阅读说明：本技术 电源电路和电源装置 (Power supply circuit and power supply device ) 是由 佐藤文彦 铃木信悟 半泽弘明 奥田正贵 干田利幸 于 2020-03-27 设计创作，主要内容包括：一种电源电路(41),包括第一P沟道MOSFET(PMOS 1)和第一电压施加电路(71)。第一P沟道MOSFET(PMOS 1)被设置在车载电源(50)与作为供电目标的车辆装置之间,并且被配置成切换向车辆装置供应电力的通电状态和电力供应中断的断电状态。第一电压施加电路(71)被配置成向栅极端子施加具有比车载电源(50)的电位低的电位的电压,使得第一P沟道MOSFET(PMOS 1)的状态切换到通电状态,以及向栅极端子施加具有与车载电源(50)的电位相等的电位的电压,使得第一P沟道MOSFET(PMOS 1)的状态切换到断电状态。(A power supply circuit (41) includes a first P-channel MOSFET (PMOS1) and a first voltage application circuit (71). A first P-channel MOSFET (PMOS1) is provided between an in-vehicle power supply (50) and a vehicle device that is a power supply target, and is configured to switch an energization state in which power is supplied to the vehicle device and a deenergized state in which power supply is interrupted. The first voltage application circuit (71) is configured to apply a voltage having a potential lower than that of the in-vehicle power supply (50) to the gate terminal so that the state of the first P-channel MOSFET (PMOS1) is switched to an energized state, and to apply a voltage having a potential equal to that of the in-vehicle power supply (50) to the gate terminal so that the state of the first P-channel MOSFET (PMOS1) is switched to a de-energized state.)

1. A power supply circuit (41), comprising:

a first P-channel MOSFET (PMOS1) that is provided between an in-vehicle power supply (50) and a vehicle device that is a power supply target, and that is configured to switch an energization state in which power is supplied to the vehicle device and a power-off state in which power supply is interrupted; and

a first voltage applying circuit (71), wherein

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, and

the first voltage application circuit (71) is configured to:

applying a voltage having a potential lower than that of the in-vehicle 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

applying a voltage having a potential equal to that of the onboard power supply (50) to the gate terminal so that the state of the first P-channel MOSFET (PMOS1) switches to the power-off state.

2. The power supply circuit (41) of claim 1, wherein the first voltage application circuit (71) comprises a switching circuit configured to: switching to a state where the gate terminal is connected to a reference potential point of the in-vehicle power supply (50) so that the state of the first P-channel MOSFET (PMOS1) is switched to the energized state; and switching to a state in which the gate terminal is connected to the in-vehicle power supply (50) so that the state of the first P-channel MOSFET (PMOS1) is switched to the power-off state.

3. The power supply circuit (41) of claim 2, further comprising:

a second P-channel MOSFET (PMOS 2) disposed between the first P-channel MOSFET (PMOS1) and the vehicle device; and

a second voltage applying circuit (81), wherein

A source terminal of the second P-channel MOSFET (PMOS 2) is connected to the vehicle device, and a drain terminal of the second P-channel MOSFET (PMOS 2) 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: switching to a state in which a gate terminal is connected to the reference potential point of the in-vehicle power supply (50) so that the state of the second P-channel MOSFET (PMOS 2) is switched to the energized state; and switching to a state in which the gate terminal is connected to the vehicular apparatus, so that the state of the second P-channel MOSFET (PMOS 2) is switched to the power-off state.

4. A power supply device, comprising:

a power supply circuit (41) according to any one of claims 1 to 3; and

a controller configured to control switching of the power-on state and the power-off state, wherein

The vehicular apparatus is a steering system configured to apply power to a steering mechanism of a vehicle, and

the controller is configured to control the power supply circuit (41) to maintain the energized state, regardless of a state of a start switch of the vehicle.

Technical Field

The invention relates to a power supply circuit and a power supply device.

