Patent Publication Number: US-2022239065-A1

Title: Light emitting module

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
     The present application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2021-010873, filed on Jan. 27, 2021. The contents of this application are incorporated herein by reference in their entirety. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present disclosure relates to a light-emitting module. 
     Discussion of the Background 
     In recent years, light-emitting modules equipped with laser diodes (LD) have been developed for lighting devices and vehicular head lamps. In such light-emitting modules, a laser light emitted from an LD is irradiated to the converting member, the wavelength of the laser light is converted by the converting member, and is emitted to the outside as a light suitable for lighting. Laser light has relatively high coherence, but by passing through the converting member, light with lower coherence than that of the laser light is emitted to the outside. 
     In such light emitting modules, if the converting member is damaged due to an external impact, laser light may leak to the outside of the light-emitting module and may enter the human eye. For this reason, there has been proposed a stop system that is configured to stop lasing of the LD when the converting member is damaged (for example, see JP 2013-191479A). When the converting member is damaged, reliable termination of the lasing is required in such a stopping system. 
     SUMMARY OF THE INVENTION 
     The embodiments of the present invention are devised in the light of such circumstances, and it is hence advantageously provide a light-emitting module in which lasing can be reliably terminated when the converting member is damaged. 
     A light-emitting module according to one embodiment of the present disclosure comprises: a laser element configured to emit a laser light; a converting member configured to reduce coherence of the laser light; a sense wiring being electrically connected to the converting member; an electric potential determining circuit configured to output a first value when an electric potential at the first end of the sense wiring is in a predetermined range, and to output a second value when the electric potential at the first end of the sense wiring is out of the predetermined range; a first switching element electrically connected in series to the laser element, the first switching element being configured to become conductive when the output of the electric potential determining circuit is the first value, and to become non-conductive when the output of the electric potential determining circuit is the second value; and a second switching element electrically connected in parallel to a circuit comprising the laser element and the first switching element, the second switching element being configured to become conductive when the output of the electric potential determining circuit is the second value, and to become non-conductive when the output of the electric potential determining circuit is the first value. 
     A light-emitting module according to another embodiment of the present disclosure, the light-emitting module includes: a laser element configured to emit a laser light; a converting member configured to reduce coherence of the laser light; a sense wiring electrically connected to the converting member; an electric potential determining circuit being configured to output a first value when an electric potential at the first end of the sense wiring is in a predetermined range, and to output a second value when the electric potential at the first end of the sense wiring is out of the predetermined range; and a first switching element electrically connected in series to the laser element, the first switching element being configured to become conductive when the output of the electric potential determining circuit is the first value, and to become non-conductive when the output of the electric potential determining circuit is the second value. The electric potential determining circuit includes: a first comparator being configured to output the first value when the electric potential at the first end of the sense wiring is lower than a first reference potential, and to output a second value when the electric potential at the first end of the sense wiring is higher than the first reference potential; a second comparator being configured to output the first value when the electric potential at the first end of the sense wiring is lower than the first reference potential, and to output the second value when the electric potential at the first end of the sense wiring is higher than the first reference potential; a third comparator being configured to output the first value when the electric potential at the first end of the sense wiring is higher than a second reference potential that is lower than the first reference potential, and to output the second value when the electric potential at the first end of the sense wiring is lower than the second reference potential; and a fourth comparator being configured to output the first value when the electric potential at the first end of the sense wiring is higher than the second reference potential, and to output the second value when the electric potential at the first end of the sense wiring is lower than the second reference potential. 
     According to the embodiments of the present disclosure, a light-emitting module is provided that can reliably stop laser light in the event of damage to the converting member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  is a block diagram of a light-emitting module according to one embodiment; 
         FIG. 2  is a schematic cross-sectional view showing a light-emitting part of a light-emitting module according to one embodiment; 
         FIG. 3  is a circuit diagram of a light-emitting module according to one embodiment; and 
         FIG. 4  is a chart illustrating operation of a light-emitting module according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Structure 
     Next, one embodiment of the present disclosure will be described.  FIG. 1  is a block diagram of a light-emitting module according to the present embodiment.  FIG. 2  is a schematic cross-sectional view showing a light-emitting part of a light-emitting module according to the present embodiment.  FIG. 3  is a circuit diagram showing a configuration of a light-emitting module according to the present embodiment. 
     As shown in  FIG. 1 , the light-emitting module  1  according to the present embodiment includes a light-emitting part  10  and a power supply part  30 . The power supply part  30  is electrically connected to an external power source  100  to supply electric power to the light-emitting part  10 . The light-emitting part  10  is caused to emit light L 1  when the power is supplied from the power supply part  30 . 
     Light-Emitting Part  10   
     As shown in  FIG. 2 , the light-emitting part  10  includes a casing  11 . The casing  11  has a box-shape with an opening in an upper surface. For illustration purposes, the top surface in  FIG. 2  is referred to as the upper surface, but a different direction may be indicated as the up/down direction in the light-emitting module  1 . The casing  11  is made of an electrically insulating material. The casing  11  can be formed of ceramics materials as its main component and, for example, can contain aluminum nitride, silicon nitride, aluminum oxide or silicon carbide. 
     A sub-mount  12  and a light-reflecting member  13  are disposed in the casing  11 . The sub-mount  12  and the light-reflecting member  13  are secured to the bottom surface  11   a  in the casing  11 . The sub-mount  12  is, for example, a block of a substantially rectangular parallelepiped shape with ceramic or metal materials as its main material. A laser element  14  is disposed on the sub-mount  12 . That is, the laser element  14  is arranged in the casing  11 . The light laser element  14  is, for example, a laser diode (LD) containing a group III nitride-based semiconductor having the laser element. The laser element  14  is configured to emit laser light L 0 . The laser light L 0  is blue, for example. At least one laser element  14  is employed. A plurality of laser elements  14  may be employed. A plurality of laser elements  14  can be electrically connected in series or a in parallel. 
