JP2011250533A - Load circuit drive device and its failure detection method and seat belt retractor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a load circuit drive device which, without operating a load circuit, can detect more failures occurring in the load circuit and a conversion circuit which sends D.C. current to the load circuit by changing its flowing frequency or direction, and a method for detecting those failures.SOLUTION: A load circuit drive device comprises a load circuit; a H bridge circuit which has a FET1 and FET2 on an upper arm connected at center to the load circuit, a FET3 on a lower arm connected to the FET1, and a FET4 on a lower arm connected to the FET2; a conversion circuit which has switching elements FET5 connected to the upper arm and FET6 connected to the lower arm and sends D.C. current to the load circuit by changing its flowing frequency or direction; a measurement unit which measures voltage at circuit points A to D; and a failure detection unit which transmits a designated switching signal to the FETs 1-6 and also detects a failure based on measurement results from the measurement unit.

Description

  The present invention relates to a drive device that drives a load circuit by changing the frequency or direction of direct current flow in an H-bridge circuit and a failure detection method thereof, and more particularly to a drive device that drives a motor and a failure detection method thereof. It can be effectively used as a seat belt retractor.

  An H-bridge circuit constituted by switching elements can change the frequency or direction of direct current flow by controlling on / off of the switching elements. By utilizing this, it is possible to drive by adjusting the rotation direction and torque of the DC motor, or to drive an AC load circuit such as an AC motor with a DC power source.

  A motor driven by such a conversion circuit is used, for example, in a seat belt retractor that winds up a seat belt of an automobile or the like. The seat belt retractor can reduce the injury of the occupant by winding up the seat belt when the automobile has a collision accident or the like.

  Since such a motor will be driven in an emergency, it is possible to periodically check whether the circuit operates normally when it is not necessary to drive the motor so that it operates reliably at that time. desired. Further, it is desirable that the check at that time be performed so as not to affect the wearer of the seat belt without rotating the motor.

Therefore, by providing a current detection circuit on the ground side of the H bridge circuit and confirming that no current flows through the current detection circuit when all the switching elements of the H bridge circuit are turned off,
It has been proposed to detect a failure (see, for example, Patent Document 1).

JP 2009-254046 A

  However, the failure detection method described in Patent Document 1 can detect only a part of the failures, for example, there is a problem that even when the switching element of the upper arm is turned on, no power is supplied or a failure in the load circuit cannot be detected. .

  Accordingly, an object of the present invention is to provide a load circuit drive device capable of detecting a failure occurring in the load circuit and a conversion circuit that changes the frequency or direction of direct current flow and flows in the load circuit without operating the load circuit. And a failure detection method thereof, and a seat belt retractor.

The load circuit driving device according to the present invention includes a load circuit and a first switching element and a second switching element on the upper arm, which are connected to the load circuit in the center, and the first switching element. A lower arm connected to the third switching element, and the second switching element
A H-bridge circuit having a fourth switching element on the lower arm connected to the switching element, a fifth switching element connected to the upper arm, and a sixth switching element connected to the lower arm. A conversion circuit that changes the frequency or direction and flows to the load circuit; a voltage at a portion that connects the fifth switching element, the first switching element, and the second switching element; the first switching element; A voltage at a portion connecting the third switching element and the load circuit, a voltage at a portion connecting the second switching element, the fourth switching element and the load circuit, and the third switching element and the first A measuring unit for measuring a voltage at a portion connecting the switching element of No. 4 and the sixth switching element, and the fifth A switching signal for turning on a switching element; a switching signal for turning on the fifth switching element and the first switching element; and a fifth switching element, the first switching element, and the third switching element. A switching signal to turn on, a switching signal to turn on the fifth switching element, the second switching element, and the fourth switching element, and the fifth switching element, the first switching element, and the fourth And a failure detection unit that detects a failure of the load circuit and the conversion circuit based on a measurement result of the measurement unit. Features.

