   In one or more embodiments, when the switch control unit decides that the detected current of the current detecting unit is the current showing the transient state, the switch control unit immediately turns on the switch unit in response to this decision in the lighting controller for a lighting device for a vehicle. 
   When the current of the semiconductor light source is the current showing the transient state, the switch unit is immediately tuned off. Thus, even when a chattering phenomenon arises that a turned on state and a turned off state are continuously alternately generated, the turning on circuit including the resistance element is immediately formed in the current supply path for connecting the current supply control unit to the semiconductor light source, so that the generation of the over-current can be assuredly suppressed. 
   In one or more embodiments, when the constant of the resistance element is set in such a way that when the current supply control unit outputs a maximum electric power during a no-load, a resistance value obtained when the current of the semiconductor light source is not higher than a maximum rated current is set as a lower limit value, and when the current supply control unit outputs a minimum electric power during a no-load, a resistance value obtained when the current of the semiconductor light source is a prescribed current is set as an upper limit value. 
   When the constant of the resistance element is set, if the resistance value of the resistance element is made to be too large, the current supplied to the semiconductor light source is excessively decreased. Thus, a prescribed current cannot be supplied to the semiconductor light source and the switch unit is not turned on. When the switch unit is not turned on, the current is always supplied to the resistance element and the power loss is generated. On the contrary, when the resistance value of the resistance element is too small; the current supplied to the semiconductor light source is not reduced. Thus, there is a fear that the over-current may be supplied to the semiconductor light source. Thus, for the constant of the resistance element, when the current supply control unit outputs a maximum electric power during a no-load, a resistance value obtained when the current of the semiconductor light source is not higher than a maximum rated current is set as a lower limit value, and when the current supply control unit outputs a minimum electric power during a no-load, a resistance value obtained when the current of the semiconductor light source is a prescribed current is set as an upper limit value. Accordingly, the over-current can be restrained from being supplied to the semiconductor light source during the transient state and the prescribed current can be supplied to the semiconductor light source during the steady state. 
   In one or more embodiments, the over-current can be restrained from being supplied to the semiconductor light source during the transient state and the power loss during the steady state can be suppressed. 
   In one or more embodiments, the over-current can be restrained from being supplied to the semiconductor light source during the transient state and the power loss during the steady state can be suppressed. 
   In one or more embodiments, the over-current can be assuredly restrained from being supplied to the semiconductor light source. 
   In one or more embodiments, the generation of the over-current can be assuredly suppressed. 
   In one or more embodiments, the over-current can be restrained from being supplied to the semiconductor light source during the transient state and the prescribed current can be supplied to the semiconductor light source during the steady state. 
   Other aspects and advantages of the invention will be apparent from the following description and the appended claims. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a circuit block diagram of a lighting controller for a lighting device for a vehicle showing a first embodiment of the present invention. 
       FIG. 2  is a circuit block diagram of a control circuit 
       FIG. 3  is a wave form diagram for explaining the operation of the control circuit. 
       FIG. 4  is a circuit diagram showing a connecting relation between a contactor and an LED. 
       FIG. 5  is a diagram for explaining a setting method of a constant of a resistance element. 
       FIG. 6  is a circuit block diagram of a lighting controller for a lighting device for a vehicle showing a second embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   Now, embodiments of the present invention will be described below by referring to the drawings.  FIG. 1  is a circuit block diagram of a lighting controller for a lighting device for a vehicle showing a first embodiment of the present invention.  FIG. 2  is a circuit block diagram of a control circuit.  FIG. 3  is a wave form diagram for explaining the operation of the control circuit.  FIG. 4  is a circuit diagram showing a connecting relation between a contactor and an LED.  FIG. 5  is a diagram for explaining a setting method of a constant of a resistance element.  FIG. 6  is a circuit block diagram of a lighting controller for a lighting device for a vehicle showing a second embodiment of the present invention. 
   In these drawings, a lighting controller for a lighting device for a vehicle includes, as shown in  FIG. 1 , a constant current control type switching regulator  12  and a protecting circuit  14  as elements of the lighting device (a light emitting device) for a vehicle. To the switching regulator  12 , a plurality of LEDs  16  as loads are connected. The LED  16  are respectively mutually connected in series and connected in parallel with the output side of the switching regulator  12  through the protecting circuit  14  as a semiconductor light source composed of semiconductor light emitting elements. 
