JP7105727B2 - Automotive battery charger - Google Patents

Description

The present invention relates to a vehicle battery charging device.

The auxiliary battery is a vehicle-mounted DC/DC converter that converts the high voltage output from the vehicle-mounted drive battery into the charging voltage of the vehicle-mounted drive battery. is charged using the voltage output from In order to protect the auxiliary equipment connected as the load of the auxiliary battery from failure, the vehicle battery charging equipment is designed so that the converted voltage output from the vehicle battery charging equipment does not become overvoltage. It is desirable to control the voltage output. For example, the vehicle-mounted battery charging device detects whether or not the converted voltage output from the vehicle-mounted battery charging device is overvoltage, and stops charging the auxiliary battery if the voltage is overvoltage. Thereby, the output of the voltage can be controlled so that the voltage does not become an overvoltage.
For example, in Patent Document 1, when drooping control of the transforming unit is performed by an output voltage control unit that controls the output voltage of the transforming unit of the DCDC converter, the amount of increase in the output current of the transforming unit per predetermined time becomes a predetermined threshold value or more, the failure detection unit determines that a failure has occurred in or around the DCDC converter, thereby detecting a failure that occurred during drooping control of the output voltage of the DCDC converter. disclosed.

Japanese Patent Laid-Open No. 03-071798

However, for example, the conventional vehicle-mounted battery charging device described in Patent Document 1 has an output voltage control unit that transmits a command value to a transformer unit when it is determined that a failure has occurred in the vehicle-mounted battery charging device or its surroundings. There was a problem that the operation of the transformer section could not be stopped when a problem occurred in the transformer.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems. It is an object of the present invention to provide a battery charging device for

A vehicle-mounted battery charging apparatus according to the present invention has an H-bridge circuit, a transformer section for converting a high voltage output from a vehicle-mounted drive battery into a charging voltage for an auxiliary battery, and a transformer section for outputting the voltage. A period in which the voltage after voltage conversion continues to exceed a first voltage higher than the charging voltage of the auxiliary battery is measured, and when the period continues for a predetermined period, a first charging stop signal is output. A second overvoltage that measures the voltage after voltage conversion output by the first overvoltage detection unit and the transforming unit and outputs a second charge stop signal when the voltage exceeds a second voltage higher than the first voltage During the period until the detection unit receives the first charging stop signal, the first system of the first system and the second system of the H bridge circuit is driven, and when the first charging stop signal is received, A first driving unit that stops driving the first system, and drives the second system out of the first system and the second system that the H bridge circuit has in the period until receiving the second charging stop signal, and drives the second system. and a second driving unit that stops driving the second system when receiving the second charging stop signal.

According to the present invention, charging of the auxiliary battery can be reliably stopped when the converted voltage output from the vehicle-mounted battery charging device is an overvoltage.

FIG. 1 is a block diagram showing an example of a configuration of a main part of a vehicle 1 to which an in-vehicle battery charging device according to Embodiment 1 is applied. FIG. 2 is a block diagram showing an example of the configuration of the essential parts of the vehicle-mounted battery charging device according to Embodiment 1. As shown in FIG. FIG. 3 is a circuit diagram showing an example of a configuration of a main part of the transformer section according to Embodiment 1. FIG. 4 is a block diagram showing an example of a configuration of a main part of the first overvoltage detector according to Embodiment 1. FIG. 5 is a block diagram showing an example of a configuration of a main part of the second overvoltage detection section according to Embodiment 1. FIG. 6 is a flowchart illustrating an example of the operation of the first overvoltage detector according to Embodiment 1. FIG. 7 is a flowchart showing an example of the operation of the second overvoltage detector according to Embodiment 1. FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Embodiment 1.
With reference to FIG. 1, the configuration of a main part of a vehicle 1 to which an in-vehicle battery charging device 100 according to Embodiment 1 is applied will be described.
FIG. 1 is a block diagram showing an example of a configuration of a main part of a vehicle 1 to which an in-vehicle battery charging device 100 according to Embodiment 1 is applied.
For example, the vehicle 1 is an automobile such as an EV (Electric Vehicle) or a PHEV (Plug-in Hybrid Electric Vehicle) that can run using electricity as an energy source.
The vehicle 1 includes an in-vehicle drive battery 2 , an inverter 3 , a motor 4 , an auxiliary battery 5 , an auxiliary device 6 , and an in-vehicle battery charging device 100 .

