Abstract:
A load drive circuit incorporated into an onboard electronic control device, the load drive circuit housing a diagnosis circuit for diagnosing load abnormalities, wherein diagnosis circuit failures are detected without affecting load drive control. When a failure has occurred in the diagnosis circuit, vehicle operation is not affected because the diagnosis circuit does not have a function for controlling the vehicle, and there may be cases in which occupants riding an the vehicle do not notice the failure. Additionally, when a failure has occurred in the diagnosis circuit, the occurrence of the failure cannot be detected even by a vehicle control system as long as there is no function for detecting occurrences of failure in the diagnosis circuit. Specifically, when a failure has occurred in the diagnosis circuit, there is a possibility that the failure is unrecognizable to occupants and undetectable by a vehicle control system. When there is no need for the diagnosis circuit to diagnose load abnormalities, a determination of whether or not the diagnosis circuit is failing is made by sending a pseudo abnormality signal to the diagnosis circuit and confirming whether the diagnosis circuit can detect the sent pseudo abnormality signal as a failure.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a load drive circuit which is incorporated into an electronic control device mounted on a vehicle and in which a diagnosis circuit is embedded. 
       BACKGROUND ART 
       [0002]    There is a case where a drive element is turned on or off according to PWM drive or frequency drive and thereby a load such as, a solenoid, a relay, a heater, or a motor is driven, for control of a vehicle. In the related art, a load drive circuit includes a diagnosis circuit that diagnoses a state of a load which is driven, and diagnoses the state of the load by measuring a predetermined physical quantity of the load drive circuit. There is a case where the diagnosis circuit continuously diagnoses whether or not abnormality occurs in the load which is driven during an operation of the vehicle. 
         [0003]    Meanwhile, in a case where the diagnosis circuit fails, a passenger riding in the vehicle may not be aware of the failure, because the diagnosis circuit does not have a function control the vehicle thereby not affecting the operation of the vehicle. In addition, in a case where the diagnosis circuit fails, a vehicle control system is also not able to detect the failure, since there is no function to detect that the diagnosis circuit fails. That is, in a case where a diagnosis circuit fails a potential failure can occur in which a passenger is not able to recognize the failure and the vehicle control system is not able to detect the failure. 
         [0004]    If abnormality occurs in a load which is driven in a state where a diagnosis circuit fails, the diagnosis circuit is not able to detect the abnormality of the load, and furthermore, it is also not possible to activate a protection function to protect a load drive circuit from the abnormality of the load. That is, if double failures occur in which abnormality occurs in the load in a state where the diagnosis circuit fails, the protection function is also not able to be activated, and thus, the load drive circuit can be broken in the worst case. 
         [0005]    In PTL 1, if a drive stop signal is inputted from a control circuit. which controls a drive circuit during initialization processing of a system after an ignition key of a vehicle is turned on or during stop processing of the system after the ignition key of the vehicle is turned off, at least the drive circuit stops, and thereby a normal operation of a diagnosis circuit which diagnoses a state of the load is confirmed in a state where the load drive circuit is incorporated into an electronic control device. 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         PTL 1: JP-A-2009-77542 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0007]    However, in the aforementioned method, whether or not the diagnosis circuit fails is confirmed when the ignition key is turned on or off, and thus, in a case where a failure occurs while a vehicle travels, it takes time to find the failure If abnormality occurs in the load which is driven during this time, the load drive circuit is broken due to double failures, and there is a possibility that the load is not able to be controlled. 
         [0008]    For this reason, in a case where the diagnosis circuit fails, it is preferable that the failure is quickly detected and thereby a passenger is notified of the failure by a warning light or the like, for example, even in a case where the failure does not affect control of the vehicle. 
         [0009]    An object of the present invention is to confirm the presence or absence of abnormality of a diagnosis circuit in a load drive circuit by inputting a pseudo abnormality signal without affecting the load drive control during an operation of a vehicle. 
       Solution to Problem 
       [0010]    The object can be achieved by inputting a pseudo abnormality signal into a diagnosis circuit to diagnose whether or not abnormality occurs in the diagnosis circuit, for example, during control of a load, when the diagnosis circuit does not diagnose abnormality of the load, as an example. 
       Advantageous Effects of Invention 
       [0011]    According to the present invention, whether or not the diagnosis circuit in a load drive circuit fails can be determined by inputting a pseudo abnormality signal in each load drive period, without affecting load drive control. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0012]      FIG. 1  is a flowchart illustrating a sequence for confirming whether or not a diagnosis circuit fails, based on a state of a drive element. 
           [0013]      FIG. 2  illustrates a load drive circuit  1  with a low side driver configuration having a battery short-circuit detection circuit, as the diagnosis circuit. 
           [0014]      FIG. 3  is a timing chart  1  illustrating an operation of  FIG. 2 . 
           [0015]      FIG. 4  is a timing chart  2  illustrating the operation of  FIG. 2 . 
           [0016]      FIG. 5  illustrates a load drive circuit with a low side driver configuration having a ground short-circuit detection circuit and a load open-circuit detection circuit as the diagnosis circuit. 
           [0017]      FIG. 6  illustrates a load drive circuit with a high side driver configuration having the ground short-circuit detection circuit, the load open-circuit detection circuit, and the battery short-circuit detection circuit as the diagnosis circuit. 
           [0018]      FIG. 7  illustrates a load drive circuit with a half bridge configuration having the ground short-circuit detection circuit and the battery short-circuit detection circuit as the diagnosis circuit. 
           [0019]      FIG. 8  illustrates a load drive circuit  2  with the low side driver configuration having the battery short-circuit detection circuit as the diagnosis circuit. 
           [0020]      FIG. 9  is a timing chart illustrating an operation of  FIG. 8 . 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiment 1 
       [0021]    Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. 
         [0022]      FIG. 1  is a flowchart illustrating a sequence for confirming whether or not a diagnosis circuit fails, based on a state of a drive element. 
         [0023]    First, in step S 10  illustrated in  FIG. 1 , it is determined whether or not a current state is a state in which it is necessary for the diagnosis circuit to diagnose abnormality of a load, based on a state of a drive element. 
         [0024]    In a case where the drive element is in a state in which it is necessary for the diagnosis circuit to diagnose abnormality of the load (S 10  determination: Yes), the diagnosis circuit diagnoses whether or not abnormality occurs in the load. In a case where the diagnosis circuit does not detect that abnormality occurs in the load (step S 21 : No), the diagnosis circuit determines that a state of the load is normal, and returns to S 10  determination. In a case where the diagnosis circuit detects that abnormality occurs in the load (step S 21 : Yes), the diagnosis circuit starts an operation of protecting a load drive circuit from abnormality which occurs if necessary, and furthermore, notifies a main control device such as a microcomputer of the occurrence of the abnormality. The main control device causes a vehicle to perform a predetermined operation according to a place where the abnormality occurs, a type of the abnormality, or the like. 
         [0025]    In a case where the drive element is in a state in which it is not necessary for the diagnosis circuit to diagnose abnormality of the load (S 10  determination: No), the diagnosis circuit does not need to diagnose whether or not abnormality occurs in the load. For this reason, during a period in which the diagnosis circuit does not need to diagnose, a pseudo abnormality signal corresponding to a physical quantity being generated when the load is abnormal is inputted to the diagnosis circuit, whether or not the diagnosis circuit can detect the pseudo abnormality signal as the abnormality of the load is confirmed, and thus, it is possible to confirm whether or not the diagnosis circuit fails. In a case where a signal indicating that the diagnosis circuit detects the abnormality of the load is outputted as a result of inputting the pseudo abnormality signal, to the diagnosis circuit (step  331 : Yes) it is determined that the diagnosis circuit does not fail, and the processing returns to  310  determination. Meanwhile, in a case where the signal indicating that the diagnosis circuit detects the failure is not outputted as a result of inputting the pseudo abnormality signal to the diagnosis circuit (step S 31 : No), it is determined that the diagnosis circuit fails, and the main control device such as a microcomputer is notified of the fact that the diagnosis circuit fails. The main control device notifies a driver by lighting a warning lamp, in accordance with a failed location or the like of the diagnosis circuit, thereby causing the vehicle to perform the predetermined operation. 
