Electricity: battery or capacitor charging or discharging – Battery or cell discharging – With charging
Reexamination Certificate
2000-03-29
2001-03-27
Tso, Edward H. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
With charging
C320S136000
Reexamination Certificate
active
06208117
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a battery pack having a battery protection monitoring circuit and to an electronic apparatus using such a battery pack.
2. Description of the Related Art
A conventional battery pack having a battery protection monitoring circuit, and an electronic apparatus using such a battery pack will be described by referring to FIG.
1
. In this figure, a conventional battery pack
100
is detachably attached to a main unit
200
, such as a portable information terminal, and supplies electric power to the main unit
200
.
The conventional battery pack
100
has a chargeable and dischargeable battery
300
, a protection circuit
400
for protecting the battery
300
, and a management circuit portion
500
for posting a state of the battery
300
to a main unit
200
by using firmware.
The protection circuit portion
400
has an overcurrent detecting circuit
130
for detecting an overcurrent, an overcharge detecting circuit
150
for detecting overcharge of the battery
300
, an overcurrent/overcharge protection circuit
140
for protecting the battery
300
from overcurrent and overcharge conditions, and a temperature detecting circuit
160
for detecting a temperature in the battery pack
100
. The management circuit portion
500
has a microcontroller unit (MCU) circuit
180
for controlling each of the detecting circuit and the protection circuit and for posting the state of each of such circuits to the main unit
200
.
A system power supply control portion
600
of the main unit
200
is operative to supply electric power POW fed from the battery pack
100
to the system of the main unit and to post the power state of the battery pack
100
to the system.
Protection devices of the conventional battery pack
100
illustrated in
FIG. 1
are connected to the battery
300
and always continue to perform necessary minimum operations. Thus, the conventional battery pack
100
consumes electric power as part of self discharge thereof, though an amount of power consumption is low. Moreover, even when the battery pack
100
mounted in the main unit
200
is not used, the protection circuit portion
400
and the management circuit
500
of the battery pack
100
continue to perform so as to clearly indicate the presence of the battery pack
100
and the possibility of use thereof.
Therefore, when a battery pack is singly distributed, and displayed in a shopwindow, and is in stock or storage, the battery pack is gradually discharged and finally becomes dead. Further, even when a main switch of a main unit is turned off, a battery still may become exhausted. It is necessary in order to avoid the occurrence of such a situation to reduce the amount of the self-discharge of an unused battery as much as possible.
When the terminal voltage of a battery pack is almost 0, it cannot be expected that the protection circuit portion
400
and the management circuit portion
500
of the battery operate normally. Even in the case of such a battery pack, it is necessary that the battery pack can be safely charged by determining the state thereof. That is, it is necessary to easily discriminate battery packs, which cannot be used or are dangerous even when recharged, from normal battery packs, which can be used by being recharged, among battery packs that have lowered terminal voltages, and whose histories are unknown. Further, in the case that the terminal voltage of the battery
300
is almost 0 V and that the battery
300
is in an overdischarged state, it cannot be expected that the protection circuit portion
400
and the management circuit portion
500
operate normally. Thus, the battery
300
is thereafter charged under the control of the system power supply control portion
600
until the management circuit portion
500
starts to operate normally. That is, the battery
300
is charged without the protection function of the battery pack
100
. Therefore, the system power supply control portion
600
needs to have the function of measuring a charging current and a pack voltage. However, the accuracy in measuring the charging current and the pack voltage in the main unit is poor owing to the fact that the ground floats relative to the battery voltage. Moreover, such a measuring function overlaps with the function of the circuit in the battery pack
100
. This results in an increase in the cost of the battery pack.
There is further a danger of smoke emission and fire occurrence, resulting from a failure, owing to the fact that the battery
300
stores a large amount of energy. Thus, a safety mechanism is employed. For example, an internal-pressure-rise relief valve for relieving an internal pressure rise due to a circuit opening, which is caused by an overcurrent, and extraordinary temperature rise is provided in a battery cell itself. The battery pack
100
has an output short-circuit protection function and an overcharge protection function. The system power supply control portion
600
has an abnormal charging control protection function and a temperature anomaly protection function.
Various detecting circuits, such as the overcurrent detecting circuit
130
and the overcharge detecting circuit
150
, are provided in the protection circuit portion
400
. These circuits perform detection operations by using comparators. The overcharge detecting circuit
150
of the conventional protection circuit portion
400
has a single threshold value for detecting an overcharge. Moreover, the overcurrent detecting circuit
130
thereof employs a single threshold value for detecting an overcurrent.
In the case that the threshold for detecting an overcharge has a single value, even when an overcharge is normally detected, the charging of the battery is continued if no protection (or control) means operate normally according to a result of the detection of an overcharge. Thus, the charging of the battery proceeds, so that in a worst case, there is a danger of emission and fire. Mechanical measures, such as an internal pressure relief valve, may be taken in each of the battery cells. It is, however, important for protecting a battery, which is adapted to store large energy, to improve the reliability thereof by doubling the protection means. In this case, the dual protection realized by employing different protection means is more effective in improving the safety of the system than that realized by employing the same protection circuits. In the case that the conventional battery pack is adapted to have two systems having protection functions, it is necessary to prevent both systems from mutually interfering with each other to thereby impede normal operation of the battery pack.
Further, in the case that the threshold for detecting an overdischarge has a single value, even when an overdischarge is normally detected, the discharging of the battery is continued if no protection (or control) means operate normally according to a result of the detection of an overcharge. Thus, the discharging of the battery proceeds, so that in a worst case, an irreversible reaction may proceed in the battery so that the battery cannot be recharged. Further, when the battery pack enters a discharge region, a drop in the terminal voltage increases with the use of energy. This may suddenly impede an operation of the system. It is, thus, important for ensuring a stable operation of the system to improve the reliability thereof by doubling the protection means. In the case of protecting the battery from an overdischarge, similarly to the case of protecting the battery from a overcharge, the dual protection realized by employing different protection means is more effective in improving the safety of the system than that realized by employing the same protection circuits. In the case that the conventional battery pack is adapted to have two systems having the protection functions, it is necessary to prevent both systems from mutually interfering with each other to thereby impede normal operation of the battery pack.
In the conventional battery pack
100
ill
Armstrong, Westerman Hattori, McLeland & Naughton
Fujitsu Limited
Tso Edward H.
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