Background

Japanese unexamined patent application publication No. 2015-23451 (JP 2015-23451A) describes a power supply circuit configured to switch a power-on state and a power-off state between a power supply and a power supply target. In the energized state, electric power is supplied to the power supply target. In the power-off state, the power supply is interrupted. The power supply circuit of JP 2015-23451A 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 be set in a power-on state, 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 due to the characteristics of the N-channel MOSFET. That is, it is necessary to apply a voltage having a higher potential than that of the source terminal connected to the power supply to the gate terminal. Therefore, when the N-channel MOSFET is turned on, the voltage application circuit applies a voltage, which is increased to be higher than the power supply voltage by the drive of the charge pump, to the gate terminal.

Disclosure of Invention

For example, when the electric power of the in-vehicle power supply is supplied to the vehicular apparatus, it is necessary to keep various types of information stored in the vehicular apparatus in the energized state. If an N-channel MOSFET is used to switch the on state and the off state as in JP 2015-23451A, it is necessary to keep the drive of the charge pump to keep the on state. If the drive of the charge pump is maintained for a long time, power consumption may increase.

The invention can provide a power supply circuit and a power supply device capable of suppressing an increase in power consumption.

The power supply circuit according to the first aspect of the invention includes a first P-channel MOSFET and a first voltage applying circuit. The first P-channel MOSFET is provided between an in-vehicle power supply and a vehicular apparatus as a power supply target, and is configured to switch an energization state in which power is supplied to the vehicular apparatus and a deenergized state in which power supply is interrupted. The source terminal of the first P-channel MOSFET is connected to a vehicle power supply, and the drain terminal of the first P-channel MOSFET is connected to a vehicle device. The first voltage application circuit is configured to: applying a voltage having a potential lower than that of the in-vehicle power supply to the gate terminal so that the state of the first P-channel MOSFET is switched to an energized state; and applying a voltage having a potential equal to that of the in-vehicle power supply to the gate terminal so that the state of the first P-channel MOSFET is switched to the power-off state.

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 boosting circuit such as a charge pump which is required when an N-channel MOSFET is used. Therefore, since it is not necessary to use a boosting circuit such as a charge pump, even if the voltage application to the gate terminal of the first P-channel MOSFET is kept in order to keep the energized state, power consumption can be reduced. Even if the energized state is maintained for a long time, an increase in power consumption can be suppressed as compared with the case of using an N-channel MOSFET.

In the above configuration, the first voltage applying circuit may include a switching circuit configured to: switching 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 is switched to an energized state; and switching 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 is switched to a power-off state.

According to the above configuration, to switch the power-on state and the power-off state, it is only necessary to provide a circuit configured to switch the connection to the contact on the existing circuit. Therefore, it is not necessary to use a circuit configured to generate a dedicated voltage for switching to the respective states. Therefore, complication of the voltage application circuit can be suppressed.

In the above configuration, the power supply circuit further includes a second P-channel MOSFET and a second voltage applying circuit. The second P-channel MOSFET is disposed between the first P-channel MOSFET and the vehicular device. The source terminal of the second P-channel MOSFET may be connected to a vehicle device, and the drain terminal of the second P-channel MOSFET may be connected to the drain terminal of the first P-channel MOSFET. The second voltage applying circuit may include a switching circuit configured to: switching 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 is switched to an energized state; and switching to a state in which the gate terminal is connected to the vehicular apparatus, so that the state of the second P-channel MOSFET is switched to a power-off state.

