Abstract:
A lamp driving apparatus includes a controller, a lamp driver, a lamp voltage detector, a switch and a switching controller. The controller outputs a switch control signal and a lamp driving control signal in response to an instructing signal for instructing a lamp to be turned on and off. The lamp driver supplies an electric power to the lamp in accordance with the lamp driving control signal. The lamp voltage detector detects a voltage applied to the lamp, and outputs a detecting signal showing the applied state of the voltage to the controller. The switch is connected to the lamp driver, a lamp driving power supply line, and a preliminary power supply line, and switches between a first state and a second state selectively. The first state is a state that the electric power for driving the lamp can be supplied to the lamp driver from the lamp driving power supply line The second state is a sate that the electric power for driving the lamp can be supplied to the lamp driver from the preliminary power supply line. The switching controller controls a switching of the switch in accordance with the switch control signal. The controller outputs the switch control signal so as to make the switch to the first state when the instructing signal for instructing the lamp to be turned on. The controller outputs the switch control signal so as to make the switch to the second state in a case that the detecting signal showing an abnormal applied state of the voltage is received from the lamp voltage detector while the controller outputs the lamp driving control signal for turning on the lump.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a lamp driving apparatus for a vehicle which can be mounted on various kinds of vehicles including motor vehicles or the like, and more particularly to a lamp driving apparatus for a vehicle having a fail safe function.  
         [0002]     A motor vehicle on which a power source part of rated DC 12 volt to 14 volt output having an alternator of 14 volt (it is referred to as “V”, hereinafter) and a 12 V battery capable of charging and discharging is mounted (that is, what is called a 14V vehicle) has been generally known as a usual motor vehicle. In this 14V vehicle, a lamp driving apparatus for a vehicle which receives an electric power from the power source part to drive various types of lamps such as a head lamp, a room lamp, etc. (that is, incandescent bulbs having filaments) applies the DC 12V to 14V to the lamps to turn on the respective lamps.  
         [0003]     In recent years, a high voltage motor vehicle (that is, what is called a 42 V vehicle) advantageous in its fuel consumption on which a power source part of rated DC 36 V to 42V output having a 42V motor/generator and a 36V battery capable charging and discharging is mounted has been progressively developed. If a general purpose 14V type electric load (that is, an electrical device) used in the 14V vehicle can be used in the 42V vehicle in place of an expensive 42V type electric load (that is, an electrical device), this will be extremely advantageous in view of cost. Thus, a method has been studied that a DC voltage converter (that is, a DC/DC converter) for converting the output voltage such as the DC 36V to 42 V of the power source part into DC 14V is provided in the 42 V vehicle so that the 14 V type electric load can be driven by supplying an electric power from the DC voltage converter.  
         [0004]     However, the DC voltage converter having a capability that while high voltage such as DC 36 V to 42 V is converted into low voltage such as DC 14V to drive several 14 V type electric loads, a heavy electric load such as a lamp for the 14 V vehicle can be further driven is extremely expensive and has problems in view of size, weight and heat generation, etc. Therefore, as for the lamp for the 14 V vehicle, a lamp driving apparatus for a vehicle has been currently studied in which pulse voltage is applied to the lamp by a PWM control (that is, a pulse width modulation control) to adjust electric energy supplied to the lamp so that the lamp for the 14 V vehicle can be driven in the 42 V vehicle. An example of such a lamp driving apparatus for a vehicle will be described by referring to  FIGS. 8 and 9 .  
         [0005]      FIG. 8  is a view showing a circuit structure of a lamp driving apparatus  1  for a vehicle. As described above, the lamp driving apparatus  1  for a vehicle adjusts electric energy supplied to the lamp L 1  by a PWM control. The lamp driving apparatus  1  includes a lamp driving part  3  which is supplied the electric power from a power source part  6  of rated DC 36V to 42 V through a lamp driving power supply line  4  for driving the lamp L 1 , and a control part  2  which controls the driving part  3 . As described above, the power source part  6  has a 42 V motor/generator  7  and a 36V battery  8  capable of charging and discharging. Supply voltage Vb applied to the lamp driving power supply line  4  is DC 36V to DC 42V in accordance with the rated output voltage of the power source part  6 .  
         [0006]     The control part  2  is electrically connected to the lamp driving part  3 . The control part  2  outputs a lamp driving control signal S 11  in accordance with an instructing signal S 1  showing the ON/OFF state of a switch SW 1  for turning on and off the lamp L 1 . The control part  2  supplies the lamp driving control signal S 11  to the lamp driving part  3  to control the operation of the lamp driving part  3 . The lamp driving part  3  is electrically connected to the lamp driving power supply line  4  and a lamp driving line  5 . The lamp driving part  3  applies or not applies voltage to the lamp L 1  through the lamp driving line  5  in accordance with the lamp driving control signal S 11  from the control part  2  so that the Lamp  1  is turned on and off.  FIG. 9  is a timing chart showing the voltage wave-form of the instructing signal S 1 , the voltage wave-form of the lamp driving control signal S 11  and the wave-form of lamp applied voltage VL applied to the lamp L 1  by the lamp driving part  3 .  
         [0007]     As shown in  FIG. 9 , the control part  2  supplies the lamp driving control signal S 11  to the lamp driving part  3  synchronously with a timing that the voltage wave-form of the instructing signal S 1  is switched from a Low level to a High level to allow the lamp driving part  3  to apply the lamp applied voltage VL to the lamp L 1  in accordance with the lamp driving control signal S 11  and to turn on the lamp L 1 . The lamp driving control signal S 11  has a pulse voltage wave-form that a High level and a Low level are alternately repeated. That is, when the control part  2  receives the instructing signal S 1  for turning on the lamp L 1 , the control part  2  outputs the lamp driving control signal S 11  to allow the lamp driving part  3  to supply an electric power to the lamp L 1 .  
         [0008]     The lamp driving control signal S 11  and the lamp applied voltage VL are respectively set a prescribed duty ratio of the pulse width of high level relative to one period when the lamp L 1  is turned on so that proper electric power is supplied to the lamp L 1 . On the other hand, the control part  2  supplies the lamp driving control signal S 11  having the voltage wave-form of low level to the lamp driving part  3  synchronously with a timing that the voltage wave-form of the instructing signal S 1  is switched from the high level to the low level so that the lamp driving part  3  does not apply voltage to the lamp L 1  in accordance with the lamp driving control signal S 11  to turn off the lamp L 1 .  
