PCB High-Impedance Trace for Power Tool Overcurrent Protection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Power tools face challenges in safely managing high current surges that can lead to overheating and damage, as existing solutions lack effective mechanisms to interrupt power and prevent motor damage during overcurrent events.
Innovation Solution
Incorporating a conductive high impedance trace on a printed circuit board that intersects the motor axis, which interrupts power when current exceeds a predetermined limit, and a thermistor-controlled system to monitor and disable the motor when the trace's temperature exceeds a threshold, using a two-ounce copper trace for effective current management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional power tool design is used without a high impedance trace, then the device complexity is low, but the reliability is poor because there is no effective mechanism to interrupt power during overcurrent events
Solution Approach 1:
A high impedance trace is introduced as an intermediary element between the power source and motor. This trace acts as a mediator that naturally limits current flow through its inherent electrical impedance, protecting the motor from overcurrent damage without requiring complex active protection circuits.
Solution Approach 2:
The high impedance trace provides self-service protection by automatically limiting current based on its electrical properties. The trace itself serves as the protection mechanism, eliminating the need for external controllers or sensors to detect and respond to overcurrent conditions.
2Reliability
If a high impedance trace is added to protect against overcurrent, then the reliability improves, but the device complexity increases due to additional circuit board requirements
Solution Approach 1:
The protection function is merged into the existing printed circuit board structure. The high impedance trace is integrated directly into the PCB layout, combining the circuit board's structural role with the current-limiting protection function, rather than adding separate protection components.
Solution Approach 2:
The printed circuit board serves multiple functions: it provides mechanical support for components, electrical connections, and now also acts as a current-limiting protection element through the high impedance trace. This multi-functionality reduces the need for additional dedicated protection components.
3Reliability
If the conductive trace is designed with high impedance to limit current, then the reliability improves, but the use of energy increases due to resistive losses in the trace
Solution Approach 1:
The electrical parameters of the conductive trace are specifically engineered to achieve the desired current-limiting effect. By carefully selecting the trace's impedance, length, and cross-sectional area, the design optimizes the balance between protection capability and energy efficiency for the specific motor power requirements.
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 motor damage by interrupting power during overcurrent events and safely managing temperature thresholds, ensuring reliable operation and extending tool lifespan.
Implementation Method 1
a conductive high impedance trace that is configured to interrupt electric power to the motor in response to a current that exceeds a current limit
Implementation Method 2
the current limit corresponds to a melting point of the conductive high impedance trace
Implementation Method 3
a thermistor and a controller connected to the thermistor. The controller is configured to receive a signal from the thermistor related to a temperature of the conductive high impedance trace
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A power tool (100) includes a housing (112) having a motor housing portion (120) and a handle portion (124). A motor (204) having a motor axis (208) is positioned within the motor housing portion (120). The power tool (100) further includes a first printed circuit board (220) positioned within the motor housing portion (120). The first printed circuit board (220) intersects the motor axis (208). The power tool (100) also includes a second printed circuit board (224) positioned within the motor housing (120). The second printed circuit board (224) intersects the motor axis (208). The second printed circuit board (208) includes a conductive high impedance trace (708) that is configured to interrupt electric power to the motor (204) in response to a current that exceeds a current limit. A method of operating a power tool (100), the method comprising: sensing, with a thermistor (230) coupled to a printed circuit board (220), a temperature of a conductive high impedance trace (708) on the printed circuit board (220); receiving, with a controller (800), a signal from the thermistor (230) related to the temperature of the conductive high impedance trace (708); determining, with the controller (800), whether the temperature of the conductive high impedance trace (708) exceeds a first threshold; and disabling operation of a motor (204) when the temperature of the conductive high impedance trace (708) exceeds the first threshold.