Patent Description:
<CIT> (<CIT>) 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 power-ON state, electric power is supplied to the power supply target. In the power-OFF state, the electric power supply is interrupted. The power supply circuit of <CIT> includes a voltage application circuit configured to apply voltages to an N-channel metal-oxide-semiconductor field-effect-transistor (MOSFET) and to a gate terminal of the MOSFET. In this power supply circuit, when the N-channel MOSFET is switched ON to set the power-ON state, it is necessary to apply a voltage to the gate terminal such that a source terminal connected to the power supply has a lower potential due to characteristics of the N-channel MOSFET. That is, it is necessary to apply, to the gate terminal, a voltage having a potential higher than that of the source terminal connected to the power supply. Therefore, when the N-channel MOSFET is switched ON, the voltage application circuit applies, to the gate terminal, a voltage increased to be higher than that of the power supply through driving of a charge pump. <CIT> discloses the subject-matter of the preamble of claim <NUM>. A power supply circuit is known from <CIT>.

For example, when electric power of an on-board power supply is supplied to a vehicular apparatus, it is necessary that various types of information stored in the vehicular apparatus be retained in the power-ON state. If the N-channel MOSFET is employed to switch the power-ON state and the power-OFF state as in <CIT>, it is necessary that the driving of the charge pump be kept to keep the power-ON state. If the driving of the charge pump is kept for a long period, power consumption may increase.

The present invention provides a power supply apparatus in which the increase in the power consumption can be suppressed. Advantageous further developments are subject-matter of the dependent claims.

A vehicle according to the invention is claimed in claim <NUM>. Advantageous developments are subject-matter of the dependent claims.

To switch the power-ON state and the power-OFF state by using the first P-channel MOSFET as in the configuration described above, it is only necessary that the voltage having a potential lower than the potential of the on-board power supply be applied to the gate terminal. Therefore, there is no need to use a booster circuit such as a charge pump, which is necessary when an N-channel MOSFET is used. Thus, even if the voltage is kept applied to the gate terminal of the first P-channel MOSFET to keep the power-ON state, the power consumption can be reduced because of no need to use the booster circuit such as the charge pump. Even if the power-ON state is kept for a long period, the increase in the power consumption can be suppressed as compared to the case where the N-channel MOSFET is used.

In the configuration described above, the first voltage application circuit may include a switching circuit configured to switch a state in which the gate terminal and a reference potential point of the on-board power supply are connected such that the state of the first P-channel MOSFET is switched to the power-ON state, and a state in which the gate terminal and the on-board power supply are connected such that the state of the first P-channel MOSFET is switched to the power-OFF state.

According to the configuration described above, to switch the power-ON state and the power-OFF state, it is only necessary to provide the circuit configured to switch connection to a contact on the existing circuit. Therefore, there is no need to use a circuit configured to generate a dedicated voltage for switching to the respective states. Thus, complication of the voltage application circuit can be suppressed.

In the configuration described above, the power supply circuit may further include 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 vehicular apparatus. A source terminal of the second P-channel MOSFET may be connected to the vehicular apparatus, and a drain terminal of the second P-channel MOSFET may be connected to the drain terminal of the first P-channel MOSFET. The second voltage application circuit may include a switching circuit configured to switch a state in which a gate terminal and the reference potential point of the on-board power supply are connected such that a state of the second P-channel MOSFET is switched to the power-ON state, and a state in which the gate terminal and the vehicular apparatus are connected such that the state of the second P-channel MOSFET is switched to the power-OFF state.

According to the configuration described above, in the power-ON state and the power-OFF state, current backflow from the power supply target to the on-board power supply can be suppressed by the second P-channel MOSFET. In the power-ON state, a supply can be suppressed by the second P-channel MOSFET. In the power-ON 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, it is only necessary that the voltage having a potential lower than the potential of the on-board power supply be applied to the gate terminal. That is, there is no need to use the booster circuit such as the charge pump, which is necessary when the N-channel MOSFET is used. Thus, even if the voltage is kept applied to the gate terminal of the second P-channel MOSFET to suppress the current backflow in the power-ON state, the power consumption can be reduced because of no need to use the booster circuit such as the charge pump. Similarly to the above, when the power-ON state and the power-OFF state are switched for the second P-channel MOSFET, it is only necessary to switch connection to a contact on the existing circuit. Therefore, there is no need to use a circuit configured to generate a dedicated voltage for switching to the respective states. Thus, complication of the other voltage application circuit can be suppressed.

