Auxiliary power supply unit

Abstract

An auxiliary power supply device (40) includes a main power supply side path (L1), an auxiliary power supply side path (L2), a power supply control circuit (70), an analog determination circuit (100) provided separately from the power supply control circuit (70), and a power supply switching circuit (110). The power supply control circuit (70) controls switching between an on state and an off state on the main power supply side path (L1) and the auxiliary power supply side path (L2). The analog determination circuit (100) determines the occurrence of an abnormality in the main power supply (50), and generates a switching signal when it is determined that an abnormality has occurred in the main power supply (50). The power supply switching circuit (110) switches the power supply for supplying power to a power supply target from the main power supply (50) to the auxiliary power supply (60).

Description

Technical Field

[0001] The invention relates to an auxiliary power supply device. Background Art

[0002] Japanese Unexamined Patent Application Publication No. 2015-136229 (JP2015-136229A) discloses a semiconductor integrated circuit that controls power output to a load. The semiconductor integrated circuit takes in a temperature measurement result as an analog signal and converts the temperature measurement result into a digital signal. The semiconductor integrated circuit switches the output of power to the load between an unstable power supply and a stable power supply based on the digital signal. Summary of the invention

[0003] In a semiconductor integrated circuit, a temperature measurement result is taken in as an analog signal, and the analog signal is converted into a digital signal. A switching decision between an unstable power supply and a stable power supply is performed based on the digital signal obtained by the conversion. The digital signal indicating the decision result is converted into an analog signal, and the switching of the power supply is performed according to the analog signal. As a result, the steps required to switch the power supply become complicated. For example, in the event of a short circuit problem in the power supply, the voltage of the power output from the power supply drops sharply. Therefore, before the power supply switching is completed, the power output from the power supply to the load may be insufficient. From the perspective of fast switching of the power supply, the semiconductor integrated circuit disclosed in JP2015-136229A can be improved.

[0004] One aspect of the present invention is an auxiliary power supply device. The auxiliary power supply device includes: a main power supply side path, an auxiliary power supply side path, a power supply control circuit, an analog determination circuit, and a power supply switching circuit. The main power supply side path is a power supply path from the main power supply to the power supply target. The auxiliary power supply side path is connected to the main power supply side path. The auxiliary power supply side path is a power supply path from the auxiliary power supply to the power supply target. The auxiliary power supply is connected to the power supply target through the auxiliary power supply side path. The power supply control circuit is configured to control the switching between the on state and the interruption state on the main power supply side path, and control the switching between the on state and the interruption state on the auxiliary power supply side path. The analog determination circuit is set separately from the power supply control circuit. The analog determination circuit is configured to determine the occurrence of an abnormality in the main power supply using an analog signal indicating the output state of the main power supply. The analog determination circuit is configured to: when it is determined that an abnormality has occurred in the main power supply, generate a switching signal as an analog signal indicating that an abnormality has occurred in the main power supply. The power supply switching circuit is configured to switch the power supply for supplying power to the power supply target from the main power supply to the auxiliary power supply based on the switching signal generated by the analog determination circuit.

[0005] With this configuration, the following steps are performed when the power source is switched: the analog determination circuit determines the occurrence of an abnormality in the main power source using an analog signal indicating the output state of the main power source, and generates a switching signal as an analog signal indicating the determination result, and the power switching circuit switches the power source according to the switching signal. That is, the switching signal as an analog signal can be generated without performing a process of converting the switching signal from the analog signal indicating the output state of the main power source to a digital value. Therefore, compared with the steps in the case where the switching signal is converted into a digital signal and then used to determine the switching of the power source, the steps required for switching the power source can be simplified. Therefore, even in the case where the voltage of the power output from the main power source drops sharply, the power source for supplying power to the power supply target can be switched from the main power source to the auxiliary power source more quickly.

[0006] In the auxiliary power supply device, the analog determination circuit may include a comparison circuit, to which a power supply voltage signal as an analog signal indicating an output state of the main power supply and an abnormal determination voltage signal depending on an abnormal determination voltage are input. The power supply voltage signal may indicate the power supply voltage of the main power supply. The abnormal determination voltage may indicate that an abnormality has occurred in the main power supply. The comparison circuit may be configured to: in the case where the voltage of the power supply voltage signal exceeds the voltage of the abnormal determination voltage signal, determine that no abnormality has occurred in the main power supply, and generate a switching signal to set the main power supply as a power supply for supplying power to a power supply target. The comparison circuit may be configured to: in the case where the voltage of the power supply voltage signal does not exceed the voltage of the abnormal determination voltage signal, determine that an abnormality has occurred in the main power supply, and generate a switching signal to set the auxiliary power supply as a power supply for supplying power to a power supply target.

[0007] With the above configuration, a specific configuration of an analog determination circuit that generates a switching signal from a power supply voltage signal can be provided without performing a process of converting a power supply voltage signal that is an analog signal indicating the output state of the main power supply into a digital value.

[0008] In the auxiliary power supply device, the power switching circuit may include: a main power supply side switch circuit arranged on the main power supply side path, an auxiliary power supply side switch circuit arranged on the auxiliary power supply side path, a main power supply side voltage application circuit, and an auxiliary power supply side voltage application circuit. The main power supply side switch circuit may include a first metal oxide semiconductor field effect transistor that performs switching between a conduction state and an interruption state. The auxiliary power supply side switch circuit may include a second metal oxide semiconductor field effect transistor that performs switching between a conduction state and an interruption state. The main power supply side voltage application circuit may be configured to apply a gate voltage for performing switching between a conduction state and an interruption state to a gate terminal of the main power supply side switch circuit. The auxiliary power supply side voltage application circuit may be configured to apply a gate voltage for performing switching between a conduction state and an interruption state to a gate terminal of the auxiliary power supply side switch circuit. The power control circuit and the comparison circuit may be configured to control the switching between the conduction state and the interruption state of the main power supply side switch circuit by outputting a control voltage signal to the main power supply side voltage application circuit. The power supply control circuit and the comparison circuit may be configured to control the switching of the auxiliary power supply side switch circuit between the on state and the interruption state by outputting a control voltage signal to the auxiliary power supply side voltage application circuit. The comparison circuit may be configured to: when the voltage of the power supply voltage signal exceeds the voltage of the abnormality determination voltage signal, output the control voltage signal for making the main power supply side switch circuit in the on state as a switching signal to the main power supply side voltage application circuit, and output the control voltage signal for making the auxiliary power supply side switch circuit in the interruption state as a switching signal to the auxiliary power supply side voltage application circuit. The comparison circuit may be configured to: when the voltage of the power supply voltage signal does not exceed the voltage of the abnormality determination voltage signal, output the control voltage signal for making the main power supply side switch circuit turn to the interruption state as a switching signal to the main power supply side voltage application circuit, and output the control voltage signal for making the auxiliary power supply side switch circuit turn to the on state as a switching signal to the auxiliary power supply side voltage application circuit.

[0009] With the above configuration, a specific configuration of a power switching circuit that switches the power supply for supplying power to a power supply target from the main power supply to the auxiliary power supply by inputting a control voltage signal as an analog signal output from a comparison circuit to the power switching circuit can be provided.

[0010] In the auxiliary power supply device, the analog determination circuit may include a pseudo operation circuit that causes a pseudo abnormality to occur in the power supply voltage signal input to the comparison circuit based on the input of a pseudo abnormality signal from the power supply control circuit. The power supply control circuit may be configured to: in the case of checking the operation of the analog determination circuit, generate a pseudo abnormality signal for causing a pseudo abnormality to occur in the power supply voltage signal input to the comparison circuit to the pseudo operation circuit. The power supply control circuit may be configured to: in the case where the comparison circuit generates a switching signal as a result of outputting the pseudo abnormality signal to the pseudo operation circuit, determine that no abnormality has occurred in the analog determination circuit. The power supply control circuit may be configured to determine that an abnormality has occurred in the analog determination circuit in the case where the comparison circuit does not generate a switching signal regardless of whether the pseudo abnormality signal is output to the pseudo operation circuit.

