Solid State Relay Zero-Crossing Control for Capacitor Recharging
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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 unknown 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, allowing the relay switch to automatically turn off when the capacitor voltage drops below a threshold and turn back on when it reaches a high threshold, ensuring optimal charging and minimizing load current during transitions.
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 disconnected for too much time or too little time depending on various factors
Solution Approach 1:
The patent implements feedback control by monitoring the capacitor voltage level and using this information to control the relay switching timing. The microcontroller continuously detects the capacitor voltage and adjusts the relay turn-off duration accordingly, ensuring the capacitor is fully charged before the relay is turned back on, thus eliminating both under-charging and excessive disconnection issues
Solution Approach 2:
The patent transitions from a fixed-time relay disconnection approach to a dynamic, adaptive approach where the disconnection duration is adjusted based on real-time capacitor voltage measurements. The system dynamically determines the optimal disconnection time required to recharge the capacitor to a sufficient voltage level, optimizing both charging reliability and minimizing unnecessary disconnection time
2Reliability
If the relay is switched off when load current is high, then the capacitor can recharge, but the load voltage may spike to a very high level causing protection components to trigger
Solution Approach 1:
The patent uses feedback control by continuously monitoring both capacitor voltage and load current levels. The microcontroller detects when the capacitor voltage drops below a threshold and determines the optimal timing to turn off the relay, ensuring this occurs when load current is low to avoid voltage spikes. The system waits for the next zero-crossing event or low current period before initiating relay disconnection
Solution Approach 2:
The patent implements preliminary detection and preparation by monitoring capacitor voltage and load current conditions before initiating relay disconnection. The system identifies the optimal moment to switch off the relay based on pre-established voltage and current thresholds, ensuring that disconnection occurs only when load current is low enough to prevent dangerous voltage spikes
Data Source
Figure 1A
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Figure 1C
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.