The power supply apparatus includes the power supply circuit described above, and a controller configured to control switching of the power-ON state and the power-OFF state. The vehicular apparatus may be a steering system configured to apply power to a steering mechanism of the vehicle. The controller is configured to control the power supply circuit to keep the power-ON state irrespective of a state of a start switch of the vehicle.

According to the configuration described above, even if the power-ON state is kept for a long period, the increase in the power consumption can be suppressed as compared to the case where the N-channel MOSFET is used. Thus, it is possible to attain a power supply apparatus in which the increase in the power consumption is suppressed even if the power-ON state is kept irrespective of the state of the start switch of the vehicle.

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

Description is given of an embodiment in which a power supply circuit and a power supply apparatus are applied to a steering system that is a vehicular apparatus. As illustrated in <FIG>, a steering system <NUM> of this embodiment includes a steering mechanism <NUM> and an assist mechanism <NUM>. The steering mechanism <NUM> turns steered wheels <NUM> based on a driver's operation of a steering wheel <NUM>. The assist mechanism <NUM> includes a motor <NUM> configured to assist the driver's steering operation. The steering system <NUM> is a so-called electric power steering system configured to assist the driver's steering operation by applying a motor torque of the motor <NUM> to the steering mechanism <NUM> as a steering assist force.

The steering mechanism <NUM> includes a steering shaft <NUM> and a rack shaft <NUM>. The steering wheel <NUM> is fixed to one end of the steering shaft <NUM>, and a pinion gear <NUM> is provided at the other end of the steering shaft <NUM>. The rack shaft <NUM> is provided with a rack gear <NUM> that meshes with the pinion gear <NUM>. The pinion gear <NUM> and the rack gear <NUM> constitute a rack and pinion mechanism. Rotational motion of the steering shaft <NUM> is converted into reciprocating linear motion in an axial direction of the rack shaft <NUM> via the rack and pinion mechanism. The steering system <NUM> is mounted on a vehicle such that the axial direction of the rack shaft <NUM> is a vehicle width direction. The reciprocating linear motion of the rack shaft <NUM> is transmitted to the right and left steered wheels <NUM> via tie rods <NUM> coupled to respective ends of the rack shaft <NUM>. Thus, the steered angles of the steered wheels <NUM> are changed, and a traveling direction of the vehicle is changed.

A torque sensor <NUM> is attached to the steering shaft <NUM> to measure a steering torque TR applied to the steering shaft <NUM> through an operation of the steering wheel <NUM>. The torque sensor <NUM> of this embodiment detects a torsion amount of a torsion bar that constitutes the steering shaft <NUM>, and measures the steering torque TR based on the torsion amount.

The assist mechanism <NUM> includes a motor <NUM> and a speed reducer <NUM> for steering assist. The motor <NUM> is coupled to the steering shaft <NUM> via the speed reducer <NUM>. The speed reducer <NUM> reduces the speed of rotation of the motor <NUM>, and transmits a rotational force obtained through the speed reduction to the steering shaft <NUM>. A three-phase brushless motor is employed as the motor <NUM> of this embodiment. A worm gear mechanism is employed as the speed reducer <NUM> of this embodiment.