[0011] With the above configuration, the power supply control circuit can detect the occurrence of an abnormality in the analog determination circuit based on the determination of whether the comparison circuit generates a switching signal by outputting a pseudo abnormality signal to the pseudo operation circuit. This is because, in the case where an abnormality occurs in the analog determination circuit, even if the power supply control circuit outputs a pseudo abnormality signal to the pseudo operation circuit, a switching signal is not generated. Therefore, information about whether an abnormality occurs in the analog determination circuit can be identified, and thus countermeasures for the occurrence of an abnormality in the analog determination circuit are executed. Since the analog determination circuit switches the power supply in a state where no abnormality occurs in the analog determination circuit, the reliability of the auxiliary power supply device can be improved.

[0012] In the auxiliary power supply device, the power supply control circuit may store an abnormality determination voltage threshold for indicating that an abnormality has occurred in the main power supply as a digital value. The power supply control circuit may be configured to acquire a power supply voltage signal and convert the acquired power supply voltage signal into a power supply voltage value as a digital value. The power supply control circuit may be configured to: when the power supply voltage value exceeds the abnormality determination voltage threshold, output an analog signal for setting the main power supply as a power supply for supplying power to a power supply target to the power supply control circuit. The power supply control circuit may be configured to: when the power supply voltage value does not exceed the abnormality determination voltage threshold, output an analog signal for setting the auxiliary power supply as a power supply for supplying power to a power supply target to the power supply control circuit.

[0013] With the above configuration, not only the analog determination circuit but also the power control circuit can determine whether an abnormality has occurred in the main power supply. Therefore, compared with the case where the determination is performed only by the analog determination circuit or the power control circuit, the power supply can be switched more appropriately in response to the occurrence of an abnormality with different forms.

[0014] In the auxiliary power supply device, the abnormality determination voltage threshold value may be set to have a potential higher than the voltage value obtained by converting the abnormality determination voltage signal into a digital value. As the abnormality of the main power supply, the following various forms are provided: a short circuit problem of the main power supply, in which the power supply voltage value of the main power supply drops sharply; an open circuit problem of the main power supply, in which the power supply voltage value of the main power supply drops slowly; and an abnormality caused by the deterioration of the main power supply over time. In the case where the power supply voltage value of the main power supply drops slowly, it is assumed that the power supply voltage value of the main power supply exceeds the voltage of the abnormality determination voltage signal but does not exceed the abnormality determination voltage threshold value before the power supply voltage value of the main power supply drops to a voltage lower than the abnormality determination voltage signal. In the case where the power supply voltage value of the main power supply drops sharply, it is assumed that the power supply voltage value of the main power supply drops to a voltage lower than the abnormality determination voltage signal instantly. Therefore, the abnormality determination voltage threshold value used in the case where the power supply control circuit determines whether an abnormality occurs in the main power supply is set to have a potential higher than the voltage of the abnormality determination voltage signal used when the analog determination circuit capable of rapid determination determines whether an abnormality occurs in the main power supply. Therefore, it is possible to distinguish between a case where an abnormality is determined to have occurred in the main power supply based on a determination that the power supply voltage value of the main power supply does not exceed the voltage of the abnormality determination voltage signal and a case where an abnormality is determined to have occurred in the main power supply based on a determination that the power supply voltage value of the main power supply exceeds the voltage of the abnormality determination voltage signal but does not exceed the abnormality determination voltage threshold. Therefore, the form of the abnormality occurring in the main power supply can be identified.

[0015] The auxiliary power supply device of the present invention enables rapid switching of power supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, in which like numerals represent like elements, and in which:

[0017] Figure 1 is a schematic diagram showing the configuration of a steering device to which an auxiliary power supply device is applied;

[0018] Figure 2 is a diagram showing an electrical configuration of an auxiliary power supply device;

[0019] Figure 3 is a graph showing transition of power supply voltage value in the case where an open circuit problem occurs in the main power supply;

[0020] Figure 4 is a graph showing transition of power supply voltage value in the case where a short circuit problem occurs in the main power supply; and

[0021] Figure 5 is a diagram showing an electrical configuration of an auxiliary power supply device according to another embodiment. DETAILED DESCRIPTION

[0022] An embodiment in which the auxiliary power supply device is applied to the steering device will be described. Figure 1 As shown, the steering device 1 includes: a steering mechanism 2, an assist mechanism 3, a steering control device 30 and an auxiliary power supply device 40. The steering mechanism 2 steers the wheel assembly 16 based on the driver's operation of the steering wheel 10. The assist mechanism 3 includes a motor 20 that assists the driver's steering operation. The steering device 1 is a so-called electric power steering device that assists the driver's steering operation by applying the motor torque of the motor 20 as a steering assist force to the steering mechanism 2.

[0023] The steering mechanism 2 includes a steering shaft 12 and a rack shaft 14. A first end of the steering shaft 12 is fixed to the steering wheel 10, and a pinion 11 is formed at a second end of the steering shaft 12. The rack shaft 14 is formed with a rack 13 meshing with the pinion 11. The pinion 11 and the rack 13 constitute a rack and pinion mechanism. The rotational motion of the steering shaft 12 is converted into a reciprocating linear motion of the rack shaft 14 in an axial direction by the rack and pinion mechanism. The steering device 1 is mounted on the vehicle in such a manner that the axial direction of the rack shaft 14 is a vehicle width direction. The reciprocating linear motion of the rack shaft 14 is transmitted to the left and right wheel assemblies 16 through tie rods 15 respectively connected to both ends of the rack shaft 14, so that the steering angle of the wheel assembly 16 changes, and the driving direction of the vehicle changes.

[0024] The steering shaft 12 is provided with a torque sensor 17 for measuring a steering torque TR applied to the steering shaft 12 by operating the steering wheel 10. The torque sensor 17 in this embodiment detects a torsion amount of a torsion bar constituting a part of the steering shaft 12 and measures the steering torque TR based on the torsion amount.

[0025] The assist mechanism 3 includes a motor 20 for assisting steering and a reducer 21. The motor 20 is connected to the reducer 21, and the reducer 21 is connected to the steering shaft 12. The reducer 21 reduces the rotation of the motor 20 and transmits the reduced rotational force to the steering shaft 12. In the present embodiment, a three-phase brushless motor is used as the motor 20. In the present embodiment, a worm gear mechanism is used as the reducer 21.

[0026] The steering control device 30 includes an inverter, which is a known circuit including two switching elements for each phase (U phase, V phase and W phase) of the motor 20. In the case where the steering device 1 is mounted on a vehicle, the auxiliary power supply device 40 is connected to the main power supply 50 mounted on the vehicle, and the steering control device 30 is connected to the auxiliary power supply device 40. The auxiliary power supply device 40 is provided between the main power supply 50 and the steering control device 30 as a power supply target. The steering control device 30 assists the driver's steering operation by controlling the operation of the motor 20 using the supply power from the main power supply 50. The steering control device 30 includes a steering control unit 31 and a memory 32. The steering control unit 31 performs various types of arithmetic processing such as calculating a control amount for controlling the operation of the motor 20. The memory 32 stores programs and data for various types of arithmetic processing. The above-mentioned torque sensor 17 and vehicle speed sensor 18 are connected to the steering control unit 31. The vehicle speed sensor 18 detects the driving speed SP of the vehicle. When the steering control unit controls the steering assist force, the steering control unit 31 determines a steering assist force corresponding to a target steering assist force as a target value of the steering assist force based on the steering torque TR and the driving speed SP. The steering control unit 31 controls the operation of the motor 20 by controlling the inverter to generate a steering assist force corresponding to the target steering assist force.

