Switchable Capacitor Circuit Mitigates Voltage Spikes in Power Tools
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Solution Overview
Problem
Power tools with brushless electric motors face high voltage spikes during high load conditions, which can damage electronic components and affect normal operation.
Innovation Solution
A power tool configuration that includes a rectifier, a switching arrangement, a switch path with an auxiliary capacitor, and a switch control circuit to detect and manage voltage thresholds, allowing the switch to control the discharge of the auxiliary capacitor to mitigate voltage spikes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a capacitor is added to reduce voltage spikes, then voltage transient protection is improved, but device complexity increases
Solution Approach 1:
The auxiliary capacitor is pre-charged during normal operation before voltage spikes occur. When over-voltage conditions are detected, the pre-charged capacitor immediately discharges to counteract the voltage transient, providing proactive protection rather than reactive protection.
Solution Approach 2:
The patent implements a switchable auxiliary capacitor that can be dynamically connected or disconnected from the DC bus based on voltage conditions. The switch control circuit monitors voltage levels and activates the capacitor only when needed, transforming a static circuit into a dynamic one that adapts to operating conditions.
2Reliability
If a switch control circuit is implemented to manage capacitor discharge, then voltage spike mitigation is improved, but device complexity increases
Solution Approach 1:
The switch control circuit continuously monitors the DC bus voltage and provides feedback control. When voltage exceeds a predetermined threshold, the control circuit activates the switch to discharge the auxiliary capacitor. This closed-loop feedback mechanism ensures precise control while maintaining simplicity through threshold-based decision logic.
3Reliability
If an auxiliary capacitor is added in parallel with the rectifier, then voltage transient reduction is improved, but manufacturing complexity increases
Solution Approach 1:
The patent divides the capacitor function into two separate components: a main DC bus capacitor for general energy storage and an auxiliary switchable capacitor specifically for voltage spike protection. This segmentation allows each capacitor to be optimized for its specific function and simplifies the overall assembly process by clearly defining connection points and roles.
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
Effectively reduces voltage transients on the DC bus, preventing damage to electronic components and ensuring normal operation by selectively activating the auxiliary capacitor when voltage thresholds are exceeded.
Implementation Method 1
The switch path may include an auxiliary capacitor in series with a switch
Implementation Method 2
Power tools with brushless electric motors use a rectifier to convert an alternating current (AC) input into a direct current (DC)
Data Source
AI summary
A power adapter is provided to supply electric power from an alternating current from an alternating current (AC) power supply to a powered apparatus. It includes a switchable capacitor circuit housed within a housing and including: a first switch path associated with a positive half cycle of the alternating current and a second switch path associated with a negative half cycle of the alternating current, both coupled across the AC power supply. Each switch path includes a switchable capacitor in series with a switch.