The steering system <NUM> includes a steering control apparatus <NUM> and a power supply apparatus <NUM>. The steering control apparatus <NUM> includes an inverter, which is a publicly-known circuit including two switching elements in each phase of the motor <NUM> (U phase, V phase, and W phase). When the steering system <NUM> is mounted on the vehicle, the power supply apparatus <NUM> is connected to an on-board power supply <NUM>, and the steering control apparatus <NUM> is connected to the on-board power supply <NUM> via the power supply apparatus <NUM>. The power supply apparatus <NUM> is provided between the on-board power supply <NUM> and the steering control apparatus <NUM>, which is a component of the steering system <NUM> that is a power supply target. The steering control apparatus <NUM> assists the driver's steering operation by controlling an operation of the motor <NUM> through electric power supply from the on-board power supply <NUM>. The steering control apparatus <NUM> includes a steering controller <NUM> and a memory <NUM>. The steering controller <NUM> executes various types of arithmetic processing for calculating, for example, a control amount for controlling the operation of the motor <NUM>. The memory <NUM> stores programs and data for the various types of arithmetic processing. The torque sensor <NUM> and a vehicle speed sensor <NUM> are connected to the steering controller <NUM>. The vehicle speed sensor <NUM> detects a traveling speed VS of the vehicle. To control the steering assist force, the steering controller <NUM> determines, based on the steering torque TR and the traveling speed VS, a steering assist force corresponding to a target steering assist force that is a target value of the steering assist force. The steering controller <NUM> controls the operation of the motor <NUM> through control of the inverter to generate the steering assist force corresponding to the target steering assist force.

Next, the electrical configuration of the power supply apparatus <NUM> is described. As illustrated in <FIG>, the power supply apparatus <NUM> includes a power supply circuit <NUM> and a power supply controller <NUM>.

The power supply circuit <NUM> has a function of switching a power-ON state and a power-OFF state between the on-board power supply <NUM> and the steering control apparatus <NUM>. In the power-ON state, electric power is supplied to the steering control apparatus <NUM>. In the power-OFF state, the electric power supply is interrupted. A power supply voltage of the on-board power supply <NUM> is input to the power supply circuit <NUM> as an input voltage Vin. The power supply circuit <NUM> outputs the input voltage Vin as an output voltage Vout to be supplied to the steering control apparatus <NUM>. In this embodiment, the power supply voltage of the on-board power supply <NUM>, that is, the input voltage Vin is, for example, <NUM> volts (V). The voltage based on electric power to be supplied to the steering control apparatus <NUM>, that is, the output voltage Vout is substantially equal to the input voltage Vin. For example, the output voltage Vout is <NUM> V.

The power supply controller <NUM> has a function of controlling the switching of the power-ON state and the power-OFF state of the power supply circuit <NUM>. The power supply voltage of the on-board power supply <NUM> is input to the power supply controller <NUM> as the input voltage Vin. The power supply controller <NUM> controls the switching of the power-ON state and the power-OFF state of the power supply circuit <NUM> based on the input voltage Vin. In this embodiment, the power supply controller <NUM> is an example of a controller.

The power supply controller <NUM> outputs a control voltage VC to switch the power-ON state and the power-OFF state of the power supply circuit <NUM>. Specifically, when the electric power steering system has no abnormality in its function and is normally operable to apply the steering assist force to the steering mechanism <NUM>, the power supply controller <NUM> outputs a power-ON switching control voltage VC to make switching to the power-ON state such that the steering control apparatus <NUM> executes control on the application of the steering assist force. When the electric power steering system has an abnormality in its function and is not normally operable to apply the steering assist force to the steering mechanism <NUM>, the power supply controller <NUM> outputs a power-OFF switching control voltage VC to make switching to the power-OFF state such that the steering control apparatus <NUM> stops the control on 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 <NUM> determines whether an abnormality occurs in the function of the electric power steering system based on, for example, an input of an abnormality signal from the steering control apparatus <NUM>. The abnormality signal indicates whether an abnormality occurs in the function of the electric power steering system.

In this embodiment, when the electric power steering system has no abnormality in its function and is normally operable to apply the steering assist force to the steering mechanism <NUM>, the power supply controller <NUM> outputs the power-ON switching control voltage VC irrespective of whether ignition is ON or OFF as a state of a start switch of the vehicle. That is, the on-board power supply <NUM> keeps supplying electric power to the steering control apparatus <NUM>, that is, the memory <NUM> when the ignition is not only ON but also OFF. Thus, when the ignition is not only ON but also OFF, the memory <NUM> can retain various types of information stored for the various types of arithmetic processing to be executed by the steering controller <NUM>.