         [0026]    Hereinafter, a specific example will be described with reference to  FIG. 2 . 
         [0027]      FIG. 2  illustrates a load drive circuit with a low side driver configuration having a battery short-circuit detection function according to overcurrent detection as the diagnosis circuit. 
         [0028]    A load drive circuit  100  with a low side driver configuration is provided in a lower portion of a power supply  103  and a load  101 , and is configured by a drive element MOSFET  19   a  and a predriver  12   a  for driving the drive element MOSFET, a current detection resistor  18   a  for diagnosing a current flowing through the drive element MOSFET  19   a,  a differential amplification circuit  14   a  which amplifies a both-terminal voltage of the current detection resistor  18   a,  a battery short-circuit threshold voltage generation circuit  13   a  which determines a threshold value determining whether or not an overcurrent flows due to a battery short-circuit, a comparison circuit  11   a  which determines whether or not the overcurrent flows by comparing an output voltage of the differential amplification circuit  14   a  with a value of the battery short-circuit threshold voltage generation circuit  13   a,  a battery short-circuit pseudo abnormality signal generation circuit  17   a  which generates a voltage corresponding to a voltage which is generated in both terminals of the current detection resistor  18   a  when the overcurrent flows due to a battery short-circuit, signal switching circuits  15   a  and  15   b  which receive a both-terminal voltage of the current detection resistor  18   a  and outputs of the battery short-circuit pseudo abnormality signal generation circuit  17   a  and switch signals that are inputted to the differential amplification circuit  14   a,  and a control circuit  10  which controls operations thereof. 
         [0029]    While not illustrated, the load drive circuit may include a clamp diode for protecting drive elements or a free wheeling diode which refluxes a current, according to characteristics of the load that is driven. 
         [0030]    The diagnosis circuit which diagnoses a battery short-circuit of  FIG. 2  is configured by the current detection resistor  18   a,  the differential amplification circuit  14   a,  the battery short-circuit threshold voltage generation circuit.  13   a,  and the comparison circuit  11   a.    
         [0031]    In a case where a battery short-circuit occurs due to abnormality of the load  101  when the drive element MOSFET  19   a  is turned on, a large current flows through the current detection resistor  18   a  and thereby the both-terminal voltage difference of the current detection resistor  18   a  increases, an output voltage of the differential amplification circuit  14   a  which amplifies the both-terminal voltage difference increases, and when the output voltage exceeds a voltage which is generated by the battery short-circuit threshold voltage generation circuit  13   a,  the diagnosis circuit determines that the overcurrent flows due to the battery short-circuit and notifies the control circuit  10 . The control circuit  10  which is notified of the generation of the battery short-circuit starts a protection operation of transmitting a signal for stopping a current by turning off the drive element MOSFET  19   a  to the predriver  12   a,  or the like. 
         [0032]    Meanwhile, when the drive element MOSFET  19   a  is turned off, a current does not flow even in a case where the battery short-circuit is generated due to the abnormality of the load  101 , and thus, the diagnosis circuit does not need to diagnose an overcurrent due to the battery short-circuit. 
         [0033]    That is, in a case where the drive element is switched to ON or OFF for load drive control, when the drive element does not need diagnosis which is performed by the diagnosis circuit, it is possible to prevent the failure of the diagnosis circuit from becoming a potential failure without affecting load drive for vehicle control, if whether or not the diagnosis circuit fails is confirmed. 
         [0034]    Hereinafter, an operation sequence to confirm whether or not the diagnosis circuit which diagnoses a battery short-circuit fails will be described with reference to  FIG. 3 . 
         [0035]    The control circuit  10  transmits a signal which controls the load drive to the predriver  12   a,  and a gate input signal N 15  of the drive element MOSFET  19   a  illustrated in  FIG. 3( a )  is inputted to the drive element MOSFET  19   a.    
         [0036]    While the gate input signal N 15  is at a high level, the drive element MOSFET  19   a  is turned on, and a current illustrated in  FIG. 3( b )  flows through the current detection resistor  18   a.  At this time, a voltage drop occurs in the current detection resistor  18   a,  and a voltage difference between an upper side signal N 11   a  of the current detection resistor  18   a  and a lower side signal N 11   b  thereof is illustrated in  FIG. 3( c ) . While the gate input signal N 15  is at a high level, the control circuit  10  controls the signal switching circuits  15   a  and  15   b,  and performs control such that the upper side signal Nita of the current detection resistor lea is outputted as an output signal N 13   a  of the signal switching circuit  15   a  and the lower side signal N 11   b  of the current detection resistor  18   a  is outputted as an output signal N 13   b  of the signal switching circuit  15   b.    
         [0037]    Meanwhile, while the gate input signal N 15  is at a low level, the drive element MOSFET  19   a  is turned off. At this time, in a case where the overcurrent flows due to the battery short-circuit, the battery short-circuit pseudo abnormality signal generation circuit  17   a  generates voltage signals with levels corresponding to voltages which are generated in the upper side signal N 11   a  and the lower side signal N 11   b  of the current detection resistor  18   a,  and respectively outputs the voltage signals to the signal switching circuits  15   a  and  15   b  as an upper side output signal N 12   a  and a lower side output signal N 12   b  of the battery short-circuit pseudo abnormality signal generation circuit  17   a.    FIG. 3( d )  illustrates a waveform of a voltage difference between the upper side output signal N 12   a  and the lower side output signal N 12   b  which are generated by the battery short-circuit pseudo abnormality signal generation circuit  17   a.  While the gate input signal N 15  is at a low level, the control circuit  10  controls the signal switching circuits  15   a  and  15   b,  and performs control such that the upper side output signal N 12   a  of the battery short-circuit pseudo abnormality signal generation circuit  17   a  is outputted as the output signal N 13   a  of the signal switching circuit  15   a  and the lower side output signal N 12   b  of the battery short-circuit pseudo abnormality signal generation circuit  17   a  is outputted as the output signal N 13   b  of the signal switching circuit  15   b.    
         [0038]    A voltage difference of the signal which is inputted to the differential amplification circuit  14   a  as a result of the control is illustrated in  FIG. 3( e ) . The differential amplification circuit  14   a  amplifies a waveform which is inputted and outputs the amplified waveform as an output signal N 16 . A voltage waveform of the output signal N 16  of the differential amplification circuit  14   a  is illustrated in  FIG. 3( f ) . 
         [0039]    The output signal N 16  of the differential amplification circuit  14   a  is inputted to the comparison circuit  11   a,  and is compared with a voltage which is generated by the battery short-circuit threshold voltage generation circuit  13   a  that determines a threshold value level of battery short-circuit determination. A signal N 17  which is generated and outputted by and from the battery short-circuit threshold voltage generation circuit  13   a  is illustrated in  FIG. 3( h ) . When an output voltage of the differential amplification circuit  14   a  exceeds a voltage which is generated by the battery short-circuit threshold voltage generation circuit  13   a,  the comparison circuit  11   a  determines that an overcurrent flows due to a battery short-circuit, and outputs an output signal N 18  with a high level to the control circuit  10 . 
         [0040]    The battery short-circuit pseudo abnormality signal generation circuit  17   a  generates a voltage corresponding to a voltage which is generated at both terminals of the current detection resistor  18   a,  when an overcurrent flows due to a battery short-circuit. Accordingly, if the differential amplification circuit  14   a,  the comparison circuit  11   a,  the battery short-circuit threshold voltage generation circuit  13   a,  the signal switching circuits  15   a  and  15   b,  or the battery short-circuit pseudo abnormality signal generation circuit  17   a  does not fail, the comparison circuit  11   a  outputs a signal with a high level to the control circuit  10 , as illustrated in  FIG. 3( g ) . Meanwhile, in a case where the comparison circuit  11   a  does not output the signal with a high level to the control circuit  10 , it is determined that at least one of the differential amplification circuit  14   a,  the comparison circuit  11   a,  the battery short-circuit threshold voltage generation circuit  13   a,  the signal switching circuits  15   a  and  15   b,  and the battery short-circuit pseudo abnormality signal generation circuit  17   a  fails. 
