JP2011160289A - Load driving circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a load driving circuit that notifies users in advance about a sign of an abnormal condition. <P>SOLUTION: A detection circuit 14 detects overcurrent or a sign thereof and another abnormal condition, as well as the occurrence of overcurrent or a sign thereof based an increase in temperature, and also detects overcurrent or a sign thereof based on a current actually applied to a load 3 through a semiconductor switching element 12. Furthermore, the detection circuit 14 detects an abnormal state of a power source voltage applied to the load 3, such as load open, and abnormal ON and OFF states. When the sign of overcurrent is detected, the information is given to a sign diagnosis circuit 18c, and a sign diagnosis signal corresponding thereto is generated. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a load driving circuit capable of notifying an anomaly sign in addition to the occurrence of an abnormality in the state of power supply to a load.

  Conventionally, for example, Patent Document 1 discloses a vehicular electronic control device (hereinafter referred to as an ECU) that can notify that an abnormality has occurred. Specifically, when the ECU is recovered in a state where the internal circuit cannot be protected and is destroyed in the market, whether the ECU was destroyed due to a defective part, or actually an overvoltage or reverse battery connection occurs Therefore, when the overvoltage or overcurrent is input, it is stored as a memory so that the history can be understood. .

JP 2007-53876 A

  However, in the ECU shown in Patent Document 1, control is performed when an abnormality occurs, and control such as actively protecting the circuit by blocking output from the ECU is performed, or contrary to the intention of the user. When the output is interrupted, the user cannot be notified of the precursor.

  An object of this invention is to provide the load drive circuit which can alert | report the precursor which abnormality generate | occur | produces with respect to a user in advance in view of the said point.

  To achieve the above object, according to the first aspect of the present invention, the semiconductor switching element (12) for controlling on / off of voltage application from the power source (2) to the load (3) and the switch (4) are turned on. An input circuit (10) that outputs a control signal based on a corresponding input signal, and an output control circuit (11) that controls on / off of the semiconductor switching element (12) based on a control signal output from the input circuit (10) An abnormality detection circuit (13-17) for detecting the occurrence of an abnormality in the state of power supply to the load (3) and its precursor and outputting a precursor signal indicating the precursor of the abnormality; And a warning diagnosis circuit (18c) that outputs a warning signal indicating a warning of abnormality detected by the abnormality detection circuits (13 to 17).

  In this way, the abnormality detection circuits (13 to 17) detect not only the occurrence of abnormality but also the precursor of abnormality. For this reason, it is possible not only to notify the user of the occurrence of the abnormality but also to notify the precursor of the abnormality in advance.

  Specifically, as described in claim 2, the abnormality detection circuit (13 to 17) generates an overcurrent indicating that the load current supplied to the load is excessive and detects its precursor. In the warning diagnostic circuit (18c), a warning signal indicating that a warning of overcurrent has been detected is transmitted from the abnormality detection circuit (13 to 17), so that a warning warning signal indicating the warning of overcurrent is output. Can be.

  For example, as described in claim 3, in the abnormality detection circuit (13 to 17), when the duration during which the load current exceeds the abnormality threshold reaches the failure determination time (T), it is determined that an overcurrent has occurred. , The duration when the load current exceeds the precursor threshold value below the abnormal threshold reaches the precursor determination time (T ′) shorter than the failure determination time (T), or exceeds the precursor threshold smaller than the abnormal threshold When the duration reaches a precursor determination time (T ′) that is equal to or shorter than the failure determination time (T), it can be determined as a precursor of an overcurrent.

  As such an abnormality detection circuit (13-17), for example, as described in claim 4, by directly detecting the load current supplied to the load (3) or the voltage applied to the load (3), An overcurrent detection circuit (15a) for detecting occurrence of an overcurrent and its precursor can be provided.

  According to a fifth aspect of the present invention, there is provided a heating detection circuit (15b) for detecting the occurrence of an overcurrent and its precursor by detecting a temperature rise of the semiconductor switching element (12) based on a load current flowing through the load (3). Can also be provided.

