Battery Protection Circuit With Current Mirroring for Fast-Charge Detection
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Solution Overview
Problem
Existing battery protection circuits face challenges in achieving high overcurrent detection precision during high-current fast charge without increasing through-current impedance and generating excessive heat.
Innovation Solution
A power protection apparatus using a switching transistor group and a protection IC with a current imaging function to detect a very low current proportional to the main through-current circuit, eliminating the need for a current sampling resistor in the charge and discharge circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a current sampling resistor is introduced for overcurrent detection, then overcurrent detection precision is improved, but impedance of the charge and discharge circuit increases causing remarkable heat generation
Solution Approach 1:
The patent uses a sampling transistor to create a scaled-down copy of the main circuit current. The sampling transistor's drain current is proportional to the main circuit current through a fixed ratio determined by transistor width ratios. This allows overcurrent detection using a tiny sampling current instead of forcing the full current through a sampling resistor, eliminating the heat generation problem while maintaining detection precision.
Solution Approach 2:
The sampling transistor acts as an intermediary between the main charge/discharge circuit and the detection circuit. It transfers a scaled version of the main current to the detection side, allowing the detection circuit to measure current without being directly in the high-current path. This intermediary approach enables precise detection while keeping the main circuit impedance low.
2Productivity
If the impedance of the charge and discharge circuit is reduced for efficient fast charge, then charging speed is improved, but overcurrent detection precision deteriorates
Solution Approach 1:
The patent segments the current measurement function from the main charge/discharge path by introducing a separate sampling transistor branch. The sampling transistor has a much higher effective impedance for detection purposes while the main circuit maintains low impedance for high-speed charging. This segmentation allows the two contradictory requirements to coexist in their respective domains.
Solution Approach 2:
The patent applies different impedance characteristics to different parts of the circuit: the main charge/discharge path has low impedance for high current flow and fast charging, while the sampling detection path has high effective impedance for precise current measurement. This local differentiation of impedance quality resolves the contradiction between fast charging and detection precision.
Data Source
AI summary
A battery protection apparatus power protection apparatus is configured to protect an electrochemical cell connected to a load, and includes a protection IC, a switching transistor group, and a sampling resistor. The protection IC includes two power input terminals respectively connected to positive and negative electrodes of the electrochemical cell, and an operational amplifier, where the operational amplifier includes a positive input pin, a negative input pin, and an output pin. The switching transistor group is connected between the negative electrode of the electrochemical cell and the load, and is configured to control turn-on and turn-off of a charge and discharge circuit of the electrochemical cell. The sampling detection resistor Rs is serially connected between the sampling circuit detection terminal and the output pin, where the main circuit detection terminal is connected to the positive input pin, and the sampling circuit detection terminal is connected to the negative input pin.