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A battery cell voltages are read in parallel to a capacitor for each battery block of a battery pack by the use of analog switches. The stored voltages of the capacitors are A/D-converted sequentially through the analog switches. Thereby, each cell voltage is measured with suppression of measurement

A battery cell voltages are read in parallel to a capacitor for each battery block of a battery pack by the use of analog switches. The stored voltages of the capacitors are A/D-converted sequentially through the analog switches. Thereby, each cell voltage is measured with suppression of measurement error by the use of the simple flying capacitor type circuit structure, while the circuit safety is secured by providing the current limitation resistor having a large resistance value between each cell and the analog switch. A noise reduction circuit having a pair of capacitors is provided.

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1. A battery pack voltage detection apparatus for detecting a voltage of a battery pack having first and second battery blocks connected in series, each battery block including a plurality of battery cells connected in series, the battery pack voltage detection apparatus comprising: a voltage detect

1. A battery pack voltage detection apparatus for detecting a voltage of a battery pack having first and second battery blocks connected in series, each battery block including a plurality of battery cells connected in series, the battery pack voltage detection apparatus comprising: a voltage detection circuit; a series capacitor circuit including a plurality of capacitors connected in series, the number of which is equal to the number of cells of the battery block; an input analog switch group that connects a terminal of each cell of the first battery block to a terminal of each capacitor individually so that each capacitor is charged by each cell of the first battery block individually, and that connects a terminal of each cell of the second battery block located on a low potential side with respect to the first battery block to a terminal of each capacitor in a potentially reverse order to the terminal of the first battery block; and an output analog switch group that connects the terminal of each capacitor to the input terminal of the voltage detection circuit separately. 2. The battery pack voltage detection apparatus as in claim 1, wherein the voltage detection circuit A/D-converts an input voltage supplied through the output analog switch group to obtain an A/D-converted value, and computes an A/D-converted value so as to convert it to a value that is equivalent to a positive value of a cell voltage if the A/D-converted value is equivalent to a negative value of the cell voltage. 3. The battery pack voltage detection apparatus as in claim 1, wherein: a reference potential is applied to a contact point between a pair of adjacent capacitors through an analog switch of the output analog switch group; and the voltage detection circuit measures the potential of the terminal different from the contact point between the pair of adjacent capacitors based on the reference potential. 4. The battery pack voltage detection apparatus as in claim 3, wherein the voltage detection circuit A/D-converts the potential of the terminal different from the contact point between the pair of capacitors and the reference potential, and subtracts the A/D-converted value of the reference potential from the A/D-converted value of the potential of the terminal to measure the voltage of the cell. 5. The battery pack voltage detection apparatus as in claim 1, wherein each cell is connected to the input analog switch group through a current limitation resistor. 6. The battery pack voltage detection apparatus as in claim 5, wherein the input analog switch group reads the cell voltage in each capacitor in parallel for a battery block one by one, and the output analog switch group reads out the potential of each capacitor sequentially to the voltage detection circuit. 7. The battery pack voltage detection apparatus as in claim 1, wherein the cells and the input analog switch group are connected in a mirror so that, each capacitor receives voltages of two battery blocks that are in mirror connection. 8. A battery pack voltage detection apparatus for detecting a voltage of a battery pack having a plurality of battery blocks connected in series, each battery block including a plurality of battery cells connected in series, the battery pack voltage detection apparatus comprising: a voltage detection circuit; a plurality of capacitors; an input analog switch group for supplying a plurality of cell voltages sequentially to the capacitors in opposite polarities; and an output analog switch for connecting a terminal of each capacitor to an input terminal of the voltage detection circuit, wherein the voltage detection circuit detects an absolute value of a capacitor voltage. 9. The battery pack voltage detection apparatus as in claim 8, wherein each cell is connected to the input analog switch group through a current limitation resistor. 10. The battery pack voltage detection apparatus as in claim 9, wherein the input analog switch group reads the cell voltage in each capacitor in parallel for a battery block one by one, and the output analog switch group reads out the potential of each capacitor sequentially to the voltage detection circuit. 11. The battery pack voltage detection apparatus as in claim 8, wherein the cells and the input analog switch group are connected in a mirror so that, each capacitor receives voltages of two battery blocks that are in mirror connection. 12. A battery pack voltage detection apparatus for detecting a voltage of a battery pack having a plurality of battery blocks connected in series, each block including a plurality of battery cells connected in series, the battery pack voltage detection apparatus comprising: a plurality of capacitors for storing a cell voltage of the battery block; an input analog switch group for supplying a voltage of each cell to the capacitor; an output analog switch for supplying a stored voltage of the capacitor to the input terminal of a voltage detection circuit; and a currect detection circuit for detecting a current of the battery pack, wherein the current detection circuit samples the current when the input analog switch is substantially turned off. 13. The battery pack voltage detection apparatus as in claim 12, wherein each cell is connected to the input analog switch group through a current limitation resistor. 14. The battery pack voltage detection apparatus as in claim 13, wherein the input analog switch group reads the cell voltage in each capacitor in parallel for a battery block one by one, and the output analog switch group reads out the potential of each capacitor sequentially to the voltage detection circuit. 