Electricity: battery or capacitor charging or discharging – Serially connected batteries or cells – With discharge of cells or batteries
Patent
1994-08-01
1998-08-18
Chea, Thorl
Electricity: battery or capacitor charging or discharging
Serially connected batteries or cells
With discharge of cells or batteries
320 22, 320 30, 429 22, H01M 1044, H01M 1046
Patent
active
057962383
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a battery pack employed as a power source for a portable telephone, personal computer or a video camera.
BACKGROUND ART
There has hitherto been known a battery pack constituted by a secondary cell, such as a lithium ion cell, NiCd cell or a nickel hydrogen cell. Such known battery pack arrangements are in need of a protective circuit which is arranged at a pre-set position within the battery pack. A charging control circuit is separately provided on a charger such as an ac adapter or on an external unit such as a personal computer employing the battery pack. If an excess discharging state is detected, the discharge is discontinued appropriately.
However, the voltage at each cell cannot be detected based solely upon the terminal voltage of the battery pack, such that the residual capacity cannot be measured accurately. Besides, if any one of the cells reaches a pre-set over-discharge voltage, the discharge is discontinued without regard to the terminal voltage.
This is particularly inconvenient with equipment, such as a personal computer, in which it is necessary to carry out an operation of data storage before discontinuing the discharge.
On the other hand, the control circuit needs to be designed uniquely in order to adapt it to the characteristics of the secondary cell of the battery pack. If the control circuit is provided outside of the battery pack, the problem of interchangeability between the charger and the secondary cells arises with inconveniences in safety and costs. It has therefore been desired to provide a small-sized compact battery pack in which control may be made so as to take account of the characteristics of the cells of the secondary battery of the battery pack and in which the load imposed on the external equipment used with the battery pack may be minimized.
In addition, when charging the battery pack with the power supplied from a power circuit connected to the external equipment, it is necessary to change over the charging operation depending on whether the external equipment is in the turned-on state or in the turned-off state.
In view of the above-described status of the art, it is an object of the present invention to provide a battery pack in which the charge/discharge operation may be performed on the side of the battery pack and in which appropriate charge/discharge control may be made depending on the state of the external equipment in such a manner as to take account of the cell characteristics.
DISCLOSURE OF THE INVENTION
The present invention provides a battery pack connected to a power source circuit and to external equipment connected to the power source circuit. The battery pack comprises means for detecting the on/off states of the external equipment and effecting charging in the turned-on state of the external equipment with the power equal to the total supplied power from the power source circuit less the maximum power consumed by the external equipment, and also effecting charging during the turned-off state of the external equipment with the supplied power from the power source circuit.
In this manner, the battery pack may be charged properly without adversely affecting the power supply to the external equipment.
In the turned-on state of the external equipment, charging is performed with low current obtained by switching control of the current supplied from the power source circuit. It is preferred to effect the charging under constant current control by constraining the current from the power source circuit to a constant low current value.
It is also possible to detect the voltage difference among the cells when charging has been terminated and to discharge the cell having the highest voltage if the voltage difference is higher than a pre-set threshold value in order to maintain what may be termed a cell voltage balance for suppressing voltage fluctuations.
By switching the discharge switch on when charging is terminated, or by detecting the voltage state of the power source circuit and controlling the discharging
REFERENCES:
patent: 5136229 (1992-08-01), Galvin
patent: 5254928 (1993-10-01), Young et al.
patent: 5282054 (1994-01-01), Oana et al.
patent: 5371456 (1994-12-01), Brainard
Eguchi Yasuhito
Hiratsuka Masaru
Murayama Shigeki
Nagai Tamiji
Chea Thorl
Kananen Ronald P.
Sony Corporation
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