The in-vehicle drive battery 2 is a storage battery that supplies an energy source for obtaining a power source for the vehicle 1 to run. The in-vehicle drive battery 2 outputs a high voltage such as 400V. The in-vehicle drive battery 2 is charged by being supplied with power from an external power supply, an alternator, or the like (not shown).
The inverter 3 receives the DC voltage output by the on-vehicle drive battery 2, converts the DC voltage into an AC voltage, and outputs the AC voltage.
The motor 4 receives the AC voltage output from the inverter 3 and uses the AC voltage as an energy source to convert the energy source into a power source for the vehicle 1 to run.
That is, the vehicle 1 is driven forward or backward by rotating the motor 4 with electric power supplied from the in-vehicle drive battery 2 via the inverter 3 .

Auxiliary machine battery 5 is a storage battery that supplies an energy source for operating auxiliary machine 6 . The auxiliary battery 5 outputs a voltage such as 12V, which is lower than the voltage output by the in-vehicle drive battery 2 . The auxiliary device battery 5 is charged by being supplied with electric power from the in-vehicle drive battery 2 .
The auxiliary device 6 is a device such as an alternator, water pump, or oil pump necessary for operating the inverter 3 or the motor 4 . FIG. 1 shows the device as a whole as one auxiliary device 6 .
The vehicle-mounted battery charging device 100 converts the high voltage output from the vehicle-mounted drive battery 2 into the charging voltage of the auxiliary battery 5 . Vehicle-mounted battery charging apparatus 100 supplies the electric power after voltage conversion to auxiliary battery 5 to charge auxiliary battery 5 .

With reference to FIG. 2, the configuration of the main part of vehicle-mounted battery charging apparatus 100 according to Embodiment 1 will be described.
FIG. 2 is a block diagram showing an example of a configuration of a main part of vehicle-mounted battery charging device 100 according to Embodiment 1. As shown in FIG.
The vehicle-mounted battery charging device 100 includes a transformer section 110, a first overvoltage detection section 120, a second overvoltage detection section 130, a first drive section 140, a second drive section 150, a drive control section 160, and an output control section 170. .
Transformation unit 110 converts the high voltage output from in-vehicle drive battery 2 into the charging voltage of auxiliary battery 5 .

Referring to FIG. 3, the configuration of the main part of transforming section 110 according to the first embodiment will be described.
FIG. 3 is a circuit diagram showing an example of a configuration of a main part of transformer section 110 according to the first embodiment.
The transformer section 110 has an H bridge circuit 111 , a transformer 112 and diodes 113 and 114 . As shown in FIG. 3, the transformer section 110 may have an inductor 115, a capacitor 116, etc. in addition to the H bridge circuit 111, the transformer 112, and the diodes 113 and 114. FIG.

The H-bridge circuit 111 has two systems: a first system 111a composed of switching elements 117a and 117b, and a second system 111b composed of switching elements 117c and 117d.
For example, each of the switching elements 117a, 117b, 117c, and 117d is configured by a transistor such as a bipolar transistor, FET (Field Effect Transistor), or MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor). Hereinafter, the switching elements 117a, 117b, 117c, and 117d are configured by bipolar transistors as an example, and the switching elements 117a, 117b, 117c, and 117d each have a collector terminal, an emitter terminal, and a base terminal. .

For example, in the first system 111a of the H bridge circuit 111, the collector terminal of the switching element 117a is connected to the positive terminal of the vehicle battery 2, and the emitter terminal of the switching element 117b is connected to the negative terminal of the vehicle battery 2. , the emitter terminal of the switching element 117a is connected to the collector terminal of the switching element 117b. Further, for example, in the second system 111b of the H bridge circuit 111, the collector terminal of the switching element 117c is connected to the positive terminal of the vehicle battery 2, and the emitter terminal of the switching element 117d is connected to the negative terminal of the vehicle battery 2. The emitter terminal of the switching element 117c is connected to the collector terminal of the switching element 117d.

The transformer 112 has a primary winding 118a and a secondary winding 118b.
One end of the primary winding 118 a of the transformer 112 is connected to the first system 111 a of the H bridge circuit 111 and the other end is connected to the second system 111 b of the H bridge circuit 111 .