   As the LED  16 , one LED may be used or a plurality of LEDs  16  mutually connected in series may be used as a light source block, or the plurality of the light blocks connected in parallel may be used. Further, the LED  16  may be formed as light sources of various kinds of lighting devices for vehicles such as a head lamp, a stop and tail lamp, a fog lamp and a turn signal lamp. 
   The switching regulator  12  includes a transformer T 1 , a capacitor C 1 , an NMOS transistor  18 , a control circuit  20 , a diode D 1 , a capacitor C 2  and a shunt resistance R 1  and is formed so that a voltage not lower than the forward voltage (a voltage drop) of each LED  16  can be applied to each LED  16 . The capacitor C 1  is connected in parallel with a primary side of the transformer T 1  and the NMOS transistor  18  is connected in series to the primary side of the transformer T 1 . One end side of the capacitor C 1  is connected to a positive terminal of a battery  24  to be mounted on a vehicle through a power switch  21  and a power supply input terminal  22  and the other end side is connected to a negative terminal of the battery  24  to be mounted on a vehicle through a power supply input terminal  26  and grounded. The NMOS transistor  18  has a drain connected to the primary side of the transformer T 1 , a source grounded and a gate connected to the control circuit  20 . With the secondary side of the transformer T 1 , the capacitor C 2  is connected in parallel through the diode D 1 . A node of the diode D 1  and the capacitor C 2  is connected to an anode side of the LED  16  in the upstream side through an output terminal  28 . One end side of the secondary side of the transformer T 1  is grounded together with one end side of the capacitor C 2  and connected to a current detecting terminal  30  through the shunt resistance R 1 . The current detecting terminal  30  is connected to an output terminal  32  through the protecting circuit  14 . The output terminal  32  is connected to a cathode side of the LED  16  in the downstream side. The shunt resistance R 1  is formed as a current detecting unit for detecting a current supplied to the LED  16 . Voltage generated at both the ends of the shunt resistance R 1  is fed back to the control circuit  20  as the voltage corresponding to the current of the LED  16 . 
   The NMOS transistor  18  is formed as a switching element turned on and off in response to an on/off signal (a switching signal) outputted from the control circuit  20 . When the NMOS transistor  18  is turned on, an input voltage from the battery  24  (a dc power source) to be mounted on a vehicle is accumulated in the transformer T 1  as electromagnetic energy. When the NMOS transistor  18  is turned off, the electromagnetic energy accumulated in the transformer T 1  is discharged to the LED  16  as light emitting energy from the secondary side of the transformer T 1  through the diode D 1 . 
   That is, the switching regulator  12  is constructed as a current supply control unit for receiving the supply of an electric power from the battery  24  to be mounted on a vehicle and controlling the supply of the current to the LED  16 . In this case, the switching regulator  12  compares the voltage of the current detecting terminal  30  with prescribed voltage to control an output current in accordance with the compared result. 
   Specifically, the control circuit  20  for controlling the output current of the switching regulator  12  includes, for instance as shown in  FIG. 2 , a comparator  34 , an error amplifier  36 , a saw tooth wave generator  38 , a reference voltage  40 , resistances R 2 , R 3 , and R 4 , and a capacitor C 3 . An output terminal  42  of the comparator  34  is directly connected to the gate of the NMOS transistor  18  or through a current amplifying preamplifier (not shown in the drawing). An input terminal  44  connected to one end of the resistance R 2  is connected to the current detecting terminal  30 . To the input terminal  44 , voltage fed back from the current detecting terminal  30  is applied. The resistances R 2  and R 3  divide the voltage applied to the input terminal  44  to apply the voltage obtained by dividing the voltage to a negative input terminal of the error amplifier  36 . The error amplifier  36  outputs voltage corresponding to the difference between the voltage applied to the negative input terminal and the reference voltage  40  to a positive input terminal of the comparator  34  as a threshold value Vth. The comparator  34  takes in a saw tooth wave Vs to a negative input terminal from the saw tooth wave generator  38  to compare the saw tooth wave Vs with the threshold value Vth and outputs an on/off signal corresponding to the result of the comparison to the gate of the NMOS transistor  18 . 
