Battery Sensing Voltage Controller for High Current Safety
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Solution Overview
Problem
Lithium ion battery packs face safety issues due to large voltage drops across power FETs during high charging currents, which can lead to uncontrolled current flow and overcharging or overdischarging when traditional voltage sensing paths are used.
Innovation Solution
A switch-based control system is implemented between the battery and the battery sense output, with a control circuit that opens the switch when a voltage differential exceeds a threshold, and a selectively switchable current source for fault recovery, preventing uncontrolled current flow and allowing accurate battery voltage measurement without introducing errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a voltage sensing path is provided around the power FETs, then accurate battery voltage sensing is achieved, but sneak current paths can cause overcharging or overdischarging under fault conditions
Solution Approach 1:
A dedicated sense FET is introduced as an intermediary component to carry the sensing current separately from the power FETs. This sense FET creates an isolated current path that allows accurate voltage measurement without allowing sneak currents to flow through the battery, thus resolving the contradiction between measurement accuracy and safety.
Solution Approach 2:
The current paths are segmented into separate channels: power FETs for main current flow and a dedicated sense FET for voltage sensing. This segmentation isolates the sensing function from the power switching function, preventing harmful current leakage while maintaining accurate voltage detection capability.
2Productivity
If higher charging currents are used for rapid charging, then charging time is reduced, but voltage drop across FETs increases causing safety issues
Solution Approach 1:
The sense FET acts as an intermediary that carries a small sensing current independent of the high charging current. This allows the system to maintain high charging currents for rapid charging while the sense FET provides an accurate reference path for voltage measurement, unaffected by the large voltage drops across the power FETs.
Data Source
AI summary
A battery pack includes a housing, a battery, a battery pack output voltage path that includes a charge power switch and a discharge power switch, and a battery sense output. A switch can be operably coupled between the battery and the battery sense output and configured to selectively open and close a battery sense path between the battery and the battery sense output. By one approach a first control circuit controls the open and close state of the aforementioned switch (in response, for example, to a comparison of the voltage differential across the switch to a predetermined threshold such that the switch is opened when the voltage differential across the switch becomes too positive or too negative with respect to battery voltage).