         [0041]    As described above, when the drive element MOSFET  19   a  is turned off, a voltage corresponding to a voltage which is generated at both terminals of the current detection resistor  18   a  is inputted to the diagnosis circuit when an overcurrent flows due to a battery short-circuit, and the diagnosis circuit confirms whether or riot abnormality is detected. Accordingly, it is possible to determine whether or not abnormality occurs in the diagnosis circuit. 
         [0042]    In  FIG. 3( d ) , while the gate input signal N 15  is at a low level, one pseudo abnormality signal is inputted, but one or more pseudo abnormality signals are inputted, and when the diagnosis circuit detects one or more abnormalities, the diagnosis circuit may be determined to be normal. 
         [0043]    In addition, as illustrated in  FIG. 4( d ) , the battery short-circuit pseudo abnormality signal generation. circuit  27   a  confirms that, after at least two types of pseudo abnormality signals of a pseudo abnormality signal P 10  of a level in which a battery short-circuit will not be detected and a pseudo abnormality signal P 11  of a level in which the battery short-circuit will be detected are inputted, the comparison circuit lie does not detect abnormality when the pseudo abnormality signal P 10  is inputted, and the comparison circuit  11   a  detects the abnormality when the pseudo abnormality signal P 11  is inputted. Accordingly, it is possible to determine that a threshold value for determining the battery short-circuit exists between a voltage level of the pseudo abnormality signal P 10  and a voltage level of the pseudo abnormality signal P 11 . 
         [0044]    Furthermore, as illustrated in  FIG. 4 , in a case where the pseudo abnormality signals are inputted in two periods of a period T 1  and a period T 2  which are continuous and the diagnosis circuit detects a failure in the two continuous periods using the pseudo abnormality signals, it may be determined that the diagnosis circuit is normal. The continuous periods in which the pseudo abnormality signals are inputted and the diagnosis circuit detects a failure may be two or more. 
         [0045]    In a case where a signal indicating flowing of an overcurrent due to the battery short-circuit is detected when the drive element MOSFET  19   a  is turned off, the abnormality detection is performed by inputting the pseudo abnormality signals, and thus, the abnormality detection is masked by the control circuit  10  or the like, and control is performed such that an operation of the load drive circuit is not affected. 
       Embodiment 2 
       [0046]      FIG. 5  relates to Embodiment 2, and illustrates a load drive circuit with a low side driver configuration having a ground short-circuit detection function and a load open-circuit detection function as the diagnosis circuit. 
         [0047]    When the drive element MOSFET  19   a  is turned off, in a case where a ground short-circuit is generated due to abnormality of the load  101 , a drain signal N 10   a  of the drive element MOSFET  19   a  reaches a ground potential, and thus, the comparison circuit  11   b  compares a potential of the drain signal N 10   a  of the drive element MOSFET  19   a  with a voltage which is generated by a ground short-circuit threshold voltage generation circuit  13   b,  and in a case where the potential of the drain signal N 10   a  is lower than the voltage which is generated by the ground short-circuit threshold voltage generation circuit  13   b,  ground short-circuit detection means in a load drive circuit illustrated in  FIG. 5  determines that the load is in a state of being ground short-circuited. 
         [0048]    Meanwhile, when the drive element MOSFET  19   a  is turned off, constant current sources  20   a  and  20   b  charge or discharge the electric charges of a capacitor  102  so as to change the potential of the drain signal N 10   a  to a predetermined potential, and a comparison circuit  11   c  compares the potential of the drain signal N 10   a  with a voltage which is generated by a load open-circuit threshold voltage generation circuit  13   c,  and in a case where the potential of the drain signal N 10   a  is higher than the voltage which is generated by the load open-circuit threshold voltage generation circuit  13   c,  load open-circuit detection means in the load drive circuit illustrated in  FIG. 5  determines that the load is in a state of being open-circuited. 
         [0049]    While not illustrated, the load drive circuit may include a clamp diode for protecting drive elements or a free wheeling diode which refluxes a current, according to characteristics of the load that is driven. 
         [0050]    Even though any one abnormality state of the ground short-circuit and the load open-circuit occurs, when the drive element MOSFET  19   a  is turned on, the potential of the drain signal N 10   a  reaches the ground potential, and thus it is not possible to detect the abnormality state. That is, when the drive element MOSFET  19   a  is turned on, it is not necessary to diagnose a load open-circuit or a ground short-circuit due to abnormality of the load  101 , and thus, during this period, a pseudo abnormality signal is inputted to the diagnosis circuit which diagnoses the ground short-circuit and the load open-circuit, and thereby, it is possible to determine whether or not the diagnosis circuit fails without affecting load drive control. 
         [0051]    Specifically, during a period in which the drive element MOSFET  19   a  is turned off, the control circuit  10  controls signal switching circuits  15   c  and  15   d,  thereby connecting the drain signal N 10   a  to the comparison circuits  11   b  and  11   c.  During this period, the comparison circuits  11   b  and  11   c  compare the potential of the drain signal N 10   a  with a voltage which is generated by the ground short-circuit threshold voltage generation circuit  13   b  that determines a threshold voltage for detecting abnormality thereof and a voltage which is generated by the load open-circuit threshold voltage generation circuit  13   c  which determines a threshold voltage for detecting abnormality thereof, and thereby ground short-circuit abnormality and load open-circuit abnormality are diagnosed. 
         [0052]    Meanwhile, during a period in which the drive element MOSFET  19   a  is turned on, the control circuit  10  controls the signal switching circuits  15   c  and  15   d,  thereby connecting a voltage which is generated by a ground short-circuit pseudo abnormality signal generation circuit  17   b  which generates a voltage corresponding to a voltage that is generated in the drain signal N 10   a  to the comparison circuit  11   b  when the ground short-circuit is generated, and connecting a voltage which is generated by a load open-circuit pseudo abnormality signal generation circuit  17   c  which generates the voltage corresponding to the voltage that is generated in the drain signal N 10   a  to the comparison circuit  11   c  when a load open-circuit occurs. 
         [0053]    The comparison circuit  11   b  compares the voltage which is generated by the ground short-circuit pseudo abnormality signal generation circuit  17   b  with the voltage which is generated by the ground short-circuit threshold voltage generation circuit  13   b,  and notifies the control, circuit  10  of detected abnormality, in a case where the voltage which is generated by the ground short-circuit pseudo abnormality signal generation circuit  17   b  is lower than the voltage which is generated by the ground short-circuit threshold voltage generation circuit  13   b.  Since the voltage which is generated by the ground short-circuit pseudo abnormality signal generation circuit  17   b  generates a voltage corresponding to the voltage which is generated in the drain signal N 10   a  when the ground short-circuit is generated, it can be determined that the diagnosis circuit is normal in a case where the comparison circuit  11   b  detects abnormality. Meanwhile, in a case where the comparison circuit  11   b  does not detect abnormality, the diagnosis circuit is determined to fail. 
         [0054]    In the same manner, the comparison circuit  11   c  compares a voltage which is generated by the load open-circuit pseudo abnormality signal generation circuit  17   c  with a voltage which is generated by the load open-circuit threshold voltage generation circuit  13   c,  and notifies the control circuit  10  of detected abnormality, in a case where the voltage which is generated by the load open-circuit pseudo abnormality signal generation circuit  17   c  is higher than the voltage which is generated by the load open-circuit threshold voltage generation circuit  13   c.  Since the voltage which is generated by the load open-circuit pseudo abnormality signal generation circuit  17   c  generates a voltage corresponding to the voltage which is generated in the drain signal N 10   a  when the load open-circuit occurs, it can be determined that the diagnosis circuit is normal in a case where the comparison circuit  11   c  detects abnormality. Meanwhile, in a case where the comparison circuit  11   c  does not detect abnormality, the diagnosis circuit is determined to fail. 
