Power management circuit for battery systems

• US 6,329,796 B1
• Filed: 07/25/2000
• Issued: 12/11/2001
• Est. Priority Date: 07/25/2000
• Status: Expired due to Term

• Current Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Original Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Inventors: Popescu, Serban-Mihai
• Primary Examiner(s): Tso, Edward H.
• Application Number:
  US09/624,918
• Time in Patent Office: 504 Days
• Field of Search: 320/134, 320/136
• US Class Current: 320/134
• CPC Class Codes: H02J 1/10 Parallel operation of dc sources
• CPC Class Codes: H02J 5/00 Circuit arrangements for transfer of electric power between ac networks and dc networks H02J3/36 takes precedence
• CPC Class Codes: H02J 7/00304 Overcurrent protection
• CPC Class Codes: H02J 7/00306 Overdischarge protection
• CPC Class Codes: H02J 7/0031 using battery or load disconnect circuits H02J9/002 takes precedence
• CPC Class Codes: H02J 7/02 for charging batteries from ac mains by converters

Abstract

A power management circuit for battery systems composed of a switch defining a single charge/discharge path. The switch is selectively controlled using analog signals to couple a battery to a power source for charging, or to couple the battery to an active load. For charging, the switch is controlled by a controller circuit that monitors the battery voltage, the power source and the individual battery cells. The battery is only coupled to the power source if it is determined that the power source is present and that each of the battery cells is capable of receiving a charge. During discharge, the controller monitors the discharge current from the battery and compares this value to a threshold current. If the discharge current falls below the threshold, the switch is controlled to decouple the battery from the load. In this way, an overcharge condition is avoided if, for example, a power source is reapplied to the system. In a multiple battery system (where the battery and battery circuits are connected in parallel to a load and a power source), the use of the threshold current prevents a cross-conduction between batteries.

Claims

1. A battery charging/discharging circuit comprising:

a first switch for selectively coupling a battery to a load along a charging/discharging path, or coupling said battery to a power source along said charging/discharging path; and

a first analog switch controller for selectively controlling the conduction state of said switch comprising a charge enable signal generator circuit for generating a first control signal indicative of the presence of said power source and the charging status of said battery, and a current comparator for comparing a threshold current to a battery discharge current and for generating a second control signal indicative of the battery discharge current;

wherein the conduction state of said switch being controlled by said first or second control signal;

a second switch coupled between said switch and said battery along said charge/discharge path for selectively coupling said battery to said load or said power source; and

a second analog switch controller for selectively controlling the conduction state of said second switch comprising a comparator for comparing a maximum battery discharge current to said battery discharge current and generating a third control signal indicative of said battery discharge current;

wherein the conduction state of said second switch being controlled by said third control signal.

2. A circuit as claimed in claim 1, wherein said switch comprising a MOSFET transistor and a diode in parallel with said transistor, said diode being in forward bias between said battery and said system.

3. A circuit as claimed in claim 1, wherein said power source includes an AC/DC adapter.

4. A circuit as claimed in claim 1, wherein said charge/discharging path comprises a converter circuit for generating a DC charging current from said power source, and a sense impedance for sensing said current being discharged by said battery.

5. A circuit as claimed in claim 4, wherein said converter circuit includes a buck converter circuit comprising an inductor coupled to said switch and said battery, a capacitor coupled to said inductor and a reference voltage, and a diode coupled to said inductor and said reference voltage and being in forward bias with respect to said reference voltage.

6. A circuit as claimed in claim 1, wherein said battery comprises a plurality of individual battery cells having individual voltages.

7. A circuit as claimed in claim 6, wherein said charge enable signal generating circuit comprising a plurality of first comparator circuits for comparing the voltage of each said battery cell to a threshold voltage and each generating a plurality of first output signals, a first AND gate receiving said first output signals and generating a second output signal, a second comparator for comparing the battery voltage and the power source voltage and generating a third output signal, and a second AND gate receiving said second and third output signals and generating a forth output signal;

said current comparator comprising a comparator circuit comparing discharge current supplied by said battery and a threshold current and generating a fifth output signal.

8. A circuit as claimed in claim 7, wherein said switch controller comprises a third AND gate receiving fourth output signal and a pulse signal and generating said first control signal, a fourth AND gate receiving the compliment of said fourth output signal and said fifth output signal and generating said second control signal, and an OR gate receiving said first and second control signals and selectively switching the conduction state of said switch based on said first or second control signals.

9. A circuit as claimed in claim 8, wherein said circuit further comprising a charger control circuit generating said pulse signal, and a feedback signal coupled to said charger control circuit representing the voltage across said battery, wherein the duty cycle of said pulse signal being adjusted by said feedback signal.

10. A circuit as claimed in claim 9, wherein said charger control circuit comprises a pulse width modulator and said pulse signal comprises a pulse width modulated signal.

11. A circuit as claimed in claim 1, wherein said switch comprising a MOSFET transistor and a diode in parallel with said transistor, said diode being in forward bias between said system and said battery.

