JP7295665B2 - vehicle power supply - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle power supply device, and more particularly to a vehicle power supply device provided in a vehicle having an idling stop function.

In recent years, vehicles equipped with an engine have come to have an idling stop function. In conventional vehicles, the engine is idling even when stopped, but with the idling stop function, unnecessary idling is stopped when the vehicle is stopped in order to save fuel and reduce exhaust gas.

When starting the vehicle from idling stop, the engine is restarted. Patent Documents 1 to 3 disclose inventions in which power is supplied from a capacitor or the like in addition to a main power source such as a battery when the engine is restarted.

Furthermore, Patent Document 4 describes an invention in which voltage is supplied from a capacitor to a starter when the engine is started.

Japanese Patent Application Laid-Open No. 2018-57179 Japanese Patent Application Laid-Open No. 2015-217919 Japanese Patent Application Laid-Open No. 2005-112250 Japanese translation of PCT publication No. 2013-027337

However, in the inventions described in Patent Documents 1 to 4, sufficient consideration has not always been given to suitable timing for charging the capacitor. Specifically, for example, in the invention described in Patent Document 4, the capacitor is charged from the beginning, and electric power is supplied from the capacitor to the starter when the engine starts. As a result, the capacitor discharges over time, and when the engine is started, there is a possibility that the voltage of the capacitor is not sufficiently secured. In addition, when the capacitor is repeatedly charged and discharged, there is a possibility that the charging performance of the capacitor deteriorates early. Furthermore, as a method of solving these problems, it is conceivable to employ a large-capacity capacitor as an auxiliary power supply, but there is a risk that problems such as an increase in the size and cost of the apparatus will occur as the capacity of the capacitor increases. rice field.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a vehicle power supply apparatus in which a power storage unit for supplying power to a load mounted on the vehicle is miniaturized.

A vehicle power supply device according to the present invention is a device for converting electric power supplied from a normal power supply to a vehicle-mounted load in a vehicle having an idling stop function, and is a first power supply unit for converting the voltage of the electric power output from the normal power supply. a booster circuit, a power storage unit connected to the normal power supply and the vehicle-mounted load, a second booster circuit interposed between the normal power supply and the vehicle-mounted load, the power storage unit and the vehicle-mounted load and a control device for controlling the first step-up circuit, the second step-up circuit and the step-down circuit. Until the voltage drops, the power storage unit is charged via the second booster circuit, and immediately before the voltage of the normal power supply drops or when the voltage of the regular power supply starts to drop. switching a voltage supply source for the load mounted on the vehicle from the normal power supply to the power storage unit, controlling the step-down circuit so that the voltage of the normal power supply reaches a predetermined threshold voltage, and Power is supplied to an on-board load, and the threshold voltage is set so that the voltage of the normal power supply does not fall below a minimum voltage after power supply from the power storage unit to the step-down circuit ends. do.

Further, in the vehicle power supply device of the present invention, the control device transfers electric power from the normal power supply to the vehicle-mounted load via the first booster circuit when the idling stop state is changed to the engine operating state. and supplying power from the normal power supply to the power storage unit via the second booster circuit.

Further, in the vehicle power supply device of the present invention, the power storage unit is maintained in a discharged state until the idling stop state ends.

Further, in the vehicle power supply device of the present invention, the power storage unit is a capacitor.

A vehicle power supply device according to the present invention is a device for converting electric power supplied from a normal power supply to a vehicle-mounted load in a vehicle having an idling stop function, and is a first power supply unit for converting the voltage of the electric power output from the normal power supply. a booster circuit, a power storage unit connected to the normal power supply and the vehicle-mounted load, a second booster circuit interposed between the normal power supply and the vehicle-mounted load, the power storage unit and the vehicle-mounted load and a control device for controlling the first step-up circuit, the second step-up circuit and the step-down circuit. Until the voltage drops, the power storage unit is charged via the second booster circuit, and immediately before the voltage of the normal power supply drops or when the voltage of the regular power supply starts to drop. switching a voltage supply source for the load mounted on the vehicle from the normal power supply to the power storage unit, controlling the step-down circuit so that the voltage of the normal power supply reaches a predetermined threshold voltage, and Power is supplied to an on-board load, and the threshold voltage is set so that the voltage of the normal power supply does not fall below a minimum voltage after power supply from the power storage unit to the step-down circuit ends. do. Thus, according to the vehicle power supply device of the present invention, the operation of the first booster circuit after the voltage of the normal power supply drops can be stabilized by supplying power from the power storage unit to the load mounted on the vehicle. Furthermore, since the electric storage unit is charged from the idling stop state until the voltage of the normal power source drops, it is possible to reduce the size and extend the life of the capacitor. Furthermore, according to the vehicle power supply device of the present invention, the operation of the first booster circuit after the voltage of the normal power supply drops can be stabilized by supplying power from the power storage unit to the load mounted on the vehicle. Furthermore, since the electric storage unit is charged from the idling stop state until the voltage of the normal power source drops, it is possible to reduce the size and extend the life of the capacitor. Furthermore, according to the vehicle power supply device of the present invention, it is possible to obtain a sufficient minimum voltage for operating the first booster circuit, thereby preventing inadvertent resetting of a vehicle-mounted load such as a car navigation system. can be suppressed.

