Systems and methods for cell balancing

• US 8,461,806 B2
• Filed: 10/15/2007
• Issued: 06/11/2013
• Est. Priority Date: 10/15/2007
• Status: Active Grant

• Current Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Original Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Inventors: Lupu, Flavius, Bucur, Constantin, Zeng, Xiaojun, Sheng, Kalyi, Xiao, Anquan
• Primary Examiner(s): Muralidar, Richard V
• Application Number:
  US11/974,530
• Publication Number:
  US 20090096420A1
• Time in Patent Office: 2,066 Days
• Field of Search: 320116-123, 320/132
• US Class Current: 320/122
• CPC Class Codes: H02J 7/0016 using shunting, discharge or bypass circuits

Abstract

A cell balancing circuit comprises a first cell having a first voltage, a second cell in series with the first cell and having a second voltage that is greater than the first voltage, and a bypass path in parallel with the second cell for enabling a bypass current for the second cell if a difference between the first voltage and the second voltage is greater than a predetermined threshold. The bypass current is enabled for a balancing time period that is proportional to the difference between the first voltage and the second voltage.

Claims

1. A cell balancing circuit for balancing a plurality of cells, comprising:

a logic core operable for detecting if any cell is in balancing phase, reading a full charge capacity (FCC) recorded in a previous cycle for each cell when no cell is in said balancing phase, checking a timer coupled to a cell if said cell is in said balancing phase, balancing said cell while said timer is counting, and terminating said balancing phase when said timer expires, for calculating a state-of-charge (SOC) for each of said cells, for searching a minimum SOC and a maximum SOC of said cells, for detecting an unbalanced condition if a difference between said maximum SOC and said minimum SOC is greater than a predetermined threshold, and for determining a balancing time period that is proportional to said difference if said unbalanced condition occurs,

wherein said cell balancing circuit enables a bypass current for a cell having said maximum SOC for said balancing time period if said unbalanced condition occurs.

2. The cell balancing circuit as claimed in claim 1, wherein said SOC for each of said cells is determined by a ratio of a cell capacity of each of said cells to said full charge capacity of each of said cells.

3. A method for balancing a plurality of cells, comprising:

detecting if any cell is in balancing phase;

reading a full charge capacity (FCC) recorded in a previous cycle for each cell when no cell is in said balancing phase;

checking a timer coupled to a cell if said cell is in said balancing phase;

balancing said cell while said timer is counting;

terminating said balancing phase when said timer expires;

calculating a state-of-charge (SOC) for each of said cells;

searching a minimum SOC and a maximum SOC of said cells;

detecting an unbalanced condition if a difference between said maximum SOC and said minimum SOC is greater than a predetermined threshold;

determining a balancing time period that is proportional to said difference if said unbalanced condition occurs; and

enabling a bypass current for a cell having said maximum SOC for said balancing time period if said unbalanced condition occurs.

4. The method as claimed in claim 3, wherein said SOC for each of said cells is determined by a ratio of a cell capacity of each of said cells to said full charge capacity of each of said cells.