D Yuniskis wrote:

On 3/20/2011 5:39 AM, William Sommerwerck wrote:
Ideally, I'd like a forum where rank amateurs like me can post
questions that may be answered by "respected regulars" with
lotsa knowledge on the subject.

I think you have to refine your overall goals/interests. There are
many places you can find out "how to use an op amp"
(or, "how an op amp works", etc.).

But, what you *want* to use that op amp for is probably where
you will get far more pertinent information/advice if you can
refine your needs better.

E.g., using an op amp to design a battery charger is different
than using an op amp to buffer the pickup from an electric
guitar or to implement a feedback loop in a robotic servo
controller.

A place that will give you "textbook" advice on how an op
amp works (or can be applied) will leave you wondering,
"OK, now how do I use that to ______?"

Not so! If you understand The Basic Rule in op-amp circuit design, you'll
see that there is no difference among these applications. Nor will you be
wondering how to do something.

No, you only "get" to that point with experience. There
are different design issues involved in each of the above
applications. If you understand how an op amp works
"in theory", you can look at an EXISTING circuit and suss
out the functionality that the op amp is providing. But,
that doesn't mean that you would be able to come up with
the particular circuit topology that is avoiding some
particular *real* (vs theoretical) limitation of that
*particular* op amp and/or leveraging some particular
characteristic thereof.

If it could all be boiled down to a simple rule, then
EVERYONE would be able to design perfect circuits "first
time, every time" -- with/without SPICE.

I want to design a 2KW, 2KV SMPS and use an op amp to
compute the error term. Should be no different than
designing a pickup for an electric guitar, right?

Wrong. A pickup for a guitar doesn't require a stable reference
voltage to regulate it's output.

Should I expect to have either/both of those designs
on my desk, this afternoon, *completed*??


Look at national Semiconductor's 'Simple Switcher' line, or Linear's
free Switchercad spice program and use ICs that are tailored to SMPS
applications. If your opamp circuit takes too long to stabilize, you'll
have an expensive failure and maybe a fire.


Switchercad III can be downloaded he
http://www.linear.com/software/

There is a Yahoo user group at:
http://groups.yahoo.com/group/LTspice/


--
You can't fix stupid. You can't even put a Band-Aid™ on it, because it's
Teflon coated.