     The light-reflecting member  13  includes, for example, a block formed of glass or semiconductor, and a light-reflecting film disposed on the surfaces of the block. When the block is formed of a light-reflecting material such as a metal material, it is not necessary to have a light reflectance film. The light-reflecting member  13  has a light-reflecting surface  13   a.  The light-reflecting surface  13   a  faces the laser element  14  and is tilted against the bottom surface  11   a  in the casing  11 . If the light-reflecting member  13  has a light-reflecting film, the surface on which the light-reflecting film is disposed is the light-reflecting surface  13   a.    
     The upper inner surfaces of the lateral wall  11   b  of the casing  11  have step structures  11   c  and  11   d.  The step structures  11   c  and  11   d  have a frame shape along the outer edge of the casing  11  in a top view. The step structure  11   d  is located at an upper and outer side with respect to the step structure  11   c.    
     A light-transmissive member  15  is disposed on the step structure  11   c  that is located at a lower and inner side than the step structure  11   d.  The light-transmissive member  15  is a plate-shaped member that transmits the laser light L 0  therethrough, and formed of, for example, sapphire or glass. The outer peripheral portion of the light-transmissive member  15  is secured to the step structure  11   c.  With this arrangement, the light-transmissive member  15  hermetically seals the opening of the casing  11 . 
     A wiring pattern  16  is disposed on the upper surface of the light-transmissive member  15 . The wiring pattern  16  is disposed on the upper surface of the light-transmissive member  15  by, for example, sputtering. A pair of wirings  17  are connected to corresponding portions of the wiring pattern  16 , respectively. The pair of wirings  17  are electrically connected to a power supply part  30  through corresponding conductive members disposed within a body of the casing  11 . A converting member  22  is disposed above the light-transmissive member  15  and the wiring pattern  16 . The converting member  22  includes a support  18  and a coherence reduction part  19 . The support  18  is, for example, formed of ceramic material and has a plate-like shape with a through-opening  18   a.    
     The coherence reduction part  19  is engaged in the through-opening  18   a  of the support  18 . The support  18  supports the coherence reduction part  19 . The coherence reduction part  19  is located where the laser light L 0 , which is emitted from the laser element  14  and is reflected at the light-reflecting surface  13   a  of the light-reflecting member  13  and is then transmitted through the light-transmissive member  15 , enters. In other words, the coherence reduction part  19  is located in the optical path of the laser light L 0 . The coherence reduction part  19  is, for example, formed of ceramics. In the coherence reduction part  19 , for example, a fluorescent material is contained in a base material formed of a light-transmissive inorganic material. The inorganic light-transmissive material is, for example, aluminum oxide. 
     The laser light L 0  emitted from the laser element  14  is guided to enter the coherence reduction part  19 , where the coherence of the laser light L 0  is reduced. For example, the coherent reduction part  19  contains a fluorescent material configured to convert the laser light L 0  to light of a different wavelength. In other words, a member containing a fluorescent material is used as the coherence reduction part  19 , for example. The fluorescent material contained in the coherence reduction part  19  absorbs, for example, the blue laser light L 0  and emits yellow light. As a result, blue light, which is diffused laser light L 0 , and yellow light emitted from the fluorescent material, are emitted from the coherence reduction part  19 , such that collective white light L 1  is emitted from the coherence reduction part  19 . The coherence reduction part  19  containing a fluorescent material allows for a reduction of coherence of the laser light L 0 , which allows emission of light L 1  having lower coherence than that of the laser light L 0 . Alternatively, a light diffusing member such as a light-diffusing plate may be used as the coherence reduction part  19 . In this case, the coherence reduction part  19  does not have to contain a fluorescent material. 
     Examples of the fluorescent material contained in the coherence reduction part  19  include a yttrium aluminum garnet (YAG) fluorescent material activated with cerium, a lutetium aluminum garnet (LAG) fluorescent material activated with cerium, a nitrogen-containing calcium aluminosilicate (CaO—Al 2 O 3 —SiO 2 ) fluorescent material activated with europium and/or chromium, a silicate fluorescent material ((Sr,Ba) 2 SiO 4 ) activated with europium, an α-sialon fluorescent material, and a ß-sialon fluorescent material. Among those, it is preferable to use a YAG fluorescent material, which has good heat resistance. 
     A sense wiring  20  is electrically connected to the converting member  22 . The sense wiring  20  is secured, for example, to a lower surface of the converting member  22 , that is, to a surface that faces toward the light-transmissive member  15 . Other than the lower surface of the converting member  22 , the position of the sense wiring  20  can be appropriately determined. For example, the sense wiring  20  can be disposed on an upper surface of the converting member  22 . The sense wiring  20  can also be electrically connected to both the support  18  and the coherence reduction part  19  of the converting member  22 , or to only one of them. When the sense wiring  20  is electrically connected only to the support  18 , a reduction in the extraction efficiency of the light caused by absorption of light by the sense wiring  20  can be suppressed. 
     The sense wiring  20  is formed of an electrically conductive material. The sense wiring  20  is formed of, for example, a material that is light-transmissive and electrically conductive. The sense wiring  20  is formed of, for example, indium tin oxide (ITO). The sense wiring  20  can include a metal material. The sense wiring  20  is electrically connected to a wiring pattern  16 . Accordingly, the sense wiring  20  is electrically connected to the power supply part  30  through the wiring pattern  16  and the wirings  17 . The converting member  22  and the sense wiring  20  can be located spaced apart from the casing  11  and a lid (for example the light-transmissive member  15 ) which encapsulate the laser element  14 . In this case, the wiring pattern  16  and the wirings  17  are optional, and the sense wiring  20  is electrically connected to the power supply part  30  through the wirings that is disposed spaced apart from the casing  11 , for example. 