         [0009]     The lamp driving part  3  includes a switching transistor Tr 1  as an NPN type bipolar transistor Tr 1  and a switching power transistor FET 1  as a P-channel type power MOSFET. The base terminal (B) of the switching transistor Tr 1  is electrically connected to the control part  2  through a resistance R 1  to receive the lamp driving control signal S 11 . Further, a conductor which connects the base terminal (B) of the switching transistor Tr 1  and the resistance R 1  is electrically connected to a ground (G) through a resistance R 2 . Further, the emitter terminal (E) of the switching transistor Tr 1  is electrically connected to the ground (G).  
         [0010]     The gate terminal (G) of the switching power transistor FET 1  is electrically connected to the collector terminal (C) of the switching transistor Tr 1  through a resistance R 3 . A drain terminal (D) of the switching power transistor FET 1  is electrically connected to the lamp driving power supply line  4 . A source terminal (S) of the switching power transistor FET 1  is electrically connected to the lamp driving line  5 .  
         [0011]     A resistance R 4  and a Zener diode D 1  are connected in parallel with the gate terminal (G) and the drain terminal (D) of the switching power transistor FET 1 . The resistance R 4 , the Zener diode D 1  and the resistance R 3  supply electric current which flows from the collector terminal (C) of the switching transistor Tr 1  to the emitter terminal (E) from the lamp driving power supply line  4  when the lamp driving control signal S 11  of high level is supplied to the base terminal (B) of the switching transistor Tr 1  from the control part  2  to turn on the switching transistor Tr 1 . At this time, voltage obtained by dividing the supplied voltage Vd of the lamp driving power supply line  4  is applied to the gate terminal (G) of the switching power transistor FET 1 .  
         [0012]     In the switching transistor Tr 1 , when the lamp driving control signal S 11  applied to the base terminal (B) thereof is located in a high level, the electric current is allowed to flow from the collector terminal (C) of the switching transistor Tr 1  to the emitter terminal (E). Since the electric current is allowed to flow from the lamp driving power supply line  4  through the resistance R 4 , the Zener diode D 1  and the resistance R 3 , the potential of the gate terminal (G) of the switching power transistor FET 1  becomes a low level to turn on the switching power transistor FET 1 . Accordingly, the electric current is supplied to the lamp L 1  electrically connected to the ground (G) from the lamp driving power supply line  4  through the switching power transistor FET 1  and the lamp driving line  5 .  
         [0013]     On the other hand, when the lamp driving control signal S 11  applied to the base terminal (B) of the switching transistor Tr 1  becomes a low level, the electric current does not flow between the collector terminal (C) and the emitter terminal (E) of the switching transistor Tr 1 . Thus, the potential of the gate terminal (G) of the switching power transistor FET 1  reaches a high level (that is, supplied voltage Vd) to turn off the switching power transistor FET 1  so that the electric current is not supplied to the lamp L 1 .  
         [0014]     When, for instance, the switching power transistor FET 1  in the above-described lamp driving apparatus  1  for a vehicle is failed due to a short mode between the drain terminal (D) and the source terminal (S), high voltage such as DC 42V is directly applied to the lamp L 1 , so that the filaments of the lamp L 1  are fused or blown out. When the switching power transistor FET 1  is brought into a failure due to the short mode, if at least the switching power transistor FET 1  is not replaced by another transistor, a normal operation of the lamp driving apparatus  1  for a vehicle cannot be obtained. Therefore, even under an unexpected state such as the generation of an abnormality in a power source system or a circuit system, a redundancy or a fault tolerance that a complete failure does not arise and a function is not lost is required for the lamp driving apparatus  1  for a vehicle.  
       SUMMARY OF THE INVENTION  
       [0015]     It is therefore an object of the present invention to provide a lamp driving apparatus having a protecting function which considers a redundancy or a fault tolerance.  
         [0016]     In order to achieve the above object, according to the present invention, there is provided a lamp driving apparatus comprising:  
         [0017]     a controller, which outputs a switch control signal and a lamp driving control signal in response to an instructing signal for instructing a lamp to be turned on and off;  
         [0018]     a lamp driver, which supplies an electric power to the lamp in accordance with the lamp driving control signal;  
         [0019]     a lamp voltage detector, which detects a voltage applied to the lamp, and outputs a detecting signal showing the applied state of the voltage to the controller;  
         [0020]     a switch, connected to the lamp driver, a lamp driving power supply line, and a preliminary power supply line, and which switches between a first state and a second state selectively; 
        wherein the first state is a state that the electric power for driving the lamp can be supplied to the lamp driver from the lamp driving power supply line; and 
            wherein the second state is a sate that the electric power for driving the lamp can be supplied to the lamp driver from the preliminary power supply line; and    
               
 
         [0023]     a switching controller, which controls a switching of the switch in accordance with the switch control signal,  
         [0024]     wherein the controller outputs the switch control signal so as to make the switch to the first state when the instructing signal for instructing the lamp to be turned on; and  
         [0025]     wherein the controller outputs the switch control signal so as to make the switch to the second state in a case that the detecting signal showing an abnormal applied state of the voltage is received from the lamp voltage detector while the controller outputs the lamp driving control signal for turning on the lump.  
         [0026]     Preferably, the switch includes a relay which having;  
         [0027]     a first relay contact, electrically connected to the lamp driver;  
         [0028]     a second relay contact, electrically connected to the lamp driving power supply line;  
         [0029]     a third relay contact, electrically connected to the preliminary power supply line;  
         [0030]     a contact piece, electrically connecting the first relay contact to the third relay contact in an initial state; and  
         [0031]     an electromagnetic coil, switching the contact piece so as to remove the contact piece from the third relay and so as to electrically connect the first relay contact with the second relay contact when an electric current is supplied to the electromagnetic coil; and  
         [0032]     wherein the switching controller includes a relay driver which supply the electric current to the electromagnetic coil in accordance with the switch control signal.  
         [0033]     Preferably, the lamp driver supplies the electric power to the lamp in accordance with a wave form of the lamp driving control signal.  
         [0034]     Preferably, the controller outputs the lamp driving control signal having a pulse wave form in voltage when the switch is in the first state, and the controller outputs the lamp driving control signal having a DC voltage when the switch is in the second state.  
         [0035]     Preferably, the lamp voltage detector outputs the detecting signal showing the abnormal applied state of the voltage to the controller when detecting that a DC voltage applied to the lamp is higher than a predetermined voltage.  
         [0036]     Preferably, the lamp voltage detector outputs the detecting signal showing the abnormal applied state of the voltage to the controller when detecting that no voltage is applied to the lamp.  
