Battery Pack Charging Switch Circuit for High-Current Fast Charging
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Solution Overview
Problem
Cordless electrical devices have limited run-time due to battery pack capacity, and existing charging circuitry cannot handle higher charging currents without adverse effects such as excessive heating or damage, limiting fast charging capabilities.
Innovation Solution
A battery pack with a charging circuit that includes a N-Channel FET and a fuse rated for higher currents, coupled with an electronic controller to manage the charging process, allowing for charging currents between 6 A and 20 A, enabling faster charging without component damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the charging current is increased to decrease charging time, then the charging speed is improved, but the battery pack components (PCB, fuse, FET) suffer from excessive heating and potential damage
Solution Approach 1:
The charging circuit is segmented into multiple parallel paths with individual FETs (e.g., Q1, Q2, Q3) and current-sharing resistors (e.g., R1, R2, R3). Each path handles a portion of the total charging current, distributing the thermal load across multiple components rather than concentrating it in a single component, thereby enabling higher total charging currents without excessive heating of individual components.
Solution Approach 2:
Current-sharing resistors (e.g., R1, R2, R3) are introduced as intermediary elements in each parallel charging path. These resistors create voltage drops that provide feedback signals to the control circuit, enabling automatic current balancing across the parallel paths. This intermediary mechanism ensures uniform current distribution and prevents any single path from overheating while maintaining high total charging current capability.
2Duration of action of moving object
If higher capacity battery cells are used to increase run-time, then the battery capacity is improved, but the charging time increases proportionally
Solution Approach 1:
The patent changes the electrical parameters of the charging circuit by introducing parallel paths with controlled resistance values. By adjusting the resistance of current-sharing resistors (e.g., R1, R2, R3) and selecting appropriate FETs, the circuit is designed to handle higher charging currents (e.g., 6A-18A or even higher) that are proportional to the battery capacity, thereby maintaining constant charging rate (C-rate) and reducing charging time while accommodating higher capacity batteries.
3Reliability
If the charging current is limited to protect components, then component reliability is improved, but the charging speed deteriorates
Solution Approach 1:
The parallel FET structure provides multi-functionality: each FET serves both as a current-carrying element and as a controllable switch with integrated current sensing capability through its associated resistor. The control circuit universally manages all parallel paths simultaneously, enabling the system to dynamically adjust total charging current based on component thermal conditions while maintaining high charging speeds when conditions permit.
Solution Approach 2:
The current-sharing resistors (e.g., R1, R2, R3) provide continuous feedback signals to the control circuit proportional to the current in each parallel path. This feedback mechanism enables the controller to monitor component loading in real-time and dynamically adjust FET gate voltages to balance current distribution and prevent any single component from exceeding its thermal limits, thereby maintaining both high charging speed and component reliability.
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
Enables faster charging of higher capacity battery packs by safely handling higher charging currents, reducing charging time while preventing component damage.
Implementation Method 1
The charging circuit includes a charging switch and a fuse coupled between the charging terminal and the charging switch. In some constructions, the charging switch may include a N-Channel FET.
Implementation Method 2
The fuse may have at least about a 8 A rating; in some constructions, the fuse may have about a 20 A rating.
Data Source
AI summary
One embodiment provides a battery pack including a housing, a plurality of battery cells supported by the housing, and a terminal block. The terminal block is configured to be coupled to a power tool to provide operating power from the plurality of battery cells to the power tool. The terminal block has a positive power terminal, a charging terminal, and a ground terminal. The battery pack also includes a charging circuit provided between the charging terminal and the plurality of battery cells. The charging circuit is configured to receive and transfer charging current above 12 Amperes to the plurality of battery cells during charging. The charging circuit includes a charging switch and a fuse coupled between the charging terminal and the charging switch.