Power supply circuit and power supply device

Abstract

A power supply circuit (41) includes a first P-channel MOSFET (PMOS 1) and a first voltage application circuit (71). The first P-channel MOSFET (PMOS 1) is provided between a vehicle-mounted power supply (50) and a vehicle device that is a power supply target, and is configured to switch between an energized state in which power is supplied to the vehicle device and a de-energized state in which the power supply is interrupted. The first voltage application circuit (71) is configured to apply a voltage having a potential lower than that of the vehicle-mounted power supply (50) to a gate terminal so that the state of the first P-channel MOSFET (PMOS 1) is switched to the energized state, and to apply a voltage having a potential equal to that of the vehicle-mounted power supply (50) to the gate terminal so that the state of the first P-channel MOSFET (PMOS 1) is switched to the de-energized state.

Description

TECHNICAL FIELD

[0001] The present application relates to a power supply circuit and a power supply device. BACKGROUND

[0002] Japanese Unexamined Patent Application Publication No. 2015-23451 (JP 2015-23451 A) describes a power supply circuit configured to switch between a power-on state and a power-off state between a power supply and a power supply target. In the power-on state, power is supplied to the power supply target. In the power-off state, the power supply is interrupted. The power supply circuit of JP 2015-23451 A includes a voltage application circuit configured to apply a voltage to an N-channel metal oxide semiconductor field effect transistor (MOSFET) and a gate terminal of the MOSFET. In this power supply circuit, when the N-channel MOSFET is turned on to set the power-on state, due to the characteristics of the N-channel MOSFET, it is necessary to apply a voltage to the gate terminal so that the source terminal connected to the power supply has a lower potential. That is, it is necessary to apply a voltage having a higher potential to the gate terminal than the voltage of the source terminal connected to the power supply. Therefore, when the N-channel MOSFET is turned on, the voltage application circuit applies a voltage raised to a higher voltage than the power supply voltage by driving of a charge pump to the gate terminal. SUMMARY

[0003] For example, when power of a vehicle-mounted power supply is supplied to a vehicle device, it is necessary to maintain various types of information stored in the vehicle device in the power-on state. If an N-channel MOSFET is employed as in JP 2015-23451 A to switch between the power-on state and the power-off state, it is necessary to maintain driving of the charge pump to maintain the power-on state. If the driving of the charge pump is maintained for a long time, power consumption can increase.

[0004] The present application can provide a power supply circuit and a power supply device capable of suppressing an increase in power consumption.

[0005] A power supply circuit according to a first aspect of the present application includes a first P-channel MOSFET and a first voltage application circuit. The first P-channel MOSFET is disposed between a vehicle-mounted power supply and a vehicle device as a power supply target, and is configured to switch between a power-on state in which power is supplied to the vehicle device and a power-off state in which the power supply is interrupted. A source terminal of the first P-channel MOSFET is connected to the vehicle-mounted power supply, and a drain terminal of the first P-channel MOSFET is connected to the vehicle device. The first voltage application circuit is configured to: apply a voltage having a potential lower than a potential of the vehicle-mounted power supply to a gate terminal so that a state of the first P-channel MOSFET switches to the power-on state; and apply a voltage having a potential equal to the potential of the vehicle-mounted power supply to the gate terminal so that the state of the first P-channel MOSFET switches to the power-off state.

[0006] To switch the power-on state and the power-off state by using the first P-channel MOSFET as in the above-described configuration, it is only necessary to apply a voltage having a potential lower than that of the vehicle-mounted power supply to the gate terminal. Therefore, it is not necessary to use a voltage boosting circuit such as a charge pump that is required when an N-channel MOSFET is used. Therefore, since it is not necessary to use a voltage boosting circuit such as a charge pump, even if a voltage is applied to the gate terminal of the first P-channel MOSFET in order to maintain the power-on state, it is possible to reduce power consumption. Even if the power-on state is maintained for a long time, it is possible to suppress an increase in power consumption compared to the case where an N-channel MOSFET is used.

[0007] In the above-described configuration, the first voltage application circuit can include a switching circuit configured to switch to a state in which the gate terminal is connected to a reference potential point of the vehicle-mounted power supply so that the state of the first P-channel MOSFET switches to the power-on state, and to switch to a state in which the gate terminal is connected to the vehicle-mounted power supply so that the state of the first P-channel MOSFET switches to the power-off state.