     Power Supply Part  30   
     As shown in  FIG. 3 , the power supply part  30  includes a wiring substrate  50  on which a first switching element  31 , a second switching element  32 , a third switching element (first transistor  33 ), a first resistance element  34 , a second resistance element  35 , a third resistance element  36 , a first comparator  41 , a second comparator  42 , a third comparator  43 , and a fourth comparator  44  are mounted. The first comparator  41 , the second comparator  42 , the third comparator  43 , and the fourth comparator  44  constitute an electric potential determining circuit  40 . The wiring substrate  50  and the light-emitting part  10  can be electrically connected by, for example, wirings with connectors. Alternatively, the power supply part  30  and the light-emitting part  10  may be secured to a single board. 
     Through an external power source  100 , a first reference potential V 1 , a second reference potential V 2 , a third reference potential V 3 , a fourth reference potential V 4 , a fifth reference potential V 5 , a sixth reference potential V 6 , an anode potential Va, and a cathode potential Vc are supplied to the power supply part  30 . The third reference potential V 3  and the sixth reference potential V 6  may be supplied through the same wire. The fourth reference potential V 4  and the fifth reference potential V 5  may be supplied via the same wire. It is not necessary that all reference potentials are supplied from the external power source  100 . For example, the first reference potential V 1  and the second reference potential V 2  can be supplied from a circuit mounted on the wiring substrate  50 . 
     The first reference potential V 1  is lower than the fifth reference potential V 5  and higher than the second reference potential V 2 . The second reference potential V 2  is lower than the first reference potential V 1  and higher than the sixth reference potential V 6 . In other words, the reference potentials are in a descending order of V 5 &gt;V 1 &gt;V 2 &gt;V 6 . 
     In one example, the fifth reference potential V 5  is 5V (supply potential), and the first reference potential V 1  is in a range of 3 to 4.5V, the second reference potential V 2  is in a range of 0.5 to 2V, and the sixth reference potential V 6  is 0V (ground potential). The third reference potential V 3  is 0V (ground potential) and the fourth reference potential V 4  is 5V (power source potential). In one example, the anode potential Va is in a range of 5 to 24 V, and the cathode potential Vc is in a range of 0 to 10 V and is lower than the anode potential Va. 
     A first end  20   a  of the sense wiring  20  is electrically connected to a first node Na and a first end  36   a  of the third resistance element  36 , and a second end  20   b  of the sense wiring  20  is electrically connected to the sixth reference potential V 6 . The second end  36   b  of the third resistance element  36  is electrically connected to the fifth reference potential V 5 . Accordingly, the third resistance element  36  and the sense wiring  20  are connected in series between the fifth reference potential V 5  and the sixth reference potential V 6 . 
     The first comparator  41 , the second comparator  42 , the third comparator  43 , and the fourth comparator  44  (hereinafter collectively referred to as “comparators”) constitute an electric potential determining circuit  40 . Each of the comparators has two input terminals and one output terminal, so as to compare potentials at the two input terminals and outputs a potential corresponding to the comparison result. Each of the comparators is supplied with a high potential side reference potential and a low potential side reference potential. The high potential side reference potential is, for example, 5V (supply potential) and the low potential side reference potential is, for example, 0V (ground potential), but other appropriate potential values can be employed. The high potential side reference potentials of the four comparators shown in  FIG. 3  can all be the same potential, and the low potential side reference potentials of the four comparators shown in  FIG. 3  can all be the same potential. 
     The first input terminal of the first comparator  41  is connected to the first reference potential V 1 , and the second input terminal is connected to the first end  20   a  (first node Na) of the sense wiring  20 . The first comparator  41  outputs a first value (H) when the potential at the first end  20   a  of the sense wiring  20  is lower than the first reference potential V 1 , and outputs a second value (L) when the potential at the first end  20   a  is higher than the first reference potential V 1 . For example, the first value (H) is the potential that sets the switching elements and the transistors that constitutes the power supply part  30  to a conductive state (ON state), and the second value (L) is the potential that sets these switching elements and the transistors to a non-conductive state (OFF state). For example, when the low potential side reference potential of the first comparator  41  is 0 V (ground potential), the second value (L) will be 0 V. 
     Similarly for the second comparator  42 , the first input terminal is connected to the first reference potential V 1 , and the second input terminal is electrically connected to the first end  20   a  (first node Na) of the sense wiring  20 . The second comparator  42  outputs a first value (H) when the potential at the first end  20   a  of the sense wiring  20  is lower than the first reference potential V 1 , and a second value (L) when the potential at the first end  20   a  is higher than the first reference potential V 1 . In other words, the second comparator  42  executes the same operation as the first comparator  41 . 
     The first input terminal of the third comparator  43  is electrically connected to the first end  20   a  (first node Na) of the sense wiring  20 , and the second input terminal is electrically connected to the second reference potential V 2 . The third comparator  43  outputs a first value (H) when the potential of the first end  20   a  of the sense wiring  20  is higher than the second reference potential V 2 , and a second value (L) when the potential of the first end  20   a  is lower than the second reference potential V 2 . 
     Similarly for the fourth comparator  44 , the first input terminal is electrically connected to the first end  20   a  (first node Na) of the sense wiring  20 , and the second input terminal is electrically connected to the second reference potential V 2 . The fourth comparator  44  outputs a first value (H) when the potential of the first end  20   a  of the sense wiring  20  is higher than the second reference potential V 2 , and the second value (L) when the potential of the first end  20   a  is lower than the second reference potential V 2 . In other words, the fourth comparator  44  executes the same operation as the third comparator  43 . 
     The output terminal of the first comparator  41 , the output terminal of the second comparator  42 , the output terminal of the third comparator  43 , and the output terminal of the fourth comparator  44  are electrically connected to the second node Nb. The second node Nb is the output point for the electric potential determining circuit  40 . When all the outputs of all the comparators are all at the first value (H), the potential of the second node Nb is at the first value (H). On the other hand, when the output of one of the comparators is a second value (L), the potential of the second node Nb is drawn to the low potential side reference potential, resulting in a second value (L). 
