JP2009118608A - Battery charger - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a battery charger protective circuit capable of preventing an abnormal current from flowing from a reversely connected battery to a battery charger when the terminals of a plurality of batteries such as a main battery and/or a sub-battery are connected to the battery charger so as to have polarity reverse to that of the battery charger. <P>SOLUTION: This battery charger protective circuit has: a battery charger for charging a first battery and a second battery; a voltage detection means, a circuit interposed between the first and second batteries and suppressing an abnormal current flowing when the batteries are reversely connected to the battery charger, which outputs a voltage corresponding to the potential difference between a first power supply terminal and a ground terminal and between a second power supply terminal and the ground terminal in the battery charger, as a first detection voltage and a second detection voltage; and switch means interposed between each of the terminals of the battery charger and each of terminals of the first and second batteries, and turning ON/OFF in response to the voltage value of the first and second detection voltages. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a battery charger having a function of protecting a battery charger from failure when the positive and negative polarities of battery electrodes are erroneously connected to the battery charger.

In general, a battery charger has a power supply terminal and a ground terminal for charging the battery, and the battery is properly charged by connecting the positive terminal of the battery to the power terminal and connecting the negative terminal to the ground terminal. It has a configuration in which a current is passed and a charging operation is performed.
However, when the negative terminal of the battery is connected to the battery charger and the positive terminal of the battery is connected to the ground terminal of the battery charger, that is, when the polarity of the potential relationship is connected in the positive and negative directions, an abnormal current flows inside the battery charger, It may cause failure.

As shown in FIG. 3, in the case of an in-vehicle battery charger corresponding to two types of batteries, for example, a main battery B1 and a sub-battery B2, either the main battery or the sub-battery is determined from the structural characteristics of the battery charger. However, when the polarity of the battery terminal is reversed and connected to the battery charger, a short-circuit current flows through the rectifier diode 2 that rectifies the current from the generator 1, and the heat causes the battery charger to fail.
In order to protect the battery charger in response to the above-described erroneous connection, fuses H1 and H2 are provided between the battery and the battery charger, respectively, and the fuses H1 and H2 are caused by an abnormal current flowing when the connection is incorrect. In order to prevent the battery charger from being destroyed by fusing, an abnormal current is prevented from flowing over a long period of time (for example, Patent Document 1).
JP 2000-50514 A

However, in the protection method shown in Patent Document 1, when either or both of the batteries are mistakenly connected in reverse and the fuses H1 and H2 are blown by the flowing abnormal current, the fuse is blown to start the vehicle. There is a disadvantage that the fuses H1 and H2 must be replaced. Furthermore, since the current flows until the fuses H1 and H2 are blown, the possibility of destruction cannot be completely removed.
Therefore, in the protection method shown in Patent Document 1, it is necessary to provide fuses H1 and H2 for both the main battery and the sub-battery, and there is a possibility that both of them are connected in reverse, and the characteristics corresponding to the two are different. There is always a need to have a fuse of a kind.

  The present invention has been made in view of such circumstances, and when a plurality of batteries, for example, main battery and / or sub-battery terminals are connected so that the polarity is reversed with respect to the battery charger, It is an object of the present invention to provide a battery charger protection circuit that prevents abnormal current from flowing from a connected battery to a battery charger.

  The battery charger of the present invention is a battery charger that charges a first battery and a second battery, and a generator, a rectifier that rectifies an AC voltage output from the generator, and outputs a DC voltage; A control circuit for controlling the voltage value of the DC voltage to be a first charging voltage and a second charging voltage for charging the first battery and the second battery, respectively, and a first charging voltage in the battery charger Corresponding to the respective potential differences when the first and second batteries are connected between the first power supply terminal for outputting the first power supply terminal, the second power supply terminal for outputting the second charging voltage, and the ground terminal. Voltage detection means for outputting the detected voltage as a first detection voltage and a second detection voltage, each terminal of the battery charger, and each terminal of the first and second batteries, 1 and 2nd detection voltage And having a switching means for turning on / off according to the voltage value.

  In the battery charger of the present invention, the voltage detecting means is provided between each of the first power supply terminal and the ground terminal and between the second power supply terminal and the ground terminal, each of which connects a plurality of resistors in series. The first and second detection voltages used for detecting whether or not the battery is normally connected are output from one of connection points of the respective resistors connected in series. It is set to do.