The configuration of the power supply circuit <NUM> is described in detail. As illustrated in <FIG>, the power supply circuit <NUM> includes a first P-channel MOSFET (PMOS <NUM>), a second P-channel MOSFET (PMOS <NUM>) different from the PMOS <NUM>, a first voltage application circuit <NUM>, and a second voltage application circuit <NUM> different from the first voltage application circuit <NUM>. The first voltage application circuit <NUM> has a function of switching switch states of the PMOS <NUM>. The second voltage application circuit <NUM> has a function of switching switch states of the PMOS <NUM>. The PMOS <NUM> and the PMOS <NUM> of this embodiment are P-channel MOSFETs having source terminals <NUM> and <NUM> associated with P-type semiconductor layers, drain terminals <NUM> and <NUM> associated with P-type semiconductor layers, and gate terminals <NUM> and <NUM> associated with N-type semiconductor layers, respectively.

As illustrated in <FIG>, the P-channel MOSFET has the following characteristics. When a potential of a gate terminal G is lower than a potential of a source terminal S and a potential difference between those terminals is equal to or larger than a preset threshold such as <NUM> V, the P-channel MOSFET is turned ON such that a current is conductive between the source terminal S and a drain terminal D. This is because the potential difference between the source terminal S and the gate terminal G is larger than the threshold and holes are gathered near the surface of an N-type semiconductor layer Ng (represented by "N" in <FIG>) on an insulating layer Z side to provide a P-type semiconductor layer Pg (represented by "P" in <FIG>) serving as an inversion layer. In this case, a P-type semiconductor layer Ps (represented by "P" in <FIG>) associated with the source terminal S and a P-type semiconductor layer Pd (represented by "P" in <FIG>) associated with the drain terminal D are electrically connected through the P-type semiconductor layer Pg. Thus, a current is conductive 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 those terminals is smaller than the threshold, the P-channel MOSFET is turned OFF such that no current is conductive 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 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 such that no current is conductive between the source terminal S and the drain terminal D.

Returning to the description with reference to <FIG>, the source terminal <NUM> of the PMOS <NUM> is connected to a high-potential side of the on-board power supply <NUM>, and the drain terminal <NUM> of the PMOS <NUM> is connected to the steering control apparatus <NUM> via the PMOS <NUM>. The gate terminal <NUM> of the PMOS <NUM> is connected to the first voltage application circuit <NUM>. A contact C1 on a connection line L1 connecting the PMOS <NUM> and the high-potential side of the on-board power supply <NUM> is connected to the first voltage application circuit <NUM>.

The drain terminal <NUM> of the PMOS <NUM> is connected to the drain terminal <NUM> of the PMOS <NUM>, and the source terminal <NUM> of the PMOS <NUM> is connected to the steering control apparatus <NUM>. The gate terminal <NUM> of the PMOS <NUM> is connected to the second voltage application circuit <NUM>. A contact C2 on a connection line L2 connecting the PMOS <NUM> and the steering control apparatus <NUM> is connected to the second voltage application circuit <NUM>.

In this embodiment, the PMOS <NUM> and the PMOS <NUM> are connected in series by connecting their drain terminals <NUM> and <NUM> such that electric power can be supplied from the on-board power supply <NUM> to the steering control apparatus <NUM>. In this case, directions of a parasitic diode D1 provided in the PMOS <NUM> and a parasitic diode D2 provided in the PMOS <NUM> are opposite to each other such that current flows are blocked from the source terminals <NUM> and <NUM> to the drain terminals <NUM> and <NUM>, respectively.

Next, the structures of the first voltage application circuit <NUM> and the second voltage application circuit <NUM> are described in more detail. As illustrated in <FIG>, the first voltage application circuit <NUM> includes a switching circuit constituted by a combination of a transistor TR1 that is an NPN bipolar transistor and a transistor TR2 that is a PNP bipolar transistor.