  In addition, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific means as described in embodiment mentioned later.

It is the block diagram which showed each part to which the load drive circuit 1 concerning 1st Embodiment of this invention and the load drive circuit 1 are connected. It is a timing chart showing a judgment image of a precursor or occurrence of overcurrent. It is a timing chart showing a judgment image of precursors or occurrence of various abnormalities such as load open. It is the timing chart which showed the determination image in the case of using only a threshold value for abnormality determination. It is the block diagram which showed the structure in the case of outputting a diagnostic signal with a serial signal. It is the block diagram which showed the modification of the memory | storage form to the past diagnosis circuit 18b.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, the same or equivalent parts are denoted by the same reference numerals in the drawings.

(First embodiment)
FIG. 1 is a block diagram showing a load driving circuit 1 according to the present embodiment and each part to which the load driving circuit 1 is connected. Hereinafter, the load driving circuit 1 and the like according to the present embodiment will be described with reference to FIG.

  A load driving circuit 1 shown in FIG. 1 drives a load 3 such as a headlamp for a vehicle based on power supply from a power source 2 such as a battery. Specifically, the switch 4 is connected to the input terminal 1a of the load driving circuit 1, the power supply 2 is connected to the power supply terminal 1b, and the load 3 is connected to the output terminal 1c. The load driving circuit 1 receives the input signal corresponding to the operation state of the switch 4 by the user through the input terminal 1a, and outputs the power supply voltage input from the power supply terminal 1b according to the input signal to the output terminal 1c. Applied to the load 3 connected to.

  One contact of the switch 4 is grounded, and when the switch 4 is turned on, the potential of the input terminal 1a becomes the ground potential. For this reason, the input signal is at a high level before the switch 4 is turned on and is at a low level after the switch 4 is turned on, and on / off of voltage application to the load 3 is controlled according to the potential of the input signal.

  The load drive circuit 1 includes an input circuit 10, an output control circuit 11, a semiconductor switching element 12, a temperature detection circuit 13, a detection circuit 14, an external short detection circuit 15, a load open detection circuit 16, an internal failure detection circuit 17, and a diagnosis output circuit. 18 and OR circuits 19a to 19c. Among these, the temperature detection circuit 13, the detection circuit 14, the external short detection circuit 15, the load open detection circuit 16, and the internal failure detection circuit 17 constitute the abnormality detection circuit of the present invention.

  The input circuit 10 controls driving of the semiconductor switching element 12 by the output control circuit 11 in accordance with an input signal input through the input terminal 1a. For example, when the switch 4 is dropped and the input signal is at a low level, the input circuit 10 outputs a control signal for turning on the semiconductor switching element 12 by the output control circuit 11, and the switch 4 is cut off and the input signal is high. At the level, the output control circuit 11 outputs a control signal for turning off the semiconductor switching element 12.

  The output control circuit 11 drives the semiconductor switching element 12 on and off based on a control signal input from the input circuit 10. For example, the output control circuit 11 outputs a high level when the control signal input from the input circuit 10 instructs to turn on the semiconductor switching element 12, and instructs to turn off the semiconductor switching element 12. When it is, it outputs a low level. Further, the output control circuit 11 receives a signal indicating the detection result of the external short detection circuit 15 and, based on the detection result, outputs the semiconductor switching element 12 regardless of the control signal from the input circuit 10 when an overcurrent occurs. The state in which the current (hereinafter referred to as load current) flowing to the load 3 becomes excessive by turning off, that is, the occurrence of overcurrent is suppressed.

  The semiconductor switching element 12 is configured by a MOS transistor, a bipolar transistor, or the like, and is turned on / off according to the output of the output control circuit 11. When the semiconductor switching element 12 is turned on, the voltage of the power supply 2 input through the power supply terminal 1b is applied to the load 3 through the output terminal 1c.

