The output is driving just DC voltages, 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.  Running a 24V rail also gives plenty of headroom=
.  The issue of using a negative supply is both cost and room...

--- On Mon, 4/26/10, Olin Lathrop <olin_piclist@embedinc.com> wrote:

> From: Olin Lathrop <olin_piclist@embedinc.com>
> Subject: Re: [EE] DAC with 2x gain - isnt working as expected
> To: "Microcontroller discussion list - Public." <piclist@mit.edu>
> Date: Monday, April 26, 2010, 7:04 AM
> Dave Tweed wrote:
> > If you really need to output 0.0 to +10V with low
> source impedance
> > over
> > the whole range, I really think you're going to have
> to bite the
> > bullet
> > and provide a negative supply, in which case, you can
> just use the
> > original opamp.
> >
> > It was simply a Bad Idea(TM) to try to do this with a
> single supply.
> =

> Yes, and a simple charge pump like is often used for this
> isn't going to be
> tractable at 100mA.=A0 Mostly likely you'll need a real
> inductive switcher.
> =

> Another things to consider is the deadband between two
> emitter followers
> (NPN and PNP) with the bases simply tied together.=A0
> Does it need to source
> and sink 100mA, or is the direction known, like always
> source for example.
> If it does have to switch between sourcing and sinking
> randomly depending on
> the load, then you have to consider the deadband.=A0
> Maybe it's no problem
> depending on what you're trying to do.=A0 The feedback
> will make the opamp
> jump over the deadband quickly, but that still causes
> distortion in the
> output.=A0 Whether you need a single transistor emitter
> follower, two
> transistors, or something more complicated depends on the
> load and what the
> signal will be used for.
> =

> =

> ********************************************************************
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> (978) 742-9014.=A0 Gold level PIC consultants since
> 2000.
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