Multi-Stage Shunt Circuit for Lithium-Ion Battery Overcharge Protection
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Solution Overview
Problem
Conventional shunt resistance schemes fail to prevent overcharging of lithium ion battery cells, particularly when cells deteriorate with aging, leading to shortened battery life due to inadequate suppression of increasing battery voltage.
Innovation Solution
A shunt circuit comprising a shunt resistor, a transistor, and OP amplifiers that compare battery voltage to a detection voltage, increasing the shunt current step-by-step to limit battery voltage, ensuring cells are not overcharged, even when cells are deteriorated.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional shunt resistance scheme using only a switch operation is used, then the device complexity is reduced, but the reliability of preventing cell overcharging deteriorates when cells deteriorate due to aging
Solution Approach 1:
The shunt current is made dynamically adjustable through multiple stages rather than being fixed. The circuit transitions from a static switch-based shunt to a dynamic multi-stage shunt circuit where the shunt current can be increased step-by-step based on battery voltage conditions, enabling adaptive response to cell deterioration
Solution Approach 2:
The shunt current parameter is changed in multiple stages rather than remaining constant. By introducing multiple shunt stages with different current levels and adjusting the detection voltage step-by-step, the system can adapt to varying cell conditions and maintain reliable overcharging prevention even when cells deteriorate
2Reliability
If the shunt current is increased step-by-step whenever battery voltage reaches detection voltage, then the reliability of overcharging prevention is improved, but the device complexity increases due to multiple OP amplifiers and control stages
Solution Approach 1:
The shunt circuit is segmented into multiple stages, each with its own OP amplifier and threshold detection level. This segmentation allows the circuit to handle different voltage ranges independently, improving reliability through staged response while keeping each individual stage relatively simple
Solution Approach 2:
The circuit implements feedback control where the battery voltage is continuously monitored and compared against detection thresholds. When voltage reaches a threshold, the corresponding shunt stage is activated, creating a closed-loop control system that automatically adjusts shunt current based on actual battery conditions
3Ease of operation
If a single-stage shunt circuit is used, then the ease of operation is improved, but the ability to handle cell deterioration and extend battery lifespan deteriorates
Solution Approach 1:
The shunt circuit transitions from static to dynamic operation, automatically adapting to cell conditions without requiring manual intervention. This maintains ease of operation while improving battery lifespan through staged shunt current adjustment that responds to cell voltage changes
Solution Approach 2:
The multi-stage shunt circuit performs self-adjustment based on battery voltage feedback, eliminating the need for manual control or monitoring. The system automatically selects appropriate shunt stages and adjusts detection voltages, maintaining operational simplicity while extending battery life through intelligent staged control
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
Effectively prevents overcharging of lithium ion battery cells by dynamically adjusting the shunt current in response to increasing battery voltage, thereby extending the battery's lifespan and ensuring uniform charging across multiple cells.
Implementation Method 1
a shunt resistor; a transistor connected in parallel to a storage element via the shunt resistor
Data Source
AI summary
A shunt circuit includes: a shunt resistor; a transistor connected in parallel to a storage element via the shunt resistor; a first OP amplifier configured to compare a battery voltage supplied to the storage element with a detection voltage; and a second OP amplifier configured to shunt a shunt current from a charging current supplied from a charging unit when the battery voltage reaches the detection voltage. The detection voltage is increased step by step, and the shunt current is increased whenever the battery voltage reaches the detection voltage.