Charging circuit for secondary battery

• US 7,274,171 B2
• Filed: 12/07/2005
• Issued: 09/25/2007
• Est. Priority Date: 09/14/2001
• Status: Expired due to Fees

• Current Assignee: Ricoh Company Limited
• Original Assignee: Ricoh Company Limited
• Inventors: Nishida, Junji, Manabe, Shinya
• Primary Examiner(s): Easthom; Karl
• Assistant Examiner(s): BERHANU, SAMUEL
• Application Number:
  US11/295,450
• Publication Number:
  US 20060087290A1
• Time in Patent Office: 657 Days
• Field of Search: 320/137, 320/139, 320/162, 320/141, 320/145
• US Class Current: 320/137
• CPC Class Codes: H02J 7/0071 with a programmable schedule
• CPC Class Codes: H02J 7/00711 with introduction of pulses during the charging process
• CPC Class Codes: H02J 7/00714 in response to battery charging or discharging current
• CPC Class Codes: H02J 7/007182 in response to battery voltage
• CPC Class Codes: H02J 7/04 Regulation of charging current or voltage

Abstract

A charging circuit for a secondary battery includes a constant-voltage circuit part outputting one of a plurality of predetermined constant voltages and charges the secondary battery by applying the constant voltage thereto, a detection circuit part detecting a battery voltage of the secondary battery, and a control circuit part controlling the selection of the constant-voltage in response to the detected battery voltage. Another charging circuit includes a constant-current circuit part outputting, to the secondary battery, one of two predetermined constant currents, a constant-voltage circuit part charging the secondary battery by applying a predetermined constant voltage thereto, a battery voltage detection circuit part detecting a battery voltage of the secondary battery, a charge current detection circuit part outputting a predetermined charge completion signal, and a charge control circuit part stopping operations of the constant-current circuit part and constant-voltage circuit part when receiving the charge completion signal.

Claims

1. A charging circuit for charging a secondary battery, comprising;

a constant-current circuit that outputs, to the secondary battery, one of first and second constant currents in response to an input control signal;

a constant-voltage circuit that charges the secondary battery by applying a predetermined constant voltage thereto;

a battery voltage detection circuit that detects and outputs a battery voltage of the secondary battery;

a charge current detection circuit that outputs a predetermined charge completion signal when a predetermined current flows to said secondary battery; and

a charge control circuit that stops operations of said constant-current circuit and said constant-voltage circuit when the charge completion signal is input,

wherein, when the battery voltage of the secondary battery is lower than a predetermined voltage, said charge control circuit outputs, to said constant-current circuit, the control signal to cause said constant-current circuit to output the first constant current, and when the battery voltage of the secondary battery is equal to or greater than the predetermined voltage, said charge control circuit outputs, to said constant-current circuit, the control signal to cause the constant-current circuit to output the second constant current that is greater than the first constant current.

2. The charging circuit as claimed in claim 1, further comprising:

a direct-current power source that supplies a charging current to the secondary battery.

3. The charging circuit as claimed in claim 1, wherein the constant-voltage circuit comprises:

a constant-voltage generation circuit that generates and outputs the predetermined constant voltage;

a voltage comparator that compares the battery voltage of the secondary battery with the predetermined constant voltage, and outputs a comparison signal indicating a comparison result; and

a control transistor that passes a current according to the comparison signal indicating the comparison result from the external direct-current power source to the secondary battery.

4. The charging circuit as claimed in claim 3, wherein the constant-voltage circuit further comprises a diode that blocks a current flowing to the voltage comparator.

5. The charging circuit as claimed in claim 1, wherein the constant-voltage circuit further comprises a diode that blocks a current flowing from the secondary battery to the external direct-current power source via the control transistor.

6. The charging circuit as claimed in claim 3, wherein the control transistor is a p channel metal oxide semiconductor field-effect transistor.

7. The charging circuit as claimed in claim 3, wherein the control transistor is a PNP bipolar transistor.

8. A charging circuit for charging a secondary battery, comprising:

a constant-current circuit that outputs, to the secondary battery, one of first and second constant currents in response to an input control signal;

a constant-voltage circuit that charges the secondary battery by applying a predetermined constant voltage thereto;

a battery voltage detection circuit that detects and outputs a battery voltage of the secondary battery;

a circuit that outputs a predetermined charge completion signal; and

a charge control circuit that stops operations of said constant-current circuit and said constant-voltage circuit when the charge completion signal is input,

wherein, when the battery voltage of the secondary battery is lower than a predetermined voltage, said charge control circuit outputs, to said constant-current circuit, the control signal to cause said constant-current circuit to output the first constant current, and when the battery voltage of the secondary battery is equal to or greater than the predetermined voltage, said charge control circuit outputs, to said constant-current circuit, the control signal to cause the constant-current circuit to output the second constant current that is greater than the first constant current.