[0008] According to the above-described configuration, to switch the power-on state and the power-off state, it is only necessary to provide a circuit configured to switch to connection of a contact on an existing circuit. Therefore, it is not necessary to use a circuit configured to generate a dedicated voltage for switching to each state. Therefore, it is possible to suppress complication of the voltage application circuit.

[0009] In the above-described configuration, the power supply circuit further includes a second P-channel MOSFET and a second voltage application circuit. The second P-channel MOSFET is provided between the first P-channel MOSFET and the vehicle device. The source terminal of the second P-channel MOSFET can be connected to the vehicle device, and the drain terminal of the second P-channel MOSFET can be connected to the drain terminal of the first P-channel MOSFET. The second voltage application circuit can include a switching circuit configured to switch to a state in which the gate terminal is connected to a reference potential point of the vehicle-mounted power supply so that the state of the second P-channel MOSFET switches to the power-on state, and to switch to a state in which the gate terminal is connected to the vehicle device so that the state of the second P-channel MOSFET switches to the power-off state.

[0010] According to the above configuration, the second P-channel MOSFET can suppress the current backflow from the power supply target to the vehicle-mounted power supply in the energized state and the de-energized state. In the energized state, a voltage is applied to the gate terminal of the second P-channel MOSFET to suppress the current backflow, but similarly to the above, only a voltage having a potential lower than that of the vehicle-mounted power supply needs to be applied to the gate terminal. That is, a boost circuit such as a charge pump, which is required when an N-channel MOSFET is used, does not need to be used. Therefore, since a boost circuit such as a charge pump does not need to be used, even if a voltage is applied to the gate terminal of the second P-channel MOSFET in the energized state to suppress the current backflow, power consumption can be reduced. Similarly to the above, when the energized state and the de-energized state are switched with respect to the second P-channel MOSFET, only the connection to the contact needs to be switched on the existing circuit. Therefore, a circuit configured to generate a dedicated voltage for switching to each state does not need to be used. Thus, the complication of other voltage application circuits can be suppressed.

[0011] The power supply device according to the second aspect of the present application includes the above-described power supply circuit and a controller configured to control the switching of the energized state and the de-energized state. The vehicle device is a steering system configured to apply power to a steering mechanism of a vehicle. The controller is configured to control the power supply circuit to maintain the energized state regardless of the state of a start switch of the vehicle.

[0012] According to the above configuration, even if the energized state is maintained for a long time, power consumption can be suppressed from increasing compared to the case where an N-channel MOSFET is used. Therefore, a power supply device can be implemented in which power consumption can be suppressed from increasing even if the energized state is maintained regardless of the state of a start switch of a vehicle.

[0013] According to the present application, power consumption can be suppressed from increasing. BRIEF DESCRIPTION OF DRAWINGS

[0014] Features, advantages, and technical and industrial significance of exemplary embodiments of the present application will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

[0015] Figure 1 is a diagram showing the overall structure of a steering system in which a power supply device is installed;

[0016] Figure 2 is a diagram showing the electrical configuration of the power supply device;

[0017] Figure 3 is a diagram showing the overall structure of a P-channel MOSFET;

[0018] Figure 4 is a circuit diagram showing the circuit structure of a first voltage application circuit of a power supply circuit of the power supply device; and

[0019] Figure 5 FIG. 2 is a circuit diagram showing a circuit structure of a second voltage application circuit of a power supply circuit of a power supply device. DETAILED DESCRIPTION

[0020] A description will be given of an embodiment in which the power supply circuit and the power supply device are applied to a steering system as a vehicle device. As shown in FIG. 1, the steering system 1 in this embodiment includes a steering mechanism 2 and an assist mechanism 3. The steering mechanism 2 turns a steering wheel 16 based on an operation of the steering wheel 10 by a driver. The assist mechanism 3 includes a motor 20 configured to assist the steering operation by the driver. The steering system 1 is a so-called electric power assisted steering system configured to assist the steering operation by the driver by applying a motor torque of the motor 20 as a steering assist force to the steering mechanism 2. Figure 1

[0021] The steering mechanism 2 includes a steering shaft 12 and a rack shaft 14. The steering wheel 10 is fixed to one end of the steering shaft 12, and a pinion 11 is provided at the other end of the steering shaft 12. The rack shaft 14 is provided with a rack 13 engaged with the pinion 11. The pinion 11 and the rack 13 constitute a gear rack mechanism. The rotational movement of the steering shaft 12 is converted into a reciprocating linear movement in the axial direction of the rack shaft 14 via the gear rack mechanism. The steering system 1 is mounted on a vehicle so that the axial direction of the rack shaft 14 is the vehicle width direction. The reciprocating linear movement of the rack shaft 14 is transmitted to the right and left steering wheels 16 via tie rods 15 coupled to each end of the rack shaft 14. Thus, the steering angle of the steering wheels 16 is changed, and the traveling direction of the vehicle is changed.

