Fault detection device

Abstract

To provide a fault detection device with which it is possible to improve the accuracy of fault detection.SOLUTION: A fault detection device 1 comprises: a first transistor TR1 that constitutes a drive circuit 2 together with a reference voltage unit 20, a voltage unit 22, and at least one load 24; a first resistor 10 connected in parallel to the at least one load 24; a second transistor TR2 connected in parallel with the at least one load 24 and the first resistor 10; a second resistor 14 connected in series to the second transistor TR2; a third resistor 16 connected to the second resistor 14; and a control unit 18 for detecting a fault of the at least one load 24 and detecting a fault of the first transistor TR1 on the basis of a midpoint potential VOUT outputted from a node 15 between the second resistor 14 and the third resistor 16 that corresponds to on / off of the second transistor TR2.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a fault detection device. [Background technology]

[0002] As a conventional technique, there is known an LED failure detection device that includes an LED (Light Emitting Diode) with an anode connected to a power supply line, a failure detection resistor connected in parallel with the LED, a failure detection signal output terminal provided at the connection point between the cathode of the LED and the failure detection resistor, and an LED drive transistor that drives the LED via a drive current control resistor at the connection point between the cathode of the LED and the failure detection resistor (see, for example, Patent Document 1).

[0003] This LED failure detection device can detect an LED failure by monitoring the voltage resulting from the division between the failure detection resistor and the drive current control resistor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2008-98495 A Summary of the Invention [Problem to be solved by the invention]

[0005] Conventional LED failure detection devices cannot detect failures in LED driving transistors, making it impossible to identify the location of the failure and resulting in low failure detection accuracy.

[0006] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide a fault detection device capable of improving the accuracy of fault detection. [Means for solving the problem]

[0007] One aspect of the present invention provides a fault detection device comprising: a first transistor which constitutes a driving circuit together with a reference voltage unit which generates a reference voltage, a voltage unit which generates a power supply voltage, and at least one load connected to the voltage unit side and is connected to the reference voltage unit side to switch the driving of the at least one load on and off; a first resistor connected in parallel to the at least one load; a second transistor connected in parallel to the at least one load and the first resistor; a second resistor connected in series to the second transistor; a third resistor having one end connected to the first transistor and the other end connected to the second resistor; and a detection unit which detects a fault in the at least one load and a fault in the first transistor based on a midpoint potential output from a node between the second resistor and the third resistor in response to the on / off of the second transistor. Effect of the Invention

[0008] According to the present invention, the accuracy of fault detection can be improved. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a circuit diagram illustrating an example of a fault detection device according to a first embodiment. [Diagram 2] FIG. 2(a) is a timing chart showing an example of a case where it is determined that the load is normal, and FIG. 2(b) is a timing chart showing an example of a case where it is determined that a short circuit fault has occurred. [Diagram 3] FIG. 3(a) is a timing chart showing an example of a case where it is determined that an open fault has occurred, and FIG. 3(b) is a timing chart showing an example of a case where it is determined that the first transistor is normal. [Figure 4] FIG. 4(a) is a timing chart showing an example of a case where it is determined that a short circuit failure has occurred, and FIG. 4(b) is a timing chart showing an example of a case where it is determined that an open circuit failure has occurred. [Diagram 5] FIG. 5 is a flowchart showing an example of the operation of the failure detection device. [Figure 6]FIG. 6 is a circuit diagram illustrating an example of a fault detection device according to the second embodiment. [Figure 7] FIG. 7 is a circuit diagram illustrating an example of a fault detection device according to the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] (Summary of the embodiment) The fault detection device of the embodiment is roughly configured to include a first transistor that forms a drive circuit together with a reference voltage unit that generates a reference voltage, a voltage unit that generates a power supply voltage, and at least one load connected to the voltage unit side and is connected to the reference voltage unit side to switch the drive of the at least one load on and off, a first resistor connected in parallel to the at least one load, a second transistor connected in parallel to the at least one load and the first resistor, a second resistor connected in series to the second transistor, a third resistor having one end connected to the first transistor and the other end connected to the second resistor, and a detection unit that detects a fault in the at least one load and a fault in the first transistor based on a midpoint potential output from a node between the second resistor and the third resistor in response to the on and off of the second transistor.

