Charging device and control method for preventing recharging of a fully charged battery

A control unit for a battery charging device having a power supply for outputting a constant voltage at a given level, a battery pack into which a rechargeable battery is inserted, and a switch for supplying said battery with said constant voltage output from said power supply through said battery pack in response to a switch control signal, said control unit comprising:

• battery voltage sensing means for sensing a battery voltage every given period of time;
• first comparing means for comparing a preset full charge threshold voltage with said sensed battery voltage and setting a temporary full charge state when said sensed battery voltage is greater than said preset full charge threshold voltage;
• second comparing means, responsive to said setting of said temporary full charge state by said first comparing means, for comparing said preset full charge threshold voltage with an output of said battery voltage sensing means at a constant unit time interval and setting a completely full charge battery recognition flag when said sensed battery voltage is greater than that of said preset full charge threshold voltage throughout a number of said constant unit time intervals;
• and
• control means for generating said switch control signal for cutting off the charging of said battery in response to the setting of said completely full charge battery recognition flag by said second comparing means.

A charging control method of a charging device including a power source for outputting a constant voltage of a given level irrespective of a current output therefrom, a rechargeable battery, a switch for supplying said battery with said constant voltage output from said power source in response to a switch control signal, analog/digital converting means connected to said battery, and a port for generating said switch control signal controlling said switch, said method comprising the steps of:

• sensing an output voltage of said battery by a period of first unit time and storing said sensed output voltage in a first memory area;
• in response to the sensing of said output voltage of said battery, determining that a charging voltage of said battery reaches a full charge state when said sensed battery voltage is more than a preset full charge threshold voltage, and that said charging voltage of said battery does not reach said full charge state when said sensed battery voltage is less than said preset full charge threshold voltage;
• and
• generating said switch control signal to cut off charging of said battery when said charging voltage of said battery is determined to reach a full charge state, and generating said switch control signal to supply said battery with said charging voltage when said charging voltage of said battery is determined not to reach a full charge state.

A method for controlling a battery charging unit, said method comprising the steps of:

• determining whether a battery has been inserted into the charging unit according to a voltage sensed by the charging unit;
• after determining that a battery has been inserted into the charging unit, sensing an initial output voltage across the battery;
• setting a temporary full charge battery recognition flag in the event that said initial sensed battery output voltage is more than a preset full charge threshold voltage, and clearing said temporary full charge battery recognition flag in the event that said initial sensed battery output voltage is not more than said preset full charge threshold voltage;
• in response to the setting of said temporary full charge battery recognition flag, waiting until expiration of a predetermined time period and comparing a current output voltage across the battery with said preset full charge threshold voltage;
• setting a completely full charge battery recognition flag in accordance with whether said current battery output voltage is more than said preset full charge threshold voltage;
• and
• supplying the battery with a charging voltage when said completely full charge battery recognition flag and said temporary full charge battery recognition flag are not set and interrupting application of said charging voltage supplied to said battery when at least one of said completely full charge battery recognition and said temporary full charge battery recognition flags are set.

A charging device for a rechargeable battery, comprising:

• a power source for generating a constant voltage at a given level irrespective of a current output therefrom;
• a connector for receiving and making electrical contact with a battery;
• a switch for selectively connecting said power source to said connector to charge the battery in response to a switch control signal;
• a battery voltage sensing means for providing battery voltage values sensed across the battery received by said connector;
• and
• a control means for comparing a preset full charge threshold voltage value with said battery voltage values provided by said battery voltage sensing means, and for generating said switch control signal for charging the received battery within a first time period after the battery is received by said connector means only when said battery voltage value sensed within said first time period is not greater than said full charge threshold voltage value.