Specifically, for example, one end of the primary winding 118a of the transformer 112 is connected to the emitter terminal of the switching element 117a in the first system 111a of the H bridge circuit 111 and the switching element 117b in the first system 111a of the H bridge circuit 111. is connected to the line that connects the collector terminal of The other end of the primary winding 118a of the transformer 112 is connected to the emitter terminal of the switching element 117c in the second system 111b of the H bridge circuit 111 and the collector terminal of the switching element 117d in the second system 111b of the H bridge circuit 111. connected to the line that connects the
The base terminal of the switching element 117a in the first system 111a of the H bridge circuit 111 and the base terminal of the switching element 117b in the first system 111a of the H bridge circuit 111 are connected to the first driving section 140, respectively. A base terminal of the switching element 117c and a base terminal of the switching element 117d are connected to the second driving section 150, respectively.

A circuit configuration including the secondary winding 118b of the transformer 112, the diodes 113 and 114, the inductor 115, and the capacitor 116 is a general circuit configuration in a DCDC converter, so description thereof will be omitted.
The switching element 117a and the switching element 117b of the transforming section 110 are driven by the first driving section 140, and the switching element 117c and the switching element 117d are driven by the second driving section 150. 2 is converted into the charging voltage of the battery 5 for auxiliary equipment.

The drive control unit 160 measures the voltage after the voltage conversion output by the transforming unit 110, and generates a PWM (Pulse Width Modulation) signal so that the voltage becomes the charging voltage of the auxiliary battery 5. The resulting PWM signal is output to the first driving section 140 and the second driving section 150 .

First overvoltage detection unit 120 measures the period during which the converted voltage output from transformation unit 110 continues to exceed a first voltage higher than the charging voltage of auxiliary battery 5 . The first overvoltage detector 120 outputs a first charging stop signal when the period continues for a predetermined period.
The first voltage is, for example, a voltage higher than the charging voltage of the auxiliary battery 5 by 0.1 V (volt). For example, when the first voltage is 0.1V higher than the charging voltage of the auxiliary battery 5 and the charging voltage of the auxiliary battery 5 is 12.0V, the first voltage is 12.1V. Become. Note that the difference between the first voltage and the charging voltage of the auxiliary battery 5 is not limited to 0.1 V, and may be a value larger than 0.1 V or smaller than 0.1 V. Also good.
The predetermined period is, for example, 100 ms (milliseconds). Note that the predetermined period is not limited to 100 ms, and may be a period longer than 100 ms or a period shorter than 100 ms. Embodiment 1 will be described assuming that the predetermined period is 100 ms.

With reference to FIG. 4, the configuration of the main part of first overvoltage detection section 120 according to the first embodiment will be described.
FIG. 4 is a block diagram showing an example of a configuration of a main part of first overvoltage detection section 120 according to Embodiment 1. As shown in FIG.
The first overvoltage detector 120 has a first voltage determiner 121 , a period determiner 122 , and a first charge stop signal transmitter 123 .
The first voltage determination unit 121 determines whether or not the voltage after voltage conversion output from the transformation unit 110 exceeds the first voltage.
The period determining unit 122 determines a period during which the voltage after voltage conversion output from the transforming unit 110 continues to exceed the first voltage. Specifically, for example, the period determining unit 122 has a timer, and the period during which the first voltage determining unit 121 continues to determine that the voltage after voltage conversion output by the transforming unit 110 exceeds the first voltage. is measured, and it is determined whether or not the period has reached a predetermined period.
When the first charging stop signal transmitting unit 123 determines that the period during which the period determining unit 122 continues to determine that the voltage after voltage conversion output by the transforming unit 110 exceeds the first voltage has reached a predetermined period. , outputs a first charging stop signal and transmits the first charging stop signal to the first driving unit 140 .

The first overvoltage detector 120 is configured by an integrated circuit, for example.
The size of the first overvoltage detection unit 120 can be reduced by configuring the first overvoltage detection unit 120 with an integrated circuit.

The second overvoltage detector 130 measures the converted voltage output from the transformer 110 . The second overvoltage detector 130 outputs a second charge stop signal when the voltage exceeds a second voltage higher than the first voltage.
The second voltage is, for example, a voltage higher than the first voltage by 0.1 V (volt). For example, if the second voltage is 0.1V higher than the first voltage and the first voltage is 12.1V, the second voltage is 12.2V. Note that the difference between the second voltage and the first voltage is not limited to 0.1V, and may be a value greater than 0.1V or a value less than 0.1V.

