Mitsubishi Electric · MELSEC iQ-R I/O Module
Excessive voltage is applied to the load when the triac output is in the OFF state. This happens because the load internally performs half-wave rectification, charging an internal capacitor (C). When the supply polarity changes, this charged voltage combined with the line voltage is applied across an internal diode (D1), potentially reaching approximately 2.2 times the supply voltage, risking D1 deterioration or fire.
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Connect a resistor (several tens to hundreds of kΩ) in parallel across the load terminals. This dissipates excess voltage and protects the internal components of the load from overvoltage during the OFF state.