         [0037]     Here, it is preferable that, the controller compares a time length of a high level voltage of the detecting signal with that of the lamp driving control signal, and the controller outputs the switch control signal so as to make the switch to the second state on the basis of the comparing.  
         [0038]     Here, it is preferable that, the controller compares the voltage applied to the lamp with threshold voltage data stored therein, and the controller outputs the switch control signal so as to make the switch to the second state on the basis of the comparing.  
         [0039]     In the above configurations, when the controller receives the instructing signal for instructing the lamp to be turned on, the controller outputs the relay driving control signal for allowing the relay driving part to carry out an operation for supplying the electric current to the electromagnetic coil so that the contact piece is made to come into contact with the second relay contact by the electromagnetic coil, and then, after a state that the electric power for driving the lamp can be supplied to the lamp driver from the lamp driving power supply line through the first and second relay contacts is obtained, the controller outputs the lamp driving control signal of a pulse wave-form for allowing the lamp driver to turn on the lamp. When the controller receives the detecting signal for informing that DC voltage not lower than a prescribed voltage is applied to the lamp from the lamp applied voltage detecting part while the controller outputs the lamp driving control signal for allowing the lamp driver to turn on the lamp, the controller outputs the relay driving control signal for stopping the operation of the relay driver for supplying the electric current to the electromagnetic coil so that the contact piece is made to come into contact with the third relay contact by the electromagnetic coil and the electric power for driving the lamp is supplied to the lamp driver from the preliminary power supply line through the first and third relay contacts. Accordingly, for instance, even when the input circuit of the lamp driver to which the electric power for driving the lamp is supplied from the lamp driving power supply line of high voltage such as DC 42V and the output circuit of the lamp driver for supplying the electric power to the lamp are failed due to the short mode, a detecting signal for informing that DC voltage not lower than a prescribed voltage which is not the pulse wave-form voltage is applied to the lamp as the lamp applied voltage is supplied to the controller from the lamp applied voltage detecting part. The controller outputs the relay driving control signal in response thereto so that the electric power for driving the lamp is supplied to the lamp driver from the preliminary power supply line having voltage lower than, for instance, 14V of the lamp driving power supply line. Therefore, the lamp driving apparatus for a vehicle has a redundancy or a fault tolerance in which a complete failure does not arise and a function is not lost. Thus, even when the above-described failure is generated in the lamp driving apparatus, the lamp can be turned on. In the lamp driving apparatus, since the lamp is turned on after the first and second relay contacts are electrically conducted to each other, even when voltage applied to the lamp driving power supply line is high voltage such as 42V, an arc is not generated in the first and second relay contacts. Consequently, when the controller receives the instructing signal for instructing the lamp to be turned off, if the controller outputs the lamp driving control signal for allowing the lamp driver to performing an operation for turning off the lamp (that is, an operation for supplying no electric power to the lamp) and outputs to the relay driver the relay driving control signal for allowing the contact piece to be separated from the second relay contact and come into contact with the third relay contact by the electromagnetic coil after the supply of the electric power from the lamp driver to the lamp is interrupted, the arc is not generated in the first and second relay contacts. As described above, if, after an electric conduction between the first and second relay contacts is achieved, the lamp is turned on, and further after the lamp is turned off, the electric conduction between the first and second relay contacts is released, an expensive 42V relay in which a countermeasure for breaking the arc is provided does not need to be used and a general purpose inexpensive 14V relay can be used.  
         [0040]     Also, in the above configurations, when the controller receives the instructing signal for instructing the lamp to be turned on, the controller outputs the relay driving control signal for allowing the relay driver to carry out an operation for supplying the electric current to the electromagnetic coil so that the contact piece is made to come into contact with the second relay contact by the electromagnetic coil, and then, after a state that the electric power for driving the lamp can be supplied to the lamp driver from the lamp driving power supply line through the first and second relay contacts is obtained, the controller outputs the lamp driving control signal for allowing the lamp driver to turn on the lamp. When the controller receives the detecting signal for informing that voltage is not applied to the lamp from the lamp applied voltage detecting part while the controller outputs the lamp driving control signal for allowing the lamp driver to turn on the lamp, the controller outputs the relay driving control signal for stopping the operation of the relay driver for supplying the electric current to the electromagnetic coil so that the contact piece is made to come into contact with the third relay contact by the electromagnetic coil and the electric power for driving the lamp is supplied to the lamp driver from the preliminary power supply line through the first and third relay contacts. Accordingly, even when the electric power for driving the lamp cannot be supplied from the lamp driving power supply line due to, for instance, the blow-out of a fuse or the like, if the controller receives a detecting signal for informing that voltage is not applied to the lamp from the lamp applied voltage detecting part while the controller outputs the lamp driving control signal for allowing the lamp driver to turn on the lamp, the controller outputs the relay driving control signal so that the electric power for driving the lamp is supplied to the lamp driver from the preliminary power supply line. Therefore, the lamp driving apparatus for a vehicle has a redundancy or a fault tolerance in which a complete failure does not arise and a function is not lost. Thus, even when the above-described failure is generated in the lamp driving apparatus for a vehicle, the lamp can be turned on. In the lamp driving apparatus for a vehicle according to the present invention, since the lamp is turned on after the first and second relay contacts are electrically conducted to each other, even when voltage applied to the lamp driving power supply line is high voltage such as 42V, an arc is not generated in the first and second relay contacts. Consequently, when the controller receives the instructing signal for instructing the lamp to be turned off, if the controller outputs the lamp driving control signal for allowing the lamp driver to performing an operation for turning off the lamp (that is, an operation for supplying no electric power to the lamp) and outputs to the relay driver the relay driving control signal for allowing the contact piece to be separated from the second relay contact and come into contact with the third relay contact by the electromagnetic coil after the supply of the electric power from the lamp driver to the lamp is interrupted, the arc is not generated in the first and second relay contacts. As described above, if, after an electric conduction between the first and second relay contacts is achieved, the lamp is turned on, and further after the lamp is turned off, the electric conduction between the first and second relay contacts is released, an expensive 42V relay in which a countermeasure for breaking the arc is provided does not need to be used and a general purpose inexpensive 14V relay can be used.  