  In addition, a load circuit and a first switching element and a second switching element connected to the load circuit at the center are provided in the upper arm, and a third switching is provided in the lower arm connected to the first switching element. And an H-bridge circuit having a fourth switching element on a lower arm connected to the second switching element, a fifth switching element connected to the upper arm, and a sixth switching connected to the lower arm. And a voltage at a portion connecting the fifth switching element, the first switching element, and the second switching element, a conversion circuit that changes the frequency or direction in which a direct current flows, and flows through the load circuit. , A voltage at a portion connecting the first switching element, the third switching element, and the load circuit, the second switching element, A measuring unit for measuring a voltage at a portion connecting the switching element, the fourth switching element and the load circuit, and a current flowing between the sixth switching element and the ground; and turning on the fifth switching element Switching signal for turning on, switching signal for turning on the fifth switching element, the first switching element, and the sixth switching element, the fifth switching element, the first switching element, and the third switching element A switching signal for turning on the fifth switching element, the second switching element, the third switching element, and the sixth switching element, and the fifth switching element and the switching element A first switching element and the fourth switching element; And sends the serial sixth switching signal for turning on the switching elements, respectively, and having a failure detection unit for the detecting the failure of the load circuit and the conversion circuit based on a measurement result of the measuring unit.

  It is preferable that the failure detection unit determines a failure part and a failure content of the load circuit and the conversion circuit.

  The seat belt retractor of the load circuit of the present invention includes a drive device for the load circuit and a vehicle seat belt, and the load circuit is a motor that winds up the vehicle seat belt.

In addition, the failure detection method for a load circuit drive device according to the present invention includes a load circuit and a first switching element and a second switching element on the upper arm connected to the load circuit in the center. An H-bridge circuit having a third switching element on a lower arm connected to the first switching element and a fourth switching element on a lower arm connected to the second switching element, and a fifth bridge connected to the upper arm And a sixth switching element connected to the lower arm, a conversion circuit that changes the frequency or direction of direct current flow to flow to the load circuit, and detects a failure of the load circuit and the conversion circuit A failure detection method for a load circuit drive device having a failure detection unit, wherein the conversion circuit performs conversion from the failure detection unit. A switching signal for turning on the fifth switching element, a switching signal for turning on the fifth switching element and the first switching element, and the fifth switching element and the first A switching signal for turning on the switching element and the third switching element, a switching signal for turning on the fifth switching element, the second switching element, and the fourth switching element, and the fifth switching A switching signal for turning on the element, the first switching element, the fourth switching element, and the sixth switching element, respectively, and the fifth switching element, the first switching element, and the second switching element; The voltage at the site connecting the switching element of the first, A voltage at a portion connecting the switching element, the third switching element, and the load circuit, a voltage at a portion connecting the second switching element, the fourth switching element, and the load circuit, and the third switching A voltage at a portion connecting the element, the fourth switching element, and the sixth switching element is measured, and the failure detection unit detects a failure of the load circuit and the conversion circuit.

  In addition, the failure detection method for a load circuit drive device according to the present invention includes a load circuit and a first switching element and a second switching element on the upper arm connected to the load circuit in the center. An H-bridge circuit having a third switching element on a lower arm connected to the first switching element and a fourth switching element on a lower arm connected to the second switching element, and a fifth bridge connected to the upper arm A switching circuit having a switching circuit and a sixth switching element connected to the lower arm, a conversion circuit for changing the frequency or direction of the flow of a direct current and flowing to the load circuit, and detecting a failure of the load circuit and the conversion circuit A failure detection method for a load circuit drive device having a failure detection unit, wherein the conversion circuit performs conversion from the failure detection unit. A switching signal for turning on the fifth switching element, a switching signal for turning on the fifth switching element, the first switching element, and the sixth switching element, A switching signal for turning on the switching element, the first switching element, and the third switching element; the fifth switching element; the second switching element; the third switching element; and the sixth switching element. And a switching signal for turning on the fifth switching element, the first switching element, the fourth switching element, and the sixth switching element, respectively. A switching element and the first switching element; A voltage at a site connecting the second switching element, a voltage at a site connecting the first switching element, the third switching element and the load circuit, the second switching element and the fourth switching element, Measuring a voltage at a portion connecting the load circuit and a current flowing between the sixth switching element and the ground, and detecting a failure of the load circuit and the conversion circuit by the failure detection unit. Features.

  It is preferable that the failure detection unit determines a failure part and a failure content of the load circuit and the conversion circuit.