[0011] This failure detection device can detect failures in the load of the drive circuit and in the first transistor, and therefore the accuracy of failure detection is improved compared to a case where failure detection is only possible in one of the two.

[0012] [First embodiment] (Outline of fault detection device 1) FIG. 1 is a circuit diagram showing an example of a fault detection device according to a first embodiment. FIG. 2(a) is a timing chart showing an example of a midpoint potential etc. when the load of the fault detection device according to the first embodiment is judged to be normal, and FIG. 2(b) is a timing chart showing an example of a midpoint potential etc. when the load is judged to be short-circuited. FIG. 3(a) is a timing chart showing an example of a midpoint potential etc. when the load of the fault detection device according to the first embodiment is judged to be open-circuited, and FIG. 3(b) is a timing chart showing an example of a midpoint potential etc. when the first transistor is judged to be normal. FIG. 4(a) is a timing chart showing an example of a midpoint potential etc. when the first transistor of the fault detection device according to the first embodiment is judged to be short-circuited, and FIG. 4(b) is a timing chart showing an example of a midpoint potential etc. when the first transistor is judged to be open-circuited.

[0013] 2(a) to 4(b), from the top, the control signal S1 is on (ON) and off (OFF), the first transistor TR1 is on and off, the control signal S2 is on and off, the second transistor TR2 is on and off, and the midpoint potential V OUT 2(a) to 4(b), the horizontal axis is time t. In Fig. 2(a) to 4(b), the first threshold value Th1 to the third threshold value Th3 are indicated by dashed lines. In Fig. 1, and Fig. 6 and Fig. 7 described later, the flow of main signals and information is indicated by arrows.

[0014] 1, the fault detection device 1 detects a fault in the drive circuit 2. As an example, the fault detection device 1 is electrically connected to an electronic device 9. As an example, the electronic device 9 is, but is not limited to, a diagnostic device that performs fault diagnosis on the drive circuit 2, a control device that controls the fault detection device 1 and the drive circuit 2, an instruction device that instructs driving of the load 24, and an alarm device that notifies the location of a fault.

[0015] The fault detection device 1 includes a reference voltage unit 20 that generates a reference voltage, a power supply voltage V CCand at least one load 24 connected to the voltage unit 22 side, the drive circuit 2 is configured with a first transistor TR1 connected to the reference voltage unit 20 side to switch on and off the drive of the at least one load 24, a first resistor 10 connected in parallel to the at least one load 24, a second transistor TR2 connected in parallel to the at least one load 24 and the first resistor 10, a second resistor 14 connected in series to the second transistor TR2, a third resistor 16 having one end connected to the first transistor TR1 and the other end connected to the second resistor 14, and a midpoint potential V output from a node 15 between the second resistor 14 and the third resistor 16 in response to the on and off of the second transistor TR2. OUT and a control unit 18 serving as a detection unit that performs failure detection of at least one load 24 and failure detection of the first transistor TR1 based on the load 24 and the first transistor TR2.

[0016] (Configuration of drive circuit 2) The drive circuit 2 of this embodiment includes one load 24. The load 24 is, for example, a light-emitting element such as an LED, a motor, a sensor, or the like. The load 24 of this embodiment is, for example, an LED that illuminates an illumination target of an in-vehicle device mounted on a vehicle. The voltage V f indicates the forward voltage of the LED.

[0017] The reference voltage unit 20 generates a reference voltage that serves as a reference for the operation of the drive circuit 2. As an example, this reference voltage is 0 V. Hereinafter, the reference voltage will be referred to as a reference voltage GND.

