Optocouplers are available in four general types, each one having an infra-red LED source but with different photo-sensitive devices. The four optocouplers are called the: Photo-transistor, Photo-darlington, Photo-SCR and Photo-triac as shown below. This unique design ensures that the two circuits remain electrically isolated. They typically consist of an LED on the input side and a photosensitive device – such as a phototransistor, diode array, or triac – on the output. An optocoupler, also known as photocoupler or opto-isolator, is a device which can transfer an electrical signal across two galvanically-isolated circuits by way of optical coupling. On the input side an infrared light emitting diode is used with all optocoupler types.
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