Battery state monitoring circuit having differentiating circuit

Details Battery state monitoring circuit having differentiating circuit Battery state monitoring circuit having differentiating circuit

2001-08-24

2002-12-03

Tso, Edward H. (Department: 2838)

Electricity: battery or capacitor charging or discharging

Battery or cell discharging

With charging

C320S136000

Reexamination Certificate

active

06489749

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a technique of improving the safety and reducing a current consumption in a battery device and in a battery state monitoring circuit capable of calculating the remaining amount of a secondary battery such as lithium ion secondary battery.
BACKGROUND ART
As a conventional battery state monitoring circuit, there has been known a device shown in a circuit block diagram of FIG.
2
. This structure is disclosed in, for example, Japanese Patent Application Laid-open No. Hei 9-312172, “Battery Pack, Charger, Charging System and Charging Method.” This relates to a battery device which is called “Smart Battery System”.
The lithium ion secondary battery used in the smart battery system requires an over-charge protecting circuit since it is not provided with a self-protecting operation unlike a nickel/cadmium battery. A battery device
22
A is equipped with a battery voltage monitoring circuit
4
A for detecting a battery voltage and a switch element
12
for stopping the charging from an external charger
21
.
The battery device
22
A controls the indication of the remaining amount of each of secondary batteries
7
to
10
, the stop of charging, etc. A microcomputer
6
A is inputted with an output voltage V
3
a
of a current monitoring circuit
3
A and an output voltage V
4
a
from a battery voltage monitoring circuit
4
A. The microcomputer
6
A is capable of calculating the charging currents and the discharging currents of the secondary batteries
7
to
10
and the respective battery voltages based on the inputted voltages V
3
a
and V
4
a
to calculate the remaining amounts of the secondary batteries
7
to
10
. Also, the microcomputer
6
A controls the on/off operation of the switching elements
12
and
13
in accordance with the state (normal, over-charging, over-discharging and over-current) of the secondary battery. That is, the microcomputer
6
A controls the protecting function (over-charging protection, over-discharging protection and over-current protection) of the battery device
22
A.
In the battery device
22
A, a battery state monitoring circuit
14
A has a total battery voltage VBa of the secondary batteries
7
to
10
as a power supply.
The microcomputer
6
A is inputted with an output V
1
a
of a regulator
1
A as a power supply of the microcomputer
6
A. since the total battery voltage VBa of the secondary batteries
7
to
10
changes in accordance with the status of a load
20
connected between a plus terminal
15
and a minus terminal
17
of the battery device
22
A, the total battery voltage Vba is regulated to a constant voltage V
1
a
such as 3.3 V or 5.0 V by a regulator
1
A and then supplied to the microcomputer
6
A.
The microcomputer
6
A is inputted with an output current I
3
a
(in the for m of a voltage V
3
a
) of the current monitoring circuit
3
A and calculates the remaining amount of the battery in accordance with the output current I
3
a
. In general, the output of the current monitoring circuit
3
A is an analog value which needs to be converted into a digital value in order to calculate the remaining amount of battery by the microcomputer
6
A. For that reason, an A/D convertor circuit is installed in the microcomputer
6
A.
As described above, because the power supply of the battery state monitor circuit
14
A is supplied from the secondary batteries
7
to
10
, an electric power is consumed from those secondary batteries.
Also, the charging and discharging voltage/current from the secondary batteries are not constant but largely change in a short period of time in accordance with the status of the load
20
or the status of the charger
21
. For that reason, in order that the battery state monitoring circuit
14
A monitors the charging and discharging current from the secondary batteries
7
to
10
with a higher precision, the operating frequency of the A/D convertor installed in the microcomputer
6
A needs to be set as high. As the operating frequency of the A/D convertor is set as high, the current consumption of the microcomputer
6
A is further increased, to thereby further increase the consumption of a power from the secondary batteries.
Under the above circumstances, there has been proposed a method of stopping the A/D convertor within the microcomputer
6
A and the charging/discharging current monitoring function as a technique in which, in the battery state monitoring circuit
14
A, when the charging and discharging current of the secondary batteries
7
to
10
is small, for example 0 to 10 mA, as compared with the battery capacity of the secondary batteries, the current consumption of the entire circuit including the charging and discharging monitoring circuit
3
A is reduced, to thereby suppress the power consumption of the secondary batteries
7
to
10
.
In this state, the consumed current of the battery state monitoring circuit
14
A is reduced down to 1/10 to 1/1000. In this way, the state where the consumed current is reduced is called “power save mode”.
However, certain conditions are required when the operation is returned from the power save mode to the normal operation. A function of returning the battery state monitoring circuit
14
A to the normal operation is called “wake up”. The condition for waking up is set, for example when “the charging and discharging current of the secondary batteries
7
to
10
exceeds 1 ampere.” Under that condition, the minus pole voltage V
21
a
of the charger
21
A is a small value lower than 50 mV.
In order to detect such a fine voltage, the current monitoring circuit
3
A must make an offset voltage small so that the fluctuation of the detected wake-up voltage is reduced. Also, since the current monitoring circuit
3
A operates even in the power save mode, the current consumption must be reduced. The current monitoring circuit of this type is complicated in structure and cannot be realized by a simple and inexpensive circuit.
DISCLOSURE OF THE INVENTION
In order to solve the above problems, according to the present invention, a filter is disposed between a sense resistor terminal and a control circuit, which is capable of reducing the current consumption of the entire circuit when the charging and discharging current value becomes small and detecting the current when the charging and discharging current becomes large.
The circuit is structured in such a manner that only the current monitoring circuit operates when the charging and discharging current value becomes small, and the sense resistor terminal and an input terminal of the control circuit current are connected with a capacitor so that all the functions for detecting the remaining amount of a battery start to be executed when the charging and discharging current changes.


REFERENCES:
patent: 09-247852 (1997-09-01), None

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