Further, in the vehicle power supply device of the present invention, the control device transfers electric power from the normal power supply to the vehicle-mounted load via the first booster circuit when the idling stop state is changed to the engine operating state. and supplying power from the normal power supply to the power storage unit via the second booster circuit. Thus, according to the vehicle power supply device of the present invention, it is possible to supply electric power with a stable voltage to the load mounted on the vehicle and to charge the power storage unit.

Further, in the vehicle power supply device of the present invention, the power storage unit is maintained in a discharged state until the idling stop state ends. Thus, according to the vehicle power supply device of the present invention, the life of the power storage unit can be extended by maintaining the discharged state of the power storage unit until immediately before the voltage drop.

Further, in the vehicle power supply device of the present invention, the power storage unit is a capacitor. Thus, according to the vehicle power supply device of the present invention, the life of the power storage unit can be extended by maintaining the discharged state of the power storage unit until immediately before the voltage drop.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a vehicle power supply device according to an embodiment of the present invention, FIG. 1A is a block diagram showing a connection configuration of a vehicle in which the vehicle power supply device is incorporated, and FIG. It is a circuit diagram showing. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a vehicle power source device according to an embodiment of the present invention, (A) is a circuit diagram showing the vehicle power source device, and (B) is a power supply voltage during a period A when the engine is restarted; is a timing chart showing changes in . BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a vehicle power source device according to an embodiment of the present invention, where (A) is a circuit diagram showing the vehicle power source device, and (B) is a power supply voltage during a period B when the engine is restarted; is a timing chart showing changes in . BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a vehicle power source device according to an embodiment of the present invention, where (A) is a circuit diagram showing the vehicle power source device, and (B) is a power supply voltage during a period C when the engine is restarted; is a timing chart showing changes in . BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a vehicle power supply device according to an embodiment of the present invention, where (A) is a circuit diagram showing the vehicle power supply device, and (B) is a power supply voltage during period D when the engine is restarted; is a timing chart showing changes in . BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a vehicle power supply device according to an embodiment of the present invention, where (A) is a circuit diagram showing the vehicle power supply device, and (B) is a power supply voltage during period E when the engine is restarted; is a timing chart showing changes in . 1A is a timing chart showing changes in the power supply voltage in the vehicle power supply device according to the embodiment of the present invention; FIG. (C) is a timing chart of a comparative example.

Hereinafter, a vehicle power supply device 11 according to an embodiment of the present invention will be described in detail based on the drawings. In the following description, in principle, the same reference numerals are used for the same members, and repeated descriptions are omitted.

The configuration of the vehicle power supply device 11 will be described with reference to FIG. FIG. 1A is a block diagram showing a schematic configuration of a vehicle 10 including a vehicle power supply device 11, and FIG. 1B is a circuit diagram showing the detailed configuration of the vehicle power supply device 11. As shown in FIG.

Referring to FIG. 1A, vehicle 10 includes normal power supply 12 , vehicle power supply 11 , and vehicle load 13 . The vehicle 10 is a vehicle that runs using an engine (not shown) as a drive source, and has an idling stop function. The idling stop function is a function to stop unnecessary idling when the vehicle 10 stops at an intersection or the like in order to save fuel or reduce exhaust gas.

The normal power supply 12 supplies electric power to the vehicle-mounted load 13 . A specific example of the normal power supply 12 is, for example, a rechargeable lead-acid battery or a lithium-ion battery that generates 12V DC power.

