Re: gEDA-user: Opamps et al...

[Peter Clifton <pcjc2@xxxxxxxxx>]

On Mon, 2006-11-20 at 19:28 -0500, al davis wrote:

> There probably is no need for a unity gain op-amp stage, except 
> for current drive capability.  Very few IC op-amps can properly 
> drive 50 ohms directly.  Most are speced for 2K.

That is probably true... I only need to drive an o'scope + another
op-amp to build a feedback loop. I was going to do this on breadboard,
however the IC I mentioned is only available in SMD, so I thought I
might as well put together a useful "building block" circuit and box it
rather than just make a one-off useful circuit.

> If you need to drive a low impedance load like 50 ohms, add a 
> class AB complementary pair emitter follower, and put it inside 
> the feedback loop, making believe it is part of the op-amp.

That is quite cunning. I guess this will even work with the
instrumentation amplifier directly. There was a hint of motivation to
use a DIL output stage, so when someone blows it up, there is an easy
part to change, but as I need this quickly, I may just fab a board with
just the SMD instrumentation amp on it, perhaps with some optional
populate / don't populate sections to try other options.

Thanks!

Peter C




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