In the transistor TR1, a base terminal TR1b is connected to the power supply controller <NUM> such that the control voltage VC output from the power supply controller <NUM> is divided through a voltage division resistor and a current based on the divided voltage flows into the base terminal TR1b. In the transistor TR1, an emitter terminal TR1e is connected to a reference potential point GND, and a collector terminal TR1c is connected to a base terminal TR2b of the transistor TR2 and the contact C1. That is, the transistor TR1 is connected to the on-board power supply <NUM> via the collector terminal TR1c and the contact C1.

When a potential difference between the base terminal TR1b and the emitter terminal TR1e is equal to or larger than a preset threshold such as <NUM> V, the transistor TR1 is turned ON such that a current is conductive between the collector terminal TR1c and the emitter terminal TR1e. In this case, a current based on electric power supply from the on-board power supply <NUM>, that is, a current based on the input voltage Vin of the power supply circuit <NUM> flows between the collector terminal TR1c and the emitter terminal TR1e.

When the potential difference between the base terminal TR1b and the emitter terminal TR1e is smaller than the threshold set in the transistor TR1, the transistor TR1 is turned OFF such that no current is conductive between the collector terminal TR1c and the emitter terminal TR1e. In this case, the current based on the electric power supply from the on-board power supply <NUM>, that is, the current based on the input voltage Vin of the power supply circuit <NUM>, does not flow between the collector terminal TR1c and the emitter terminal TR1e.

In this embodiment, the power-OFF switching voltage that is the high-level signal output from the power supply controller <NUM> is set to a value equal to or larger than the threshold set in the transistor TR1, but the power-ON switching voltage that is the low-level signal output from the power supply controller <NUM> is set to a value smaller than the threshold set in the transistor TR1.

In the transistor TR2, the base terminal TR2b is connected to the on-board power supply <NUM> such that, when the transistor TR1 is ON, a current based on a voltage obtained by dividing the input voltage Vin by a voltage division resistor flows into the base terminal TR2b. The transistor TR2 is connected such that, when the transistor TR1 is OFF, a current based on the input voltage Vin flows into the base terminal TR2b. 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 <NUM> of the PMOS <NUM> via voltage division resistors. That is, the transistor TR2 is connected to the on-board power supply <NUM> via the emitter terminal TR2e and the contact C1, and is connected to the PMOS <NUM> the collector terminal TR2c and the gate terminal <NUM>.

The transistor TR2 is configured such that, when the transistor TR1 is ON, a potential difference between the base terminal TR2b and the collector terminal TR2c is equal to or larger than a preset threshold such as <NUM> V, and the transistor TR2 is turned ON such that a current is conductive between the collector terminal TR2c and the emitter terminal TR2e. In this case, the current based on the electric power supply from the on-board power supply <NUM>, that is, the current based on the input voltage Vin of the power supply circuit <NUM> flows between the collector terminal TR2c and the emitter terminal TR2e. Thus, the high-potential side of the on-board power supply <NUM> and the gate terminal <NUM> of the PMOS <NUM> are connected via the first voltage application circuit <NUM>.

The transistor TR2 is configured such that, when the transistor TR1 is OFF, the potential difference between the base terminal TR2b and the collector terminal TR2c is not equal to or larger than the threshold set in the transistor TR2, and the transistor TR2 is turned OFF such that no current is conductive between the collector terminal TR2c and the emitter terminal TR2e. In this case, the current based on the electric power supply from the on-board power supply <NUM>, that is, the current based on the input voltage Vin of the power supply circuit <NUM> does not flow between the collector terminal TR2c and the emitter terminal TR2e. Thus, the reference potential point GND and the gate terminal <NUM> of the PMOS <NUM> are connected via the first voltage application circuit <NUM>.

As illustrated in <FIG>, the second voltage application circuit <NUM> includes a switching circuit constituted by a combination of a transistor TR3 that is an NPN bipolar transistor and a transistor TR4 that is a PNP bipolar transistor.