  When a failure is detected in at least one of the conversion circuit and the load circuit by the failure detection method, the failure detection unit sets the conversion circuit to a state in which the conversion operation is not performed, and determines the failed part and the failure. Depending on the contents, it is preferable to repeatedly send a switching signal that can determine whether the failed part has recovered from the failure.

  When the failure part is recovered from the failure by the failure detection method, the failure detection unit is preferably in a state in which the conversion circuit can perform the conversion operation.

  According to the load circuit drive device of the present invention, it is possible to detect a failure of the load circuit and the conversion circuit flowing in the load circuit by changing the frequency or direction of the direct current flow without substantially operating the load circuit. .

  In addition, according to the method for detecting a load circuit drive device of the present invention, the load circuit and the conversion circuit that causes the load circuit to flow by changing the frequency or direction of the direct current flow without substantially operating the load circuit can be detected. Can be detected.

(A) is the drive device of the load circuit which concerns on one Embodiment of this invention, (b) is the drive device of the other load circuit of this invention. (A) is an example of the switching signal sent to the drive device of the load circuit of FIG. 1 (a), and (b) is an example of the switching signal sent to the drive device of the load circuit of FIG. 1 (b). is there.

  FIG. 1A shows a drive device for a load circuit according to an embodiment of the present invention. This driving device drives a load circuit M with a DC power source, and measures the voltage of each part of the conversion circuit, the conversion circuit that changes the frequency or direction in which the DC current flows, and flows through the load circuit. A measurement unit; and a failure detection unit that detects a failure of the load circuit M and the conversion circuit. The load circuit M is a DC motor, for example.

The conversion circuit is a circuit connected from the DC power source to the ground, which is configured around an H bridge circuit connected to the load circuit M at the center. In the following description, an example in which an FET (Field Effect Transistor) is used as a switching element is described, but the switching element may be another element such as a relay.

  The H bridge circuit has FET1 and FET2 on the upper arm, FET3 on the lower arm connected to FET1, and FET4 on the lower arm connected to FET2. An FET 5 is provided between the upper arm having the FET 1 and FET 2 and the power source. An FET 6 is provided between the lower arm having the FET 3 and the FET 4 and the ground. When these FETs 1 to 6 are turned on / off by a switching signal sent from an MPU (micro processor unit), the frequency or direction of the direct current flows is changed and flows to the load circuit M.

  Although not shown, the measurement unit that measures the state of the circuit in order to detect a failure is a circuit that measures the voltage at points A to D of the circuit. Point A is a part connecting FET5, FET1, and FET2, Point B is a part connecting FET1, FET3, and load circuit M, and Point C is a part connecting FET2, FET4, and load circuit M. Yes, point D is a part connecting FET3, FET4 and FET6. When such a load circuit driving device is used for a seat belt retractor or the like, the points A to D are provided in the circuit on the control board on which the FETs 1 to 6 and the MPU are mounted, and the measurement unit is also provided on the control board. The parts can be concentrated on the control board, making it easy to mount on the vehicle. In addition, if the points B and C measured by the measuring unit are provided in the immediate vicinity of the motor, it is possible to know which of the harnesses that electrically connect the control board and the motor has failed, and to replace the failed component Becomes easier.

MPU also serves as a failure detection unit, and MPU sends a switching signal to FETs 1 to 6,
At this time, it is possible to detect that a failure has occurred from the voltage measured by the measurement unit, and to determine the failure location and the failure content. In addition, it is useful for investigating the cause of a failure when the failure is recovered by having a portion for holding a record in the failure detection unit so that a record of the failure content can be held.

  First, the operation of the conversion circuit when driving the load circuit M will be described before description of failure detection. The conversion circuit sends an ON signal to FET5 and FET6 to energize FET5 and FET6, sends an ON signal to FET1 and FET4, and sends an OFF signal to FET2 and FET3. A current flowing toward point C flows. Further, when an ON signal is sent to FET5 and FET6, the FET5 and FET6 are energized, an OFF signal is sent to FET1 and FET4, and an ON signal is sent to FET2 and FET3, the load circuit M is transferred from point C to point B. The electric current which goes to Further, when an OFF signal is sent to the FET 5 or FET 6, no current flows through the load circuit M. By doing so, the conversion circuit can cause a current to flow through the load circuit M with a predetermined frequency and direction by a signal sent from the outside, and the load circuit M performs a predetermined operation with the converted current. Can do.