[0022] The steering torque sensor 17 detects the amount of torsion of a torsion bar constituting the steering shaft 12, and measures the steering torque TR based on the amount of torsion.

[0023] The assist mechanism 3 includes the motor 20 and a reducer 21 for steering assist. The motor 20 is coupled to the steering shaft 12 via the reducer 21. The reducer 21 reduces the rotational speed of the motor 20, and transmits the rotational force obtained by the reduction to the steering shaft 12. A three-phase brushless motor is employed as the motor 20 of this embodiment. A worm gear mechanism is employed as the reducer 21 of this embodiment.

[0024] ​The steering system 1 includes a steering control device 30 and a power supply device 40. The steering control device 30 includes an inverter, which is a well-known circuit including two switching elements in each phase (U phase, V phase, and W phase) of the motor 20. When the steering system 1 is installed on a vehicle, the power supply device 40 is connected to a vehicle-mounted power supply 50, and the steering control device 30 is connected to the vehicle-mounted power supply 50 via the power supply device 40. The power supply device 40 is provided between the vehicle-mounted power supply 50 and the steering control device 30, which is a component of the steering system 1 as a power supply target. The steering control device 30 assists the driver's steering operation by controlling the operation of the motor 20 by the power supply from the vehicle-mounted power supply 50. The steering control device 30 includes a steering controller 31 and a memory 32. The steering controller 31 performs various types of arithmetic processing to calculate, for example, 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 torque sensor 17 and the vehicle speed sensor 18 are connected to the steering controller 31. The vehicle speed sensor 18 detects the running speed VS of the vehicle. To control the steering assist force, the steering controller 31 determines a steering assist force corresponding to a target steering assist force, which is a target value of the steering assist force, on the basis of the steering torque TR and the running speed VS. The steering controller 31 controls the operation of the motor 20 by control of the inverter to generate the steering assist force corresponding to the target steering assist force.

[0025] Next, the electrical configuration of the power supply device 40 is described. As shown in FIG. 2, the power supply device 40 includes a power supply circuit 41 and a power supply controller 42. Figure 2

[0026] The power supply circuit 41 has a function of switching between an energized state and a de-energized state between the vehicle-mounted power supply 50 and the steering control device 30. In the energized state, the power is supplied to the steering control device 30. In the de-energized state, the power supply is interrupted. The power supply voltage of the vehicle-mounted power supply 50 is input to the power supply circuit 41 as an input voltage Vin. The power supply circuit 41 outputs the input voltage Vin as an output voltage Vout to be supplied to the steering control device 30. In this embodiment, the power supply voltage of the vehicle-mounted power supply 50, that is, the input voltage Vin is, for example, 12 volts (V). The voltage of the power to be supplied to the steering control device 30, that is, the output voltage Vout is substantially equal to the input voltage Vin. For example, the output voltage Vout is 12 V.

[0027] The power supply controller 42 has a function of controlling the switching of the energized state and the de-energized state of the power supply circuit 41. The power supply voltage of the vehicle-mounted power supply 50 is input to the power supply controller 42 as an input voltage Vin. The power supply controller 42 controls the switching of the energized state and the de-energized state of the power supply circuit 41 on the basis of the input voltage Vin. In this embodiment, the power supply controller 42 is an example of a controller. ​

[0028] The power controller 42 outputs a control voltage VC to switch the power supply circuit 41 between its on and off states. Specifically, when the electric power steering system functions normally and can apply steering assistance force to the steering mechanism 2, the power controller 42 outputs an on-state switching control voltage VC to switch to the on state, causing the steering control device 30 to control the application of steering assistance force. When the electric power steering system malfunctions and cannot apply steering assistance force to the steering mechanism 2, the power controller 42 outputs a off-state switching control voltage VC to switch to the off state, causing the steering control device 30 to stop controlling the application of steering assistance force. In this embodiment, the on-state switching control voltage VC is a low-level signal with a potential lower than the off-state switching control voltage VC. That is, the off-state switching control voltage VC is a high-level signal with a potential higher than the on-state switching control voltage VC. The power controller 42 determines whether the electric power steering system is malfunctioning based on, for example, an abnormal signal input from the steering control device 30. The abnormal signal indicates whether the electric power steering system is malfunctioning.