  The battery charger according to the present invention includes a first switch in which the switch means is interposed between a first power supply terminal of the battery charger and a terminal of the first battery, and a second power supply of the battery charger. A first switch indicating that the first battery is normally connected with the first detection voltage. If the second threshold is exceeded, the first switch is turned on, and if the second detection voltage exceeds the second threshold indicating that the second battery is normally connected, the second switch Is turned on.

  In the battery charger of the present invention, the first switch is a P-channel type MOS transistor, the first detection voltage is input to the gate, and the source is connected to the first power supply terminal of the battery charger. The drain is connected to the positive terminal of the first battery, the second switch is a P-channel MOS transistor, the second detection voltage is input to the gate, and the source is the battery charge. And a drain connected to the positive terminal of the second battery.

  In the battery charger of the present invention, the first switch is a first IGBT, the first detection voltage is input to a gate, a collector is connected to a first power supply terminal of the battery charger, The emitter is connected to the positive terminal of the first battery, the second switch is a second IGBT, the second detection voltage is input to the gate, and the collector is the second of the battery charger. Connected to the positive terminal of the second battery, provided in parallel with the first IGBT, connected to the positive terminal of the first battery, and connected to the positive terminal of the first battery. The first diode connected to the first power supply terminal of the battery charger and the second IGBT are provided in parallel, the anode is connected to the positive terminal of the second battery, and the cathode is connected to the battery. Characterized in that it comprises a second diode and a further connected to the second power supply terminal Terri charger.

  In the battery charger of the present invention, the switch means is provided between a connection point of the negative terminal of each of the first battery and the second battery and a ground terminal of the battery charger, and the voltage detection means However, the first detection voltage exceeds a first threshold value indicating that the first battery is normally connected, and the second detection voltage indicates that the second battery is normally connected. When the second threshold value is exceeded, the switch means is turned on.

  In the battery charger of the present invention, when the voltage detection unit is not connected to the second battery, the first detection voltage indicates that the first battery is normally connected. The switch means is turned on when the value exceeds.

  In the battery charger of the present invention, the switch means is an N-channel MOS transistor, the first detection voltage is input to the gate, the source is connected to the ground terminal of the battery charger, and the drain is the first The first and second batteries are connected to terminals on the negative electrode side.

  In the battery charger of the present invention, the switch means is an IGBT, the first detection voltage is input to a gate, an emitter is connected to a ground terminal of the battery charger, and a collector is the first and second collectors. It is connected to the terminal on the negative electrode side of the battery.

As described above, according to the present invention, in a battery charger for connecting a plurality of batteries used as a power source, even if any battery is connected with the polarity reversed, the battery is connected via the rectifier diode. Therefore, it is possible to prevent an abnormal current from flowing from the battery to the charger, so that the fuse is not blown by the abnormal current as in the conventional example, and it is not necessary to replace the fuse by reverse connection of the battery.
Further, according to the present invention, it is not necessary to prepare spare fuses corresponding to a plurality of batteries in the battery charger.

According to the present invention (Claim 3), a MOS transistor is used as the switch means, that is, a p-channel MOS transistor is used as a MOS transistor for connecting the positive side of the generator and the + side terminal of each battery. Since it is used, there is little voltage drop, and when it is normally connected, the voltage generated by the generator can be efficiently applied to each battery.
Similarly, according to the present invention (Claim 6), a MOS transistor is used for the switch means, that is, the negative terminal of the generator and the negative terminals of a plurality of batteries (the negative terminals of the batteries are all common). Since the n-channel MOS transistor is used, the voltage drop is small, and the voltage generated by the generator is efficiently applied to the battery when connected normally. The electrical connection between the generator and each battery can be disconnected with only one MOS transistor, and the manufacturing cost can be reduced.

<First Embodiment>
Hereinafter, a battery charger according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration example of the battery charger according to the embodiment.
In this figure, each of the battery B1 and the battery B2 is a battery having a different power supply voltage.
The generator 1 generates charging power for charging the battery B1 and the battery B2, and in the case of a car, the generator 1 uses the rotation of a crankshaft or a fan belt to generate an alternating voltage.