         [0041]     According to the present invention, there is also provided a lamp driving apparatus, comprising:  
         [0042]     a controller, which outputs a relay driving control signal and a first lamp driving control signal in response to an instructing signal for instructing a lamp to be turned on and off;  
         [0043]     a lamp driver, which supplies an electric power to the lamp in accordance with the first lamp driving control signal;  
         [0044]     a relay, which includes: 
        a first relay contact, electrically connected to the lamp driver;     a second relay contact, electrically connected to the lamp driving power supply line for supplying an electric power to the lamp driver;     a third relay contact, electrically connected to the preliminary power supply line for supplying an electric power to the lamp driver instead of connection to the lamp driving power supply line;     a contact piece, electrically connecting the first relay contact to the third relay contact in an initial state; and     an electromagnetic coil, switching the contact piece so as to remove the contact piece from the third relay and so as to electrically connect the first relay contact with the second relay contact when an electric current is supplied to the electromagnetic coil;        
 
         [0050]     a relay driver, which supplies the electric current to the electromagnetic coil in accordance with the relay driving control signal; and  
         [0051]     a coil voltage detector, which detects a voltage applied to the electromagnetic coil, and outputs a detecting signal showing the applied state of the voltage to the controller,  
         [0052]     wherein the controller outputs the first lamp driving control signal for controlling the lump to be turned on, after the controller outputs the relay driving control signal based on the instructing signal for instructing a lamp to be turned on so that the relay is made to a state that the electric power for driving the lamp can be supplied to the lamp driver from the lamp driving power supply line; and  
         [0053]     wherein the controller outputs a second lamp driving control signal being different from the first lamp driving control signal in kind of a wave form in a case that the detecting signal showing that no voltage is applied to the electromagnetic coil is received from the lamp voltage detector while the controller outputs the relay driving control signal.  
         [0054]     Preferably, the first lamp driving control signal has a pulse wave form in voltage, and the second lamp driving control signal has a DC voltage.  
         [0055]     In the above configurations, when the controller receives the instructing signal for instructing the lamp to be turned on, the controller outputs the relay driving control signal for allowing the relay driver to carry out an operation for supplying the electric current to the electromagnetic coil so that the contact piece is made to come into contact with the second relay contact by the electromagnetic coil, and then, after a state that the electric power for driving the lamp can be supplied to the lamp driver from the lamp driving power supply line through the first and second relay contacts is obtained, the controller outputs the lamp driving control signal of a pulse voltage wave-form for allowing the lamp driver to turn on the lamp. When the controller receives the detecting signal for informing that voltage is not applied to the electromagnetic coil from the coil applied voltage detecting part while the controller outputs the relay driving control signal for allowing the relay driver to supply the electric current to the electromagnetic coil, the controller outputs the lamp driving control signal of DC voltage for allowing the lamp driver to turn on the lamp. Accordingly, even when the relay driver cannot perform an operation for supplying the electric current to the electromagnetic coil due to, for instance, the blow-out of a fuse or the like, if the controller receives a detecting signal for informing that voltage is not applied to the electromagnetic coil from the coil applied voltage detecting part while the controller outputs the relay driving control signal for allowing the relay driver to supply the electric current to the electromagnetic coil, the controller outputs the lamp driving signal of DV voltage for allowing the lamp driver to turn on the lamp. Therefore, the lamp driving apparatus for a vehicle has a redundancy or a fault tolerance in which a complete failure does not arise and a function is not lost. Thus, even when the above-described failure is generated in the lamp driving apparatus for a vehicle, the lamp can be turned on. In the lamp driving apparatus for a vehicle according to the present invention, since the lamp is turned on after the first and second relay contacts are electrically conducted to each other, even when voltage applied to the lamp driving power supply line is high voltage such as 42V, an arc is not generated in the first and second relay contacts. Consequently, when the controller receives the instructing signal for instructing the lamp to be turned off, if the controller outputs the lamp driving control signal for allowing the lamp driver to performing an operation for turning off the lamp (that is, an operation for supplying no electric power to the lamp) and outputs to the relay driver the relay driving control signal for allowing the contact piece to be separated from the second relay contact and come into contact with the third relay contact by the electromagnetic coil after the supply of the electric power from the lamp driver to the lamp is interrupted, the arc is not generated in the first and second relay contacts. As described above, if, after an electric conduction between the first and second relay contacts is achieved, the lamp is turned on, and further after the lamp is turned off, the electric conduction between the first and second relay contacts is released, an expensive 42V relay in which a countermeasure for breaking the arc is provided does not need to be used and a general purpose inexpensive 14V relay can be used.  
         [0056]     The present invention was briefly explained as stated above. Further, embodiments of the present invention described below will be read by referring to the accompanying drawings, so that the detail of the present invention will become more apparent. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0057]     The above objects and advantages of the present invention will become more apparent by describing in detail preferred exemplary embodiments thereof with reference to the accompanying drawings, wherein:  
         [0058]      FIG. 1  is a diagram showing a structure of a circuit of a lamp driving apparatus for a vehicle according to the present invention;  
         [0059]      FIG. 2  is a timing chart of a voltage waveform of an instructing signal, a voltage wave-form of a relay driving control signal, a voltage wave-form of a lamp driving control signal and a wave-form of lamp applied voltage shown in  FIG. 1 ;  
         [0060]      FIG. 3  is a timing chart of the voltage wave-forms of the signals in respective points of  FIG. 1  for explaining the control operations of the lamp driving apparatus  10  for a vehicle upon failure of a switching power transistor FET 1  or a switching transistor Tr 1  under a short mode;  
         [0061]      FIG. 4  is a timing chart of the voltage wave-forms of the signals in the respective points of  FIG. 1  for explaining the control operation of the lamp driving apparatus  10  for a vehicle when the fuse F 42  of a lamp driving power supply line  4  is blown out;  
         [0062]      FIG. 5  is a timing chart of the voltage wave-forms of the signals in the respective points of  FIG. 1  for explaining the control operation of the lamp driving apparatus  10  for a vehicle when the fuse F 14  of a relay driving power supply line  9  is blown out;  
         [0063]      FIG. 6  is a view showing a modified example of the lamp driving apparatus for a vehicle shown in  FIG. 1 ;  
         [0064]      FIG. 7  is a timing chart of the voltage wave-forms of signals in respective points of  FIG. 6 ;  
         [0065]      FIG. 8  is a view showing a structure of a circuit of a usual lamp driving apparatus for a vehicle;  
         [0066]      FIG. 9  is a timing chart of the voltage wave-forms of an instructing signal, the voltage wave-forms of a lamp driving control signal and the wave-forms of lamp applied voltage. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0067]     Now, preferred embodiments of the present invention will be described in detail by referring to the drawings.  FIG. 1  is a view showing a circuit structure of a lamp driving apparatus  10  for a vehicle of the present invention. In this embodiment, parts capable of using the same circuits or signals as those shown in  FIGS. 8 and 9  referred to for explaining the usual lamp driving apparatus  1  for a vehicle are designated by the same reference numerals to clarify them.  