15. The battery pack voltage detection apparatus as in claim 12, wherein the cells and the input analog switch group are connected in a mirror so that, each capacitor receives voltages of two battery blocks that are in mirror connection. 16. A voltage detection apparatus comprising: a voltage source; a flying capacitor; a pair of input side analog switches that connect both ends of the voltage source to both ends of the flying capacitor; a differential amplifier circuit; a pair of output side analog switches that connect a pair of input terminals of the differential amplifier circuit to both ends of the flying capacitor individually; and a common noise reduction circuit comprising a pair of capacitors having approximately the same electrostatic capacity that connect differential amplifier side terminals of both output side analog switches to a predetermined reference potential source individually. 17. The voltage detection apparatus as in claim 16, wherein the differential amplifier circuit has a low frequency passing filter characteristic having a time constant longer than a time constant that is determined based on a combined impedance of an impedance of an input resistance of the differential amplifier circuit and an impedance of the common noise reduction circuit and an OFF capacity of the input side analog switch. 18. The voltage detection apparatus as in claim 17, wherein: the voltage detection circuit is provided with a signal processing circuit for sampling an output voltage of the differential amplifier circuit; and the signal processing circuit samples the output voltage of the differential amplifier circuit at the time at least after elapse of the time equivalent to the time constant from the turning-on of the output side analog switch. 19. The voltage detection apparatus as in claim 16, further comprising: a second common noise reduction circuit having a pair of intermediate analog switches that connect both ends of the flying capacitor to a pair of input side analog switches individually, and having a pair of capacitors, which have approximately the same electrostatic capacity and connect the connection point between the input side analog switch and the intermediate analog switch to a predetermined reference potential source individually. 20. The voltage detection app aratus as in claim 16, wherein the reference potential source side ends of the pair of capacitors are connected to a reference potential source through a current limitation resistor. 21. The voltage detection apparatus as in claim 16, further comprising: a compensation means for compensating attenuation of a signal voltage arising from charge transfer from the flying capacitor to the capacitors when the output side analog switch is turned on. 22. A voltage detection apparatus comprising: a voltage source; a flying capacitor; a pair of input side analog switches that connect both ends of the voltage source to both ends of the flying capacitor individually; a differential amplifier circuit having a low frequency passing type filter characteristic; a pair of output side analog switches that connect a pair of input terminals of the differential amplifier to both ends of the flying capacitor individually; a common noise reduction circuit having approximately a same electrostatic capacity that connect the differential amplifier circuit side terminal of both output side analog switches to a predetermined reference potential source individually; and a signal processing circuit for sampling the output voltage of the differential amplifier circuit at the time at least after elapse of the time equivalent to the time constant from the turning-on of the output side analog switch, wherein the time constant of the differential amplifier circuit is longer than the time constant that is determined based on the combined impedance of the impedance of the input resistance of the differential amplifier circuit and the impedance of the common noise reduction circuit and OFF capacity of the input side analog switch. 23. The voltage detection apparatus as in claim 22, further comprising: a second common noise reduction circuit having a pair of intermediate analog switches that connect both ends of the flying capacitor to a pair of input side analog switches individually and having a pair of capacitors, which have approximately the same electrostatic capacity and connect the connection point between the input side analog switch and the intermediate analog switch to a predetermined reference potential source individually. 24. A voltage detection circuit comprising: a voltage source; a flying capacitor; a pair of input side analog switches that connect both ends of the voltage source to both ends of the flying capacitor individually; a differential amplifier circuit; a pair of output side analog switches that connect a pair of input terminals of the differential amplifier to both ends of the flying capacitor individually; a pair of capacitors having approximately the same electrostatic capacity and connecting the differential amplifier side terminals of both output side analog switches to a predetermined reference potential source individually; and a pair of reset switches for discharging both capacitors when connected in parallel to the pair of capacitors individually. 25. A battery pack voltage detection apparatus for detecting a voltage of a battery pack having a plurality of battery blocks connected in series, each block including a plurality of battery cells connected in series, the battery pack voltage detection apparatus comprising: a plurality of capacitors for storing cell voltages of the battery block; an input analog switch group for supplying the voltage of each cell to the capacitor; an output analog switch for supplying a stored voltage of the capacitor to the input terminal of a voltage detection circuit; and a current detection circuit for detecting a current of the battery pack, wherein the input analog switch group supplies the voltage of each cell at different input timings, and wherein the current detection circuit sequentially samples the current synchronously with the input analog switch. 26. The battery pack voltage detection apparatus as in claim 25, wherein each cell is connected to the input analog switch group through a current limitation resistor. 27. The battery pack voltage detection apparatus as in claim 26, wherein the input analog switch group reads the cell voltage in each capacitor in parallel for a battery block one by one, and the output analog switch group reads out the potential of each capacitor sequentially to the voltage detection circuit. 28. The battery pack voltage detection apparatus as in claim 25, wherein the cells and the input analog switch group are connected in a mirror so that, each capacitor receives voltages of two battery blocks that are in mirror connection. 