What Do Optocouplers Do?


An optocoupler -- also referred to as an opto-isolator, photocoupler or photoMOS -- is a piece of an electric circuit that transfers electricity between two other parts without allowing them to make a direct connection. While optocouplers offer element isolation similar to a relay component, they are often a better choice than relay components for circuit designers, as optocouplers are smaller than relay components and fit easily into the microcircuit systems used in electronics.


  • An optocoupler is essentially an optical transmitter and an optical receiver connected by a non-conductive barrier. It uses a beam of light to transfer energy from one circuit element to another, and it can handle incoming voltages of up to 7500V. The barrier that separates the two side of the optocoupler is made from a transparent glass or plastic polymer that does not conduct electricity but does conduct light. The actual physical device of the optocoupler is usually encased in a dark, non-conductive casing and is attached into the electric circuit through small metal teeth with holes on either end of the small cabinet for wire connections to pass through.


  • The most important feature of an optocoupler is its electricity transfer efficiency. An optocoupler’s efficiency is measured through its current transfer ratio, which is the relationship between the current change on the output side of the barrier and the current change on the input side of the barrier. Most optocouplers work at a CTR between 10 and 50 percent.


  • Optocouplers are most often used to separate two circuit elements that are operating on extremely different voltages, which prevents damage to the part working at a lower voltage. They also work to keep the two elements from being damaged by reverse voltage or power surges. Because of this trait, optocouplers are best utilized in associated with on/off switches and the transfer of digital data. They are commonly found between a transmitter and a receiver in an electric circuit.


  • Optocouplers are often constructed with light emitting diodes as part of the optical transmitter side. An LED produces light when voltage is added to it, making it a perfect light source for an optocoupler. Incandescent lamps are also sometimes used in optocouplers, but they are not as efficient as LEDs as they distort input signals and do not last very long.


  • Optocouplers play integral roles in many common household items including telephones, cellular phones, computer circuits, Internet modems and even the entire house's electrical circuit. Optocouplers have also become essential to modern televisions as the technology and complexity of digital components has grown. They are used extensively to separate the parts of the circuit that manage the cable receiver, screen performance and screen settings.

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