According to the above configuration, the second P channel MOSFET can suppress a backflow of current from the power supply target to the vehicle-mounted power supply in the power-on state and the power-off state. In the energized state, a voltage is applied to the gate terminal of the second P-channel MOSFET to suppress the current from flowing back, 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 to the gate terminal. That is, it is not necessary to use a boosting circuit such as a charge pump which is required when an N-channel MOSFET is used. Therefore, since it is not necessary to use a boosting circuit such as a charge pump, power consumption can be reduced even if the voltage application to the gate terminal of the second P-channel MOSFET is kept in the energized state in order to suppress the current from flowing back. Similarly to the above, in switching the power-on state and the power-off state for the second P-channel MOSFET, only the connection to the contact needs to be switched on the existing circuit. Therefore, it is not necessary to use a circuit configured to generate a dedicated voltage for switching to the respective states. Therefore, the complexity of other voltage applying circuits can be suppressed.

A power supply device according to a second aspect of the present invention includes the above power supply circuit and a controller configured to control switching of the power-on state and the power-off state. The vehicular apparatus 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 a state of a start switch of the vehicle.

According to the above configuration, even if the energized state is maintained for a long time, an increase in power consumption can be suppressed as compared with the case of using an N-channel MOSFET. Therefore, it is possible to realize a power supply device that: even if the energization state is maintained regardless of the state of the start switch of the vehicle, an increase in power consumption can be suppressed.

According to the present invention, an increase in power consumption can be suppressed.

Drawings

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 reference numerals represent like elements, and wherein:

fig. 1 is a diagram showing the overall structure of a steering system mounted with a power supply device;

fig. 2 is a diagram showing an electrical configuration of a power supply device;

fig. 3 is a diagram showing the overall structure of a P-channel MOSFET;

fig. 4 is a circuit diagram showing a circuit configuration of a first voltage applying circuit of a power supply circuit of the power supply device; and

fig. 5 is a circuit diagram showing a circuit configuration of a second voltage applying circuit of the power supply device.

Detailed Description

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

The steering mechanism 2 includes a steering shaft 12 and a rack shaft 14. The steering wheel 10 is fixed to one end of a 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 that meshes with the pinion 11. The pinion gear 11 and the rack gear 13 constitute a rack and pinion mechanism. The rotational motion of the steering shaft 12 is converted into a reciprocating linear motion in the axial direction of the rack shaft 14 via a rack-and-pinion mechanism. The steering system 1 is mounted on a vehicle such that the axial direction of the rack shaft 14 is the vehicle width direction. The reciprocating linear motion of the rack shaft 14 is transmitted to the right and left steered wheels 16 via tie rods 15 coupled to each end of the rack shaft 14. Therefore, the steering angle of the steered wheels 16 changes, and the traveling direction of the vehicle changes.

A torque sensor 17 is attached to the steering shaft 12 for measuring a steering torque TR applied to the steering shaft 12 by the operation of the steering wheel 10. The torque sensor 17 of this embodiment detects the torsion amount of the torsion bar constituting the steering shaft 12, and measures the steering torque TR based on the torsion amount.

The assist mechanism 3 includes a motor 20 and a reduction gear 21 for steering assist. The motor 20 is coupled to the steering shaft 12 via a reducer 21. The reducer 21 reduces the rotation speed of the motor 20, and transmits the rotation 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 adopted as the speed reducer 21 of this embodiment.

The steering system 1 includes a steering control device 30 and a power supply device 40. 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 motor 20. When the steering system 1 is mounted on a vehicle, the power supply device 40 is connected to the 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 in-vehicle power supply 50 and the steering control device 30 that is a component of the steering system 1 that is a power supply target. The steering control device 30 assists the steering operation of the driver by controlling the operation of the motor 20 by the supply of electric power from the in-vehicle 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 a 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 as a target value of the steering assist force based on the steering torque TR and the running speed VS. The steering controller 31 controls the operation of the motor 20 through control of the inverter to generate a steering assist force corresponding to the target steering assist force.

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.

The power supply circuit 41 has a function of switching an energized state and a de-energized state between the in-vehicle power supply 50 and the steering control device 30. In the energized state, electric power is supplied to steering control device 30. In the power-off state, the power supply is interrupted. The power supply voltage of the in-vehicle 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 (i.e., the input voltage Vin) of the in-vehicle power supply 50 is, for example, 12 volts (V). The voltage based on the electric power to be supplied to the steering control device 30 (i.e., the output voltage Vout) is substantially equal to the input voltage Vin. For example, the output voltage Vout is 12V.