[0018] The voltage section 22 supplies the power supply voltage V CC This power supply voltage V CC For example, it is 5V.

[0019] The first transistor TR1 is an NPN bipolar transistor. The collector terminal 26a of the first transistor TR1 is connected to the terminal 16b of the third resistor 16, the emitter terminal 26b is connected to the reference voltage section 20, and the base terminal 26c is connected to the control section 18. The voltage V CE1 indicates the saturation voltage between the collector and the emitter. Note that the base terminal 26c of the first transistor TR1 and the base terminal 12c of a second transistor TR2 (described later) may be connected to the control unit 18 via resistors.

[0020] (Configuration of the first resistor 10) The first resistor 10 has a terminal 10a connected between the voltage section 22 and the load 24, and a terminal 10b connected between the load 24 and the second resistor 14. The first resistor 10 has a resistance value R1. The resistance value R1 is large enough that no current flows through the first resistor 10 when the load 24 is normal.

[0021] (Configuration of second transistor TR2) The second transistor TR2 is a PNP bipolar transistor. The collector terminal 12a of the second transistor TR2 is connected to the terminal 14a of the second resistor 14, the emitter terminal 12b is connected to the voltage section 22, and the base terminal 12c is connected to the control section 18. The voltage V CE2 indicates the saturation voltage between the collector and the emitter.

[0022] (Configuration of second resistor 14) The second resistor 14 has a terminal 14a connected to the load 24 and a terminal 14b connected to a third resistor 16. The second resistor 14 has a resistance value R2.

[0023] (Configuration of the third resistor 16) The third resistor 16 has a terminal 16a connected to the second resistor 14 and a terminal 16b connected to the first transistor TR1. The third resistor 16 has a resistance value R3.

[0024] (Configuration of control unit 18) The control unit 18 is a microcomputer including a CPU (Central Processing Unit) that performs calculations and processing on acquired data according to a stored program, a RAM (Random Access Memory) that is a semiconductor memory, and a ROM (Read Only Memory). The ROM stores, for example, a program for operating the control unit 18. The RAM is used, for example, as a storage area for temporarily storing calculation results. The control unit 18 also has a means for generating a clock signal therein and operates based on this clock signal.

[0025] The control unit 18 has a first threshold value Th1 and a second threshold value Th2 for detecting a short circuit failure and an open circuit failure of the load 24, a third threshold value Th3, a fourth threshold value Th4, and a time threshold value Th5 relating to the first time T1 and the second time T2 for detecting a short circuit failure and an open circuit failure of the first transistor TR1.

[0026] When the control unit 18 controls the second transistor TR2 to be off and the first transistor TR1 to be on, the midpoint potential V OUT is greater than the first threshold Th1, and the power supply voltage V CC If the voltage V OUT If the second threshold voltage Th2 is smaller than the second threshold voltage Th2 and is equal to or greater than the reference voltage GND, it is determined that the load 24 has an open circuit failure.

[0027] When the second transistor TR2 is on and the first transistor TR1 is controlled to be repeatedly turned on and off, the control unit 18 controls the midpoint potential V OUT If the state where the voltage V is smaller than the third threshold value Th3 continues for a first time T1 or more, it is determined that the first transistor TR1 has a short circuit failure, and the midpoint potential V OUTWhen the state where the first transistor TR1 is equal to the fourth threshold value Th4 continues for a second time T2 or longer, it is determined that the first transistor TR1 has an open circuit failure.

[0028] The control unit 18 outputs a control signal S1 for turning on and off the first transistor TR1 to the base terminal 26c, and also outputs a control signal S2 for turning on and off the second transistor TR2 to the base terminal 12c.

[0029] When detecting a short circuit failure or an open circuit failure of the first transistor TR1, the control unit 18 periodically turns the first transistor TR1 on and off at a predetermined duty ratio. Specifically, the control unit 18 outputs a control signal S1, which is a PWM (Pulse Width Modulation) signal with a duty ratio of 50%, to the first transistor TR1 to periodically turn it on and off, but is not limited to this, and other duty ratios that switch between on and off may be used.

