BMS Driver Circuit With LOS Current Sink for Voltage Offset Cancellation
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Solution Overview
Problem
In battery management systems, voltage offsets arise due to bias currents flowing through voltage rails, leading to inaccuracies in voltage measurement, particularly when one or more bias currents are sourced or sunk from the pins of the IC, causing a voltage offset that deviates from the actual cell voltage.
Innovation Solution
A driver circuit with a current sink circuit arrangement that detects the lower voltage rail (LOS) and draws a current equal to the sum of bias currents from that rail to ground, using current mirrors to neutralize the bias currents, thereby reducing or eliminating voltage offsets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bias currents are sourced or sunk from voltage rails to power circuit blocks, then the circuit blocks can operate, but voltage offsets are introduced that reduce measurement precision
Solution Approach 1:
The patent applies preliminary anti-action by introducing a counter-bias current through the current sink circuit arrangement that opposes and neutralizes the voltage offset caused by the bias current. The determination circuit detects the LOS voltage rail, and the current sink circuit arranges to source a counter-bias current from the LOS rail through the balance resistor, which creates an opposing voltage drop that cancels the original offset, thereby preserving measurement precision while maintaining circuit operation
Solution Approach 2:
The patent uses an intermediary approach by introducing a current sink circuit arrangement as a mediating element between the bias current source and the voltage measurement system. This intermediary circuit detects the LOS rail and introduces a counter-bias current that acts as a mediator to neutralize the harmful voltage offset, allowing both circuit operation and accurate measurement to coexist
2Productivity
If current flows through balance resistors to balance battery cells, then cell balancing is achieved, but ohmic losses create additional voltage offsets
Solution Approach 1:
The patent applies the blessing in disguise principle by converting the harmful effect of ohmic losses into a beneficial counter-voltage. The determination circuit identifies the LOS rail, and the current sink circuit arrangement sources a counter-bias current that flows through the balance resistor in the opposite direction to the balancing current, creating a counter-voltage that exactly compensates for the ohmic loss voltage drop, thereby transforming the harmful ohmic loss into a useful compensation mechanism
Solution Approach 2:
The patent uses parameter changes by dynamically adjusting the magnitude and direction of the counter-bias current based on the detected LOS rail condition. When the LOS rail changes, the current sink circuit arrangement changes the parameter of current flow direction and magnitude to maintain the counter-voltage that compensates for ohmic losses, ensuring continuous accurate measurement despite ongoing cell balancing operations
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 effectively reduces or eliminates voltage offsets caused by ohmic losses, ensuring accurate voltage measurement and balancing across battery cells.
Implementation Method 1
voltage offsets arising from ohmic losses in or along voltage rail, or through the respective balance resistor may be reduced or even eliminated
Data Source
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AI summary
A driver circuit for a BMS and method are disclosed, comprising a series arrangement of at least a cell and at least a busbar, and comprising: a first and second voltage rail having a respective first and second terminals for connection to ends of one of the busbar and the cell; a power supply voltage rail, configured to operate at a voltage which is higher than the second voltage rail; a determination circuit, for detecting a lower of supply, LOS, being the one of the first and second voltage rail which is at a lower voltage, and drawing a first bias current from the power supply draw to the LOS; further analog circuit blocks drawing a second bias current from the power supply rail to the LOS; and a current sink circuit arrangement drawing the sum of the first and second bias currents, from the LOS to a ground.