Electricity: battery or capacitor charging or discharging – Battery or cell discharging – Regulated discharging
Reexamination Certificate
2000-03-29
2001-11-20
Wong, Peter S. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
Regulated discharging
C320S134000
Reexamination Certificate
active
06320355
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a low power consumption circuit and secondary battery cell protection circuit, and more particularly, to a low power consumption circuit and secondary battery cell protection circuit not easily susceptible to outside interference.
2. Description of the Related Art
Compared to the conventional nickel-cadmium battery cell or nickel-hydrogen battery, the light, compact lithium-ion battery that is one type of secondary battery cell delivers approximately three times as much operating voltage, approximately twice as much power per unit of weight and substantially greater power per unit of volume as well. The power, lightness and compactness of the lithium-ion battery cell has led to its widespread use in video cameras, portable telephones, PHS, notebook-type personal computers and a wide array of other portable electronic products.
However, over-discharge shortens the useful life of the lithium-ion battery cell, and moreover, the lithium-ion battery cell cannot be reused once it is completely discharged. On the other hand, continuing to charge the lithium-ion battery cell to a state of overcharge increases the cell voltage and poses a hazard, also shortening the useful life of the lithium-ion battery cell.
Therefore, in order to ensure the safety and enhance the performance of these light, compact but powerful battery cells, protection circuits are used.
FIG. 1
is a block diagram for the purpose of explaining a conventional secondary battery cell protection circuit for a secondary battery cell such as a lithium-ion battery cell. The circuit has either a charger or a load connected between +B power terminal and −B power terminal. When a charger is connected to the power terminals, the lithium-ion battery cell is charged, and when a load is connected to the power terminals, the lithium-ion battery cell is discharged.
The secondary battery cell protection circuit for a lithium-ion battery cell has a secondary battery cell protection circuit
2
, a power line
5
that connects the secondary battery cell
1
and the +B power terminal, a resistor
3
connected between the power line
5
and the secondary battery cell protection circuit
2
, a resistor
4
connected between the secondary battery cell protection circuit
2
and a power line
12
that is connected to the −B power terminal, discharge control field-effect transistor (hereinafter FET) FET #
1
and charge control FET #
2
.
The secondary battery cell protection circuit
2
comprises over-discharge detection circuit
13
for detecting an over-discharge, overcharge detection circuit
14
for detecting an overcharge, overcharge control circuit
15
for applying a control signal to a terminal {circle around (
5
)} and cutting off charge control FET #
2
when the overcharge detection circuit
14
detects an overcharge, and an over-discharge control circuit
16
for applying a control signal to a terminal {circle around (
3
)} and cutting off over-discharge control FET #
1
when the over-discharge detection circuit
13
detects an over-discharge.
Additionally, the secondary battery cell protection circuit
2
comprises terminals {circle around (
1
)}, {circle around (
2
)}, {circle around (
3
)}, {circle around (
4
)}, {circle around (
5
)}. Terminal {circle around (
2
)} is a terminal for detecting an electric potential at a negative side of the secondary battery cell
1
, terminal {circle around (
4
)} is a terminal for detecting an electric potential at the power line
12
connected to the −B power terminal. The secondary battery cell protection circuit
2
is constructed so that the circuitry involved with over-discharge control and overcharge control is activated whenever the electric potential at terminal {circle around (
4
)} is lower than the electric potential at terminal {circle around (
2
)}.
Terminal {circle around (
1
)} is a terminal for detecting an electric potential at a positive side of the secondary battery cell
1
. Based on the electric potential at this terminal, the over-discharge detection circuit
13
and the overcharge detection circuit
14
carry out a determination as to the over-discharge state or overcharge state of the secondary battery cell
1
. If the electric potential falls below a predetermined electric potential and the over-discharge detection circuit
13
detects an over-discharge, then the over-discharge control circuit
16
switches terminal {circle around (
3
)} to LOW level and cuts off over-discharge control FET #
1
. If, on the other hand, the electric potential at terminal {circle around (
1
)} rises above a predetermined electric potential and the overcharge detection circuit
14
detects an overcharge, then the overcharge control circuit
15
switches terminal {circle around (
3
)} to LOW level and cuts off overcharge control FET #
2
. By so doing, the secondary battery cell
1
can be protected from both excessive charge and excessive discharge.
However, consider a state in which a load is connected between the +B power terminal and the −B power terminal of the circuit shown in
FIG. 1
, with the secondary battery cell
1
supplying power to the load.
When the secondary battery cell
1
reaches an over-discharge state as a result of supplying power to the load for a long period of time, the electric potential at terminal {circle around (
1
)} drops and the over-discharge detection circuit
13
detects an over-discharge. When an over-discharge is detected the over-discharge control FET #
1
is cut off by the over-discharge control circuit
16
. At the same time, in order to prevent damage to the secondary battery cell
1
, the secondary battery cell protection circuit
2
is shut off except for a portion of the secondary battery cell protection circuit
2
, thus halting operation of the secondary battery cell protection circuit
2
. As a result, high impedance arises at the power line
12
between the −B power terminal and the FET #
1
.
However, the high-impedance power line
12
is very susceptible to the effects of external noise or interference, caused, for example, by the placement of a finger on the −B power terminal or power line
12
, as a result of which the electric potential at the power line
12
fluctuates. That fluctuation in the electric potential can cause the electric potential at terminal {circle around (
4
)} to drop below the electric potential at terminal {circle around (
2
)}, activating the discharge control and charge control circuits of the secondary battery cell protection circuit
2
as a result.
The activation of the discharge control and charge control circuits of the secondary battery cell protection circuit
2
circuit that the secondary battery cell protection circuit
2
is mistakenly activated by external interference despite the operation of the secondary battery cell protection circuit
2
having been halted in order to protect the secondary battery cell
1
from damage due to over-discharge of the secondary battery cell
1
.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved and useful low power consumption circuit and secondary battery cell protection circuit.
Another object of the present invention is to provide an improved and useful low power consumption circuit and secondary battery cell protection circuit in which, when the supply of power has been halted in order to reduce power consumption, the effects of external noise on a high impedance circuit arising as the power is cut can be eliminated.
Another object is that as the supply of power is cut to the circuit in order to reduce power consumption, a portion of the circuit becomes a high impedance circuit, and thus the effects of external interference can be eliminated.
The present invention is a low power consumption circuit comprising
a circuit that cuts power to a portion of the low power consumption circuit under previously specified conditions in order to reduce consumption
Ladas & Parry
Mitsumi Electric Co. Ltd.
Tibbits Pia
Wong Peter S.
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