The power supply controller 42 has a function of controlling switching of the power-on state and the power-off state of the power supply circuit 41. The power supply voltage of the in-vehicle power supply 50 is input to the power supply controller 42 as an input voltage Vin. The power supply controller 42 controls switching of the power-on state and the power-off state of the power supply circuit 41 based on the input voltage Vin. In this embodiment, the power supply controller 42 is an example of a controller.

The power supply controller 42 outputs a control voltage VC to switch the power-on state and the power-off state of the power supply circuit 41. Specifically, when the electric power steering system is not abnormally functioning and is able to normally operate to apply the steering assist force to the steering mechanism 2, the power supply controller 42 outputs the energization switching control voltage VC to switch to the energized state, so that the steering control device 30 performs application control of the steering assist force. When the electric power steering system is malfunctioning and cannot operate normally to apply the steering assist force to the steering mechanism 2, the power supply controller 42 outputs the power-off switching control voltage VC to switch to the power-off state, so that the steering control device 30 stops the control of the application of the steering assist force. In this embodiment, the power-on switching control voltage VC is a low-level signal having a potential lower than that of the power-off switching control voltage VC. That is, the power-off switching control voltage VC is a high-level signal having a potential higher than that of the power-on switching control voltage VC. The power supply controller 42 determines whether or not an abnormality occurs in the function of the electric power steering system based on, for example, an abnormality signal input from the steering control device 30. The abnormality signal indicates whether or not an abnormality occurs in the function of the electric power steering system.

In this embodiment, when the electric power steering system is not abnormally functioning and is normally operable to apply the steering assist force to the steering mechanism 2, the power supply controller 42 outputs the energization switching control voltage VC regardless of whether the ignition is turned on or off (a state as a start switch of the vehicle). That is, the in-vehicle power supply 50 keeps supplying electric 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 retain various types of information stored for various types of arithmetic processing to be executed by the steering controller 31 not only when the ignition is on but also when the ignition is off.

The configuration of the power supply circuit 41 is described in detail. As shown in fig. 2, the power supply circuit 41 includes a first P-channel MOSFET (PMOS1), a second P-channel MOSFET (PMOS 2) 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 a function of switching the switching state of PMOS 1. The second voltage application circuit 81 has a function of switching the switching state of PMOS 2. PMOS1 and PMOS2 of this embodiment are P-channel MOSFETs having source terminals 72 and 82 associated with the P-type semiconductor layer, drain terminals 73 and 83 associated with the P-type semiconductor layer, and gate terminals 74 and 84 associated with the N-type semiconductor layer, respectively.

As shown in fig. 3, 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 (e.g., 2V), the P-channel MOSFET is turned on so that a current is conducted 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 larger than the threshold value, and holes are accumulated in the vicinity of the surface of the N-type semiconductor layer Ng (denoted by "N" in fig. 3) on the insulating layer Z side to provide a P-type semiconductor layer Pg (denoted by "P" in fig. 3) serving as an inversion layer. In this case, the P-type semiconductor layer Ps (denoted by "P" in fig. 3) associated with the source terminal S and the P-type semiconductor layer Pd (denoted by "P" in fig. 3) associated with the drain terminal D are electrically connected through the P-type semiconductor layer Pg. Thus, there is current conduction between the source terminal S and the drain terminal D.

Further, 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 smaller than the threshold value, the P-channel MOSFET is turned off so that no current is conducted 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 smaller 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 no current is conducted between the source terminal S and the drain terminal D.