  Such a drive device for a load circuit can be used as a seat belt retractor that winds up a vehicle seat belt using a motor as the load circuit M. The seat belt retractor is equipped with an acceleration line sensor, a wheel rotation sensor, a driver's brake operation and steering wheel operation sensor, a radar that can measure the distance from the front, a camera, etc. When it is determined that the state is close, the seat belt is wound up. As a result, the gap between the occupant and the seat belt is reduced, and the impact of the occupant on the steering wheel and the seat belt due to the collision can be reduced. Thus, since the seat belt retractor operates in an emergency, it is necessary to confirm whether or not a failure has occurred in normal times so that the seat belt retractor can be reliably operated in an emergency. In addition, it is uncomfortable for the occupant to confirm the operation by winding the seat belt in the normal time when the occupant is tightening the seat belt, so it is necessary to detect the failure without substantially rotating the motor. is there.

  Failure detection is performed when the conversion circuit is not performing the above-described conversion operation. That is, it is performed in a standby state in which the power source of the load circuit driving device is turned on but no conversion operation is performed. Such detection of a failure is useful not only for a seat belt retractor but also for various drive devices that want to detect a failure but are desired not to be driven except when actually used.

  FIG. 2 (a) is an example of a signal sent when failure detection is performed, a portion where the level is raised is an ON signal, and a portion where the level is low is a state where no signal is sent. Represents. In the following description, the switching element is in a state where it can be energized while an ON signal is being sent, and is in a state where it cannot be energized while no signal is being sent. Further, it is omitted that it is in an off state within a range not causing misunderstanding, and when it is not described that an on signal is transmitted, it is in an off state. The actual signal may be an off signal corresponding to a low level part or may be upside down.

In FIG. 2A, five signals 1 to 5 are sent to the FETs 1 to 6. The signal 1 turns on the FET 5 and turns off the FETs 1 to 4 and 6 (hereinafter omitted for the off state), the signal 2 turns on the FET 5 and the FET 1, and the signal 3 A signal that turns on FET5, FET1, and FET3, a signal 4 is a signal that turns on FET5, FET2, and FET4, and a signal 5 is a signal that turns on FET5, FET1, FET4, and FET6. The ON time of the signal 5 is set to a short time when the load circuit M does not perform an actual operation. For example, if the load circuit M is a general DC motor, it can be prevented from operating even when a current is passed if the duty is about 1% or less. Also,
Immediately after the signal 5, a signal for turning on the FET 5, FET 2, FET 4, and FET 6 may be sent in a time as short as the signal 5, and the influence of the signal 5 may be canceled by controlling the motor in the reverse direction.

  The failure detection unit sends these signals 1-5, the timing at which the FET1-6 should be in the state of the signal sent, and the state where the ON signal is not sent, that is, the state where the FET1-6 is off (for convenience, Hereinafter, this state is sometimes referred to as a state where the signal 0 is transmitted), and a failure is detected based on the voltages at the points A to D measured by the measurement unit. Note that it is not necessary to measure all the voltages at the points A to D after all the signals are transmitted, and only the points necessary for the determination need to be measured in the determination table described later. The current consumption can be reduced.

  The failure detection unit detects a failure in the load circuit M and the conversion circuit by sending signals 1 to 5 respectively. In the example of FIG. 2A, the signals 1 to 5 are sent as signals having an on-time of about 10 μsec at intervals of 125 μsec. By repeatedly sending such a signal, it can be confirmed whether or not a failure has occurred at all times in the standby state. For example, after the signal 5 is transmitted, the OFF state is continued for 500 μsec, and the operation of transmitting the signals 1 to 5 is repeated to detect the failure. The order and timing of sending the signals are not limited to this, and the signals 1 to 5 may be sent individually at an arbitrary timing that needs to detect a failure. That is, the signals 1 to 5 may be sent in an arbitrary order, and the signals 1 to 2 are not handled as one set, and the signals 1, 2, 1, 3, 3, 1, 4, , Signal 5 may be sent in this order. In addition, for example, a signal may be sent when a power source of a load circuit driving device is turned on or as a predetermined operation before the power source is turned off.