With reference to FIG. 5, the configuration of the main part of second overvoltage detection section 130 according to the first embodiment will be described.
FIG. 5 is a block diagram showing an example of the configuration of the main part of the second overvoltage detector 130 according to the first embodiment.
The second overvoltage detector 130 has a second voltage determiner 131 and a second charge stop signal transmitter 132 .
The second voltage determination unit 131 determines whether or not the voltage after voltage conversion output from the transformation unit 110 exceeds the second voltage.
The second charge stop signal transmission unit 132 outputs a second charge stop signal when the second voltage determination unit 131 determines that the converted voltage output from the transformation unit 110 exceeds the second voltage. Then, the second charging stop signal is transmitted to the second driving section 150 .

The second overvoltage detector 130 is configured such that the failure rate of the second overvoltage detector 130 is lower than the failure rate of the first overvoltage detector 120 .
Specifically, for example, the second overvoltage detection unit 130 is configured by a discrete circuit configured by discrete parts such as resistance elements.
Since the second overvoltage detection unit 130 is configured by a discrete circuit, the durability of the second overvoltage detection unit 130 is improved as compared with the case where the second overvoltage detection unit 130 is configured by an integrated circuit. Therefore, even if the first overvoltage detection unit 120 configured by an integrated circuit or the like has a problem and the first overvoltage detection unit 120 cannot output the first charge stop signal, the second overvoltage detection unit 130 The second charging stop signal can be reliably output.

The first drive unit 140 drives the first system 111a. Specifically, for example, the first drive unit 140 receives the PWM signal output by the drive control unit 160 and generates the first drive signal based on the PWM signal. The first drive unit 140 drives the first system 111a by transmitting the first drive signal to the switching elements 117a and 117b in the first system 111a of the H bridge circuit 111 of the transforming unit 110.
The first driving section 140 stops driving the first system 111a when receiving the first charging stop signal output by the first overvoltage detecting section 120 . Specifically, for example, when the first drive unit 140 receives the first charge stop signal output by the first overvoltage detection unit 120, the first drive unit 140 performs switching in the first system 111a of the H bridge circuit 111 included in the transformation unit 110. By transmitting the first stop signal to the element 117a and the switching element 117b, the driving of the first system 111a is stopped.

That is, the first driving unit 140 drives the first system 111a included in the H bridge circuit 111 during the period until the first charging stop signal is received, and when the first charging stop signal is received, the first system 111a is driven. 111a is stopped.
When the first drive unit 140 stops driving the first system 111a, no current flows through the primary winding 118a. It will not be charged.

The second driving section 150 drives the second system 111b. Specifically, for example, the second drive unit 150 receives the PWM signal output by the drive control unit 160 and generates the second drive signal based on the PWM signal. The second drive section 150 drives the second system 111b by transmitting the second drive signal to the switching elements 117c and 117d in the second system 111b of the H bridge circuit 111 of the transforming section 110.
The second drive unit 150 stops driving the second system 111b when receiving the second charge stop signal output by the second overvoltage detection unit 130 . Specifically, for example, when the second drive unit 150 receives the second charge stop signal output by the second overvoltage detection unit 130, the second drive unit 150 switches the second system 111b of the H bridge circuit 111 included in the transformation unit 110. By transmitting the second stop signal to the element 117c and the switching element 117d, the driving of the second system 111b is stopped.

That is, the second driving unit 150 drives the second system 111b of the H bridge circuit 111 during the period until the second charging stop signal is received, and when the second charging stop signal is received, the second system 111b is driven. 111b is stopped.
When the second drive unit 150 stops driving the second system 111b, no current flows through the primary winding 118a. It will not be charged.

With the configuration described above, the vehicle-mounted battery charging device 100 reliably charges the auxiliary battery 5 when the converted voltage output from the vehicle-mounted battery charging device 100 is an overvoltage. can be stopped.

The output control unit 170 outputs voltage information indicating the voltage after voltage conversion output by the transforming unit 110 to the outside.
The voltage information is generated by the first overvoltage detector 120, for example.
For example, when the first overvoltage detector 120 generates voltage information, the output controller 170 outputs the voltage information generated by the first overvoltage detector 120 to the outside.
The voltage information output by the output control unit 170 is displayed on, for example, a display device (not shown).
A user such as an occupant of the vehicle 1 can grasp the state of the in-vehicle battery charging device 100 by confirming the voltage after voltage conversion output by the voltage transforming unit 110 indicated by the voltage information displayed on the display device. .

