Assembled battery total voltage detection circuit

1. An assembled battery total voltage detection circuit for detecting a total voltage of an assembled battery configured by connecting a plurality of batteries, comprising:

a main control circuit that includes an A/D converter operating with a positive single power supply;

a divider resistor connected between a plus terminal and a minus terminal of the assembled battery insulated from the main control circuit;

a differential amplifier circuit, including a first buffer, a second buffer and a differential amplifier, that amplifies voltage divided by the divider resistor and that outputs the amplified voltage to the A/D converter, the first buffer, the second buffer and the differential amplifier each being constituted by an operational amplifier operating with a positive single power supply; and

a third buffer for applying a bias voltage to the midpoint of the divider resistor, the third buffer being constituted by an operational amplifier that operates with a positive single power supply, wherein

the bias voltage is a positive constant electric potential relative to a ground of the main control circuit and is set based upon an operating voltage of the operational amplifier;

the amplified voltage output from the differential amplifier circuit and input to the A/D converter varies within a range of the operating voltage of the operational amplifier; and

the main control circuit:

inputs the voltage divided by the divider resistor, the midpoint of which is biased to the positive electric potential by the third buffer, to the A/D converter via the differential amplifier circuit, and measures the total voltage of the assembled battery; and

inputs output voltages of the first and second buffers and the bias voltage to the A/D converter, measures the output voltages of the first and second buffers and the bias voltage, and performs fault diagnosis of the assembled battery total voltage detection circuit based upon the measured total voltage, the measured output voltages of the first and second buffers and the measured bias voltage.

2. An assembled battery total voltage detection circuit according to claim 1 , wherein

a plurality of operational amplifiers packed in a single package are used for the first buffer, the second buffer, the third buffer and the differential amplifier.

3. An assembled battery total voltage detection circuit according to claim 1 , further comprising

a resistor of which a resistance value is smaller than that of the divider resistor, the resistor being connected in parallel to the divider resistor.

4. An assembled battery total voltage detection circuit according to claim 1 , further comprising

two switching elements, one of which is inserted between the plus terminal of the assembled battery and the divider resistor, the other of which is inserted between the minus terminal of the assembled battery and the divider resistor, wherein,

at a time of measuring the total voltage of the assembled battery, the main control circuit controls the switching elements to be ON, inputs the voltage divided by the divider resistor, the midpoint of which is biased to the positive electric potential by the third buffer, to the A/D converter via the differential amplifier circuit, and measures the total voltage of the assembled battery.

5. An assembled battery total voltage detection circuit according to claim 1 , wherein

the main control circuit includes a first failure detection unit that performs failure detection for the differential amplifier circuit based upon whether or not a ratio of the measured total voltage to the difference between the measured output voltages of the first and second buffers is within a predetermined range.

6. An assembled battery total voltage detection circuit according to claim 1 , wherein

the main control circuit includes a second failure detection unit that performs failure detection for the third buffer based upon whether or not the measured bias voltage is within a predetermined range.

7. An assembled battery total voltage detection circuit according to claim 5 , wherein

the main control circuit includes a second failure detection unit that performs failure detection for the third buffer based upon whether or not the measured bias voltage is within a predetermined range.

8. An assembled battery total voltage detection circuit for detecting a total voltage of an assembled battery configured by connecting a plurality of batteries, comprising:

a main control circuit that includes an A/D converter operating with a positive single power supply;

a divider resistor connected between a plus terminal and a minus terminal of the assembled battery insulated from the main control circuit, the divider resistor being constituted by a series circuit consisting of first, second, third and fourth resistors;

a differential amplifier circuit that includes a first buffer, a second buffer and a differential amplifier, that amplifies voltage divided by the divider resistor and that outputs the amplified voltage to the A/D converter, the first buffer, the second buffer and the differential amplifier each being constituted by an operational amplifier operating with a positive single power supply; and

a third buffer for applying a bias voltage to a connection point of the second and third resistors, the third buffer being constituted by an operational amplifier that operates with a positive single power supply, wherein

