Calvin Craig

US Patent:

62116509, Apr 3, 2001

Filed:

Jan 12, 2000

Appl. No.:

9/482150

Inventors:

Susan J. Mumaw - Littleton CO
Jeffrey Evers - Parker CO
Calvin L. Craig - Parker CO
Stuart D. Walker - Littleton CO

Assignee:

Lockheed Martin Corporation - Bethesda MD

International Classification:

H02J 700

US Classification:

320122

Abstract:

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: 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; and by-passing the charging current around the individual cell necessary to keep the individual cell voltage level generally equal to the 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 current is accomplished by dissipating the by-passed current as heat.