Systems and methods for balancing battery cells

1. A system comprising:

a primary winding configured to receive an input power; and

a plurality of secondary windings configured to transform said input power into a plurality of currents to balance a plurality of cells in a battery pack, wherein a ratio between a first turn number of a first secondary winding of said secondary windings and a second turn number of a second secondary winding of said secondary windings is determined by a nominal voltage ratio between two corresponding cells of said plurality of cells.

2. The system as claimed in claim 1 , wherein said ratio between said first turn number and said second turn number is approximately equal to said nominal voltage ratio between said two corresponding cells.

3. The system as claimed in claim 1 , wherein said cells are charged by said currents, and wherein a current for charging a first cell of said cells is less than a current for charging a second cell of said cells if a voltage across said first cell is greater than a voltage across said second cell.

4. The system as claimed in claim 1 , wherein said currents flow through a plurality of paths to charge said cells, and wherein a path of said plurality of paths is disabled when an input switch that is coupled in series to said primary winding is turned on, and wherein said path is enabled when said input switch is turned off.

5. The system as claimed in claim 4 , wherein said path comprises a diode.

6. The system as claimed in claim 4 , wherein said path comprises an output switch.

7. The system as claimed in claim 6 , wherein a switch controller controls said output switch based on a state of said input switch.

8. The system as claimed in claim 1 , wherein a secondary winding of said secondary windings receives energy from said primary winding if an input switch coupled to said primary winding is turned on, and wherein said secondary winding of said secondary windings transforms said energy into a corresponding current of said currents if said input switch is turned off.

9. A method comprising:

receiving an input power at a primary winding;

transforming said input power into a plurality of currents using a plurality of secondary windings;

balancing a plurality of cells using said currents, wherein a ratio between a first turn number of a first secondary winding of said secondary windings and a second turn number of a second secondary winding of said secondary windings is determined by a nominal voltage ratio between two corresponding cells of said plurality of cells.

10. The method as claimed in claim 9 , wherein said ratio between said first turn number and said second turn number is approximately equal to said nominal voltage ratio between said two corresponding cells.

11. The method as claimed in claim 9 , further comprising:

charging said cells using said currents; and

controlling a current for charging a first cell of said cells to be less than a current for charging a second cell of said cells if a voltage across said first cell is greater than a voltage across said second cell.

12. The method as claimed in claim 9 , further comprising:

transferring said currents to said cells via a plurality of paths;

disabling a path of said plurality of paths when an input switch that is coupled in series to said primary winding is turned on; and

enabling said path when said input switch is turned off.

13. The method as claimed in claim 9 , wherein said transforming comprises:

receiving energy from said primary winding if an input switch coupled to said primary winding is turned on; and

transforming said energy into said currents if said input switch is turned off.

14. A system comprising:

a plurality of terminals configured to provide a plurality of currents to balance a plurality of cells; and

a plurality of secondary windings coupled to said terminals and configured to transform an input power provided by a primary winding into said currents, wherein a ratio between a first turn number of a first secondary winding of said secondary windings and a second turn number of a second secondary winding of said secondary windings is determined by a nominal voltage ratio between two corresponding cells of said plurality of cells.

15. The system as claimed in claim 14 , wherein said ratio between said first turn number and said second turn number is approximately equal to said nominal voltage ratio between said two corresponding cells.

16. The system as claimed in claim 14 , wherein said cells are charged by said currents, and wherein a current for charging a first cell of said cells is less than a current for charging a second cell of said cells if a voltage across said first cell is greater than a voltage across said second cell.

17. The system as claimed in claim 14 , wherein a secondary winding of said secondary windings is coupled to a corresponding cell of said cells via a path, and wherein a state of said path is controlled by a state of an input switch that is coupled in series to said primary winding.

18. The system as claimed in claim 14 , wherein a secondary winding of said secondary windings receives energy from said primary winding if an input switch coupled to said primary winding is turned on, and wherein said secondary winding of said secondary windings transforms said energy into a corresponding current of said currents if said input switch is turned off.

19. The system as claimed in claim 14 , further comprising:

a controller configured to adjust said input power by comparing a sensing signal indicative of said input power with a reference signal, and to adjust a sum of said currents by adjusting said reference signal.

20. The system as claimed in claim 19 , wherein said controller is further configured to adjust said reference signal according to a voltage across each cell of said cells.