What is an optocoupler used for?

• A. A device that filters noise from signals
• B. A device that stores data
• C. A device used to isolate electronic devices by using diodes and light.
• D. A device that converts AC to DC

Answer: (C)

Electrical isolation between circuits is what an optocoupler provides, using light to transfer the signal across an insulating barrier. It has an input side with an LED (a diode) and an output side with a light-sensitive detector such as a phototransistor or photodiode, and the two sides are optically coupled but electrically separated. When the input LED is driven, it emits light that the detector on the other side senses, turning the output circuit on or off without any direct electrical connection. This separation protects sensitive electronics from voltage spikes, noise, or ground loops on the other side and is especially useful for interfacing low-voltage control circuitry with high-voltage or noisy equipment.

Other concepts don’t fit the purpose of isolation: filtering noise is about shaping a signal with passive components, data storage involves memory devices, and converting AC to DC is the job of rectifiers in power supplies.