Optocouplers: Can someone explain this to me?

[Earthscum]

I'm looking at getting some 6-pin dip optocouplers. I have a choice between the H11AA1 and the H11AA4 at Electronics Goldmine. The -4 is a couple cents cheaper, so it's definitely not a price decision.

The applications will be mostly shunting (and voltage splitting), unless I get wacky creative. I'm going to try using it in the feedback of an op amp and see if I can get something tweaked for a compressor and other envelope effects. Just something a "little" different, but should be able to incorporate it into quite a few existing designs. I'm going to try, first, the Nurse Quacky because of the simplicity, using the LED section of the chip as clippers to ground, and incorporating the normal filtering on the base.

Anyways, this is what I was wondering about:

Here's the Fairchild datasheet.

So, what the Motorolla and Fairchild sheets are both showing me is the only difference between H11AA1-4 is the Collector to Emitter Current Transfer Ratio.

What the sheets are showing is that when a signal is hitting the LED section at +/-10mA @10V, the Current Transfer Ratio for each are as follows:
H11AA1 = 20%, Ic=2mA
H11AA2 = 10%, Ic=1mA
H11AA3 = 50%, Ic=5mA
H11AA4 = 100%, Ic=10mA

What difference does this make to what I propose to use them for?
(this is kind of the equivalent of a fet's "on-resistance", right?)

The motorola sheet is showing hFE of 500, right about where 508x's are. I expect to do some tweaking, though, since the detector and control element are direct coupled, unlike most of the circuits that use a transistor as a control. This should be fun

[Hides-His-Eyes]

Optocoupler? As in a digital optocoupler for interfacing 5V and 3V3 digital signals?

Not an analogue optocoupler, as in an LDR/LED rolled together?

[R.G.]

The applications will be mostly shunting (and voltage splitting), unless I get wacky creative. I'm going to try using it in the feedback of an op amp and see if I can get something tweaked for a compressor and other envelope effects. Just something a "little" different, but should be able to incorporate it into quite a few existing designs. I'm going to try, first, the Nurse Quacky because of the simplicity, using the LED section of the chip as clippers to ground, and incorporating the normal filtering on the base.

There are some sincere limitations on applying these to audio where you're not wanting distortion. The way a photo transistor works is that light hitting the reverse biased base-collector junction creates hole-electron pairs which then act like they were a current injected in the base. A normal bipolar transistor only acts like a variable resistance for 50-150mv across the collector emitter before it starts saturating and acting like a current controlled current source. So the signals which can be "varied" by a bipolar without gross distortion are small. But you may be able to get something to work. Keep the LED currents small to keep them in the linear region as much as possible.

What the sheets are showing is that when a signal is hitting the LED section at +/-10mA @10V, the Current Transfer Ratio for each are as follows:
H11AA1 = 20%, Ic=2mA
H11AA2 = 10%, Ic=1mA
H11AA3 = 50%, Ic=5mA
H11AA4 = 100%, Ic=10mA
What difference does this make to what I propose to use them for?

None. Each one will have a different relationship-curve of change in the output transistor versus current into the LED. You're working a region of operation the manufacturers don't bother to specify well if they talk about it at all. About all you can say about these differences is that some of them can use higher microscopic LED currents than the others.

(this is kind of the equivalent of a fet's "on-resistance", right?)

No. The current transfer ratio is how much current goes through the phototransistor collector-emitter per current in the LED. It's a current-to-current relationship, with nothing to say about resistance.

The motorola sheet is showing hFE of 500, right about where 508x's are. I expect to do some tweaking, though, since the detector and control element are direct coupled, unlike most of the circuits that use a transistor as a control. This should be fun

Good luck.

I tried this back in the 80s and didn't like it. But maybe todays LED-phototransistor optocouplers are better for it, or maybe I was applying them wrong.

[edvard]

Seems like anytime somebody finds a curious part they have an itch to build with, Occam's razor says distort something.
Here's a short path to instant gratification:
http://www.thetonegod.com/tech/thunder_alley/thunder_alley.html

After that, play with the more subtle properties.
Good luck!

[Earthscum]

...

Keep the LED currents small to keep them in the linear region as much as possible.
...

Good luck.

I tried this back in the 80s and didn't like it. But maybe todays LED-phototransistor optocouplers are better for it, or maybe I was applying them wrong.

Thanks much. (I didn't ignore the rest of what you said by any means). The neat thing about these is that the input is a pair of LED's back to back, like what we use as clippers. This is where I plan on eliminating some of the distortion first, and why I'm even giving this a shot. I went ahead and just ordered 3 of each (and a couple of the 15x2 EQ panels with all the sliders... they are on sale for $5 til the end of the month).

I'm digging on that Thunder Alley. I may have a couple other couplers around here to try that out.

[amptramp]

Thanks much. (I didn't ignore the rest of what you said by any means). The neat thing about these is that the input is a pair of LED's back to back, like what we use as clippers. This is where I plan on eliminating some of the distortion first, and why I'm even giving this a shot. I went ahead and just ordered 3 of each (and a couple of the 15x2 EQ panels with all the sliders... they are on sale for $5 til the end of the month).

I'm digging on that Thunder Alley. I may have a couple other couplers around here to try that out.

If you have LED's back to back, you could get the equivalent of fullwave rectification which would give you an octave up plus a few other harmonics if you take the output from the phototransistor.  It could do interesting things even if you do manage to use the optocoupler in a low distortion connection.

[Derringer]

Seems like anytime somebody finds a curious part they have an itch to build with, Occam's razor says distort something.
Here's a short path to instant gratification:
http://www.thetonegod.com/tech/thunder_alley/thunder_alley.html

After that, play with the more subtle properties.
Good luck!

in this schem
http://www.thetonegod.com/tech/thunder_alley/thunder_alley.html

How is the base of the transistor section inside those phototransistors getting signal?
I see that the LED section is AC coupled to the previous section, so is the ac signal making the led flicker in a way that corresponds to the amplified signal which in turn causes the transistor to somehow amplify that signal?

[Derringer]

bump