Secondary cell protection circuit and battery

1. A secondary cell protection circuit configured to protect plural secondary cells connected in series comprising:

plural switching parts configured to be connected in parallel with the secondary cells respectively; and

a charge controller configured to turn on the switching part connected to the secondary cell of which cell voltage is greater than or equal to a return voltage, and to turn off the switching part when all cell voltages of the secondary cells become greater than or equal to the return voltage,

wherein the return voltage is less than the voltage of a fully charged secondary cell.

2. The secondary cell protection circuit as claimed in claim 1 , further comprising:

an over discharge detecting part configured to detect an over discharge state of any of the secondary cells; and

a discharge controller configured to form a discharge path by turning on the switching part in order to discharge the secondary cell, which is not in the over discharge state, via the discharge path when the over discharge detecting part detects the over discharge state of any of the secondary cells;

wherein the over discharge detecting part detects the over discharge state when the cell voltage becomes less than a detection voltage.

3. A battery comprising:

a plurality of secondary cells; and

the secondary cell protection circuit as claimed in claim 2 .

4. A battery comprising:

a plurality of secondary cells; and

the secondary cell protection circuit as claimed in claim 1 .

5. The secondary cell protection circuit as claimed in claim 1 , wherein the charge controller includes:

a plurality of comparators to which reference voltages and voltages based on the cell voltage are input, respectively,

a first NOR circuit to which outputs of the comparators are input, and

a second NOR circuit to which an output of the first NOR circuit and the outputs of the comparators are input.

6. The secondary cell protection circuit as claimed in claim 1 , wherein the discharge controller includes:

a plurality of comparators to which reference voltages and voltages based on the cell voltage are input, respectively,

a first NOR circuit to which outputs of the comparators are input, and

a second NOR circuit to which an output of the first NOR circuit and the outputs of the comparators are input.

7. A secondary cell protection circuit configured to protect plural secondary cells connected in series comprising:

plural switching parts configured to be connected in parallel with the secondary cells respectively;

plural over discharge detecting parts configured to detect an over discharge state of the secondary cells respectively;

an over discharge detection signal outputting part configured to output an over discharge detection signal when any of the plural over discharge detecting parts detect the over discharge state;

a discharge controller configured to form a discharge path by turning on the switching part in order to discharge the secondary cell, which is not in the over discharge state, via the discharge path when the over discharge detection signal outputting part outputs the over discharge detection signal;

a charge controller configured to turn on the switching part connected to the secondary cell of which cell voltage is greater than or equal to a return voltage, and to turn off the switching part when all cell voltages of the secondary cells become greater than or equal to the return voltage, when the secondary cells are being charged;

wherein the over discharge detecting parts respectively detect the over discharge state when the cell voltage becomes less than a detection voltage, and

wherein the return voltage is greater than or equal to the detection voltage and less than the voltage of a fully charged secondary cell.

8. The secondary cell protection circuit as claimed in claim 7 , further comprising:

a detection level shifting part configured to shift detection voltage of the over discharge detecting part which does not detect the over discharge state to the return voltage when the over discharge detection signal outputting part outputs the over discharge detection signal;

wherein, when any of the over discharge detecting parts detect the over discharge state of the cell by detecting that the cell voltage becomes less than or equal to the detection voltage which is shifted to the return voltage by the detection level shifting part, the discharge controller shuts off the discharge path by turning off the switching part corresponding to the cell of which the over discharge state is detected by the over discharge detecting part.

9. A battery comprising:

a plurality of secondary cells; and

the secondary cell protection circuit as claimed in claim 8 .

10. A battery comprising:

a plurality of secondary cells; and

the secondary cell protection circuit as claimed in claim 7 .

11. The secondary cell protection circuit as claimed in claim 7 , wherein the charge controller includes:

a plurality of comparators to which reference voltages and voltages based on the cell voltage are input, respectively,

a first NOR circuit to which outputs of the comparators are input, and

a second NOR circuit to which an output of the first NOR circuit and the outputs of the comparators are input.

12. The secondary cell protection circuit as claimed in claim 7 , wherein the discharge controller includes:

a plurality of comparators to which reference voltages and voltages based on the cell voltage are input, respectively,

a first NOR circuit to which outputs of the comparators are input, and

a second NOR circuit to which an output of the first NOR circuit and the outputs of the comparators are input.

13. A secondary cell protection circuit configured to protect plural secondary cells connected in series comprising:

plural switching parts configured to be connected in parallel with the secondary cells respectively;

plural over discharge detecting parts configured to detect an over discharge state of the secondary cells respectively;

an over discharge detection signal outputting part configured to output an over discharge detection signal when any of the plural over discharge detecting parts detect the over discharge state;

a discharge controller configured to form a discharge path by turning on the switching part in order to discharge the secondary cell, which is not in the over discharge state, via the discharge path when the over discharge detection signal outputting part outputs the over discharge detection signal;

a charge controller configured to turn on the switching part connected to the secondary cell of which cell voltage is greater than or equal to a return voltage, and to turn off the switching part when all cell voltages of the secondary cells become greater than or equal to the return voltage, when the secondary cells are being charged; and

a detection level shifting part configured to shift detection voltage of the over discharge detecting part which does not detect the over discharge state to the return voltage when the over discharge detection signal outputting part outputs the over discharge detection signal,

wherein the over discharge detecting parts respectively detect the over discharge state when the cell voltage becomes less than a detection voltage, and the return voltage is greater than or equal to the detection voltage; and

wherein, when any of the over discharge detecting parts detect the over discharge state of the cell by detecting that the cell voltage becomes less than or equal to the detection voltage which is shifted to the return voltage by the detection level shifting part, the discharge controller shuts off the discharge path by turning off the switching part corresponding to the cell of which the over discharge state is detected by the over discharge detecting part.

14. A battery comprising:

a plurality of secondary cells; and

the secondary cell protection circuit as claimed in claim 13 .