[0030] The control unit 18 has a time threshold value Th5 for the first time T1 and the second time T2. The first time T1 and the second time T2 may be different times or may be the same time. In the present embodiment, the first time T1 and the second time T2 are the same time. As an example, the first time T1 and the second time T2 are 1 second.

[0031] When the control unit 18 detects a short circuit failure and an open circuit failure in the load 24, and a short circuit failure and an open circuit failure in the first transistor TR1, it outputs failure information S3 to the connected electronic device 9. This failure information S3 is information related to the short circuit failure and the open circuit failure in the load 24, and the short circuit failure and the open circuit failure in the first transistor TR1.

[0032] The electronic device 9 notifies the user of the malfunction based on the malfunction information S3, for example. The notification may be, for example, by displaying the malfunction on a display device, by sound, or by both, but is not limited thereto.

[0033] Furthermore, the fault detection device 1 may detect a fault in response to an instruction from the electronic device 9, or may perform the detection according to a predetermined cycle.

[0034] The following describes the cases where the load 24 is normal, where the load 24 has a short circuit fault, and where the load 24 has an open circuit fault.

[0035] When load 24 is normal When the first transistor TR1 is on, the second transistor TR2 is off, and the load 24 is normal, the current I follows a current path I1 that passes through the load 24, as shown in Fig. 1. That is, the current path I1 includes the voltage unit 22, the load 24, the second resistor 14, the third resistor 16, the first transistor TR1, and the reference voltage GND.

[0036] Midpoint potential V OUT If the current is I, then equation (3) can be obtained by eliminating the current I from equations (1) and (2), which are derived from the voltage drop. V CC =V f +R2I+R3I+V CE1 (1) V OUT =R3I+V CE1 (2) V OUT =R3(V CC -V f -V CE1 ) / (R2+R3)+V CE1 (3)

[0037] The midpoint potential V shown in equation (3) OUT is a calculated voltage and has variations due to variations in electronic components and temperature. Therefore, the second threshold value Th2 is set to the calculated midpoint potential V OUT It is designed to be smaller.

[0038] When load 24 is short-circuited When the first transistor TR1 is on, the second transistor TR2 is off, and the load 24 has a short circuit fault, the current I follows the current path I1 through the load 24 in the same manner as in the normal case, as shown in FIG.

[0039] Midpoint potential V OUT If the current is I, the voltage drop can be calculated by eliminating the current I from the following equations (4) and (5). Note that the load 24 is shorted, so the voltage V f is effectively 0V. V CC =R2I+R3I+V CE1 (4) V OUT =R3I+V CE1 (5) V OUT =R3(V CC -V CE1 ) / (R2+R3)+V CE1 (6)

[0040] The midpoint potential V OUT Since the voltage V is calculated, it is subject to variations in electronic components and temperature. Therefore, the first threshold value Th1 is set to the calculated midpoint potential V OUT The control unit 18 controls the midpoint potential V OUT is greater than the first threshold Th1, and the power supply voltage V CC If it is equal to or less than this, it is determined that the load 24 is suffering from a short circuit fault.

[0041] When load 24 has an open circuit fault When the first transistor TR1 is on, the second transistor TR2 is off, and the load 24 has an open fault, the current I does not pass through the load 24 but takes a current path I2 that passes through the first resistor 10, as shown in Fig. 1. In other words, the current path I2 is the voltage unit 22, the first resistor 10, the second resistor 14, the third resistor 16, the first transistor TR1, and the reference voltage GND.

[0042] Midpoint potential V OUT If the current is I, then equation (9) can be obtained by eliminating the current I from equations (7) and (8) derived from the voltage drop. V CC =R1I+R2I+R3I+V CE1 (7) V OUT =R3I+V CE1 (8) V OUT =R3(V CC -V CE1 ) / (R1+R2+R3)+V CE1 (9)

[0043] As shown in FIG. 3(a), the control unit 18 controls the midpoint potential V OUT If the second threshold voltage Th2 is smaller than the second threshold voltage Th2 and is equal to or greater than the reference voltage GND, it is determined that the load 24 has an open circuit failure.