The transistor TR3 has the same structure as that of the transistor TR1 of the first voltage application circuit <NUM>, 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 apparatus <NUM> via the collector terminal TR3c and the contact C2. When the transistor TR3 is turned ON such that a current is conductive between the collector terminal TR3c and an emitter terminal TR3e, a current based on the electric power supply from the on-board power supply <NUM> to the steering control apparatus <NUM>, that is, a current based on the output voltage Vout of the power supply circuit <NUM> flows between the collector terminal TR3c and the emitter terminal TR3e. When the transistor TR3 is turned OFF such that no current is conductive between the collector terminal TR3c and the emitter terminal TR3e, the current based on the output voltage Vout of the power supply circuit <NUM> does not flow between the collector terminal TR3c and the emitter terminal TR3e.

The transistor TR4 has the same structure as that of the transistor TR2 of the first voltage application circuit <NUM>, 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 apparatus <NUM> via the emitter terminal TR4e and the contact C2.

When the transistor TR4 is turned ON such that a current is conductive between a collector terminal TR4c and the emitter terminal TR4e, the current based on the output voltage Vout of the power supply circuit <NUM> flows between the collector terminal TR4c and the emitter terminal TR4e. Thus, a high-potential side of the steering control apparatus <NUM> and the gate terminal <NUM> of the PMOS <NUM> are connected via the second voltage application circuit <NUM>.

When the transistor TR4 is turned OFF such that no current is conductive between the collector terminal TR4c and the emitter terminal TR4e, the current based on the output voltage Vout of the power supply circuit <NUM> does not flow between the collector terminal TR4c and the emitter terminal TR4e. Thus, the reference potential point GND and the gate terminal <NUM> of the PMOS <NUM> are connected via the second voltage application circuit <NUM>.

Next, description is given of an operation of the power supply circuit <NUM> when the power-ON state and the power-OFF state for the steering control apparatus <NUM> are switched. As illustrated in <FIG>, when the control voltage VC is input from the power supply controller <NUM> to the first voltage application circuit <NUM> as the low-level signal, the transistor TR1 is turned OFF. When the transistor TR1 is OFF, the transistor TR2 is turned OFF. Therefore, the gate terminal <NUM> and the reference potential point GND are connected as indicated by an arrow of a long dashed short dashed line in <FIG>. Thus, the potential of the gate terminal <NUM> is switched to a potential of the reference potential point GND. In this case, the potential of the gate terminal <NUM> is lower than a potential of the source terminal <NUM>, and a potential difference between those terminals is <NUM> V that is equal to or larger than the threshold set in the PMOS <NUM>. Thus, the PMOS <NUM> is turned ON.

As illustrated in <FIG>, when the control voltage VC is input from the power supply controller <NUM> to the second voltage application circuit <NUM> as the low-level signal, the transistor TR3 is turned OFF. When the transistor TR3 is OFF, the transistor TR4 is turned OFF. Therefore, the gate terminal <NUM> and the reference potential point GND are connected as indicated by an arrow of a long dashed short dashed line in <FIG>. Thus, the potential of the gate terminal <NUM> is switched to the potential of the reference potential point GND. In this case, the potential of the gate terminal <NUM> is lower than a potential of the source terminal <NUM>, and a potential difference between those terminals is <NUM> V that is equal to or larger than the threshold set in the PMOS <NUM>. Thus, the PMOS <NUM> is turned ON.

As described above, the power supply controller <NUM> switches the state of the power supply circuit <NUM> to the power-ON state by outputting the low-level signals to the first voltage application circuit <NUM> and the second voltage application circuit <NUM> and switching ON the PMOS <NUM> and the PMOS <NUM>.