[0029] In this embodiment, when the electric power steering system functions normally and can apply steering assistance force to the steering mechanism 2, the power controller 42 outputs the power switching control voltage VC regardless of whether the ignition is on or off (as the state of the vehicle's start switch). That is, the vehicle power supply 50 continues to supply power to the steering control device 30 (i.e., the memory 32) not only when the ignition is on but also when the ignition is off. Therefore, the memory 32 can store various types of information for various types of arithmetic operations to be performed by the steering controller 31, both when the ignition is on and when the ignition is off.

[0030] Describe the configuration of power supply circuit 41 in detail. For example... Figure 2 As shown, the power supply circuit 41 includes a first P-channel MOSFET (PMOS1), a second P-channel MOSFET (PMOS2) different from PMOS1, a first voltage application circuit 71, and a second voltage application circuit 81 different from the first voltage application circuit 71. The first voltage application circuit 71 has the function of switching the switching state of PMOS1. The second voltage application circuit 81 has the function of switching the switching state of PMOS2. In this embodiment, PMOS1 and PMOS2 are P-channel MOSFETs, each having source terminals 72 and 82 associated with a P-type semiconductor layer, drain terminals 73 and 83 associated with a P-type semiconductor layer, and gate terminals 74 and 84 associated with an N-type semiconductor layer, respectively.

[0031] like Figure 3As shown, the P-channel MOSFET has the following characteristics. When the potential of the gate terminal G is lower than the potential of the source terminal S, and the potential difference between these terminals is equal to or greater than a preset threshold value (for example, 2 V), the P-channel MOSFET turns on, so that there is current conduction between the source terminal S and the drain terminal D. This is because the potential difference between the source terminal S and the gate terminal G is greater than the threshold value, and holes are accumulated near the surface of the N-type semiconductor layer Ng (indicated by "N" in Figure 3 ) on the insulating layer Z side to provide a P-type semiconductor layer Pg (indicated by "P" in Figure 3 ) that functions as an inversion layer. In this case, a P-type semiconductor layer Ps (indicated by "P" in Figure 3 ) associated with the source terminal S and a P-type semiconductor layer Pd (indicated by "P" in Figure 3 ) associated with the drain terminal D are electrically connected by the P-type semiconductor layer Pg. Therefore, there is current conduction between the source terminal S and the drain terminal D.

[0032] Furthermore, the P-channel MOSFET has the following characteristics. When the potential of the source terminal S is closer to the potential of the gate terminal G, and the potential difference between these terminals is less than the threshold value, the P-channel MOSFET turns off, so that there is no current conduction between the source terminal S and the drain terminal D. This is because the potential difference between the source terminal S and the gate terminal G is less than the threshold value, and the N-type semiconductor layer Ng associated with the gate terminal G electrically interrupts the P-type semiconductor layer Ps associated with the source terminal S and the P-type semiconductor layer Pd associated with the drain terminal D, so that there is no current conduction between the source terminal S and the drain terminal D.

[0033] Referring back to the description of Figure 2 , the source terminal 72 of the PMOS 1 is connected to the high potential side of the vehicle-mounted power supply 50, and the drain terminal 73 of the PMOS 1 is connected to the steering control device 30 via the PMOS 2. The gate terminal 74 of the PMOS 1 is connected to the first voltage application circuit 71. The contact C1 on the connection line L1 that connects the PMOS 1 and the high potential side of the vehicle-mounted power supply 50 is connected to the first voltage application circuit 71.

[0034] The drain terminal 83 of the PMOS 2 is connected to the drain terminal 73 of the PMOS 1, and the source terminal 82 of the PMOS 2 is connected to the steering control device 30. The gate terminal 84 of the PMOS 2 is connected to the second voltage application circuit 81. The contact C2 on the connection line L2 that connects the PMOS 2 and the steering control device 30 is connected to the second voltage application circuit 81.

[0035] In this embodiment, PMOS 1 and PMOS 2 are connected in series by connecting the drain terminals 73 and 83 of PMOS 1 and PMOS 2, so that electric power can be supplied from the vehicle-mounted power supply 50 to the steering control device 30. In this case, the directions of the parasitic diode D1 provided in PMOS 1 and the parasitic diode D2 provided in PMOS 2 are opposite to each other, so that the current flow from the source terminals 72 and 82 to the drain terminals 73 and 83, respectively, is blocked.