[0027] The configuration of the auxiliary power supply device 40 will be described. Figure 2 As shown, the auxiliary power supply device 40 includes an auxiliary power supply 60 , a power supply control unit 70 , a voltage detection circuit 80 , an analog determination circuit 100 , and a power supply switching circuit 110 .

[0028] A main power supply side power supply path L1 and an auxiliary power supply side power supply path L2 are provided in the auxiliary power supply device 40. The main power supply side power supply path L1 is provided as a power supply path from the main power supply 50 to the steering control device 30 as a power supply target. The auxiliary power supply side power supply path L2 is connected to the main power supply side power supply path L1, and serves as a power supply path from the auxiliary power supply 60 to the steering control device 30. The auxiliary power supply side power supply path L2 is connected to a connection point P1 on the main power supply side power supply path L1.

[0029] The auxiliary power source 60 is connected to the steering control device 30 through the auxiliary power source side power supply path L2. The auxiliary power source 60 can be charged and discharged. For example, a lithium ion capacitor is used as the auxiliary power source 60.

[0030] The power switching circuit 110 includes a main power side switch unit 150, an auxiliary power side switch unit 160, a main power side voltage application unit 170, and an auxiliary power side voltage application unit 180. The main power side switch unit 150 is disposed between the main power supply 50 and a connection point P1 on the main power side power supply path L1. The main power side switch unit 150 includes a first MOSFET (metal-oxide-semiconductor field-effect-transistor) 151 and a second MOSFET 152. Each of the first MOSFET 151 and the second MOSFET 152 is a P-channel MOSFET including a source terminal associated with a P-type semiconductor layer, a drain terminal associated with the P-type semiconductor layer, and a gate terminal associated with an N-type semiconductor layer. Figure 2 , the source terminal is indicated by "S", the drain terminal is indicated by "D", and the gate terminal is indicated by "G".

[0031] The source terminal of the first MOSFET 151 is connected to the high potential side of the main power supply 50 and the drain terminal is connected to the drain terminal of the second MOSFET 152. The drain terminal of the second MOSFET 152 is connected to the drain terminal of the first MOSFET 151, and the source terminal is connected to the steering control device 30 through the main power supply side power supply path L1. The gate terminal of the first MOSFET 151 and the gate terminal of the second MOSFET 152 are connected to the main power supply side voltage applying unit 170. In the main power supply side switch unit 150, switching between the on state and the interruption state is performed by the first MOSFET 151 and the second MOSFET 152. In the on state, power supply is performed through the main power supply side power supply path L1 between the main power supply 50 and the steering control device 30. In the interruption state, power supply is interrupted.

[0032] The auxiliary power supply side switch unit 160 is provided on the auxiliary power supply side power supply path L2. The auxiliary power supply side switch unit 160 includes a third MOSFET 161 and a fourth MOSFET 162. Each of the third MOSFET 161 and the fourth MOSFET 162 is an N-channel MOSFET including a source terminal associated with an N-type semiconductor layer, a drain terminal associated with the N-type semiconductor layer, and a gate terminal associated with a P-type semiconductor layer.

[0033] The drain terminal of the third MOSFET 161 is connected to the high potential side of the auxiliary power supply 60 and the source terminal is connected to the source terminal of the fourth MOSFET 162. The drain terminal of the fourth MOSFET 162 is connected to the connection point P1 on the main power supply side power supply path L1 through the auxiliary power supply side power supply path L2. The gate terminal of the third MOSFET 161 and the gate terminal of the fourth MOSFET 162 are connected to the auxiliary power supply side voltage applying unit 180. In the auxiliary power supply side switch unit 160, switching between the on state and the interruption state is performed by the third MOSFET 161 and the fourth MOSFET 162. In the on state, power supply is performed through the auxiliary power supply side power supply path L2 between the auxiliary power supply 60 and the steering control device 30. In the interruption state, power supply is interrupted.

[0034] The voltage detection circuit 80 is connected to a connection point P1 on the main power supply side power supply path L1 and a connection point P2 between the steering control device 30. The power control unit 70 is connected to the voltage detection circuit 80 and to the analog determination circuit 100. The power control unit 70 is connected to the main power supply side voltage application unit 170 and the auxiliary power supply side voltage application unit 180.

[0035] The power control unit 70 has a function of controlling the switching between the on state and the interruption state on the main power supply side power supply path L1 and a function of controlling the switching between the on state and the interruption state on the auxiliary power supply side power supply path L2. Although not shown, the power control unit 70 controls the various units of the auxiliary power supply device 40 based on the input voltage of the main power supply 50. The power control unit 70 outputs a first control voltage signal SC1 for performing the switching between the on state and the interruption state on the main power supply side power supply path L1 to the main power supply side voltage applying unit 170, and outputs a first control voltage signal SC1 for performing the switching between the on state and the interruption state on the auxiliary power supply side power supply path L2 to the auxiliary power supply side voltage applying unit 180. The first control voltage signal SC1 is an analog signal including a high-level voltage signal and a low-level voltage signal.

[0036] In the case where it is determined that no abnormality has occurred in the main power supply 50, the power control unit 70 outputs the first control voltage signal SC1 for turning on the first MOSFET 151 and the second MOSFET 152 on the main power supply side power supply path L1 to the main power supply side voltage application unit 170, so that the steering control device 30 performs control related to the application of the steering assist force based on the power supply from the main power supply 50. In the case where it is determined that no abnormality has occurred in the main power supply 50, the power control unit 70 outputs the first control voltage signal SC1 for turning on the third MOSFET 161 and the fourth MOSFET 162 on the auxiliary power supply side power supply path L2 to the auxiliary power supply side voltage application unit 180. In the case where it is determined that an abnormality has occurred in the main power supply 50, the power control unit 70 outputs the first control voltage signal SC1 for turning on the third MOSFET 161 and the fourth MOSFET 162 on the auxiliary power supply side power supply path L2 to the auxiliary power supply side voltage application unit 180, so that the steering control device 30 performs control related to the application of the steering assist force based on the power supply from the auxiliary power supply 60. In the case where it is determined that an abnormality has occurred in the main power supply 50, the power supply control unit 70 outputs a first control voltage signal SC1 for turning the first MOSFET 151 and the second MOSFET 152 on the main power supply side power supply path L1 to the interruption state to the main power supply side voltage applying unit 170. The first control voltage signal SC1 output from the power supply control unit 70 in the case where it is determined that no abnormality has occurred in the main power supply 50 is a high-level signal having a potential higher than the potential of the first control voltage signal SC1 output from the power supply control unit 70 in the case where it is determined that an abnormality has occurred in the main power supply 50.

[0037] In the case where the first control voltage signal SC1 for turning the first MOSFET 151 and the second MOSFET 152 on the main power supply side power supply path L1 into the on state is input from the power supply control unit 70, the main power supply side voltage application unit 170 applies the gate voltage Vg1 to the gate terminal of the first MOSFET 151 and the gate terminal of the second MOSFET 152. The potential of the gate voltage Vg1 is lower than the potential of the source terminal. In this case, the gate voltage Vg1 is set to a voltage value as large as the voltage value in the case where an inversion layer is formed in the P-type semiconductor layer associated with the gate terminal. In the case where the first control voltage signal SC1 for turning the first MOSFET 151 and the second MOSFET 152 on the main power supply side power supply path L1 into the off state is input from the power supply control unit 70, the main power supply side voltage application unit 170 applies the gate voltage Vg1 such that the potential at the source terminal is equal to the potential at the gate terminal to the gate terminal of the first MOSFET 151 and the gate terminal of the second MOSFET 152. In this case, the gate voltage Vg1 is set to a voltage value as large as that in a case where an inversion layer is not formed in the P-type semiconductor layer associated with the gate terminal.

