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Normally open and closed relays

2017-08-16 12:44  
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A relay is an electrically operated switch.Current flowing through the coil of the relay creates a magnetic field which attracts a lever and changes the switch contacts.Relays allow one circuit to switch a second circuit which can be completely separate from the first.The phototransistor and photodarlington couplers act as 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.These circuits provide several approaches to implement the relay function and serve as practical, costeffective examples.