As illustrated in <FIG>, when the control voltage VC is input from the power supply controller <NUM> to the first voltage application circuit <NUM> as the high-level signal, the transistor TR1 is turned ON. When the transistor TR1 is ON, the transistor TR2 is turned ON. Therefore, the contact C1 and the gate terminal <NUM> are connected via the transistor TR2 as indicated by an arrow of a long dashed double-short dashed line in <FIG>. Thus, the potential of the gate terminal <NUM> is switched to a potential of the contact C1. In this case, the potential of the source terminal <NUM> is equal to the potential of the gate terminal <NUM>, and the potential difference between those terminals is <NUM> V that is smaller than the threshold set in the PMOS <NUM>. Thus, the PMOS <NUM> is turned OFF.

As illustrated in <FIG>, when the control voltage VC is input from the power supply controller <NUM> to the second voltage application circuit <NUM> as the high-level signal, the transistor TR3 is turned ON. When the transistor TR3 is ON, the transistor TR4 is turned ON. Therefore, the contact C2 and the gate terminal <NUM> are connected via the transistor TR4 as indicated by an arrow of a long dashed double-short dashed line in <FIG>. Thus, the potential of the gate terminal <NUM> is switched to a potential of the contact C2. In this case, the potential of the source terminal <NUM> is equal to the potential of the gate terminal <NUM>, and the potential difference between those terminals is <NUM> V that is smaller than the threshold set in the PMOS <NUM>. Thus, the PMOS <NUM> is turned OFF.

As described above, the power supply controller <NUM> switches the state of the power supply circuit <NUM> to the power-OFF state by outputting the high-level signals to the first voltage application circuit <NUM> and the second voltage application circuit <NUM> and switching OFF the PMOS <NUM> and the PMOS <NUM>.

Effects of this embodiment are described below. (<NUM>) To switch the power-ON state and the power-OFF state of the power supply circuit <NUM> of this embodiment by using the PMOS <NUM> and the PMOS <NUM>, it is only necessary that voltages having potentials lower than that of the on-board power supply <NUM> be applied to the gate terminals <NUM> and <NUM>. Therefore, there is no need to use a booster circuit such as a charge pump, which is necessary when N-channel MOSFETs are used. Thus, even if the voltages are kept applied to the gate terminals <NUM> and <NUM> of the PMOS <NUM> and the PMOS <NUM> to keep the power-ON state, power consumption can be reduced because of no need to use the booster circuit such as the charge pump. Even if the power-ON state is kept for a long period, an increase in the power consumption can be suppressed as compared to the case where the N-channel MOSFETs are used.

(<NUM>) To switch the power-ON state and the power-OFF state, the power supply circuit <NUM> of this embodiment only needs to have the circuits configured to switch connection to the reference potential point GND and connection to the contacts C1 and C2 on the existing circuits. Therefore, there is no need to use circuits configured to generate dedicated voltages for switching to the respective states. Thus, complication of the voltage application circuits <NUM> and <NUM> can be suppressed.

(<NUM>) In the power-ON state and the power-OFF state of the power supply circuit <NUM> of this embodiment, current backflow from the power supply target to the on-board power supply <NUM> can be suppressed by the PMOS <NUM> different from the PMOS <NUM>. In the power-ON state, a voltage is applied to the gate terminal <NUM> of the PMOS <NUM> to suppress the current backflow, but similarly to the above, it is only necessary that a voltage having a potential lower than that of the on-board power supply <NUM> be applied to the gate terminal <NUM>. That is, there is no need to use the booster circuit such as the charge pump, which is necessary in the case of N-channel MOSFETs. Thus, even if the voltage is kept applied to the gate terminal <NUM> of the PMOS <NUM> to suppress the current backflow in the power-ON state, the power consumption can be reduced because of no need to use the booster circuit such as the charge pump. Similarly to the above, when the power-ON state and the power-OFF state are switched for the PMOS <NUM>, it is only necessary to provide the circuit configured to switch connection to the reference potential point GND and connection to the contact C2 on the existing circuit. Therefore, there is no need to use the circuit configured to generate a dedicated voltage for switching to the respective states. Thus, the complication of the second voltage application circuit <NUM> can be suppressed.

