Method and apparatus for detecting a battery voltage

• US 20060267555A1
• Filed: 05/27/2005
• Published: 11/30/2006
• Est. Priority Date: 05/27/2005
• Status: Active Grant

• Current Assignee: Savi Technology Incorporated
• Original Assignee: Savi Technology Incorporated
• Inventors: Chan, Joseph S., Cargonja, Nikola, Ahn, Don H.
• Granted Patent: US 7,911,182 B2
• Time in Patent Office: Days
• US Class Current: 320/132
• CPC Class Codes: G01R 19/16542 for batteries charge condition monitoring in G01R31/36
• CPC Class Codes: G01R 31/3648 comprising digital calculation means, e.g. for performing an algorithm
• CPC Class Codes: G01R 31/374 with means for correcting the measurement for temperature or ageing
• CPC Class Codes: H02J 7/0047 with monitoring or indicating devices or circuits

Abstract

One aspect of the invention involves: maintaining a record of how long a circuit operates in each of a plurality of different operating modes thereof, starting from a point in time at which a battery that powers the circuit is replaced; calculating for each of the operating modes as a function of the record a cumulative current drain from the point in time to a current time; and determining as a function of the cumulative current drains whether the battery is subject to a low voltage condition. Another aspect involves: monitoring a voltage of a battery; periodically determining whether the voltage of the battery is subject to a low voltage condition; and maintaining a count of the number of times that the determining results in a determination that the battery is subject to a low voltage condition.

Claims

1. A method comprising:

causing a circuit having a plurality of different operating modes to maintain a record of how long said circuit operates in each of said operating modes, starting from a point in time at which a battery that powers said circuit is replaced;

calculating for each of said operating modes as a function of said record a cumulative current drain from said point in time to a current time; and

determining as a function of said cumulative current drains whether said battery is subject to a low voltage condition.

2. A method according to claim 1, including:

determining a respective current drain rate for each of said operating modes; and

carrying out said calculating of respective said cumulative current drains as a function of respective said current drain rates.

3. A method according to claim 1, wherein said determining includes evaluating a discharge specification for said battery in relation to current drain information that is a function of said cumulative current drains.

4. A method according to claim 1, including providing a radio frequency identification tag, said circuit being a portion of said tag.

5. A method according to claim 4, including:

configuring said circuit to have a transmitter and a receiver; and

configuring said operating modes of said circuit to include a transmit mode in which said transmitter is enabled and said receiver is disabled, a receive mode in which said transmitter is disabled and said receiver is enabled, and a standby mode in which said transmitter and receiver are both disabled.

6. A method according to claim 4, including configuring said tag to have an antenna and said circuit to have a transmitter coupled to said antenna, said circuit transmitting through said transmitter and said antenna a radio frequency signal that indicates whether a determination has been made that said battery is subject to a low battery condition.

7. A method according to claim 1, including selecting a lithium cell to serve as said battery.

8. A method according to claim 1, including:

evaluating whether a rate of voltage decrease of said battery is in excess of a threshold; and

indicating that said battery is subject to a low voltage condition when said rate of voltage decrease exceeds said threshold.

9. A method according to claim 8,

wherein said evaluating includes:

tracking the drain of charge from said battery;

determining a series of points in time for which a substantially equal amount of charge is drained from said battery between each pair of successive said points in time;

sampling said voltage of said battery at each of said points in time;

calculating the difference between said voltage samples from successive said points in time; and

comparing the calculated difference to said threshold.

10. An apparatus comprising a battery and a circuit powered by said battery that has a plurality of different operating modes, wherein said circuit:

maintains a record of how long said circuit operates in each of said operating modes, starting from a point in time at which battery replacement occurs;

calculates for each of said operating modes as a function of said record a cumulative current drain from said point in time to a current time; and

determines as a function of said cumulative current drains whether said battery is subject to a low voltage condition.

11. An apparatus according to claim 10,

including a radio frequency identification tag, said circuit and said battery being portions of said tag;

wherein said circuit has a transmitter and a receiver; and

wherein said operating modes of said circuit include a transmit mode in which said transmitter is enabled and said receiver is disabled, a receive mode in which said transmitter is disabled and said receiver is enabled, and a standby mode in which said transmitter and receiver are both disabled.

12. An apparatus according to claim 10,

including a radio frequency identification tag, said circuit and said battery being portions of said tag;

wherein said tag has an antenna; and

wherein said circuit has a transmitter coupled to said antenna, said circuit transmitting through said transmitter and said antenna a radio frequency signal that indicates whether a determination has been made that said battery is subject to a low battery condition.

13. An apparatus according to claim 10, wherein said battery is a lithium cell.

14. An apparatus according to claim 10, wherein said circuit:

evaluates whether a rate of voltage decrease of said battery is in excess of a threshold; and

determines that said battery is subject to a low voltage condition when said rate of voltage decrease exceeds said threshold.

15. An apparatus according to claim 14, wherein said circuit effects said evaluation of said rate of decrease of said voltage by:

tracking the drain of charge from said battery;

determining a series of points in time for which a substantially equal amount of charge is drained from said battery between each pair of successive said points in time;

sampling said voltage of said battery at each of said points in time;

calculating the difference between said voltage samples from successive said points in time; and

comparing the calculated difference to said threshold.

16. An apparatus according to claim 10, wherein said circuit:

determines a respective current drain rate for each of said operating modes; and

carries out said calculating of respective said cumulative current drains as a function of respective said current drain rates.

17. An apparatus according to claim 10, wherein said circuit effects said determining of whether said battery is subject to a low voltage condition in a manner that includes evaluating a discharge specification for said battery in relation to current drain information that is a function of said cumulative current drains.

18. A method comprising:

monitoring a voltage of a battery;

periodically determining whether said voltage of said battery is subject to a low voltage condition; and

maintaining a count of the number of times that said determining results in a determination that said battery is subject to a low voltage condition.

19. A method according to claim 18, wherein said maintaining includes maintaining as said count the number of successive times that said determining results in a determination that said battery is subject to a low voltage condition.