     Accordingly, the electric potential determining circuit  40  outputs a first value (H) when the potential at the first end  20   a  (first node Na) of the sense wiring  20  is in a predetermined range, that is, in a range that is higher than the second reference potential V 2  and lower than the first reference potential V 1 . In the description below, the range of the potential that is higher than the second reference potential V 2  and lower than the first reference potential V 1  will be referred to as “normal range”. On the other hand, the electric potential determining circuit  40  outputs a second value (L) when the potential at the first end  20   a  (first node Na) of the sense wiring  20  is outside of the normal range, that is, lower than the second reference potential V 2  or higher than the first reference potential V 1 . 
     A second resistance element  35  is electrically connected between the second node Nb and the fourth reference potential V 4  (for example, the power potential). The first resistance element  34  and the third switching element (first transistor  33 ) are connected in series between the circuit that applies the fourth reference potential V 4  and the circuit that applies the third reference potential V 3  (for example, ground potential). Although the third switching element is not limited to a transistor, the use of the first transistor  33  as the third switching element can increase the switching speed. The first transistor  33  is, for example, an n-channel type field-effect transistor (FET). The first transistor  33  is, for example, an n-channel type metal-oxide-semiconductor field-effect transistor (MOSFET). The first transistor  33  includes a third gate  33   g,  a third source  33   s,  and a third drain  33   d.  The first transistor  33  is in a conducting state when the first value (H) is inputted in the third gate  33   g,  and in a non-conducting state when the second value (L) is inputted. In other words, the threshold voltage at which the third gate  33   g  is switched on is between the first value (H) and the second value (L). 
     The third gate  33   g  of the first transistor  33  is electrically connected to the output point of the second node Nb, that is, the electric potential determining circuit  40 , and the third source  33   s  is electrically connected to the third reference potential V 3  (for example: ground potential). The third drain  33   d  is electrically connected to the first end of the first resistance element  34 . The second end of the first resistance element  34  is electrically connected to the fourth reference potential V 4  (for example, the power source potential). 
     In  FIG. 3 , a transistor (second transistor) is used as the second switching element  32 . The second switching element  32  is, for example, an n-channel type FET. The second switching element  32  is, for example, an n-channel type MOSFET. The second switching element  32  includes a second gate  32   g,  a second source  32   s,  and a second drain  32   d.  The second gate  32   g  is electrically connected to the third node Nc, which is the connection point of the first transistor  33  and the first resistance element  34 . The second source  32   s  is electrically connected to the cathodic potential Vc. The second drain  32   d  is electrically connected to the anode potential Va. The resistance of the first resistance element  34  is lower than the resistance between the second gate  32   g  of the second switching element  32  and the second source  32   s.  Although the second switching element  32  is not limited to a transistor, it is preferable to use a transistor as the second switching element  32  because transistors are suitable for carrying relatively large currents. 
     The electric potential at the connection point of the first resistance element  34  and the first transistor  33 , that is, the electric potential at the third node Nc, is substantially equal to the third reference potential V 3  when the first transistor  33  is in the conducting state. Accordingly, the third reference potential V 3  is set to a value lower than the threshold value at which the second switching element  32  becomes conductive. With this arrangement, when the first transistor  33  is in the conducting state, the second switching element  32  does not conduct electrically. When the second value “L” and the third reference potential V 3  are equal potentials (for example, ground potential), the potential of the third node Nc when the first transistor  33  is in the conductive state is approximately equal to the second value “L”. 
     On the other hand, when the first transistor  33  is in a non-conductive state, the potential of the third node Nc is drawn to the fourth reference potential V 4  (for example, the power source potential), resulting in a higher potential than when the first transistor  33  is in a conductive state. The fourth reference potential V 4  is set such that the potential of the third node Nc when the first transistor  33  is in a non-conductive state is higher than the threshold for the second switching element  32  to be in a conductive state. The potential of the third node Nc when the first transistor  33  is in a non-conductive state is, for example, equal to the first value “H”. Therefore, when the first transistor  33  is in a non-conductive state, the second switching element  32  is in a conductive state. Thus, the second switching element  32  is in a conductive state when the output of the electric potential determining circuit  40 , that is, the potential of the second node Nb is at the second value (L), and is in a non-conductive state when the output of the electric potential determining circuit  40  is at the first value (H). 
     In  FIG. 3 , a transistor (third transistor) is used as the first switching element  31 . The first switching element  31  is, for example, is an n-channel type FET. The first switching element  31  is a transistor having a same conductivity type as that of the second switching element  32  and the first transistor  33 , for example, an n-channel MOSFET. The first switching element  31  includes a first gate  31   g,  a first source  31   s,  and a first drain  31   d.  The first gate  31   g  is connected to the second node Nb, i.e. the output point of the electric potential determining circuit  40 . Accordingly, the first switching element  31  switches between a conductive state and a non-conductive state depending on the potential of the second node Nb, i.e. the output point of the electric potential determining circuit  40 . The first switching element  31  is in a conductive state when the potential at the output point of the electric potential determining circuit  40  is at the first value (H) and not at the second value (L). Other than transistors, any suitable element that can perform such an operation can be employed for the first switching element  31 , but it is preferable to use a transistor as the first switching element  31  because the transistor is suitable for earning relatively large current. 
     The first drain  31   d  of the first switching element  31  is connected to the cathode of laser element  14 . The first source  31   s  is connected to a circuit that applies a cathodic potential Vc. The anode of laser element  14  is connected to a circuit that applies an anode potential Va. With this arrangement, the laser element  14  and the first switching element  31  are connected in series between the circuits that apply anode potential Va and cathode potential Vc. The second switching element  32  is connected in parallel to the circuit that includes the laser element  14  and the first switching element  31 , and between the circuits that apply anode potential Va and cathode potential Vc. 
     The current that flows to the laser element  14  can flow to the first switching element  31  and the second switching element  32 . On the other hand, the current that flows to the laser element  14  does not flow to the first transistor  33 . For this reason, a rated value of the drain current of the first transistor  33  can be lower than a rated value of the first switching element  31  and a rated value of the second switching element  32 . The rated value of the drain current of the first transistor  33  can be equal to or less than 10% or equal to or less than 1% of the nominal value of the first switching element  31  and of the nominal value of the second switching element  32 . For example, the rated values of the drain current of the first switching element  31  and the second switching element  32  are in a range of several tens to several hundreds of amperes (A), and the rated value of the drain current of the first transistor  33  can be less than 1 A. Reducing the rated value of the first transistor  33  allows for a reduction in the size and cost of the light-emitting module  1 . 
