Back-to-Back MOS Switch for Accurate Battery Cell Voltage Sensing
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Solution Overview
Problem
High-voltage battery management systems face challenges in accurately measuring battery cell voltages due to control current injection into the channel path of analog switches, leading to measurement inaccuracies, and high current consumption when switches are in the OFF state, which multiplies and contributes to overall power consumption.
Innovation Solution
A high-voltage switch design that injects zero or minimal control current into the channel path and consumes zero or minimal current when in the OFF state, utilizing a back-to-back configuration of MOS transistors with control circuitry that includes current sources and switching arrangements to manage the ON/OFF states, ensuring minimal current flow and accurate voltage measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional analog switches are used for high-voltage battery cell voltage measurement, then the switch can connect/disconnect battery cells, but control current is injected into the channel path causing measurement inaccuracies
Solution Approach 1:
The patent introduces a bootstrap circuit as an intermediary mechanism that generates a floating reference voltage (Vref) that dynamically tracks the common-mode voltage at the switch input. This intermediary voltage reference allows the switch control to operate without injecting current into the measurement channel, thereby eliminating measurement errors while maintaining switch functionality.
Solution Approach 2:
The patent changes the reference voltage parameter from a fixed ground reference to a dynamic floating reference that adjusts its voltage level to match the common-mode voltage. This parameter change enables the switch to operate in a voltage-tracking mode where the control signals remain at appropriate potential differences without creating current injection paths into the measurement channel.
2Loss of energy
If conventional analog switches are used in high-voltage multiplexer, then the switch can route battery cell signals, but current consumption is high when switch is in OFF state
Solution Approach 1:
The patent employs periodic charging of the bootstrap capacitor during the switch ON state, which stores energy that is then reused during the OFF state to maintain the floating reference voltage. This periodic energy storage and reuse mechanism allows the switch to remain in the OFF state without continuous current consumption, as the stored charge sustains the reference voltage temporarily.
3Extent of automation
If conventional switch control circuits are used, then the switch can be turned ON/OFF, but control circuit complexity increases with additional transistors and current sources
Solution Approach 1:
The patent makes the bootstrap circuit serve multiple functions: it generates the floating reference voltage for accurate switching control, provides the reference for the OFF-state leakage current measurement, and enables the high-impedance state during measurement. This multi-functionality reduces the need for separate dedicated circuits for each function, thereby reducing overall circuit complexity while maintaining comprehensive control capability.
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
The solution provides accurate battery cell voltage measurements with reduced measurement inaccuracies and significantly lower power consumption during the OFF state, enhancing the efficiency of high-voltage multiplexers in battery management systems.
Implementation Method 1
a first MOS transistor and a second MOS transistor arranged back to back with a common source terminal and a common gate terminal
Data Source
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AI summary
A switch comprising: a channel path comprising first and second MOS transistors with common source and gate terminals and drain terminals defining first and second terminals of the channel path; and control circuitry comprising: a third MOS transistor comprising: a gate coupled to the common source terminal; a source coupled to the common gate terminal by a resistor; and a drain coupled to a first reference terminal; a first current source coupled between the first reference terminal and the common gate terminal for providing a first current; a second current source coupled between the source terminal of the third MOS transistor and a second reference terminal for providing a second current greater than the first current; and a first switching arrangement configured to selectively enable and disable the first current source; and a second switching arrangement configured to selectively couple the common source terminal to the second reference terminal.