The operation of first overvoltage detector 120 according to the first embodiment will be described with reference to FIG.
FIG. 6 is a flow chart showing an example of the operation of the first overvoltage detector 120 according to the first embodiment.
The first overvoltage detection unit 120 repeatedly executes the processing of the flowchart until the first charging stop signal is output.
First, in step ST<b>601 , first voltage determination section 121 measures the converted voltage output from transformation section 110 .
Next, in step ST602, first voltage determination section 121 determines whether or not the voltage measured by first voltage determination section 121 in step ST601 exceeds the first voltage.

In step ST602, when the first voltage determination unit 121 determines that the voltage measured by the first voltage determination unit 121 does not exceed the first voltage in step ST601, in step ST603, the period determination unit 122 , reset the timer. After the processing of step ST603, the first overvoltage detection unit 120 ends the processing of the flowchart, returns to step ST601, and repeats the processing of the flowchart.
In step ST602, when the first voltage determination unit 121 determines that the voltage measured by the first voltage determination unit 121 in step ST601 exceeds the first voltage, in step ST604, the period determination unit 122 , to determine whether a timer has been started.

When period determination section 122 determines in step ST604 that the timer has not started, period determination section 122 starts the timer in step ST605. After the processing of step ST605, the first overvoltage detection unit 120 ends the processing of the flowchart, returns to step ST601, and repeats the processing of the flowchart.
When period determination section 122 determines in step ST604 that the timer has started, in step ST606 period determination section 122 determines whether the value indicated by the timer is equal to or greater than the value indicating the first period. determine whether

In step ST606, when period determining section 122 determines that the value indicated by the timer is not greater than or equal to the value indicating the first period, that is, period determining section 122 determines that the value indicated by the timer is less than the value indicating the first period. If so, the first overvoltage detection unit 120 ends the processing of the flowchart, returns to step ST601, and repeats the processing of the flowchart.
When period determining section 122 determines in step ST606 that the value indicated by the timer is equal to or greater than the value indicating the first period, in step ST607 first charging stop signal transmitting section 123 outputs the first charging stop signal to output After the process of step ST607, the first overvoltage detector 120 ends the process of the flowchart.

The operation of the second overvoltage detector 130 according to the first embodiment will be described with reference to FIG.
FIG. 7 is a flow chart showing an example of the operation of the second overvoltage detector 130 according to the first embodiment.
The second overvoltage detection unit 130 repeatedly executes the processing of the flowchart until the second overvoltage detection unit 130 outputs the second charge stop signal.
First, in step ST<b>701 , second voltage determination section 131 measures the voltage after voltage conversion output from transformation section 110 .
Next, in step ST702, second voltage determination section 131 determines whether or not the voltage measured by second voltage determination section 131 in step ST701 exceeds the second voltage.
In step ST702, when the second voltage determination section 131 determines that the voltage measured by the second voltage determination section 131 in step ST701 does not exceed the first voltage, the second overvoltage detection section 130 follows the flow chart , the second overvoltage detection unit 130 returns to step ST701 and repeats the process of the flowchart.
In step ST702, when the second voltage determination unit 131 determines that the voltage measured by the second voltage determination unit 131 in step ST701 exceeds the first voltage, in step ST703, the second charging stop signal The transmitter 132 outputs a second charging stop signal. After the process of step ST703, the second overvoltage detector 130 ends the process of the flowchart.

As described above, the in-vehicle battery charging device 100 includes the H bridge circuit 111, and the transforming unit 110 that converts the high voltage output from the in-vehicle drive battery 2 into the charging voltage of the auxiliary battery 5. , measuring the period during which the voltage after voltage conversion output by the voltage transforming unit 110 continues to exceed the first voltage higher than the charging voltage of the auxiliary battery 5, and when the period continues for a predetermined period, The first overvoltage detection unit 120 that outputs the first charging stop signal and the voltage after voltage conversion output by the transformation unit 110 are measured, and when the voltage exceeds the second voltage higher than the first voltage, the 2 During the period until the second overvoltage detection unit 130 that outputs the charge stop signal and the first charge stop signal is received, the first system 111a of the first system 111a and the second system 111b that the H bridge circuit 111 has and stops driving the first system 111a when the first charging stop signal is received, and the H bridge circuit 111 has and a second driving unit 150 that drives the second system 111b out of the first system 111a and the second system 111b and stops driving the second system 111b when the second charging stop signal is received. .
With this configuration, charging of the auxiliary battery 5 can be reliably stopped when the converted voltage output from the in-vehicle battery charging device 100 is an overvoltage.