     Operation 
     Next, operation of the light-emitting module according to the present embodiment will be described.  FIG. 4  is a chart illustrating operation of a light-emitting module according to the present embodiment. In the present embodiment, the term “normal mode” indicates that the sense wiring  20  is in a normal state, the term “open mode” indicates that an open failure occurs in the sensing wiring  20 , and the term “short circuit mode” indicate that a short circuit occurs in the sense wiring  20 . 
     When the light emitting module  1  is normal, the sensing wiring  20  is also normal, and the light-emitting module  1  is in “normal mode”. In the normal mode, it is required that laser element  14  emits light when power is supplied to light-emitting module  1 , that is, lasing occurs in the laser element  14  and a laser light L 0  is emitted from the laser element  14 . 
     On the other hand, for example, when the converting member  22  is damaged and disconnects the sense wiring  20 , it is in an “open mode”. In the open mode, in order to prevent the laser light L 0  from leaking to the outside of the casing  11 , termination of laser oscillation of the laser element  14  is demanded. In the present specification, “termination of lasing” refers to stop the lasing of the laser element  14  so that the laser light L 0  is not emitted. For example, a state in which an electric current below the threshold of lasing is presence in the laser element  14  is included in “termination of lasing”. 
     Also, for example, when short circuit of the sense wiring  20  occurs due to a foreign material attaching on the sense wiring  20 , it is in a “short circuit mode”. Also, when a foreign material is attached to the conductive path that is electrically connected to sense wiring  20  and not to the sense wiring  20  and causes a substantially the same short circuit as short circuit of the sense wiring  20 , it is also included in “short circuit mode”. In the short circuit mode, even when the converting member  22  is damaged and disconnection of the sense wiring  20  occurs, continuity of the sense wiring  20  may be maintained by a foreign object, and it is possible that the damage of the converting member  22  cannot be detected. For this reason, even in the short circuit mode, termination of lasing of the laser element  14  is required. 
     In  FIG. 4 , when the potential at the output terminal of each of the comparators or the potential at each of the nodes is at the first value, it is denoted as “H” and when it is at the second value, it is denoted as “L”. The two types of potentials that the third node Nc would take may not necessarily match the first and second values, but  FIG. 4  shows an example where they match. When a comparator, a switching element or a transistor fails in an open state, it is denoted as “NG”. When a switching element or a transistor is in continuity, it is denoted as “ON”, while when a switching element or a transistor is not in continuity, it is denoted as “OFF”. When the laser element  14  is emitting light, it is denoted as “ON” and when the laser element  14  is not emitting light, it is denoted as “OFF”. In  FIG. 4 , the row numbers are included for the convenience of explanation. Next, the operation of the light-emitting module  1  in each mode will be described. 
     Normal Mode 
     First, an operation in a normal mode will be described. As illustrated above, in a normal mode, the converting member  22  is normal, and the sense wiring  20  is also normal. 
     With reference to the first row of  FIG. 4 , each circuit element in power supply part  30  is also normal. In the present specification, the term “circuit element” refers collectively to each comparator, the first switching element  31 , the second switching element  32 , and the first transistor  33 . 
     As shown in  FIG. 1 , when the light-emitting module  1  is electrically connected to an external power source  100 , a predetermined potential is applied to each part of the light-emitting module  1 . More specifically, a fifth reference potential V 5  (for example, power source potential) and a sixth reference potential V 6  (for example, ground potential) are applied to both ends of the circuit to which the third resistance element  36  and the sense wiring  20  are connected in series. In addition, the first reference potential V 1  and the second reference potential V 2  are applied to the electric potential determining circuit  40 . The second reference potential V 2  is lower than the first reference potential V 1 . The fourth reference potential V 4  (for example, power source potential) and the third reference potential V 3  (for example, ground potential) are applied to both ends of the circuit where the first resistance element  34  and the first transistor  33  are connected in series. Further, anode potential Va and cathode potential Vc are applied to both ends of the circuit where the laser element  14  and the first switching element  31  are connected in series. 
     The potential difference between the fifth reference potential V 5  and the sixth reference potential V 6  is divided by the third resistance element  36  and the sense wiring  20 . This results in the potential of the first node Na being within the range (normal range) which is higher than the second reference potential V 2  and lower than the first reference potential V 1 . 
     The first comparator  41  compares the first reference potential V 1  with the potential at the first node Na. In the state shown in the first row of  FIG. 4 , the first comparator  41  outputs the first value (H) because the potential at the first node Na, that is, the potential at the first end  20   a  of the sense wiring  20  is lower than the first reference potential V 1 . The second comparator  42  also compares the first reference potential V 1  and the potential of the first node Na with outputs the first value (H) because the potential of the first node Na is lower than the first reference potential V 1 . 
     The third comparator  43  compares the potential of the first node Na with the second reference potential V 2 . Because the potential of the first node Na is higher than the second reference potential V 2 , the third comparator  43  outputs the first value (H). Similarly, the fourth comparator  44  compares the potential of the first node Na with the second reference potential V 2  and outputs the first value (H) because the potential of the first node Na is higher than the second reference potential V 2 . Thus, because all the comparators output the first value (H), the potential of the output point of the electric potential determining circuit  40 , i.e. the potential at the second node Nb is the first value (H). 
     This causes the first value (H) to be applied to the first gate  31 g of the first switching element  31 , turns the first switching element  31  in continuity. Meanwhile, the first value (H) is also applied to the third gate  33   g  of the first transistor  33 , turns the first transistor  33  in continuity. Accordingly, the potential of the third node Nc is drawn to the third reference potential V 3  to the second value (L). This causes the second value (L) applied to the second gate  32   g  of the second switching element  32 , which turns the second switching element  32  in a non-conductive state. 