[0038] In the case where the first control voltage signal SC1 for turning the third MOSFET 161 and the fourth MOSFET 162 on the auxiliary power supply side power supply path L2 into the on state is input from the power supply control unit 70, the auxiliary power supply side voltage application unit 180 applies the gate voltage Vg2 to the gate terminal of the third MOSFET 161 and the gate terminal of the fourth MOSFET 162. The potential of the gate voltage Vg2 is higher than the potential at the source terminal. In this case, the gate voltage Vg2 is set to a voltage value as large as the voltage value in the case where an inversion layer is formed in the N-type semiconductor layer associated with the gate terminal. In the case where the first control voltage signal SC1 for turning the third MOSFET 161 and the fourth MOSFET 162 on the auxiliary power supply side power supply path L2 into the interrupted state is input from the power supply control unit 70, the auxiliary power supply side voltage application unit 180 applies the gate voltage Vg2 such that the potential at the source terminal is equal to the potential at the gate terminal to the gate terminal of the third MOSFET 161 and the gate terminal of the fourth MOSFET 162. In this case, the gate voltage Vg2 is set to a voltage value as large as that in a case where an inversion layer is not formed in the N-type semiconductor layer associated with the gate terminal.

[0039] The power control unit 70 detects the power supply voltage signal Sv indicating the voltage at the connection point P2 through the voltage detection circuit 80. For example, the voltage detection circuit 80 divides the voltage indicated by the power supply voltage signal Sv at the connection point P2 through a voltage-dividing resistor, and outputs the divided voltage to the power control unit 70. The power control unit 70 converts the input divided voltage into a digital value, and identifies the power supply voltage value Vv of the main power supply 50 indicated by the power supply voltage signal Sv from the digital value. The power control unit 70 stores the abnormality determination voltage threshold Vth indicating that an abnormality has occurred in the main power supply 50 as a digital value. The abnormality determination voltage threshold Vth is set to a value as large as the abnormality determination voltage threshold Vth in the case where it is determined that an abnormality has occurred in the main power supply 50 when the power supply voltage value Vv of the main power supply 50 becomes smaller than the abnormality determination voltage threshold Vth. In the case where the state in which the power supply voltage value Vv of the main power supply 50 does not exceed the abnormality determination voltage threshold value Vth does not continue for a predetermined period of time, the power supply control unit 70 generates a high-level first control voltage signal SC1 for setting the main power supply 50 as a power supply for supplying power to the steering control device 30 as a power supply target. In the case in which the power supply voltage value Vv of the main power supply 50 does not exceed the abnormality determination voltage threshold value Vth continues for a predetermined period of time, the power supply control unit 70 generates a low-level first control voltage signal SC1 for setting the auxiliary power supply 60 as a power supply for supplying power to the steering control device 30 as a power supply target. The predetermined period of time is set to a time as long as it is considered that the state in which the power supply voltage value Vv of the main power supply 50 does not exceed the abnormality determination voltage threshold value Vth is not a state that occurs temporarily due to noise or the like.

[0040] The analog determination circuit 100 is provided separately from the power supply control unit 70, and performs determination of whether an abnormality has occurred in the main power supply 50 separately from the power supply control unit 70. The analog determination circuit 100 is a circuit that determines an abnormality in the main power supply 50 using the power supply voltage signal Sv indicating the power supply voltage value Vv of the main power supply 50 without converting the power supply voltage signal Sv indicating the power supply voltage value Vv of the main power supply 50 into a digital value, and generates an analog signal indicating that an abnormality has occurred in the main power supply 50 when the analog determination circuit determines that an abnormality has occurred in the main power supply 50.

[0041] The analog determination circuit 100 includes a comparison circuit 120 , a voltage division circuit 130 , and a dummy operation circuit 140 .

[0042] The pseudo operation circuit 140 is connected to a connection point P3 between a connection point P1 and a connection point P2 on the main power supply side power supply path L1. The power supply voltage signal Sv indicating the voltage at the connection point P3 is equal to the power supply voltage signal Sv indicating the voltage at the connection point P2. The pseudo operation circuit 140 is a circuit that causes a pseudo abnormality to occur in the power supply voltage signal Sv output to the comparison circuit 120 described later. The pseudo operation circuit 140 includes a voltage dividing resistor 141, a voltage dividing resistor 142, a fifth MOSFET 143, and a digital transistor 144.

[0043] The voltage dividing resistor 141 has a first end connected to the connection point P3 on the main power supply side power supply path L1 and a second end connected to the voltage dividing resistor 142. The voltage dividing resistor 142 has a first end connected to the voltage dividing resistor 141 and a second end connected to the collector terminal of the digital transistor 144.

[0044] The fifth MOSFET 143 is a P-channel MOSFET including a source terminal associated with a P-type semiconductor layer, a drain terminal associated with a P-type semiconductor layer, and a gate terminal associated with an N-type semiconductor layer. The fifth MOSFET 143 has a source terminal connected to a connection point P4 between a connection point P3 and a voltage dividing resistor 141, and a drain terminal connected to the voltage dividing circuit 130. The gate terminal of the fifth MOSFET 143 is connected to a connection point P5 between the voltage dividing resistors 141 and 142. The fifth MOSFET 143 performs switching between an on state and an off state between the connection point P3 and the voltage dividing circuit 130, in which power supply is performed according to the power supply voltage signal Sv, and in which power supply is interrupted.

[0045] The digital transistor 144 has a built-in bias resistor. The base terminal of the digital transistor 144 is connected to the built-in bias resistor, and the bias resistor is connected to the power supply control unit 70. The emitter terminal of the digital transistor 144 is connected to the ground, and the collector terminal is connected to the voltage dividing resistor 142. In the case of checking the operation of the analog determination circuit 100 during the initial check at the start of the vehicle, the power supply control unit 70 outputs a pseudo abnormality signal Sa for causing a pseudo abnormality to occur in the power supply voltage signal Sv input to the comparison circuit 120 to the digital transistor 144.

[0046] In the case where the pseudo abnormal signal Sa is input from the power control unit 70, the digital transistor 144 is turned off so that the current cannot flow between the collector terminal and the emitter terminal. Therefore, the source terminal and the gate terminal of the fifth MOSFET 143 have equal potentials, and the fifth MOSFET 143 is transformed into an interrupt state. In this case, the gate voltage is set to a voltage value as large as the voltage value in the case where the inversion layer is not formed in the P-type semiconductor layer associated with the gate terminal. In the case where the pseudo abnormal signal Sa is not input from the power control unit 70, the digital transistor 144 is turned on so that the current can flow between the collector terminal and the emitter terminal. Therefore, a gate voltage with a potential lower than the potential at the source terminal is applied to the gate terminal of the fifth MOSFET 143, and the fifth MOSFET 143 becomes a conducting state in which the current can flow between the source terminal and the drain terminal. In this case, the gate voltage is set to a voltage value as large as the voltage value in the case where the inversion layer is formed in the P-type semiconductor layer associated with the gate terminal.

[0047] The voltage dividing circuit 130 includes a voltage dividing resistor 131 and a voltage dividing resistor 132. The voltage dividing resistor 131 has a first end connected to the drain terminal of the fifth MOSFET 143 and a second end connected to the voltage dividing resistor 132. The voltage dividing resistor 132 has a first end connected to the voltage dividing resistor 131 and a second end connected to the ground. A connection point P6 between the voltage dividing resistors 131 and 132 is connected to the comparison circuit 120.