12. A multiple battery system for delivering power to a load, comprising

two or more batteries each having a charge/discharge circuit, respectively, each said charge/discharge circuit being connected in parallel with a load;

a power source coupled in parallel to said load and said batteries;

said charge/discharge circuit comprising;

a first switch selectively coupling said battery to a power source to charge said battery, or coupling said battery to said load;

a first analog switch controller for controlling the conduction state of said switch comprising a charge enable signal generating circuit for coupling said battery to said power source and to a modulated signal source, and a current comparator for comparing a battery discharge current to a threshold current and coupling said battery to said system based on the comparison of said battery discharge current and said threshold current;

a second switch coupled between said switch and said battery along said charge/discharge path for selectively coupling said battery to said load or said power source; and

a second analog switch controller for selectively controlling the conduction state of said second switch comprising a comparator for comparing a maximum battery discharge current to said battery discharge current and generating a third control signal indicative of said battery discharge current;

wherein the conduction state of said second switch being controlled by said third control signal.

13. A circuit as claimed in claim 12, wherein said switch comprising a transistor and a diode in parallel with said transistor, said diode being in forward bias between said battery and said system.

14. A circuit as claimed in claim 12, wherein said power source includes an AC/DC adapter.

15. A circuit as claimed in claim 12, wherein said charge/discharging path comprises a converter circuit for generating a DC charging current from said power source, and a sense impedance for sensing said current being discharged by said battery.

16. A circuit as claimed in claim 15, wherein said converter circuit includes a buck converter circuit comprising an inductor coupled to said switch and said battery, a capacitor coupled to said inductor and a reference voltage, and a diode coupled to said inductor and said reference voltage and being in forward bias with respect to said reference voltage.

17. A circuit as claimed in claim 12, wherein said battery comprises a plurality of individual battery cells having individual voltages.

18. A circuit as claimed in claim 17, wherein said charge enable signal generating circuit comprising a plurality of first comparator circuits for comparing the voltage of each said battery cell to a threshold voltage and each generating a plurality of first output signals, a first AND gate receiving said first output signals and generating a second output signal, a second comparator for comparing the battery voltage and the power source voltage and generating a third output signal, and a second AND gate receiving said second and third output signals and generating a forth output signal;

said current comparator comprising a comparator circuit comparing discharge current supplied by said battery and a threshold current and generating a fifth output signal.

19. A circuit as claimed in claim 18, wherein said switch controller comprises a third AND gate receiving fourth output signal and a pulse signal and generating said first control signal, a fourth AND gate receiving the compliment of said fourth output signal and said fifth output signal and generating said second control signal, and an OR gate receiving said first and second control signals and selectively switching the conduction state of said switch based on said first or second control signals.

20. A circuit as claimed in claim 19, wherein said circuit further comprising a charger control circuit generating said pulse signal, and a feedback signal coupled to said charger control circuit representing the voltage across said battery, wherein the duty cycle of said pulse signal being adjusted by said feedback signal.

21. A circuit as claimed in claim 20, wherein said charger control circuit comprises a pulse width modulator and said pulse signal comprises a pulse width modulated signal.

22. A circuit as claimed in claim 12, wherein said switch comprising a MOSFET transistor and a diode in parallel with said transistor, said diode being in forward bias between said system and said battery.

23. A method for controlling the charging and discharging of a battery, said method comprising the steps of:

coupling a battery to a load along a charging/discharging path through a switch,

coupling said battery to a power source along said charging/discharging path through said switch;

generating a first analog control signal indicative of the presence of said power source and the charging status of said battery;

generating a second analog control signal indicative of the battery discharge current;

selectively controlling the conduction state of said switch using said first or second control signal;

wherein generating said first analog control signal comprising the steps of;

comparing the voltage of each said battery cell to a threshold voltage and each generating a plurality of first output signals;

ANDing said first output signals and generating a second output signal;

comparing the battery voltage and the power source voltage and generating a third output signal;

ANDing said second and third output signals and generating a forth output signal;

ANDing said fourth output signal and a pulse width modulated signal and generating said first analog control signal.

24. A method as claimed in claim 23, further comprising the step of generating a DC charging current from said power source.

25. A method as claimed in claim 23, wherein generating said second analog control signal comprising the steps of:

comparing said discharge current supplied by said battery and a threshold current and generating a fifth output signal; and

ANDing the compliment of said fourth output signal and said fifth output signal and generating said second control signal.

26. A method as claimed in claim 25, further comprising the step of

ORing said first and second analog control signals and selectively switching the conduction state of said switch based on said first or second control signals.

27. A method as claimed in claim 23, further comprising the steps of coupling said pulse width modulated signal to said switch and generating a battery charging signal to deliver charging current to said battery when said battery is coupled to said power source through said switch.

28. A method as claimed in claim 27, further comprising the steps of:

generating a feedback signal indicative of the current delivered to said battery; and

adjusting the duty cycle of said pulse width modulated signal based on said feedback signal.

29. A method as claimed in claim 23, further comprising the steps of:

coupling said battery to said load or said power source through a second switch along said charging/discharging path;

generating a third control signal indicative of the discharge current generated by said battery; and

selectively controlling the conduction state of said second switch using said third control signal.

30. A method as claimed in claim 29, wherein generating said third control signal comprises the step of comparing said discharge current to a maximum permitted discharge current;

wherein if said discharge current is less than said maximum discharge current, said conduction state of said second switch is closed to permit current to enter or exit said battery; and

wherein if said discharge current exceeds said maximum permitted discharge current, said conduction state of said second switch is opened to create an open circuit between said battery, and said power supply and said load.