Hi Gary,

I want to use the simulator for a Monte carlo analyse for the following
To simplify what I mean is, imagine a bridge circuit with four resistors of
1% tolerance.
The circuit is usable, if the bridge - voltage is below a certain limit. How
percent of my circuits are usable so that I can decide what's cheaper, to
throw away
the bad samples or use of more expensive resistors.

Do you know how this is done ?
When I looked at the examples, they only calculated the worst case of a
circuit, but
that's not the question, I want to get the distribution of a parameter.


Afshin Salehi wrote:
> Just out of curiosity, what types of things do you guys run simulations

Amplifiers, linear and switching power supplies, filters, and just about
anything else that will need tweaking on the bench.

> What drives you to run a simulation on that specific device?

Testing for stability, what range of component values (tolerance) will
work reliably, gain, rolloff, keeping signal levels away from the rails
when designing high gain multi-stage amplifiers, and most important of
all, gaining rapid insight into what happens when you go outside the
box.  Also, nothing catches fire or explodes in a simulator!

>How accurate is the simulation to a real world bread boarded device?
Once you learn how to use simulation I would say about 98% accurate, but
there is a giant proviso here, you must have accurate models and you
must understand the limitations of the simulation process.  I cannot
remember the last time a finished product did not behave as the
simulation did.  The more often you simulate, the better you and your
results get.

> Jon Elson said it takes a day at first then maybe an hour or so each time
> remember things, how is that justified to your boss?  I am really just
> curious as to what things people run sims on, how complex those circuits
> that are simulated are, and if the tests are worth while?
I use an old but very capable DOS version ($15,000 when new) of PSPICE.
I can hand type an ASCII circuit description page in about a half-hour
(three or four op-amps and twenty or thirty passive parts).  Another
twenty minutes to patch typos and missed connections. After the circuit
is running you can do a number of tests in minutes that would take a
week on the bench.  Whether it is worth the trouble or not all depends
on what you're doing.  The last thing I did was a strain gauge amplifier
(something I never did before).  Had the circuit up and running in one
afternoon, cost of components about $10 versus a packaged product with
similar specs from Omega for $400.  Is that worthwhile?  My boss thought

It all depends...
Gary Packman

> Thanks,
> Afshin
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