[0036] Next, the structure of the first voltage application circuit 71 and the second voltage application circuit 81 will be described in more detail. As shown in FIG. 7, the first voltage application circuit 71 includes a switching circuit composed of a combination of a transistor TR1, which is an NPN bipolar transistor, and a transistor TR2, which is a PNP bipolar transistor. Figure 4

[0037] In the transistor TR1, the base terminal TR1b is connected to the power supply controller 42, so that a control voltage VC output from the power supply controller 42 is divided by a voltage dividing resistor, and a current based on the voltage division flows into the base terminal TR1b. In the transistor TR1, the emitter terminal TR1e is connected to a reference potential point GND, and the collector terminal TR1c is connected to the base terminal TR2b of the transistor TR2 and the contact C1. That is, the transistor TR1 is connected to the vehicle-mounted power supply 50 via the collector terminal TR1c and the contact C1.

[0038] When the potential difference between the base terminal TR1b and the emitter terminal TR1e is equal to or greater than a preset threshold value (for example, 0.5 V), the transistor TR1 is turned on, so that a current conduction is made between the collector terminal TR1c and the emitter terminal TR1e. In this case, a current based on the electric power supply from the vehicle-mounted power supply 50, that is, a current based on the input voltage Vin of the power supply circuit 41, flows between the collector terminal TR1c and the emitter terminal TR1e.

[0039] When the potential difference between the base terminal TR1b and the emitter terminal TR1e is less than the threshold value provided in the transistor TR1, the transistor TR1 is turned off, so that no current conduction is made between the collector terminal TR1c and the emitter terminal TR1e. In this case, the current based on the electric power supply from the vehicle-mounted power supply 50, that is, the current based on the input voltage Vin of the power supply circuit 41, does not flow between the collector terminal TR1c and the emitter terminal TR1e.

[0040] In this embodiment, the power-off switching voltage, which is a high-level signal output from the power supply controller 42, is set to a value equal to or greater than the threshold value provided in the transistor TR1, and the power-on switching voltage, which is a low-level signal output from the power supply controller 42, is set to a value less than the threshold value provided in the transistor TR1.​

[0041] In the transistor TR2, the base terminal TR2b is connected to the vehicle power supply 50, so that when the transistor TR1 is turned on, a current based on a voltage obtained by dividing the input voltage Vin by the voltage dividing resistor flows into the base terminal TR2b. The transistor TR2 is connected so that when the transistor TR1 is turned off, a current based on the input voltage Vin flows into the base terminal TR2b. In the transistor TR2, the emitter terminal TR2e is connected to the contact C1, and the collector terminal TR2c is connected to the reference potential point GND and the gate terminal 74 of the PMOS 1 via the voltage dividing resistor. That is, the transistor TR2 is connected to the vehicle power supply 50 via the emitter terminal TR2e and the contact C1, and is connected to the PMOS 1 via the collector terminal TR2c and the gate terminal 74.

[0042] The transistor TR2 is configured so that when the transistor TR1 is turned on, the potential difference between the base terminal TR2b and the collector terminal TR2c is equal to or greater than a preset threshold value (for example, 0.5 V), and the transistor TR2 is turned on so that there is current conduction between the collector terminal TR2c and the emitter terminal TR2e. In this case, a current based on the power supply from the vehicle power supply 50 (i.e., a current based on the input voltage Vin of the power supply circuit 41) flows between the collector terminal TR2c and the emitter terminal TR2e. Therefore, the high potential side of the vehicle power supply 50 and the gate terminal 74 of the PMOS 1 are connected via the first voltage application circuit 71.

[0043] The transistor TR2 is configured so that when the transistor TR1 is turned off, the potential difference between the base terminal TR2b and the collector terminal TR2c is not equal to and not greater than the threshold value set in the transistor TR2, and the transistor TR2 is turned off so that there is no current conduction between the collector terminal TR2c and the emitter terminal TR2e. In this case, a current based on the power supply from the vehicle power supply 50 (i.e., a current based on the input voltage Vin of the power supply circuit 41) does not flow between the collector terminal TR2c and the emitter terminal TR2e. Therefore, the reference potential point GND and the gate terminal 74 of the PMOS 1 are connected via the first voltage application circuit 71.

