types of optocoupler / optoisolator - understanding them

[pedake]

OPTOCOUPLER PROBLEM

I was playing around with different optocouplers yesterday.

PC123
http://www.sharpsme.com/download/pc123-epdf
MOC3051
http://www.datasheets.pl/optocoupler/MOC3051.pdf

I understand that one is a random phase and the other a zero crossing (is that right?)
Attached I captured the characteristics.
I am absolutely ignorant of the hows here. But my guess was: The zero crossing will only show a sharp drop after it crossed zero from the top (however that would work with a simple IR LED). But no... I tried my cheap-ass FuncGen and: same behavior.

Now:

• How do they work, exactly? ( not the principle. that I understand, of course)
• Why does the PC123 discharge like a cap?
• Why does the MOC3051 follow the input so nicely?
• What type of other optocouplers are there?

I tried finding some literature online, of course. And I am packing for the next trip :-/ I will not have my books for a few days
I am taking my DSO though :-) I want to try to get it running with my own software (based on DSO-USB-Tool) for the Hantek / Tekway / Voltcraft cheapies.


Of course I put a big fat 1M resistor there...




Maybe someone can provide me a link to a comprehensive explanation for the different types of otptocouplers. The light stuff... "optoisolators for total morons"-level.


EDIT:
Thanks, Kilrah
BJT transistor characteristics...
http://ecee.colorado.edu/~bart/book/book/chapter5/ch5_6.htm#top


Thanks and good week to all

[Kilrah]

Instead of looking for "different types of optocouplers" you should rather look up the different types of transistors and other switching devices like the simple bipolar transistor that is in the PC123 and the triac you find in the MOC3051.
What I mean is that an optocoupler is typically just that bog standard transistor/switching semiconductor, but that is switched by a light beam instead of the usual electrical connection, so the generic behavior of that particular device applies.

Also, would be good to see what circuit you had, captures mean nothing when we don't know what you wired and what you were measuring.

The triac (look it up) is typically used to switch AC, and turns off when the AC it switches crosses zero and the control signal is absent. It seems you're talking of a zero crossing of your LED supply which obviously is something else.

[pedake]

Kilrah

Very helpful, thank you!

http://ecee.colorado.edu/~bart/book/book/chapter5/ch5_6.htm#top

I was never aware that BJT have a capacitance. It does, of course, absolutely make sense now.
I feel a little dumb now