Power Tool Battery Pack Overcurrent Protection Circuit
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Solution Overview
Problem
Existing power tools with battery packs face challenges in preventing overcurrent and overdischarge, leading to battery life reduction and potential breakdowns, as the number of Field-Effect Transistors (FETs) required to interrupt excessive current is either insufficient or excessive, causing FET breakdown or inefficiency.
Innovation Solution
A power tool design that includes a battery pack with a battery state monitoring unit, a first switch unit for arbitrary power supply control, and a second switch unit for power supply control based on detection signals, along with a retaining unit to prevent repeated power interruptions, and signal output units with different time constants to manage overcurrent and overdischarge effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the number of FETs in the battery pack is increased to ensure interruption of overcurrent, then the reliability of overcurrent protection is improved, but the cost and device complexity increase and the FETs become useless for small current applications
Solution Approach 1:
The patent divides the switching function into two separate units: a first switch unit in the battery pack and a second switch unit in the power tool. This segmentation allows each unit to handle appropriate current levels independently, with the second switch unit specifically designed to handle large currents in the power tool, eliminating the need to overspecify FETs in the battery pack.
Solution Approach 2:
The patent implements dynamic control where the second switch unit is controlled by a control unit that receives detection signals from a battery state monitoring unit. This dynamic control allows the system to activate the second switch unit only when overcurrent or overdischarge conditions are detected, optimizing the number of FETs needed based on actual operational requirements.
2Device complexity
If the number of FETs in the battery pack is decreased to reduce cost and complexity, then the device complexity and cost are reduced, but the ability to interrupt large overcurrent is compromised leading to FET breakdown
Solution Approach 1:
The patent divides the switching function into two separate units: a first switch unit in the battery pack and a second switch unit in the power tool. This segmentation allows each unit to handle appropriate current levels independently, with the second switch unit specifically designed to handle large currents in the power tool, eliminating the need to overspecify FETs in the battery pack.
Solution Approach 2:
The patent introduces a control unit as an intermediary that receives detection signals from the battery state monitoring unit and controls the second switch unit. This intermediary ensures that the second switch unit is activated only when necessary, providing reliable overcurrent protection without requiring excessive FETs to be always active.
3Device complexity
If a single switch unit is used for power supply control, then the device complexity is reduced, but the ability to provide arbitrary control and automatic protection simultaneously is compromised
Solution Approach 1:
The patent divides the switching function into two separate units: a first switch unit for arbitrary user control and a second switch unit for automatic protection control. This segmentation allows the first switch unit to provide manual ON/OFF functionality while the second switch unit automatically responds to overcurrent and overdischarge conditions, ensuring both user control and safety protection.
Solution Approach 2:
The patent implements a feedback mechanism where the battery state monitoring unit continuously monitors battery conditions and sends detection signals to the control unit, which then activates the second switch unit when overcurrent or overdischarge is detected. This feedback loop ensures automatic protection while maintaining user control through the first switch unit.
Data Source
Figure 1
Figure 2A~2C
Figure 3A~3B
AI summary
A power tool 1 is connected to a battery pack 5 including an overcurrent detector 533 which detects overcurrent of a battery module 51 and outputs a detection signal, and an overdischarge detector 532 which detects overdischarge of the battery module 51 and outputs a detection signal. The power tool 1 includes a motor 2 which is driven by electric power supplied from the battery pack 5, a trigger switch 31 for setting the power supply from the battery pack 5 to the motor 2 in ON/OFF state, and an FET 410 which sets the power supply to the motor 2 in ON/OFF state on the basis of the detection signal from the overcurrent detector 533 or the over discharge detector 532.