29. A battery pack voltage detection apparatus comprising: a battery pack including m battery blocks connected in series to each other; first and second flying capacitors connected in series; a differential voltage detection circuit for detecting a potential difference between first and second input terminals; first and second input resistors connected to the differential voltage detection circuit; a first output side analog switch that connects an independent end of the first flying capacitor to the first input terminal of the differential voltage detection circuit through the first input resistor; a second output side analog switch that connects an independent end of the second flying capacitor to the first input terminal of the differential voltage detection circuit through the second input resistor; a third output side analog switch that connects connection ends of both capacitors to the second input terminal of the differential voltage detection circuit; a first group input side analog switch that connects (4m+1)-th (m=0 or a positive integer) electrode terminals of electrode terminals of the battery pack to the independent end of the first flying capacitor individually; a second group input side analog switch that connects (4m+3)-th (m=0 or a positive integer) electrode terminals of the electrode terminals to the independent end of the second flying capacitor individually; a third group input side analog switch that connects 2m-th (m=a positive integer) electrode terminals of the electrode terminals to the connection ends of both flying capacitors individually; and a control unit for controlling the analog switches, wherein the control unit turns on the first and the second output side analog switches simultaneously to cause discharging of both flying capacitors. 30. The battery voltage detection apparatus as in claim 29, further comprising: a third input resistor connected between the connection ends of both flying capacitors and the second input terminal of the voltage detection circuit in series with the third output side analog switch. a third output side analog switch that connects connection ends of both capacitors to the second input terminal of the differential voltage detection circuit; a first group input side analog switch that connects (4m+1)-th (m=0 or a positive integer) electrode terminals of electrode terminals of the battery pack to the independent end of the first flying capacitor individually; a second group input side analog switch that connects (4m+3)-th (m=0 or a positive integer) electrode terminals of the electrode terminals of the battery pack to the independent end of the second flying capacitor individually; a third group input side analog switch that connects 2m-th (m=a positive integer) electrode terminals of the electrode terminals to the connection end of both flying capacitors individually; and a control unit for controlling the analog switches, wherein the control unit turns on the first and the second output side analog switches simultaneously to cause discharging of both flying capacitors. 31. The battery pack voltage detection circuit comprising: a battery pack including m battery blocks connected in series to each other; first and second flying capacitors connected in series; a differential voltage detection circuit for detecting the potential difference between first and second input terminals thereof; first and second input resistors connected to the differential voltage detection circuit; a first output side analog switch that connects an independent end of the first flying capacitor to the first input terminal of the differential voltage detection circuit through the first input resistor; a second output side analog switch that connects an independent end of the second flying capacitor to the first input terminal of the differential voltage detection circuit through the second input resistor; a third output side analog switch that connects connection ends of both capacitors to the second input terminal of the differential voltage detection circuit; a first group input side analog switch that connects (4m+1)-th (m=0 or a positive integer) electrode terminals of electrode terminals of the battery pack to the independent end of the first flying capacitor individually; a second group input side analog switch that connects (4m+3)-th (m=0 or a positive integer) electrode terminals of the electrode terminals to the independent end of the second flying capacitor individually; a third group input side analog switch that connects 2m-th (m=a positive integer) electrode terminals of the electrode terminals to the connection ends of both flying capacitors individually; a control unit for controlling the analog switches; and a short-circuit switch for short-circuiting between the first and the second input terminals of the differential voltage detection circuit to cause discharging of stored charge in the flying capacitors when the first or second analog switch and the third analog switch are turned on. 32. The battery voltage detection apparatus as in claim 31, further comprising: a third input resistor connected between the connection ends of both flying capacitors and the second input terminal of the voltage detection circuit in series with the third output side analog switch. 33. The battery pack voltage detection apparatus comprising: a first differential voltage detection circuit for detecting a potential difference between first and second input terminals; a second differential voltage detection circuit for detecting a potential difference between second and third input terminals; first, second and third input resistors connected to the first, second and third input terminals, respectively; first and second flying capacitors connected in series; a first output side analog switch that connects an independent end of the first flying capacitor to the first input terminal through the first input resistor; a second output side analog switch that connects the connection ends of both capacitors to the second input terminal through the second input resistor; a third output side analog switch that connects an independent end of the second flying capacitor to the third input terminal through the third input resistor; a control unit for controlling the analog switch; a first short-circuit switch for short-circuiting the first and second input terminals to cause discharging of stored charge in the first flying capacitor when the first analog switch and the second analog switch are turned on; and a second short-circuit switch for short-circuiting the second and third input terminals to cause discharging of stored charge in the second flying capacitor when the second analog switch and the third analog switch are turned on.