         [0068]     The lamp driving apparatus  10  for a vehicle adjusts electric energy supplied to a lamp L 1  by a PWM control. The lamp driving apparatus  10  for a vehicle includes a control part  20 , a lamp driving part  3 , a relay  40 , a diode (rectifier)  50  and a relay driving part  60 .  
         [0069]     The control part  20  outputs a relay driving control signal S 15  to the relay  40  in accordance with an instructing signal S 1  showing the ON/OFF state of a switch SW 1  for instructing the lamp L 1  to be turned on and off and also outputs a lamp driving control signal S 20  to the lamp driving part  3  to control the operation of the relay  40  and the operation of the lamp driving part  3 . The control part  20  can be composed of a semiconductor integrated circuit such as a CPU and incorporates a processing circuit for outputting the relay driving control signal S 15  and the lamp driving control signal S 20  based on the input of the instructing signal S 1 . The lamp driving part  3  is electrically connected to the control part  20  to supply electric power to the lamp L 1  in accordance with the lamp driving control signal S 20  supplied from the control part  20 .  
         [0070]     The relay  40  includes a first relay contact  42 , a second relay contact  44 , a third relay contact  43 , a contact arm  46  and an electromagnetic coil. The first relay contact  42  is electrically connected to the lamp driving part  3 . The second relay contact  44  is electrically connected to a lamp driving power supply line  4  for supplying electric power to the lamp driving part  3 . The third relay contact  43  is electrically connected to a preliminary power supply line  11  for supplying the electric power to the lamp driving part  3  in place of the lamp driving power supply line  4 . The contact arm  46  is electrically connected to the first relay contact  42  and comes into contact with the third relay contact  43  to make the first and third relay contacts  42  and  43  conduct to each other. The electromagnetic coil allows the contact arm  46  so as to be separated from the third relay contact  43  and come into contact with the second relay contact  44  so that the second relay contact  44  is conduct to the first relay contact  42 .  
         [0071]     When the relay  40  is not driven, the first and third relay contacts  42  and  43  are located in a short state (that is, a conducted state) and the first and second relay contacts  42  and  44  are located in an open state (that is, a non-conducted state). In other words, the relay  40  is what is called a transfer type relay that the first and third relay contacts  42  and  43  are respectively normally close (NC) contact type, and the first and second relay contacts  42  and  44  are respectively normally open (NO) contact type.  
         [0072]     The lamp driving part  3  receives the supply of electric power from a power source part  6  of rated DC 36 V to 42 V output through the lamp driving power supply line  4  to drive the lamp L 1  when the first and second relay contacts  42  and  44  of the relay  40  are located in the short state (that is, a conducted state). The power source part  6  includes a 42V motor/generator  7  and a 36V battery  8  capable of charging and discharging. Supplied voltage Vb applied to the lamp driving power supply line  4  is DC 36V to DC 42V in accordance with the rated output voltage of the power source part  6 . A fuse F 42  for protecting an over-current is inserted into the lamp driving power supply line  4 . A fuse F 1  for protecting an over-current is inserted into a conductor for connecting the first relay contact  42  to the lamp driving part  3 .  
         [0073]     One end  48   a  of an electromagnetic coil  48  of the relay  40  is electrically connected to a relay driving power supply line  9  to receive the supply of an electric current from the relay driving power supply line  9 . The relay driving power supply line  9  is electrically connected to the output of a DC voltage converter (that is, a DC/DC converter)  14  for converting the output voltage of the power source part  6  into DC 14V. As shown in  FIG. 1 , the DC voltage converter  14  is provided mainly for the purpose of supplying an electric power to a main 14V type electric load (that is, an electrical device). Further, a fuse F 14  for protecting an over-current is inserted into the relay driving power supply line  9 .  
         [0074]     A diode  50  serving as a rectifier has its anode terminal (A) electrically connected to the other end  48   b  of the electromagnetic coil  48  to regulate the flow of electric current so that the electric current flows only in one direction from the relay driving power supply line  9  to the electromagnetic coil  48 . A rectifier for regulating the flow of electric current so that the electric current flows only in one direction from the relay driving power supply line  9  to the electromagnetic coil  48  may be used in place of the diode  50 .  
         [0075]     The relay driving part  60  is electrically connected to the cathode terminal (C) of the diode  50  to supply an electric current to the electromagnetic coil  48  from the relay driving power supply line  9  in accordance with the relay driving control signal S 15 . In this connection, a configuration that the cathode terminal (C) of the diode  50  is electrically connected to one end  48   a  of the electromagnetic coil  48  and the anode terminal (A) is electrically connected to the relay driving power supply line  9  may be used. In this case, the relay driving part  60  is electrically connected to the other end  48   b  of the electromagnetic coil  48 .  
         [0076]     The relay driving part  60  is provided with a relay driving transistor Tr 2  as an NPN type bipolar transistor. The base terminal (B) of the relay driving transistor Tr 2  is electrically connected to the control part  20  through a resistance R 5  to receive the relay driving control signal S 15 . Further, a conductor for connecting the base terminal (B) of the relay driving transistor Tr 2  to the resistance R 5  is electrically connected to a ground (G) through a resistance R 6 . An emitter terminal (E) of the relay driving transistor Tr 2  is electrically connected to the ground (G). A collector terminal (C) is electrically connected to the cathode terminal (C) of the diode  50 .  
         [0077]     The lamp driving part  3  is electrically connected to the control part  20 , the lamp driving power supply line  4  and a lamp driving line  5  to apply voltage and apply no voltage to the lamp L 1  through the lamp driving line  5  in accordance with the lamp driving control signal S 20  so that the lamp L 1  is turned on and off. Since the circuit structure of the lamp driving part  3  has been already described by referring to  FIG. 8 , its explanation will be omitted. In this embodiment, although the NPN type bipolar transistor is used as one example of a switching transistor Tr 1 , other transistors such as a PNP type bipolar transistor, an MOSFET, etc. may be properly employed. Further, the phase of the lamp driving control signal S 20  may be suitably inverted in accordance with the type of the switching transistor Tr 1  to be used. Further, in this embodiment, although a P channel type power MOSFET is employed as one example of a switching power transistor FET 1 , other transistors such as an N channel type power MOSFET, a bipolar transistor, etc. may be properly employed. Further, the phase of the lamp driving control signal S 20  may be suitably inverted in accordance with the type of the switching power transistor FET 1  to be used.  
