Integrated GFCI Circuit With Variable Delay to Prevent False Trips
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Solution Overview
Problem
Existing GFCI products face issues with increased PCB real estate usage, reduced reliability, false trips due to lack of signal conditioning, and inability to alter functionality post-manufacturing, necessitating a two-chip solution and fixed threshold values.
Innovation Solution
Integration of sensing circuitry on an integrated circuit with control logic to analyze digitized leakage current or voltage, employing a variable delay based on average values to prevent premature power disconnection, and incorporating a backup circuit for reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a two-chip solution is used for GFCI functionality, then manufacturing flexibility is improved, but device complexity and PCB real estate usage increase
Solution Approach 1:
The patent merges the GFCI sensing circuitry and microcontroller functionality into a single integrated circuit chip. This consolidation reduces the number of discrete components, simplifies the PCB layout, and decreases overall device complexity while maintaining the ability to program different GFCI functionalities through software, thus preserving manufacturing flexibility.
2Device complexity
If fixed threshold values are used for ground fault detection, then device simplicity is improved, but adaptability to different applications is reduced
Solution Approach 1:
The patent implements programmable threshold values and detection parameters that can be configured through software. This allows the GFCI device to adapt to different applications and requirements by changing the threshold settings, while the underlying hardware structure remains simple and unchanged.
3Device complexity
If signal conditioning is not implemented, then device simplicity is improved, but false trips increase
Solution Approach 1:
The patent incorporates signal conditioning circuits that process and filter the sensed signals before they are analyzed by the microcontroller. This preliminary processing of the signal removes noise and artifacts that could cause false trip detections, thereby improving reliability while maintaining relatively simple device architecture.
4Device complexity
If integrated circuit implementation is used, then component count is reduced, but manufacturing precision requirements increase
Solution Approach 1:
By integrating multiple functions (sensing, signal conditioning, processing, and control) into a single integrated circuit, the patent reduces the total component count and interconnections. This integration also reduces the cumulative tolerance errors that would arise from multiple discrete components, thereby managing manufacturing precision requirements more effectively.
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
Enhances programmability, reduces component count, increases reliability, and minimizes nuisance trips by using a programmable integrated circuit with variable delay and backup protection.
Implementation Method 1
The GFCI device may contain a current transformer with two coils: one for the hot wire and one for the neutral wire. When the current flowing out of the sensing circuit does not match the current flowing in, which indicates a ground fault, a difference is detected by the current transformer.
Data Source
AI summary
An integrated circuit includes a transimpedance amplifier (TIA) coupled to a hot-to-ground (H/G) sensing coil. The H/G sensing coil is coupled to alternating current (AC) mains. The TIA converts a leakage current, received from the H/G sensing coil, to a leakage voltage. An analog-to-digital converter (ADC), coupled to the transimpedance amplifier, converts the leakage voltage to a digital signal. Control logic is coupled to the ADC and processes the digital signal to determine an average value associated with the leakage voltage over time and determines a trigger delay period corresponding to the average value. The control logic outputs, in response to the leakage voltage still satisfying the average value after waiting the trigger delay period, a trip signal to trip logic to cause a disconnect of a current supplied to a load by the AC mains.