alan smith wrote:
> The output is driving just DC voltages,

That's a silly statement.  DC as apposed to what, AC?  And what's that
supposed to tell me?  If it were really DC it couldn't change.  Obviously
your output must have some AC component, so this statement tells me nothing
useful about the load.

> sourcing the current with the
> loads being actuators and the like used in HVAC
> so it never needs to
> go negative (or should never)at all.

Then a NPN emitter follower will work fine as long as you have a opamp that
can drive near ground on the output and with a common mode input range
extending to ground.  You will need at least the B-E drop headroom for the
opamp on the high side, but probably more for the opamp itself.

> Running a 24V rail also gives plenty of headroom.

Yes, that is way more than enough headroom even with the emitter follower in
there.  Your 3904 transistor isn't going to handle that at 100mA though.  As
I suspected, you need something considerably more beefy, probably with a
collector resistor.


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