Auxiliary Capacitor Switch Path for Power Tool Voltage Spike Protection
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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 without affecting 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 voltage thresholds and control the switch state, preventing current flow during low voltages and allowing discharge when voltages exceed a predetermined threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a capacitor is added to mitigate voltage spikes, then reliability is improved, but device complexity increases
Solution Approach 1:
The auxiliary capacitor is pre-charged to a threshold voltage during normal operation before voltage spikes occur. When a voltage spike is detected, the capacitor immediately discharges to counteract the spike, providing proactive protection rather than reactive protection. This preliminary charging action during normal operation enables the system to respond quickly to voltage transients without adding complex control circuitry.
Solution Approach 2:
The auxiliary capacitor acts as an intermediary energy storage element between the power supply and the electronic components. It mediates voltage fluctuations by absorbing excess energy during spikes and releasing stored energy during voltage drops, isolating the sensitive electronic components from direct exposure to power supply transients without requiring complex active protection circuits.
2Reliability
If the auxiliary capacitor is always connected, then reliability is improved, but energy loss increases
Solution Approach 1:
The connection state of the auxiliary capacitor is dynamically changed based on operating conditions. The capacitor is connected to the DC power bus when voltage protection is needed and disconnected when not needed, transforming the system from a static configuration to a dynamic one that adapts to real-time voltage conditions, thereby reducing continuous energy loss while maintaining protection when required.
Solution Approach 2:
The switch control circuit continuously monitors the voltage on the DC power bus and provides feedback to control the switch state. When the bus voltage exceeds the capacitor voltage by a threshold amount, the circuit activates the switch to connect the capacitor for discharge. This feedback mechanism ensures the capacitor operates only when needed, preventing continuous energy loss while maintaining reliable protection against voltage spikes.
3Reliability
If the capacitance of the auxiliary capacitor is increased, then voltage spike mitigation is improved, but device complexity and space requirements increase
Solution Approach 1:
The invention changes the operational parameters of a fixed-capacitance auxiliary capacitor by dynamically controlling its connection and disconnection timing through a switch. Instead of relying on a large capacitor that would be permanently connected, the system achieves equivalent or superior voltage spike mitigation by optimizing the capacitor's engagement duration and timing, thereby reducing the required capacitance value and associated complexity.
Solution Approach 2:
The auxiliary capacitor is pre-charged to an optimal voltage level during normal operation, storing energy in advance for spike mitigation. This preliminary charging allows the use of a smaller capacitor compared to systems that would require continuously connected large capacitors, as the pre-charged capacitor can deliver its full energy content quickly when needed, reducing both capacitance requirements and device complexity.
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 mitigates high voltage spikes, preventing damage to electronic components while maintaining normal power tool operation by selectively charging and discharging the auxiliary capacitor based on detected voltage levels.
Implementation Method 1
The auxiliary capacitor may have a capacitance of about 50μF to 200μF... The switch control circuit may be configured to open the switch to prevent current flow through the discharge path when the detected voltage is less than or equal to a first voltage threshold and close the switch to allow current flow through the discharge path when the detected voltage is greater than a second voltage threshold greater than the first voltage threshold
Implementation Method 2
The rectifier may be configured to receive an alternating current from an alternating current (AC) power supply and output a rectified signal supplied to a DC power bus
Implementation Method 3
The switch control circuit may be configured to detect voltage associated with at least one of the AC power supply or the DC power bus and to control state of the switch in accordance with magnitude of the detected voltage
Data Source
Figure 1
Figure 2
Figure 3A
AI summary
A power tool is configured to receive power from a power supply. The power tool may include a rectifier that may output a rectified signal to a DC power bus. A switching arrangement may operate to deliver electric power from the DC power bus to an electric motor. A switch path may be electrically coupled in parallel with the rectifier on the DC power bus. The switch path includes an auxiliary capacitor in series with a switch and a state of the switch controls a discharging path for the auxiliary capacitor. A switch control circuit may be configured to detect voltage associated with at least one of the AC power supply or the DC power bus and to control state of the switch in accordance with magnitude of the detected voltage.