Referring back to the description of fig. 2, source terminal 72 of PMOS1 is connected to the high potential side of on-vehicle power supply 50, and drain terminal 73 of PMOS1 is connected to steering control device 30 via PMOS 2. The gate terminal 74 of PMOS1 is connected to the first voltage application circuit 71. The contact C1 on the connection line L1 connecting the PMOS1 and the high potential side of the vehicle-mounted power supply 50 is connected to the first voltage applying circuit 71.

Drain terminal 83 of PMOS2 is connected to drain terminal 73 of PMOS1, and source terminal 82 of PMOS2 is connected to steering control device 30. The gate terminal 84 of PMOS2 is connected to the second voltage applying circuit 81. A contact C2 on a connection line L2 connecting the PMOS2 and the steering control device 30 is connected to the second voltage applying circuit 81.

In this embodiment, PMOS1 and PMOS2 are connected in series by connecting drain terminals 73 and 83 of PMOS1 and PMOS2, so that electric power can be supplied from the in-vehicle power supply 50 to the steering control device 30. In this case, the directions of the parasitic diode D1 provided in PMOS1 and the parasitic diode D2 provided in PMOS2 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.

Next, the structures of the first voltage application circuit 71 and the second voltage application circuit 81 are described in more detail. As shown in fig. 4, the first voltage application circuit 71 includes a switching circuit constituted by a combination of a transistor TR1 (which is an NPN bipolar transistor) and a transistor TR2 (which is a PNP bipolar transistor).

In the transistor TRl, the base terminal TRlb is connected to the power supply controller 42, so that the control voltage VC output from the power supply controller 42 is divided by a voltage dividing resistor, and a current based on the divided voltage flows into the base terminal TR1 b. In the transistor TR1, the emitter terminal TR1e is connected to the reference potential point GND, and the collector terminal TR1C is connected to the base terminal TR2b and the contact C1 of the transistor TR 2. That is, the transistor TR1 is connected to the vehicle power supply 50 via the collector terminal TR1C and the contact C1.

When the potential difference between the base terminal TR1b and the emitter terminal TR1e is equal to or greater than a preset threshold (e.g., 0.5V), the transistor TR1 is turned on so that a current is conducted between the collector terminal TR1c and the emitter terminal TR1 e. In this case, a current based on the power supply from the in-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 TR1c and the emitter terminal TR1 e.

When the potential difference between the base terminal TR1b and the emitter terminal TR1e is smaller than a threshold value set in the transistor TR1, the transistor TR1 is turned off so that no current is conducted between the collector terminal TR1c and the emitter terminal TR1 e. In this case, a current based on the power supply from the in-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 TR1c and the emitter terminal TR1 e.

In this embodiment, the power-off switching voltage as a high-level signal output from the power supply controller 42 is set to a value equal to or greater than the threshold value set in the transistor TR1, and the power-on switching voltage as a low-level signal output from the power supply controller 42 is set to a value less than the threshold value set in the transistor TR 1.

In the transistor TR2, a base terminal TR2b is connected to the vehicle-mounted 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 through a voltage dividing resistor flows into the base terminal TR2 b. The transistor TR2 is connected such that when the transistor TR1 is turned off, a current based on the input voltage Vin flows into the base terminal TR2 b. In the transistor TR2, an emitter terminal TR2e is connected to the contact C1, and a collector terminal TR2C is connected to the reference potential point GND and the gate terminal 74 of PMOS1 via a 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 PMOS1 via the collector terminal TR2C and the gate terminal 74.

The transistor TR2 is configured such that when the transistor TR1 is turned on, a potential difference between the base terminal TR2b and the collector terminal TR2c is equal to or larger than a preset threshold value (for example, 0.5V), and the transistor TR2 is turned on so that a current is conducted between the collector terminal TR2c and the emitter terminal TR2 e. In this case, a current based on the power supply from the vehicle-mounted 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 TR2 e. Therefore, the high potential side of the in-vehicle power supply 50 and the gate terminal 74 of the PMOS1 are connected via the first voltage application circuit 71.

