Dual Semiconductor Switches for Electric Power Tool Reliability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional electric power tools with semiconductor switches face reliability issues due to short-circuit faults, which can cause continuous motor operation, necessitating large contact capacity contact switches and increased size and cost, while parallel use of semiconductor and contact switches complicates the design.
Innovation Solution
An electric power tool configuration using two semiconductor switches in series on the current path to the motor, with a control unit managing one switch to prevent continuous operation in case of short-circuit failures, allowing for reliable operation without the need for large contact capacity contact switches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a contact switch with large contact capacity is provided on the current path to directly interrupt current to the motor, then reliability against semiconductor switch failure is improved, but device size and cost increase
Solution Approach 1:
The current interruption function is segmented between two semiconductor switches (first and second) positioned at different locations in the current path. The first semiconductor switch handles normal operation control, while the second semiconductor switch provides backup protection against short-circuit failures. This segmentation eliminates the need for a single large-capacity contact switch, reducing device size and cost while maintaining reliability.
2Reliability
If a contact switch with large contact capacity is provided on the current path to directly interrupt current to the motor, then reliability against semiconductor switch failure is improved, but manufacturing cost increases
Solution Approach 1:
The current interruption function is segmented between two semiconductor switches (first and second) positioned at different locations in the current path. The first semiconductor switch handles normal operation control, while the second semiconductor switch provides backup protection against short-circuit failures. This segmentation eliminates the need for a single large-capacity contact switch, reducing device size and cost while maintaining reliability.
3Reliability
If thick wiring lines are installed over long distances to accommodate contact switch placement, then reliability is improved, but device size and cost increase further
Solution Approach 1:
The current interruption function is segmented between two semiconductor switches (first and second) positioned at different locations in the current path. The first semiconductor switch handles normal operation control, while the second semiconductor switch provides backup protection against short-circuit failures. This segmentation eliminates the need for a single large-capacity contact switch, reducing device size and cost while maintaining reliability.
Solution Approach 2:
The first semiconductor switch acts as an intermediary between the user-operated contact switch and the motor. It converts the low-current control signal from the contact switch into high-current switching, eliminating the need for thick wiring lines to connect the contact switch to the motor. This intermediary function allows thin wiring to be used while maintaining the ability to interrupt large motor currents.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
An electric power tool (1) includes a motor (18,25,56,79,93) as a driving source, a first operation switch (11,31,51), a first semiconductor switch (Q1), and a second semiconductor switch (Q2,Q20,Q30). The first operation switch is operated by a user to be turned ON/OFF. The first semiconductor switch, provided on a current path from the power source (7,41,52,87,92) to the motor, includes at least one semiconductor switching device. When the first operation switch is OFF, the first semiconductor switch is turned OFF to interrupt the current path. When the first operation switch is ON, the first semiconductor switch is turned ON to close the current path. The second semiconductor switch is provided on the current path in series with the first semiconductor switch and includes at least one semiconductor switching device. The second semiconductor switch closes/interrupts the current path by being turned ON/OFF in accordance with an input control signal.