     As a result, current flows between the anode potential Va and the cathode potential Vc in the path that includes the first switching element  31 , and substantially no current flows into the path that includes the second switching element  32 . As a result, current flows to the laser element  14 , causing lasing of the laser element  14 , and a laser light L 0  is emitted from the laser element  14 . 
     As shown in  FIG. 2 , the laser light L 0  emitted from the laser element  14  is reflected at the light-reflecting surface  13   a  of the light-reflecting member  13 , which then passes through the light-transmissive member  15 , and enters the coherence reduction part  19  of the converting member  22 . Coherence of a portion of the laser light L 0  incident on the coherence reduction part  19  decreases through the fluorescent material contained in the coherence reduction part  19 , and for example, converted into a light having a different wavelength. For example, a blue laser light L 0  is converted to a yellow light. The rest of the laser light L 0  that enter the coherence reduction part  19  travels through the coherence reduction part  19  while being diffused within the coherence reduction part  19 . As a result, white light L 1 , a mixture of yellow light and blue light, is emitted from the coherence reduction part  19 . 
     Next, open states caused by failures of a part of the circuit elements that constitute the power supply part  30  will be described. 
     As shown in the second row of  FIG. 4 , when the first comparator  41  fails in an open state, the output terminal of the first comparator  41  enters an electrically floating state. Meanwhile, the second comparator  42  outputs the first value (H), and the third comparator  43  and the fourth comparator  44  also output the first value (H). Thus, the potential at the output point (second node Nb) of the electric potential determining circuit  40  remains at the first value (H). For this reason, the laser element  14  emits light, and light L 1  is emitted from the light-emitting module  1 , as similar to the operation shown in the first row of  FIG. 4 . 
     As shown in the third row of  FIG. 4 , when the second comparator  42  fails in an open state, the output terminal of the second comparator  42  enters an electrically floating state. Meanwhile, the first comparator  41  outputs the first value (H), and the third comparator  43  and the fourth comparator  44  also output the first value (H). Thus, the potential at the output point (second node Nb) of the electric potential determining circuit  40  remains at the first value (H). For this reason, the laser element  14  emits light, and light L 1  is emitted from the light-emitting module  1 , as similar to the operation shown in the first row of  FIG. 4 . Thus, in the normal mode, the first comparator  41  and the second comparator  42  are in a complementary relation. 
     As shown in the fourth row of  FIG. 4 , when the third comparator  43  fails in an open state, the output terminal of the third comparator  43  enters an electrically floating state. Meanwhile, the fourth comparator  44  outputs the first value (H), and the first comparator  41  and the second comparator  42  also output the first value (H). Thus, the potential at the output point (second node Nb) of the electric potential determining circuit  40  remains at the first value (H). For this reason, the laser element  14  emits light, and light L 1  is emitted from the light-emitting module  1 , as similar to the operation shown in the first row of  FIG. 4 . 
     As shown in the fifth row of  FIG. 4 , when the fourth comparator  44  fails in an open state, the output terminal of the fourth comparator  44  enters an electrically floating state. Meanwhile, the third comparator  43  outputs the first value (H), and the first comparator  41  and the second comparator  42  also output the first value (H). Thus, the potential at the output point (second node Nb) of the electric potential determining circuit  40  remains at the first value (H). For this reason, the laser element  14  emits light, and light L 1  is emitted from the light-emitting module  1 , as similar to the operation shown in the first row of  FIG. 4 . Thus, in normal mode, the third comparator  43  and the fourth comparator  44  are in a complementary relation. 
     As shown in the sixth row of  FIG. 4 , when the first transistor  33  fails in an open state, the third node Nc is electrically disconnected from the circuit that applies the third reference potential V 3  (for example, ground potential). Thus, the potential of the third node Nc is drawn to the fourth reference potential V 4  (for example, power source potential) to the first value (H). This provides continuity for the second switching element  32 . Meanwhile, the potential of the second node Nb is the first value (H), accordingly, the first switching element  31  is also in continuity. However, in this case, sufficient current will not flow to the laser element  14  the lasing of the laser element  14  stops. For example, FETs are used as the first switching element  31  and the second switching element  32 , and a laser diode that includes a group III nitride-based semiconductor is used as the laser element  14 . In this case, when both the first switching element  31  and the second switching element  32  are in continuity, the current flow to laser element  14  can be less than the threshold for laser oscillation of the laser element  14 . 
     As shown in the seventh row of  FIG. 4 , even when the second switching element  32  fails in an open state, the first switching element  31  maintains continuity, and laser element  14  emits light. 
     As shown in the eighth row of  FIG. 4 , when the first switching element  31  fails in an open state, current is no longer supplied to the laser element  14 , and laser oscillation of the laser element  14  stops. 
     As illustrated above, in the normal mode, when the first transistor  33  fails (sixth row of  FIG. 4 ) and when the first switching element  31  fails (eighth row of  FIG. 4 ), the laser oscillation of the laser element  14  stops, but when a comparator or the second switching element fails, the laser oscillation of the laser element  14  continues. Therefore, the light-emitting module  1  can maintain its light-emitting state with high probability even when some of the circuit elements in the power supply part  30  fail. 
     Open Mode 
     Next, the operation in an open mode will be described. As described above, when the converting member  22  is damaged, the sense wiring  20  is disconnected and enters an open mode. In an open mode, termination of the lasing of the laser element  14  is required. 
     As shown in the ninth row of  FIG. 4 , if disconnection of the sense wiring  20  occurs when each circuit element in the power supply part  30  is normal, the potential at the first node Na is drawn to the fifth reference potential V 5  (for example, power source potential) and becomes higher than the first reference potential V 1 . As a result, the output of the first comparator  41  and the output of the second comparator  42  become the second value (L) and the potential at the output point (second node Nb) of the electric potential determining circuit  40  becomes the second value (L). The output of the third comparator  43  and the output of the fourth comparator  44  remain at the first value (H). 
