Battery charger circuit including battery temperature control

• US 5,504,416 A
• Filed: 12/15/1993
• Issued: 04/02/1996
• Est. Priority Date: 12/15/1993
• Status: Expired due to Term

• Current Assignee: Unitrode Corp. (Texas Instruments, Inc.)
• Original Assignee: Unitrode Corp. (Texas Instruments, Inc.)
• Inventors: Holloway, Peter R., Mammano, Robert A.
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): Law, Patrick B.
• Application Number:
  US08/168,268
• Time in Patent Office: 839 Days
• Field of Search: 320/20, 320/22, 320/23, 320/24, 320/31, 320/32, 320/35, 320/36, 320/39, 320/40
• US Class Current: 320/152
• CPC Class Codes: H01M 10/44 Methods for charging or discharging circuits for charging H02J7/00
• CPC Class Codes: H01M 10/443 in response to temperature
• CPC Class Codes: H02J 7/007182 in response to battery voltage
• CPC Class Codes: H02J 7/007194 of the battery
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

An adaptive battery charger circuit including a state machine adjusts the charging current in accordance with the battery charge acceptance. The battery charging cycle includes an initial charging phase characterized by a relatively high charge acceptance, an intermediate charging phase characterized by a decreasing charge acceptance and a rising battery temperature, and a final charging phase characterized by the battery being at substantially full charge and the charge acceptance approaching zero. Each charging phase corresponds to one or more states of the state machine. Multiple sets of conditions causing transitions between the states of operation are derived from a model of a battery under charge which relates charge acceptance, battery temperature, and cumulative supplied charge. During the intermediate charging phase, the charging current is adjusted to maintain a predetermined battery temperature for a predetermined duration. With this arrangement, the maximum product of charging current and charge acceptance maintainable for the battery without exceeding a safe temperature is continuously achieved.

Claims

1. A circuit for charging a rechargeable battery, comprising:

a temperature sensor coupled to said battery to provide a battery temperature signal indicative of the temperature of said battery;

a voltage sensor coupled to said battery for providing a battery voltage signal indicative of the voltage across said battery;

an adjustable current source for providing current to said battery; and

a processor receiving said battery temperature signal and said battery voltage signal, for providing a feedback signal to said current source to adjust said current provided to said battery in order to maintain said battery temperature at a predetermined value for a predetermined duration, wherein said predetermined value of said battery temperature and said predetermined duration are selected in order to maintain the charge acceptance of said battery above a predetermined percentage.

2. The circuit recited in claim 1 wherein said predetermined value of said battery temperature is selected based on a model of a battery under charge correlating charge acceptance, battery temperature, and cumulative supplied current parameters.

3. The circuit recited in claim 2 wherein said processor includes a state machine having state transitions which are based on said model.

4. The circuit recited in claim 1 wherein said predetermined value of said battery temperature is adjustable.

5. The circuit recited in claim 1 wherein said predetermined value of said battery temperature is approximately 40°

C. for a first predetermined duration.

6. The circuit recited in claim 1 wherein said processor provides said feedback signal to said current source to adjust said current provided to said battery in order to maintain said battery temperature substantially at a second, lower predetermined value of approximately 33.5°

C. for a second predetermined duration.

7. The circuit recited in claim 1 further comprising a peak detector coupled to said battery for providing a signal indicating whether a peak of said battery voltage has occurred.

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

a temperature sensor coupled to said battery to provide a battery temperature signal indicative of the temperature of said battery;

a voltage sensor coupled to said battery for providing a battery voltage signal indicative of the voltage across said battery;

an adjustable current source for providing current to said battery; and

a processor, receiving said battery temperature signal and said battery voltage signal for providing a feedback signal to said current source to adjust said current provided to said battery in order to maintain said battery temperature at a predetermined value for a predetermined duration, wherein said predetermined duration is a function of the cumulative charge supplied to said battery.

9. A battery charger circuit comprising:

an adjustable current source for supplying a charging current to a re-chargeable battery with an adjustable duty cycle, said duty cycle of said charging current being adjustable in response to a control signal to adjust the effective level of said charging current;

a battery temperature sensor for measuring the temperature of said battery; and

a processor receiving said battery temperature measurement for generating said control signal, said processor including a state machine having a first state of operation during which said battery temperature is maintained substantially at a first predetermined temperature and a second state of operation during which said battery temperature is maintained substantially at a second, lower predetermined temperature, wherein said state machine has an initial state corresponding to an initial charging phase during which an initial level of charging current is supplied to said battery.

