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In this article, we'll cover some of the basics of analog optoisolator/couplers, as we explore a few circuits that you can experiment with on your own or, perhaps, incorporate into your next project.
Digital optoisolator/couplers are very common today, and most people involved in electronics are aware of their purpose and application. Optoisolator/couplers are used to provide a "visual" path (optical coupling) between two circuits or devices, while keeping them electrically separated (isolated) from each other. The optical path eliminates ground loops and electrical interface problems that can occur when two circuits are physically connected to one another. And in many situations optoisolator/couplers are used to satisfy safety concerns.
Analog optoisolator/couplers are not nearly as common as the digitol type, but they provide the same advantages for analog circuits as digital units provide for digital circuits. Analog optoisolator/couplers eliminate ground loops and noise problems, provide an additional level of safety through electrical isolation, and, in addition, have characteristics that can be used to their best advantage in certain circuit configurations.
Analog optoisolator/couplers can also be used for switching operations in certain digital applications where they are better suited to a particular operation than digital types. Analog optoisolator/couplers, which are available in many different configurations, are inexpensive, reliable, and fairly readily available. In addition, they can also be fabricated by the hobbyist, allowing their characteristics to be tailored to specific applications.
What's An Analog Optoisolator/ Coupler? Analog optoisolator/couplers are comprised of a light source (input device) and a light detector (output device), which are housed in a light-tight package. There are several different light sources and several detectors that can be used in this application, one of which may be better suited to a specific application than the others.
Figure 1A is a schematic representation of a typical analog optoisolator/coupler that uses an incandescent lamp as the input device and a photocell as the output device. Although an incandescent lamp is used as the input device in that illustration, a neon lamp, light-emitting diode (LED), or any other light source could have easily been used. The light source has a great impact on the optoisolator/coupler's characteristics and must be selected to optimize the unit's desired traits.
Incandescent Lamp. Incandescent lamps may be operated from...