(<NUM>) In the power supply apparatus <NUM> of this embodiment, even if the power-ON state is kept for a long period, the increase in the power consumption can be suppressed as compared to the case where the N-channel MOSFETs are used. Thus, it is possible to attain a power supply apparatus <NUM> in which the increase in the power consumption is suppressed even if the power-ON state is kept irrespective of the state of the start switch of the vehicle.

The embodiment described above may be modified as follows. The following other embodiments may be combined without causing any technical contradiction. The PMOS <NUM> is provided to suppress the current backflow from the power supply target to the on-board power supply <NUM>, but the PMOS <NUM> need not be provided. In this case, there is no need to provide even the second voltage application circuit <NUM> configured to switch ON and OFF of the PMOS <NUM>.

When the PMOS <NUM> is switched ON, the potential of the gate terminal <NUM> of the PMOS <NUM> is equal to the potential of the reference potential point GND, but it is only necessary to apply a voltage to the gate terminal <NUM> of the PMOS <NUM> such that the potential difference between the gate terminal <NUM> and the source terminal <NUM> of the PMOS <NUM> is equal to or larger than the threshold. The same applies to the PMOS <NUM>.

When the PMOS <NUM> is switched OFF, the potential of the gate terminal <NUM> of the PMOS <NUM> is the potential of the on-board power supply <NUM>, but it is only necessary to apply a voltage to the gate terminal <NUM> of the PMOS <NUM> such that the potential difference between the gate terminal <NUM> and the source terminal <NUM> of the PMOS <NUM> is smaller than the threshold. The same applies to the PMOS <NUM>.

The electric power supply to the inverter of the steering control apparatus <NUM> may be configured to be interrupted after the start switch is turned OFF until the start switch is turned ON next time.

In the embodiment described above, the steering system <NUM> to which the power supply apparatus <NUM> is applied is the electric power steering system in which the motor <NUM> is coupled to the steering shaft <NUM> via the speed reducer <NUM>, but may be an electric power steering system in which the motor <NUM> is coupled to the rack shaft <NUM> via the speed reducer <NUM>. Further, the steering system <NUM> is not limited to the electric power steering system to which the power supply apparatus <NUM> is applied. For example, the power supply apparatus <NUM> may be applied to a steer-by-wire type steering system.

Claim 1:
A vehicle comprising a power supply apparatus (<NUM>), a vehicular apparatus (<NUM>), and an on-board power supply (<NUM>), the power supply apparatus (<NUM>) comprising a power supply circuit (<NUM>) comprising:
a first P-channel MOSFET (PMOS <NUM>) provided between the on-board power supply (<NUM>) and the vehicular apparatus (<NUM>), wherein the vehicular apparatus is a power supply target and has a memory (<NUM>) for retaining various types of information, the first P-channel MOSFET being configured to switch a power-ON state in which electric power is supplied to the vehicular apparatus (<NUM>) and a power-OFF state in which the supply of the electric power is interrupted; and
a first voltage application circuit (<NUM>), wherein
a source terminal (<NUM>) of the first P-channel MOSFET (PMOS <NUM>) is connected to the on-board power supply (<NUM>), and a drain terminal (<NUM>) of the first P-channel MOSFET (PMOS <NUM>) is connected to the vehicular apparatus (<NUM>), and
the first voltage application circuit (<NUM>) is configured to:
apply a voltage having a potential lower than a potential of the on-board power supply (<NUM>) to a gate terminal (<NUM>) such that a state of the first P-channel MOSFET (PMOS <NUM>) is switched to the power-ON state; and
apply a voltage having a potential equal to the potential of the on-board power supply (<NUM>) to the gate terminal (<NUM>) such that the state of the first P-channel MOSFET (PMOS <NUM>) is switched to the power-OFF state, wherein
the power supply apparatus (<NUM>) additionally comprises a controller (<NUM>) configured to control switching of the power-ON state and the power-OFF state, wherein
the controller (<NUM>) is configured to control the power supply circuit (<NUM>) to keep the power-ON state irrespective of a state of a start switch of the vehicle.