[0048] The comparison circuit 120 includes a comparator 121 and a pull-up resistor 122. The positive input terminal of the comparator 121 is connected to a connection point P6 between the voltage-dividing resistors 131 and 132 in the voltage-dividing circuit 130. Therefore, the power supply voltage signal Sv divided by the voltage-dividing circuit 130 is input to the positive input terminal of the comparator 121. The negative input terminal of the comparator 121 is connected to the abnormality determination voltage signal generating unit. The abnormality determination voltage signal generating unit generates an abnormality determination voltage signal Sref as a voltage indicating that an abnormality has occurred in the main power supply 50, and outputs the abnormality determination voltage signal Sref to the negative input terminal of the comparator 121. The resistance value of the voltage-dividing resistor 131 and the resistance value of the voltage-dividing resistor 132 constituting the voltage-dividing circuit 130 are adjusted so that the divided power supply voltage signal Sv is allowed to be compared with the abnormality determination voltage signal Sref. The abnormality determination voltage signal Sref is set to a value as large as the value of the abnormality determination voltage signal Sref in the case where it is determined that an abnormality occurs in the main power supply 50 when the divided voltage of the power supply voltage signal Sv becomes smaller than the voltage of the abnormality determination voltage signal Sref. The positive power supply terminal of the comparator 121 is connected to the abnormality determination voltage signal generating unit that generates the abnormality determination voltage signal Sref. The abnormality determination voltage signal generating unit is a circuit that generates a constant voltage. The negative power supply terminal of the comparator 121 is connected to the ground. The output terminal of the comparator 121 is connected to the power supply control unit 70, and is connected to the main power supply side voltage applying unit 170 and the auxiliary power supply side voltage applying unit 180. In the case where the abnormality determination voltage signal Sref is converted into a digital value in consideration of the voltage division of the voltage dividing circuit 130, the voltage value of the abnormality determination voltage signal Sref is set to a potential lower than the potential of the abnormality determination voltage threshold Vth.

[0049] The pull-up resistor 122 is provided between the abnormality determination voltage signal generating unit and the output terminal of the comparator 121. The pull-up resistor 122 is provided to stabilize the second control voltage signal SC2 output from the output terminal of the comparator 121. The second control voltage signal SC2 corresponds to a switching signal described in the claims.

[0050] The comparator 121 compares the divided voltage of the power supply voltage signal Sv input from the positive input terminal with the voltage of the abnormality determination voltage signal Sref input from the negative input terminal. In the case where the divided voltage of the power supply voltage signal Sv exceeds the voltage of the abnormality determination voltage signal Sref, the comparator 121 determines that there is no abnormality in the main power supply 50, and outputs a high-level second control voltage signal SC2 for making the main power supply 50 serve as a power supply for supplying power to the steering control device 30 from the output terminal. In the case where the divided voltage of the power supply voltage signal Sv does not exceed the voltage of the abnormality determination voltage signal Sref, the comparator 121 determines that an abnormality has occurred in the main power supply 50, and outputs a low-level second control voltage signal SC2 for making the auxiliary power supply 60 serve as a power supply for supplying power to the steering control device 30 from the output terminal.

[0051] In the case where the second control voltage signal SC2 for turning the first MOSFET 151 and the second MOSFET 152 on the main power supply side power supply path L1 into the on state is input from the comparison circuit 120, the main power supply side voltage application unit 170 applies a gate voltage Vg1 having a potential lower than the potential at the source terminal to the gate terminal of the first MOSFET 151 and the gate terminal of the second MOSFET 152. In this case, the gate voltage Vg1 is set to a voltage value as large as a voltage value in the case where an inversion layer is formed in the P-type semiconductor layer associated with the gate terminal. In the case where the second control voltage signal SC2 for turning the first MOSFET 151 and the second MOSFET 152 on the main power supply side power supply path L1 into the off state is input from the comparison circuit 120, the main power supply side voltage application unit 170 applies the gate voltage Vg1 such that the potential at the source terminal is equal to the potential at the gate terminal to the gate terminal of the first MOSFET 151 and the gate terminal of the second MOSFET 152. In this case, the gate voltage Vg1 is set to a voltage value as large as that in a case where an inversion layer is not formed in the P-type semiconductor layer associated with the gate terminal.

[0052] In the case where the second control voltage signal SC2 for turning the third MOSFET 161 and the fourth MOSFET 162 on the auxiliary power supply side power supply path L2 into the on state is input from the comparison circuit 120, the auxiliary power supply side voltage application unit 180 applies a gate voltage Vg2 having a potential higher than the potential at the source terminal to the gate terminal of the third MOSFET 161 and the gate terminal of the fourth MOSFET 162. In this case, the gate voltage Vg2 is set to a voltage value as large as a voltage value in the case where an inversion layer is formed in the N-type semiconductor layer associated with the gate terminal. In the case where the second control voltage signal SC2 for turning the third MOSFET 161 and the fourth MOSFET 162 on the auxiliary power supply side power supply path L2 into the off state is input from the comparison circuit 120, the auxiliary power supply side voltage application unit 180 applies the gate voltage Vg2 such that the potential at the source terminal is equal to the potential at the gate terminal to the gate terminal of the third MOSFET 161 and the gate terminal of the fourth MOSFET 162. In this case, the gate voltage Vg2 is set to a voltage value as large as that in a case where an inversion layer is not formed in the N-type semiconductor layer associated with the gate terminal.

[0053] The operation in this embodiment will be described.

[0054] In the case where no abnormality occurs in the main power supply 50, the power supply voltage value Vv indicated by the power supply voltage signal Sv of the main power supply 50 exceeds the abnormality determination voltage threshold value Vth, and the divided voltage of the power supply voltage signal Sv exceeds the voltage of the abnormality determination voltage signal Sref. The power supply control unit 70 determines that the situation where the power supply voltage value Vv of the main power supply 50 identified by the voltage detection circuit 80 does not exceed the abnormality determination voltage threshold value Vth does not continue for a predetermined period of time, and outputs the first control voltage signal SC1 of a high level. Since the pseudo abnormality signal Sa is not input from the power supply control unit 70, the pseudo operation circuit 140 outputs the power supply voltage signal Sv input from the connection point P3 to the voltage dividing circuit 130 through the source terminal and the drain terminal of the fifth MOSFET 143. The voltage dividing circuit 130 outputs the power supply voltage signal Sv divided by the voltage dividing resistors 131 and 132 to the comparison circuit 120. Since the voltage of the power supply voltage signal Sv divided by the voltage dividing circuit 130 exceeds the voltage of the abnormality determination voltage signal Sref, the comparison circuit 120 determines that there is no abnormality in the main power supply 50, and outputs the second control voltage signal SC2 of high level from the output terminal. The first control voltage signal SC1 of high level and the second control voltage signal SC2 of high level are input to the main power supply side voltage applying unit 170, and the gate voltage Vg1 having a potential lower than the potential at the source terminal is applied to the gate terminal of the first MOSFET 151 and the gate terminal of the second MOSFET 152. The first control voltage signal SC1 of high level and the second control voltage signal SC2 of high level are input to the auxiliary power supply side voltage applying unit 180, and the gate voltage Vg2 that makes the potential at the source terminal equal to the potential at the gate terminal is applied to the gate terminal of the third MOSFET 161 and the gate terminal of the fourth MOSFET 162. Therefore, the power supplied to the steering control device 30 by the main power supply 50 is maintained. The power control unit 70 recognizes that there is no abnormality in the main power supply 50 based on the input high-level second control voltage signal SC2 and the high-level first control voltage signal SC1 generated by the power control unit.