  The temperature detection circuit 13 is for detecting the temperature of the semiconductor switching element 12. For example, the temperature detection circuit 13 includes a plurality of diodes connected in series, and the like. A voltage of a constant voltage source (not shown) is applied to the plurality of diodes, and the forward voltage Vf of the plurality of diodes varies depending on the temperature characteristics. Therefore, the value of the current flowing through the plurality of diodes or the amount of voltage drop across the plurality of diodes varies depending on the temperature of the semiconductor switching element 12. Since this current value or voltage drop amount indicates the temperature of the semiconductor switching element 12, the temperature detection circuit 13 outputs these current value or voltage drop amount to the detection circuit 14.

  The detection circuit 14 detects an abnormality or a sign of a power supply state to the load 3. Specifically, the detection circuit 14 detects the occurrence of an overcurrent, its precursor, and other abnormalities, detects the occurrence of the overcurrent or its precursor based on a temperature rise, or actually performs semiconductor switching. Based on the current flowing to the load 3 through the element 12, the occurrence of an overcurrent and its precursor are detected, and abnormalities in the state of application of the power supply voltage to the load 3, such as load open, output ON failure, and output OFF failure Detect the occurrence of

  Specifically, the output of the temperature detection circuit 13 is input to the detection circuit 14. Based on the output of the temperature detection circuit 13, the detection circuit 14 detects the temperature rise of the semiconductor switching element 12 to detect the occurrence of overcurrent and its precursor. That is, since the temperature rise is caused by the heat generation of the semiconductor switching element 12 according to the magnitude of the load current, the load current can be estimated from the current value or voltage drop detected by the temperature detection circuit 13. For this reason, the detection circuit 14 estimates the load current by inputting the current value or voltage drop detected by the temperature detection circuit 13 to the detection circuit 14, and detects the occurrence of an overcurrent and its precursor based on the estimated load current.

  In addition, the low-side voltage of the semiconductor switching element 12 is input to the detection circuit 14. The detection circuit 14 estimates the load current flowing through the load 3 from this voltage because the low-side potential of the semiconductor switching element 12 represents the voltage applied to the load 3, and generates an overcurrent. Detect signs and signs. For example, since the overcurrent is generated due to a short circuit of the load 3 or the like, for example, when the overcurrent is generated, for example, the potential on the low side of the semiconductor switching element 12 is greatly lowered and becomes close to zero. By detecting this, an overcurrent and its precursor can be detected. Furthermore, the detection circuit 14 detects a load open, an output ON failure, an output OFF failure, and its precursor based on the voltage on the low side of the semiconductor switching element 12.

  The load open means a situation in which no current flows to the load 3 even though the semiconductor switching element 12 is on, and a path connected to the load 3 (for example, For example, wire breakage. For example, when the potential on the low side of the semiconductor switching element 12 is the power supply voltage because no current flows to the load 3, the load is opened when the potential is different from that when no load is open. Detected. The output ON failure means a state in which voltage application by the power source 2 is continued even when the semiconductor switching element 12 is turned off, and is inside the power source terminal 1b and the output terminal 1c, that is, in the load driving circuit 1. This corresponds to the failure. The output OFF failure means a state in which no voltage is applied from the power source 2 even when the semiconductor switching element 12 is turned on. For example, an open failure of the semiconductor switching element 12 corresponds.

  When the detection circuit 14 detects the occurrence of an overcurrent or its precursor, or detects the occurrence of a load open, output ON failure, or output OFF failure, a signal indicating this is sent to the external short detection circuit 15 or the load open detection circuit. 16 and the internal failure detection circuit 17 are used to notify each part of the occurrence of overcurrent, its precursor, and the occurrence of an abnormality.

  Here, the occurrence of overcurrent and its precursor are detected by inputting the low-side potential of the semiconductor switching element 12 to the detection circuit 14, but other methods may be used. . For example, the semiconductor switching element 12 is configured by a current mirror circuit having a main element that supplies current to the load 3 and a sense element that allows a sufficiently small current to flow in proportion to the current flowing through the main element. Even if the current on the side is input to the detection circuit 14, the overcurrent can be directly detected.

