Buffer battery power supply system

• US 6,326,771 B1
• Filed: 10/16/2000
• Issued: 12/04/2001
• Est. Priority Date: 03/08/1999
• 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-Stanesti, Vlad
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): TIBBITS, PIA FLORENCE
• Application Number:
  US09/690,200
• Time in Patent Office: 414 Days
• Field of Search: 323/908, 363/136, 320/132, 320/134, 320/139
• US Class Current: 320/139
• CPC Class Codes: H02J 7/0068 Battery or charger load switching, e.g. concurrent charging and load supply H02J7/0013 takes precedence

Abstract

A buffer battery power supply circuit is provided. In one embodiment, a battery charger circuit supplies a total output current which is delivered to both an active system and a battery. The total output current and the current delivered to a battery are sensed and compared to a preset threshold total output current signal and threshold battery current signal, respectively. The compared signals generate error signals which are provided as feedback to the battery charger circuit, so that the total output current can be controlled. In another embodiment, in addition to sensing the total output current and the battery current, the total output voltage is sensed and multiplied by the total output current, generating a total output power error signal. The error signals are provided as feedback to the battery charger circuit, so that the total output current and/or the total output voltage can be controlled. In other embodiments, a battery switch is provided that couples/decouples the battery from the load based on the minimum required voltage of the load, and provides a path between the battery and a power source so that the battery can receive a trickle charge even in a deeply discharged state, while permitting the power source to power the load. The circuitry of the present invention provides self-adjusting current management between a load and a rechargeable battery where the load requirements get priority over the battery recharge power requirements.

Claims

1. A power supply system, comprising a charger circuit for generating a duty cycle for delivering power to an active system and a battery;

a first feedback loop to sense the total output current generated by the charger circuit and a second feedback loop to sense the current delivered to said battery by said charger circuit; and

a battery switch circuit adapted to decouple said battery from said active system when said battery voltage is less than the minimum voltage required to power said active system, and couple said battery to said charger circuit to receive a charging current;

said first and second feedback loops including error circuits for generating an error signal to said charger circuit, wherein said charger circuit adjusting said duty cycle for adjusting the total output current delivered to the active system and the battery based on the value of said error signal.

2. A power supply system as claimed in claim 1, further comprising an input power source connected to said charger circuit.

3. A power supply system as claimed in claim 2, wherein said charger circuit including a pulse width modulator (PWM) circuit connected to said input power source, said PWM providing said duty cycle to regulate said input power source based on said error signals supplied by said first and second feedback loops.

4. A power supply system as claimed in claim 1, wherein said charger circuit, said active system and said battery being connected in parallel.

5. A power supply system as claimed in claim 1, wherein said first feedback loop comprising a sense resistor for sensing a total output current signal delivered to said active system, a first sense amplifier for amplifying said total output current signal, a first comparator for comparing said amplified total output current signal with a predetermined total output current threshold value to generate a first error signal, and a first switch for permitting said first error signal to flow to said charger circuit;

said second feedback loop comprising a second sense resistor for sensing the current signal delivered to said battery, a second sense amplifier for amplifying said current signal delivered to said battery, a second comparator for comparing said amplified current signal delivered to said battery with a predetermined battery current threshold value to generate a second error signal, and a second switch for permitting said second error signal to flow to said charger circuit;

wherein said first and second switches being connected in parallel and wherein the largest of said first and second error signals being permitted to flow through said first and second switches as said error signal supplied to said charger circuit.

6. A power supply system as claimed in claim 5, further comprising a power limiting feedback loop comprising a multiplier circuit for multiplying said total output current with a total output voltage to generate a total output power signal, a power comparator for comparing said total output power signal to a predetermined power output threshold signal to generate a power output error signal, and a power switch for permitting said power output error signal to flow to said charger circuit;

wherein said first, second and power switches being connected in parallel and wherein the largest of said first, second and power error signals being permitted to flow through said first, second and power switches as said error signal supplied to said charger circuit.

7. A power supply system as claimed in claim 6, wherein said multiplier circuit comprises a transconductance amplifier for generating a total current signal, a transistor having said duty cycle as control line input from said charger circuit and for chopping said total current signal in accordance with said duty cycle for multiplying said total output current with said output voltage to generate a power current signal proportional to said total output power and an integrating circuit for generating an output voltage signal proportional to said total output power.

