Method for protecting an excess discharge of a battery

A method of protecting a battery from excessive discharge, in which the battery is formed of a battery cell and first and second connection terminals to which one of a load or a battery charger is connected, the method comprising the steps of:

• connecting a transistor switch having a collector terminal and an emitter terminal between the second connection terminal and the battery cell and forming a series connection with the battery cell;
• detecting a voltage of the battery cell;
• causing a low bias current to flow to a base terminal of the transistor switch to change a collector terminal voltage of the transistor switch obtained when the load or the battery charger is connected to the first and second connection terminals when it is detected that the voltage of the battery cell is a predetermined value or greater;
• causing a positive current to flow from the battery cell to the load or causing a negative charging current to flow from the battery charger to the battery cell by increasing a control voltage applied to the base terminal of the transistor switch in response to a change of the collector terminal voltage of the transistor switch connected to the second connection terminal;
• interrupting the supply of the bias current to the base terminal of the transistor switch and thereby turning the transistor switch off when it is detected that the voltage of the battery cell is smaller than the predetermined value;
• detecting that the collector terminal voltage of the transistor switch is a negative voltage;
• and
• superimposing a control current upon the bias current, so that an operation current of negative direction flows in the transistor switch.

A method of protecting a battery from excessive discharge, in which the battery is formed of a battery cell and first and second connection terminals to which one of a load or a battery charger is connected, the method comprising the steps of:

• connecting a transistor switch having a collector terminal and an emitter terminal between the second connection terminal and the battery cell and forming a series connection with the battery cell;
• detecting a voltage of the battery cell;
• causing a low bias current to flow to a base terminal of the transistor switch to change a collector terminal voltage of the transistor switch obtained when the load or the battery charger is connected to the first and second connection terminals when it is detected that the voltage of the battery cell is a predetermined value or greater;
• causing a positive current to flow from the battery cell to the load or causing a negative charging current to flow from the battery charger to the battery cell by increasing a control voltage applied to the base terminal of the transistor switch in response to a change of the collector terminal voltage of the transistor switch connected to the second connection terminal;
• interrupting the supply of the bias current to the base terminal of the transistor switch and thereby turning the transistor switch off when it is detected that the voltage of the battery cell is smaller than the predetermined value;
• detecting that the collector terminal of the voltage of the electronic switch is a positive voltage;
• and
• interrupting the control current when the battery charger is connected to the first and second connection terminals and a charging operation is stopped.

A method of protecting a battery from excessive discharge, in which the battery is formed of a battery cell and first and second connection terminals to which one of a load or a battery charger is connected, the method comprising the steps of:

• connecting a transistor switch having a collector terminal and an emitter terminal between the second connection terminal and the battery cell and forming a series connection with the cell;
• detecting a voltage of the battery cell;
• causing a low bias current to flow to a base terminal of the transistor switch to change a collector terminal voltage of the transistor switch obtained when the load or battery charger is connected to the first and second connection terminals when it is detected that the voltage of the battery cell is a predetermined value or greater;
• controlling a positive current flowing from the battery cell to the load or a negative charging current flowing from the battery charger to the battery cell by increasing a control voltage applied to the base terminal of the transistor switch in response to a change of the collector terminal voltage of the transistor switch connected to the second connection terminal;
• disabling a connection between the second connection terminal and the battery cell by interrupting the supply of the bias current to the base terminal of the transistor switch and turning the transistor switch off when it is detected that the voltage of the battery cell is smaller than the predetermined value;
• connecting a temperature detector in series in a line through which the bias current is supplied to the base terminal of the transistor switch;
• and
• controlling the bias current to be a predetermined value in response to a detected temperature.