optocoupler enquiry

[Einly]

Hi, just browse through types of optocoupler and a bit confused why some of the optocouplers need 6 pins(4basic pins + 1 base and one NC)(e.g. CN17), and some other (e.g. SFH615A) only needs 4 pins.

Any additional advantage by using 6 pins configuration? Because I found it is quite wasting space. If we can use only 4 pins type to solve same problem.

REgards: Einly,
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Einly

[SherpaDoug]

The base pin of a six pin optocoupler is rarely used. It can be used for noise filtering, for temperature compensation, or for injecting a test signal to simulate a real input.
Four pins is standard for commercial digital use.
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The search for better is endless. Instead simply find very good and get the job done.

[Guest]

Or for speed up the transmission speed up to 3-5 times faster. Using a 220kohm-1Mohm resistor helps to discarge the base-emitter capacity.