Patent Publication Number: US-10761144-B2

Title: Electronic device

Description:
TECHNICAL FIELD 
     The present invention relates to an electronic device. 
     BACKGROUND ART 
     There is an electronic device which supplies power to a load circuit by a power supply circuit to drive the load circuit. The load circuit is, for example, a sensor. In such an electronic device, a detection of an abnormality such as a short circuit of a power supply line connecting the power supply circuit and the load circuit is performed. In PTL 1, a voltage of the power supply line is divided, and input to a port of a microcomputer as a monitor voltage to monitor the voltage by the microcomputer, so that the short circuit of the power supply line is determined. 
     CITATION LIST 
     Patent Literature 
     PTL 1: JP 2014-117084 A 
     SUMMARY OF INVENTION 
     Technical Problem 
     There has been a problem that, in a case where a power supply line connecting a power supply circuit and a load circuit is increased in number by two or more systems, the number of ports of a microcomputer is increased to detect an abnormality of the power supply lines. 
     Solution to Problem 
     An electronic device according to the present invention includes: a first power supply circuit which supplies power to a first load circuit through a first power supply line; a second power supply circuit which supplies power to a second load circuit through a second power supply line; a first resistor of which one end is connected to the first power supply line; a second resistor of which one end is connected to the second power supply line; a third resistor which is connected to the other ends of the first and second resistors; and a monitor circuit which receives a monitor voltage through the third resistor, in which the monitor circuit determines an abnormality of the first power supply line and the second power supply line on the basis of the voltage. 
     Advantageous Effects of Invention 
     According to the present invention, even in a case where a power supply line connecting a power supply circuit and a load circuit is increased in number by a plurality of systems, there is no need to increase the number of ports of a microcomputer. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a circuit diagram of an electronic device according to a first embodiment. 
         FIGS. 2(A), 2(B), 2(C), 2(D) , and  2 (E) are equivalent circuits of the electronic device according to the first embodiment. 
         FIG. 3  is a diagram illustrating an example of a constant of the equivalent circuit according to the first embodiment. 
         FIG. 4  is a graph illustrating a monitor voltage according to the first embodiment. 
         FIG. 5  is a circuit diagram of an electronic device according to a second embodiment. 
         FIGS. 6(A), 6(B) , and  6 (C) are diagrams illustrating equivalent circuits of the electronic device according to the second embodiment. 
         FIG. 7  is a graph illustrating a monitor voltage according to the second embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
       FIG. 1  is a circuit diagram of an electronic device according to a first embodiment. 
     A first power supply circuit  11  is supplied with a voltage V as a power source, and outputs a voltage V 1  on the basis of the voltage V. The voltage V 1  is supplied to a first load circuit  12  through a first power supply line L 1  as a power source of the first load circuit  12 . Examples of the first load circuit  12  include a sensor and a DC fan. 
     A second power supply circuit  13  is supplied with the voltage V as a power source, and outputs a voltage V 2  on the basis of the voltage V. The voltage V 2  is supplied to a second load circuit  14  through a second power supply line L 2  as a power source of the second load circuit  14 . Examples of the second load circuit  14  include a sensor and a DC fan. 
     One end of a first resistor R 1  is connected to the first power supply line L 1 , and one end of a second resistor R 2  is connected to the second power supply line L 2 . The other end of the first resistor R 1  and the other end of the second resistor R 2  are commonly connected to one end of a third resistor R 3 . The other end of the third resistor R 3  is input to a monitor port of a microcomputer  15 , and is grounded through a fourth resistor R 4 . The microcomputer  15  determines a value of a monitor voltage input to the monitor port to determine an abnormality of the first power supply line L 1  and the second power supply line L 2 . Specifically, the microcomputer determines whether the first power supply line L 1  and the second power supply line L 2  are short-circuited to a ground side (hereinafter, referred to as “short”) or a voltage is not output to the first power supply line L 1  and the second power supply line L 2  due to an open circuit (hereinafter, referred to as “open”) or the like. 
     Here, the description will be given about a relation among resistance values of the first to fourth resistors R 1  to R 4 . The resistance values of the first to fourth resistors R 1  to R 4  are set to R 1  to R 4 . Next, as shown Formula (1) or (2), a ratio of the resistance value of the first resistor R 1  and the resistance value of the second resistor R 2  is about two times. Further, as shown in Formula (3), the resistance value of the fourth resistor R 4  is about four times a combined resistance value of the first resistor R 1 , the second resistor R 2 , and the third resistor R 3 . About two times and four times may be resistance values causing voltages that enables identification of features  41  to  45  of  FIG. 4  to be described below. 
     