     As a result, the potential at the first gate  31   g  of the first switching element  31  also becomes the second value (L), and the first switching element  31  becomes non-conductive. Meanwhile, the potential at the third gate  33   g  of the first transistor  33  also becomes the second value (L), and the first transistor  33  also enters a non-conductive state. This causes the potential of the third node Nc drawn to the fourth reference potential V 4  to become the first value (H), and the potential at the second gate  32   g  of the second switching element  32  also becomes the first value (H). Therefore, the second switching element  32  is in a conductive state. 
     As a result, current flows between the anode potential Va and the cathode potential Vc in the path containing the second switching element  32 , and no current flows to the path containing the first switching element  31 . This prevents current from flowing to the laser element  14  and stops the laser oscillation. Therefore, light L 1  is not emitted from the light-emitting module  1 . 
     As shown in the tenth row of  FIG. 4 , when the first comparator  41  fails in an open state, the output terminal of the first comparator  41  enters in an electrically floating state. However, because the second comparator  42  outputs a second value (L), the potential at the output point (second node Nb) of the electric potential determining circuit  40  remains at the electric potential determining circuit remains at the second value (L). As a result, the laser element  14  does not emit light, as does the operation shown in the 9th row of  FIG. 4 . Therefore, light L 1  is not emitted from the light-emitting module  1 . 
     As shown in the 11th row of  FIG. 4 , if the second comparator  42  fails in an open state, the output terminal of the second comparator  42  enters in an electrically floating state. However, because the first comparator  41  outputs a second value (L), the potential at the output point (second node Nb) of the electric potential determining circuit  40  remains at the second value (L). As a result, the laser element  14  does not emit light, as does the operation shown in the 9th row of  FIG. 4 . Therefore, light L 1  is not emitted from the light-emitting module  1 . Thus, in an open mode, the first comparator  41  and the second comparator  42  complement with each other. 
     As shown in the 12th row of  FIG. 4 , even when the third comparator  43  fails in an open state, the first comparator  41  and the second comparator  42  output a second value (L), such that the potential at the output point (second node Nb) of the electric potential determining circuit  40  remains at the second value (L). As a result, the laser element  14  does not emit light, as does the operation shown in the 9th row of  FIG. 4 . Therefore, light L 1  is not emitted from the light-emitting module  1 . 
     As shown in the 13th row of  FIG. 4 , even when the fourth comparator  44  fails in an open state, the first comparator  41  and the second comparator  42  output a second value (L), such that the potential at the output point (second node Nb) of the electric potential determining circuit  40  remains at the second value (L). As a result, the laser element  14  does not emit light, as does the operation shown in the 9th row of  FIG. 4 . Therefore, light L 1  is not emitted from the light-emitting module  1 . 
     As shown in the 14th row of  FIG. 4 , even when the first transistor  33  fails in an open state, it is equivalent in operation to the first transistor  33  being in a non-conductive state, and thus, the laser element  14  does not emit light as the operation shown in the 9th row of FIG,  4 . Therefore, light L 1  is not emitted from the light-emitting module  1 . 
     As shown in the 15th row of  FIG. 4 , when the second switching element  32  fails in an open state, electric current does not flow to the path containing the second switching element  32 . However, because the potential at the second node Nb is the second value (L), the potential at the first gate  31   g  of the first switching element  31  is also the second value (L), and thus the first switching element  31  is not in continuity. Therefore, the laser element  14  does not emit light, and light L 1  is not emitted from the light-emitting module  1 . 
     As shown in the 16th row of  FIG. 4 , even when the first switching element  32  fails and becomes open, it is equivalent in operation to the first switching element  31  being in a non-conductive state, and thus, the laser element  14  does not emit light. Therefore, light L 1  is not emitted from the light-emitting module  1 . Meanwhile, the second switching element  32  is in a conductive state, current flows between the anode potential Va and the cathode potential Vc to the path containing the second switching element  32 . 
     As illustrated above, in an open mode, the laser element  14  remains in a state where the laser oscillation has stopped when any one of the circuit elements fails. Accordingly, when the converting member  22  is damaged and also any one of the circuit elements fails, leakage of laser light L 0  to the outside of the light-emitting part  10  does not occur. 
     Short Circuit Mode 
     Next, the operation in a short circuit mode will be described. As described above, a short circuit mode failure may occur when substantial short circuit occurs due to, for example, a foreign matter attaching to the sense wiring  20 . In a short circuit mode, the sense wiring  20  may not be able to detect damage of the converting member  22 . Therefore, it is necessary to stop the laser oscillation of the laser element  14 . 
     As shown in the 17th row of  FIG. 4 , when each circuit element of the power supply part  30  is in normal, when the sense wiring  20  is short circuited, the potential of the first node Na is drawn by the sixth reference potential V 6  (for example, ground potential) and becomes lower than the second reference potential V 2 . As a result, the output of the third comparator  43  and the output of the fourth comparator  44  become the second value (L) and the potential at the output point (second node Nb) of the electric potential determining circuit  40  becomes the second value (L). Therefore, laser element  14  does not emit light, and light L 1  is not emitted from the light-emitting module  1 . The output of the first comparator  41  and the output of the second comparator  42  are the first value (H). 
     As shown in the 18th row of  FIG. 4 , even when the first comparator  41  fails in an open state, the third comparator  43  and the fourth comparator  44  output a second value (L), such that the potential at the output point (second node Nb) of the electric potential determining circuit  40  remains at the second value (L). Therefore, laser element  14  does not emit light, and light L 1  is not emitted from the light-emitting module  1  as in the operation shown in the 17th row of  FIG. 4 . 
     As shown in the 19th row of  FIG. 4 , even when the second comparator  42  fails in an open state, the third comparator  43  and the fourth comparator  44  output a second value (L), such that the potential at the output point (second node Nb) of the electric potential determining circuit  40  remains at the second value (L). Therefore, laser element  14  does not emit light, and light L 1  is not emitted from the light-emitting module  1  as in the operation shown in the 17th row of  FIG. 4 . 