[0044] Next, the following will explain the cases where the first transistor TR1 is normal, where the first transistor TR1 has a short-circuit fault, and where the first transistor TR1 has an open-circuit fault.

[0045] When the first transistor TR1 is normal 3(b) to 4(b), the control unit 18 outputs a control signal S1 that periodically turns the first transistor TR1 on and off in order to detect a short circuit failure and an open circuit failure in the first transistor TR1. The control unit 18 also turns on the second transistor TR2 so that the load 24 is not driven.

[0046] In this case, the current I passes through the second transistor TR2 via a current path I3 as shown in Fig. 1. This current path I3 passes through the voltage unit 22, the second transistor TR2, the second resistor 14, the third resistor 16, the first transistor TR1, and the reference voltage GND.

[0047] Midpoint potential V OUTIf the current is I, then equation (12) can be obtained by eliminating the current I from equations (10) and (11) below, which are derived from the voltage drop. V CC =V CE2 +R2I+R3I+V CE1 (10) V OUT =R3I+V CE1 (11) V OUT =R3(V CC -V CE2 -V CE1 ) / (R2+R3)+V CE1 (12)

[0048] When the first transistor TR1 is normal, the midpoint potential V OUT As shown in FIG. 3B, the third threshold Th3 varies in conjunction with the on / off state of the first transistor TR1. The third threshold Th3 is the midpoint potential V obtained from the equation (12) when the first transistor TR1 is on. OUT The third threshold value Th3 is determined based on the power supply voltage V CC It is -0.5.

[0049] When the first transistor TR1 is short-circuited When the first transistor TR1 has a short circuit fault, the current path I3 passes through the voltage unit 22, the second transistor TR2, the second resistor 14, the third resistor 16, the first transistor TR1, and the reference voltage GND.

[0050] Midpoint potential V OUT If the current is I, the current I can be eliminated from the following equations (13) and (14) derived from the voltage drop to obtain equation (15). Note that since the first transistor TR1 is shorted, the voltage V CE1 is effectively 0V. V CC =V CE2 +R2I+R3I···(13) V OUT =R3I···(14) V OUT =R3(V CC -V CE2 ) / (R2+R3) (15)

[0051] Since the first transistor TR1 has a short circuit, the midpoint potential V OUT As shown in FIG. 4(a), the midpoint potential V OUT If the state in which the first transistor TR1 is greater than the third threshold value Th3 continues for a first time T1 based on the time threshold value Th5 or longer, it is determined that the first transistor TR1 has a short-circuit failure.

[0052] When the first transistor TR1 has an open fault When the first transistor TR1 has an open circuit fault, the impedance of the first transistor TR1 becomes infinite. OUT As shown in Figure 4(b), the power supply voltage V CC Therefore, the fourth threshold value Th4 is the power supply voltage V CC The control unit 18 determines the midpoint potential V OUT is the power supply voltage V CC continues for a second time T2 or longer, it is determined that the first transistor TR1 has an open circuit failure.

[0053] An example of the operation of the fault detection device 1 of this embodiment will be described below with reference to the flowchart of Fig. 5. Here, the case where the load 24 is an LED will be described.

[0054] (operation) The control unit 18 of the fault detection device 1 starts fault detection when the timing for fault detection arrives (Step 1). The control unit 18 may start fault detection in response to an input of a signal that triggers fault detection from the electronic device 9, or may start fault detection according to a predetermined cycle, but is not limited to these. As an example, when the LED is turned on, the control unit 18 performs fault detection for the load 24, and when the LED is turned off, the control unit 18 performs fault detection for the first transistor TR1.