         [0078]     In the lamp driving apparatus  10  for a vehicle constructed as mentioned above, when the control part  20  receives the instructing signal S 1  for instructing the lamp L 1  to be turned on, the control part  20  outputs the relay driving control signal S 15  for allowing the relay driving part  60  to supply an electric current to the electromagnetic coil  48  of the relay  40  from the relay driving power supply line  9 , so that the electromagnetic coil  48  allows the contact arm  46  of the relay  40  to be separated from the third relay contact  43  and come into contact with the second relay contact  44  to make the second relay contact conduct to the first relay contact  42 . Accordingly, an electric power for driving the lamp L 1  can be supplied to the lamp driving part  3  from the lamp driving power supply line  4  through the first and second relay contacts  42  and  44 .  
         [0079]      FIG. 2  is a timing chart showing the voltage wave-form of the instructing signal S 1 , the voltage wave-form of the relay driving control signal S 15 , the voltage wave-form of the lamp driving control signal S 20 , and the wave-form of lamp applied voltage VL applied to the lamp L 1  by the lamp driving part  3 .  
         [0080]     As shown in  FIG. 2 , the control part  20  outputs the relay driving control signal S 15  having the voltage wave-form that the voltage wave-form is switched from a low level to a high level synchronously with a timing that the voltage wave-form of the instructing signal S 1  is changed from a low level to a high level. The instructing signal S 1  at this time instructs the lamp L 1  to be turned on.  
         [0081]     When the base terminal (B) of the relay driving transistor Tr 2  of the relay driving part  60  receives the relay driving control signal S 15  of high level through the resistance R 5 , a state that an electric current is allowed to flow from the collector terminal (C) of the relay driving transistor Tr 2  to the emitter terminal (E) is established so that the electric current flows to the electromagnetic coil  48  of the relay  40  from the relay driving power supply line  9 . At this time, the contact arm  46  is attracted to the electromagnetic coil  48  by an electromagnetic force so that the first and second relay contacts  42  and  44  are brought into a short state. Accordingly, an electric power for driving the lamp L 1  can be supplied to the lamp driving part  3  from the lamp driving power supply line  4 .  
         [0082]     The control part  20  outputs the lamp driving control signal S 20  for allowing the lamp driving part  3  to perform an operation for turning on the lamp L 1  (that is, an operation for supplying electric power to the lamp L 1 ) after the state that the electric power for driving the lamp L 1  can be supplied to the lamp driving part  3  from the lamp driving power supply line  4  is obtained. That is, as shown in  FIG. 2 , a rise timing that the voltage wave-form of the lamp driving control signal S 20  is switched from the low level to the high level is slightly delayed from both a rise timing that the voltage wave-form of the instructing signal S 1  and the voltage wave-form of the relay driving control signal S 15  are switched from the low level to the high level. This lamp driving control signal  20  has a pulse voltage wave-form that the high level and the low level are alternately repeated. The lamp driving part  3  applies the lamp applied voltage VL to the lamp L 1  in accordance with the lamp driving control signal S 20  to turn on the lamp L 1 . As for the lamp driving signal S 20  and the lamp applied voltage VL upon turning on the lamp L 1 , a prescribed duty ratio is set to the pulse width of high level in one period so that a proper electric power is supplied to the lamp L 1 .  
         [0083]     On the other hand, as shown in  FIG. 2 , the control part  20  outputs the lamp driving control signal S 20  for allowing the lamp driving part  3  to perform an operation for turning off the lamp L 1  (that is, an operation for supplying no electric power to the lamp L 1 ) synchronously with a timing that the voltage wave-form of the instructing signal S 1  is switched from the high level to the low level. The instructing signal S 1  instructs the lamp L 1  to be turned off.  
         [0084]     When the lamp driving control signal S 20  applied to the base terminal (B) of the switching transistor Tr 1  becomes a low level, an electric current does not flow between the collector terminal (C) and the emitter terminal (E) of the switching transistor Tr 1 . Thus, the potential of the gate terminal (G) of the switching power transistor FET 1  becomes a high level (that is, supplied voltage Vb), so that the switching power transistor FET 1  is brought into an OFF state and the supply of electric power to the Lamp L 1  from the lamp driving part  3  is interrupted.  
         [0085]     After the supply of electric power to the lamp L 1  from the lamp driving part  3  is interrupted, the control part  20  outputs to the relay driving part  60  the relay driving control signal S 15  for allowing the contact arm  46  to open between the first and second relay contacts  42  and  44 . That is, after the voltage wave-form of the lamp driving control signal S 20  and the wave-form of the lamp applied voltage VL are switched from a high level to a low level, the control part  20  outputs the relay driving control signal S 15  having the wave-form changing from a high level to a low level. As shown in  FIG. 2 , a fall timing that the voltage wave-form of the relay driving control signal S 15  is switched from the high level to the low level is slightly delayed relative to a fall timing that the voltage wave-form of the lamp driving control signal S 20  and the wave-form of the lamp applied voltage VL are switched from the high level to the low level.  
         [0086]     When the relay driving control signal S 15  applied to the base terminal (B) of the relay driving transistor Tr 2  of the relay driving part  60  becomes a low level, an electric current does not flow between the collector terminal (C) and the emitter terminal (E) of the relay driving transistor Tr 2  so that the electric current does not flow to the electromagnetic coil  48  of the relay  40  from the relay driving power supply line  9 . Accordingly, the contact arm  46  attracted by the electromagnetic force of the electromagnetic coil  48  is separated from the second relay contact  44  to come into contact with the third relay contact  43 . Consequently, the electric power for driving the lamp L 1  is not supplied to the lamp driving part  3  from the lamp driving power supply line  4 . Only when an ignition switch IG 1  is located at an IG position or an Acc position, the electric power for driving the lamp L 1  can be supplied to the lamp driving part  3  from the preliminary power supply line  11  through the third and first relay contacts  43  and  42 .  
