Constant Current Leakage Circuit for Stable GFCI Testing
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Solution Overview
Problem
Conventional line voltage circuits with GFCI protection face issues due to varying leakage currents caused by line voltage fluctuations, leading to unreliable automatic testing and potential device failure during line perturbations.
Innovation Solution
A constant current circuit is designed to maintain a steady leakage current independent of line voltage changes, utilizing a rectifier bridge, MOSFET, and BJT to ensure a fixed leakage current through a load, even during voltage fluctuations or perturbations, using a bias resistor and enable transistor to regulate current flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed value resistor is used to generate leakage current for GFCI testing, then the circuit structure is simple, but the leakage current varies with line voltage fluctuations causing unreliable testing
Solution Approach 1:
The patent changes the parameter of leakage current from voltage-dependent to constant by introducing a constant current circuit. The circuit uses a current setting resistor and transistor configuration to maintain fixed leakage current regardless of line voltage fluctuations, thereby ensuring reliable GFCI testing.
Solution Approach 2:
The patent introduces a constant current circuit as an intermediary between the line voltage and the GFCI testing mechanism. This intermediary circuit decouples the leakage current from line voltage variations, providing stable testing conditions while maintaining circuit simplicity.
2Device complexity
If leakage current is generated using a fixed resistor, then the circuit is simple, but the current varies during line perturbations causing device failure
Solution Approach 1:
The patent transforms the leakage current parameter from being voltage-proportional to being constant by implementing a constant current source. The circuit uses a reference voltage, current setting resistor, and transistor arrangement to maintain stable leakage current during line perturbations, preventing device failure.
Solution Approach 2:
The patent prepares for line perturbations by designing a constant current circuit that anticipates voltage fluctuations. The circuit maintains predetermined leakage current levels even when line voltage changes, cushioning against potential device failures before they occur.
3Productivity
If automatic testing is performed during low voltage conditions, then the testing frequency is high, but the leakage current is insufficient to trip the current sense circuit
Solution Approach 1:
The patent decouples leakage current magnitude from line voltage by implementing a constant current circuit. This allows automatic testing to be performed at any voltage level with sufficient and consistent leakage current, ensuring the current sense circuit can reliably detect and trip on GFCI faults regardless of voltage conditions.
Data Source
AI summary
Disclosed is an electrical circuit that includes an input terminal configured to receive a power signal as input; a rectifier bridge configured to receive the power signal from the input terminal; a resistive load connected between the input terminal and the rectifier bridge, the resistive load configured to control the current of the power signal to the rectifier bridge; a current limiter circuit configured to receive a constant current from the rectifier bridge; and an output terminal configured to provide an output power signal based on the constant current flowing through the current limiter circuit.