The rectifier diode 2 includes a series connection of a diode D1 and a diode D2, a series connection of a diode D3 and a diode D4, and a series connection of a diode D5 and a diode D6 in parallel. The diodes D7, D8, and D9 are connected so that the direction is the forward direction and the forward direction is connected to the terminal 13 from the connection point between the respective directly connected diodes, and the diodes D1 and D2 are connected in series. The AC voltage (three-phase AC voltage in the present embodiment) input from the generator 1 is rectified at each connection point of the diodes in the diode D3 and the diode D4, and the charging voltage VB for the battery B is rectified. Is output.
The charging voltage adjusting unit 3 is composed of, for example, thyristors T1, T2, and T3. On / off control of the thyristors T1, T2, and T3 according to a control signal from the control circuit 4 (at the connection point 14 in the on state). The voltage value of the charging voltage VB is controlled by adjusting the voltage value of the connection point between the diodes of the series diode pairs connected in parallel in the rectifier diode 2.
The control circuit 4 detects the voltage values of the charging voltage VB1 and the charging voltage VB2, and outputs the control signal for adjusting the voltage value to the charging adjusting unit 3 so as to be a preset voltage.

The charger protection unit 5 is a characteristic configuration of the present invention, and when one of the batteries B1 and B2 is connected with the reverse polarity, the reversely connected battery is connected to the rectifier diode 2 above. Do not connect.
Hereinafter, the configuration of the charge protection circuit 5 will be described in detail.
The charge protection unit 5 includes p-channel MOS transistors M1 and M2 and resistors R11, R12, R21, and R22.
The resistor R11 and the resistor R12 are connected in series between a terminal 12 on the + side (anode side) that outputs the charging voltage VB1 in the rectifier diode 2 and a terminal 14 on the − side (cathode side) of the rectifier diode 2. Yes. Here, a divided voltage (first detection voltage) corresponding to the resistance ratio is output from the connection point S <b> 1 as a voltage corresponding to the voltage applied to the + side terminal 12 and the − side terminal 14.

The MOS transistor M1 has a drain connected to the positive terminal 12 of the rectifier diode 2, a gate connected to the connection point S1 of the resistors R11 and R12, and a source connected to a terminal T11 connected to the positive terminal of the battery B1. It is connected. When the battery B1 is normally connected to the terminal T11 and the terminal T12, the resistance ratio between the resistor R11 and the resistor R12 exceeds the threshold voltage of the MOS transistor M1 at the connection point S1 (the voltage at which the MOS transistor M1 is turned on). Is set to be generated (a first threshold voltage).
Here, in the normal connection state, the battery B1 has a positive terminal connected to the terminal T11 and a negative terminal connected to a terminal T12 connected to the negative terminal 14 of the rectifier diode 2.
The resistor R21 and the resistor R22 are connected in series between the + side terminal 13 that outputs the charging voltage VB2 in the rectifier diode 2 and the − side terminal 14 of the rectifier diode 2. A divided voltage (second detection voltage) corresponding to the resistance ratio is output from the connection point S2 as a voltage corresponding to the voltage applied to the + side terminal 13 and the-side terminal 14.

The MOS transistor M2 has a drain connected to the positive terminal 13 of the rectifier diode 2, a gate connected to the connection point S2 of the resistors R21 and R22, and a source connected to a terminal T21 connected to the positive terminal of the battery B2. It is connected. When the battery B2 is normally connected to the terminals T21 and T22, the resistance ratio of the resistors R21 and R22 exceeds the threshold voltage of the connection point S12 MOS transistor M2 (exceeds the voltage at which the MOS transistor M2 is turned on). ) Voltage (second threshold voltage) is generated.
Here, in the normal connection state, the battery B2 has a positive terminal connected to the terminal T21 and a negative terminal connected to the terminal T12.
Further, an IGBT (Insulated Gate Bipolar Transistor) can be used in place of the MOS transistors M1 and M2.
In this case, the IGBT replaced with the MOS transistor M1 has a collector connected to the + side terminal 12 of the rectifier diode 2, a gate connected to the connection point S1 of the resistor R11 and the resistor R12, and an emitter connected to the + side terminal of the battery B1. It is connected to a terminal T11 to be connected. Further, the IGBT that replaces the MOS transistor M2 has a collector connected to the + side terminal 13 of the rectifier diode 2, a gate connected to the connection point S2 of the resistors R21 and R22, and an emitter connected to the + side terminal of the battery B2. Connected to the terminal T21. In this case, instead of the parasitic diodes D1 and D2, it is necessary to connect the diodes in parallel with the IGBTs in the same direction as in FIG.

