Nothing wrong with the existing 723 design. It's just that I believe the
ideal design has zero parts, so if I could get from the chip and a power
fet (with a few other parts) down to a power chip (like a 317) with a few
resistors, I thought we'd be closer to ideal. Doesn't look like we're
gonna get there.
        The 723 DOES do a great job. In the 1970s I worked with an FM station
that couldn't meet the FCC noise requirements due to power supply hum in
the stereo generator. Single chip regulators did not have enough ripple
rejection. The 723 did it!

Harold


On Tue, 23 Jan 2001 18:59:37 -0700 Dwayne Reid <dwayner@PLANET.EON.NET>
writes:
> At 04:37 PM 1/23/01 -0800, Harold M Hallikainen wrote:
> >         Thanks! I've looked at that and it appears similar in
> complexity (not
> >much) to the existing 723 design.
> >
> > >
> > > I don't see any easy way to use a linear pass regulator as a
> shunt
> > > reg.  But have you considered something like a TL431 with a
> boost
> > > transistor?  That beastie *is* a shunt reg and is both
> inexpensive
> > > as well as easy to use.
>
> Gosh - my memory could be failing me (yet again), but I thought that
> a
> TL431 shunt reg with boost transistor was: PNP boost transistor, C
> to gnd,
> E to +V to be shunted, B to cathode of TL431.  Use a swamping
> resistor of
> 100R or so between E & B of the transistor.  Shunt voltage is set as
> per
> normal: resistor divider from +V to be shunted to control pin on
> TL431.  The boost circuit adds only the transistor and swamping
> resistor to
> the standard TL431 circuit.
>
> Just out of curiosity - what is wrong with the existing 723 circuit?
>  Are
> 723 regulators getting hard to source?  That would be a shame - it
> is one
> of my favorite chips from years gone by.
>
> dwayne
>
>
>
> Dwayne Reid   <dwayner@planet.eon.net>
> Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
> (780) 489-3199 voice          (780) 487-6397 fax
>
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