[0044] As Figure 5 shown, the second voltage application circuit 81 includes a switching circuit composed of a combination of a transistor TR3, which is an NPN bipolar transistor, and a transistor TR4, which is a PNP bipolar transistor.

[0045] The structure of transistor TR3 is the same as that of transistor TR1 in the first voltage application circuit 71, but the difference is that the collector terminal TR3c is connected to the contact C2. That is, transistor TR3 is connected to the steering control device 30 via the collector terminal TR3c and the contact C2. When transistor TR3 is turned on, causing current to flow between the collector terminal TR3c and the emitter terminal TR3e, the current based on the power supply from the vehicle power supply 50 to the steering control device 30 (i.e., the current based on the output voltage Vout of the power supply circuit 41) flows between the collector terminal TR3c and the emitter terminal TR3e. When transistor TR3 is turned off, causing no current to flow between the collector terminal TR3c and the emitter terminal TR3e, the current based on the output voltage Vout of the power supply circuit 41 does not flow between the collector terminal TR3c and the emitter terminal TR3e.

[0046] The structure of transistor TR4 is the same as that of transistor TR2 in the first voltage application circuit 71, but the difference is that the emitter terminal TR4e is connected to the contact C2. That is, transistor TR4 is connected to the steering control device 30 via the emitter terminal TR4e and the contact C2.

[0047] When transistor TR4 is turned on, allowing current to flow between collector terminal TR4c and emitter terminal TR4e, current based on the output voltage Vout of power supply circuit 41 flows between collector terminal TR4c and emitter terminal TR4e. Therefore, the high-potential side of steering control device 30 is connected to the gate terminal 84 of PMOS 2 via the second voltage application circuit 81.

[0048] When transistor TR4 is turned off, so that there is no current conduction between collector terminal TR4c and emitter terminal TR4e, the current based on the output voltage Vout of power supply circuit 41 does not flow between collector terminal TR4c and emitter terminal TR4e. Therefore, the reference potential point GND is connected to the gate terminal 84 of PMOS 2 via the second voltage application circuit 81.

[0049] The operation of the power supply circuit 41 when switching between the energized and de-energized states of the steering control device 30 is described below. For example... Figure 4 As shown, when the control voltage VC is input as a low-level signal from the power controller 42 to the first voltage application circuit 71, transistor TR1 is turned off. With transistor TR1 off, transistor TR2 is also turned off. Therefore, as... Figure 4As indicated by the dotted arrow, gate terminal 74 is connected to the reference potential point GND. Therefore, the potential of gate terminal 74 is switched to the potential of the reference potential point GND. In this case, the potential of gate terminal 74 is lower than the potential of source terminal 72, and the potential difference between these terminals is 12V, which is equal to or greater than the threshold value set in PMOS 1. Therefore, PMOS 1 is turned on.

[0050] like Figure 5 As shown, when the control voltage VC is input as a low-level signal from the power controller 42 to the second voltage application circuit 81, transistor TR3 is turned off. With transistor TR3 off, transistor TR4 is also turned off. Therefore, as... Figure 5 As indicated by the dotted-line arrow, gate terminal 84 is connected to the reference potential point GND. Therefore, the potential of gate terminal 84 is switched to the potential of the reference potential point GND. In this case, the potential of gate terminal 84 is lower than the potential of source terminal 82, and the potential difference between these terminals is 12V, which is equal to or greater than the threshold value set in PMOS 2. Therefore, PMOS 2 is turned on.

[0051] As described above, the power controller 42 switches the state of the power circuit 41 to the powered-on state by outputting a low-level signal to the first voltage application circuit 71 and the second voltage application circuit 81 and turning on PMOS 1 and PMOS 2.

[0052] like Figure 4 As shown, when the control voltage VC is input as a high-level signal from the power controller 42 to the first voltage application circuit 71, transistor TR1 is turned on. With transistor TR1 turned on, transistor TR2 is also turned on. Therefore, as... Figure 4 As indicated by the double-dotted arrow, contact C1 is connected to gate terminal 74 via transistor TR2. Therefore, the potential of gate terminal 74 is switched to the potential of contact C1. In this case, the potential of source terminal 72 is equal to the potential of gate terminal 74, and the potential difference between these terminals is 0V, which is less than the threshold value set in PMOS 1. Therefore, PMOS 1 is turned off.

