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A control system for charging enabling efficient charging of rechargeable batteries in an electronic apparatus which charges its rechargeable batteries by using a charger circuit when driving the apparatus by using an external power source, including first detecting unit for detecting a differential

A control system for charging enabling efficient charging of rechargeable batteries in an electronic apparatus which charges its rechargeable batteries by using a charger circuit when driving the apparatus by using an external power source, including first detecting unit for detecting a differential value between a maximum permissible charging current allowed by the rechargeable batteries and a charging current flowing to the rechargeable batteries; second detecting unit for detecting a maximum usable current by detecting a differential value between a maximum supplyable current allowed by the external power source and the current consumption of the apparatus; third detecting unit for detecting a differential value between a maximum useable current and the charging current flowing to the rechargeable batteries; and control unit for controlling the system in accordance with the differential values detected by the first and third detecting units so that the charger circuit generates the maximum charging current within the range where the charging current flowing to the rechargeable batteries does not exceed either of the maximum permissible charging current and the maximum useable current.

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1. A system for controlling the supply of power from an external power source to rechargeable batteries in an apparatus which can be powered either by the external power source or the rechargeable batteries, comprising: a first detector for detecting a difference between a maximum permissible chargi

1. A system for controlling the supply of power from an external power source to rechargeable batteries in an apparatus which can be powered either by the external power source or the rechargeable batteries, comprising: a first detector for detecting a difference between a maximum permissible charging current allowed by the rechargeable batteries and a charging current flowing to the rechargeable batteries;a second detector for detecting a maximum useable current by detecting a difference between a maximum suppliable current allowed by the external power source and the current being consumed by the apparatus;a third detector for detecting a difference between the maximum useable current and the charging current flowing to the rechargeable batteries; anda controller for controlling power supplied from the external power source to the rechargeable batteries in accordance with the differences detected by the first and third detectors so that the charging current flowing to the rechargeable batteries does not exceed the maximum permissible charging current and does not exceed the maximum useable current. 2. A system for controlling as set forth in claim 1, further comprising a fourth detector for detecting a difference between a maximum permissible supply voltage allowed by said rechargeable batteries and a voltage applied to said rechargeable batteries, said control means controlling the power supplied from the external power source to the rechargeable batteries in accordance with the difference detected by the fourth detector so that the voltage applied to the rechargeable batteries does not exceed the maximum permissible supply voltage. 3. A system for controlling the supply of power from an external power source to rechargeable batteries in an apparatus which can be powered by either the external power source or the rechargeable batteries, comprising: a first detector for detecting a difference between a maximum permissible charging current allowed by the rechargeable batteries and a charging current flowing to the rechargeable batteries;a second detector for detecting a difference between a lowest permissible output voltage allowed by the external power source and an output voltage which is being output by the external power source; anda controller for controlling power supplied from the external power source to the rechargeable batteries in accordance with the differences detected by the first and second detectors so that the charging current flowing to the rechargeable batteries does not exceed the maximum permissible charging current and the output voltage being output by the external power source is not less than the lowest permissible output voltage. 4. A control system for controlling as set forth in claim 3, further comprising a third detector for detecting a difference between the maximum permissible supply voltage allowed by the rechargeable batteries and a voltage applied to said rechargeable batteries, said control means controlling the power supplied from the external power source to the rechargeable batteries in accordance with the difference detected by the third detector so that the voltage applied to the rechargeable batteries does not exceed the maximum permissible supply voltage. 5. A system for controlling as set forth in claim 1, wherein said controller controls the power supplied from the external power source to the rechargeable batteries by determining if either the first or third detector detects a negative difference thus indicating that the charging current exceeds a maximum,wherein if either of the first or third detector detects a negative difference, the controller selects the largest negative difference and controls the charging current to increase the largest negative difference to a zero difference, andwherein if neither of the first or third detector detects a negative difference, the controller selects the largest positive difference and controls the charging current to decrease the largest positive difference to a zero difference. 6. A system for controlling as set forth in claim 2, wherein said controller controls the power supplied from the external power source to the rechargeable batteries by determining if any of the first, third or fourth detector detects a negative difference thus indicating that the charging current or the supply voltage exceeds a maximum,wherein if any of the first, third or fourth detector detects a negative difference, the controller selects the largest negative difference and controls the charging current to increase the largest negative difference to a zero difference, andwherein if none of the first, third or fourth detector detects a negative difference, the controller selects the largest positive difference and controls the charging current to decrease the largest positive difference to a zero difference. 