Next, operation | movement of the charge protection circuit 5 in the battery charger in this embodiment is demonstrated using FIG. When the batteries B1 and B2 are attached, the vehicle is stopped and the generator 1 is not operating.
[When both batteries B1 and B2 are normally connected to the battery charger]
Since the positive terminal of the battery B1 is connected to the terminal T11 and the negative terminal is connected to the terminal T12, the positive potential of the battery B1 is connected in series via the parasitic diode D1 of the MOS transistor M1 and the resistors R11 and R12. In the meantime, a divided voltage VS1 (first detection voltage corresponding to the potential difference between the terminal T11 and the terminal T12) corresponding to the ratio of the resistance values of these resistors is generated at the connection point S1.

At this time, since the generator 1 is not activated, the voltage at the terminal T2 is substantially the same as the potential on the negative side of the batteries B1 and B1, and the MOS transistor M1 has a source voltage and a drain voltage that are higher than the gate voltage. Since it is high, the threshold voltage is exceeded and the on state is entered.
However, since a + side voltage is applied to the terminal 12 and a − side voltage is applied to the terminal 14, a reverse voltage is applied to the rectifier diode 2 and no abnormal current flows.

Similarly, since the positive terminal of the battery B2 is connected to the terminal T21 and the negative terminal is connected to the terminal T22, the positive potential of the battery B2 is connected in series via the parasitic diode D2 of the MOS transistor M2. The divided voltage VS2 (second detection voltage corresponding to the potential difference between the terminal T21 and the terminal T22) corresponding to the ratio of the resistance values of these resistors is generated at the connection point S2.
At this time, since the generator 1 is not activated, the voltage at the terminal 12 is almost the same as the negative potential of the batteries B1 and B1, and the MOS transistor M2 has a source voltage and a drain voltage that are higher than the gate voltage. Since it is high, the threshold voltage is exceeded and the on state is entered.
However, since a + side voltage is applied to the terminal 13 and a − side voltage is applied to the terminal 14, a reverse voltage is applied to the rectifier diode 2 and no abnormal current flows.

[When battery B1 is reversed and battery B2 is normally connected to the battery charger]
Since the negative terminal of the battery B1 is connected to the terminal T11 and the positive terminal is connected to the terminal T12, the negative potential of the battery B1 is applied to the terminal T11.
However, due to the reverse voltage, no current flows through the parasitic diode D1 of the terminal MOS transistor M1, no voltage is applied between the resistors R11 and R12 connected in series, and the divided voltage VS1 is not generated at the connection point S1.
At this time, since the generator 1 is not activated, the voltage at the terminal 12 is substantially the same as the negative potential of the battery B2, and the gate voltage of the MOS transistor M1 is higher than the source voltage and the drain voltage. Then, the threshold voltage is not exceeded and the device is turned off.
Therefore, a negative voltage is applied to the terminal 12, a positive voltage is applied to the terminal 14, and a forward voltage is applied to the rectifier diode 2. However, the MOS transistor M1 is turned off, and the parasitic diode D1 is Since it is in the reverse direction, no abnormal current flows.

On the other hand, since the + side terminal of the battery B2 is connected to the terminal T21 and the-side terminal is connected to the terminal T22, the + potential of the battery B2 is connected to the resistor R21 connected in series via the parasitic diode D2 of the MOS transistor M2. A divided voltage VS2 corresponding to the ratio between the resistance values of the resistors R22 is generated at the connection point S2.
At this time, since the generator 1 is not activated, the voltage at the terminal 12 is almost the same as the potential on the negative side of the batteries B1 and B1, and the MOS transistor M2 has a gate voltage higher than the source voltage and the drain voltage. Since it is low, the threshold voltage is exceeded and the on state is entered.
However, since a + side voltage is applied to the terminal 13 and a − side voltage is applied to the terminal 14, a reverse voltage is applied to the rectifier diode 2 and no abnormal current flows.