         [0055]    In inputting the pseudo abnormality signal to the diagnosis circuit, one or more pseudo abnormality signals are inputted while the drive element MOSFET  19   a  is turned on within one cycle of the control signal, and when the diagnosis circuit detects one or more abnormalities, it may be determined that the diagnosis circuit is normal. 
         [0056]    In addition, in the same manner as in  FIG. 4 ( d )  of Embodiment 1, the ground short-circuit pseudo abnormality signal generation circuit  17   b  and the load open-circuit pseudo abnormality signal generation circuit  17   c  generate at least two types of pseudo abnormality signals of the pseudo abnormality signal of a level in which abnormality will not be detected and the pseudo abnormality signal of a level in which abnormality will be detected, and thus, it is possible to determine that a threshold value for detecting abnormality exists between the two types of pseudo abnormality signal levels. 
         [0057]    Furthermore, in the same manner as in  FIG. 4  of Embodiment 1, in a case where the pseudo abnormality signal is inputted in one or more continuous periods and the diagnosis circuit detects a failure using the pseudo abnormality signal in the one or snore continuous periods, it may be determined that the diagnosis circuit is normal. 
         [0058]    In a case where a signal indicating abnormality is detected when the drive element MOSFET  19   a  is turned on, the abnormality detection is performed by inputting the pseudo abnormality signal, and thus, the abnormality detection is masked by the control circuit  10  or the like and control is performed such that an operation of the load drive circuit is not affected. 
       Embodiment 3 
       [0059]      FIG. 6  relates to Embodiment 3, and illustrates a load drive circuit with a high side driver configuration having a battery short-circuit detection function, a load open-circuit detection function, and a ground short-circuit detection function as the diagnosis circuit. 
         [0060]    When the drive element MOSFET  19   b  is turned off, in a case where a battery short-circuit is generated due to abnormality of the load  101 , a source signal NUM of the drive element MOSFET  19   b  reaches a battery potential, and thus, a comparison circuit lid compares a potential of the source signal N 10   b  with a voltage which is outputted from a battery short-circuit threshold voltage generation circuit  13   d,  and in a case where the potential of the source signal N 10   b  higher than the voltage which is outputted from the battery short-circuit threshold voltage generation circuit  13   d,  battery short-circuit detection means in a load drive circuit illustrated in  FIG. 6  determines that the load is in a state of being battery short-circuited. 
         [0061]    In addition, when the drive element MOSFET  19   b  is turned off, constant current sources  20   a  and  20   b  charge or discharge the electric charges of a capacitor  102  so as to change the potential of the source signal N 10   b  to a predetermined potential, and a comparison circuit lie compares the potential of the source signal N 10   b  with the voltage which is generated by the load open-circuit threshold voltage generation circuit  13   c,  and in a case where the potential of the source signal N 10   b  is higher than the voltage which is outputted from the load open-circuit threshold voltage generation circuit  13   c,  load open-circuit detection means in the load drive circuit illustrated in  6  determines that the load is in an open-circuit state. 
         [0062]    Furthermore, when the drive element MOSFET  19   b  is turned on, in a case where a ground short-circuit is generated due to abnormality of the load  101 , a large current flows through a current detection resistor  18   b  and thereby a both-terminal voltage difference of the current detection resistor  18   b  increases, an output voltage of a differential amplification circuit  14   b  which amplifies the both-terminal voltage difference increases, and a comparison circuit  11   f  compares the output voltage of the differential amplification circuit  14   b  with a voltage which is generated by a ground short-circuit threshold voltage generation circuit  13   f,  and in a case where the output voltage of the differential amplification circuit  14   b  is higher than the voltage which is generated by the ground short-circuit, threshold voltage generation circuit  13   f,  ground short-circuit detection means according to an overcurrent detection of the load drive circuit illustrated in  FIG. 6  determines that the ground is in a short-circuit state. 
         [0063]    While not illustrated, the load drive circuit may include a clamp diode for protecting drive elements or a free wheeling diode which refluxes a current, according to characteristics of the load that is driven. 
         [0064]    Even though an abnormality state of the battery short-circuit or the load open-circuit occurs, when the drive element MOSFET  19   b  is turned on, the potential of the source signal N 10   b  reaches the ground potential, and thus it is not possible to detect the abnormality state by using the potential of the source signal N 10   b.  That is, when the drive element MOSFET  19   b  is turned on, it is not necessary to diagnose the battery short-circuit and the load open-circuit due to abnormality of the load  101 , and thus, during this period, a pseudo abnormality signal is inputted to the diagnosis circuit which diagnoses the battery short-circuit and the load open-circuit, and thereby, it is possible to determine whether or not the diagnosis circuit fails without affecting the load drive control. 
         [0065]    Specifically, in relation to the battery short-circuit and the load open-circuit, during a period in which the drive element MOSFET  19   b  is turned off, the control circuit  10  controls signal switching circuits  15   e  and  15   f,  thereby connecting the source signal N 10   b  to the comparison circuits  11   d  and  11   e.  During this period, the comparison circuits  11   d  and  11   e  compare the potential of the source signal N 10   b  with a voltage which is generated by the battery short-circuit threshold voltage generation circuit  13   d  that determines a threshold voltage for detecting abnormality thereof and a voltage which is generated by the load open-circuit threshold voltage generation circuit  13   e  which determines a threshold voltage for detecting abnormality thereof, and thereby battery short-circuit abnormality and load open-circuit abnormality are diagnosed. 
         [0066]    Meanwhile, in relation to the battery short-circuit and the load open-circuit, during a period in which the drive element MOSFET  19   b  is turned on, the control circuit  10  controls the signal switching circuits  15   e  and  15   f,  thereby connecting a voltage which is generated by a battery short-circuit pseudo abnormality signal generation circuit  17   d  which generates a voltage corresponding to a voltage that is generated in the source signal N 10   b  when the battery short-circuit is generated to the comparison circuit  11   d,  and connecting a voltage which is generated by a load open-circuit pseudo abnormality signal generation circuit  17   e  which generates the voltage corresponding to the voltage that is generated in the source signal N 10   b  when a load open-circuit occurs the comparison circuit  11   e.    
         [0067]    The comparison circuit  11   d  compares the voltage which is generated by the battery short-circuit pseudo abnormality signal generation circuit  17   d  with the voltage which is generated by the battery short-circuit threshold voltage generation circuit  13   d,  and notifies the control circuit  10  of detected battery short-circuit, in a case where the voltage which is generated by the battery short-circuit pseudo abnormality signal generation circuit  17   d  is higher than the voltage which is generated by the battery short-circuit threshold voltage generation circuit  13   d.  Since the voltage which is generated by the battery short-circuit pseudo abnormality signal generation circuit  17   d  generates a voltage corresponding to the voltage which is generated in the source signal N 10   b  when the battery short-circuit is generated, it can be determined that the diagnosis circuit is normal in a case where the comparison circuit  11   d  detects abnormality. Meanwhile, in a case where the comparison circuit  11   d  does not detect abnormality, the diagnosis circuit is determined to fail. 
         [0068]    In the same manner, the comparison circuit  11   e  compares a voltage which is generated by the load open-circuit, pseudo abnormality signal generation circuit  17   e  with a voltage which is generated by the load open-circuit threshold voltage generation circuit  13   e,  and notifies the control circuit  10  of detected abnormality, in a case where the voltage which is generated by the load open-circuit pseudo abnormality signal generation circuit  17   e  is higher than the voltage which is generated by the load open-circuit threshold voltage generation circuit  13   e.  Since the voltage which is generated by the load open-circuit pseudo abnormality signal generation circuit  17   e  generates a voltage corresponding to the voltage which is generated in the source signal N 10   b  when the load open-circuit occurs, it can be determined that the diagnosis circuit, is normal in a case where the comparison circuit lie detects abnormality. Meanwhile, in a case where the comparison circuit lie does riot detect abnormality, the diagnosis circuit is determined to fail. 