  The external short detection circuit 15 detects an external short such as a load short circuit. Since an overcurrent occurs at the time of an external short, an external short is detected by detecting the occurrence of an overcurrent and its precursor. Specifically, the external short detection circuit 15 includes an overcurrent detection circuit 15a and a heating detection circuit 15b.

  When the overcurrent detection circuit 15a outputs a signal indicating that the detection circuit 14 has detected the occurrence or precursor of overcurrent based on the low-side potential of the semiconductor switching element 12, the overcurrent detection circuit 15a inputs the signal and responds accordingly. Generate a signal. For example, in the case of this embodiment, a high level is output from the overcurrent detection circuit 15a. Moreover, when the detection circuit 14 outputs a signal indicating that the detection circuit 14 has detected the occurrence of an overcurrent or its precursor based on the temperature rise, the heating detection circuit 15b inputs the signal and generates a signal corresponding thereto. For example, in this embodiment, a high level is output from the heating detection circuit 15b.

  A signal indicating the occurrence of overcurrent or heating by the overcurrent detection circuit 15a or the heating detection circuit 15b (hereinafter referred to as a precursor signal) is input to the first OR circuit 19a, and the overcurrent detection circuit 15a and the heating are detected. If any one of the precursor signals of the detection circuit 15b is at a high level, the first OR circuit 19a also outputs a high level as a precursor signal. A signal indicating the occurrence of overcurrent or heating by the overcurrent detection circuit 15a or the heating detection circuit 15b (hereinafter referred to as a generation signal) is input to the second OR circuit 19b, and the overcurrent detection circuit 15a and the heating detection circuit If any one of the generated signals 15b is at a high level, the second OR circuit 19b also outputs a high level as the generated signal.

  When the load open detection circuit 16 outputs a signal indicating that the detection circuit 14 has detected the occurrence of a load open, the load open detection circuit 16 inputs the signal and generates a signal corresponding thereto. For example, in this embodiment, a high level is output from the load open detection circuit 16.

  The internal failure detection circuit 17 detects an internal failure of the load drive circuit 1. Specifically, the internal failure detection circuit 17 includes an output ON failure detection circuit 17a and an output OFF failure detection circuit 17b.

  When the output ON failure detection circuit 17a outputs a signal indicating that the detection circuit 14 has detected the occurrence of the output ON failure based on the low-side potential of the semiconductor switching element 12, the signal is input and a signal corresponding thereto Is generated. For example, in the case of this embodiment, a high level is output from the output ON failure detection circuit 17a. Further, when the output OFF failure detection circuit 17b outputs a signal indicating that the detection circuit 14 has detected the occurrence of the output OFF failure, the output OFF failure detection circuit 17b inputs the signal and generates a signal corresponding thereto. For example, in the case of this embodiment, a high level is output from the output OFF failure detection circuit 17b.

  A signal indicating the occurrence of the output ON failure or the output OFF failure by the output ON failure detection circuit 17a or the output OFF failure detection circuit 17b is input to the third OR circuit 19c, and the output ON failure detection circuit 17a and the output OFF failure detection circuit If any one of the outputs of 17b is at a high level, the third OR circuit 19c also outputs a high level.

  The diagnosis output circuit 18 outputs a diagnosis signal (inspection signal) indicating the occurrence of an overcurrent or a sign or abnormality thereof. Specifically, the diagnosis output circuit 18 includes a current diagnosis circuit 18a, a past diagnosis circuit 18b, and a precursor diagnosis circuit 18c.

  The current diagnosis circuit 18a outputs a diagnosis signal indicating the current situation, and generates a current diagnosis signal corresponding to the detection results of the external short detection circuit 15, the load open detection circuit 16 and the internal failure detection circuit 17 as an output. . Specifically, the current diagnosis circuit 18a receives the output of the second OR circuit 19b, the output of the load open detection circuit 16 and the third OR circuit 19c, and generates a corresponding current diagnosis signal.