The vehicle-mounted load 13 is a load mounted on the vehicle 10, and includes, for example, a starter for starting the engine, a car navigation device, an audio device, a meter device, an ECU, a ROM, a RAM, an electric steering wheel, a seat heater, a defroster heater, These include lighting devices such as headlights, wipers, air conditioners, cameras, sensors, displays, and advanced safety systems such as collision damage mitigation brakes.

The vehicle power supply 11 converts electric power supplied from the vehicle power supply 11 to the vehicle load 13 .

The circuit configuration of the vehicle power supply device 11 will be described with reference to FIG. The vehicle power supply device 11 has a first path 171 and a second path 172 as paths that directly connect the normal power supply 12 and the vehicle-mounted load 13 . The first path 171 and the second path 172 are connected via the third contact 233 .

In addition, the vehicle power supply device 11 has a first booster circuit 141, a second booster circuit 142, and a step-down circuit 143 as voltage conversion circuits. DC-DC converters are employed as these voltage converters.

A first path 171 connects the normal power supply 12 and the first booster circuit 141 . A first contact 231 , a second switch 292 and a third contact 233 are interposed in the first path 171 from the normal power supply 12 side. In this embodiment, semiconductor switches such as field effect transistors or bipolar transistors, or mechanical switches such as relays can be used as various switches such as the second switch 292 .

The second path 172 connects the third contact 233 of the first path 171 and the vehicle-mounted load 13, and the first switch 291 and the second contact 232 are interposed from the third contact 233 side. there is

A fourth path 174 branches off from the first contact 231 of the first path 171 , and the other end of the fourth path 174 is connected to the second booster circuit 142 . A third switch 293 is interposed in the fourth path 174 .

A seventh path 177 extends from the second booster circuit 142, and the end of the seventh path 177 is grounded. A diode 18, a resistor 19, a fifth contact 235 and a capacitor 15 are interposed in the seventh path 177 from the second booster circuit 142 side.

A fifth path 175 is formed between the second contact 232 of the second path 172 and the step-down circuit 143 . A third path 173 is connected to the fourth contact 234 interposed in the fifth path 175 . The other end of the third path 173 is connected to the first booster circuit 141 .

A sixth path 176 is formed between the step-down circuit 143 and the fifth contact 235 of the seventh path 177 . A fourth switch 294 is interposed in the sixth path 176 .

The control device 16 includes a CPU, RAM, ROM, etc., and is also called an ECU (Electronic Control Unit). Based on the voltage of the normal power supply 12 and the like, the control device 16 controls the conduction state of each switch described above, the operations of the first booster circuit 141, the second booster circuit 142 and the step-down circuit 143, and the like.

Next, with reference to FIGS. 2 to 6, the operation of the vehicle power supply device 11 described above will be described. Here, the vehicle power supply device 11 compensates for the voltage applied to the vehicle-mounted load 13 above a certain level in the restart operation in which the vehicle 10 having the idling stop function transitions from the idling stop state to the engine restart. are doing. This allows the vehicle-mounted load 13 to operate stably.

Such operation of vehicle 10 includes periods A through E, each of which is described below.

A period A, which is the first period of the restart operation, will be described with reference to FIG. 2A is a circuit diagram showing the operation of the vehicle power supply 11 during the period A, and FIG. 2B is a timing chart showing the voltage value of the normal power supply 12 during the period A. FIG. Period A is, for example, a period during which the passenger depresses the brake pedal, the vehicle 10 stops at an intersection or the like, and the engine is stopped by the idling stop function. In FIG. 2A, the flow of current in the vehicle power supply device 11 is indicated by a dashed line, and the same applies to each figure described later.

Referring to FIG. 2A, in period A, control device 16 supplies electric power to vehicle-mounted load 13 . During the period A, the ISS (Idling Stop System) signal issued from the control device 16 is in the Low state. Further, the control device 16 brings the first switch 291 into a conductive state, brings the second switch 292 into a conductive state, brings the third switch 293 into a cut-off state, and brings the fourth switch 294 into a cut-off state.

By setting the vehicle power supply device 11 to the above state, power is directly supplied from the normal power supply 12 to the vehicle-mounted load 13 without going through the first booster circuit 141 and the like. Specifically, the power from the normal power supply 12 via the first path 171, the first contact 231, the second switch 292, the third contact 233, the second path 172, the first switch 291, and the second contact 232 is supplied to the vehicle-mounted load 13 .

