Leakage Current Detection Circuit for Noise-Resistant Welding Power
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Solution Overview
Problem
Welding, plasma cutting, and induction heating power supplies lack effective ground fault interrupt circuits due to high frequency noise, making it difficult to implement low voltage ground fault protection without being susceptible to noise.
Innovation Solution
A leakage detection circuit using a lock-in amplifier and test signal generator to measure leakage current, with a comparator to determine if the current is within acceptable thresholds, enabling or disabling the power supply based on the measurement, and a feedback cable to monitor the workpiece for leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a ground fault interrupt circuit is implemented in welding, plasma cutting, and induction heating power supplies, then ground fault protection is improved, but the circuit becomes susceptible to high frequency noise
Solution Approach 1:
A feedback cable is introduced as an intermediary component to provide a dedicated return path for leakage current. This separates the measurement function from the noisy power circuit environment, allowing the ground fault interrupt circuit to detect leakage current without being directly exposed to high frequency noise from welding, plasma cutting, and induction heating operations
Solution Approach 2:
The patent replaces traditional mechanical ground fault detection methods with electronic signal processing. By using a feedback cable to conduct leakage current back to the power supply and employing electronic comparison circuits, the system achieves noise-resistant detection without relying on mechanical components that are susceptible to high frequency interference
2Reliability
If a reduced open circuit output voltage is used, then safety is improved, but starting circuits become more complex
Solution Approach 1:
The patent employs periodic action through high frequency oscillating circuits and pulse-width modulation (PWM) control to achieve reduced open circuit output voltage. The power supply operates by switching at high frequencies, allowing voltage reduction while maintaining effective power delivery during welding operations, thereby improving safety without requiring complex starting circuits
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
Enables reliable low voltage operation in high noise environments by accurately detecting excessive leakage current and preventing faults, ensuring safe operation while minimizing noise interference.
Implementation Method 1
a lock-in amplifier (aka, synchronous demodulator) is used to detect excessive leakage current
Implementation Method 2
a low voltage AC test signal is applied to the welding-type circuit and the resulting current is measured
Data Source
AI summary
An example apparatus to monitor a welding-type system includes: a test signal generator configured to output a test signal to a monitored circuit; and a lock-in amplifier configured to: receive a reference signal based on the test signal; measure a leakage current in the monitored circuit based on the reference signal; and generate an output signal representative of the leakage current.