         [0087]     Accordingly, the lamp driving apparatus  10  for a vehicle allows the contact arm  46  to locate the first and second relay contacts  42  and  44  of the relay  40  in a short state before the lamp L 1  is turned on, and to locate the first and second relay contacts  42  and  44  of the relay  40  in an open state after the lamp L 1  is turned off. In other words, the lamp driving apparatus  10  for a vehicle allows the lamp L 1  to be turned on after the first and second relay contacts  42  and  44  are conducted to each other and releases the electric conduction between the first and second relay contacts  42  and  44  after the lamp L 1  is turned off. Therefore, even when voltage applied to the lamp driving power supply line  4  is high voltage such as 42V, an arc is not generated in the first and second relay contacts  42  and  44 , so that an expensive 42V relay provided with a countermeasure for breaking the arc does not required to be used. A general purpose inexpensive 14V relay can be used. A quantity of electric current supplied to the first and second relay contacts  42  and  44  is reduced since the PWM control is employed.  
         [0088]     The lamp driving apparatus  10  for a vehicle further includes a coil applied voltage detecting part  12  and a lamp applied voltage detecting part  16 . The coil applied voltage detecting part  12  detects voltage applied to the electromagnetic coil  48  and informs the control part  20  of a coil applied voltage detecting signal S 5  showing the applied state of the voltage. The lamp applied voltage detecting part  16  detects lamp applied voltage VL applied to the lamp L 1  by the lamp driving part  3  to inform the control part  20  of a lamp applied voltage detecting signal S 10  showing the applied state f the lamp applied voltage VL.  
         [0089]     The coil applied voltage detecting part  12  includes a resistance R 7  and a resistance R 8 . The control part  20  is electrically connected to the electromagnetic coil  48  through the resistance R 7  for obtaining the coil applied voltage detecting signal S 5 . A conductor for connecting the resistance R 7  to the electromagnetic coil  48  is electrically connected to a ground (G) through the resistance R 8 . The lamp applied voltage detecting part  16  includes a resistance R 9  and a resistance R 10 . The control part  20  is electrically connected to the source terminal (S) of the switching power transistor FET 1  of the lamp driving part  3  and the input terminal of the lamp L 1  through the resistance R 9  so as to obtain the lamp applied voltage detecting signal S 10 . A conductor for connecting the resistance R 9 , the source terminal (S) and the input terminal of the lamp L 1  is electrically connected to a ground (G) through the resistance R 10 .  
         [0090]     As described above, the lamp driving apparatus  10  for a vehicle includes the coil applied voltage detecting part  12  and the lamp applied voltage detecting part  16 . Even when the lamp L 1  is, for instance, a head lamp, a turn lamp, a stop lamp, etc. which are important for moving a vehicle and the failure of the lamp driving apparatus  10  for a vehicle is generated during driving the vehicle, the lamp driving apparatus  10  for a vehicle can turn on the lamp L 1 . Now, the redundancy or the fault tolerance of the lamp driving apparatus  10  for a vehicle in which a complete failure does not arise and a function is not lost will be described below (see  FIGS. 3, 4  and  5 ).  
         [0091]     For example, even when the switching power transistor FET 1  of the lamp driving part  3  is failed due to the short between a drain terminal (D) and a source terminal (S) or the switching transistor Tr 1  is failed due to the short between the collector terminal (C) and the emitter terminal (E), the lamp driving apparatus  10  for a vehicle is provided with the redundancy or the fault tolerance in which the complete failure of the apparatus does not arise and the function of the apparatus is not lost.  
         [0092]     Specifically, in a case that the control part  20  receives the lamp applied voltage detecting signal S 10  for informing that prescribed DC voltage is applied to the lamp L 1  from the lamp applied voltage detecting part  16  while the control part  20  outputs the lamp driving control signal S 20  for allowing the lamp driving part  3  to turn on the lamp L 1 , the control part  20  outputs the relay driving control signal S 15  for stopping the operation of the relay driving part  60  for supplying an electric current to the electromagnetic coil  48 . Thus, the contact arm  46  is brought into contact with the third relay contact  43  by the electromagnetic coil  48 , and an electric power for driving the lamp L 1  is supplied to the lamp driving part  3  from the preliminary power supply line  11  through the first and third relay contacts  42  and  44 .  
         [0093]     That is, the lamp applied voltage detecting signal S 10  for informing that the prescribed DC voltage which is not a pulse wave-form voltage is applied to the lamp L 1  as the lamp applied voltage VL is supplied to the control part  20  from the lamp applied voltage detecting part  16 . The control part  20  outputs the relay driving control signal S 15  in accordance therewith so that an electric power for driving the lamp L 1  is supplied to the lamp driving part  3  from the preliminary power supply line  11  having voltage lower than that of the lamp driving power supply line  4 . The control part  20  compares the time length of the high level voltage of the lamp applied voltage detecting signal S 10  with the time length of the high level voltage of the lamp driving control signal S 20  to decide whether or not the DC voltage having constant voltage which is not the pulse wave-form voltage is applied to the lamp L 1  as the lamp applied voltage VL. Further, in the control part  20 , threshold voltage (data) for deciding whether or not the lamp applied voltage VL at the a high level is the prescribed voltage or higher is stored. The control part  20  monitors the lamp applied voltage VL on the basis of the applied voltage detecting signal S 10  to compare the voltage of the lamp applied voltage detecting signal S 10  with the threshold voltage. As a further example of such a control operation of the control part  20 , when the control part  20  receives from the lamp applied voltage detecting part  16  the lamp applied voltage detecting signal S 10  for informing that the DC voltage not lower than prescribed voltage is applied to the Lamp L 1  while the control part  20  outputs the lamp driving control signal S 20  for allowing the lamp driving part  3  to turn on the lamp L 1 , the control part  20  outputs the relay driving control signal S 15  for preventing the relay driving part  60  from supplying an electric current to the electromagnetic coil  48 . That is, the lamp applied voltage detecting signal S 10  for informing that, for instance, the prescribed DC voltage such as, not 14V but 42V is applied to the lamp L 1  as the lamp applied voltage VL is supplied to the control part  20  from the lamp applied voltage detecting part  16 . In response thereto, the control part  20  outputs the relay driving control signal S 15  so that an electric power for driving the lamp L 1  is supplied to the lamp driving part  3  from the preliminary power supply line  11  having voltage lower than that of the lamp driving power supply line  4   
         [0094]     The control operations of the lamp driving apparatus  10  for a vehicle upon failure of the switching power transistor FET 1  or the switching transistor Tr 1  due to the short are apparent from a timing chart shown in  FIG. 3  with the voltage wave-forms of the signals at the respective points of  FIG. 1 .  