[0053] like Figure 5 As shown, when the control voltage VC is input as a high-level signal from the power controller 42 to the second voltage application circuit 81, transistor TR3 is turned on. With transistor TR3 turned on, transistor TR4 is also turned on. Therefore, as... Figure 5The contact C2 is connected to the gate terminal 84 via the transistor TR4 as indicated by the double-dot chain arrow. Therefore, the potential of the gate terminal 84 is switched to the potential of the contact C2. In this case, the potential of the source terminal 82 is equal to the potential of the gate terminal 84, and the potential difference between these terminals is 0 V, which is smaller than the threshold value set in the PMOS 2. Therefore, the PMOS 2 is turned off.

[0054] As described above, the power supply controller 42 switches the state of the power supply circuit 41 to the power-off state by outputting a high-level signal to the first voltage application circuit 71 and the second voltage application circuit 81 and turning off the PMOS 1 and the PMOS 2.

[0055] The effects of this embodiment are described below. (1) To switch the power-on state and the power-off state of the power supply circuit 41 of this embodiment by using the PMOS 1 and the PMOS 2, it is only necessary to apply a voltage having a potential lower than that of the vehicle-mounted power supply 50 to the gate terminals 74 and 84. Therefore, it is not necessary to use a voltage boosting circuit such as a charge pump that is required when an N-channel MOSFET is used. Therefore, since it is not necessary to use a voltage boosting circuit such as a charge pump, even if the voltage is applied to the gate terminals 74 and 84 of the PMOS 1 and the PMOS 2 in order to maintain the power-on state, it is possible to reduce the power consumption. Even if the power-on state is maintained for a long time, it is possible to suppress an increase in the power consumption compared to the case where an N-channel MOSFET is used.

[0056] (2) To switch the power-on state and the power-off state, the power supply circuit 41 of this embodiment only needs to have connections configured to be switched to the reference potential point GND on an existing circuit and to the contacts C1 and C2. Therefore, it is not necessary to use a circuit configured to generate a dedicated voltage for switching to each state. Therefore, it is possible to suppress the complication of the voltage application circuits 71 and 81.

[0057] (3) In the power supply circuit 41 of this embodiment, current backflow from the power supply target to the vehicle-mounted power supply 50 can be suppressed by the PMOS 2 different from the PMOS 1 in the energized state and the de-energized state of the power supply circuit 41. In the energized state, a voltage is applied to the gate terminal 84 of the PMOS 2 to suppress the current backflow, but, similarly to the above, it is only necessary to apply a voltage having a potential lower than that of the vehicle-mounted power supply 50 to the gate terminal 84. That is, it is not necessary to use a voltage-boosting circuit such as a charge pump required in the case of an N-channel MOSFET. Therefore, since it is not necessary to use a voltage-boosting circuit such as a charge pump, even if a voltage is applied to the gate terminal 84 of the PMOS 2 to suppress the current backflow in the energized state, it is possible to reduce power consumption. Similarly to the above, when switching the energized state and the de-energized state with respect to the PMOS 2, it is only necessary to provide a circuit configured to switch a connection to the reference potential point GND and a connection to the contact C2 on the existing circuit. Therefore, it is not necessary to use a circuit configured to generate a dedicated voltage for switching to each state. Therefore, it is possible to suppress the complication of the second voltage application circuit 81.

[0058] (4) In the power supply device 40 of this embodiment, even if the energized state is maintained for a long time, it is possible to suppress an increase in power consumption compared to the case where an N-channel MOSFET is used. Therefore, it is possible to realize a power supply device 40 that can suppress an increase in power consumption even if the energized state is maintained regardless of the state of the start switch of the vehicle.

[0059] The above embodiment can be modified as follows. The following other embodiments can be combined without causing any technical contradiction. The PMOS 2 is provided to suppress current backflow from the power supply target to the vehicle-mounted power supply 50, but it is not necessary to provide the PMOS 2. In this case, it is not even necessary to provide the second voltage application circuit 81 configured to turn on or off the PMOS 2.

[0060] When the PMOS 1 is on, the potential of the gate terminal 74 of the PMOS 1 is equal to the potential of the reference potential point GND, but it is only necessary to apply a voltage to the gate terminal 74 of the PMOS 1 such that the potential difference between the gate terminal 74 and the source terminal 72 of the PMOS 1 is equal to or greater than the threshold value. The same applies to the PMOS 2.