It should be noted that during the period A, the capacitor 15 is not charged and remains in a state in which no charge is accumulated.

Referring to FIG. 2B, in period A, the voltage of normal power supply 12 is stable at about 12V, for example.

The period B will be described with reference to FIG. 3A is a circuit diagram showing the operation of the vehicle power supply 11 during the period B, and FIG. 3B is a timing chart showing the voltage value of the normal power supply 12 during the period B. FIG. In the period B, the electric power boosted by the first booster circuit 141 is applied to the vehicle load 13 in order to prevent the voltage supplied to the vehicle load 13 from dropping when the engine is restarted from the idling stop state. are supplying. Also, in period B, the control device 16 transmits an electrical signal for preparing to start the engine to each component of the vehicle power supply device 11 . Furthermore, in the period B, the capacitor 15 is charged in order to stabilize the operation of the second booster circuit 142 in the later period.

Referring to FIG. 3A, in period B, the ISS signal issued from control device 16 is in a High state. Further, the control device 16 brings the first switch 291 into the cut-off state, the second switch 292 into the conducting state, the third switch 293 into the conducting state, and the fourth switch 294 into the cut-off state.

By setting the vehicle power supply device 11 to the above state, the power from the normal power supply 12 is supplied to both the vehicle-mounted load 13 and the capacitor 15 . The path through which power is supplied from the normal power source 12 to the vehicle-mounted load 13 is the first path 171, the first contact 231, the second switch 292, the third contact 233, the first booster circuit 141, the third path 173, the fourth A contact 234 , a fifth path 175 , a second contact 232 and a second path 172 . The paths through which power is supplied from the normal power supply 12 to the capacitor 15 are the first path 171, the first contact 231, the fourth path 174, the third switch 293, the second booster circuit 142, the seventh path 177, the diode 18 , the resistor 19 and the fifth contact 235 .

The capacitor 15 is charged to a predetermined voltage by supplying power from the normal power supply 12 during the period B. FIG.

Here, the power boosted by the second booster circuit 142 is supplied to the capacitor 15 . The second booster circuit 142 boosts the voltage of the power supplied from the normal power supply 12 from 12V to 24V, for example. Therefore, the capacitor 15 with a small capacity can be used, and the time required for charging the capacitor 15 can be shortened.

As shown in FIG. 3B, the period B is, for example, the period from when the occupant takes his/her foot off the brake pedal until the engine is restarted while the engine is stopped by the idling stop function. be. In the period B, the voltage drop of the normal power supply 12 has not yet occurred. Here, the boundary between period A and period B is, for example, the timing at which the control device 16 terminates the idling stop function.

The period C will be described with reference to FIG. 4A is a circuit diagram showing the operation of the vehicle power supply 11 during period C, and FIG. 4B is a timing chart showing the voltage value of the normal power supply 12 during period C. FIG. A period C includes the moment when the engine is restarted, and power is supplied from the capacitor 15 to the vehicle-mounted load 13 . That is, the control device 16 switches the voltage supply source of the vehicle-mounted load 13 from the normal power supply 12 to the capacitor 15 .

Referring to FIG. 4A, control device 16 sets first switch 291 to the cut-off state, sets second switch 292 to the cut-off state, sets third switch 293 to the cut-off state, and sets fourth switch 294 to the on state. do.

By placing the vehicle power supply device 11 in the above state, the seventh path 177, the fifth contact 235, the sixth path 176, the fourth switch 294, the step-down circuit 143, the fifth path 175, the fourth contact 234, the second Power is supplied from capacitor 15 to vehicle load 13 via contact 232 and second path 172 . Also, the step-down circuit 143 converts the voltage of the power supplied from the capacitor 15 from 24V to 12V, for example.

Referring to FIG. 4B, period C is, for example, a period between the moment the engine is restarted by operating the starter motor from a state in which the engine is stopped by the idling stop function, and the period immediately after that. . Here, the transition from period B to period C, that is, the switching of the voltage supply source from the normal power supply 12 to the capacitor 15 occurs immediately before or immediately after the voltage drop in the normal power supply 12 occurs.