8. A power supply system as claimed in claim 6, wherein said multiplier circuit comprises a differential amplifier circuit for generating an output voltage proportional to said total output power.

9. A power supply system as claimed in claim 5, and further comprising a third feedback loop comprising a third comparator for comparing a battery voltage with a predetermined battery voltage threshold signal to generate a third error signal, and a third switch for permitting said third error signal to flow to said charger circuit;

wherein said first, second and third switches being connected in parallel and wherein the largest of said first, second and third error signals being permitted to flow through said first, second and third switches as said error signal supplied to said charger circuit.

10. A power supply system as claimed in claim 9, wherein said predetermined total output current threshold value and said predetermined battery voltage threshold signal being generated by a voltage divider circuit dividing the total output voltage and the voltage across said battery.

11. A power supply system as claimed in claim 5, wherein said predetermined total output current threshold value and said predetermined battery voltage threshold signal being generated by a programmable circuit.

12. A power supply system as claimed in claim 1, further comprising a dc-dc converter circuit for receiving said output current delivered by said charger circuit and delivering power to said active system.

13. A power supply system as claimed in claim 1, further comprising a reverse current limiting circuit for limiting current from flowing from said battery to said charger circuit.

14. A power supply system as claimed in claim 13, wherein said reverse current limiting circuit comprises a diode having a forward bias in the direction of said total output current.

15. A power supply system as claimed in claim 13, wherein said reverse current limiting circuit comprises a transistor, a comparator connected to the input and output lines of said transistor and for generating a control signal connected to the control line of said transistor, and a voltage source for biasing said transistor in a positive manner;

wherein said transistor conducting when a current flows from said input to said output.

16. A power supply system as claimed in claim 1, wherein said battery switch comprises a controllable switch coupled between said battery said charger circuit and said active system, an impedance in parallel with said controllable switch, and a comparator to control the activation state of said controllable switch, wherein said comparator comparing said minimum voltage required to power said active system and said battery voltage and generating a control signal to control the conduction state of said controllable switch, and wherein said impedance providing a path between said battery and said charger circuit if said switch is nonconducting.

17. A power supply system as claimed in claim 16, wherein said impedance chosen to have an impedance value larger than said active system.

24. A power supply system as claimed in claim 16, further comprising a reverse current limiting circuit for limiting current from flowing from said battery to said charger circuit, wherein said reverse current limiting circuit comprises a transistor, a comparator connected to the input and output lines of said transistor and for generating a control signal connected to the control line of said transistor, and a voltage source for biasing said transistor in a positive manner;

wherein said transistor conducting when a current flows from said input to said output.

18. A power supply system comprising, an input power source, a charger circuit for generating a duty cycle for controlling said input power source to deliver controlled power to an active system and a battery;

a first feedback loop to sense the total output current-generated by the charger circuit, said first feedback loop generating a first error signal based on said total output current and a preset threshold total output current signal;

a second feedback loop to sense the current delivered to said battery by said charger circuit, said second feedback loop generating a second error signal based on said current delivered to said battery and a preset threshold battery current signal;

a third feedback loop for sensing the total output power generated by said charger circuit, said third feedback loop generating a third error signal based on said total output power and a preset threshold total output power signal; and

a battery switch circuit adapted to decouple said battery from said active system when said battery voltage is less than the minimum voltage required to power said active system, and simultaneously couple said battery to said charger circuit to receive a charging current;

, wherein said charger circuit adjusting said duty cycle for adjusting the total output current and power delivered to the active system and the battery based on the value of said first, second or third error signal.

19. A power supply system as claimed in claim 18, and further comprising a fourth feedback loop to sense the voltage delivered to said battery, said fourth feedback loop generating a fourth error signal based on said voltage delivered to said battery and a preset threshold battery voltage signal;

wherein said charger circuit adjusting said duty cycle for adjusting the total output current and power delivered to the active system and the battery based on the value of said first, second, third or fourth error signal.

20. A power supply system as claimed in claim 18, wherein said first feedback loop includes a first comparator for comparing said total output current and said preset threshold total output current signal;

said second feedback loop including a second comparator for comparing said current delivered to said battery and said preset threshold battery current signal;

said third feedback loop including a third comparator for comparing said total output power and said preset threshold total output power signal;

each said first second and third comparators generating said first second and third error signals, respectively.