[When battery B1 is connected normally and battery B2 is connected to the battery charger]
Since the positive terminal of the battery B1 is connected to the terminal T11 and the negative terminal is connected to the terminal T12, the positive potential of the battery B1 is connected in series via the parasitic diode D1 of the MOS transistor M1 and the resistors R11 and R12. The divided voltage VS1 corresponding to the ratio of the resistance values of these resistors is generated at the connection point S1.
At this time, since the generator 1 is not activated, the voltage at the terminal 12 is substantially the same as the potential on the negative side of the batteries B1 and B1, and the MOS transistor M1 has a gate voltage higher than the source voltage and the drain voltage. Since it is low, the threshold voltage is exceeded and the on state is entered.
However, since a + side voltage is applied to the terminal 12 and a − side voltage is applied to the terminal 14, a reverse voltage is applied to the rectifier diode 2 and no abnormal current flows.

On the other hand, since the negative terminal of battery B2 is connected to terminal T21 and the positive terminal is connected to terminal T22, the negative potential of battery B2 is applied to terminal T21.
However, due to the reverse voltage, no current flows through the parasitic diode D2 of the terminal MOS transistor M2, no voltage is applied between the resistors R21 and R22 connected in series, and the divided voltage VS2 is not generated at the connection point S2.
At this time, since the generator 1 is not activated, the voltage at the terminal T13 is almost the same as the negative potential of the battery B1, and the gate voltage of the MOS transistor M2 is higher than the source voltage and the drain voltage. Then, the threshold voltage is not exceeded and the device is turned off.
Therefore, a negative voltage is applied to the terminal 13, a positive voltage is applied to the terminal 14, and a forward voltage is applied to the rectifier diode 2, but the MOS transistor M2 is turned off and the parasitic diode D2 is Since it is in the reverse direction, no abnormal current flows.

[When both battery B1 and battery B2 are connected to the battery charger in reverse]
When the battery B1 is connected in reverse and the battery B2 is connected in reverse, both the MOS transistors M1 and M2 are turned off, and the reverse voltage is applied to the parasitic diodes D1 and D2. Current does not flow when applied.
Therefore, even when both of the batteries B1 and B2 are connected to the battery charger with the voltage polarity reversed, no abnormal current flows through the rectifier diode 2 of the battery charger.

<Second Embodiment>
Hereinafter, a battery charger according to a second embodiment of the present invention will be described with reference to the drawings. FIG. 2 is a block diagram showing a configuration example of the battery charger according to the embodiment.
In this figure, each of the battery B1 and the battery B2 is a battery having a different power supply voltage.
Since the generator 1, the rectifier diode 2, the charging voltage adjustment unit 3 and the control circuit 4 are the same as those in the first embodiment, description thereof will be omitted.

The charger protection unit 5 is a characteristic configuration of the present invention. When either one of the batteries B1 and B2 is connected with the opposite polarity, both the batteries B1 and B2 are connected to the rectifier diode 2. Do not do.
Hereinafter, the configuration of the charge protection circuit 5 will be described in detail.
The charge protection unit 5 includes an n-channel MOS transistor M3, npn bipolar transistors BT1 and BT2, pnp bipolar transistors BT3, diodes D3 and D4, resistors R31, R32, R33, R34, R41, R42, R43, and R44.

The resistor R31 and the resistor R32 are connected in series between the + side terminal 12 that outputs the charging voltage VB1 in the rectifier diode 2 and the − side terminal 14 of the rectifier diode 2. Here, a divided voltage (first detection voltage) corresponding to the resistance ratio is output from the connection point S3 as a voltage corresponding to the voltage applied to the + side terminal 12 and the − side terminal 14. .
The bipolar transistor BT3 has a collector connected to the terminal 12 and an emitter connected to the negative terminal 14 via a series connection of resistors R33 and R44.
The MOS transistor M3 is interposed between the terminal 12, the terminal T12 and the terminal T22, the source is connected to the terminal 14, the drain is connected to the terminal T12 and the terminal T22, and the gate is a resistor R31 and a resistor R32. Are connected to the connection point S3. When the battery B1 is normally connected to the terminal T11 and the terminal T12, the resistance ratio between the resistor R31 and the resistor R32 exceeds the threshold voltage of the MOS transistor M3 at the connection point S3 (the voltage at which the MOS transistor M3 is turned on). Is set to be generated (a first threshold voltage).

  The bipolar transistor BT1 has a collector connected to the connection point S3, an emitter connected to the drain of the MOS transistor M3, and a base connected to the connection point S4 of the resistors R33 and R34. The resistance ratio between the resistor R33 and the resistor R34 is such that when the bipolar transistor BT3 is turned on and a current flows, a base current that turns on the bipolar transistor BT1 flows at the connection point S4 (the bipolar transistor BT1 is turned on). The voltage is set to be generated.

