Charge measurement circuit for a battery in which oscillators are used to indicate mode of operation

• US 5,592,095 A
• Filed: 08/28/1995
• Issued: 01/07/1997
• Est. Priority Date: 08/28/1995
• Status: Expired due to Term

• Current Assignee: Amperex Technology Limited (TDK Corporation)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Meadows, Vernon
• Primary Examiner(s): Regan, Maura K.
• Application Number:
  US08/520,362
• Time in Patent Office: 498 Days
• Field of Search: 324/433, 324/427, 324/436, 324/120, 340/636, 340/825.44, 320/21, 320/48
• US Class Current: 324/436
• CPC Class Codes: H02J 7/00036 Charger exchanging data with battery
• CPC Class Codes: H02J 7/00047 with provisions for charging different types of batteries
• CPC Class Codes: H02J 7/0048 Detection of remaining charge capacity or state of charge [SOC]
• CPC Class Codes: H02J 7/005 Detection of state of health [SOH]

Abstract

A battery pack (10) has a charge measurement circuit (12) for estimating the state of charge during use. The charge measurement circuit (12) includes a sense resistor (24), amplifier (26), at least one oscillator (28), counter (30), and a communications circuit (32). The battery pack powers a host device (16), which has a limited number of modes of operation, each mode requiring a different current level. The number of oscillators (28) equals the number of modes of operation of the host device (16). As current is drawn from the battery cells (18), the sense resistor (24) and amplifier (26) act to convert the current to a voltage level. The voltage level is fed to each oscillator (28) present. Each oscillator (28) provides a clock signal at a frequency corresponding to one mode of operation of the host device, and is activated when the voltage level is within a preselected range. The clock signal is fed to a counter (30), which counts at a rate determined by the frequency of the active oscillator (28). The host device (16) can request the current count value from communications circuit (30) to estimate the state of charge of the battery cells (18).

Claims

1. A charge measurement circuit for a battery pack having at least one battery cell, comprising:

means for converting current through said at least one battery cell to a voltage level;

a plurality of oscillators connected to said means for converting, each of said oscillators providing a dock signal comprised of regular pulses at a different preselected frequency corresponding to an operating mode of a host device in response to said voltage level being within a corresponding exclusive range;

means for generating a count of said pulses connected to said at least one oscillator, said means for generating a count being reset to an initial state in response to said at least one battery cell being recharged; and

means for communicating said count to a host device.

2. A charge measurement circuit as recited in claim 1, wherein said means for converting comprises:

a sense resistor coupled in series with said at least one battery cell for providing a low level voltage signal proportional to said current; and

an amplifier connected across said sense resistor for amplifying said low level voltage signal, thereby providing said voltage level.

3. A charge measurement circuit as recited in claim 2, wherein:

said low level voltage signal has a polarity and a magnitude, said voltage level is provided by said amplifier proportional only to said magnitude, said amplifier further provides a bistable output having a first level and a second level indicative of said polarity; and

said means for generating a count is an up/down counter having a CLOCK input, U/D SELECT input, and a RESET input, said CLOCK input for receiving said pulses, said U/D SELECT input connected to said bistable output of said amplifier, said RESET input for resetting said up/down counter to said initial state in response to a reset signal from a charger, said up/down counter for maintaining a count of said pulses and increasing said count when said bistable output is at said first level and decreasing said count when said bistable output is at said second level.

4. A charge measurement circuit as recited in claim 1, further comprising an accumulator, connected to said means for communicating, for accumulating and storing a total lifetime pulse count, said total lifetime pulse count being provided to said host device through said means for communicating upon request from said host device.

5. A charge measurement circuit for a battery pack having at least one battery cell, said battery pack for powering a host device having plurality of operating modes, each said operating mode characterized by a unique current level, and being rechargeable in a charger, said charger providing a reset signal upon charging said battery pack, said circuit comprising:

a sense resistor coupled in series with said at least one battery cell for providing a low level voltage signal proportional to current through said at least one battery cell, said low level voltage signal having a magnitude and a polarity;

an amplifier connected across said sense resistor for amplifying said magnitude of said low level voltage signal, thereby providing a voltage level, and further providing a bistable output having a first level and a second level indicative of said polarity;

a plurality of oscillators connected to said means for converting, each of said oscillators providing a clock signal comprised of regular pulses at a different preselected frequency corresponding to one of said operating modes of said host device in response to said voltage level being within a corresponding exclusive range;

an up/down counter having CLOCK, U/D SELECT, and RESET inputs, said CLOCK input for receiving said pulses, said U/D SELECT input connected to said bistable output of said amplifier, said RESET input for resetting said up/down counter to an initial state in response to receiving said reset signal from said charger, said up/down counter for maintaining a count of said pulses and increasing said count when said bistable output is at said first level and decreasing said count when said bistable output is at said second level; and

a communication circuit connected to said up/down counter for communicating said count to said host device.

6. A charge measurement circuit as defined in claim 5, further comprising an accumulator connected to said communication circuit for maintaining a total lifetime pulse count of pulses occurring when said bistable output is at said first level.

7. A charge measurement circuit as defined in claim 6, wherein said accumulator provides said total lifetime pulse count to said host device by means of said communication circuit upon request from said host device.

8. A battery pack for powering a host device having a plurality of operating modes each requiring a different level of current, said battery pack being rechargeable by a charger, said battery pack comprising:

at least one battery cell, said at least one battery cell having a temperature;

means for sensing temperature proximally located with said at least one battery cell for providing said charger with a signal indicative of said temperature of said at least one battery cell;

means for converting current through said at least one battery cell to a voltage level proportional to said current;

a plurality of oscillators connected to said means for converting, each of said oscillators providing a clock signal comprised of regular pulses at a different preselected frequency corresponding to one of said operating mode of said host device in response to said voltage level being within a corresponding exclusive range;

means for counting said pulses connected to said at least one oscillator, for maintaining a count of said pulses, said means for counting being reset to an initial state in response to said at least one battery cell being recharged; and

means for communicating said count to a host device.

9. A battery pack as recited in claim 8, wherein said means for converting comprises:

a sense resistor coupled in series with said at least one battery cell for providing a low level voltage signal proportional to said current; and

an amplifier connected across said sense resistor for amplifying said low level voltage signal, thereby providing said voltage level.

10. A battery pack as recited in claim 9, wherein:

said low level voltage signal has a polarity and a magnitude, said voltage level is provided by said amplifier proportional only to said magnitude, said amplifier further provides a bistable output having a first level and a second level indicative of said polarity; and

said means for counting is an up/down counter having CLOCK, U/D SELECT, and RESET inputs, said CLOCK input for receiving said pulses, said U/D SELECT input connected to said bistable output of said amplifier, said RESET input for resetting said up/down counter to said initial state in response to a reset signal from a charger, said up/down counter for maintaining a count of said pulses and increasing said count when said bistable output is at said first level and decreasing said count when said bistable output is at said second level.

11. A battery pack as recited in claim 8, further comprising an accumulator, connected to said means for communicating, for accumulating and storing a total lifetime pulse count, said total lifetime pulse count being provided to said host device through said means for communicating upon request from said host device.

12. A battery pack as defined by claim 8, wherein said means for sensing temperature is a thermistor.