optoisolated

Optoisolated refers to circuits or systems that use optical means to provide galvanic isolation between two electrical domains. This is typically achieved with an optocoupler (optical isolator), which contains an LED on the input side and a photosensitive device on the output side. Light from the LED conveys the signal across an isolation barrier, while the electrical circuits remain physically separate.

Common implementations include transistor-output optocouplers, photodarlington and photodiode variants, and devices with MOSFET or TRIAC outputs for switching AC or DC loads. Photomos relays offer solid-state isolation with relay-like contact behavior. Some optocouplers are integrated into digital isolators, providing high-speed data transfer with robust isolation.

Isolation performance is specified by isolation voltage (the maximum voltage the barrier can withstand) and by creepage and clearance distances, which influence safety and reliability. Typical devices provide kilovolt-level isolation, with higher ratings for reinforced or functional isolation depending on standards and application. In addition to voltage ratings, key performance parameters include current transfer ratio (CTR), propagation delay, and output leakage, which affect signal fidelity and speed. The barrier also helps prevent ground loops, protects sensitive electronics from voltage transients, and reduces EMI coupling between domains.

Applications span power supplies, motor drives, industrial automation, medical equipment, and data communication interfaces, wherever different voltage domains must communicate without direct electrical connection. Limitations include slower response relative to direct connections, dependence on LED life and temperature, and potential leakage or degradation of isolation under extreme conditions.