9. The charging circuit as claimed in claim 8, further comprising;

a direct-current power source supplies that a charging current to the secondary battery.

10. The charging circuit as claimed in claim 8, wherein the constant-voltage circuit comprises;

a constant-voltage generation circuit that generates and outputs the predetermined constant voltage;

a voltage comparator that compares the battery voltage of the secondary battery with the predetermined constant voltage, and outputs a comparison signal indicating a comparison result; and

a control transistor that passes a current according to the comparison signal indicating the comparison result from the external direct-current power source to the secondary battery.

11. The charging circuit as claimed in claim 10, wherein the constant-voltage circuit further comprises a diode that blocks a current flowing to the voltage comparator.

12. The charging circuit as claimed in claim 8, wherein the constant-voltage circuit further comprises a diode that blocks a current flowing from the secondary battery to the external direct-current power source via the control transistor.

13. The charging circuit as claimed in claim 10, wherein the control transistor is a p channel metal oxide semiconductor field-effect transistor.

14. The charging circuit as claimed in claim 10, wherein the control transistor is a PNP bipolar transistor.

15. A charging circuit for charging a secondary battery, comprising;

a constant-current circuit that outputs, to the secondary battery, one of first and second constant currents in response to an input control signal;

a constant-voltage circuit that charges the secondary battery by applying a predetermined constant voltage thereto;

a battery voltage detection circuit that detects a battery voltage of the secondary battery, and outputs a signal representative of a battery voltage of the secondary battery;

a charge current detection circuit that outputs a predetermined charge completion signal when a predetermined current flows to said secondary battery; and

a charge control circuit that stops operations of said constant-current circuit and said constant-voltage circuit when the charge completion signal is input,

wherein, when the battery voltage of the secondary battery is lower than a predetermined voltage, said charge control circuit outputs, to said constant-current circuit, the control signal to cause said constant-current circuit to output the first constant current, and when the battery voltage of the secondary battery is equal to or greater than the predetermined voltage, said charge control circuit outputs, to said constant-current circuit, the control signal to cause the constant-current circuit to output the second constant current that is greater than the first constant current.

16. The charging circuit as claimed in claim 15, wherein the constant-voltage circuit comprises:

a constant-voltage generation circuit that generates and outputs the predetermined constant voltage;

a voltage comparator that compares the signal representative of the battery voltage of the secondary battery with the predetermined constant voltage, and outputs a comparison signal indicating a comparison result; and

a control transistor that passes a current according to the comparison signal indicating the comparison result from the external direct-current power source to the secondary battery.

17. A charging circuit for charging a secondary battery, comprising:

a constant-current circuit that outputs, to the secondary battery, one of first and second constant currents in response to an input control signal;

a constant-voltage circuit that charges the secondary battery by applying a predetermined constant voltage thereto;

a battery voltage detection circuit that detects a battery voltage of the secondary battery, and outputs a signal representative of a battery voltage of the secondary battery;

a charge completion circuit that outputs a predetermined charge completion signal; and

a charge control circuit that stops operations of said constant-current circuit and said constant-voltage circuit when the charge completion signal is input,

wherein, when the battery voltage of the secondary battery is lower than a predetermined voltage, said charge control circuit outputs, to said constant-current circuit, the control signal to cause said constant-current circuit to output the first constant current, and when the battery voltage of the secondary battery is equal to or greater than the predetermined voltage, said charge control circuit outputs, to said constant-current circuit, the control signal to cause the constant-current circuit to output the second constant current that is greater than the first constant current.

18. The charging circuit as claimed in claim 17, wherein the constant-voltage circuit comprises;

a constant-voltage generation circuit that generates and outputs the predetermined constant voltage;

a voltage comparator that compares the signal representative of the battery voltage of the secondary battery with the predetermined constant voltage, and outputs a comparison signal indicating a comparison result; and

a control transistor that passes a current according to the comparison signal indicating the comparison result from the external direct-current power source to the secondary battery.