A resistor R41 and a resistor R42 are connected in series, one end of the resistor R41 is connected to the terminal 13, and the other end of the resistor R41 is connected to one end of the resistor R42 at the connection point S5. The end is connected to the cathode of the diode D4, and the anode of the diode D4 is connected to the emitter of the bipolar transistor BT1. Here, when a forward current flows through the diode D4 as a voltage corresponding to the voltage applied to the positive terminal 13 and the negative terminal 14 via the diode D4, the resistance ratio is determined from the connection point S5. The divided voltage (second detection voltage) is output.
The resistance ratio between the resistor R41 and the resistor R42 is such that when the battery B2 is connected in reverse to the terminals T21 and T22, a base current that turns on the bipolar transistor BT2 flows to the connection point S5 (the bipolar transistor BT2 is turned on). A voltage (second threshold voltage) exceeding the voltage to be in a state is set to be generated with respect to the emitter voltage. That is, when the battery B2 is normally connected, a voltage similar to the emitter voltage is generated at the connection point S5, so that the bipolar transistor BT2 is not turned on.

A resistor R43 and a resistor R44 are connected in series, one end of the resistor R43 is connected to the terminal 12, and the other end of the resistor R43 is connected to one end of the resistor R44 at a connection point S6. The other end of the resistor R44 is connected to the anode of the diode D3, and the cathode of the diode D3 is connected to the collector of the bipolar transistor BT2. The resistance ratio between the resistor R43 and the resistor R44 is such that when the current flows when the bipolar transistor BT2 is turned on, a base current that turns on the bipolar transistor BT3 flows at the connection point S6 (the bipolar transistor BT3 is turned on). The voltage is set to be generated.
The bipolar transistor BT2 has a base connected to the connection point S5 and an emitter connected to the terminal 13. The base of the bipolar transistor BT3 is connected to the connection point S6.
Further, an IGBT (Insulated Gate Bipolar Transistor) can be used instead of the MOS transistor M3.
In this case, an IGBT replacing the MOS transistor M3 is inserted between the terminal 12 and the terminal T14, the emitter is connected to the terminal 14, the collector is connected to the terminal T12 and the terminal T22, and the gate is the resistor R31. And the connection point S3 of the resistor R32. In this case, instead of the parasitic diode D5, it is necessary to connect the diodes in parallel with the IGBTs in the same direction as in FIG.

Next, operation | movement of the charge protection circuit 5 in the battery charger in this embodiment is demonstrated using FIG. When the batteries B1 and B2 are attached, the vehicle is in a stopped state as in the first embodiment, and the generator 1 is not operating.
[When both batteries B1 and B2 are normally connected to the battery charger]
Since the positive terminal of the battery B1 is connected to the terminal T11 and the negative terminal is connected to the terminal T12, a voltage corresponding to the resistance value ratio of the resistor R31 and the resistor R32 (first detection voltage) ) Occurs.
Further, the positive terminal of the battery B2 is connected to the terminal T21 and the negative terminal is connected to the terminal T22, but the diode D4 is connected in the reverse direction with respect to the voltage. Therefore, no current flows through the series connection of the resistor R31 and the resistor R32, and the connection point S5 (that is, the base of the bipolar transistor BT2) and the emitter of the bipolar transistor BT2 are at the same potential (second detection voltage). No current flows through the bipolar transistor BT2.

Therefore, no current flows through the series connection of the resistor R43 and the resistor R44, the connection point S6 (that is, the base of the bipolar transistor BT3) and the emitter of the bipolar transistor BT3 are at the same potential, and no current flows through the bipolar transistor BT3. Not flowing.
Therefore, no current flows through the resistors R33 and R34 connected in series, the potential at the connection point S4 is the same as that of the negative side of the batteries B1 and B2, and the bipolar transistor BT1 remains off.
Therefore, a divided voltage proportional to the resistance values of the resistors R31 and R32 is generated at the connection point S3. The resistance ratio between the resistor R31 and the resistor R32 is set so that when the battery B1 is normally connected to the terminal T11 and the terminal T12, a voltage exceeding the threshold voltage of the MOS transistor M3 is generated at the connection point S3. Yes.
Therefore, the MOS transistor M3 is turned on because a positive voltage is applied to the gate, and the terminal 14 and the terminals T12 and T22 are brought into conduction.