[0055] like Figure 2 and Figure 3As shown, in the case where the power supply voltage value Vv of the main power supply 50 is slowly reduced, the divided voltage of the power supply voltage signal Sv exceeds the voltage of the abnormality determination voltage signal Sref. However, it may happen that the power supply voltage value Vv of the main power supply 50 does not exceed the abnormality determination voltage threshold Vth. Since the pseudo abnormality signal Sa is not input from the power supply control unit 70, the pseudo operation circuit 140 outputs the power supply voltage signal Sv input from the connection point P3 to the voltage divider circuit 130 through the source terminal and the drain terminal of the fifth MOSFET 143. The voltage divider circuit 130 outputs the power supply voltage signal Sv divided by the voltage divider resistors 131 and 132 to the comparison circuit 120. Since the voltage of the power supply voltage signal Sv divided by the voltage divider circuit 130 exceeds the voltage of the abnormality determination voltage signal Sref, the comparison circuit 120 determines that there is no abnormality in the main power supply 50, and outputs the second control voltage signal SC2 of a high level from the output terminal. In the case where the power supply voltage value Vv of the main power supply 50 identified by the use voltage detection circuit 80 does not exceed the abnormality determination voltage threshold value Vth continues for a predetermined period of time, the power supply control unit 70 determines that an abnormality occurs in the main power supply 50, and generates a low-level first control voltage signal SC1. The low-level first control voltage signal SC1 and the high-level second control voltage signal SC2 are input to the main power supply side voltage application unit 170 and the auxiliary power supply side voltage application unit 180. In the case where the low-level first control voltage signal SC1 is input, the main power supply side voltage application unit 170 applies a gate voltage Vg1 that makes the potential at the source terminal equal to the potential at the gate terminal to the gate terminal of the first MOSFET 151 and the gate terminal of the second MOSFET 152. In the case where the low-level first control voltage signal SC1 is input, the auxiliary power supply side voltage application unit 180 applies a gate voltage Vg2 having a potential higher than the potential at the source terminal to the gate terminal of the third MOSFET 161 and the gate terminal of the fourth MOSFET 162. Therefore, the power supply for supplying power to the steering control device 30 is switched to the auxiliary power supply 60. The power control unit 70 recognizes that an abnormality has occurred in the main power supply 50 based on the input high-level second control voltage signal SC2 and the low-level first control voltage signal SC1 generated by the power control unit. The power control unit 70 can recognize that the following abnormalities have occurred among the abnormalities of the main power supply 50: an open circuit problem of the main power supply 50 in which the power supply voltage value Vv of the main power supply 50 slowly decreases, an abnormality caused by the deterioration of the main power supply 50 over time, and the like.

[0056] like Figure 2 and Figure 4As shown, in the case where the power supply voltage value Vv of the main power supply 50 decreases sharply, a situation may occur where the divided voltage of the power supply voltage signal Sv does not exceed the voltage of the abnormality determination voltage signal Sref and the power supply voltage value Vv of the main power supply 50 does not exceed the abnormality determination voltage threshold value Vth. The power supply control unit 70 converts the power supply voltage signal Sv, which is an analog signal detected by the voltage detection circuit 80, into a power supply voltage value Vv, which is a digital value, and determines an abnormality in the main power supply 50 based on the power supply voltage value Vv. During a predetermined period of time in which the power supply voltage value Vv of the main power supply 50 does not exceed the abnormality determination voltage threshold value Vth, the power supply control unit 70 determines that there is no abnormality in the main power supply 50, and generates a high-level first control voltage signal SC1. Since the pseudo abnormality signal Sa is not input from the power supply control unit 70, the pseudo operation circuit 140 outputs the power supply voltage signal Sv input from the connection point P3 to the voltage dividing circuit 130 through the source terminal and the drain terminal of the fifth MOSFET 143. The voltage dividing circuit 130 outputs the power supply voltage signal Sv divided by the voltage dividing resistors 131 and 132 to the comparison circuit 120. Since the voltage of the power supply voltage signal Sv divided by the voltage dividing circuit 130 does not exceed the voltage of the abnormality determination voltage signal Sref, the comparison circuit 120 determines that an abnormality has occurred in the main power supply 50, and generates a second control voltage signal SC2 of a low level.

[0057] It is assumed that the determination of whether an abnormality occurs in the main power supply 50 by the analog determination circuit 100 and the determination of whether an abnormality occurs in the main power supply 50 by the power control unit 70 start at the same timing. The determination of whether an abnormality occurs in the main power supply 50 by the power control unit 70 is performed after the process of converting the analog signal into a digital value. However, the determination of whether an abnormality occurs in the main power supply 50 by the analog determination circuit 100 is performed without performing the process of converting the analog signal into a digital value. Therefore, the determination of whether an abnormality occurs in the main power supply 50 by the analog determination circuit 100 can be faster than the determination of whether an abnormality occurs in the main power supply 50 by the power control unit 70 by the time period in which the process of converting the analog signal into a digital value is not performed. Therefore, just after the abnormality that the power supply voltage value Vv of the main power supply 50 decreases sharply occurs, the second control voltage signal SC2 of a low level is generated by the analog determination circuit 100, and the first control voltage signal SC1 of a high level is generated by the power control unit 70.

[0058] The high-level first control voltage signal SC1 from the power control unit 70 and the low-level second control voltage signal SC2 from the analog determination circuit 100 are input to the main power supply side voltage application unit 170 and the auxiliary power supply side voltage application unit 180. In the case where the low-level second control voltage signal SC2 is input, the main power supply side voltage application unit 170 applies the gate voltage Vg1 that makes the potential at the source terminal equal to the potential at the gate terminal to the gate terminal of the first MOSFET 151 and the gate terminal of the second MOSFET 152. As a result, the first MOSFET 151 and the second MOSFET 152 are turned into the interruption state. In the case where the low-level second control voltage signal SC2 is input, the auxiliary power supply side voltage application unit 180 applies the gate voltage Vg2 having a potential higher than the potential at the source terminal to the gate terminal of the third MOSFET 161 and the gate terminal of the fourth MOSFET 162. As a result, the third MOSFET 161 and the fourth MOSFET 162 are turned into the on state. As described above, in the case of an abnormality in which the power supply voltage value Vv of the main power supply 50 decreases sharply, the analog determination circuit 100 can quickly generate a low-level control voltage for switching the power supply for supplying power to the steering control device 30 to the auxiliary power supply 60. Therefore, the power supply can be quickly switched. The power supply control unit 70 recognizes that an abnormality has occurred in the main power supply 50 based on the input low-level second control voltage signal SC2 and the high-level first control voltage signal SC1 generated by the power supply control unit. The power supply control unit 70 can recognize a short circuit problem of the main power supply 50 in which the power supply voltage value Vv of the main power supply 50 decreases sharply among the abnormalities of the main power supply 50.