   For instance, as shown in  FIGS. 3(   a ) and  3 ( b ), when the level of the threshold value Vth is located at a substantially intermediate part of the saw tooth wave Vs, the on/off signal of on duty as high as about 50% is outputted. On the other hand, when the level of the voltage fed back from the current detecting terminal  30  is lower than the reference voltage  40  as the output current of the switching regulator  12  is decreased, the level of the threshold value Vth by the output of the error amplifier  36  is high. Thus, as shown in  FIGS. 3(   c ) and  3 ( d ), the on/off signal of on duty higher than 50% is outputted from the comparator  34 . As a result, the output current of the switching regulator  12  is increased. 
   On the contrary, when the level of the voltage fed back from the current detecting terminal  30  is higher than the reference voltage  402  as the output current of the switching regulator  12  is increased and the level of the threshold value Vth by the output of the error amplifier  36  is lowered, the on/off signal of on duty lower than 50% is outputted from the comparator  34 , as shown in  FIGS. 3(   e ) and  3 ( f ). As a result, the output current of the switching regulator  12  is decreased. A chopping wave generator for generating a chopping wave (a chopping wave signal) can be used in place of the saw tooth wave generator  38 . 
   The protecting circuit  14  includes a resistance R 5  as a resistance element that consumes the current when the LED is turned on, an NMOS transistor  46 , a PNP transistor  48 , resistances R 6  and T 7  and a capacitor C 4  as a switch unit and an operation amplifier  50  as a switch control unit for controlling the on-off operation of the switch unit. The control circuit  14  is inserted between the current detecting terminal  30  and the output terminal  32 . 
   The resistance R 5  is inserted into a current supply path  52  for connecting the current detecting terminal  30  to the output terminal  32 . To both the ends of the resistance R 5 , a drain and a source of the NMOS transistor  46  are respectively connected. The operation amplifier  50  has a positive input terminal connected to the current detecting terminal  30  and a negative input terminal connected to a threshold voltage Vth to compare the voltage of the current detecting terminal  30  with the threshold voltage Vth, decides whether or not the current supplied to the LED  16  is a current showing a transient state and outputs a voltage corresponding to the decided result. Here, the transient state means a state established before the current begins to be supplied or when an over-current is supplied. 
   For instance, when the voltage of the current detecting terminal  30  is lower than the threshold voltage Vth, the operation amplifier  50  decides that the current of the LED  16  is the current showing the transient state and outputs the voltage of a low level as an affirmative decided result. When the voltage of the current detecting terminal  30  exceeds the threshold voltage vth, the operation amplifier  50  decides that the current of the LED  16  is a prescribed current showing a steady state and outputs the voltage of a high level as a negative decided result When the voltage of the high level is outputted from the operation amplifier  50 , this voltage is applied to both the ends of the capacitor C 4  through the resistances R 7  and R 6 . The voltage at both the ends of the capacitor C 4  is increased in accordance with a time constant determined by the resistances R 7 , R 6  and the capacitor C 4 . Then, when the voltage at both the ends of the capacitor C 4  exceeds the threshold value of the NMOS transistor  46 , the NMOS transistor  46  is turned on. That is, the NMOS transistor  46  is turned on with the elapse of a set time after the voltage of the high level is outputted from the operation amplifier  50 . 
   When the NMOS transistor  46  is turned off, a turning on circuit including the resistance R 5  is formed in the current supply path  52 . However, when the NMOS transistor  46  is turned on, a bypass circuit for bypassing the resistance R 5  is formed in the current supply path  52 . 
   Namely, when the current of the LED  16  is in a transient state, the current is supplied to the turning on circuit including the resistance R 5  to consume the current with the resistance R 5 . On the other hand, when the current of the LED  16  shifts to a steady state from the transient state, the bypass circuit, in which the current is not supplied to the resistance R 5 , to bypass the resistance R 5  is formed by the NMOS transistor  46  so that a prescribed current is supplied through the NMOS transistor  46 . 