       
         
           
             
               
                 
                   [ 
                   
                     Mathematical 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     Formula 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       R 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       1 
                     
                     
                       R 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       2 
                     
                   
                   ⁢ 
                   
                       
                   
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                   ⁢ 
                   2 
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
             
               
                 
                   
                     
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                       ⁢ 
                       
                           
                       
                       ⁢ 
                       2 
                     
                     
                       R 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       1 
                     
                   
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   2 
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
             
               
                 
                   R 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   4 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   ⁢ 
                   
                       
                   
                   ⁢ 
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                   × 
                   
                     ( 
                     
                       
                         
                           R 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           1 
                           × 
                           R 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           2 
                         
                         
                           
                             R 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                           + 
                           
                             R 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             2 
                           
                         
                       
                       + 
                       
                         R 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                       
                     
                     ) 
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
       FIG. 2  is a diagram illustrating equivalent circuits of a circuit configuration illustrated in  FIG. 1 .  FIG. 2(A)  illustrates an equivalent circuit in the case of a normal state where there is no short or open in the first power supply line L 1  and the second power supply line L 2 .  FIG. 2(B)  illustrates an equivalent circuit in a case where the first power supply line L 1  is opened.  FIG. 2(C)  illustrates an equivalent circuit in a case where the second power supply line L 2  is opened.  FIG. 2(D)  illustrates an equivalent circuit in a case where the first power supply line L 1  is shorted.  FIG. 2(E)  illustrates an equivalent circuit in a case where the second power supply line L 2  is shorted. Here, the values of the voltages V 1  and V 2  are set to V 1  and V 2 , the resistance values of the first to fourth resistors R 1  to R 4  are set to R 1  to R 4 , and the currents flowing to the first to third resistors R 1  to R 3  are respectively set to Ia, Ib, and Ic. In addition, “X” depicted in  FIGS. 2(B) and 2(C)  indicates an open circuit. 
       FIG. 3  is a diagram illustrating an example of constants of the equivalent circuit. Typical values (typ), minimum values (min), and maximum values (max) of the values of the voltages V 1  and V 2  and the resistance values of the first to fourth resistors R 1  to R 4  are listed. Here, the first resistor R 1  has a resistance value sufficiently larger than the internal resistance of the first load circuit  12 . The second resistor R 2  has a resistance value sufficiently larger than the internal resistance of the second load circuit  14 . In addition, the current flowing to the first power supply line L 1  and the second power supply line L 2  is set to about 20 mA. 
       FIG. 4  is a graph illustrating a monitor voltage input to the monitor port of the microcomputer  15 . A vertical axis of  FIG. 4  represents the monitor voltage, and a horizontal axis represents time. In the case of the normal state where there is no short or open in the equivalent circuit of  FIG. 2(A) , the feature  41  of the monitor voltage is about 3.9 to 4.1 V. In a case where the first power supply line L 1  illustrated in the equivalent circuit of  FIG. 2(B)  is opened, the feature  42  of the monitor voltage is about 3.6 to 3.8 V. In a case where the second power supply line L 2  illustrated in the equivalent circuit of  FIG. 2(C)  is opened, the feature  43  of the monitor voltage is about 3.1 to 3.2 V. In a case where the first power supply line L 1  illustrated in the equivalent circuit of  FIG. 2(D)  is shorted, the feature  44  of the monitor voltage is about 2.5 to 2.7 V. In a case where the second power supply line L 2  illustrated in the equivalent circuit of  FIG. 2(E)  is shorted, the feature  45  of the monitor voltage is about 1.3 to 1.4 V. The microcomputer  15  determines an abnormality of the first power supply line L 1  and the second power supply line L 2  on the basis of the monitor voltage input to the monitor port. Specifically, the abnormality is determined according to the features  41  to  45  to which the monitor voltage belongs. 
     Next, the description below will be given about a case where the monitor voltage corresponds to the features illustrated in  FIG. 4  according to an abnormality. 
     First, the description will be given about the case of the normal state where there is no short or open illustrated in the equivalent circuit of  FIG. 2(A) . The following Formulas (4) to (6) are satisfied from the equivalent circuit of  FIG. 2(A) .
 