[When battery B1 is reversed and battery B2 is normally connected to the battery charger]
Since the negative terminal of battery B1 is connected to terminal T11 and the positive terminal is connected to terminal T12, the negative potential of battery B1 is applied to terminal T11.
For this reason, when the voltage of the battery B1 is applied to the resistor R31 and the resistor R32 inserted between the terminal 12 and the terminal 14, a negative voltage is applied to the terminal 12, and a positive voltage is applied to the terminal 14 side. This voltage is applied.
As a result, the voltage applied to the gate of the MOS transistor M3, that is, the voltage generated at the connection point S3 becomes lower than the source of the MOS transistor M3, and the MOS transistor M3 is turned off.
As a result, since the terminal T12 and the terminal 14 are disconnected, no abnormal current flows between the positive terminal and the negative terminal of the battery B1 via the rectifier diode 2. At this time, the terminal T22 and the terminal 14 are also disconnected.

[When battery B1 is connected normally and battery B2 is connected to the battery charger]
Since the negative terminal of battery B2 is connected to terminal T21 and the positive terminal is connected to terminal T22, the negative potential of battery B2 is applied to terminal T21.
Therefore, since the voltage at the terminal T22 becomes higher than the voltage at the terminal T21, a forward current flows through the diode D4, and a potential higher than that at the terminal T21 is generated at the connection point S5 between the resistor R42 and the resistor R41.
That is, a voltage higher than that of the source is applied to the base of the bipolar transistor BT2, and the bipolar transistor BT2 is turned on.

Thereby, since the battery B1 is normally connected, the voltage at the terminal T12 is higher than the voltage at the terminal T13. Therefore, when the bipolar transistor BT2 is turned on, the diode D3 is sequentially connected to the diode D3 via the resistor R43 and the resistor R44. Directional current flows.
For this reason, since the voltage at the connection point S6, that is, the voltage applied to the base of the bipolar transistor BT3 is lower than the collector voltage, the base current flows, the bipolar transistor BT3 is turned on, and the collector current flows.
When the collector current of the bipolar transistor BT3 flows through the resistor R33 and the resistor R34, a divided voltage opposite to the resistance value ratio of the resistor R33 and the resistor R34 is generated at the connection point S4.

When the divided voltage is generated at the connection point S4, the bipolar transistor BT1 is turned on when the voltage applied to the base becomes larger than the voltage of the emitter, causing the base current to flow.
Thereby, when the battery B1 is normally connected, the divided voltage generated at the connection point S3 of the resistor R31 and the resistor R32 is lowered to the same voltage as that of the terminal T12 by the bipolar transistor BT1.
Accordingly, since the voltage applied to the gate of the MOS transistor M3 (voltage at the connection point S3) is the same potential as the drain and source of the MOS transistor M3, the MOS transistor M3 is turned off.
As a result, since the terminal T22 and the terminal 14 are disconnected, no abnormal current flows between the positive terminal and the negative terminal of the battery B2 via the rectifier diode 2. At this time, the terminal T12 and the terminal 14 are also disconnected.

[Battery B1 and Battery B2 are both connected to the battery charger in reverse]
In this case, since it is the same as “the case where the battery B1 is reversed and the battery B2 is normally connected to the battery charger” described above, the description is omitted.
In any state where the polarities are connected in reverse, the diode D5 of the MOS transistor M3 is in the opposite direction to the abnormal current. Therefore, the abnormal current cannot flow through the diode D5.

  As described above, in the second embodiment, when either one of the two batteries B1 and B2 is connected with the voltage polarity reversed with respect to the terminal of the battery charger, the MOS transistor M3 is turned off. By setting the state, the connection between the negative side terminals T12 and T22 of both batteries and the terminal T14 is cut off, so that no abnormal current flows through the rectifier diode 2.