  The signal sent when the failure is detected is selected so that the current passing only through the FET does not flow if the operation of each part is normal, and the current flows through the load circuit M. Only the signal 5 including the path is used. As a result, a large amount of power is not consumed by the current flowing through the failure detection.

  The measurement of the measurement unit is performed after sending the signals 1 to 5 or after a lapse of time when it is considered that the FETs 1 to 6 are in a state based on the signal in a state where no signal is sent (signal 0). . Table 1 shows the voltages at points A to D when each unit is in a normal state corresponding to signals 0 to 5. The failure detection unit has data corresponding to the normal state, and the measurement result is compared with it, and it is assumed that the failure is detected when it is out of the range. V is a voltage VBAT of the DC power supply, 0 is 0 V, V2 is a circuit through which current flows through FET5, FET1, load circuit M, FET4, and FET6. M, a voltage drop value by FET4. V2 is a value determined by the circuit and can be set in advance. The failure detection unit determines that a failure has occurred when values other than those described in the normal state of Table 1 are measured. Since the numerical value actually measured varies due to fluctuations in the power supply and disturbances, it may become a value deviated from VBT, 0, V2, so the normal range is set with a certain range, Suppose that a failure occurs when out of range.

  The failure detection unit performs the following operation when a failure is detected. For example, the notification unit notifies the outside that a failure has occurred with a display, sound, or the like. In the case of a seat belt retractor, an LED (Light Emitting Diode) is displayed on the dashboard. Further, the failure detection unit puts the conversion circuit into a state where conversion is not performed. More specifically, this means that even if there is a request from the outside to perform a conversion operation on the conversion circuit, the conversion operation is not performed.

  Next, the determination of the failure site and the failure content when the measurement result is not normal will be described. The parts and the contents that can be determined as faults are a power fault, a ground fault, a disconnection, and a short circuit and an open circuit of FETs 1 to 6 on the point B side or the point C side of the load circuit M. The power supply means that the DC power supply is short-circuited. Also. An FET short-circuit represents a state where the connection is not cut off even when a signal to turn off is applied to the FET, and an open state of the FET represents a state where the connection is not established even when a signal to turn on is applied to the FET.

  The failure detection unit has, as data, a portion surrounded by at least double ruled lines in Table 1 in the MPU, and measures this and the measurement unit to compare the result and determine the failure site and its contents. In Table 1, a portion surrounded by double ruled lines is a portion different from the normal state. In the MPU, tables other than the part surrounded by the double ruled line are also stored, and when this part is also compared, if a special failure other than the contents described later occurs, it is treated as other failure. , Misjudgments can be reduced. If they do not match any of the failure states, they may be treated as other failures.

  The result of specifying the fault location and fault details (including the specification as other faults) is communicated to the outside that the fault has occurred by display, sound, electrical signal, etc., or recorded in the fault detection unit, When there is a request from the outside to the failure detection unit, for example, during repairs, the record is transmitted. Thus, repair can be performed according to the specified failure content.

  If a failure occurs, if the failure detection operation described above is continued, the operation will be performed in a state different from the originally assumed state, which may cause other problems. Although it is desirable to stop the operation, it may be possible to return to a normal state for some reason without repairing.

  Therefore, the failure detection unit sends only a switching signal that can confirm the return from the failure to the FETs 1 to 6 according to the specified failure site and the content of the failure, and measures the voltages at points A to D, so that only the failure site is detected. In particular, it detects whether the failure continues. Table 2 shows an FET control method corresponding to the failure content determined in Table 1. The failure detection unit sends a switching signal for performing the control shown in Table 2 and examines whether there is a change from the measurement result of the measurement unit when it is determined as a failure.

  When there is a change in the measurement result, signals 1 to 5 for detecting a failure are sent, and the measurement result of the measurement unit at that time is examined. When the measurement result matches the normal state shown in Table 1, it is determined that the load circuit and the conversion circuit are normal. In that case, the failure detection unit communicates that it has returned to the normal state with a display, sound, electrical signal, etc., or records it in the failure detection unit, and when making repairs, there is a request from the outside to the failure detection unit. If so, the record is transmitted.

  In addition, when the normal state is restored, the conversion circuit can perform the conversion operation, so that the load circuit M can perform a predetermined operation when an external request is made.