  The past diagnosis circuit 18b stores a diagnosis state indicated by the detection result of the external short detection circuit 15 in conjunction with the current diagnosis circuit 18a in a memory (not shown) and generates a past diagnosis signal corresponding to the stored contents as an output. For example, the past diagnosis circuit 18b updates the current diagnosis state every predetermined period, but when the switch 4 is shut off, the contents stored immediately before the shut-off are held as they are. Then, for example, when an erasing command by a diagnostic tool or the like is input from the outside, the stored diagnostic state is reset.

  The warning diagnosis circuit 18c outputs a diagnosis signal indicating a sign of occurrence of overcurrent, and generates a current diagnosis signal corresponding to the detection result of the external short detection circuit 15 as an output. Specifically, the warning diagnosis circuit 18c receives the output of the first OR circuit 19a and generates a warning warning signal corresponding thereto.

  The current diagnosis signal generated by the current diagnosis circuit 18a, the past diagnosis signal generated by the previous diagnosis circuit 18b, and the warning diagnosis signal generated by the warning diagnosis circuit 18c are output from the first to third diagnosis output terminals 1d to 1f, respectively. Is done.

  Then, various diagnostic signals output from the first to third diagnostic output terminals 1d to 1f are input to another ECU such as a body ECU 5 provided outside the load drive circuit 1, for example. It is read that there are signs of occurrence, overcurrent or abnormality. Based on this, a notification command signal is output from the body ECU 5 to the warning lamp 6 when there is a sign of the occurrence of an overcurrent or when an overcurrent or an abnormality occurs. As a result, the warning lamp 6 notifies the user that there is a sign of the occurrence of an overcurrent, the occurrence of an overcurrent, or the occurrence of an abnormality.

  Next, the operation of the load drive circuit 1 configured as described above will be described. First, before the switch 4 is turned on, since the input signal input to the input circuit 10 through the input terminal 1a is not at a low level, the control signal for turning on the semiconductor switching element 12 is output from the input circuit 10. Not. For this reason, the output of the output control circuit 11 is also at a low level, the semiconductor switching element 12 is turned off, and the power supply voltage of the power supply 2 is not applied to the load 3.

  Next, when the switch 4 is turned on, an input signal input to the input circuit 10 through the input terminal 1a becomes a low level, so that a control signal for turning on the semiconductor switching element 12 is output from the input circuit 10. Therefore, the output of the output control circuit 11 becomes high level, the semiconductor switching element 12 is turned on, and the power supply voltage of the power supply 2 is applied to the load 3. Thereby, the load 3 is driven. For example, if the load 3 is a headlamp, the headlamp is turned on.

  At this time, when an external short circuit due to a short circuit of the load 3 or the like occurs, the potential on the low side of the semiconductor switching element 12 becomes a voltage close to zero. Based on this potential, the detection circuit 14 detects overcurrent. For example, the detection circuit 14 uses both time and a threshold for determining overcurrent.

  FIG. 2 is a timing chart showing a determination image of a precursor or occurrence of overcurrent. As described above, the load current is estimated from the potential on the low side of the semiconductor switching element 12. As shown in FIG. 2, when the load current exceeds a precursor threshold where it is assumed that there is a precursor to an overcurrent, and the exceeding time exceeds the precursor determination time T ′, the overcurrent is exceeded. It is determined that there is a sign of occurrence. In addition, when the estimated load current exceeds an abnormal threshold that is assumed to be an overcurrent, and the exceeded time exceeds a failure determination time T that is longer than the precursor determination time T ′ It is determined that an overcurrent has occurred, and for example, the semiconductor switching element 12 is cut off to cut off the voltage application to the load 3. In this way, not only the occurrence of an overcurrent but also a sign of the occurrence of an overcurrent can be detected.