[0055] The control unit 18 checks the lighting status of the LED. If the control unit 18 is outputting the control signal S1, which is a lighting signal for lighting the LED (Step 2: Yes), the control unit 18 turns off the second transistor TR2 to perform failure detection of the load 24 (Step 3), and the midpoint potential V OUT At this time, the control unit 18 performs failure detection of the LED, which is the load 24, and therefore sets a first threshold value Th1 and a second threshold value Th2 as threshold values, and a midpoint potential V OUT Compare with.

[0056] The control unit 18 detects a midpoint potential V OUT is large, that is, the midpoint potential V OUT is greater than the first threshold Th1, and the power supply voltage V CC If the above is true (Step 4: Yes), it is determined that the LED, which is the load 24, has a short circuit fault (Step 5). The control unit 18 generates fault information S3 indicating the short circuit fault of the LED, which is the load 24, outputs it to the electronic device 9 (Step 6), and ends the operation related to the fault detection of the LED, which is the load 24.

[0057] In step 4, the control unit 18 determines whether the midpoint potential V OUTis equal to or less than the first threshold value Th1 (Step 4: No) and is smaller than the second threshold value Th2, i.e., is smaller than the second threshold value Th2 and equal to or greater than the reference voltage GND (Step 7: Yes), an open fault is determined in the LED that is the load 24 (Step 8). The control unit 18 generates fault information S3 indicating an open fault in the LED that is the load 24, outputs it to the electronic device 9 (Step 6), and ends the operation related to the fault detection of the LED that is the load 24.

[0058] In step 7, the control unit 18 controls the midpoint potential V OUT is equal to or less than the first threshold value Th1 (Step 4: No) and is equal to or more than the second threshold value Th2 (Step 7: No), the LED serving as the load 24 is determined to be normal (Step 9), and the operation relating to the failure detection of the LED serving as the load 24 is terminated. As a modified example, the control unit 18 may be configured to generate failure information S3 indicating that the LED serving as the load 24 is normal, and output it to the electronic device 9.

[0059] Furthermore, in step 2, if the control signal S1, which is a light-up signal, is not output (Step 2: No), the control unit 18 outputs the control signal S2 to turn on the second transistor TR2 (Step 10).

[0060] The control unit 18 drives the first transistor TR1 with a predetermined duty ratio (Step 11). That is, the control unit 18 generates a control signal S1 having a predetermined duty ratio and outputs it to the first transistor TR1 to periodically turn it on and off, thereby controlling the midpoint potential V OUT Note that the load 24 is not driven even if the first transistor TR1 is turned on, because the second transistor TR2 is on.

[0061] In addition, the control unit 18 detects a failure of the first transistor TR1, and therefore sets a third threshold value Th3 and a fourth threshold value Th4 as threshold values, and a midpoint potential V OUT The time is measured while comparing the values ​​of the two.

[0062] The control unit 18 controls the midpoint potential V OUT is smaller than the third threshold value Th3 and this state continues for the first time T1 or more (Step 12: Yes), the control unit 18 determines that the first transistor TR1 has a short circuit fault (Step 13). The control unit 18 generates fault information S3 indicating the short circuit fault of the first transistor TR1 and outputs it to the electronic device 9 (Step 14), and ends the operation related to the fault detection of the first transistor TR1.

[0063] In step 12, the control unit 18 determines whether the midpoint potential V OUT is smaller than the third threshold value Th3, and this state does not continue for the first time T1 or more (Step 12: No), and further the midpoint potential V OUT is equal to the fourth threshold Th4, that is, the midpoint potential V OUT is the power supply voltage V CC If this state continues for the second time T2 or more (Step 15: Yes), the control unit 18 determines that the first transistor TR1 has an open circuit fault (Step 16). The control unit 18 generates fault information S3 indicating the open circuit fault of the first transistor TR1, outputs the fault information S3 to the electronic device 9 (Step 14), and ends the operation related to the fault detection of the first transistor TR1.

