Method of charging rechargeable battery and protection circuit for rechargeable battery

1. A method of charging a rechargeable battery including a bare cell and a charging component through which current can flow to charge the bare cell, the method comprising:

determining a charge state of the bare cell across terminals of the bare cell; and

controlling a charging current flowing through the charging component to be at a first relatively low level during a pre-charging phase and at a second higher level during a charging phase, in dependence on the determined charge state, with the step of controlling the charging current flowing through the charging component comprising the steps of:

electrically connecting a charging field effect transistor between a terminal of the bare cell and a terminal of a charger, with the charging field effect transistor comprising a drain electrode electrically connected to the terminal of the bare cell, a source electrode electrically connected to the terminal of the charger, and a gate electrode;

controlling a duty ratio of a pulse width modulation signal generated by a pulse generating device;

filtering the alternating voltage of the pulse width modulation signal; and

applying the filtered signal to the source electrode of the charging field effect transistor to control the amount of charging current flowing from the source electrode to the drain electrode of the charging field effect transistor.

2. The method of charging a rechargeable battery as claimed in claim 1 , further comprising:

detecting a voltage increase of the bare cell to determine whether a terminal voltage of the bare cell is above a threshold level; and

in the event that the terminal voltage is above the threshold level, switching the charging current to the second higher level.

3. The method of charging a rechargeable battery as claimed in claim 1 , further comprising:

switching the charging current to the second higher level after a predetermined period of time at the first relatively low level.

4. The method of charging a rechargeable battery as claimed in claim 1 , with the step of controlling the current to be at the second higher level comprising applying a relatively high voltage between the gate electrode and the source electrode of the charging field effect transistor to induce more charging current flowing through the charging field effect transistor, the charging current flowing through the charging field effect transistor being more than the first relatively low charging current, and the voltage applied to the gate electrode of the charging field effect transistor being higher than the voltage applied to provide the first relatively low current.

5. The method of charging a rechargeable battery as claimed in claim 4 , with the step of applying a relatively high voltage between the gate electrode and the source electrode of the charging field effect transistor comprising controlling the duty ratio of the pulse width modulation signal, filtering the alternating voltage of the pulse width modulation signal and applying the filtered signal to the source electrode of the charging field effect transistor.

6. The method of charging a rechargeable battery as claimed in claim 1 , with the step of controlling the charging current to be at the second higher level comprising normally charging the bare cell by an normal-charge driver which turns on the charging field effect transistor by applying a low signal to the gate electrode of the charging field effect transistor.

7. A protection device for a rechargeable battery comprising:

a bare cell;

a charging field effect transistor comprising a drain electrode electrically connected with the bare cell and a source electrode electrically connected with a charger;

means for determining a charge state of the bare cell across terminals of the bare cell;

a smoothing circuit for filtering a pulse width modulation signal and applying the filtered signal to the source electrode of the charging field effect transistor;

a pulse generating device electrically connected to the smoothing circuit to provide the pulse width modulation signal to the smoothing circuit periodically; and

a protection circuit electrically connected to the pulse generating device and provided with a pre-charge driver for changing the duty-ratio of the periodic pulse signal generated by the pulse generating device.

8. The protection device for a rechargeable battery as claimed in claim 7 , with the protection circuit comprising a normal-charge driver electrically connected to a gate electrode of the charging field effect transistor to either turn on or turn off the charging field effect transistor.

9. The protection device for a rechargeable battery as claimed in claim 8 , further comprising a second diode connecting in series between the gate electrode of the charging field effect transistor and the normal-charge driver to interrupt the current flowing from the normal-charge driver to the charging field effect transistor.

10. The protection device for a rechargeable battery as claimed in claim 9 , comprising a fourth resistor connected between the second diode and the gate electrode of the charging field effect transistor.

11. The protection device for a rechargeable battery as claimed in any one of claims 7 , and 8 to 10 , with the smoothing circuit comprising:

a first resistor connected to the source electrode of the charging field effect transistor in series;

a capacitor connected to the first resistor in parallel;

a first diode connected between the pulse generating device and the gate electrode of the charging field effect transistor to interrupt the current from the pulse generating device to the charging field effect transistor; and

a second resistor connected between the point in which the first resistor is connected with the first diode and the pulse generating device.

12. The protection device for a rechargeable battery as claimed in any one of claims 7 , and 8 to 10 , with the charging field effect transistor comprising a P-channel field effect transistor.

13. The protection device for a rechargeable battery as claimed in any one of claims 7 , and 8 to 10 , comprising a third resistor connected between the source electrode and the gate electrode of the charging field effect transistor.

14. A method for charging a rechargeable battery including a bare cell and a charging component through which current can flow to charge the bare cell, the method comprising:

determining a charge state of the bare cell across terminals of the bare cell; and

controlling a charging current flowing through the charging component in dependence on the determined charge state, with the step of controlling the charging current flowing through the charging component comprising the steps of:

electrically connecting a charging field effect transistor between a terminal of the bare cell and a terminal of a charger, with the charging field effect transistor comprising a first principal current conducting electrode electrically connected to the terminal of the bare cell, a second principal current conducting electrode electrically connected to the terminal of the charger, and a gate electrode;

controlling a duty ratio of a pulse width modulation signal generated by a pulse generating device;

filtering an alternating voltage of the pulse width modulation signal; and

applying the filtered signal to the second principal current conducting electrode of the charging field effect transistor to control the amount of charging current flowing from the second principal current conducting electrode to the first principal current conducting electrode of the charging field effect transistor.