         [0069]    In relation to a ground short-circuit, even though an abnormality state of the ground short-circuit is generated, when the drive element MOSFET  19   b  is turned off, a current does not flow, and thus it is not possible to detect the ground short-circuit abnormality by using the current detection resistor  18   b.  That is, when the drive element MOSFET  19   b  is turned off, it is not necessary to diagnose the ground short-circuit due to abnormality of the load  101 , and thus, a pseudo abnormality signal is inputted to the diagnosis circuit which diagnoses the ground short-circuit, and thereby, it is possible to determine whether or not the diagnosis circuit fails without affecting the load drive control. 
         [0070]    Specifically, during a period in which the drive element MOSFET  19   b  is turned on, the control circuit  10  controls signal switching circuits  15   g  and  15   h,  thereby connecting an upper side signal and a lower side signal of the current detection resistor  18   b  to the differential amplification circuit  14   b.  By the ground short-circuit, a large current flows through the current detection resistor  18   b  and thereby a both-terminal voltage difference of the current detection resistor  18   b  increases, an output voltage of the differential amplification circuit  14   b  which amplifies the both-terminal voltage difference increases, and when the output voltage exceeds a voltage which is generated by the ground short-circuit threshold voltage generation circuit  13   f,  it is determined that an overcurrent flows due to the ground short-circuit and the control circuit  10  is notified of the ground short-circuit. The control circuit  10  which is notified of the generation of the ground short-circuit transmits a signal for stopping a current by turning off the drive element MOSFET  19   b  to a predriver  12   b.    
         [0071]    Meanwhile, during a period in which the drive element MOSFET  19   b  is turned off, the control circuit  10  controls the signal switching circuits  15   g  and  15   h,  thereby connecting a voltage which is generated by the ground short-circuit pseudo abnormality signal generation circuit  17   f  which generates a voltage corresponding to a voltage that is generated on an upper side and a lower side of the current detection resistor  18   b  in a case where an overcurrent flows due to the ground short-circuit to the differential amplification circuit  14   b.    
         [0072]    The comparison circuit  11   f  compares the voltage which is generated by the ground short-circuit pseudo abnormality signal generation circuit  17   f  and is amplified by the differential amplification circuit  14   b  with the voltage which is generated by the ground short-circuit threshold voltage generation circuit  13   f,  and notifies the control circuit  10  of detected abnormality, in a case where the voltage which is generated by the ground short-circuit pseudo abnormality signal generation circuit  17   f  and is amplified by the differential amplification circuit  14   b  is higher than the voltage which is generated by the ground short-circuit threshold voltage generation circuit  13   f.  Since the voltage which is generated by the ground short-circuit pseudo abnormality signal generation circuit  17   f  generates a voltage corresponding to the voltage which is generated on the upper side and the lower side of the current detection resistor  18   b  when the ground short-circuit is generated, it can be determined that the diagnosis circuit is normal in a case where the comparison circuit  11   f  detects abnormality. Meanwhile, in a case where the comparison circuit  11   f  does not detect abnormality, the diagnosis circuit is determined to fail. 
         [0073]    In inputting the pseudo abnormality signal to the diagnosis circuit, one or more pseudo abnormality signals are inputted while the drive element MOSFET  19   b  is turned on within one cycle of the control signal, and when the diagnosis circuit detects one or more abnormalities, it may be determined that the diagnosis circuit is normal. 
         [0074]    In the same manner as in  FIG. 4( d )  of Embodiment 1, the battery short-circuit pseudo abnormality signal generation circuit  17   d,  the load open-circuit pseudo abnormality signal generation circuit  17   e,  and the ground short-circuit pseudo abnormality signal generation circuit  17   f  input at least two types of pseudo abnormality signals of the pseudo abnormality signal of a level in which abnormality will not be detected and the pseudo abnormality signal of a level in which abnormality will be detected, and thus, it is possible to determine that a threshold value for detecting abnormality exists between the two types of pseudo abnormality signal levels. 
         [0075]    Furthermore, in the same manner as in  FIG. 4  of Embodiment 1, in a case where the pseudo abnormality signal is inputted in one or more continuous periods and the diagnosis circuit detects a failure using the pseudo abnormality signal in the one or more continuous periods, it may be determined that the diagnosis circuit is normal. 
         [0076]    In a case where abnormality is detected by inputting the pseudo abnormality signal, the abnormality detection is masked by the control circuit  10  or the like and control is performed such that an operation of the load drive circuit is not affected. 
       Embodiment 4 
       [0077]      FIG. 7  relates to Embodiment 4, and illustrates a load drive circuit with a half bridge configuration which has a battery short-circuit detection function and a ground short-circuit detection function according to an overcurent detection as the diagnosis circuit and is configured with a high side drive element MOSFET  19   c  and a low side drive element MOSFET  19   d.    
         [0078]    A load drive element of a load drive circuit illustrated in  FIG. 7  performs operations of causing a current to flow to the load  101  from a power supply  103  by turning on the high side drive element MOSFET  19   c  and turning off the low side drive element MOSFET  19   d,  and causing a freewheeling current to flow through the load  101  according to the accumulated energy by turning off the high side drive element MOSFET  19   c  and turning on the to side drive element MOSFET  19   d.  That is, the high side drive element MOSFET  19   c  and the low side drive element MOSFET  19   d  drive the load  101  without being simultaneously turned on. 
         [0079]    When the high side drive element MOSFET  19   c  is turned on and the low side drive element MOSFET  19   d  is turned off, in a case where a around short-circuit occurs due to abnormality of the load  101 , a large current flows through a current detection resistor  18   c  and thereby a both-terminal voltage difference of the current detection resistor  18   c  increases, an output voltage of the differential amplification circuit  14   c  which amplifies the both-terminal voltage difference increases, and a comparison circuit  11   g  compares the output voltage of the differential amplification circuit  14   c  with a voltage which is generated by a ground short-circuit threshold voltage generation circuit  13   g,  and in a case were the output voltage of the differential amplification circuit  14   c  is higher than the voltage which is generated by The ground short-circuit threshold voltage generation circuit  13   g,  ground short-circuit detection means in the load drive circuit. illustrated in  FIG. 7  determines that an overcurrent state occurs due to a ground short-circuit. 
         [0080]    In addition, when the high side drive element MOSFET  19   c  is turned off and the low side drive element MOSFET  19   d  is turned on, in a case where the battery short-circuit occurs due to abnormality of the load  101 , a large current flows through a current detection resistor  18   d  and thereby a both-terminal voltage difference of the current detection resistor  18   d  increases, an output voltage of a differential amplification circuit  14   d  which amplifies the both-terminal voltage difference increases, and a comparison circuit  11   h  compares the output voltage of the differential amplification circuit  14   d  with a voltage which is generated by a battery short-circuit threshold voltage generation circuit  13   h,  and in a case where the output voltage of the differential amplification circuit  14   d  is higher than the voltage which is generated by the battery short-circuit threshold voltage generation circuit  13   h,  battery short-circuit detection means of the load drive circuit illustrated in  FIG. 7  determines that the overcurrent state occurs due to the battery short-circuit. 
         [0081]    Furthermore, while e not illustrated, when the drive element MOSFET  19   d  is turned off and the drive element MOSFET  19   c  is turned on, in a case where a current flowing through the current detection resistor  18   c  is less than a predetermined current value, load open-circuit detection means of the load drive circuit illustrated in  FIG. 7  can also determine that the load is in an open state. 
