Electricity: battery or capacitor charging or discharging – Battery or cell discharging – With charging
Reexamination Certificate
1999-05-24
2001-03-06
Wong, Peter S. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
With charging
C320S127000
Reexamination Certificate
active
06198252
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a battery device (hereinafter, referred to as “battery pack”) including a circuit required to be monitored for a battery state such as a voltage or a charge/discharge current, a battery state monitoring circuit for monitoring the circuit, an external connection terminal outside of the battery device, a switch element, a secondary battery and a sense resistor in a battery device for a secondary battery.
As a conventional battery pack, there has been known a device shown in a circuit block diagram of FIG.
2
. For example, Japanese unexamined patent application publication No. H 9-312172 (1997) entitled “Battery pack, charger and charging system as well as charging method” discloses the structure of this type. This is directed to a battery pack which is commonly called a “smart battery system” or the like. That is, a battery pack
120
is structured by a battery state monitoring circuit
18
A, a switch element
102
a
and
102
b
, a sense resistor
10
, a cut out circuit
19
and secondary batteries
6
to
8
. The battery state monitoring circuit
18
A is structured by a microcomputer
4
A, a battery voltage monitoring circuit
20
A and an amplifier
3
, and has a function of monitoring a voltage and the charge/discharge current of the secondary battery. Such a battery pack
120
can conduct communication with a charger
17
, external equipment such as a microcomputer
5
, or with a load
16
.
Employing the battery pack
120
thus structured, it is possible to recognize a battery state by communication with the charger
17
, the microcomputer
5
within a personal computer, a load
16
or the like. The use of this information allows an indication of the residual amount of the battery, a suspension of battery charge, etc., to be conducted accurately.
In the case where a lithium ion battery is used for the secondary battery, since a self-protecting action is not provided unlike a nickel cadmium battery, an over-charge protecting circuit is required. That is, the lithium ion battery is provided with some circuit for detection of a battery voltage and a switch element
102
a
and
102
b
for suspending charging operation from outside.
SUMMARY OF THE INVENTION
In the battery pack structured as shown in
FIG. 2
, a microcomputer
4
A is used. The battery pack is also equipped with an amplifier for monitoring the voltage of the secondary batteries
6
to
8
and a sense resistor
10
and an amplifier
3
for monitoring a charge/discharge current. The microcomputer
4
A is supplied with electric signals from a battery voltage monitor circuit
20
A and an amplifier. Since the microcomputer
4
A has a calculating function and an A/D converter it can calculate the voltage and the capacity of the secondary battery from the above-described signals, and it can monitor a battery state. This makes it possible for the microcomputer
4
A to control the on/off state of the switch element
102
a
and
102
b
, and therefore the microcomputer
4
A adds safety with respect to over-charging in the battery pack
9
A in which lithium ion batteries
6
to
8
maybe used.
It is necessary that a constant voltage is supplied as a power supply of the microcomputer
4
A which is a structurally important part. For example, a voltage of 3.3 V or 5.0 V is a normal value. It the supply voltage applied to the microcomputer
4
A is unstable, the detection accuracy of the battery voltage, etc., is degraded. In the worst case, there generally occurs a phenomenon called “runaway” of the microcomputer
4
A. This is an environment in which the microcomputer
4
A is not controlled at all, with the result that the safety of the battery pack
120
is not assured at all.
Because the power supply for the battery state monitoring circuit
18
A within the battery pack
120
is made up of a secondary battery
6
to
8
, the voltage is varied according to the state of the battery. In the case where the battery pack
120
is discharged to the load
16
, the supply voltage becomes low, whereas in the case where the battery pack
120
is charged, the supply voltage becomes high. In order to apply a constant voltage to the microcomputer
4
A and the amplifier
3
equipped within the battery pack
120
, a voltage regulator is disposed within the battery pack
120
. The voltage regulator serves to maintain its output voltage constant even if the supply voltage is varied.
However, if the voltage regulator is disposed in this manner, the battery voltage as the power supply becomes low if the discharging continues. The potential of the secondary battery
6
to
8
is a supply voltage of the voltage regulator, therefore, as the supply voltage of the voltage regulator becomes lower, the output voltage naturally becomes lower. In this state, the supply voltage required for the stable operation of the microcomputer
4
A cannot be applied.
Further, to monitor the residual amount of the battery, charge/discharge current to the secondary battery
6
to
8
must be monitored. Therefore, an amplifier
3
for adjusting the voltage drop of sense resistor
10
to a level which can be read by the microcomputer
4
A is needed. The amplifier
3
applies a voltage to an A/D port of the microcomputer
4
A after amplifying the voltage between the sense resistor
10
terminals through which the charge/discharge current flows. The amplifier
3
is supplied with a high voltage so as to widen the operation voltage range.
The amplifier
3
is not always required to output. This is because the microcomputer
4
A is not always reading the output from the amplifier
3
. Since the secondary battery
6
to
8
is used for the power supply of the amplifier
3
, if the amplifier
3
is normally operated, consumption of the secondary battery
6
to
8
is increased. To improve this, it must be configured such that the consumption current of the amplifier
3
is suppressed by the microcomputer
4
A.
As described above, since the supply voltage of the microcomputer
4
A is supplied from the voltage regulator, the maximum voltage of the signal output from the microcomputer
4
A is lower than the voltage of the secondary battery
6
to
8
, and is identical with the output voltage of the voltage regulator. To obtain such a circuit structure in which an amplifier
3
suppresses the consumption current by a signal of the microcomputer
4
A, a control circuit which converts a low voltage signal of the microcomputer
4
A to a high voltage signal must be equipped. The power supply of the control circuit is in high voltage level.
However, in the thus structured battery state monitoring circuit
18
A, it is impossible to obtain a structure to suppress the consumption current of the amplifier
3
. When the voltage of the secondary battery
6
to
8
lowers and the output of the voltage regulator within the battery state monitoring circuit
18
A is suspended, the output of the microcomputer
4
A becomes unstable to cause the input voltage of the control circuit to become unstable. Therefore, the output signal of the control circuit also becomes unstable.
In such a state, the consumption current of the battery state monitoring circuit
18
A can not be suppressed; therefore, consumption current from the secondary battery
6
to
8
is increased and the life of the battery pack is shortened. Further, the signal of the amplifier
3
becomes unstable. In the above circumstances, the state monitoring of the secondary battery
6
to
8
can not be conducted accurately and the safety of the battery pack
120
is impaired.
In order to solve the above problems, according to the present invention, in a battery state monitoring circuit including a voltage regulator therein and being capable of controlling an internal circuit with a signal from a microcomputer, a circuit is provided in which the control of the internal circuit is available by the signal from the microcomputer in the case where the output of the voltage regulator is normal, and the signal of the internal circuit is decided regardless of the signal from the microcompu
Adams & Wilks
Luk Lawrence
Seiko Instruments Inc.
Wong Peter S.
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