7. A system for controlling as set forth in claim 3, wherein said controller controls the power supplied from the external power source to the rechargeable batteries by determining if either of the detector detects a negative difference thus indicating that the charging current exceeds a maximum or the output voltage is less then a minimum,wherein if either of the detector detects a negative difference, the controller selects the largest negative difference and controls the charging current to increase the largest negative difference to a zero difference, andwherein if neither of the detector detects a negative difference, the controller selects the largest positive difference and controls the charging current to decrease the largest positive difference to a zero difference. 8. A system for controlling as set forth in claim 4, wherein said controller controls the power supplied from the external power source to the rechargeable batteries by determining if any of the detector detects a negative difference thus indicating that a current or a voltage is greater than a maximum or less than a minimum,wherein if any of the detector detects a negative difference, the controller selects the largest negative difference and controls the charging current to increase the largest negative difference to a zero difference, andwherein if none of the detector detects a negative difference, the controller selects the largest positive difference and controls the charging current to decrease the largest positive difference to a zero difference. 9. A system for controlling the supply of power from a charger circuit to rechargeable batteries, the rechargeable batteries being used to supply power to a power supply circuit, comprising: a sense resistor having two ends, located between the rechargeable batteries and a connection point for the charger circuit and the power supply circuit, the sense resistor detecting current flowing into and out of the rechargeable batteries;a current measurement device having two inputs connected respectively to the two ends of the sense resistor, the current measurement device determining which of the two inputs has a larger voltage and generating a voltage in accordance with the difference between the voltages of the two inputs to thereby measure the current flowing into or out of the rechargeable battery; anda control circuit regulating to a constant current the current flowing into the rechargeable batteries, based on the current flowing into the rechargeable batteries detected by the sense resistor. 10. A system for controlling as set forth in claim 9, wherein the control circuit has two inputs connected respectively to the two ends of the sense resistor. 11. A charge control circuit for controlling a charger for an electronic apparatus that applies an input voltage supplied from a power source to a load and has the charger for charging a battery by using the input voltage, the input voltage supplied from said power source being a substantially constant voltage for power source currents less than or equal to a predetermined value, the charge control circuit comprising: a first detector which detects the input voltage from the power source;a second detector which detects a difference between charging current toward the battery and a given value, the given value being a maximum permissible charging current allowed by the battery; anda control circuit which reduces the charging current according to at least one of the detected input voltage and the difference detected by the second detector. 12. The charge control circuit as set forth in 11, wherein power applied to the load varies based on the state of the load. 13. A charge control circuit as set forth in claim 12, wherein the charger comprises a switch which turns charging power to the battery ON and OFF, and the control circuit controls the charging power by controlling the switch. 14. A charge control circuit as set forth in claim 12, wherein the control circuit controls the charging current with the second detector so that the charging current toward the battery becomes equal to or lower than said given value. 15. A charge control circuit as set forth in claim 12, wherein the control circuit controls the charging voltage so that a charging voltage detected by a charging voltage detector which detects the charging voltage of the battery becomes, equal to or lower than a voltage value assigned to the battery. 16. A charge control circuit as set forth in claim 12, wherein the power source is an AC adapter. 17. A charge control circuit as set forth in claim 12, wherein the power source is a power source for generating a DC voltage. 18. A charge control circuit as set forth in 11, wherein the input voltage decreases toward a lesser value for power source currents greater than the predetermined value, and the control circuit controls the charger based on the detected input voltage value so that the input voltage does not decrease below the lesser value due to the supplying of charging power. 19. A charge control circuit as set forth in claim 18, wherein the charger comprises a switch which turns charging power to the battery ON and OFF, and the control circuit controls the charging power by controlling the switch. 20. A charge control circuit as set forth in claim 18, wherein the control circuit controls the charging current with the second detector so that the charging current toward the battery becomes equal to or lower than said given value. 21. A charge control circuit as set forth in claim 18, wherein the control circuit controls the charging voltage so that a charging voltage detected by a charging voltage detector which detects the charging voltage of the battery becomes equal to or lower than a voltage value assigned to the battery. 22. A charge control circuit as set forth in claim 18, wherein the power source is an AC adapter. 23. A charge control circuit as set forth in claim 18, wherein the power source is a power source for generating a DC voltage. 24. A charge control circuit as set forth in claim 11, wherein the charger comprises a switch which turns charging power to the battery ON and OFF, and the control circuit controls the charging power by controlling the switch. 25. A charge control circuit as set forth in claim 11, wherein the control circuit controls the charging current with the second detector so that the charging current toward the battery becomes equal to or lower than said given value. 26. A charge control circuit as set forth in claim 11, wherein the control circuit controls the charging voltage so that a charging voltage detected by a charging voltage detector which detects the charging voltage of the battery becomes equal to or lower than a voltage value assigned to the battery. 27. A charge control circuit as set forth in claim 11, wherein the power source is an AC adapter. 28. A charge control circuit as set forth in claim 11, wherein the power source is a power source for generating a DC voltage. 29. The charge control circuit according to claim 11, wherein the control circuit reduces the charging current if the detected input voltage is decreased.