BMS Driver Circuit With Current Sink for Accurate Cell Voltage Sensing
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Solution Overview
Problem
Existing battery management systems (BMS) face inaccuracies in voltage measurement due to bias currents flowing through voltage rails, causing voltage offsets that compromise measurement accuracy, particularly when the currents through the balancing resistors are not equal, leading to significant errors even with low current consumption.
Innovation Solution
A driver circuit with a current sink circuit arrangement that detects the lower voltage rail (LOS) and draws an equal current from both voltage rails to ground, using current mirrors and switches to neutralize bias currents, thereby reducing or eliminating voltage offsets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If bias currents are drawn 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 extracts the bias currents from the voltage rails by introducing a current sink circuit that draws these currents to ground. The current sink is controlled to draw current proportional to the bias currents, effectively removing them from the voltage rails and preventing the voltage offsets they cause, thereby maintaining measurement precision while allowing the circuit blocks to continue operating.
Solution Approach 2:
The patent introduces a current sink circuit as an intermediary element between the voltage rails and ground. This current sink acts as a mediator that absorbs the bias currents without allowing them to create voltage drops across the rails. The current sink is controlled by control signals that regulate its current drawing behavior, effectively mediating between the power consumption needs and measurement accuracy requirements.
2Reliability
If current is drawn through balancing resistors, then cell balancing is achieved, but voltage drops across the resistors cause measurement errors
Solution Approach 1:
The patent extracts the problematic current paths by introducing a current sink that draws current from the voltage rails proportional to the bias currents. This removes the source of voltage drops across the balancing resistors, allowing the balancing function to continue while eliminating the measurement errors caused by ohmic losses in the resistors and rails.
Solution Approach 2:
The patent implements a feedback mechanism where the current sink is controlled by control signals that regulate its current drawing behavior. The current sink draws current proportional to the bias currents, creating a feedback loop that dynamically compensates for the voltage drops and maintains accurate voltage measurements while preserving the cell balancing function.
3Power
If bias currents flow through voltage rails, then circuit blocks receive power, but unequal currents create voltage offsets that compromise measurement accuracy
Solution Approach 1:
The patent extracts the bias currents from the voltage rails by introducing a current sink circuit. The current sink draws current proportional to the bias currents to ground, effectively removing them from the voltage rails. This prevents the creation of unequal voltage drops that would cause measurement offsets, while the circuit blocks continue to receive the power they need through the controlled current sinking action.
Solution Approach 2:
The current sink circuit serves as an intermediary that mediates between the power delivery requirements and measurement accuracy needs. It draws current proportional to the bias currents, acting as a controlled intermediary that removes the harmful unequal currents while maintaining the necessary power supply to the circuit blocks through regulated current management.
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 arising from ohmic losses, maintaining accurate voltage measurement by balancing the current flow across the voltage rails, ensuring precise cell voltage determination.
Implementation Method 1
the current sink circuit arrangement may comprise a first current mirror configured to copy the current equal to the third current to a first grounding current path between the LOS and the ground
Implementation Method 2
voltage offsets arising from ohmic losses in or along voltage rail
Data Source
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.