Electricity: battery or capacitor charging or discharging – Serially connected batteries or cells – Having variable number of cells or batteries in series
Reexamination Certificate
2000-01-12
2001-04-03
Wong, Peter S. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Serially connected batteries or cells
Having variable number of cells or batteries in series
C320S120000
Reexamination Certificate
active
06211650
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to the field of charging systems for batteries and, in particular, to charging system that prevents over charging of individual cells with a battery composed of a plurality of cells in series.
2. Description of Related Art
Certain types of batteries, such as Lithium-ion batteries are subject to damage if over charged. If there is a single battery cell in use, charging presents no problem. A simple charging system can be used that senses when the cell is fully charged and thereafter trickle charging are used to maintain the charge. One type of system switches off the charging current; for example U.S. Pat. No. 5,539,299 “Protection Switch For A Battery Powered Device” by J. M. Ferandez, U.S. Pat. No. 5,853,908 “Protection Device For Secondary Batteries” by T. Okutoh and U.S. Pat. No. 5,892,145 “Battery Pack Unit, Control Method Therefore; Electronic Equipment Driven Power Supplied From Same Battery Pack Unit, And Recording Medium On Which Program For Controlling The Same Battery Pack Unit Is Recorded” by Y. Eguchi.
U.S. Pat. No. 5,049,804 “Universal Battery Charging System And A Method” by P. D. Hutchings and U.S. Pat. No. 5,164,652 “Method And Apparatus For Determining Battery Type And Modifying Operating Characteristics” by R. M. Johnson, et al., and U.S. Pat. No. 5,420,493 “Power Supply And Battery Charger” by A. Hargadon, et al. all disclose charging systems that can be used to charge various types of batteries. There are literally hundreds of battery charger designs for charging a single battery cell. However, when a battery is composed of a plurality of cells in series, such systems will not prevent an individual cell from being over charged, especially when the battery is composed of a plurality of Lithium-ion cells.
U.S. Pat. No. 5,969,502 “Battery Charger Capable Of Independently Charging Electromagnetic Cells”. P. Beard discloses a charging system for a pair of cells arranged in series wherein the system independently controls charging of each cell. A resistor limits the current to the battery and a voltage equalizer is used to balance the cell voltage between the cells during charging. However, while this will work for a pair of cells in series it is not useful for a higher number of cells.
Thus, it is a primary object of the invention to provide a circuit for preventing the overcharging of an individual cell of a battery composed of a plurality of cells in series.
It is another primary object of the invention to provide a circuit for preventing the overcharging of an individual cell of a battery composed of a plurality of cells in series wherein each individual cell is provided with a charging by-pass circuit.
It is a further object of the invention to provide a circuit for preventing the overcharging of an individual cell of a battery composed of a plurality of cells in series wherein each individual cell is provided with a charging by-pass circuit and where the by-pass circuit dissipates the charging current by converting it into heat.
It is a further object of the invention to provide a circuit, which allows current to by-pass all cells at a specific state of charge with the purpose of equalizing the state of charge of each individual cell with the battery.
SUMMARY OF THE INVENTION
The invention is a circuit and method of limiting the charging voltage applied to an individual cell of a plurality of cells making up a battery being charged in series. It is particularly designed for use with batteries that can be damaged by overcharging, such as Lithium-ion type batteries. In detail, the method includes the following steps:
1. sensing the actual voltage level of the individual cell;
2. comparing the actual voltage level of the individual cell with a reference value and providing an error signal representative thereof; and
3. by-passing the charging current around individual cell necessary to keep the individual cell voltage level generally equal to a specific voltage level while continuing to charge the remaining cells. Preferably this is accomplished by by-passing the charging current around the 125 individual cell if said actual voltage level is above the specific voltage level and allowing the charging current to the individual cell if the actual voltage level is equal or less than the specific voltage level. In the step of bypassing the charging current the current is accomplished by dissipating the by-passed current as heat.
The by-pass circuit for limiting the charging voltage applied to an individual cell of a series of cells forming a battery, the cells being charged in series includes a voltage detection circuit to sense the actual voltage level of the individual cell. A voltage comparison circuit is used to compare the actual voltage level of the individual cell with a reference value and to provide an error signal representative thereof. A third circuit, designed to be responsive to the error signal, is provided for maintaining the individual cell voltage level generally equal to the specific voltage level. Circuitry is provided in the third circuit for bypassing charging current around the individual cell if the actual voltage level is above the specific voltage level and converts the excess charging current to heat. This is preferably accomplished by a MOSFET and power resistor in series placed in parallel with the individual cell for converting the by-passed current into heat. The circuitry also allows charging of the individual cell if the actual voltage level is equal or less than the specific voltage level.
The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description in connection with the accompanying drawings in which the presently preferred embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawings are for purposes of illustration and description only and are not intended as a definition of the limits of the invention.
REFERENCES:
patent: 5049804 (1991-09-01), Hutchings
patent: 5164652 (1992-11-01), Johnson et al.
patent: 5420493 (1995-05-01), Hargadon et al.
patent: 5539299 (1996-07-01), Fernandez et al.
patent: 5818199 (1998-10-01), Beard
patent: 5853908 (1998-12-01), Okutoh
patent: 5932990 (1999-08-01), Kaneko
patent: 5982145 (1999-11-01), Eguchi
patent: 6014013 (2000-01-01), Suppanz et al.
Craig, Jr. Calvin L.
Evers Jeffrey
Mumaw Susan J.
Walker Stuart D.
Dachs Louis L.
Lockheed Martin Corporation
Luk Lawrence
Wong Peter S.
LandOfFree
Battery cell by-pass circuit does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Battery cell by-pass circuit, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Battery cell by-pass circuit will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2452652