Electricity: measuring and testing – Electrolyte properties – Using a battery testing device
Reexamination Certificate
1999-02-16
2001-05-22
Wong, Peter S. (Department: 2838)
Electricity: measuring and testing
Electrolyte properties
Using a battery testing device
C320S118000
Reexamination Certificate
active
06236215
ABSTRACT:
RELATED APPLICATION DATA
The present application claims priority to Japanese Application No. P10 039320 filed Feb. 20, 1998 which application is incorporated herein by reference to the extent permitted by law.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a voltage detection circuit for a plurality of cells, such as lithium ion cells or nickel cadmium cells, connected in series to each other in a battery, and to a method of detecting a cell voltage.
2. Description of Related Art
In some cases, so-called cells such as lithium ion cells or nickel cadmium cells are connected in series to each other for use as a battery pack or a battery to supply an electric power to an electronic equipment such as handy-type video tape recorder, electronic camera, portable computer or the like.
A cell is a single unit of a battery.
FIG. 1
is a circuit diagram of a conventional cell voltage detection circuit.
FIG. 2
shows an example in which a plurality of such cells (
1
(
1
a
to
1
d
) is connected in series to each other and each of them is connected to a cell voltage detector
9
. Of these cells, a one indicated with the reference
1
a
has a highest potential, while a one indicated with the reference
1
d
has a lowest potential.
FIG. 2
is a circuit diagram of the cell voltage detector
9
included in the cell voltage detection circuit in FIG.
1
. The cell voltage detector
9
comprises an operational amplifier
8
having a noninverting terminal
8
a
and an inverting terminal
8
b.
For example, the cell
1
a
having the highest potential has a positive electrode thereof connected to the noninverting terminal
8
a
of the operational amplifier
8
of the cell voltage detector
9
via a sense line
2
and resistor R
1
, and a negative electrode thereof connected to the inverting terminal
8
b
of the operational amplifier
8
via a sense line
3
and resistor R
2
. Similarly, each of the other cells has positive and negative electrodes thereof connected to an operational amplifier
8
via a sense line and resistor. Thus, the operational amplifier
8
will detect a voltage from the corresponding cell
1
and provide it as its voltage output
11
individually.
As shown in
FIG. 2
, each voltage detector
9
in
FIG. 1
as provided therein a plurality of resistors R
1
to R
4
for the operational amplifier
8
.
The detecting accuracy of the cell voltage detector
9
having the above-mentioned configuration greatly depends upon the accuracy of each of the resistors R
1
to R
4
and that of the detected voltage output
11
. Therefore, a resistor of which the resistance is set with a high accuracy should be used as the resistors R
1
to R
4
.
Also, the detecting accuracy of te voltage detector
9
becomes lower proportionally to a higher common mode voltage. This will be explained with reference to FIG.
3
.
The output Vo of the operational amplifier is simply expressed (offset error of the operational amplifier is neglected):
Vp=Rb
(V
1
+V
2
)/(
Ra+Rb
)
where Vp:
Ra, Rb: Resistance of resistors R
1
and R
2
V
1
: Voltage of cell having highest voltage
V
2
: Total voltage of other cells
Therefore,
Vo=Vp−Rd
(V
2
−
Vp
)/
Rc
where Rc., Rd: Resistance of resistors R
3
and R
4
Assume that Ra=Rc and Rb=Rd (1)
Then,
Vo=Rd·
V
1
/
Rc
(2)
When V
1
=
O
V, the output
Vo
of the operational amplifier should be
O
. Actually, however, V
1
will not be
O
V because of the error due to the common mode voltage at the operational amplifier.{circle around (1)}
The expression (1) is not practically possible. When the expression (1) is impossible, the output
Vo
of the operational amplifier has an error proportional to a voltage V
2
.{circle around (2)}
These errors {circle around (1)} and {circle around (2)} cause to low the detecting accuracy of the cell voltage detection circuit.
Further, since in the conventional cell voltage detection circuit shown in
FIG. 2
needs one cell voltage detector
9
for each cell, it is much complicated.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a cell voltage detection circuit simplified in construction and capable of detecting a voltage of each of the cells in a battery with a high accuracy
The above object can be attained by providing a cell voltage detection circuit for a plurality of cells connected in series to each other in a battery and adapted to detect a voltage of each cell, comprising, according to the present invention,
a first input selecting means connected to positive and negative electrodes of each cell to select either the positive or negative electrode of a selected cell and acquire a voltage of the cell;
a second input selecting means connected to the positive and negative electrodes of each cell to select either the positive or negative electrode of the selected cell and acquire a voltage of the cell;
a voltage detecting means for acquiring a detected output voltage from output voltages from the first and second input selecting means; and
a processing means for converting the detected cell output voltage from the voltage detecting means from analog to digital for calculation to thereby determine the voltage of the individual cell.
According to the present invention, to detect the voltage of each of the plurality of cells connected in series to each other in a battery, the positive and negative electrodes of the cell are connected to the first input selecting means to select either the positive or negative electrode of a selected cell and acquire the voltage of the selected cell. Also the positive and negative electrodes of the cell are connected to the second input selecting means to select the positive or negative electrode of a selected cell and acquire the voltage of the selected cell.
The voltage detecting means is adapted to acquire a detected cell output voltage from a first cell output voltage from the first input selecting means and a second cell output voltage from the second input selecting means.
The processing means converts the detected cell output voltage from the voltage detecting means from analog to digital for calculation to thereby determine the voltage of the individual cell.
Therefore, it is not necessary to provide a voltage detecting means for each of the plurality of cells. Each of the cells is selected by a single voltage detecting means and an output voltage detected by the voltage detecting means is converted from analog to digital for calculation to determine the voltage of each cell. Thus since a plurality of voltage detecting means may not be provided corresponding to the plurality of cells connected in series to each other, the voltage detection circuit can be simply constructed.
The voltage detection circuit according to the present invention can also be used to detect a voltage of a single cell.
According to the present invention, the voltage detection circuit should preferably comprise a noninverting input terminal and an inverting input terminal, an operational amplifier, and a plurality of adjusting resistors provided for the operational amplifier. The processing means comprises an analog/digital converter to convert a detected output voltage from analog to digital, and an arithmetic unit to calculate the digital signal to provide a voltage of each cell. Thus, the detected output voltage from the voltage detecting means can be digitally calculated by the processing means to determine the cell voltage.
According to the present invention, the first input selecting means should preferably be able to select and be connected to a ground potential and the second input selecting means should also preferably be able to select a positive-voltage calibrating voltage to which a cell voltage is calibrated with reference.
According to the present invention, the first input selecting means should preferably be able to select a positive voltage calibrating voltage to which a cell voltage is calibrated with reference and the second input selecting means should pr
Luk Lawrence
Sonnenschein Nath & Rosenthal
Sony Corporation
Wong Peter S.
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