[0059] like Figure 2As shown, in the case where the operation of the analog determination circuit 100 is checked during the initial check at the start of the vehicle, the power supply control unit 70 outputs a pseudo abnormality signal Sa for causing a pseudo abnormality to occur in the power supply voltage signal Sv input to the comparison circuit 120 to the pseudo operation circuit 140. As a result, the digital transistor 144 is turned off, and the fifth MOSFET 143 is turned into an interrupt state. Since the fifth MOSFET 143 is in the interrupt state, the divided power supply voltage signal Sv is not input to the comparison circuit 120, and a simulated situation in which the power supply voltage value Vv is sharply reduced, such as a short circuit problem, is generated. Since the voltage input to the positive input terminal does not exceed the voltage of the abnormality determination voltage signal Sref, the comparison circuit 120 determines that an abnormality occurs in the main power supply 50, and generates a low-level second control voltage signal SC2. In the case where the comparison circuit 120 generates a low-level second control voltage signal SC2 due to the output of the pseudo abnormality signal Sa to the pseudo operation circuit 140, the power supply control unit 70 determines that there is no abnormality in the analog determination circuit 100. In the case where the comparison circuit 120 does not generate the second control voltage signal SC2 of the low level regardless of whether the pseudo abnormality signal Sa is output to the pseudo operation circuit 140, the power control unit 70 determines that an abnormality occurs in the analog determination circuit 100. In the case where there is no abnormality in the analog determination circuit 100, the second control voltage signal SC2 of the low level is input to the main power supply side voltage application unit 170 and the auxiliary power supply side voltage application unit 180. The main power supply side voltage application unit 170 and the auxiliary power supply side voltage application unit 180 start the operation of switching the power supply for supplying power to the steering control device 30 to the auxiliary power supply 60 based on the second control voltage signal SC2 of the low level. However, in the case where the power control unit 70 determines that there is no abnormality in the analog determination circuit 100, the power control unit 70 outputs a reset signal for resetting the auxiliary power supply device 40 so that the state returns to the state before the power control unit 70 checks the operation of the analog determination circuit 100. That is, the power supply for supplying power to the steering control device 30 is brought back to the main power supply 50. When an abnormality occurs in the analog determination circuit 100, the second control voltage signal SC2 of a high level is input to the main power supply side voltage applying unit 170 and the auxiliary power supply side voltage applying unit 180. When the power control unit 70 determines that an abnormality occurs in the analog determination circuit 100, the power control unit 70 reports the occurrence of the abnormality by, for example, lighting a lamp.

[0060] The effects in this embodiment will be described.

[0061] (1) When switching the power supply, the following steps can be performed, wherein: the analog determination circuit 100 determines that an abnormality has occurred in the main power supply 50 using the power supply voltage signal Sv as an analog signal indicating the output state of the main power supply 50, and generates a second control voltage signal SC2 as an analog signal indicating the determination result; and the power supply switching circuit 110 switches the power supply according to the second control voltage signal SC2. That is, the second control voltage signal SC2 as an analog signal can be generated without performing a process of converting the power supply voltage signal Sv into a digital value. Therefore, compared with the steps in the case where the switching signal is converted into a digital signal and then used to determine the switching of the power supply, the steps required for switching the power supply can be simplified. Therefore, even in the case where the voltage of the power output from the main power supply 50 drops sharply, the power supply that supplies power to the steering control device 30 can be switched from the main power supply 50 to the auxiliary power supply 60 more quickly.

[0062] (2) In this embodiment, the specific configuration of the analog determination circuit 100 is provided as described above. Since the comparison circuit 120 is used, the second control voltage signal SC2 can be generated using the power supply voltage signal Sv without performing a process of converting the power supply voltage signal Sv into a digital value.

[0063] (3) In this embodiment, the specific configuration of the power switching circuit 110 is provided as described above. Since the second control voltage signal SC2 is input from the comparison circuit 120 to the main power supply side voltage applying unit 170 and the auxiliary power supply side voltage applying unit 180, the power supply for supplying power to the steering control device 30 can be switched from the main power supply 50 to the auxiliary power supply 60.

[0064] (4) During the initial check, the power control unit 70 can detect the occurrence of an abnormality in the analog determination circuit 100 based on whether the comparison circuit 120 generates the second control voltage signal SC2 of a low level by outputting the pseudo abnormality signal Sa to the pseudo operation circuit 140. Therefore, it is possible to recognize information on whether an abnormality has occurred in the analog determination circuit 100, and thus perform a countermeasure such as fail-safe for the occurrence of an abnormality in the analog determination circuit 100. Since during the initial check, the switching of the power supply is performed by the analog determination circuit 100 after the analog determination circuit 100 checks a state in which no abnormality has occurred, the reliability of the auxiliary power supply device 40 can be improved.

[0065] (5) Not only the analog determination circuit 100 but also the power supply control unit 70 can determine whether an abnormality has occurred in the main power supply 50. Therefore, in response to the occurrence of abnormalities having different forms, the power supply can be switched more appropriately than in the case where only the analog determination circuit or the power supply control circuit performs determination.

[0066] (6) It is possible to distinguish between a case where an abnormality is determined to have occurred in the main power supply 50 based on a determination that the power supply voltage value Vv of the main power supply 50 does not exceed the voltage of the abnormality determination voltage signal Sref and a case where an abnormality is determined to have occurred in the main power supply 50 based on a determination that the power supply voltage value Vv of the main power supply 50 exceeds the voltage of the abnormality determination voltage signal Sref but does not exceed the abnormality determination voltage threshold value Vth. Therefore, the form of the abnormality occurring in the main power supply 50 can be identified.

[0067] This embodiment can be modified as follows. The following other embodiments can be combined with each other within the scope of technical consistency.

[0068] The first MOSFET 151, the second MOSFET 152, and the fifth MOSFET 143 may be N-channel MOSFETs. The third MOSFET 161 and the fourth MOSFET 162 may be P-channel MOSFETs.

[0069] The detection of the occurrence of an abnormality in the analog determination circuit 100 using the dummy operation circuit 140 is not limited to the time during the initial inspection, and may be performed intermittently with the start switch turned on.

[0070] The abnormality determination voltage threshold Vth may be set to a potential equal to a voltage value obtained by converting the abnormality determination voltage signal Sref into a digital value, or may be set to a low potential.

[0071] The power control unit 70 determines that an abnormality has occurred in the main power supply 50 based on whether the situation that the power supply voltage value Vv of the main power supply 50 does not exceed the abnormality determination voltage threshold value Vth continues for a predetermined period of time. The condition of the predetermined period of time may not be provided. That is, in the case where the power supply voltage value Vv of the main power supply 50 does not exceed the abnormality determination voltage threshold value Vth, the power control unit 70 may determine that an abnormality has occurred in the main power supply 50. In the case where the power supply voltage value Vv of the main power supply 50 exceeds the abnormality determination voltage threshold value Vth, the power control unit 70 may determine that there is no abnormality in the main power supply 50.

[0072] The power control unit 70 may not identify the form of the abnormality of the main power supply 50 based on the second control voltage signal SC2 generated by the analog determination circuit 100. The second control voltage signal SC2 generated by the analog determination circuit 100 may be input to the power control unit 70.

[0073] The power control unit 70 may not have a function of determining whether an abnormality occurs in the main power supply 50. That is, the determination of whether an abnormality occurs in the main power supply 50 may be performed only by the analog determination circuit 100.

[0074] The specific configuration of the comparison circuit 120, the specific configuration of the voltage divider circuit 130, and the specific configuration of the pseudo operation circuit 140 are not limited to those in the above-mentioned embodiments. For example, a configuration for stabilizing the output, such as the pull-up resistor 122 of the comparison circuit 120, may be omitted. For example, the positive power supply terminal and the negative power supply terminal may be connected to each other by a connection line, and a component such as a capacitor for stabilizing the output of the comparison circuit 120 may be added to the connection line. That is, the specific configuration of the comparison circuit 120, the specific configuration of the voltage divider circuit 130, and the specific configuration of the pseudo operation circuit 140 may be appropriately changed.

[0075] A power supply voltage signal Sv indicating a voltage at the connection point P2 may be input to the dummy operation circuit 140 .

[0076] like Figure 5 As shown, the pseudo operation circuit 140 may not be provided in the analog determination circuit 100. In this case, the voltage dividing resistor 131 of the voltage dividing circuit 130 has a first end connected to the connection point P3 and a second end connected to the voltage dividing resistor 132. The power supply control unit 70 may not have a function of outputting the pseudo abnormality signal Sa.

[0077] The voltage divider circuit 130 may not be provided in the analog determination circuit 100. In this case, the comparator 121 of the comparison circuit 120 needs to have a withstand voltage performance that can withstand the voltage of the undivided power supply voltage signal Sv. The abnormality determination voltage signal Sref is set to have a voltage that allows comparison with the undivided power supply voltage signal Sv.