10. The circuit recited in claim 9 wherein said state machine has a final state corresponding to a final charging phase during which the battery is maintained at full charge.

11. The circuit recited in claim 9 further comprising a battery voltage sensor for measuring the voltage across said battery.

12. The circuit recited in claim 9 wherein said predetermined temperature at which said battery is maintained during said first state is approximately 40°

C.

13. The circuit recited in claim 9 wherein said predetermined temperature at which said battery is maintained during said second state is approximately 33.5°

C.

14. A battery charger circuit comprising:

an adjustable current source for supplying a charging current to a re-chargeable battery with an adjustable duty cycle, said duty cycle of said charging current being adjustable in response to a control signal to adjust the effective level of said charging current;

a battery temperature sensor for measuring the temperature of said battery; and

a processor receiving said battery temperature measurement for generating said control signal, said processor including a state machine having a first state of operation corresponding to an initial charging phase during which a first level of charging current is supplied to said battery, a second state of operation corresponding to an intermediate charging phase during which said battery temperature is maintained at or below a predetermined temperature, and a third state corresponding to the intermediate charging phase during which said battery temperature is maintained at or below a second predetermined temperature, wherein each of said first, second, and third states of operation have corresponding first, second, and third durations corresponding to predetermined values of cumulative charge supplied to said battery.

15. The circuit recited in claim 14 wherein said predetermined values of cumulative supplied to said battery are selected in accordance with a model of a battery under charge relating the battery temperature, charge acceptance, and cumulative charge supplied to said battery.

16. The circuit recited in claim 14 wherein said predetermined values of cumulative charge supplied to said battery are approximately 90% of the rated charge of said battery for said first state, approximately 30% of the rated charge of said battery for said second state, and approximately 40% of the rated charge of said battery for said third state.

17. A circuit for charging a rechargeable battery, said rechargeable battery having a charge acceptance percentage indicative of the percentage of incremental input current provided to said battery that is recoverable, said circuit comprising:

a temperature sensor coupled to said battery to provide a battery temperature signal indicative of the temperature of said battery;

an adjustable current source for providing current to said battery; and

a processor, receiving said battery temperature signal, for providing a feedback signal to said current source to adjust said current provided to said battery in order to maintain said battery temperature substantially at a predetermined level until a predetermined amount of charge is supplied to said battery.

18. The circuit recited in claim 17 wherein said feedback signal adjusts said current so as to maintain said battery temperature at a plurality of predetermined levels until a corresponding plurality of amounts of charge supplied to said battery.

19. The circuit recited in claim 18 wherein said processor includes a state machine having a plurality of states corresponding to said plurality of predetermined levels of battery temperature.

20. The circuit recited in claim 17 wherein said adjustable current source includes means for varying the average current provided to said battery.

21. The circuit recited in claim 17 wherein said battery temperature signal is indicative of a temperature rise of said battery.

22. A method for charging a rechargeable battery comprising the steps of:

sensing the temperature of said battery;

supplying a charging current to said battery until said battery temperature reaches a first predetermined value;

maintaining the temperature of said battery substantially at said first predetermined value for a first predetermined duration, wherein said first predetermined duration is a function of cumulative charge supplied to said battery.

23. The method recited in claim 22 wherein said temperature maintaining step further comprising the steps of:

interrupting said charging current supplied to said battery for a second predetermined duration if said battery temperature exceeds said first predetermined value; and

supplying said charging current to said battery for a third predetermined duration if said battery temperature does not exceed said first predetermined value.

24. The method recited in claim 22 further comprising the step of maintaining the temperature of said battery substantially at a second predetermined value for a second predetermined duration.

25. A circuit for charging rechargeable battery, comprising:

a temperature sensor in thermal communication with said battery to provide a battery temperature signal indicative of the temperature of said battery;

a voltage sensor coupled to said battery for providing a battery voltage signal indicative of the voltage across said battery;

an adjustable current source for providing current to said battery; and

a processor, receiving said battery temperature signal and said battery voltage signal for providing a feedback signal to said current source causing said current source to supply a high charging current to said battery during an initial charging phase which is terminable when said battery temperature reaches a predetermined value and to provide a lower charging current to said battery during a temperature controlled phase so as to maintain said battery temperature substantially at said predetermined value for a predetermined duration, wherein said temperature controlled phase is entered when said battery temperature reaches said predetermined value or when a predetermined amount of charge has been supplied to said battery.