[0064] The control unit 18 also controls the midpoint potential V OUT is smaller than the third threshold value Th3, and this state does not continue for the first time T1 or more (Step 12: No), and further the midpoint potential V OUT is not equal to the fourth threshold value Th4 for the second time T2 or more (Step 15: No), the first transistor TR1 is determined to be normal (Step 17), and the operation for detecting a fault in the first transistor TR1 is terminated. As a modified example, the control unit 18 may be configured to generate fault information S3 indicating that the first transistor TR1 is normal and output it to the electronic device 9.

[0065] (Effects of the First Embodiment) The fault detection device 1 according to the present embodiment can improve the accuracy of fault detection. The fault detection device 1 includes a first resistor 10 connected in parallel with a load 24, and a midpoint potential V OUT By monitoring the load 24, it is possible to detect a short circuit fault and an open circuit fault in the load 24. The fault detection device 1 then turns on the second transistor TR2 connected in parallel with the load 24 and turns on and off the first transistor TR1 at a predetermined duty ratio to detect the midpoint potential V OUT By monitoring these, it is possible to detect a short circuit fault and an open circuit fault in the first transistor TR1. Therefore, the fault detection device 1 can detect what type of fault has occurred in either the load 24 of the drive circuit 2 or the first transistor TR1, and therefore the accuracy of fault detection can be improved compared to a case where only one of the faults is detected.

[0066] Since the fault detection device 1 can notify the fault location and the reason for the fault, it becomes easier to identify the fault location and to appropriately replace the part, compared to a case where this configuration is not adopted.

[0067] Since the fault detection device 1 can detect a fault in the first transistor TR1 without driving the load 24, the user does not feel annoyed by driving the load 24 during fault detection, as compared to a case where this configuration is not adopted. For example, if the load 24 is an LED, the user may feel annoyed if the LED lights up during fault detection of the first transistor TR1. However, since the fault detection device 1 can detect a fault in the first transistor TR1 without lighting the LED, the user does not feel annoyed.

[0068] [Second embodiment] The second embodiment differs from the other embodiments in that fault detection can be performed on a plurality of loads 24 connected in series.

[0069] 6 is a circuit diagram showing an example of a fault detection device according to the second embodiment. In the following embodiments, parts having the same functions and configurations as those in the first embodiment are given the same reference numerals as those in the first embodiment, and the description thereof will be omitted.

[0070] In the fault detection device 1 of this embodiment, as shown in FIG. 6, a first resistor 10 is connected in parallel to a plurality of loads 24 connected in series, and a second transistor TR2 is connected in parallel to the plurality of loads 24 and the first resistor 10.

[0071] 6, the plurality of loads 24 are configured by connecting n loads 241 to 24n in series, where n is an integer of 2 or more.

[0072] In the fault detection device 1, similarly to the first embodiment, the midpoint potential V OUT By monitoring these, it is possible to detect short circuit failures and open circuit failures in the loads 241 to 24n, and to detect short circuit failures and open circuit failures in the first transistor TR1.

[0073] (Advantages of the second embodiment) The fault detection device 1 of the present embodiment can detect short-circuit faults and open-circuit faults in a plurality of loads 24 connected in series.

[0074] [Third embodiment] The third embodiment differs from the other embodiments in that fault detection can be performed on a plurality of loads 24 connected in parallel.

[0075] FIG. 7 is a circuit diagram illustrating an example of a fault detection device according to the third embodiment.

[0076] As shown in FIG. 7, the control unit 18 of the fault detection device 1 of the present embodiment controls a plurality of midpoint potentials V outputted from a plurality of nodes between the second resistor 14 and the third resistor 16 in a plurality of load circuits 3 having a first resistor 10, at least one load 24, a second transistor TR2, a second resistor 14 and a third resistor 16. OUT Based on this, a fault detection is performed for at least one load 24 for each of the plurality of load circuits 3, and a fault detection is performed for the first transistor TR1.

