science

Opto-isolator

Opto-isolator is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Opto-isolator rather than just read about it. In short: 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. Opto-isolators prevent high voltages from affecting the system receiving the signal.

Key takeaways

Opto-isolator belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Opto-isolator to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Opto-isolator from memory before moving on to harder problems.

Reference excerpt

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. Opto-isolators prevent high voltages from affecting the system receiving the signal. Commercially available opto-isolators withstand input-to-output voltages up to 10 kV and voltage transients with speeds up to 25 kV/μs. 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.

History The value of optically coupling a solid state light emitter to a semiconductor detector for the purpose of electrical isolation was recognized in 1963 by Akmenkalns, et al. (US patent 3,417,249). Photoresistor-based opto-isolators were introduced in 1968. They are the slowest, but also the most linear isolators and still retain a niche market in the audio and music industries. Commercialization of LED technology in 1968–1970 caused a boom in optoelectronics, and by the end of the 1970s the industry developed all principal types of opto-isolators. The majority of opto-isolators on the market use bipolar silicon phototransistor sensors. They attain medium data transfer speed, sufficient for applications like electroencephalography. The fastest opto-isolators use PIN diodes in photoconductive mode.

Operation

An opto-isolator contains a source (emitter) of light, almost always a near infrared light-emitting diode (LED), that converts electrical input signal into light, a closed optical channel (also called dielectrical channel), and a photosensor, which detects incoming light and either generates electric energy directly, or modulates electric current flowing from an external power supply. The sensor can be a photoresistor, a photodiode, a phototransistor, a silicon-controlled rectifier (SCR) or a triac. Since LEDs can sense light in addition to emitting it, construction of symmetrical, bidirectional opto-isolators is possible. An optocoupled solid-state relay contains a photodiode opto-isolator which drives a power switch, usually a complementary pair of MOSFETs. A slotted optical switch contains a source of light and a sensor, but its optical channel is open, allowing modulation of light by external objects obstructing the path of light or reflecting light into the sensor.

Electric isolation

… excerpt ends here. Continue reading the full article.

Illustrations

Opto-isolator: A fast photodiode opto-isolator with an output-side amplifier circuit — A fast photodiode opto-isolator with an output-side amplifier circuit

Worked examples

Example 1 — a first encounter with Opto-isolator

Start with the simplest possible case. Write down what Opto-isolator claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Opto-isolator before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Opto-isolator ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Opto-isolator

In research: Opto-isolator appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Opto-isolator in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Opto-isolator is common in secondary-school and first-year university syllabi. It links to neighbouring topics Electrical components, Optoelectronics, Semiconductor devices, so understanding it makes those chapters shorter.
In everyday life: Look for Opto-isolator outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Opto-isolator in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Opto-isolator means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Opto-isolator out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Opto-isolator in simple terms?

Why does Opto-isolator matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Opto-isolator?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Opto-isolator.