Charging circuit for secondary battery

• US 20040090209A1
• Filed: 10/16/2003
• Published: 05/13/2004
• Est. Priority Date: 09/14/2001
• Status: Active Grant

• Current Assignee: Ricoh Company Limited
• Original Assignee: Ricoh Company Limited
• Inventors: Nishida, Junji, Manabe, Shinya
• Granted Patent: US 7,012,405 B2
• Time in Patent Office: Days
• US Class Current: 320/149
• 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 a secondary battery, comprising:

a constant-voltage circuit part that selects and outputs one constant voltage among a plurality of predetermined constant-voltages in response to an input control signal and charges the secondary battery by applying the selected constant voltage thereto;

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

a control circuit part that controls the selection of a constant voltage applied from said constant-voltage circuit part in response to the detected battery voltage from said detection circuit part,

said control circuit part causing said constant-voltage circuit part to charge the secondary battery by applying a predetermined first constant voltage thereto when the battery voltage of the secondary battery is equal to or less than the first constant voltage, and to charge the secondary battery by alternately applying thereto a predetermined second constant voltage and a predetermined third constant voltage that is lower than the second constant voltage in a constant cycle when the battery voltage of the secondary battery exceeds the first constant voltage.

2. The charging circuit as claimed in claim 1, wherein the control circuit part detects completion of charging of the secondary battery and performs a predetermined charge complete operation when the battery voltage of the secondary battery exceeds a predetermined charge complete voltage while causing the constant-voltage circuit part to apply the third constant voltage to the secondary battery.

3. The charging circuit as claimed in claim 1, wherein the second constant voltage is equal to the first constant voltage.

4. The charging circuit as claimed in claim 1, wherein the second constant voltage is higher than the first constant voltage.

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

a load circuit part that connects a load in parallel with the secondary battery according to the third constant voltage output from the constant-voltage circuit part.

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

a constant-voltage generation circuit that generates and outputs the first constant voltage, the second constant voltage and the third constant-voltage;

a voltage switch circuit that, according to the control signal from the control circuit part, selects and outputs one of the first constant-voltage, the second constant voltage and the third constant voltage output from said constant-voltage generation circuit;

a voltage comparator that compares the constant voltage output from said voltage switch circuit with the battery voltage of the secondary battery and outputs a comparison signal according to a comparison result;

a control transistor that passes a current according to the comparison signal from a predetermined direct-current power source to the secondary battery; and

a diode that blocks a current flowing from the secondary battery to the predetermined direct-current power source via said control transistor.

7. A charging circuit charging a secondary battery, comprising:

a constant-current circuit part that is serially connected between an external direct-current power source and the secondary battery, and outputs, to the secondary battery, one of first and second constant currents in response to an input control signal;

a constant-voltage circuit part that is connected in parallel with said constant-current circuit part, and charges the secondary battery by applying a predetermined constant voltage thereto;

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

a charge current detection circuit part that outputs a predetermined charge completion signal when said constant-voltage circuit part stops outputting a current; and

a charge control circuit part that stops operations of said constant-current-circuit part and said constant-voltage circuit part 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 part outputs, to said constant-current circuit part, the control signal to cause said constant-current circuit part 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 part outputs, to said constant-current circuit part, the control signal to cause the constant-current circuit part to output the second constant current that is greater than the first constant current.

8. The charging circuit as claimed in claim 7, further comprising:

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

9. The charging circuit as claimed in claim 7, further comprising:

a charge current control circuit part that controls the current output from the constant-voltage circuit part,

wherein said charge current control circuit part performs operation control on the constant-voltage circuit part so that a maximum value of the current output from the constant-voltage circuit part becomes a predetermined value; and

the charge control circuit part further stops an operation of said charge current control circuit part when the predetermined charge completion signal is input.

10. The charging circuit as claimed in claim 7, wherein the constant-voltage circuit part 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 part further comprises a diode that blocks a current flowing to the voltage comparator.

12. The charging circuit as claimed in claim 11, wherein the charge current control circuit part comprises:

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

a second voltage comparator that compares a voltage applied to a control terminal of the control transistor with the second constant voltage, and outputs a comparison signal indicating a comparison result; and

a second diode that blocks a current flowing from the control terminal to the second voltage comparator.

13. The charging circuit as claimed in claim 10, wherein the charge current detection circuit part detects the comparison signal output from the voltage comparator, and determines, from the detected comparison signal, that the constant-voltage circuit part stops outputting the current.

14. The charging circuit as claimed in claim 13, wherein the charge current detection circuit part comprises:

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

a third voltage comparator that compares a voltage applied to a control terminal of the control transistor with the predetermined third constant voltage, and outputs the predetermined charge completion signal when the voltage applied to the control terminal is equal to the predetermined third constant-voltage,

wherein the predetermined third constant-voltage is a voltage that is applied to the control terminal so that the control transistor cuts off.

22. The charging circuit as claimed in claim 7, wherein the constant-voltage circuit part further comprises a third diode that blocks a current flowing from the secondary battery to the external direct-current power source via the control transistor.

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

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

15. A charging circuit charging a secondary battery, comprising:

a constant-voltage circuit part that is connected between an external direct-current power source and the secondary battery, and charges the secondary battery by applying a predetermined constant-voltage thereto;

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

a charge current detection circuit part that outputs a predetermined charge completion signal when a current output from said constant-voltage circuit part becomes a predetermined value; and

a charge control circuit part that stops an operation of said constant-voltage circuit part when the predetermined charge completion signal is input,

said constant-voltage circuit part-comprising;

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, and

said charge current detection circuit part detecting the comparison signal output from said voltage comparator, and outputs the predetermined charge completion signal-by determining, from the detected comparison signal, that the current passed by said control transistor is a predetermined value.

16. The charging circuit as claimed in claim 15, further comprising:

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

17. The charging circuit as claimed in claim 15, wherein the charge current detection circuit part comprises:

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

a second voltage comparator that compares a voltage applied to a control terminal of the control transistor with the predetermined second constant voltage, and outputs the predetermined charge completion signal in a case where the voltage applied to the control terminal is equal to the predetermined second constant voltage, and

the predetermined second constant voltage is a voltage applied to the control terminal so that the current passed by the control transistor becomes the predetermined value.

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

a diode that blocks a current flowing to the voltage comparator.

19. The charging circuit as claimed in claim 18, further comprising:

a charge current control circuit part that controls the current output from the constant-voltage circuit part,

wherein said charge current control circuit part performs operation control on the constant-voltage circuit part so that a maximum value of the current output from the constant-voltage circuit part becomes a predetermined value, and

the charge control circuit part further stops an operation of said charge current control circuit part when the predetermined charge completion signal is input.

20. The charging circuit as claimed in claim 19, wherein the charge current control circuit part comprises:

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

a third voltage comparator that compares a voltage applied to a control terminal of the control transistor with the predetermined third constant voltage, and outputs a comparison signal indicating a comparison result; and

a second diode that blocks a current flowing from the control terminal to said third voltage comparator.

21. The charging circuit as claimed in claim 15, further comprising:

a constant-current circuit part that is connected in parallel with the constant-voltage circuit part and outputs a predetermined constant current to the secondary battery,

wherein, when the battery voltage of the secondary battery is lower than a predetermined voltage, the charge control circuit part drives said constant-current circuit part, and when the battery voltage of the secondary battery is equal to or more than the predetermined voltage, the charge control circuit part stops said constant-current circuit part.

23. The charging circuit as claimed in claim 15, wherein the constant-voltage circuit part further comprises a third diode that blocks a current flowing from the secondary battery to the external direct-current power source via the control transistor.