         [0082]    In a case where the around short-circuit occurs due to abnormality of the load, when the high side drive element MOSFET  19   c  is turned off, the current does not flow through the current detection resistor  18   c,  and thus, it is not possible to detect the ground short-circuit due to the overcurrent. That is, when the high side drive element MOSFET  19   c  is turned off, it is not necessary to diagnose the ground short-circuit due to abnormality of the load  101 , and thus, during this period, a pseudo abnormality signal is inputted to the diagnosis circuit which diagnoses the ground short-circuit, and thereby it is possible to determine whether or not the diagnosis circuit fails without affecting the load drive control. 
         [0083]    Specifically, during a period in which the drive element MOSFET  19   c  is turned on, the control circuit  10  controls signal switching circuits  15   i  and  15   j,  thereby connecting an upper side signal and a lower side signal of the current detection resistor  18   c  to the differential amplification circuit  14   c.  By the ground short-circuit, a large current flows through the current detection resistor  18   c  and thereby a both-terminal voltage difference of the current detection resistor  18   c  increases, and an output voltage of the differential amplification circuit  14   c  which amplifies the both-terminal voltage difference increases, and if the output voltage exceeds a voltage which is generated by the ground short-circuit threshold voltage generation circuit  13   g,  it is determined that an overcurrent flows due to the ground short-circuit and the control circuit  10  is notified of the ground short-circuit. The control circuit  10  which is notified of the generation of the ground short-circuit transmits a signal for stopping a current by turning off the high side drive element MOSFET  19   b  to a predriver  12   c.    
         [0084]    Meanwhile, during a period in which the high side drive element MOSFET  19   c  is turned off, the control circuit  10  controls the signal switching circuits  15   i  and  15   j,  thereby connecting a voltage which is generated by the ground short-circuit pseudo abnormality signal generation circuit  17   e  which generates a voltage corresponding to a voltage that is generated on an upper side and a lower side of the current detection resistor  18   c  in a case where an overcurrent flows due to the ground short-circuit to the differential amplification circuit  14   c.    
         [0085]    The comparison circuit  11   g  compares the voltage which is generated by the ground short-circuit pseudo abnormality signal generation circuit  17   e  and is amplified by the differential amplification circuit  14   c  with the voltage which is generated by the ground short-circuit threshold voltage generation circuit  13   g,  and notifies the control circuit  10  of detected abnormality, in a case where the voltage which is generated by the ground short-circuit pseudo abnormality signal generation circuit  17   e  and amplified by the differential amplification circuit  14   c  is higher than the voltage which is generated by The ground short-circuit threshold voltage generation circuit  13   g.  Since the voltage which is generated by the ground short-circuit pseudo abnormality signal generation circuit  17   e  generates a voltage corresponding to the voltage which is generated on the upper side and the lower side of the current detection resistor  18   c  when the ground short-circuit occurs, it can be determined that the diagnosis circuit is normal in a case where the comparison circuit  11   g  detects abnormality. Meanwhile, in a case where the comparison circuit  11   g  does not detect abnormality, the diagnosis circuit is determined to fail. 
         [0086]    In the same manner, in a case where the battery short-circuit occurs due to abnormality of the load, when the low side drive element MOSFET  19   d  is turned off, a current does not flow through the current detection resistor  13   d,  and thus, it is not possible to detect the battery short-circuit due to an overcurrent. That is, when the low side drive element MOSFET  19   d  is turned off, it is not necessary to diagnose the battery short-circuit due to the abnormality of the load  101 , and thus, a pseudo abnormality signal is inputted to the diagnosis circuit which diagnoses the battery short-circuit during this period, and thereby, it is possible to determine whether or not the diagnosis circuit fails without affecting the load drive control. 
         [0087]    Here, if the battery short-circuit occurs when the low side drive element MOSFET  19   d  is turned on, a current flows from a drain side to a source side of the low side drive element MOSFET  19   d.  Meanwhile, in a case where a freewheeling current flows due to energy accumulated in the load  101 , the freewheeling current flows from the source side to the drain side. The freewheeling current increases due to effects on drift of resistance components or inductance components of the load  101 , and there is also a possibility that an overcurrent flows by the freewheeling current. That is, since a current. flows in both directions of the current detection resistor  18   d,  an overcurrent diagnosis circuit including the current detection resistor  18   d  has a configuration in which an overcurrent which further flows can also be detected. 
         [0088]    Specifically, during a period in which the drive element MOSFET  19   d  is turned on, the control circuit  10  controls signal switching circuits  15   k  and  15   m,  thereby connecting an upper side signal (here, drain side of the drive element MOSFET  19   d ) and a lower side signal (here, source side of the drive element MOSFET  19   d ) of the current detection resistor  18   d  to the differential amplification circuit  14   d.  By the battery short-circuit, a large current flows through the current detection resistor  18   d  and thereby a both-terminal voltage difference of the current detection resistor  18   d  increases, the output voltage of the differential amplification circuit  14   d  which amplifies the both-terminal voltage difference increases, and when the output voltage exceeds a voltage which is generated by the battery short-circuit threshold voltage generation circuit  13   h,  it is determined that an overcurrent flows due to the battery short-circuit and the control circuit  10  is notified of the battery short-circuit. The control circuit  10  which is notified of the generation of the ground short-circuit transmits a signal for stopping a current by turning off the low side drive element MOSFET  19   d  to a predriver  12   d.    
         [0089]    Meanwhile, during a period in which the drive element MOSFET  19   d  is turned off, the control circuit  10  controls the signal switching circuits  15   k  and  15   m,  thereby connecting a voltage which is generated by the battery short-circuit pseudo abnormality signal generation circuit  17   f  which generates a voltage corresponding to a voltage: that is generated on an upper side and a lower side of the current detection resistor  18   d  in a case where an overcurrent flows due to the battery short-circuit to the differential amplification circuit  14   d.    
         [0090]    The comparison circuit  11   h  compares the voltage which is generated by the battery short-circuit, pseudo abnormality signal generation circuit  17   f  and is amplified by the differential amplification circuit  14   d  with the voltage which is generated by the battery short-circuit threshold voltage generation circuit  13   h,  and notifies the control circuit  10  of detected abnormality, in a case where the voltage which is generated by the battery short-circuit pseudo abnormality signal generation circuit  17   f  and is amplified by the differential amplification circuit  14   d.  is higher than the voltage which is generated by the battery short-circuit threshold voltage generation circuit  13   h.  Since, the voltage which is generated by the battery short-circuit pseudo abnormality signal generation circuit  17   f  generates a voltage corresponding to the voltage which is generated on the upper side and the lower side of the current detection resistor  18   d  when the battery short-circuit occurs, it can be determined that the diagnosis circuit is normal in a case where the comparison circuit  11   h  detects abnormality. Meanwhile, in a case where the comparison circuit  11   h  does not detect abnormality, the diagnosis circuit is determined to fail. 
         [0091]    In order to determine abnormality of an overcurrent which flows in both directions of the current detection resistor  18   d,  the battery short-circuit pseudo abnormality signal generation circuit  17   f  generates pseudo abnormality signals of at least two types (an overcurrent flowing from a drain to a source of the low side drive element MOSFET  19   d  and an overcurrent flowing from the source to the drain), the differential amplification circuit  14   d  includes a bias circuit. if necessary, the comparison circuit  11   h  is configured by two comparison circuits which include two threshold voltage generation circuits different from each other, if necessary. 
         [0092]    Here, as described above, when the high side drive element MOSFET  19   c  is turned on and the low side drive element MOSFET  19   d  is turned off, in a case where a current flowing through the current detection resistor  18   c  is less than a predetermined current value, the load open-circuit detection means (not illustrated) of the load drive circuit illustrated in  FIG. 7  can also determine that the load is in an open state. That is, when the high side drive element. MOSFET  19   c  is turned off and the low side drive element MOSFET  19   d  is turned on, a pseudo abnormality voltage corresponding to the voltage which is generated in the current detection resistor  18   d  when a load open-circuit occurs is inputted to the load open-circuit detection means, and thus, it is determined whether or not the diagnosis circuit which diagnoses the load open-circuit fails. 