  Here, the precursor determination time T ′ is shorter than the failure determination time T and the precursor threshold is set smaller than the abnormality threshold. However, if the precursor threshold is smaller than the abnormality threshold, the precursor determination time T ′ is The determination threshold T may be made equal, or conversely, if the precursor determination time T ′ is made shorter than the failure determination time T, the precursor threshold may be made equal to the abnormality threshold. That is, the precursor determination time T ′ is set to be shorter than or equal to the failure determination time T and the precursor threshold is set to a value smaller than the abnormality threshold, or the precursor determination time T ′ is set to the failure determination time while the precursor threshold is set to the abnormality threshold or less. It may be shorter than T.

  Moreover, the heating detection is also performed by the same detection method. That is, as shown in FIG. 2, the current value or voltage drop amount detected by the temperature detection circuit 13 is also input to the detection circuit 14 and the load current is estimated from the detected temperature. When the load current exceeds a precursor threshold that is assumed to be an overcurrent, and when the load current exceeds the precursor determination time T ′, there is a precursor that an overcurrent will occur. Is determined. Furthermore, when the estimated load current exceeds an abnormal threshold that is assumed to be an overcurrent, and the time when the load current exceeds the failure determination time T, it is determined that an overcurrent has occurred. Thus, also in heating detection, the heating state assumed to be caused by overcurrent can be determined by both time and threshold. Thereby, generation | occurrence | production of the overcurrent based on a heating detection can be detected, and the precursor of generation | occurrence | production of an overcurrent can also be detected.

  When a sign of occurrence of overcurrent is detected in this way, a signal indicating that the sign of occurrence of overcurrent has been detected is output from the detection circuit 14 to the overcurrent detection circuit 15a, and the overcurrent detection circuit 15a. The high level is output from the heating detection circuit 15b to the first OR circuit 19a. This signal is input to the precursor diagnostic circuit 18c, and the precursor diagnostic circuit 18c generates a precursor diagnostic signal.

  Furthermore, when a load open, output ON failure, or output OFF failure occurs, the potential on the low side of the semiconductor switching element 12 is different from that at the time of failure. When this state continues for a predetermined time, it is determined that an abnormality sign or abnormality has occurred.

  For example, when the load is open, the power supply voltage is not applied to the load 3 even though the switch 4 is turned on and the semiconductor switching element 12 is turned on. The potential is higher than normal when the load is not open or vice versa. That is, when the potential input to the detection circuit 14 is abnormal, the value is different from the normal value. Therefore, when the duration of the different value exceeds the failure determination time T, it is determined that the load is open. Similarly, even when an output ON failure or an output OFF failure occurs, the low-side potential of the semiconductor switching element 12 has a different value from that in the normal state, so that the duration of the different value exceeds the failure determination time T. Sometimes it is determined that an output ON failure or an output OFF failure has occurred.

  In this way, when the occurrence of an overcurrent, load open, output ON failure or output OFF failure is detected, a signal indicating the occurrence of these abnormalities is output from the detection circuit 14. Based on this, when a high level is output from the overcurrent detection circuit 15a or the heating detection circuit 15b to the second OR circuit 19b, a high level is output from the second OR circuit 19b, or a high level is output from the load open detection circuit 16 When the high level is output from the output ON failure detection circuit 17a or the output OFF failure detection circuit 17b to the third OR circuit 19c, the high level is output from the third OR circuit 19c. This signal is input to the current diagnosis circuit 18a, and the current diagnosis circuit 18a generates a current diagnosis signal.

  In addition, the current diagnosis state is stored in the memory of the past diagnosis circuit 18b in synchronization with the current diagnosis circuit 18a, and the past diagnosis circuit 18b generates a past diagnosis signal based on the current diagnosis state.

  As described above, when the warning diagnosis signal, the current diagnosis signal, or the past diagnosis signal is output, these signals are input to the body ECU 5, so that a notification command signal corresponding to each signal is output from the body ECU 5 as a warning lamp. 6 is output. As a result, when the warning signal is output, the lamp indicating the warning of overcurrent among the warning lamps 6 is turned on. When the current warning signal is output, the warning lamp 6 generates an overcurrent or other abnormality. For example, it is possible to make a notification according to the overcurrent or abnormality occurrence state, such as turning on a lamp indicating the occurrence of a fault.

