Posted on Dec 6, 2012

The phototransistor and photodarlington couplers act as de relays in saturated switching at currents up to 5 mA and 50 mA, respectively. When higher currents or higher voltage capabilities are required, additional devices are required to buffer or amplify the photocoupler output. The addition of hysteresis to provide fast switching and stable pick-up and drop-out points can be easily implemented simultaneously.

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These circuits provide several approaches to implement the de relay function and serve as practical, costeffective examples.

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