SESKStuff Everyone Should Know
SESK: Stuff Everyone Should Know · sesk.info/hame-optoisolator-config

What is the most common configuration of an optoisolator?

An LED and a phototransistor in one package.

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  1. An LED and a phototransistor ✔
  2. A lens and a photomultiplier
  3. A helium-neon laser and a mirror

Why: The LED shines on the phototransistor, so the signal crosses by light instead of by wire. The two sides stay electrically isolated.

Huh, didn't know that: Silicon is the most common material in power-generating photovoltaic cells (E6F10).

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Why doesn't a photodiode like fatty food? It prefers to keep things light.
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References

Answer: An LED and a phototransistor. The LED shines on the phototransistor, so the signal crosses by light instead of by wire. The two sides stay electrically isolated.

  1. NCVEC 2024-2028 Amateur Extra Question Pool, E6F03 (4th errata, Feb. 4, 2026) www.ncvec.org/downloads/2024-2028%20Extra%20Class%20Question%20Pool%20and%20Syllabus%20Public%20Release%20with%204th%20Errata%20Feb%204%202026.pdf
    D. An LED and a phototransistor
    Checked 2026-10-11.
  2. NCVEC 2024-2028 Amateur Extra Question Pool, E6F10 (4th errata, Feb. 4, 2026) www.ncvec.org/downloads/2024-2028%20Extra%20Class%20Question%20Pool%20and%20Syllabus%20Public%20Release%20with%204th%20Errata%20Feb%204%202026.pdf
    B. Silicon
    Checked 2026-10-11.

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