A voltage drop that occurs in period C will be described. When the voltage is boosted by the first booster circuit 141, the amount of input current increases because a low voltage and a specified amount of power are required at the time of input. Specifically, when the input power input to the first booster circuit 141 is 6V×20A=120W, the output power output from the first booster circuit 141 is 12V×10A=120W. Therefore, as the input current value increases, the voltage drop due to the wiring resistance also increases, and a phenomenon occurs in which the input voltage drops. In addition, power consumption by a starter such as a starter that restarts the engine is also one of the causes of the voltage drop.

When the voltage drop occurs, there is a possibility that the performance of the first booster circuit 141 cannot be exhibited in the next period, period D. If the first voltage step-up circuit 141 cannot exhibit sufficient performance, for example, a sufficient voltage cannot be applied to the car navigation system, which is an example of the vehicle-mounted load 13, and the setting of the car navigation system is inadvertently reset. There is a risk of being

In order to protect the vehicle-mounted load 13 from a voltage drop, generally, the first booster circuit 141 supplies boosted electric power to the vehicle-mounted load 13 . It is difficult to fully demonstrate the performance of 141.

Therefore, in this embodiment, power is supplied from the capacitor 15 to the vehicle-mounted load 13 during the period C in which the voltage drop occurs. By doing so, the voltage of the normal power supply 12 can be recovered to a threshold voltage, which will be described later, and the boosting function of the first booster circuit 141 can be fully exhibited. Further, power is supplied from the capacitor 15 to the first booster circuit 141 only during a period in which the voltage of the normal power supply 12 drops sharply. Therefore, the capacitor 15 having a small size can be used, and the increase in cost and size due to the use of the capacitor 15 can be suppressed. This matter will be described later with reference to FIG.

The period D will be described with reference to FIG. 5A is a circuit diagram showing the operation of the vehicle power supply 11 during the period D, and FIG. 5B is a timing chart showing the voltage value of the normal power supply 12 during the period D. FIG. Period D is a period in which the voltage of the normal power source 12 is compensated by the first booster circuit 141 while the engine is running after the idling stop period.

Referring to FIG. 5A, in period D, control device 16 brings first switch 291 into the disconnected state, second switch 292 into the conductive state, third switch 293 into the disconnected state, and fourth switch 293 into the disconnected state. The switch 294 is turned off.

By setting the vehicle power supply device 11 to the above state, the power output from the normal power supply 12 is boosted by the first booster circuit 141 and then supplied to the vehicle load 13 . Specifically, the first path 171, the first contact 231, the second switch 292, the third contact 233, the first step-up circuit 141, the third path 173, the fourth contact 234, the fifth path 175, the second contact 232 and the second path 172 , power is supplied from the normal power supply 12 to the vehicle-mounted load 13 . On the other hand, power is not supplied to the capacitor 15 .

As shown in FIG. 5B, in this embodiment, the voltage of the normal power supply 12 is recovered to the threshold voltage by supplying power from the capacitor 15 to the first booster circuit 141 during the period C described above. Therefore, even if a voltage drop occurs due to wiring resistance or the like during the period D, the voltage of the normal power supply 12 is prevented from falling below the minimum voltage, and the boosting performance of the first booster circuit 141 is fully demonstrated. can do.

The period E will be described with reference to FIG. 6A is a circuit diagram showing the operation of the vehicle power supply 11 during the period E, and FIG. 6B is a timing chart showing the voltage value of the normal power supply 12 during the period E. FIG. Here, the period E is, for example, the period during which the vehicle 10 runs with the driving force of the engine after the idling stop function ends.

6A, in period E, control device 16 brings first switch 291 into conduction, second switch 292 into conduction, third switch 293 into interruption, and fourth switch 294 into conduction. is cut off.

By setting the vehicle power supply device 11 to the above state, power is directly supplied from the normal power supply 12 to the vehicle-mounted load 13 without going through the first booster circuit 141 and the like. Specifically, the power from the normal power supply 12 via the first path 171, the first contact 231, the second switch 292, the third contact 233, the second path 172, the first switch 291, and the second contact 232 is supplied to the vehicle-mounted load 13 . It should be noted that during the period E, the capacitor 15 is not charged and remains in a state in which no charge is accumulated.

Referring to FIG. 6B, in period E, the voltage of normal power supply 12 is stable at about 12V, for example.