         [0093]    In inputting the pseudo abnormality signal to the diagnosis circuit, one or more pseudo abnormality signals are inputted while the drive element MOSFETs  19   c  and  19   d  are turned on within one cycle of the control signal, and when the diagnosis circuit detects one or more abnormalities, it may be determined that the diagnosis circuit is normal. 
         [0094]    In addition, in the same manner as in  FIG. 4 ( d )  of Embodiment 1, the battery short-circuit pseudo abnormality signal generation circuit  17   f,  and the around short-circuit pseudo abnormality signal generation circuit  17   e  input at least two types of pseudo abnormality signals of the pseudo abnormality signal of a level in which abnormality will not be detected and the pseudo abnormality signal of a level in which abnormality will be detected, and thus, it is possible to determine that a threshold value for detecting abnormality exists between the two types of pseudo abnormality signal levels. 
         [0095]    Furthermore, in the same manner as in  FIG. 4  of Embodiment 1, in a case where the pseudo abnormality signal is inputted in one or more continuous periods and the diagnosis circuit detects a failure using the pseudo abnormality signal in the one or more continuous periods, it may be determined that the diagnosis circuit is normal. 
         [0096]    In a case where a failure is detected by inputting the pseudo abnormality signal, the abnormality detection is masked by the control circuit  10  or the like and control is performed such that an operation of the load drive circuit is not affected. 
       Embodiment 5 
       [0097]      FIG. 8  relates to Embodiment 5, and illustrates a load drive circuit with the low side driver configuration having a battery short-circuit detection function according to overcurrent detection as the diagnosis circuit. 
         [0098]    A load drive circuit  100  illustrated in  FIG. 8  is a circuit which is provided in a lower portion of the power supply  103  and the load  101 , and is configured by a drive element MOSFET  19   e  and a predriver  12   a  for driving the drive element MOSFET, a current detection resistor  18   e  for monitoring a current flowing through the drive element MOSFET  19   e,  a differential amplification circuit  23  which includes a predetermined gain for amplifying a signal that is converted into a voltage by the current detection resistor  18   e,  and at least two types of gains among gains higher than the predetermined gain, and in which the two types of gains can be changed, a battery short-circuit threshold voltage generation circuit  13   i  which determines a threshold value determining whether or not an overcurrent flows due to the battery short-circuit, comparison circuit  11   i  which determines whether or not the overcurrent flows by comparing an output voltage of the differential amplification circuit  23  that can change a gain with the battery short-circuit threshold voltage generation circuit  13   i,  a drive control circuit  21  which controls the drive element MOSFET  19   e  for load drive control, a diagnosis drive control circuit  22  which is separately provided from the drive control circuit  21  and controls the drive element MOSFET  19   e  for confirming whether or not a battery short-circuit detection. circuit fails, a signal switching circuit  15   n  which is connected to the predriver  12   a  and switches a signal of the drive control circuit  21  and a signal of the diagnosis drive control circuit  22  to each other, and a control circuit  10  which controls operations thereof. 
         [0099]    While not illustrated, the load drive circuit may include a clamp diode for protecting drive elements or a free wheeling diode which refluxes a current, according to characteristics of the load that is driven. 
         [0100]    The diagnosis circuit which diagnoses a battery short-circuit of  FIG. 8  is configured by the current detection resistor  18   e,  the differential amplification circuit  23  which can change a gain, the battery short-circuit threshold voltage generation circuit  131 , and the comparison circuit  11   i.    
         [0101]    In a case where a battery short-circuit occurs due to abnormality of the load  101  when the drive element MOSFET  19   e  is turned on, a large current flows through the current detection resistor  18   e  and thereby the both-terminal voltage difference of the current detection resistor  18   e  increases, an output voltage of the differential amplification circuit which amplifies the both-terminal voltage difference increases, and when the output voltage exceeds a voltage which is generated by the battery short-circuit threshold voltage generation circuit  13   i,  the diagnosis circuit which diagnoses the battery short-circuit determines that an overcurrent flows due to the battery short-circuit and notifies the control circuit  10 . The control circuit  10  which is notified of the generation of the battery short-circuit transmits a signal for stopping a current by turning off the drive element MOSFET  19   e  to the predriver  12   e.    
         [0102]    Meanwhile, when the drive element MOSFET  19   e  is turned off, a current does not flow even in a case where the battery short-circuit occurs due to the abnormality of the load  101 , and thus, the diagnosis circuit does not need to diagnose the battery short-circuit. 
         [0103]    That is, in a case where the drive element is switched to ON or OFF for load drive control, when the drive element does not need diagnosis which is performed by the diagnosis circuit, it is possible to prevent the failure of the diagnosis circuit from becoming a potential failure without affecting the load drive for vehicle control, if whether or not the diagnosis circuit fails is confirmed. 
         [0104]    Hereinafter, an operation of Embodiment 5 will be described with reference to  FIG. 9 . 
         [0105]      FIG. 9 ( a )  illustrates an output signal N 102  of the drive control circuit  21  for controlling the drive element MOSFET  19   e  for load drive. 
         [0106]      FIG. 9( b )  illustrates an output signal N 102  of the diagnosis drive control circuit  22 . When the drive control circuit  21  outputs a signal with a low level and the drive element MOSFET  19   e  is in a turn-off state, the diagnosis drive control circuit  22  generates a signal with a frequency which satisfies conditions that will be described below and characteristics of a duty, and outputs the output signal N 102 . 
         [0107]    The control circuit  10  confirms whether the drive element MOSFET  19   e  is in a state of being turned on or in a state of being turned off so as to perform load drive control, and switches the signal switching circuit  15   n,  according to a state thereof. The signal switching circuit  15   n  outputs an output of the drive control circuit  21  to the predriver  12   e,  when the drive element MOSFET  19   e  is turned on, and outputs an output of the diagnosis drive control circuit  22  to the predriver  12   e,  when the drive element MOSFET  19   e  is turned off. 
         [0108]    An output signal N 103  of the signal switching circuit  15   n  which is connected to the predriver  12   e  becomes a signal of  FIG. 9 ( c ) , according to control of the signal switching circuit  15   n,  and the drive element MOSFET  19   e  is driven at a timing of a waveform of  FIG. 9( c ) . 
         [0109]    Here, illustrated in  FIG. 9 ( d ) , a gain of the differential amplification circuit  23  is set to a predetermined gain which is required for load drive control when the drive element MOSFET  19   e  is turned on, and is set to a gain higher than the predetermined gain when the drive element MOSFET  19   e  is turned off. When the gain is changed to a gain higher than the predetermined gain, false detection of the overcurrent is prevented by a discharging current or the like of the energy accumulated in the load, and thus, delay time is generated in switching timing. 
         [0110]    Next, a current flowing through the current detection resistor  18   e  is illustrated in  FIG. 9( e ) . When the drive control circuit  21  outputs a signal with a high level and thereby the drive element MOSFET  19   e  is turned on, it is necessary for a current sufficient for driving the load to flow, and thus, a signal with a high level is outputted during a period required for the flowing. Meanwhile, when the diagnosis drive control circuit  22  controls the drive element MOSFET  19   e,  a frequency and a duty are set to be equal to or less than the current amount which does not drive the load, during a period in which the drive control circuit  21  outputs a signal with a low level. 
         [0111]    A period in which the diagnosis drive control circuit  22  controls the drive element MOSFET  19   e  is a period in which the drive element MOSFET  19   e  has to be turned off for load control, but during this period, a current flows which is equal to or less than the current amount which does not drive the load in accordance with adjustment of a frequency and a duty, the current is inputted to the diagnosis circuit which diagnoses a battery short-circuit by detecting an overcurrent, as a pseudo abnormality signal, and thus, it is determined whether or not the diagnosis circuit fails. Since a negative overcurrent flowing during this period does not affect negative drive control the diagnosis drive control circuit  22  adjusts a frequency and a duty of the output signal so that the current is equal to or less than a current amount which does not drive the load and to be a desired current amount. 