 Ia=Ic−Ib   (4)
 
 V 1=( R 3 +R 4)× Ic+R 1 ×Ia   (5)
 
 V 2=( R 3 +R 4)× Ic+R 2 ×Ib   (6)
 
     Formula (4) is substituted in Formula (5).
 
 V 1=( R 3 +R 4 +R 1)× Ic−R 1 ×Ib   (7)
 
     Both sides of Formula (6) are multiplied by R 1 , and both sides of Formula (7) are multiplied by R 2 , and left sides and right sides of both formulas are respectively added so as to obtain the following Formula (8). 
     
       
         
           
             
               
                 
                   [ 
                   
                     Mathematical 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     Formula 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     2 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   Ic 
                   = 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         R 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                       
                       + 
                       
                         V 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         R 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                       
                     
                     
                       
                         R 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         R 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                       
                       + 
                       
                         R 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         R 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                       
                       + 
                       
                         R 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                         ⁢ 
                         R 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         4 
                       
                       + 
                       
                         R 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         R 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         3 
                       
                       + 
                       
                         R 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         R 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         4 
                       
                     
                   
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
           
         
       
     
     The monitor voltage is represented by the following Formula (9).
 
Monitor voltage= R 4 ×Ic   (9)
 
     When the constants shown in  FIG. 3  are input to Formulas (8) and (9) to obtain the monitor voltage, the typical value (typ) becomes 4.02 V, the minimum value (min) becomes 3.94 V, and the maximum value (max) becomes 4.10 V. The monitor voltage is a voltage indicated by the feature  41  of  FIG. 4 . 
     In addition, the monitor voltage in a case where the first power supply line L 1  illustrated in the equivalent circuit of  FIG. 2(B)  is opened is represented by the following Formula (10). 
     
       
         
           
             
               
                 
                   [ 
                   
                     Mathematical 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     Formula 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     3 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     Monitor 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     Voltage 
                   
                   = 
                   
                     V 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     2 
                     × 
                     
                       
                         R 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         4 
                       
                       
                         
                           R 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           4 
                         
                         + 
                         
                           R 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           3 
                         
                         + 
                         
                           R 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           2 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   10 
                   ) 
                 
               
             
           
         
       
     
     In addition, the monitor voltage in a case where the second power supply line L 2  illustrated in the equivalent circuit of  FIG. 2(C)  is opened is represented by the following Formula (11). 
     
       
         
           
             
               
                 
                   [ 
                   
                     Mathematical 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     Formula 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     4 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     Monitor 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     Voltage 
                   
                   = 
                   
                     V 
                     ⁢ 
                     
                         
                     
                     ⁢ 
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                     × 
                     
                       
                         R 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         4 
                       
                       
                         
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                           ⁢ 
                           
                               
                           
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                           1 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   11 
                   ) 
                 
               
             
           
         
       
     
     In addition, the monitor voltage in a case where the first power supply line L 1  illustrated in the equivalent circuit of  FIG. 2(D)  is shorted is represented by the following Formula (12). 
     
       
         
           
             
               
                 
                   [ 
                   
                     Mathematical 
                     ⁢ 
                     
                         
                     
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                     Formula 
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                     5 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     Monitor 
                     ⁢ 
                     
                         
                     
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                     Voltage 
                   
                   = 
                   
                     V 
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                       [ 
                       
                         
                           
                             
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                         ⁢ 
                         
                             
                         
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                           ⁢ 
                           
                               
                           
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                           3 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   12 
                   ) 
                 
               
             
           
         
       
     
     In addition, the monitor voltage in a case where the second power supply line L 2  illustrated in the equivalent circuit of  FIG. 2(E)  is shorted is represented by the following Formula (13). 
     
