Power Tool No-Volt Prevention Circuit for Dangerous Restart
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Solution Overview
Problem
Existing power tools with brushless DC motors lack effective no-volt release features to prevent dangerous restarts when connected to a power supply while the tool's trigger switch is actuated, posing safety risks to users.
Innovation Solution
A no-volt prevention circuit using a resistor-capacitor (RC) circuit and semiconductor switches is implemented to ensure the power tool remains off when the battery pack is plugged in while the trigger is pressed, utilizing an active-low or active-high Switch Signal to control the main semiconductor switch, thereby preventing unintended startup.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a no-volt release feature is implemented using conventional methods (triac switch for universal motors or solenoid switch for BLDC motors), then the power tool can prevent dangerous restart, but the device complexity and cost increase
Solution Approach 1:
The patent replaces mechanical switch systems (triac, solenoid) with an electronic control circuit using a controller, semiconductor switches, and timing circuitry. This substitution eliminates the need for expensive mechanical components while achieving the same no-volt release function through electronic control of the main semiconductor switch based on timing relationships between power application and trigger activation.
Solution Approach 2:
The controller in the patent serves multiple functions: it controls the main semiconductor switch, monitors trigger switch status, implements no-volt release prevention, and manages motor operation. This multi-functionality consolidates what would otherwise require separate components (triac, solenoid, timing circuits) into a single integrated control unit, reducing overall device complexity.
2Reliability
If a solenoid switch is used to prevent no-volt condition in cordless power tools, then the tool can prevent dangerous restart, but the cost increases and it is not practical for compact tools
Solution Approach 1:
The patent replaces the expensive solenoid switch with inexpensive electronic components including a controller, semiconductor switches, and passive circuit elements. These electronic components are significantly cheaper than solenoid mechanisms while providing equivalent or superior functionality, making the solution economically viable for mass production of compact power tools.
Solution Approach 2:
The patent eliminates the mechanical solenoid switch entirely, replacing it with an electronic control system that uses semiconductor devices and timing circuits. This substitution removes the need for moving parts, magnetic fields, and mechanical actuation mechanisms, thereby reducing cost, size, and complexity while maintaining the no-volt release prevention function.
3Speed
If the power tool allows immediate startup when power is supplied, then the tool responds quickly to power application, but dangerous restart occurs when trigger is already actuated
Solution Approach 1:
The controller is configured to check the trigger switch status before enabling the main semiconductor switch upon power application. By performing this preliminary check and conditionally delaying startup based on trigger state, the system prevents dangerous restart while maintaining quick response when the trigger is not actuated. The timing circuitry ensures the check occurs immediately upon power detection.
Solution Approach 2:
The system continuously monitors the trigger switch status and uses this feedback to control the main semiconductor switch. When power is applied, the controller reads the trigger state and adjusts the startup behavior accordingly - preventing activation if the trigger is pressed, or enabling immediate startup if the trigger is released. This feedback mechanism resolves the contradiction between quick response and safety.
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 power tool startups during no-volt conditions, enhancing user safety by ensuring the tool remains off until the trigger is intentionally activated, without requiring expensive hardware or additional software control.
Implementation Method 1
a first capacitor coupled between the power supply node and a source of the main semiconductor switch
Data Source
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AI summary
A power tool including a power supply interface, a motor control circuit configured to regulate supply of power from the power supply interface to a motor, and an input unit actuatable by a user. A no-volt prevention circuit receives a first voltage signal from the power supply interface and a second voltage signal from the input unit. The no-volt protection circuit includes a main semiconductor switch arranged on a current path from the power supply interface to at least one component of the motor control circuit, and a resistor-capacitor circuit to turn the main semiconductor switch ON when the input unit is actuated after the power supply interface is coupled to the power supply, but not when the input unit is actuated before to the power supply interface is coupled to the power supply.