[0078] The comparison circuit 120 determines whether an abnormality occurs in the main power supply 50 based on the voltage of the power supply voltage signal Sv. The comparison circuit 120 can determine whether an abnormality occurs in the main power supply 50 based on a signal indicating the current at the connection point P3. That is, the comparison circuit 120 can determine whether an abnormality occurs in the main power supply 50 based on an analog signal indicating the output state of the main power supply 50.

[0079] The power switching circuit 110 may be a mechanical switch that switches the power connected to the connection point P1 between the main power source 50 and the auxiliary power source 60 .

[0080] In the present embodiment, the steering device 1 to which the auxiliary power supply device 40 is applied is configured as an electric power steering device in which the motor 20 is connected to the steering shaft 12 via the reducer 21. The steering device may be configured as an electric power steering device in which the motor 20 is connected to the rack shaft 14 via the reducer 21. The steering device is not limited to the electric power steering device to which the auxiliary power supply device 40 is applied. The auxiliary power supply device 40 may be applied to, for example, a steer-by-wire type steering device.

[0081] The power supply target of the auxiliary power supply device 40 may be an air bag device, a brake device, etc. The power supply target may be a control device for an automatic guided vehicle, an electric vehicle, etc.

Claims

1. An auxiliary power supply device (40), characterized in that include: a main power supply side path (L1) which is a power supply path from a main power supply (50) to a power supply target; an auxiliary power supply side path (L2) connected to the main power supply side path (L1), the auxiliary power supply side path (L2) being a power supply path from an auxiliary power supply (60) to the power supply target, and the auxiliary power supply (60) being connected to the power supply target via the auxiliary power supply side path (L2); A power supply control circuit (70) configured to control switching between a conduction state and an interruption state on the main power supply side path (L1) and to control switching between a conduction state and an interruption state on the auxiliary power supply side path (L2); an analog determination circuit (100) which is provided separately from the power supply control circuit (70), The analog determination circuit (100) is configured to determine the occurrence of an abnormality in the main power supply (50) using an analog signal indicating an output state of the main power supply (50), and The analog determination circuit (100) is configured to: when the analog determination circuit (100) determines that an abnormality has occurred in the main power supply (50), generate a switching signal as an analog signal indicating that an abnormality has occurred in the main power supply (50); as well as a power supply switching circuit (110) configured to: switch a power supply for supplying power to the power supply target from the main power supply (50) to the auxiliary power supply (60) based on the switching signal generated by the analog determination circuit (100), The analog determination circuit (100) includes a comparison circuit (120), a power supply voltage signal as the analog signal indicating the output state of the main power supply (50) and an abnormality determination voltage signal depending on an abnormality determination voltage are input to the comparison circuit (120), the power supply voltage signal indicating the power supply voltage of the main power supply (50), and the abnormality determination voltage indicating that an abnormality has occurred in the main power supply (50), The comparison circuit (120) is configured to: determine that no abnormality has occurred in the main power supply (50) when the voltage of the power supply voltage signal exceeds the voltage of the abnormality determination voltage signal, and generate the switching signal for setting the main power supply (50) as a power supply for supplying power to the power supply target, and The comparison circuit (120) is configured to determine that an abnormality has occurred in the main power supply (50) when the voltage of the power supply voltage signal does not exceed the voltage of the abnormality determination voltage signal, and to generate the switching signal for setting the auxiliary power supply (60) as the power supply for supplying power to the power supply target, The power supply control circuit (70) stores an abnormality determination voltage threshold value for indicating an abnormality occurring in the main power supply (50) as a digital value, The power supply control circuit (70) is configured to acquire the power supply voltage signal and convert the acquired power supply voltage signal into a power supply voltage value as a digital value, The power supply control circuit (70) is configured to: output to the power supply switching circuit (110) an analog signal for setting the main power supply (50) as a power supply for supplying power to the power supply target when the power supply voltage value exceeds the abnormality determination voltage threshold; and The power supply control circuit (70) is configured to output, to the power supply switching circuit (110), an analog signal for setting the auxiliary power supply (60) as a power supply for supplying power to the power supply target when the power supply voltage value does not exceed the abnormality determination voltage threshold.

2. The auxiliary power supply device (40) according to claim 1, characterized in that The power switching circuit (110) comprises: A main power supply side switch circuit (150) is provided on the main power supply side path (L1), an auxiliary power supply side switch circuit (160), which is arranged on the auxiliary power supply side path (L2), a main power supply side voltage applying circuit (170), and an auxiliary power supply side voltage applying circuit (180), The main power supply side switch circuit (150) includes a first metal oxide semiconductor field effect transistor (151, 152) for performing switching between the on state and the interrupt state, the auxiliary power supply side switch circuit (160) includes a second metal oxide semiconductor field effect transistor (161, 162) for performing switching between the on state and the interrupt state, and the main power supply side voltage application circuit (170) is configured to apply a gate voltage for performing switching between the on state and the interrupt state to a gate terminal of the main power supply side switch circuit (150). The auxiliary power supply side voltage application circuit (180) is configured to apply a gate voltage for performing switching between the on state and the off state to a gate terminal of the auxiliary power supply side switch circuit (160), The power supply control circuit (70) and the comparison circuit (120) are configured to control the switching of the main power supply side switch circuit (150) between the on state and the interrupt state by outputting a control voltage signal to the main power supply side voltage application circuit (170), and the power supply control circuit (70) and the comparison circuit (120) are configured to control the switching of the auxiliary power supply side switch circuit (160) between the on state and the interrupt state by outputting a control voltage signal to the auxiliary power supply side voltage application circuit (180), The comparison circuit (120) is configured to: when the voltage of the power supply voltage signal exceeds the voltage of the abnormality determination voltage signal, output a control voltage signal for putting the main power supply side switch circuit (150) in the on state as the switching signal to the main power supply side voltage application circuit (170), and output a control voltage signal for putting the auxiliary power supply side switch circuit (160) in the off state as the switching signal to the auxiliary power supply side voltage application circuit (180), and The comparison circuit (120) is configured to: when the voltage of the power supply voltage signal does not exceed the voltage of the abnormality judgment voltage signal, output the control voltage signal for changing the main power supply side switch circuit (150) to the interrupt state as the switching signal to the main power supply side voltage application circuit (170), and output the control voltage signal for changing the auxiliary power supply side switch circuit (160) to the conduction state as the switching signal to the auxiliary power supply side voltage application circuit (180).

3. The auxiliary power supply device (40) according to claim 1 or 2, characterized in that The analog determination circuit (100) includes a pseudo operation circuit (140) which generates a pseudo abnormality in the power supply voltage signal input to the comparison circuit (120) based on an input of a pseudo abnormality signal from the power supply control circuit (70). The power supply control circuit (70) is configured to: when checking the operation of the analog determination circuit (100), output the pseudo abnormality signal for causing a pseudo abnormality to occur in the power supply voltage signal input to the comparison circuit (120) to the pseudo operation circuit (140), The power supply control circuit (70) is configured to: determine that no abnormality has occurred in the analog determination circuit (100) when the comparison circuit (120) generates the switching signal as a result of outputting the pseudo abnormality signal to the pseudo operation circuit (140); and The power supply control circuit (70) is configured to determine that an abnormality has occurred in the analog determination circuit (100) when the comparison circuit (120) does not generate the switching signal regardless of whether the pseudo abnormality signal is output to the pseudo operation circuit (140).

4. The auxiliary power supply device (40) according to claim 1, characterized in that The abnormality determination voltage threshold is set to have a potential higher than a voltage value obtained by converting the abnormality determination voltage signal into a digital value.

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