a connection point of the first and second resistors is connected to a positive phase input side of the differential amplifier;

a connection point of the third and fourth resistors is connected to a negative phase input side of the differential amplifier;

the bias voltage is a positive constant electric potential relative to a ground of the main control circuit and is set based upon an operating voltage of the operational amplifier;

the amplified voltage output from the differential amplifier circuit and input to the A/D converter varies within a range of the operating voltage of the operational amplifier; and

the main control circuit:

inputs voltage between the connection point of the first and second resistors and the connection point of the third and fourth resistors of the divider resistor, the connection point of the second and third resistors of which is biased to the positive electric potential by the third buffer, to the A/D converter via the differential amplifier circuit, and measures the total voltage of the assembled battery; and

inputs output voltages of the first and second buffers and the bias voltage to the A/D converter, measures the output voltages of the first and second buffers and the bias voltage, and performs fault diagnosis of the assembled battery total voltage detection circuit based upon the measured total voltage, the measured output voltages of the first and second buffers and the measured bias voltage.

9. An assembled battery total voltage detection circuit according to claim 8 , wherein:

the connection point of the first and second resistors is connected to an input terminal of the first buffer;

the connection point of the third and fourth resistors is connected to an input terminal of the second buffer;

output terminal of the first buffer is connected to the positive phase input terminal of the differential amplifier; and,

output terminal of the second buffer is connected to the negative phase input terminal of the differential amplifier.

10. An assembled battery total voltage detection circuit according to claim 8 , wherein

a plurality of operational amplifiers packed in a single package are used for the first buffer, the second buffer, the third buffer and the differential amplifier.

11. An assembled battery total voltage detection circuit according to claim 8 , further comprising:

a first and a second switching elements, the first switching element being inserted between the plus terminal of the assembled battery and the first resistor, the second switching element being inserted between the minus terminal of the assembled battery and the fourth resistor; and

a resistor of which a resistance value is smaller than that of a sum of the first, second, third and fourth resistors, the resistor being connected in parallel between a connection point at which the first switching element and the first resistor are connected, and a connection point at which the second switching element and the fourth resistor are connected, wherein,

at a time of measuring the total voltage of the assembled battery, the main control circuit controls the first and second switching elements to be ON, inputs the voltage between the connection point of the first and second resistors and the connection point of the third and fourth resistors, the connection point of the second and third resistors of which is biased to the positive electric potential by the third buffer, to the A/D converter via the differential amplifier circuit, and measures the total voltage of the assembled battery.

12. An assembled battery total voltage detection circuit according to claim 8 , wherein

the main control circuit further includes a second failure detection unit that performs failure detection for the third buffer based upon whether or not the measured bias voltage is within a predetermined range.

13. An assembled battery total voltage detection circuit according to claim 12 , wherein

if the measured bias voltage is outside the predetermined range, the second failure detection unit judges the third buffer to be at fault.

14. An assembled battery total voltage detection circuit according to claim 8 , wherein

the main control circuit includes a first failure detection unit that performs failure detection for the differential amplifier circuit based upon whether or not a ratio of the measured total voltage to the difference between the measured output voltages of the first and second buffers is within a predetermined range.

15. An assembled battery total voltage detection circuit according to claim 14 , wherein

if a value obtained by “(the measured total voltage)/{(the measured output voltage of the first buffer)−(the measured output voltage of the second buffer)}” is outside a range of a predetermined amplification factor of the differential amplifier circuit, the first failure detection unit judges the differential amplifier circuit to be at fault.

16. An assembled battery total voltage detection circuit according to claim 14 , wherein

the main control circuit further includes a second failure detection unit that performs failure detection for the third buffer based upon whether or not the measured bias voltage is within a predetermined range.

17. An assembled battery total voltage detection circuit according to claim 16 , wherein

if the measured bias voltage is outside the predetermined range, the second failure detection unit judges the third buffer to be at fault.