Ground Leakage Power Supply Circuit for Neutral-Free Wall Switches
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Solution Overview
Problem
Existing building automation systems face challenges in powering smart controllers within wall- or surface-mounted switches without a neutral wire, as conventional ground leakage current limits are insufficient for practical operation, and existing solutions either rely on batteries or exceed allowed ground leakage limits.
Innovation Solution
A ground leakage current power supply circuit that uses an AC hot wire and earth ground, incorporating a rectifier, energy storage component, and current limiter to charge the energy storage component at a rate that limits ground leakage current, while also including a low voltage power supply with a linear voltage regulator to generate a regulated output voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ground leakage current is limited to less than 5 milliamperes to comply with regulatory constraints, then safety and compliance are improved, but the power available for ground-referenced controllers becomes insufficient
Solution Approach 1:
The patent transitions from a two-wire system (hot and neutral) to a three-wire system (hot, neutral, and ground), utilizing the ground wire as an additional power delivery path. This dimensional change in the electrical system allows power to be delivered through multiple pathways, resolving the contradiction between ground leakage limits and power availability by using the ground return path in a controlled manner that exceeds traditional ground leakage constraints while maintaining safety.
Solution Approach 2:
The patent changes the operational parameters of the ground wire from its traditional role as a safety reference only to an active power delivery path. By modifying the current carrying capacity and functional role of the ground wire, the system can deliver sufficient power to controllers while implementing protective measures such as isolation and monitoring to maintain safety.
2Use of energy by moving object
If transformers and triacs are used to harvest power from the AC hot lead, then power availability for controllers is improved, but ground leakage current exceeds allowed limits
Solution Approach 1:
The patent segments the power delivery function across multiple components and pathways: the hot wire provides forward power, the ground wire provides return path, and isolation components separate different electrical domains. This segmentation allows power harvesting while controlling ground leakage by distributing the function across isolated stages rather than a single component that would exceed leakage limits.
Solution Approach 2:
The patent introduces isolation components and controlled rectification circuits as intermediary elements between the AC power source and the controller. These intermediaries convert AC power to controlled DC power while preventing excessive ground leakage current from reaching the ground wire, thus enabling power harvesting without violating ground leakage constraints.
3Use of energy by moving object
If batteries are used as power source within the switch, then power availability is improved, but device complexity and maintenance requirements increase
Solution Approach 1:
The patent implements a self-service power supply system where the controller harvests its own operating power from the AC line through controlled rectification and energy storage components. The system automatically manages power conversion, storage, and distribution without requiring external battery replacement or complex power management, thereby reducing device complexity and maintenance while ensuring continuous power availability.
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 sufficient power supply to remote or local loads for a prescribed period without requiring an AC neutral line, while maintaining ground leakage current within safe limits, supporting both local switch controllers and wireless transceivers in multimode switches.
Implementation Method 1
a rectifier, coupled to the hot node and to the earth ground node
Implementation Method 2
an energy storage component, coupled to a return node and coupled in series to a current limiter that is coupled to receive rectified power from the rectifier
Implementation Method 3
a current limiter that is coupled to receive rectified power from the rectifier, where the current limiter enables the energy storage component to charge to a voltage value at a rate that limits ground leakage current to a prescribed leakage value
Implementation Method 4
a low voltage power supply that includes a linear voltage regulator and is coupled to the energy storage component and to a return node
Data Source
AI summary
A ground leakage current power supply is provided that includes a hot node coupled to a hot wire of an AC power source, and an earth ground node coupled to an earth ground, where a neutral wire is not present. The supply also has an energy storage component and a low voltage power supply. The energy storage component is coupled in series to a current limiter that is coupled to receive rectified power from the AC power source, where the current limiter enables the energy storage component to charge to a voltage value at a rate that limits ground leakage current. The low voltage power supply includes a linear voltage regulator and is coupled to the energy storage component and to a return node, the return node providing a return reference voltage, and is configured to receive the voltage value, and is configured generate a regulated output voltage that is referenced to the return reference voltage.