Optokopplern

Optokopplern, commonly known as optocouplers or optical isolators, are electronic components that transfer signals between two electrically separated circuits using light. They provide galvanic isolation to protect low-voltage circuitry from high voltages, noise, and surges in the other side of the system.

A typical optokoppler consists of a light source, usually an LED, on the input side and a photosensitive detector on the output side, both enclosed in a light-tight package with a transparent barrier between them. When current flows through the LED, light is produced and detected by the photodetector, which generates an electrical signal in the output circuit. The isolation barrier keeps the input and output circuits electrically isolated while allowing signal transmission.

Common variants include phototransistor, photodarlington, and photodiode output types, as well as logic-output optocouplers that interface directly with TTL or CMOS logic. There are also specialized versions such as triac optocouplers for AC mains control and photomos relays for switching applications. High-speed optocouplers use different detectors and amplification stages to achieve faster response times.

Key specifications include the isolation voltage (rated to withstand voltage between input and output, often several kilovolts), the current transfer ratio (CTR, the ratio of output current to LED current, which varies with temperature and aging), and the response time (rise and fall times). Other important factors are package type (DIP, SO, surface-mount), creepage and clearance distances for safety standards, and operating temperature range.

Typical applications are signal isolation in microcontroller interfaces, measurement and instrumentation, power-supply control, gate driving for switches, and safety-critical systems where galvanic isolation is required. Standards such as IEC 61010 and UL 1577 govern isolation components to ensure safety and reliability.