       
         
           
             
               
                 
                   [ 
                   
                     Mathematical 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     Formula 
                     ⁢ 
                     
                         
                     
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                     6 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     Monitor 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     Voltage 
                   
                   = 
                   
                     V 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                     × 
                     
                       [ 
                       
                         
                           
                             
                               ( 
                               
                                 
                                   R 
                                   ⁢ 
                                   
                                       
                                   
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                                   4 
                                 
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                             × 
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                               + 
                               
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                                 ⁢ 
                                 
                                     
                                 
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                                 2 
                               
                             
                           
                           + 
                           
                             R 
                             ⁢ 
                             
                                 
                             
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                             1 
                           
                         
                       
                       ] 
                     
                     × 
                     
                       
                         R 
                         ⁢ 
                         
                             
                         
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                         4 
                       
                       
                         
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                           ⁢ 
                           
                               
                           
                           ⁢ 
                           4 
                         
                         + 
                         
                           R 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           3 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   13 
                   ) 
                 
               
             
           
         
       
     
     When the constants shown in  FIG. 3  are input to Formulas (10) to (13) to calculate the monitor voltage, the voltages indicated by the features  42  to  45  of  FIG. 4  are obtained. 
     According to the first embodiment of the present invention, even in a case where the power supply line connecting the power supply circuit and the load circuit is increased in number by a plurality of systems, it is possible to detect an abnormality of the first power supply line L 1  and the second power supply line L 2  without increasing the number of ports of the microcomputer. 
     Second Embodiment 
     Next, a second embodiment of the electronic device of the present invention will be described.  FIG. 5  is a circuit diagram of the electronic device according to the second embodiment. From the circuit diagram of the second embodiment, the fourth resistor R 4  of the circuit diagram illustrated in  FIG. 1  is removed. The same parts as those of the circuit diagram of  FIG. 1  will be attached with the same symbols, and the description will be omitted. 
     As illustrated in  FIG. 5 , one end of the first resistor R 1  is connected to the first power supply line L 1 , and one end of the second resistor R 2  is connected to the second power supply line L 2 . The other end of the first resistor R 1  and the other end of the second resistor R 2  are commonly connected to one end of a third resistor R 3 . The other end of the third resistor R 3  is input to the monitor port of the microcomputer  15 . The microcomputer  15  determines a value of a monitor voltage input to the monitor port to determine an abnormality of the first power supply line L 1  and the second power supply line L 2 . Specifically, the microcomputer detects whether the first power supply line L 1  and the second power supply line L 2  are short-circuited to a ground side (hereinafter, referred to as “short”). 
     Here, the description will be given about a relation among resistance values of the first to fourth resistors R 1  to R 4 . As shown in Formula (1) or (2), a ratio of the resistance value of the first resistor R 1  and the resistance value of the second resistor R 2  is about two times. 
       FIG. 6  is a diagram illustrating equivalent circuits of a circuit configuration illustrated in  FIG. 5 .  FIG. 6(A)  illustrates an equivalent circuit in the case of the normal state where there is no short.  FIG. 6(B)  illustrates an equivalent circuit in a case where the first power supply line L 1  is shorted.  FIG. 6(C)  illustrates an equivalent circuit in a case where the second power supply line L 2  is shorted. Here, the values of the voltages V 1  and V 2  are set to V 1  and V 2 , the resistance values of the first to third resistors R 1  to R 3  are set to R 1  to R 3 , and the currents flowing to the first to third resistors R 1  to R 3  are respectively set to Ia, Ib, and Ic. 
     The constants of the equivalent circuit illustrated in  FIGS. 6(A)  to (C) are considered as the same as those illustrated in  FIG. 3 . Note that the constants are given as an example. Here, the first resistor R 1  has a resistance value sufficiently larger than the internal resistance of the first load circuit  12 . The second resistor R 2  has resistance value sufficiently larger than the internal resistance of the second load circuit  14 . In addition, the current flowing to the first power supply line L 1  and the second power supply line L 2  is set to about 20 mA. 
       FIG. 7  is a graph illustrating the monitor voltage input to the monitor port of the microcomputer  15 . A vertical axis of  FIG. 7  represents the monitor voltage, and a horizontal axis represents time. In the case of the normal state where there is no short in the equivalent circuit of  FIG. 6(A) , a feature  71  of the monitor voltage is about 4.9 to 5.1 V. In a case where the first power supply line L 1  illustrated in the equivalent circuit of  FIG. 7(B)  is shorted, a feature  72  of the monitor voltage is about 3.2 to 3.4 V. In a case where the second power supply line L 2  illustrated in the equivalent circuit of  FIG. 7(C)  is shorted, a feature  73  of the monitor voltage is about 1.66 to 1.72 V. The microcomputer  15  determines an abnormality of the first power supply line L 1  and the second power supply line L 2  on the basis of the monitor voltage input to the monitor port. Specifically, the abnormality is determined according to the features  71  to  73  to which the monitor voltage belongs. 
     Next, the description below will be given about a case where the monitor voltage corresponds to the features illustrated in  FIG. 7  according to an abnormality. 
     The monitor voltage in a case where the first power supply line L 1  illustrated in the equivalent circuit of  FIG. 6(B)  is shorted is represented by the following Formula (14). 
     