It is a block diagram which shows the structural example of the battery charging circuit using the battery charging protection circuit by the 1st Embodiment of this invention. It is a block diagram which shows the structural example of the battery charging circuit using the battery charging protection circuit by the 2nd Embodiment of this invention. It is a block diagram which shows the structure of the conventional battery charging circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Generator 2 ... Rectifier diode 3 ... Charging voltage adjustment part 4 ... Control circuit 12, 13, 14, T11, T12, T21, T22 ... Terminal B1, B2 ... Battery BT1, BT2, BT3 ... Bipolar transistor D1, D2, D3, D4, D5 ... Diodes M1, M2, M3 ... MOS transistors R11, R12, R21, R22 ... Resistors R31, R32, R33, R34, R41, R42, R43, R44 ... Resistors S1, S2, S3, S4, S5 , S6: Connection point

Claims (9)

A battery charger for charging the first battery and the second battery;
A generator,
A rectifier that rectifies the AC voltage output from the generator and outputs a DC voltage;
A control circuit for controlling the voltage value of the DC voltage to be a first charging voltage and a second charging voltage for charging the first battery and the second battery, respectively;
The first and second batteries are connected between the first power supply terminal that outputs the first charging voltage and the second power supply terminal that outputs the second charging voltage and the ground terminal in the battery charger. Voltage detection means for outputting a voltage corresponding to each potential difference when connecting the first detection voltage and the second detection voltage,
Each terminal of the battery charger; and switch means that is inserted between the terminals of the first and second batteries and that is turned on / off according to the voltage values of the first and second detection voltages. A battery charger characterized by that.   The voltage detecting means is provided between each of the first power supply terminal and the ground terminal, and between the second power supply terminal and the ground terminal, each of which is constituted by a voltage dividing circuit in which a plurality of resistors are connected in series. And that the first and second detection voltages used for detecting whether or not the battery is normally connected are set to be output from one of the connection points of the respective resistors connected in series. The battery charger according to claim 1. A first switch interposed between the first power supply terminal of the battery charger and the terminal of the first battery;
A second switch interposed between the second power supply terminal of the battery charger and the terminal of the second battery;
When the voltage detection means exceeds the first threshold value indicating that the first battery is normally connected, the first detection voltage is turned on, and the second detection voltage 3. The battery charger according to claim 1, wherein when the first threshold value exceeds a second threshold value indicating that the second battery is normally connected, the second switch is turned on. 4. . The first switch is a P-channel MOS transistor, the first detection voltage is input to the gate, the source is connected to the first power supply terminal of the battery charger, and the drain is the first power supply. Connected to the positive terminal of the battery,
The second switch is a P-channel MOS transistor, the second detection voltage is input to the gate, the source is connected to the second power supply terminal of the battery charger, and the drain is the second The battery charger according to claim 3, wherein the battery charger is connected to a positive terminal of the battery. The first switch is a first IGBT, the first detection voltage is input to a gate, a collector is connected to a first power supply terminal of the battery charger, and an emitter is connected to the first battery. Connected to the positive terminal,
The second switch is a second IGBT, the second detection voltage is input to the gate, the collector is connected to the second power supply terminal of the battery charger, and the emitter is the second battery. Connected to the positive terminal,
A first diode provided in parallel with the first IGBT, having an anode connected to a positive terminal of the first battery and a cathode connected to a first power supply terminal of the battery charger;
A second diode provided in parallel with the second IGBT, having an anode connected to a positive terminal of the second battery and a cathode connected to a second power supply terminal of the battery charger; The battery charger according to claim 3. The switch means comprises:
Provided between the connection point of the negative terminal of each of the first battery and the second battery and the ground terminal of the battery charger;
The voltage detecting means has the first detection voltage exceeding a first threshold indicating that the first battery is normally connected, and the second detection voltage is normally connected to the second battery. 3. The battery charger according to claim 1, wherein the switch unit is turned on when a second threshold value indicating that the threshold value is exceeded.   When the voltage detection means is not connected to the second battery and the first detection voltage exceeds a first threshold value indicating that the first battery is connected normally, the switch 7. The battery charger according to claim 6, wherein the means is turned on.   The switch means is an N-channel MOS transistor, the first detection voltage is input to the gate, the source is connected to the ground terminal of the battery charger, and the drain is the negative electrode of the first and second batteries. The battery charger according to claim 6, wherein the battery charger is connected to a terminal on the side.   The switch means is an IGBT, the first detection voltage is input to the gate, the emitter is connected to the ground terminal of the battery charger, and the collector is connected to the negative terminal of the first and second batteries. The battery charger according to claim 6, wherein the battery charger is provided.

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