  The load drive circuit 1 according to the present embodiment described above detects not only the occurrence of overcurrent but also the precursor of overcurrent. For this reason, it is possible not only to notify the user of the occurrence of an overcurrent, but also to notify the precursor of the overcurrent in advance. Therefore, for example, even when the output of the load driving circuit 1 is interrupted and the voltage application to the load 3 is stopped against the user's intention, the user can be informed of the precursor.

(Other embodiments)
(1) In the above embodiment, the presence of the precursor is detected only with respect to the overcurrent, but the presence of the precursor with respect to other abnormalities is detected and the user is notified. good.

  With reference to FIG. 3, a case will be described in which a sign of occurrence of load open, output ON failure, or output OFF failure is detected. FIG. 3 is a timing chart showing a judgment image of signs or occurrences of various abnormalities such as the above-described load open.

  For example, when the load is open, the power supply voltage is not applied to the load 3 even though the switch 4 is turned on and the semiconductor switching element 12 is turned on. The potential is higher than normal when the load is not open or vice versa. That is, as shown in FIG. 3, when the potential input to the detection circuit 14 is abnormal, the potential is different from that in the normal state. Therefore, when the failure determination time T is exceeded, it is determined that the load is open. For example, the semiconductor switching element 12 is cut off to cut off the voltage application to the load 3. For this reason, it is also possible to detect a sign of a load open by determining that there is a sign that a load open occurs when the duration of different values exceeds a sign determination time T ′ shorter than the failure determination time T. It becomes possible. As described above, for other abnormalities, the sign may be detected in advance and notified to the user before the abnormality occurs. For the output ON failure and the output OFF failure, their precursors can be detected by the same detection method.

  (2) The above describes the case where both time and threshold are used for overcurrent determination, and the case where only time is used for abnormality determination for other abnormalities such as load open is described. However, only a threshold value may be used to determine these abnormalities. FIG. 4 is a timing chart showing a determination image when only a threshold is used for abnormality determination.

  For example, regarding overcurrent, it can be determined that overcurrent has occurred when the estimated load current exceeds an abnormal threshold, and for example, the semiconductor switching element 12 can be cut off to cut off voltage application to the load 3. For this reason, as shown in FIG. 4, a precursor threshold value lower than an abnormal threshold value that is determined to be an occurrence of overcurrent is set, and when the load current exceeds the precursor threshold value, it is determined as a precursor of overcurrent. Also good. Even in such a determination method, before an overcurrent occurs, the precursor can be detected in advance and notified to the user. Although the overcurrent has been described here, it is possible to detect the precursor of the load open, the output ON failure, or the output OFF failure by a similar detection method.

  (3) In the above embodiment, as shown in FIG. 1, the diagnosis signals output from the current diagnosis circuit 18a, the past diagnosis circuit 18b, and the precursor diagnosis circuit 18c are input to the body ECU 5 through separate lines. An example was given. On the other hand, each diagnosis signal may be input to the body ECU 5 through one output line.

  For example, as shown in FIG. 5, a serial conversion circuit 18d for converting each diagnostic signal into a serial signal is provided, and each diagnostic signal is input to the serial conversion circuit 18d and converted into a serial signal. A serial signal can be output from the serial conversion circuit 18d through one output line and input to the body ECU 5.

  (4) In the above embodiment, the detection result of the external short detection circuit 15 is stored in the memory of the past diagnosis circuit 18b in conjunction with the current diagnosis circuit 18a. For example, as shown in FIG. 6, the detection result of the external short detection circuit 15 is inputted to the current diagnosis circuit 18a, and when the ignition switch is turned off, the contents of the current diagnosis circuit 18a are changed. It may be stored in the past diagnosis circuit 18b.

