Re: Speeding optoisolators

On Thu, 04 Oct 2007 15:24:36 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@xxxxxxxxxxxxxxx> wrote:

On Thu, 04 Oct 2007 14:50:56 -0700, James Arthur
<dagmargoodboat@xxxxxxxxx> wrote:

On Oct 4, 1:22 pm, Jim Thompson <To-Email-Use-The-Envelope-I...@My-Web-
Site.com> wrote:
[snip]

My maxim is a twist on Murphy... if there's ANY chance of smoke, no
matter how minute, there WILL be smoke.


If my push-pull opto thing is done right, it will never smoke. And if
you're really paranoid, change the LED driver circuit. It ain't rocket
science.

I've used total-pole optos in linear mode too, as the output stage of
a 400 volt p-p swing opamp; I posted that a while back.



...Jim Thompson

Sure. The question is then "What's the chance a transistor will have
20x its expected gain?"

In general use I'd believe a 4:1 spread, when selected for
optoisolators, I'd expect the spread to be a little tighter, and
surely not even 10:1. What say you, o silicon sculpting sage?

You are correct that it's VERY unlikely to have a problem. But, in my
world, I NEVER take chances.

Of course you do. It's just a matter of how many sigmas you're willing
to pay for.

We often take chances, particularly in the performance-critical heart
of a product. If a phemt is rated at 9 volts max, but tests ok to 25,
we'll use it at 12. And often we test parts for behaviors that just
aren't specified... we often know stuff about parts that the makers
don't.

Extreme performance sometimes requires taking calculated risks. But
there's no point in taking significant chances on the routine parts of
a product.

John

.

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