         [0095]     Further, the lamp driving apparatus  10  for a vehicle includes the redundancy or the fault tolerance in which the apparatus is not completely failed, and the function of the apparatus is not lost even when the fuse F 42  of the lamp driving power supply line  4  is blown out. Specifically, when the control part  20  receives from the lamp applied voltage detecting part  16  the lamp applied voltage detecting signal S 10  for informing that voltage is not applied to the lamp L 1  while the control part  20  outputs the lamp driving control signal S 20  for allowing the lamp driving part  3  to turn on the lamp L 1 , the control part  20  outputs the relay driving control signal S 15  for preventing the relay driving part  60  from supplying an electric current to the electromagnetic coil  48 . Thus, the contact arm  46  is brought into contact with the third relay contact  43  by the electromagnetic coil  48  and the electric power for driving the lamp is supplied to the lamp driving part  3  from the preliminary power supply line  11  through the first and third relay contacts  42  and  43 .  
         [0096]     That is, even if an electric power for driving the lamp L 1  cannot be supplied from the lamp driving power supply line  4 , when the control part  20  receives from the lamp applied voltage detecting part  16  the lamp applied voltage detecting signal S 10  for informing that voltage is not applied to the lamp L 1  while the control part  20  outputs the lamp driving control signal S 20  for allowing the lamp driving part  3  to turn on the lamp L 1 , the control part  20  outputs the relay driving control signal S 15  so that the electric power for driving the lamp L 1  is supplied to the lamp driving part  3  from the preliminary power supply line  11 . The control operation of the lamp driving apparatus  10  for a vehicle in a case that the fuse F 42  of the lamp driving power supply line  4  is blown out is apparently shown in a timing chart shown in  FIG. 4  with the voltage wave-forms of the signals in the respective points of  FIG. 1 .  
         [0097]     Further, the lamp driving apparatus  10  for a vehicle is provided with the redundancy or the fault tolerance that the apparatus is not completely failed and the function of the apparatus is not lost even when for instance, the fuse F 14  of the relay driving power supply line  9  is blown out. Specifically, when the control part  20  receives from the coil applied voltage detecting part  12  the coil applied voltage detecting signal S 5  for informing that voltage is not applied to the electromagnetic coil  48  while the control part  20  outputs the relay driving control signal S 15  for allowing the relay driving part  60  to supply an electric current to the electromagnetic coil  48 , the control part  20  outputs the lamp driving control signal S 20  of DC voltage for allowing the lamp driving part  3  to turn on the lamp L 1 .  
         [0098]     That is, even if the control part cannot allow the relay driving part  60  to supply the electric current to the electromagnetic coil  48 , when the control part  20  receives from the coil applied voltage detecting part  12  the coil applied voltage detecting signal S 5  for informing that voltage is not applied to the electromagnetic coil  48  while the control part  20  outputs the relay driving control signal for allowing the relay driving part  60  to supply an electric current to the electromagnetic coil  48 , the control part  20  outputs the lamp driving control signal S 20  of DC voltage for allowing the lamp driving part  3  to turn on the lamp L 1 . The control operation of the lamp driving apparatus  10  for a vehicle when the fuse F 14  of the relay driving power supply line  9  is blown out is apparent from a timing chart shown in  FIG. 5  with the voltage wave-forms of the signals in the respective points of  FIG. 1 .  
         [0099]     In the above-described embodiment, although one lamp L 1  is assigned to one relay  40 , a plurality of lamps (for instance, a head lamp, a turn lamp, a stop lamp, etc.) which are considered to be important lighting member in the vehicle may be assigned to one relay  40 . When a plurality of lamps are assigned to one relay  40  as described above, a cost can be reduced, because a plurality of relays  40  do not need to be provided. The above-described lamp driving apparatus for a vehicle will be described by referring to  FIG. 6 .  
         [0100]      FIG. 6  shows a second embodiment of the lamp driving apparatus  10  for a vehicle shown in  FIG. 1 . A lamp driving apparatus  100  for a vehicle in which the plural lamps L 1 , L 2 , . . . , Ln are assigned to one relay  40  is shown in  FIG. 6 . Parts which can use the same circuits or signals as those shown in  FIGS. 1 and 2  referred to for explaining the above-described lamp driving apparatus  10  for a vehicle are designated by the same reference numerals to make them clear.  
         [0101]     A control part  200  outputs a relay driving control signal S 15  to the relay  40  and lamp driving control signals S 20 , S 30 , S 40  respectively to a plurality of lamp driving circuits  3  in accordance with instructing signals S 1 , S 2  . . . ,Sn showing the ON/OFF states of switches SW 1 , SW 2  . . . , SWn respectively for instructing the lamps L 1 , L 2 ,Ln to be turned on and off to control the operation of the relay  40  and the operations of the lamp driving circuits  3 . A plurality of lamp driving circuits  3  are respectively electrically connected to a control part  200  to supply electric power to the lamps L 1 , L 2  . . . ,Ln in accordance with the lamp driving control signals S 20 , S 30 , S 40  supplied from the control part  200 . To the first relay contact  42  of the relay  40 , a plurality of lamp driving parts  3  (note: In  FIG. 6 , the illustration of the lamp driving parts  3  for the lamps L 2  and Ln is simplified) are electrically connected.  
         [0102]      FIG. 7  shows a timing chart of voltage wave-forms of the signals at the respective points of  FIG. 6 . As shown in  FIG. 7 , the driving apparatus  100  for a vehicle allows the first and second relay contacts of the relay  40  to be located in a short state before at least one of the lamps L 1 , L 2 , . . . ,Ln is turned on, and after all the lamps L 1 , L 2 , . . . ,Ln are turned off, the apparatus allows the first and second relay contacts  42  and  44  of the relay  40  to be located in an open state. Since other circuit structures, the operations of the circuit or the like of the lamp driving apparatus  100  for a vehicle are readily estimated from the already described contents by referring to FIGS.  1  to  5 , the description thereof will be omitted.  
         [0103]     The present invention is not limited to the above-described embodiment or the modified example, modifications, improvements, or the like may be suitably made. Further, when the present invention can be achieved, any number of respective components, any places where they are arranged, etc. in the above-described embodiment and the modified example, and any wave-forms, any numeric values, etc. may be used and they are not limitative.  
         [0104]     The above-described wave-forms of the signals are not limited to rectangular waves as shown in FIGS.  2  to  5  and  7 , for instance, a triangular wave, a serrated wave, etc. may be suitably used. Further, in the above-described embodiment, although the instructing signal having a voltage wave-form formed by the potential difference between the high level and the low level is used, for instance, several kinds of logic signals may be respectively inputted to the control part to deduce the ON/OFF states of the switches on the basis of these logic signals by the control part and properly form the relay driving control signal and the lamp driving control signal.