Opto-isolator

An opto-isolator is a device that uses optical techniques to electrically isolate two related circuits, typically a transmitter and a receiver. See also list of optical topics. ... There are many kinds of circuit An electric circuit interconnects electrical elements. ... Crystal Palace transmitter, London A transmitter is an electronic device which with the aid of an antenna propagates an electromagnetic signal such as radio, television, or other telecommunications. ... The word receiver has a number of different meanings: In communications and information processing, a receiver is the recipient (observer) of a message (information), which is sent from a source (object). ...

A common implementation involves an LED and a light sensor, separated so that light may travel across a barrier but electrical current may not. When an electrical signal is applied to the input of the opto-isolator, its LED lights, its light sensor then activates, and a corresponding electrical signal is generated at the output. Various light-emitting diodes (5 mm reds, 3 mm greens and yellows) A light-emitting diode (LED) is a semiconductor device that emits incoherent monochromatic light when electrically biased in the forward direction. ... In electricity, current refers to electric current, which is the flow of electric charge. ...

With a photodiode as the detector, the output current is proportional to the amount of incident light supplied by the emitter. The diode can be used in a photovoltaic mode or a photoconductive mode. A solar cell, a form of photovoltaic cell, is a device that uses the photoelectric effect to generate electricity from light, thus generating solar power (energy). ... A photoresistor is an electronic component whose resistance decreases with increasing incident light intensity. ...

In photovoltaic mode, the diode acts like a current source in parallel with a forward-biased diode. The output current and voltage are dependent on the load impedance and light intensity. The input impedance or load impedance of a circuit or electronic device is the impedance actually experienced by a signal which is connected to it. ...

In photoconductive mode, the diode is connected to a supply voltage, and the magnitude of the current conducted is directly proportional to the intensity of light.

Among other applications, opto-isolators can help cut down on ground loops and block voltage spikes. In an electrical system, ground loop refers to an unwanted current that flows in a conductor connecting two points that are nominally at the same potential, ground, but are actually at different potentials. ... Voltage spikes are fast, short duration surges in the electric potential in a given circuit. ...

One of the requirements of the MIDI (Musical Instrument Digital Interface) standard is that input connections be opto-isolated. Musical Instrument Digital Interface, or MIDI, is a system designed to transmit information between electronic musical instruments. ...

An opto-isolator can also be constructed using a small incandescent lamp in place of the LED; such a device, because the lamp has a much slower response time than an LED, will filter out noise or half-wave power in the input signal. In so doing, it will also filter out any audio- or higher-frequency signals in the input. It has the further disadvantage, of course, (an overwhelming disadvantage in most applications) that incandescent lamps have finite life spans. Thus, such an unconventional device is of extremely limited usefulness, suitable only for applications such as science projects or crude alarm systems. The incandescent light bulb uses a glowing wire filament heated to white-hot by electrical resistance, to generate light (a process known as thermal radiation). ...

External links

• Optocouplers: When and how to use them (PDF)
• Optocouplers & Optoisolators Applications