   When the prescribed current is supplied to the LED  16 , if a chattering phenomenon arises that, when a lead wire for connecting the output terminal  28  or the output terminal  32  to the LED  16  is disconnected from contactors  29  and  31  shown in  FIG. 4  and then connected again to the contactors  29  and  31  so that a period is generated during which the current is not supplied to the LED  16 , the output of the operation amplifier  50  shifts to the low level from the high level. Then, the PNP transistor  48  is turned on and an electric charge accumulated in the capacitor C 4  is instantaneously discharged and the NMOS transistor  46  is immediately turned off. At this time, because, as the current is not supplied to the LED  16 , the control circuit  20  performs a control for increasing the output current of the switching regulator  12 , the output voltage of the switching regulator  12  is suddenly elevated. In this process, when the LED  16  is connected to the switching regulator  12 , a high voltage is applied to the LED  16 . However, because the NMOS transistor  46  is turned off, the current of the LED  16  is supplied through the resistance R 5 . Accordingly, even when the chattering phenomenon arises, the over-current can be prevented from being supplied to the LED  16 . 
   Further, the constant of the resistance R 5  is set in such a way that when the switching regulator  12  outputs a maximum electric power during a no load state, a resistance value obtained when the current of the LED  16  is not higher than a maximum rated current is set as a lower limit value, and when the switching regulator  12  outputs a minimum electric power during a no load state, a resistance value obtained when the current of the LED  16  is the prescribed current is set as an upper limit value. 
   That is, when the resistance value of the resistance R 5  is too large, the current supplied to the LED  16  is excessively decreased, so that the prescribed current is not supplied to the LED  16  and the NMOS transistor  46  is not turned on. When the NMOS transistor  46  is not turned on, the current is always supplied through the resistance R 5  to generate a power loss. 
   On the other hand, when the resistance value R 5  is too small, the current of the LED  16  is not decreased and the over-current is supplied to the LED  16 . Therefore, in this embodiment, the resistance value of the resistance R 5  is set to such a value as to suppress the supply of the over-current to the LED  16  during the transient state and supply the prescribed current to the LED  16  during the steady state. 
   Specifically, when an unevenness arises in the temperature characteristics of the resistance element such as the resistance R 1  or the temperature characteristics of the reference voltage  40 , a consideration is directed to a fact that an unevenness is generated in the output voltage of the switching regulator  12  during the no load state and an unevenness is generated in the forward voltage Vf of the LED  16  due to the temperature characteristics or a solid difference. Then, as shown in  FIG. 5 , the constant (the resistance value) of the resistance R 5  is set in such a way that the current not higher than the maximum rated current is supplied to the LED  16  under a voltage difference Va between the maximum value Vmax of the output voltage of the switching regulator  12  during the no load and the minimum value Vfmin of the forward voltage Vf of the LED  16 , and the current not lower than the prescribed current is supplied to the LED  16  under the voltage difference Vb between the minimum value Vmin of the output voltage of the switching regulator  12  during the no load and the maximum value Vfmax of the forward voltage Vf of the LED  16 . 
   In the above-described structure, during the process that the power switch  21  is turned on to activate the switching regulator  12  and the current is supplied to the LED  16  from the switching regulator  12 , at the time of the transient state immediately after the power is turned on, the voltage of the current detecting terminal  30  is lower than the threshold voltage Vth. Thus, the NMOS transistor  46  is kept turned off and the current of the LED  16  is supplied through the resistance R 5 . Therefore, when the power is turned on, even if the output voltage of the switching regulator  12  is abruptly elevated, the over-current can be prevented from being supplied to the LED  16  and the LED  16  can be prevented from failing. 
   After the power is turned on, the transient state shifts to the steady state and when the voltage of the current detecting terminal  30  exceeds the threshold voltage Vth, the NMOS transistor  46  is turned on to form the bypass circuit for bypassing the resistance R 5  and the prescribed current is supplied to the LED  16 . At this time, because the current of the LED  16  flows through the NMOS transistor  46 , the power loss can be avoided during the steady state. 
   During the process that the prescribed current is supplied to the LED  16 , when the chattering phenomenon due to the sudden change of the load, the output of the operation amplifier  50  shifts to the low level from the high level to immediately turn off the NMOS transistor  46 . Accordingly, when the output voltage of the switching regulator  12  subsequently becomes a high voltage, even if the LED  16  is connected to the switch regulator  12 , the current is supplied to the LED through the resistance R 5 , so that the over-current can be prevented from being supplied to the LED  16 . 