[0077] In the present embodiment, the number of load circuits 3 is, for example, n. The control unit 18 also outputs a control signal S 21 ~Control signal S 2n and output it to the corresponding load circuit 3. Note that n is an integer equal to or greater than 2. Therefore, multiple midpoint potentials V OUT is the midpoint potential V OUT1 ~midpoint potential V OUTn It is.

[0078] The control unit 18 controls the midpoint potential V OUT1 ~midpoint potential V OUTn By sequentially monitoring these, it is possible to detect short circuit failures and open circuit failures of the loads 24 included in each load circuit 3, and to detect short circuit failures and open circuit failures of the first transistor TR1. As a modified example, the load circuit 3 may have a plurality of loads 24 connected in series. Furthermore, the plurality of load circuits 3 may be configured to have different numbers of loads 24.

[0079] (Effects of the third embodiment) The fault detection device 1 of this embodiment can detect short-circuit faults and open-circuit faults in a plurality of loads 24 connected in parallel.

[0080] According to the fault detection device 1 of at least one of the embodiments described above, it is possible to improve the accuracy of fault detection.

[0081] Although some embodiments and modifications of the present invention have been described above, these embodiments and modifications are merely examples and do not limit the invention according to the claims. These novel embodiments and modifications can be implemented in various other forms, and various omissions, substitutions, modifications, etc. can be made without departing from the gist of the present invention. In addition, not all combinations of features described in these embodiments and modifications are necessarily essential to the means for solving the problems of the invention. Furthermore, these embodiments and modifications are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0082] REFERENCE SIGNS LIST 1...fault detection device, 2...drive circuit, 3...load circuit, 10...first resistor, 14...second resistor, 15...node, 16...third resistor, 18...control section, 20...reference voltage section, 22...voltage section, 24...load

Claims

1. a first transistor that configures a drive circuit together with a reference voltage unit that generates a reference voltage, a voltage unit that generates a power supply voltage, and at least one load connected to the voltage unit side, the first transistor being connected to the reference voltage unit side and switching on and off the drive of the at least one load; a first resistor connected in parallel with at least one of the loads; a second transistor connected in parallel with at least one of the load and the first resistor; a second resistor connected in series with the second transistor; a third resistor having one end connected to the first transistor and the other end connected to the second resistor; a detection unit that detects a fault in at least one of the loads and a fault in the first transistor based on a midpoint potential output from a node between the second resistor and the third resistor in response to an on / off state of the second transistor; A fault detection device comprising:

2. the detection unit has a first threshold value and a second threshold value for detecting a short circuit failure and an open circuit failure of at least one of the loads, and a third threshold value, a fourth threshold value, and a time threshold value related to a first time and a second time for detecting a short circuit failure and an open circuit failure of the first transistor; when the second transistor is off and the first transistor is on, if the midpoint potential is greater than the first threshold value and less than the power supply voltage, it is determined that at least one of the loads has a short circuit failure, and if the midpoint potential is less than the second threshold value and greater than the reference voltage, it is determined that at least one of the loads has an open circuit failure; when the second transistor is on and the first transistor is controlled to be repeatedly turned on and off, if a state in which the midpoint potential is smaller than the third threshold value continues for the first time or more, it is determined that the first transistor has a short circuit failure, and if a state in which the midpoint potential is equal to the fourth threshold value continues for the second time or more, it is determined that the first transistor has an open circuit failure. The fault detection device according to claim 1 .

3. the first resistor is connected in parallel with the plurality of loads connected in series; the second transistor is connected in parallel to the plurality of loads and the first resistor; 3. The fault detection device according to claim 1 or 2.

4. the detection unit performs failure detection of at least one of the loads for each of a plurality of load circuits, the load circuits including the first resistor, at least one of the loads, the second transistor, the second resistor, and the third resistor, based on a plurality of midpoint potentials output from a plurality of nodes between the second resistor and the third resistor, and a failure detection of the first transistor.

3. The fault detection device according to claim 1 or 2.

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