       
         
           
             
               
                 
                   [ 
                   
                     Mathematical 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     Formula 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     7 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     Monitor 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     Voltage 
                   
                   = 
                   
                     V 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     2 
                     × 
                     
                       
                         R 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         1 
                       
                       
                         
                           R 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           1 
                         
                         + 
                         
                           R 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           2 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   14 
                   ) 
                 
               
             
           
         
       
     
     In addition, the monitor voltage in a case where the second power supply line L 2  illustrated in the equivalent circuit of  FIG. 6(C)  is shorted is represented by the following Formula (15). 
     
       
         
           
             
               
                 
                   [ 
                   
                     Mathematical 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     Formula 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     8 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     Monitor 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     Voltage 
                   
                   = 
                   
                     V 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                     × 
                     
                       
                         R 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                       
                       
                         
                           R 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           1 
                         
                         + 
                         
                           R 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           2 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   15 
                   ) 
                 
               
             
           
         
       
     
     When the constants shown in  FIG. 3  are input to Formulas (14) and (15) to calculate the monitor voltage, the voltages indicated by the features  72  and  73  of  FIG. 7  are obtained. Note that, since Ia to Ic are significantly small, the voltage of the feature  71  of  FIG. 7  is almost equal to the voltage V 1  or V 2 . 
     According to the second embodiment of the present invention, even in a case where the power supply line connecting the power supply circuit and the load circuit is increased in number by a plurality of systems, it is possible to determine whether the abnormality of the first power supply line L 1  and the second power supply line L 2  is a short circuit without increasing the number of ports of the microcomputer. 
     According to the above-described embodiment, the following operational effect is obtained. 
     (1) An electronic device includes a first power supply circuit  11  which supplies power V 1  to a first load circuit  12  through a first power supply line L 1 , a second power supply circuit  13  which supplies power V 2  to a second load circuit  14  through a second power supply line L 2 , a first resistor R 1  of which one end is connected to the first power supply line L 1 , a second resistor R 2  of which one end is connected to the second power supply line L 2 , a third resistor R 3  which is connected to the other ends of the first resistor R 1  and the second resistor R 2 , and a monitor circuit (microcomputer)  15  which receives a monitor voltage through the third resistor R 3 . The monitor circuit  15  determines an abnormality of the first power supply line L 1  and the second power supply line L 2  on the basis of a voltage. With this configuration, even in a case where the power supply line connecting the power supply circuit and the load circuit is increased in number by a plurality of systems, there is no need to increase the number of ports of the microcomputer. 
     The present invention is not limited to the above embodiments, and other modifications considered to fall within a range of the technical ideas of the present invention may also be deemed to fall within the scope of the present invention as long as the features of the present invention is not impaired. 
     REFERENCE SIGNS LIST 
     
         
           11  first power supply circuit 
           12  first load circuit 
           13  second power supply circuit 
           14  second load circuit 
         L 1  first power supply line 
         L 2  second power supply line 
         R 1  to R 4  first to fourth resistors