With reference to FIG. 7, the effect produced by the present embodiment described above will be described. FIG. 7A is a timing chart showing the voltage value of the normal power supply 12 according to the present embodiment described above, and FIG. FIG. 7C is a timing chart showing a comparative example in the case where the boost in period C is made higher than the threshold.

Referring to FIG. 7A, in the present embodiment, during period C, power is supplied from capacitor 15 to vehicle-mounted load 13 until the voltage of normal power supply 12 reaches the threshold voltage. Here, the threshold voltage means that once the voltage of the normal power supply 12 is restored to that voltage, the voltage of the normal power supply 12 does not fall below the minimum voltage in the subsequent period, and the performance of the first booster circuit 141 is ensured. is the lower limit of the voltage that can be applied, for example 8V to 10V. By raising the voltage of the normal power supply 12 to the threshold in the period C, it is possible to prevent the voltage of the normal power supply 12 from falling below the minimum voltage in the period after the period C. Here, the minimum voltage is a voltage below which the performance of the first booster circuit 141 cannot be ensured at that time, for example, 6V.

On the other hand, referring to FIG. 7B, if the voltage of the normal power supply 12 does not reach the threshold voltage in the period C, the voltage of the normal power supply 12 falls below the minimum voltage in the next period, and the first boost voltage is applied. Circuit 141 may not be able to boost voltage sufficiently.

Further, referring to FIG. 7(C), if the voltage of normal power supply 12 becomes excessively higher than the threshold voltage in period C, a large-capacity capacitor shown by hatching is used to increase the voltage of normal power supply 12 . 15 is required, which may lead to an increase in size and cost of the capacitor 15 .

From the above, in the present embodiment, during the period C, power is supplied from the capacitor 15 to the vehicle-mounted load 13 until the voltage of the normal power supply 12 reaches the threshold voltage. As a result, the voltage can be stably boosted by the first booster circuit 141, and the size of the capacitor 15 can be reduced.

Although the embodiments of the present invention have been described above, the present invention is not limited to these, and modifications can be made without departing from the gist of the present invention.

For example, referring to FIG. 1, a second booster circuit 142 and a step-down circuit 143 are arranged for the purpose of miniaturizing the capacitor 15. The device 11 can also be configured.

10 Vehicle 11 Vehicle power supply 12 Normal power supply 13 Vehicle-mounted load 141 First step-up circuit 142 Second step-up circuit 143 Step-down circuit 15 Capacitor 16 Control device 171 First path 172 Second path 173 Third path 174 Fourth path 175 5 path 176 6th path 177 7th path 18 diode 19 resistor 231 first contact 232 second contact 233 third contact 234 fourth contact 235 fifth contact 291 first switch 292 second switch 293 third switch 294 fourth switch

Claims (4)

A device for converting power supplied from a normal power supply to a vehicle-mounted load in a vehicle having an idling stop function,
a first booster circuit that converts the voltage of the power output from the normal power supply;
a power storage unit connected to the normal power supply and the vehicle-mounted load;
a second booster circuit interposed between the normal power supply and the power storage unit;
a step-down circuit interposed between the power storage unit and the vehicle-mounted load;
a control device that controls the first booster circuit , the second booster circuit, and the step-down circuit ;
The control device is
charging the power storage unit via the second booster circuit during a period from the idling stop state until the voltage of the normal power supply drops;
immediately before the voltage of the normal power supply drops or when the voltage of the normal power supply starts to drop, switching a voltage supply source for the vehicle-mounted load from the normal power supply to the power storage unit ;
controlling the step-down circuit so that the voltage of the normal power supply reaches a predetermined threshold voltage to supply power to the vehicle-mounted load;
The power supply device for a vehicle, wherein the threshold voltage is set so that the voltage of the normal power supply does not fall below a minimum voltage after the supply of power from the power storage unit to the step-down circuit ends. The control device is
When transitioning from the idling stop state to the engine operating state,
Power is supplied from the normal power supply to the on-vehicle load via the first booster circuit, and power is supplied from the normal power supply via the second booster circuit to the power storage unit. The vehicle power supply device according to claim 1 . 3. The power supply device for a vehicle according to claim 1, wherein said power storage unit is maintained in a discharged state until said idling stop state ends. 4. The vehicle power supply device according to claim 1 , wherein the power storage unit is a capacitor.

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