  As described above, the load circuit driving device that can detect the failure of the FETs 1 to 6 and the load circuit M when the FETs 1 to 6 are connected as shown in FIG. 1A has been described. Instead of measuring the voltage at the point D, the current flowing through the point D2 between the FET 6 and the ground may be measured as shown in FIG. In this case, in order to detect the failure of the FETs 1 to 6 in the same manner, the signals 1a to 5b shown in FIG. The order of sending the signals 1a to 5b may be changed in the same manner as the signals 1 to 5.

  The signal 1a is a signal for turning on the FET 5 and turning off the FETs 1 to 4 and 6 (hereinafter, the signal to be turned off is omitted and only the signal to be turned on is written), and the signal 2a is turned on the FET 5, FET 1, and FET 6. Signal 3a is a signal for turning on FET5, FET1, and FET3. Signal 4a is a signal for turning on FET5, FET2, FET3, and FET6. Signal 5a is a signal that turns on FET5, FET1, and FET4. This signal turns on the FET 6. The ON time of the signal 5a is set to a short time during which the load circuit M does not perform an actual operation. For example, if the load circuit M is a general DC motor, it can be prevented from operating even if a current is passed if the duty is about 1% or less.

  The failure detection unit sends these signals 1a to 5a, and the timing at which the FETs 1 to 6 should be in the state of the signal and the on signal are not sent (signal 0), that is, the FETs 1 to 6 should be off. A failure is detected by the voltage at the above-described points A to C and the current at D2 measured by the measurement unit at the timing.

  Table 3 shows a measurement result when the circuit in this case is normal, and a table for determining the failure site and the failure content. Shown in the D2 column is the current value, 0 is 0A, I1 is the current value of the circuit passing through only one of the FETs, I2 is the current value passing through the load circuit M, and the load If the circuit M is a motor, it has a higher resistance than the FET, so I1 >> I2. These are values determined by the circuit and can be set in advance. The notation “≈I2” in Table 3 indicates a state in which there is a change in value due to a failure, but there is little change from I2. Since this state is difficult to distinguish from I2, the distinction between “≈I2” and I2 is not used for failure detection.

  When the failure part is specified by Table 3, the return can be detected by the FET control pattern for detecting the return shown in Table 4.

Claims (9)