     As shown in the 20th row of  FIG. 4 , when the third comparator  43  fails in an open state, the output terminal of the third comparator  43  enters an electrically floating state. However, because the fourth comparator  44  outputs a second value (L), the potential at the output point (second node Nb) of the electric potential determining circuit  40  remains at the second value (L). As a result, the laser element  14  does not emit light, as the operation shown in line 17th row of  FIG. 4 . Therefore, light L 1  is not emitted from the light-emitting module  1 . 
     As shown in the 21th row of  FIG. 4 , when an open state is caused by a failure of the fourth comparator  44 , the output terminal of the fourth comparator  44  enters an electrically floating state. However, because the third comparator  43  outputs a second value (L), the potential at the output point (second node Nb) of the electric potential determining circuit  40  remains at the second value (L). As a result, the laser element  14  does not emit light, as the operation shown in the 17th row of  FIG. 4 . Therefore, light L 1  is not emitted from the light-emitting module  1 . Thus, in a short circuit mode, the third comparator  43  and the fourth comparator  44  complement with each other. 
     As shown in the 22th row of  FIG. 4 , even when the first transistor  33  fails and becomes open, it is equivalent in operation to the first transistor  33  being in a non-conductive state, and thus, the laser element  14  does not emit light as the operation shown in the 17th row of  FIG. 4 . Therefore, light L 1  is not emitted from the light-emitting module  1 . 
     As shown in the 23rd row of  FIG. 4 , when the second switching element  32  fails in an open state, electric current does not flow to the path containing the second switching element  32 . However, because the potential at the second node Nb is the second value (L), the potential at the first gate  31   g  of the first switching element  31  is also the second value (L), and thus the first switching element  31  is not in continuity. Therefore, the laser element  14  does not emit light, and light L 1  is not emitted from the light-emitting module  1 . 
     As shown in the 24th row of  FIG. 4 , if the first switching element  31  fails in an open state, the laser element  14  does not emit light because it is equivalent to that of the first switching element  31  in the non-conductive state for circuit operation. Therefore, light L 1  is not emitted from the light-emitting module  1 . Meanwhile, the second switching element  32  is in a conductive state, current flows between the anode potential Va and the cathode potential Vc to the path containing the second switching element  32 . 
     As illustrated above, in a short circuit mode, the laser element  14  remains in a state where the laser oscillation has stopped when any one of the circuit elements fails. Accordingly, in a short circuit mode, when the converting member  22  is damaged and also any one of the circuit elements fails, leakage of laser light L 0  to the outside of the light-emitting part  10  does not occur. 
     Other Failure Modes 
       FIG. 4  illustrates failure of a comparator, a switching element or a transistor is in an open state, but the failure may be in a short circuit state. For example, these failure condition may be in an open state via a short circuit state. 
     When the first switching element  31  is in a failure condition with a short circuit and the failure of the sense wiring  20  is in open mode or short circuit mode, the corresponding comparator outputs a second value (L), but the first switching element  31  is in a short circuit state, and therefore does not enter a non-conductive state. However, the comparator outputs a second value (L), which causes the second switching element  32  to carry on. With this arrangement, the portion lasing at the laser elements  14  can be protected. 
     When the second switching element  32  is in a short-circuit fault condition, the laser oscillation of the laser element  14  is stopped, regardless of whether it is in normal mode, open mode or short circuit mode. If the first transistor  33  is in a short-circuit fault condition, the second switching element  32  enters a non-conductive state, and depending on whether the first switching element  31  is in a continuity state, whether to execute lasing of the laser element  14  is determined. A failure condition other than the open condition of a corresponding one of the comparators is assumed to output a second value (L) regardless of the input value, for example by a short circuit of a part of the comparator, but in this case the second node Nb will be the second value (L), so that regardless of the normal mode, open mode, or short circuit mode, the laser oscillation of the laser element  14  stops. 
     Effects 
     Next, effects of the present embodiment will be described. The light-emitting module  1  according to the present embodiment is configured such that in an open mode, the first comparator  41  and the second comparator  42  are complementary, such that even when one of the first comparator  41  and the second comparator  42  fails, the other can output the second value (L). Therefore, it is possible to maintain the potential of the second node Nb at the second value (L), thereby more reliably stopping the laser oscillation of the laser element  14 . 
     Meanwhile, in a short circuit mode, the third comparator  43  and the fourth comparator  44  are complementary, such that even when one of the third comparator  43  and the fourth comparator  44  fails, the other can output the second value (L). Therefore, it is possible to maintain the potential of the second node Nb at the second value (L), thereby more reliably stopping the laser oscillation of the laser element  14 . 
     Further, by having the second switching element  32 , the light-emitting module  1  according to the present embodiment can stop laser oscillation of the laser element  14  even when the failure condition of the first switching element  31  is not in an open state but in a short circuit state. Accordingly, lasing of the laser element  14  can be more securely stopped. 
     As described above, according to the present embodiment, even if some circuit elements fail, the laser oscillation of the laser element  14  can be stopped more reliably in an open mode and in a short circuit mode, while maintaining light emission with a high probability in a normal mode. Accordingly, it is possible to realize a light-emitting module that can reliably stop laser light when the converting member is damaged. 
     For example, when the light-emitting module  1  in the present embodiment is used as a headlight for vehicles such as automobiles, and the light emitting module  1  is damaged due to a vehicle accident, and some of the power supply part  30  along with the converting member  22  is damaged, laser light L 0  can be prevented from going out of the light emitting module  1 . As a result, high safety can be realized. 
     Note that depending on the failure condition of a comparator, a switching element, or a transistor, laser oscillation of the laser element  14  may stop even though the sense wiring  20  is in normal mode, but in such a case, there is an advantage that the user of the light emitting module  1  can be notified of the failure before further failure occurs. 
     The embodiment described above is to exemplify a light emitting module for embodying the technical idea of the present invention, and the technical idea of the present invention is not limited thereto. For example, the present invention includes the addition, deletion or modification of some components in the embodiment described above. 
     The present invention can be used for, for example, lighting devices and vehicular head lamps.