[0061] When the PMOS 1 is off, the potential of the gate terminal 74 of the PMOS 1 is the potential of the vehicle-mounted power supply 50, but it is only necessary to apply a voltage to the gate terminal 74 of the PMOS 1 such that the potential difference between the gate terminal 74 and the source terminal 72 of the PMOS 1 is less than the threshold value. The same applies to the PMOS 2.

[0062] The power supply to the inverter of the steering control device 30 can be configured to be interrupted after the start switch is turned off until the next time the start switch is turned on.

[0063] In the above-described embodiment, the steering system 1 to which the power supply device 40 is applied is an electric power assisted steering system in which the motor 20 is coupled to the steering shaft 12 via the speed reducer 21, but can also be an electric power assisted steering system in which the motor 20 is coupled to the rack shaft 14 via the speed reducer 21. Furthermore, the steering system 1 is not limited to the electric power assisted steering system to which the power supply device 40 is applied. For example, the power supply device 40 can be applied to a steer-by-wire type steering system.

[0064] The power supply target of the power supply device 40 can be other vehicle devices such as an airbag device. For example, the vehicle device to which the power supply device 40 is a power supply target can be an unmanned transport vehicle.

Claims

1. A power supply device (40) provided with a power supply circuit (41) and a controller (42), characterized by the power supply circuit (41) including: a first P-channel MOSFET (PMOS1) provided between a vehicle-mounted power supply (50) and a vehicle device (30) that is a power supply target and is provided with a memory (32) that stores various information, and configured to switch between an energized state in which power is supplied to the vehicle device (30) and a de-energized state in which power supply is interrupted; and a first voltage application circuit (71), a source terminal of the first P-channel MOSFET (PMOS1) is connected to the vehicle-mounted power supply (50), and a drain terminal of the first P-channel MOSFET (PMOS1) is connected to the vehicle device (30), and the first voltage application circuit (71) is configured to: apply a voltage having a potential lower than that of the vehicle-mounted power supply (50) to a gate terminal, so that the state of the first P-channel MOSFET (PMOS1) is switched to the energized state; and apply a voltage having a potential equal to that of the vehicle-mounted power supply (50) to the gate terminal, so that the state of the first P-channel MOSFET (PMOS1) is switched to the de-energized state, the first voltage application circuit (71) includes a switching circuit composed of a combination of an NPN bipolar transistor (TR1) and a PNP bipolar transistor (TR2), the NPN bipolar transistor (TR1) is connected to the vehicle-mounted power supply (50) via a collector terminal (TR1c) and a contact (C1), the PNP bipolar transistor (TR2) is connected to the vehicle-mounted power supply (50) via an emitter terminal (TR2e) and the contact (C1), and to the first P-channel MOSFET via a collector terminal (TR2c) and the gate terminal, a collector terminal (TR1c) of the NPN bipolar transistor (TR1) and a base terminal (TR2b) of the PNP bipolar transistor (TR2) are connected, the controller (42) is configured to control switching between the energized state and the de-energized state, and is configured to control the power supply circuit (41) to maintain the energized state regardless of the state of a start switch of the vehicle.

2. The power supply device (40) according to claim 1, characterized in that the first voltage application circuit (71) includes a switching circuit configured to switch to a state in which the gate terminal is connected to a reference potential point of the vehicle-mounted power supply (50), so that the state of the first P-channel MOSFET (PMOS1) is switched to the energized state, and to a state in which the gate terminal is connected to the vehicle-mounted power supply (50), so that the state of the first P-channel MOSFET (PMOS1) is switched to the de-energized state.

3. The power supply device (40) according to claim 2, characterized by the power supply circuit (41) further including: a second P-channel MOSFET (PMOS2) provided between the first P-channel MOSFET (PMOS1) and the vehicle device; and a second voltage application circuit (81), a source terminal of the second P-channel MOSFET (PMOS2) is connected to the vehicle device (30), and a drain terminal of the second P-channel MOSFET (PMOS2) is connected to a drain terminal of the first P-channel MOSFET (PMOS1), and the second voltage application circuit (81) includes a switching circuit configured to switch to a state in which a gate terminal is connected to the reference potential point of the vehicle-mounted power supply (50) so that a state of the second P-channel MOSFET (PMOS2) is switched to the power-on state, and to a state in which the gate terminal is connected to the vehicle device (30) so that the state of the second P-channel MOSFET (PMOS2) is switched to the power-off state.

4. The power supply device (40) according to any one of claims 1 to 3, characterized in that the vehicle device (30) is a steering system configured to apply power to a steering mechanism of a vehicle.

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