The transistor TR2 is configured such 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 nor greater than the threshold value set in the transistor TR2, and the transistor TR2 is turned off so that no current is conducted between the collector terminal TR2c and the emitter terminal TR2 e. In this case, a current based on the power supply from the in-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 TR2 e. Therefore, the reference potential point GND is connected to the gate terminal 74 of PMOS1 via the first voltage application circuit 71.

As shown in fig. 5, the second voltage application circuit 81 includes a switch circuit constituted by a combination of a transistor TR3 (which is an NPN bipolar transistor) and a transistor TR4 (which is a PNP bipolar transistor).

The transistor TR3 has the same structure as the transistor TR1 of the first voltage application circuit 71, but differs from the transistor TR1 in that a collector terminal TR3C is connected to the contact C2. That is, the transistor TR3 is connected to the steering control device 30 via the collector terminal TR3C and the contact C2. When the transistor TR3 is turned on so that a current is conducted between the collector terminal TR3c and the emitter terminal TR3e, a current based on the power supply from the vehicle-mounted power supply 50 to the steering control device 30 (i.e., a current based on the output voltage Vout of the power supply circuit 41) flows between the collector terminal TR3c and the emitter terminal TR3 e. When the transistor TR3 is turned off so that no current is conducted between the collector terminal TR3c and the emitter terminal TR3e, a 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 TR3 e.

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

When the transistor TR4 is turned on so that a current is conducted between the collector terminal TR4c and the emitter terminal TR4e, a current based on the output voltage Vout of the power supply circuit 41 flows between the collector terminal TR4c and the emitter terminal TR4 e. Therefore, the high potential side of the steering control device 30 is connected to the gate terminal 84 of the PMOS2 via the second voltage application circuit 81.

When the transistor TR4 is turned off so that no current is conducted between the collector terminal TR4c and the emitter terminal TR4e, a current based on the output voltage Vout of the power supply circuit 41 does not flow between the collector terminal TR4c and the emitter terminal TR4 e. Therefore, the reference potential point GND is connected to the gate terminal 84 of the PMOS2 via the second voltage applying circuit 81.

Next, description will be given regarding the operation of the power supply circuit 41 when switching the power-on state and the power-off state of the steering control device 30. As shown in fig. 4, when the control voltage VC is input from the power controller 42 to the first voltage application circuit 71 as a low-level signal, the transistor TR1 is turned off. With the transistor TR1 turned off, the transistor TR2 is turned off. Therefore, as indicated by a dot-and-dash arrow in fig. 4, the gate terminal 74 is connected to the reference potential point GND. Accordingly, the potential of the gate terminal 74 is switched to the potential of the reference potential point GND. In this case, the potential of the gate terminal 74 is lower than the potential of the source terminal 72, and the potential difference between these terminals is 12V, equal to or larger than the threshold value set in PMOS 1. Thus, PMOS1 is turned on.

As shown in fig. 5, when the control voltage VC is input from the power controller 42 to the second voltage application circuit 81 as a low-level signal, the transistor TR3 is turned off. With the transistor TR3 turned off, the transistor TR4 is turned off. Therefore, as indicated by a dot-and-dash arrow in fig. 5, the gate terminal 84 is connected to the reference potential point GND. Therefore, the potential of the gate terminal 84 is switched to the potential of the reference potential point GND. In this case, the potential of the gate terminal 84 is lower than that of the source terminal 82, and the potential difference between these terminals is 12V, equal to or larger than the threshold value set in PMOS 2. Thus, PMOS2 is turned on.

As described above, the power supply controller 42 switches the state of the power supply circuit 41 to the energized state by outputting the low-level signal to the first voltage application circuit 71 and the second voltage application circuit 81 and turning on the PMOS1 and the PMOS 2.

