Battery monitoring circuit and method

• US 20060226844A1
• Filed: 03/30/2005
• Published: 10/12/2006
• Est. Priority Date: 03/30/2005
• Status: Active Grant

• Current Assignee: Aceinna Transducer Systems Company Limited
• Original Assignee: Crossbow Technology Incorporated (Moog Incorporated)
• Inventors: Broad, Alan S.
• Granted Patent: US 7,554,299 B2
• Time in Patent Office: Days
• US Class Current: 324/426
• CPC Class Codes: G01R 31/3832 without measurement of battery voltage
• CPC Class Codes: G01R 35/04 of instruments for measuring time integral of power or current

Abstract

A battery-monitoring circuit detects rapid changes in current drawn from a battery by a device powered thereby. The circuit includes calibrating operating modes that determine voltage-to-frequency conversion parameters, and amplifier errors at various levels of battery voltage.

Claims

1. A circuit including a differential amplifier having inverting and non-inverting inputs for operation over a selected range of applied voltages, the circuit comprising:

a source of voltage at various amplitudes;

circuitry for connecting the source of voltage to the inverting and non-inverting inputs of the differential amplifier for supplying thereto a plurality of different voltages within the selected range;

a converter connected to an output of the differential amplifier for producing a signal indicative of common-mode rejection error of the differential amplifier at each of the plurality of different voltages; and

a memory communicating with the converter for storing signals representative of common-mode rejection errors at storage locations having addresses indicative of the corresponding plurality of different voltages.

2. The circuit according to claim 1 including a processor communicating with the memory and with the converter for producing an output representative of a correction by an amount of an error signal stored in the memory at an address location corresponding to a voltage at an input of the differential amplifier within the selected range.

3. The circuit according to claim 2 in which the converter converts an applied voltage to a corresponding frequency;

and

the memory stores frequency values at the storage locations having addresses corresponding to the plurality of different voltages within the selected range.

4. The circuit according to claim 3 in which the processor controls the circuitry for connecting the source of voltage to the differential amplifier or for connecting other voltages within the selected range to the inputs of the differential amplifier.

5. A method for operating an electronic circuit, including a differential amplifier having inverting and non-inverting inputs, the method comprising:

applying each of selected different voltages within a range of voltages to the inverting and non-inverting inputs of the differential amplifier to produce at an output thereof signals indicative of common-mode rejection errors at the corresponding selected applied voltages; and

storing the error signals at memory locations having addresses indicative of the corresponding selected different voltages.

6. The method according to claim 5 including retrieving a stored error signal from a memory location at an address corresponding to a voltage applied to an input of the differential amplifier for logically combining with an output thereof to correct for common-mode rejection error of the differential amplifier.

7. The method according to claim 5 including converting the error signals to associated frequency values for storage at the memory locations having addresses corresponding to the different applied voltages.

8. The method according to claim 7 in which errors in converting error signals to associated frequency values are combined with the errors indicative of common-mode rejection errors for storage at the memory locations having addresses indicative of the corresponding selected different voltages.

9. A circuit for monitoring current supplied by a battery, the circuit comprising:

a detector connected between the battery and a device powered thereby for providing an output representative of current drawn by the device from the battery;

a voltage-to-frequency converter coupled to receive the output from the detector for generating an output frequency proportional to the received output from the detector; and

a processor coupled to receive the output frequency from the voltage-to-frequency converter for producing an output representative of an integral of current over time drawn from the battery.

10. The circuit of claim 9 in which the detector includes:

a resistor connected between the battery and the device; and

a differential amplifier connected to terminals of the resistor to receive and amplify the voltage across the resistor to supply an output representative thereof to the voltage-to-frequency converter.

11. The circuit as claimed in claim 10 wherein the output of the amplifier is proportional to the current drawn from the battery by the device.

12. The circuit as claimed in claim 9 in which the processor accumulates a count of the output frequency from the voltage-to-frequency converter to produce an output representative of the integral of current drawn from the battery by the device over time.

13. The circuit of claim 9 in which the detector further comprises:

a reference resistor selectively connectable to the resistor;

a reference voltage; and

a switching circuit for selectively supplying the reference voltage to a series connection of resistor and reference resistor for establishing a reference level of input to the differential amplifier.

14. The circuit as claimed in claim 13 wherein the switching circuit switches the resistor between the battery and the device in one mode, and applies the reference voltage to a series connection of the resistor and the reference resistor in another mode.

15. The circuit as claimed in claim 13 in which the processor calibrates a transform factor relating the output frequency of the voltage-to-frequency converter to the applied reference voltage.

16. The circuit of claim 9 further comprising:

a source of voltage variable over a range of voltages substantially representative of an operating range of battery voltages; and

a switching circuit operable in one mode for connecting the source of variable voltage substantially in common to the inputs of the differential amplifier.

17. The circuit of claim 16 in which the processor accumulates a voltage-to-frequency output for each of selected voltages from the source of variable voltages as error values at such selected voltages.

18. The circuit of claim 17 in which the switching circuit operable in another mode connects the resistor between the battery and the device;

and

the processor alters by the error values the voltage to frequency output as a calibrated representation of current drawn by the device from the battery.

19. A method for monitoring a battery comprising the steps for:

forming an input value representative of the current drawn by a device from the battery;

generating a frequency proportional to the input value; and

converting the frequency to an output value representative of an integral of current over time drawn from the battery.

20. The method as claimed in claim 19 wherein conversion of the frequency comprises:

accumulating a count of the frequency representative of the integral of current drawn from the battery by the device over time.