Opto-isolator

This article is about the electronic component. For the optical component, see optical isolator.
Schematic diagram of an opto-isolator showing source of light (LED) on the left, dielectric barrier in the center, and sensor (phototransistor) on the right[note 1]

An opto-isolator (also called an optocoupler, photocoupler, or optical isolator) is an electronic component that transfers electrical signals between two isolated circuits by using light.[1] Opto-isolators prevent high voltages from affecting the system receiving the signal.[2] Commercially available opto-isolators withstand input-to-output voltages up to 10 kV[3] and voltage transients with speeds up to 25 kV/μs.[4]

A common type of opto-isolator consists of an LED and a phototransistor in the same opaque package. Other types of source-sensor combinations include LED-photodiode, LED-LASCR, and lamp-photoresistor pairs. Usually opto-isolators transfer digital (on-off) signals and can act as an electronic switch, but some techniques allow them to be used with analog signals.


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  1. ^ Graf, p. 522.
  2. ^ Lee et al., p. 2.
  3. ^ Hasse, p. 145.
  4. ^ Joffe and Kai-Sang Lock, p. 279.