Circuit and method for cell balancing

1. A cell balancing circuit, for balancing a plurality of cells in a battery connected in series, comprising:

a first shunt path, for a first shunt current, connected in parallel to a first cell;

a controller, for balancing the plurality of cells and for detecting balance conditions of each cell, coupled to the first shunt path;

a timer for measuring balance times for each cell; and

a storage unit for storing the balance times,

wherein

the controller pre-balances the first cell by enabling the first shunt path for a first pre-balance time and balances the first cell by enabling the first shunt path for a first balance time if an unbalance condition of the first cell is detected by the controller, and

the controller updates the first pre-balance time for each balancing cycle based on the first pre-balance time and the first balance time from a previous balancing cycle.

2. The cell balancing circuit of claim 1 , wherein the controller updates the first pre-balance time of the first cell based on a sum of the first pre-balance time and the first balance time from the previous balancing cycle.

3. The cell balancing circuit of claim 1 , further comprising a second shunt path connected in parallel to a second cell, wherein the controller pre-balances the second cell by enabling the second shunt path for a second pre-balance time and balances the second cell by enabling the second shunt path for a second balance time if an unbalance condition of the second cell is detected by the controller, and wherein the controller updates the second pre-balance time for each balancing cycle based on the second pre-balance time and the second balance time from a previous balancing cycle, and wherein the controller further adjusts the first pre-balance time of the first cell and the second pre-balance time of the second cell based on a minimum value between the updated first pre-balance time and the updated second pre-balance time.

4. The cell balancing circuit of claim 3 , wherein the controller adjusts the first pre-balance time of the first cell by subtracting the minimum value from the first updated pre-balance time.

5. The cell balancing circuit of claim 1 , wherein the controller enables the first shunt path in a plurality of discrete time slots if the first cell is unbalanced, and generates the first balance time by summing up the discrete time slots.

6. A controller for balancing a plurality of cells connected in series, the controller comprising:

a sensing unit for monitoring cell voltage of each cell;

a timer for measuring balancing time for each cell;

a storage unit for storing the balancing time for each cell; and

a control unit for controlling pre-balancing and balancing of each cell according to the cell voltage sensed by the sensing unit and the balancing time retrieved from the storage unit,

wherein the controller pre-balances a first cell by enabling a first shunt path connected in parallel to the first cell for a first pre-balance time and balances the first cell by enabling the first shunt path for a first balance time if an unbalance condition of the first cell is detected by the controller based on the cell voltage sensed by the sensing unit.

7. The controller of claim 6 , wherein the controller updates the first pre-balance time for each balancing cycle based on the first pre-balance time and the first balance time from a previous balancing cycle.

8. The controller of claim 7 , wherein the controller updates the first pre-balance time of the first cell based on a sum of the first pre-balance time and the first balance time from the previous balancing cycle.

9. The controller of claim 7 , wherein the controller pre-balances a second cell by enabling a second shunt path connected in parallel to the second cell for a second pre-balance time and balances the second cell by enabling the second shunt path for a second balance time if an unbalance condition of the second cell is detected by the controller, and wherein the controller updates the second pre-balance time for each balancing cycle based on the second pre-balance time and the second balance time from a previous balancing cycle, and wherein the controller further adjusts the first pre-balance time of the first cell and the second pre-balance time of the second cell based on a minimum value between the updated first pre-balance time and the updated second pre-balance time.

10. The controller of claim 9 , wherein the controller adjusts the first pre-balance time of the first cell by subtracting the minimum value from the first updated pre-balance time.

11. A method for balancing a plurality of cells of a battery connected in series, comprising:

pre-balancing a first cell by enabling a first shunt path connected in parallel to the first cell for a first pre-balance time;

monitoring an unbalanced condition of the first cell;

balancing the first cell by enabling the first shunt path for a first balance time if the first cell is unbalanced;

measuring the first balance time of the first cell; and

updating the first pre-balance time for each balancing cycle based on the first pre-balance time and the first balance time from a previous balancing cycle.

12. The method of claim 11 , further comprising:

updating the first pre-balance time by adding up the first pre-balance time of the first cell and the first balance time of the first cell from the previous balancing cycle.

13. The method of claim 11 , further comprising:

pre-balancing a second cell by enabling a second shunt path connected in parallel to the second cell for a second pre-balance time;

monitoring an unbalanced condition of the second cell;

balancing the second cell by enabling the second shunt path for a second balance time if the second cell is unbalanced;

measuring the second balance time of the second cell;

updating the second pre-balance time for each balancing cycle based on the second pre-balance time and the second balance time from the previous balancing cycle; and

adjusting the first pre-balance time of the first cell and the second pre-balance time of the second cell based on a minimum value between the updated first pre-balance time and the updated second pre-balance time.

14. The method of claim 13 , further comprising:

adjusting the first pre-balance time of the first cell by subtracting the minimum value from the first pre-balance time.

15. The method of claim 11 , further comprising:

enabling the first shunt path in a plurality of discrete time slots if the first cell is unbalanced; and

summing up the discrete time slot to generate the first balance time.