Secondary Battery Protection Circuit Back-Gate Control
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Solution Overview
Problem
Existing secondary battery protection circuits face challenges in reducing the chip area required for changeover switches due to the high on-resistance values of FETs, leading to increased circuit size and complexity.
Innovation Solution
A secondary battery protection circuit using a metal-oxide-semiconductor transistor with a control circuit and anomaly detection system, where the resistance values of specific switches are designed to be greater than the on-resistance of the transistor, reducing the impedance and chip area required for the control lines, thereby minimizing the overall circuit area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a FET with low on-resistance value is used for the changeover switch, then the switching performance is improved, but the chip area increases significantly
Solution Approach 1:
The patent divides the protection circuit into two separate paths: a main current path through the MOS transistor for high-current switching, and a control signal path through the changeover switch for low-current back-gate control. This segmentation allows each component to be optimized independently - the MOS transistor handles the bulk current with low on-resistance, while the changeover switch only handles control signals, reducing its area requirements
Solution Approach 2:
The patent combines the MOS transistor's body diode function with the changeover switch's control function into a unified back-gate control mechanism. The back-gate terminal serves dual purposes: controlling the MOS transistor's channel and providing a controlled path for current when the MOS transistor is off, eliminating the need for separate control circuitry
2Area of stationary object
If the resistance value of the changeover switch path is increased, then the chip area is reduced, but the control precision may be affected
Solution Approach 1:
The patent applies different resistance characteristics to different parts of the control circuit. The changeover switch path uses higher resistance (reducing area) while the MOS transistor gate control path maintains low resistance for precise voltage control. The back-gate terminal provides localized control with appropriate resistance values for its specific function of modulating the MOS transistor channel
Data Source
AI summary
A secondary battery protection circuit includes a first terminal connected to a power supply path between a secondary battery and a MOS transistor, a second terminal connected to the power supply path between a load and the MOS transistor, a third terminal connected to a gate of the MOS transistor, a fourth terminal connected to a back gate of the MOS transistor, a control circuit that outputs a switch control signal based on a detected abnormal state of the secondary battery, and a switch control circuit including a first switch for connecting the fourth terminal with the first terminal and a second switch for connecting the fourth terminal with the second terminal. At least one of the resistance between the fourth terminal and the first terminal and the resistance between the fourth terminal and the second terminal is greater than the on resistance value of the MOS transistor.