As shown in fig. 4, when the control voltage VC is input from the power controller 42 to the first voltage application circuit 71 as a high-level signal, the transistor TR1 is turned on. With the transistor TR1 turned on, the transistor TR2 is turned on. Therefore, as indicated by a two-dot chain line arrow in fig. 4, the contact C1 and the gate terminal 74 are connected via the transistor TR 2. Accordingly, the potential of the gate terminal 74 is switched to the potential of the contact C1. In this case, the potential of the source terminal 72 is equal to the potential of the gate terminal 74, and the potential difference between these terminals is 0V, which is smaller than the threshold value set in PMOS 1. Thus, PMOS1 is turned off.

As shown in fig. 5, when the control voltage VC is input as a high-level signal from the power controller 42 to the second voltage application circuit 81, the transistor TR3 is turned on. With the transistor TR3 turned on, the transistor TR4 is turned on. Therefore, as indicated by a two-dot chain line arrow in fig. 5, the contact C2 and the gate terminal 84 are connected via the transistor TR 4. 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 0V, which is smaller than the threshold value set in PMOS 2. Thus, PMOS2 is off.

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 PMOS1 and the PMOS 2.

The effect of this embodiment is 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 PMOS1 and PMOS2, it is only necessary to apply a voltage having a potential lower than that of the in-vehicle power supply 50 to the gate terminals 74 and 84. Therefore, it is not necessary to use a boosting circuit such as a charge pump which is required when an N-channel MOSFET is used. Therefore, since it is not necessary to use a boosting circuit such as a charge pump, even if the application of the voltage to the gate terminals 74 and 84 of PMOS1 and PMOS2 is kept in order to keep the energized state, power consumption can be reduced. Even if the energized state is maintained for a long time, an increase in power consumption can be suppressed as compared with the case of using an N-channel MOSFET.

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

(3) In the power-on state and the power-off state of the power supply circuit 41 of this embodiment, the backflow of current from the power supply target to the vehicle-mounted power supply 50 can be suppressed by PMOS2 different from PMOS 1. In the energized state, a voltage is applied to the gate terminal 84 of PMOS2 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 boosting circuit such as a charge pump which is required in the case of an N-channel MOSFET. Therefore, since it is not necessary to use a booster circuit such as a charge pump, even if the voltage application to the gate terminal 84 of the PMOS2 is kept in order to suppress the current backflow in the energized state, the power consumption can be reduced. Similarly to the above, when the power-on state and the power-off state are switched for PMOS2, it is only necessary to provide a circuit configured to switch the connection to the reference potential point GND and the connection to the contact point C2 on the existing circuit. Therefore, it is not necessary to use a circuit configured to generate a dedicated voltage for switching to the respective states. Therefore, complication of the second voltage applying circuit 81 can be suppressed.

(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 as compared with the case of using an N-channel MOSFET. Therefore, the power supply device 40 can be realized: even if the energization state is maintained regardless of the state of the start switch of the vehicle, an increase in power consumption can be suppressed.

The above embodiment may be modified as follows. The following other embodiments may be combined without causing any technical contradiction. PMOS2 is provided to suppress a current return from the power supply target to the vehicle-mounted power supply 50, but PMOS2 is not necessarily provided. 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.

When PMOS1 is turned on, the potential of the gate terminal 74 of PMOS1 is equal to the potential of the reference potential point GND, but a voltage such that the potential difference between the gate terminal 74 and the source terminal 72 of PMOS1 is equal to or larger than the threshold value need only be applied to the gate terminal 74 of PMOS 1. The same applies to PMOS 2.

When PMOS1 is turned off, the potential of the gate terminal 74 of PMOS1 is the potential of the vehicle-mounted power supply 50, but a voltage such that the potential difference between the gate terminal 74 and the source terminal 72 of PMOS1 is smaller than a threshold value only needs to be applied to the gate terminal 74 of PMOS 1. The same applies to PMOS 2.

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

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

The power supply target of the power supply device 40 may be other vehicle devices such as an airbag device. For example, the vehicle device that is the power supply target of the power supply device 40 may be an unmanned transport vehicle.