What is an opto-isolator?

Photodiodes are common light receivers.

An opto-isolator is an electronic device that uses light to send signals between parts of a circuit. This allows circuit elements to communicate without an electrical connection. The advantage of this isolation is to prevent voltage spikes from affecting multiple circuits. It also helps to reduce noise and interference in audio and video equipment by preventing electrical current from flowing where it is not wanted. Most optoisolators are very inexpensive, costing less than $1 USD.

Operating an opto-isolator is a very basic process. When an electronic signal hits the opto-isolator, that signal is converted into light. The light is then transmitted to a receiver. Once the signal is received, it is converted back into an electronic signal.

There are two basic types of opto-isolators that have their own uses. A digital opto-isolator changes the state of its output to match that of the input. Must be used when bit or pulse output is required. An analog isolator reproduces the input using an analog signal. This type of opto-isolator should be used when signal quantity is the crucial factor.

The average opto-isolator is made up of three basic parts. A solid housing protects against external light leakage into the isolator. A light emitting diode (LED) or other small light source sends the signal and a photosensitive part receives the signal. The most common light receivers are photodiodes and phototransistors. From the outside, an opto-isolator looks like a transistor that has extra wires attached.

In many cases, the term “opto-coupler” is used interchangeably with “opto-isolator”, but there is a difference between the two devices. Both transmit information between the elements of a circuit while allowing the elements to remain isolated. The difference comes from the potential voltage of the circuits. An opto-isolator is designed for use with systems where the potential voltage is between 5,000 and 50,000 volts, and optocouplers are only designed for use with systems where the potential voltage is less than 5,000 volts. Using the wrong device can cause the system to crash.

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Moisture can also cause major problems for optoisolators. If there is too much moisture in the air, electricity can arcing, destroying the electronic insulation. Similar problems can be caused by barometric pressure and air pollution can cause similar problems. The best way to avoid this problem is to keep electronics that use opto-isolators in a climate-controlled area.

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