   According to this embodiment, during the transient state, the turning on circuit including the resistance R 5  is formed in the current supply path  52  and the current is consumed by the resistance R 5 . Thus, the over-current can be prevented from being supplied to the LED  16 . On the other hand, during the steady state, the bypass circuit for bypassing the resistance R 5  is formed in the current supply path  52  by the NMOS transistor  46  so that the current is not consumed by the resistance R 5 . Thus, the power loss can be suppressed. 
   Now, a second embodiment of the present invention will be described with reference to  FIG. 6 . In this embodiment, a protecting circuit  54  is provided in place of the protecting circuit  14 . Other structures are the same as those shown in  FIG. 1 . Further, in the first embodiment, the state obtained before the current begins to be supplied or the state accompanied by the over-current is decided to be the transient state. However, in this embodiment, only the generation of an over-current is decided to be a transient state. 
   The protecting circuit  54  includes a resistance R 5  as a resistance element that consumes a current when an LED is turned on, an NMOS transistor  46  and a resistance R 6  as a switch unit, and an operation amplifier  50  as a switch control unit for controlling the on-off operation of the switch unit. The control circuit  54  is inserted between a current detecting terminal  30  and an output terminal  32 . 
   The resistance R 5  is inserted into a current supply path  52  for connecting the current detecting terminal  30  to the output terminal  32 . To both the ends of the resistance R 5 , a drain and a source of the NMOS transistor  46  are respectively connected. The operation amplifier  50  has a negative input terminal connected to the current detecting terminal  30  and a positive input terminal connected to a threshold voltage Vth to compare the voltage of the current detecting terminal  30  with the threshold voltage Vth, determines whether or not the current supplied to the LED  16  is a current showing a transient state exceeding a prescribed range and outputs a voltage corresponding to the determined result. 
   For instance, when the voltage of the current detecting terminal  30  is lower than the threshold voltage Vth, the operation amplifier  50  decides that the current of the LED  16  is not the over-current showing the transient state, that is, the current not higher than the over-current and outputs the voltage of a high level as a negative decided result. When the voltage of the current detecting terminal  30  exceeds the threshold voltage Vth, the operation amplifier  50  decides that the current of the LED  16  is the over-current showing the transient state and outputs the voltage of a low level as an affirmative decided result. 
   When the voltage of the high level is outputted from the operation amplifier  50 , the NMOS transistor  46  is turned on. When the NMOS transistor  46  is turned on, a bypass circuit for bypassing the resistance R 5  is formed in the current supply path  52  for connecting the current detecting terminal  30  to the output terminal  32 . 
   When the NMOS transistor  46  is turned on, the bypass circuit for bypassing the resistance R 5  is formed in the current supply path  52 . However, when the over-current is supplied to the LED  16  as the current of the LED  16  increases, the voltage of the low level is outputted from the operation amplifier  50  to turn off the NMOS transistor  46  and a turning on circuit including the resistance R 5  is formed in the current supply path  52 . 
   That is, when the current of the LED  16  is the over-current, the current is supplied through the turning on circuit including the resistance R 5  and the current is consumed by the resistance R 5 . Thus, the LED  16  can be protected form the over-current. 
   According to this embodiment, when the over-current is supplied to the LED  16 , because the turning on circuit including the resistance R 5  is formed in the current supply circuit  52 , the LED  16  can be protected from the over-current. 
   DESCRIPTION OF REFERENCE NUMERALS AND SIGNS 
     10  . . . . lighting controller for lighting device for vehicle  12  . . . switching regulator  14  . . . protecting circuit  16  . . . LED  18  . . . NMOS transistor  20  . . . control circuit  34  . . . comparator  36  . . error amplifier  38  . . . saw tooth wave generator  46  . . . NMOS transistor  48  . . PNP transistor  50  . . operation amplifier  52  . . current supply path  54  . . . protecting circuit 
   [ FIG. 1 ] 
     20  . . . control circuit Vth . . . threshold voltage 
   [ FIG. 4 ] 
     29 ,  31  . . . contactor 
   [ FIG. 5 ] 
   a . . . voltage 
   While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.