A load circuit; a first switching element and a second switching element connected to the load circuit at a center; and a third switching element connected to the lower arm connected to the first switching element. And an H-bridge circuit having a fourth switching element on a lower arm connected to the second switching element, a fifth switching element connected to the upper arm, and a sixth switching element connected to the lower arm A conversion circuit that changes the frequency or direction of direct current flow to the load circuit, and a voltage at a portion connecting the fifth switching element, the first switching element, and the second switching element, A voltage at a portion connecting the first switching element, the third switching element, and the load circuit; Measure the voltage at the site connecting the chucking device, the fourth switching device, and the load circuit, and the voltage at the site connecting the third switching device, the fourth switching device, and the sixth switching device. A measurement unit; a switching signal for turning on the fifth switching element; a switching signal for turning on the fifth switching element and the first switching element; the fifth switching element and the first switching element; A switching signal for turning on the third switching element; a switching signal for turning on the fifth switching element; the second switching element; and the fourth switching element; and the fifth switching element and the first switching element. 1 switching element, the fourth switching element, and the sixth switching element. A load circuit drive device comprising: a failure detection unit that sends a switching signal to turn on the switching element and detects a failure of the load circuit and the conversion circuit based on a measurement result of the measurement unit . A load circuit; a first switching element and a second switching element connected to the load circuit at a center; and a third switching element connected to the lower arm connected to the first switching element. And an H-bridge circuit having a fourth switching element on a lower arm connected to the second switching element, a fifth switching element connected to the upper arm, and a sixth switching element connected to the lower arm A conversion circuit that changes the frequency or direction of direct current flow to the load circuit, and a voltage at a portion connecting the fifth switching element, the first switching element, and the second switching element, A voltage at a portion connecting the first switching element, the third switching element, and the load circuit; A measuring unit for measuring a voltage at a portion connecting the chucking element, the fourth switching element and the load circuit, and a current flowing between the sixth switching element and the ground, and turning on the fifth switching element. Switching signal for turning on, switching signal for turning on the fifth switching element, the first switching element, and the sixth switching element, the fifth switching element, the first switching element, and the third switching element A switching signal for turning on the fifth switching element, the second switching element, the third switching element, and the sixth switching element, and the fifth switching element and the switching element The first switching element, the fourth switching element, and the first switching element And a failure detection unit for detecting a failure of the load circuit and the conversion circuit based on a measurement result of the measurement unit and driving a load circuit. apparatus. 3. The load circuit drive device according to claim 1, wherein the failure detection unit determines a failure part and a failure content of the load circuit and the conversion circuit. 4. A seat belt retractor comprising: the load circuit drive device according to any one of claims 1 to 3; and a vehicle seat belt, wherein the load circuit is a motor that winds up the vehicle seat belt. A load circuit; a first switching element and a second switching element connected to the load circuit at a center; and a third switching element connected to the lower arm connected to the first switching element. And an H-bridge circuit having a fourth switching element on a lower arm connected to the second switching element, a fifth switching element connected to the upper arm, and a sixth switching element connected to the lower arm A fault detection method for a load circuit drive device, comprising: a conversion circuit that changes the frequency or direction of direct current flow and that flows through the load circuit; and a fault detection unit that detects a fault in the load circuit and the conversion circuit. When the conversion circuit is on standby from the failure detection unit without performing conversion, the fifth switching element Switching signal for turning on, switching signal for turning on the fifth switching element and the first switching element, switching for turning on the fifth switching element, the first switching element and the third switching element Signal, a switching signal for turning on the fifth switching element, the second switching element, and the fourth switching element, and the fifth switching element, the first switching element, and the fourth switching element. And a switching signal for turning on the sixth switching element, and a voltage at a portion connecting the fifth switching element, the first switching element and the second switching element, and the first switching element. An element, the third switching element, and the A voltage at a portion connecting a load circuit, a voltage at a portion connecting the second switching element, the fourth switching element, and the load circuit, and the third switching element, the fourth switching element, and the second 6. A failure detection method for a load circuit drive device, comprising: measuring a voltage of a portion connecting to the switching element 6 and detecting a failure of the load circuit and the conversion circuit by the failure detection unit. A load circuit; a first switching element and a second switching element connected to the load circuit at a center; and a third switching element connected to the lower arm connected to the first switching element. And an H-bridge circuit having a fourth switching element on a lower arm connected to the second switching element, a fifth switching element connected to the upper arm, and a sixth switching element connected to the lower arm A fault detection method for a load circuit drive device, comprising: a conversion circuit that changes the frequency or direction of a direct current that flows through the load circuit, and a fault detection unit that detects a fault in the load circuit and the conversion circuit. When the conversion circuit is on standby from the failure detection unit without performing conversion, the fifth switching element A switching signal to turn on, a switching signal to turn on the fifth switching element, the first switching element, and the sixth switching element, the fifth switching element, the first switching element, and the third switching A switching signal for turning on an element, a switching signal for turning on the fifth switching element, the second switching element, the third switching element, and the sixth switching element, and the fifth switching element, A switching signal for turning on the first switching element, the fourth switching element, and the sixth switching element is sent, and the fifth switching element, the first switching element, and the second switching element are sent. The voltage at the site connecting the element, the first A voltage at a portion connecting the switching element, the third switching element, and the load circuit, a voltage at a portion connecting the second switching element, the fourth switching element, and the load circuit, and the sixth A failure detection method for a load circuit drive device, comprising: measuring a current flowing between a switching element and a ground; and detecting a failure of the load circuit and the conversion circuit by the failure detection unit. 7. The failure detection method for a load circuit drive device according to claim 5, wherein the failure detection unit determines a failure part and a failure content of the load circuit and the conversion circuit. 8. 8. The failure detection unit according to claim 7, wherein when the failure is detected in at least one of the conversion circuit and the load circuit, the failure detection unit does not perform the conversion operation. A failure detection method for a drive device of a load circuit, wherein a switching signal capable of determining whether the failure part has recovered from the failure is repeatedly sent according to the determined failure part and the failure content. 9. The failure detection method for a load circuit drive device according to claim 8, wherein the failure detection unit is in a state in which the conversion circuit can perform a conversion operation when the failure part is recovered from the failure. A failure detection method for a load circuit driving device.

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