Charging circuit for secondary battery

• US 7,012,405 B2
• Filed: 09/12/2002
• Issued: 03/14/2006
• 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): Sherry, Michael
• Assistant Examiner(s): Berhanu, Samuel
• Application Number:
  US10/467,682
• Publication Number:
  US 20040090209A1
• Time in Patent Office: 1,279 Days
• Field of Search: 320/129, 320/135, 320/137, 320/139, 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 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.

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, 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.

4. 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 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.

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

6. The charging circuit as claimed in claim 5, 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.

7. The charging circuit as claimed in claim 4, 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.

8. The charging circuit as claimed in claim 7, 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.

9. The charging circuit as claimed in claim 4, wherein the control transistor is a p-channel metal oxide semiconductor field-effect transistor.

10. The charging circuit as claimed in claim 4, wherein the control transistor is a PNP bipolar transistor.

11. The charging circuit as claimed in claim 1, 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.

12. 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 a predetermined current flows to said secondary battery; 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.

13. 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 circuit part that determines charge completion so as to output a predetermined charge completion signal; 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.