Solid State Relay Zero-Crossing Control for Load Power Harvesting
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Solution Overview
Problem
Existing relay circuits that derive power from a load face challenges in accurately charging a supply capacitor, leading to incomplete charging or excessive disconnection due to variable charging times and high load currents, which can cause voltage spiking and stress on protection components.
Innovation Solution
A solid state relay circuit with a control circuit that includes a voltage detection circuit and a zero crossing circuit, which automatically toggles the relay switch between ON and OFF states based on capacitor voltage thresholds, ensuring optimal charging and minimizing load current during switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the relay is turned off for a fixed time to recharge the capacitor, then the capacitor can be recharged, but the relay may be turned off for too little time (incomplete charging) or too much time (excessive disconnection)
Solution Approach 1:
The patent employs feedback by monitoring the capacitor voltage level and using this information to control the relay switching timing. The control circuit detects when the capacitor voltage drops below a threshold and triggers the relay to switch off, then monitors when the voltage rises above a threshold to trigger the relay to switch on, creating a closed-loop control system that adapts to varying charging conditions
Solution Approach 2:
The patent transitions from a fixed-time switching approach to a dynamic, voltage-level-based switching approach. The relay switching timing is no longer predetermined but dynamically adjusted based on the actual capacitor voltage levels, allowing the system to adapt to varying load conditions, capacitor sizes, and charging rates
2Reliability
If the relay is switched off when load current is high, then the capacitor can be recharged, but the load voltage may spike to a very high level, causing protection components such as TVS to trigger
Solution Approach 1:
The control circuit continuously monitors both capacitor voltage and load current levels, using this feedback to determine the optimal switching moment. By detecting when load current approaches zero and capacitor voltage drops below threshold, the system can trigger relay switching at the precise moment that avoids voltage spiking while ensuring adequate capacitor recharging
Solution Approach 2:
The system performs preliminary monitoring of both capacitor voltage and load current conditions before initiating the relay switch-off action. By anticipating the charging state and load current trajectory, the control circuit can determine the optimal switching moment in advance, preventing voltage spiking before it occurs
Data Source
AI summary
A relay circuit, including a solid state relay switch, connected to a first relay line and to a charging capacitor, and connected to a second relay line. The relay circuit may also include a solid state relay control circuit, coupled between the charging capacitor and the solid state relay switch. The solid state relay control circuit may include a voltage detection circuit, having an input coupled to an output of the charging capacitor, and having an output arranged to generate a LOW voltage signal when a voltage level of the charging capacitor is below a low threshold value. The solid state relay control circuit may also include a zero crossing circuit, coupled to the first relay line and the second relay line, and having an output to generate a clock signal when a zero crossing event takes place between the first relay line and the second relay line.