is there a difference between an optocoupler and an optoisolator?

[Michael]

Hi - is there any difference between an optocoupler and an optoisolator?
Looking at datasheets for them they seem to be the same thing. Also when
would you use an optocoupler/optoisolator and when would you use a solid
state relay? Again all three seem to serve about the same purpose. I'm
guessing that solid state relays are normally intended for higher power
applications - but that's just a guess.

Also is there a classic optoisolator or optocoupler? The one I have seen
used the most is the 4N27 - but my experience is very limited.

Thanks!

Michael

 

[John Popelish]

Hi - is there any difference between an optocoupler and an optoisolator?
Looking at datasheets for them they seem to be the same thing. Also when
would you use an optocoupler/optoisolator and when would you use a solid
state relay? Again all three seem to serve about the same purpose. I'm
guessing that solid state relays are normally intended for higher power
applications - but that's just a guess.

Also is there a classic optoisolator or optocoupler? The one I have seen
used the most is the 4N27 - but my experience is very limited.

Thanks!

Michael

A solid state relay is optimized for on off operation with larger
voltages and currents that couplers carry, including ones that handle
line voltage and 10s of amperes. Opto couplers are intended to carry
information in the form of either a digital or analog signals.
Digital is most common, including ones that have gate outputs that
look just like any other logic. But most have photo transistor or
darlington outputs, but some have photo diode, mosfet, triac, photo
resistor or photo voltaic (solar cell) outputs. The gate and triac
outputs are strictly off on operation, but most of the others and the
photo resistor specifically can be used for analog signals to some
degree.

Inputs are generally either a single infrared led or a pair in inverse
parallel (to respond to current in either direction) but some of the
photo resistor types still have light bulbs as input. There are
single, dual and quad channel devices. There are also matched two
channel devices so you can isolate an analog signal with one and use
the other for feedback to linearize the output.

With all this variety, there is no point listing a part number or two
and expecting that to be representative. Ask Digikey for a catalog
and browse through pages of choices arranged by category. Then
download some data sheets from their web site and study the specs. It
is a pretty dense subject.