  (5) In the above embodiment, the temperature detection circuit 13, the detection circuit 14, the external short detection circuit 15, the load open detection circuit 16, and the internal failure detection circuit 17 constitute an abnormality detection circuit. When the detection circuit 14 detects the occurrence of an overcurrent or a precursor, or when other abnormality is detected, a signal to that effect is sent to the external short detection circuit 15, the load open detection circuit 16, or the internal failure detection circuit. 17, and the diagnosis state is transmitted from each of the circuits 15 to 17 (or through the first to third OR circuits 19 a to 19 b) to the diagnosis output circuit 18. However, this configuration is merely an example of the abnormality detection circuit, and other configurations may be used. For example, without providing the detection circuit 14, the detection result of the temperature detection circuit 13 may be directly input to the heating detection circuit 15b, and the heating detection circuit 15b may determine the heating state. Further, the low-side potential of the semiconductor switching element 12 is directly input to the overcurrent detection circuit 15a, the load open detection circuit 16 or the internal failure detection circuit 17, and each of these circuits 15a, 16, 17 You may make it perform abnormality determination, such as load open.

1 Load Drive Circuit 2 Power Supply 3 Load 4 Switch 5 Body ECU
6 warning lamp 10 input circuit 11 output control circuit 12 semiconductor switching element 13 temperature detection circuit 14 detection circuit 15 external short detection circuit 15a overcurrent detection circuit 15b heating detection circuit 16 load open detection circuit 17 internal failure detection circuit 17a output ON failure detection Circuit 17b Output OFF fault detection circuit 18 Diag output circuit 18a Current diagnostic circuit 18b Past diagnostic circuit 18c Predictive diagnostic circuit

Claims (5)

A semiconductor switching element (12) for controlling on / off of voltage application from the power source (2) to the load (3);
An input circuit (10) for outputting a control signal based on an input signal corresponding to the input state of the switch (4);
In a load drive circuit comprising an output control circuit (11) for controlling on / off of the semiconductor switching element (12) based on a control signal output from the input circuit (10),
An abnormality detection circuit (13-17) for detecting the occurrence of an abnormality in the state of power supply to the load (3) and its precursor and outputting a precursor signal indicating the precursor of the abnormality;
A load driving circuit, comprising: a warning diagnosis circuit (18c) that outputs a warning signal indicating a warning of abnormality detected by the abnormality detection circuits (13 to 17). The abnormality detection circuits (13 to 17) detect the occurrence of an overcurrent indicating that the load current supplied to the load is excessive and the precursor thereof,
The precursor diagnosis circuit (18c) transmits the precursor signal indicating the precursor of the overcurrent by transmitting the precursor signal indicating that the precursor of the overcurrent is detected from the abnormality detection circuit (13 to 17). The load driving circuit according to claim 1, wherein the load driving circuit outputs the load.   The abnormality detection circuits (13 to 17) determine that the overcurrent has occurred when a duration time during which the load current exceeds the abnormality threshold reaches a failure determination time (T), and the load current is determined to be the abnormality threshold. The continuation time exceeding the following precursor threshold reaches the precursor determination time (T ′) shorter than the failure determination time (T), or the duration exceeding the precursor threshold smaller than the abnormality threshold The load drive circuit according to claim 2, wherein when the precursor determination time (T ′) equal to or less than the failure determination time (T) is reached, the precursor is determined as the precursor of the overcurrent.   The abnormality detection circuit (13-17) directly detects the load current supplied to the load (3) or the voltage applied to the load (3), thereby detecting the occurrence of the overcurrent and its precursor. The load drive circuit according to claim 2 or 3, further comprising an overcurrent detection circuit (15a) for detection.   In the abnormality detection circuits (13 to 17), heating that detects the occurrence of the overcurrent and its precursor is detected by detecting the temperature rise of the semiconductor switching element (12) based on the load current flowing through the load (3). The load driving circuit according to any one of claims 2 to 4, further comprising a detection circuit (15b).

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