Voltage-Based Fuel Gauge Eliminates Sense Resistor
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Solution Overview
Problem
Existing battery fuel gauges face limitations such as the need for current sense resistors, integration errors, and inability to accurately track state of charge during partial charging and discharging, especially in devices with variable loads.
Innovation Solution
A voltage-based fuel gauge system that models the battery using an RC circuit, eliminating the need for current sense resistors and tracking state of charge independently of the load, by monitoring open circuit battery voltage, which is a good indicator of the battery's state of charge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a current sense resistor is used to monitor battery current, then the state of charge can be tracked, but power is lost due to voltage drop and power dissipation in the resistor
Solution Approach 1:
The patent extracts the voltage measurement function from the current measurement function. Instead of measuring current directly with a sense resistor, the system measures battery terminal voltage and uses it to infer state of charge. This eliminates the need for a current sense resistor and its associated power losses while maintaining state of charge monitoring capability.
Solution Approach 2:
The patent replaces the electrical measurement mechanism (current sense resistor) with a voltage measurement mechanism. By substituting the current sensing approach with voltage sensing and computational analysis, the system achieves the same state of charge tracking function without the power loss inherent in resistive current sensing.
2Measurement precision
If a current sense resistor is used to monitor battery current, then the state of charge can be tracked, but circuit area and cost increase due to the discrete component
Solution Approach 1:
The patent removes the current sense resistor from the circuit architecture, eliminating the need for additional discrete components and the circuit area they occupy. The state of charge monitoring function is achieved through voltage measurement and computational methods that integrate with existing battery management circuitry.
Solution Approach 2:
The voltage measurement system serves multiple functions: it monitors battery terminal voltage for state of charge determination and can be used for other battery management functions. This multi-functionality eliminates the need for dedicated current sensing components, reducing overall circuit area and component count.
3Duration of action of moving object
If coulomb counting is used to track state of charge, then ongoing monitoring is provided, but integration errors accumulate over time
Solution Approach 1:
The patent implements a feedback mechanism where the voltage-based state of charge estimate continuously corrects the coulomb counting results. The system compares the integrated charge/discharge measurements with voltage-based measurements and uses the voltage information to reset and correct accumulation errors, maintaining long-term accuracy while preserving continuous monitoring capability.
Solution Approach 2:
The system performs preliminary voltage-based state of charge estimation to establish reference points before coulomb counting begins or to reset integration errors. By using voltage measurements to set initial conditions and periodic reference points, the system prevents error accumulation while maintaining continuous monitoring through the hybrid approach.
4Device complexity
If terminal voltage monitoring is used to detect state of charge, then simplicity is achieved and no current sense resistor is needed, but ongoing indication of state of charge is not provided due to variable load
Solution Approach 1:
The patent applies dynamic correction to the static voltage-based state of charge estimation. By incorporating coulomb counting to track charge and discharge dynamics and using voltage measurements to correct for load-dependent voltage drops, the system maintains circuit simplicity while achieving accurate ongoing state of charge indication under variable load conditions.
Solution Approach 2:
The system changes the interpretation parameter from raw terminal voltage to corrected state of charge estimate. By using voltage as a reference point and applying corrections based on coulomb counting and load characteristics, the system transforms the simple voltage measurement into an accurate ongoing state of charge indication without adding significant complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach provides accurate and ongoing state of charge monitoring, reducing power consumption and integration errors, and is applicable to various battery types, including Li-Ion, Ni-Cad, and Ni-MH, with improved accuracy over traditional coulomb counters.
Implementation Method 1
A voltage-based fuel gauge system that models the battery using an RC circuit
Data Source
AI summary
Enhanced voltage-based fuel gauges and methods that increase the accuracy of voltage-based fuel gauges and allow the use of voltage-based fuel gauges to detect current, and particularly excessive current from a battery without the use of a sense resistor. When used with a coulomb counter, the outputs of a voltage-based fuel gauge and a coulomb counter may be combined in a manner that allows the combination to provide better performance that either alone may provide. Various embodiments and methods of operation are disclosed.