In-vehicle battery charging apparatus 100 is configured such that the failure rate of second overvoltage detection section 130 is lower than the failure rate of first overvoltage detection section 120 . For example, in the on-vehicle battery charging device 100, the second overvoltage detection unit 130 is configured by a discrete circuit, so that the failure rate of the second overvoltage detection unit 130 is lower than the failure rate of the first overvoltage detection unit 120. configured to be
With this configuration, when the converted voltage output from vehicle-mounted battery charging device 100 is overvoltage, first overvoltage detection unit 120 malfunctions, and first overvoltage detection unit 120 detects overvoltage. Since the second overvoltage detector 130 can output the second charge stop signal even if the first charge stop signal cannot be output, the charging of the auxiliary battery 5 can be stopped reliably.

Also, in the vehicle-mounted battery charging device 100, the first overvoltage detection section 120 is configured by an integrated circuit.
By configuring in this way, the size of the first overvoltage detector 120 can be reduced.

In addition to the configuration described above, vehicle-mounted battery charging apparatus 100 also includes output control section 170 that outputs voltage information indicating the voltage after voltage conversion output from transformation section 110 to the outside.
With this configuration, a user such as an occupant of the vehicle 1 can confirm the voltage after voltage conversion output by the voltage transforming unit 110 indicated by the voltage information displayed on the display device, thereby enabling the on-vehicle battery charging device 100 to operate. status can be grasped.

It should be noted that, within the scope of the invention, any component of the embodiment can be modified or any component can be omitted from the embodiment.

Reference Signs List 1 vehicle, 2 vehicle drive battery, 3 inverter, 4 motor, 5 auxiliary battery, 6 auxiliary device, 100 vehicle battery charger, 110 transformer, 111 H bridge circuit, 111a first system, 111b second system , 112 transformer, 113, 114 diode, 115 inductor, 116 capacitor, 117a, 117b, 117c, 117d switching element, 118a primary winding, 118b secondary winding, 120 first overvoltage detection unit, 121 first voltage determination unit , 122 period determination unit, 123 first charge stop signal transmission unit, 130 second overvoltage detection unit, 131 second voltage determination unit, 132 second charge stop signal transmission unit, 140 first drive unit, 150 second drive unit, 160 drive control unit, 170 output control unit.

Claims (6)

a transformer unit having an H-bridge circuit for converting a high voltage output from an in-vehicle drive battery into a charging voltage of an auxiliary battery;
Measure the voltage after voltage conversion output by the transforming unit, measure the period during which the voltage continues to exceed a first voltage higher than the charging voltage of the auxiliary battery, and measure the period during which the period is a predetermined period a first overvoltage detection unit that outputs a first charging stop signal when continuing;
a second overvoltage detection unit that measures the voltage after voltage conversion output by the transforming unit and outputs a second charging stop signal when the voltage exceeds a second voltage higher than the first voltage;
During the period until the first charging stop signal output by the first overvoltage detection unit is received, the first system out of the first system and the second system of the H bridge circuit is driven, and the first charging is performed. a first driving unit that stops driving the first system when a stop signal is received;
During the period until the second charging stop signal output by the second overvoltage detection unit is received, of the first system and the second system included in the H bridge circuit, the second system is driven, and the second charging is performed. a second driving unit that stops driving the second system when a stop signal is received;
An in-vehicle battery charging device comprising: 2. The on-vehicle battery charging device according to claim 1, wherein a failure rate of said second overvoltage detection section is lower than a failure rate of said first overvoltage detection section. 3. The on-vehicle battery charging device according to claim 2, wherein the second overvoltage detector is configured by a discrete circuit. 3. The vehicle-mounted battery charging device according to claim 2, wherein the first overvoltage detector is configured by an integrated circuit. 5. The in-vehicle battery charging device according to any one of claims 1 to 4, further comprising: an output control section for outputting to the outside voltage information indicating the voltage after voltage conversion outputted by the transforming section. . The first overvoltage detection unit has a function of generating the voltage information indicating the voltage after voltage conversion output by the transformation unit,
The vehicle-mounted battery charging device according to claim 5, wherein the output control section outputs the voltage information generated by the first overvoltage detection section to the outside.

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