Battery Pack Current Limiting Circuit with Bypass Switch
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Solution Overview
Problem
Portable communication devices face the risk of sparking and potential fires due to battery removal and replacement, especially in combustible environments, and existing solutions struggle to balance safety, component count, board space, and manufacturability for intrinsically safe devices.
Innovation Solution
A power limiting circuit comprising a power limiting resistor and a positive temperature coefficient (PTC) device is integrated into the battery pack, which limits maximum battery current and prevents sparking by using a semiconductor switch to bypass the resistor and PTC device during normal operation, while engaging them during battery engagement and disengagement to protect against overcurrent conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a power limiting circuit is added to prevent sparking and ensure safety, then product safety is improved, but device complexity and component count increase
Solution Approach 1:
The patent combines the power limiting resistor and PTC device into a single integrated circuit board assembly, where the PTC device is mounted directly on the circuit board in close proximity to the power limiting resistor. This merging reduces the overall component count and simplifies the battery pack structure while maintaining the dual-functionality of current limiting and overcurrent protection.
Solution Approach 2:
The PTC device serves multiple functions: it acts as both an overcurrent protection device and a current limiting element. The power limiting resistor also contributes to both normal operation current limiting and short-circuit protection. This multi-functionality reduces the need for separate dedicated components for each safety function.
2Reliability
If a power limiting circuit with multiple components is used to ensure safety, then product safety is improved, but board space increases
Solution Approach 1:
The PTC device is nested or mounted directly on the circuit board in close proximity to the power limiting resistor, effectively utilizing the existing board space. The compact arrangement allows the PTC device to be integrated into the existing circuit layout without requiring significant additional board area, as it works in conjunction with the already-present power limiting resistor.
3Reliability
If a complex power limiting circuit is implemented to meet safety standards, then product safety is improved, but ease of manufacture decreases
Solution Approach 1:
The power limiting resistor and PTC device are combined into a single integrated assembly on the circuit board, which simplifies the manufacturing process. Instead of requiring separate installation steps for multiple discrete safety components, the merged design allows for more streamlined assembly operations and reduces the complexity of quality control checks during manufacturing.
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
The solution effectively prevents sparking and ensures product safety by limiting current within rated limits, complying with safety standards like ITE EN60950-1, while reducing component count and board space requirements, thus enhancing manufacturability and compliance with safety directives.
Implementation Method 1
a positive temperature coefficient (PTC) device which limits the maximum battery current
Implementation Method 2
The power limiting resistor limits the maximum battery system current so that a fuse within the battery pack remains within its rated limits
Data Source
AI summary
A battery pack (200) includes a power limiting apparatus (230) comprising a power limiting resistor (232) in series with an overcurrent protection device (234). A switch (236) under the control of a data line (202) is placed in parallel with the series coupled power limiting resistor (232) and overcurrent protection device (234). When the switch (236) is enabled via the data line (202), current limiting is provided via the switch and a fuse. When the switch (236) is disabled via the data line (202) current limiting is provided via the overcurrent protection device (234) which limits the maximum battery system current.