Battery cell by-pass circuit

• US 6,271,646 B1
• Filed: 07/05/2000
• Issued: 08/07/2001
• Est. Priority Date: 07/05/2000
• Status: Expired due to Fees

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation), The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Inventors: Gelger, Ronald V., Evers, Jeffrey
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): LUK, LAWRENCE W
• Application Number:
  US09/610,351
• Time in Patent Office: 398 Days
• Field of Search: 320/122, 320/119, 320/120, 320/132, 320/136, 320/116, 320/117, 320/118
• US Class Current: 320/122
• CPC Class Codes: H02J 7/0016 using shunting, discharge or bypass circuits

Abstract

The invention is a circuit and method of limiting the charging current voltage from a power supply net work 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 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 by-passed current is transferred at a proper voltage level to the power supply. The by-pass circuit 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 transfers the excess charging current to the power supply net work. The circuitry also allows charging of the individual cell if the actual voltage level is equal or less than the specific voltage level.

Claims

1. A method of limiting the charging current from a power supply applied to an individual cell of a plurality of cells making up a battery being charged in series, the method comprising the steps of:

sensing the actual voltage level of the individual cell;

comparing the actual voltage level of the individual cell with a specific voltage level and providing an error signal representative thereof;

by-passing the charging current around the individual cell necessary to keep the individual cell voltage level generally equal to said specific voltage level while continuing to charge the remaining cells; and

transferring the by-passed current at a proper voltage level to the power supply.

2. The method as set forth in claim 1 wherein the step of by-passing the charging current around the individual cell necessary to keep the individual cell voltage level generally equal to said specific voltage level includes the steps of:

by-passing said charging current around said individual cell if said actual voltage level is above said specific voltage level; and

allowing said charging current to charge said individual cell if said actual voltage level is equal or less than said reference level.

3. The method as set forth in claim 2 wherein said series of cells are Lithium-ion cells.

4. A by-pass circuit for limiting the charging current applied to an individual cell of a series of cells forming a battery, the cells being charged in series, the by-pass circuit comprising:

first means to sense the actual voltage level of the individual cell;

second means to compare the actual voltage level of the individual cell with a specific voltage level and to provide an error signal representative thereof;

third means responsive to said error signal for maintaining the individual cell voltage level generally equal to said reference level; and

fourth means for transferring the by-passed current at a proper voltage level to the power supply.

5. The by-pass circuit as set forth in claim 4 wherein said third means includes:

means to by-pass said charging current around said individual cell if the actual voltage level is above said specific voltage level; and

means to allow charging of the individual cell if the actual voltage level is equal or less than said specific voltage level.

6. The by-pass circuit as set forth in claim 5 wherein said first means is a voltage detection circuit.