         [0112]    A gain higher than the predetermined gain of the differential amplification circuit  23  which can change a gain is set to a value which can be used as a pseudo abnormality signal by a load current according to control of the diagnosis drive control circuit  22 . That is, the load current according to the control of the diagnosis drive control circuit  22  is converted into a voltage by the current detection resistor  18   e  and the differential amplification circuit  23  amplifies the voltage, and as the result, a gain thereof is set such that an output of the differential amplification circuit  23  becomes a voltage exceeding a voltage which is generated by the battery short-circuit threshold voltage generation circuit  13   i.    
         [0113]    An output waveform of the differential amplification circuit  23  which is obtained as the result of switching a gain of the differential amplification circuit  23  is illustrated in  FIG. 9( f ) .  FIG. 9( h )  illustrates a voltage which is generated by the battery short-circuit threshold voltage generation circuit  13   i.  When a current, flows which is equal to or less than a current amount which does not drive the load, a gain higher than the predetermined gain of the differential amplification circuit  23  is set such that an output voltage of the differential amplification circuit  23  exceeds the voltage which is generated by the battery short-circuit threshold voltage generation circuit  13   i,  and thus, the comparison circuit  11   e  detects generation of an overcurrent and notifies the control circuit  10  of the generation of the overcurrent.  FIG. 9( g )  illustrates an output waveform of the comparison circuit  11   e.  Meanwhile, in a case where the comparison circuit  11   e  does not detect a failure, it is determined that a failure occurs in at least one portion of the diagnosis circuit which is configured with the current detection resistor  18   e,  the differential amplification circuit  23  which can change a gain, the battery short-circuit threshold voltage generation circuit  13   i,  and the comparison. circuit  11   i.    
         [0114]    As described above, in a period in which the drive element MOSFET  19   e  is turned off, the drive element MOSFET  19   e  is controlled by a drive signal for diagnosing, a negative overcurrent flowing at that time is inputted to a battery short-circuit diagnosis circuit, as a pseudo abnormality signal, and thus, it is possible to perform diagnosis by including the current detection resistor. 
         [0115]    In inputting the pseudo abnormality signal to the diagnosis circuit, one or more pseudo abnormality signals are inputted while the drive element MOSFET  19   a  is turned on within one cycle of the control signal, and when the diagnosis circuit detects one or more abnormalities, it may be determined that the diagnosis circuit is normal. 
         [0116]    In addition, in the same manner as in  FIG. 4 ( d )  of Embodiment 1, the diagnosis drive control circuit  22  inputs at least two types of pseudo abnormality signals among a current of a level in which abnormality will not be detected and a current of a level in which abnormality will be detected, and thus, it is possible to determine that a threshold value for detecting abnormality exists between the two types of pseudo abnormality signal levels. 
         [0117]    Furthermore, in the same manner as in  FIG. 4  of Embodiment 1, in a case where the pseudo abnormality signal is inputted in one or more continuous periods and the diagnosis circuit detects a failure using the pseudo abnormality signal in the one or more continuous periods, it may be determined that the diagnosis circuit is normal. 
         [0118]    In a case where abnormality is detected by inputting the pseudo abnormality signal, the abnormality detection is masked by the control circuit  10  or the like and control is performed such that an operation of the load drive circuit is not affected. 
       Embodiment 6 
       [0119]    While not illustrated, the method of confirming whether or not the diagnosis circuit fails by inputting the pseudo abnormality signal to the diagnosis circuit, as described in Embodiments 1 to 5, when the diagnosis circuit does not need to diagnose, can also be applied to a function which detects an overcurrent of a switching regulator. 
         [0120]    A switching element of the switching regulator repeats a turn-on state and a turn-off state. When the switching element is turned on, diagnosis of an overcurrent is performed, but when the switching element is turned off, a current does not flow and thus, it is not necessary to diagnose the overcurrent. At the time of this state, a pseudo abnormality signal corresponding to a signal which is generated at the time of the overcurrent is inputted to a diagnosis circuit which diagnoses the overcurrent, and thus, it is possible to determine whether or not an overcurrent diagnosis function fails. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           10 : control circuit 
           11   a  to  11   i:  comparison circuit 
           12   a  to  12   e:  predriver 
           13   a:  battery short-circuit threshold voltage generation circuit (low side driver configuration) 
           13   b:  ground short-circuit threshold voltage generation circuit (low side driver configuration) 
           13   c:  load open-circuit threshold voltage generation circuit (low side driver configuration) 
           13   d:  battery short-circuit threshold voltage generation circuit (high side driver configuration) 
           13   e:  load open-circuit threshold voltage generation circuit (high side driver configuration) 
           13   f:  ground short-circuit threshold voltage generation circuit (high side driver configuration) 
           13   g:  ground short-circuit threshold voltage generation circuit (half bridge configuration) 
           13   h:  battery short-circuit threshold voltage generation circuit (half bridge configuration) 
           14   a  to  14   d:  differential amplification circuit 
           15   a  to  15   n:  signal switching circuit 
           17   a:  battery short-circuit pseudo abnormality signal generation circuit (low side driver configuration) 
           17   b:  ground short-circuit pseudo abnormality signal generation (low side driver configuration) 
           17   c:  load open-circuit pseudo abnormality signal generation (low side driver configuration) 
           17   d:  battery short-circuit pseudo abnormality signal generation (high side driver configuration) 
           17   e:  load open-circuit pseudo abnormality signal generation (high side driver configuration) 
           17   f:  ground short-circuit pseudo abnormality signal generation circuit (high side driver configuration) 
           17   e:  ground short-circuit pseudo abnormality signal generation circuit (half bridge configuration) 
           17   g:  battery short-circuit pseudo abnormality signal generation circuit (half bridge configuration) 
           18   a  to  18   e:  current detection resistor 
           19   a  to  19   e:  drive element MOSFET 
           20   a,    20   h:  constant current source 
           21 : drive control circuit 
           22 : diagnosis drive control circuit 
           23 : differential amplification circuit which can change gain 
           100 : load drive circuit 
           101 : load 
           102 : capacitor 
           103 ,  104 : power supply 
         N 10   a:  drain signal of drive element MOSFET  19   a  (low side configuration) 
         N 10   b:  source signal of drive element MOSFET  19   b  (high side configuration) 
         N 11   a:  upper side signal of current detection resistor  18   a    
         N 11   b:  lower side signal of current detection resistor  18   a    
         N 12   a:  upper side output signal of battery short-circuit pseudo abnormality signal generation circuit  17   a    
         N 12   b:  lower side output signal of battery short-circuit pseudo abnormality signal generation circuit  17   a    
         N 13   a:  output signal of signal switching circuit  15   a    
         N 13   b:  output signal of signal switching circuit  15   b    
         N 14 : switching signal of signal switching circuits  15   a  and  15   b    
         N 15 : gate input signal of drive element MOSFET  19   a    
         N 16 : output signal of differential amplification circuit  14   a    
         N 17 : output signal of battery short-circuit threshold voltage generation circuit  13   a    
         N 18 : output signal of comparison circuit  11   a    
         N 101 : output signal of drive control circuit  21   
         N 102 : output signal of diagnosis drive control circuit 
         N 103 : output signal of signal switching circuit  15   g    
         N 104 : output signal of differential amplification circuit  23  which can change gain 
         N 105 : output signal of battery short-circuit threshold voltage generation circuit  13   i    
         N 106 : output signal of comparison circuit  11   a    
         P 10 : pseudo abnormality signal of level in which overcurrent will not be detected 
         P 11 : pseudo abnormality signal of level in which overcurrent will be detected