The optocoupler can transmit signals between two circuits that are not in common ground, even if there is a high voltage between the two circuits. Commercial optocouplers can withstand voltages up to 10 kV from input to output, and the voltage change rate can be as fast as 10 kV/μs.
Optocouplers can be divided into analog and digital types, both of which consist of an optical emitter and a light detector. Optical emitters and light detectors are usually integrated into the same package, but there will be no electrical or physical connection between them other than the beam.
A common photocoupling component is a light-emitting diode (LED) and an optical transistor (LED) in an opaque package. Other combinations are LED-photodiode, LED-LASCR and bulb-photoresistor. Optocouplers typically transmit digital signals, but with some technologies, analog signals can also be transmitted with optocouplers.
Optocouplers are widely used in galvanic isolation, level shifting, drive circuits, and industrial communications, but due to parasitic input and output capacitance, their common-mode transient immunity is weak, and their speed limitations, high power consumption of optocoupler components, and easy aging of components are all problems.