21. A power supply system as claimed in claim 20, wherein said third feedback loop further comprising a multiplier circuit for multiplying said total output current and a total output voltage and generating a signal proportional to the total output power.

22. A power supply system as claimed in claim 18, wherein said first, second and third error signals being supplied to a switch, wherein said switch conducts based on the largest one of said first, second or third error signals.

23. A power supply system as claimed in claim 18, wherein said charger circuit including a pulse width modulator (PWM) circuit connected to said input power source and generating said duty cycle based on said first, second or third error signals.

25. A power supply system as claimed in claim 18, wherein said battery switch comprises a controllable switch coupled between said battery said charger circuit and said active system, an impedance in parallel with said controllable switch, and a comparator to control the activation state of said controllable switch, wherein said comparator comparing said minimum voltage required to power said active system and said battery voltage and generating a control signal to control the conduction state of said controllable switch, and wherein said impedance providing a path between said battery and said charger circuit if said switch is nonconducting.

26. A power supply system as claimed in claim 25, wherein said impedance chosen to have an impedance value larger than said active system.

27. A method of regulating the current delivered by a charger circuit to an active system and a battery, said method comprising the steps of:

sensing a first error signal based on the total output current of said charger circuit and a preset threshold total output current signal;

sensing a second error signal based on the current delivered to said battery by said charger circuit and a preset threshold battery current signal;

providing one of said first or second error signals to said charger circuit as feedback signals, and adjusting the current delivered by said charger circuit based on said first or second feedback error signals;

sensing the voltage of said battery and decoupling said battery from a load if said battery voltage is less than a required minimum voltage for said load; and

coupling said battery to said charger circuit if said battery voltage is less than a required minimum voltage for said load.

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

sensing a third error signal based on said total output current and a total output voltage of said charger circuit and providing one of said first, second or third error signals to said charger circuit as feedback signals, and adjusting the current and/or voltage delivered by said charger circuit based on said first, second or third feedback error signals.

29. A method as claimed in claim 28, further comprising the step of:

multiplying said total output current and said total output voltage of said charger circuit to generate said third error signal, said third error signal being proportional to the total output power of said charger circuit.

30. A method as claimed in claim 27, further comprising the step of:

sensing a fourth error signal based on a voltage delivered to said battery by said charger circuit and a preset threshold battery voltage signal and providing one of said first second or fourth or signals to said charger circuit as feedback signals, and adjusting the current and/or voltage delivered by said charger circuit based on said first, second or fourth feedback error signals.

31. A method as claimed in claim 27, further comprising the step of:

limiting a reverse current coming from said battery and flowing to said charger circuit.

32. A method as claimed in claim 27, further comprising the step of:

amplifying said total output current and comparing said total output current to said preset threshold total output current signal to generate said first error signal; and

amplifying said current delivered to said battery by said charger circuit and comparing said current delivered to said battery to said preset threshold battery current signal to generate said second error signal.

33. A power supply system, comprising a power source;

a battery in parallel with said power source;

a load in parallel with said battery and said power source; and

a battery switch circuit placed between said battery and said power source, said battery switch circuit adapted to decouple said battery from said load when said battery voltage is less than the minimum voltage required to power said active system, and simultaneously couple said battery to a charger circuit to receive a charging current.

34. A power supply system as claimed in claim 33, wherein said battery switch circuit comprising a controllable switch coupled between said battery said charger circuit and said active system, an impedance in parallel with said controllable switch, and a comparator to control the activation state of said controllable switch, wherein said comparator comparing said minimum voltage required to power said active system and said battery voltage and generating a control signal to control the conduction state of said controllable switch, and wherein said impedance providing a path between said battery and said charger circuit if said switch is nonconducting.

35. A power supply system as claimed in claim 34, wherein said impedance chosen to have an impedance value larger than said active system.

36. A power supply system as claimed in claim 33, wherein said power source comprising a current limited power source and said system further comprising a controllable switch for coupling said power source to said load and said battery and a comparator comparing said battery voltage with a maximum threshold battery voltage and generating a control signal to control the conduction state of said controllable switch.

37. A power supply system as claimed in claim 33, wherein said power source comprising a current and voltage limited power source.

38. A power supply system as claimed in claim 37, wherein said power source having rectangular current and voltage characteristics.