> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On
Behalf
> Of William "Chops" Westfield
> Sent: 23 March 2011 01:21
> To: Microcontroller discussion list - Public.
> Subject: Re: [EE] Digital adjustment of LM317
>=20
>=20
> On Mar 21, 2011, at 6:48 AM, Olin Lathrop wrote:
>=20
> > If you're going to go so far as adding a opamp to control the LM317,
> > you
> > might as well just have the opamp drive something like a PNP pass
> > transistor.  The fancy electronics in the LM317 isn't doing much for
> > you at
> > this point.  You're mostly using the LM317 as a pass element anyway.
>=20
> A *fancy* pass element with features like overcurrent and overtemp
> shutdown.  And pretty cheap, too.
>=20
> I have a desire to build a general purpose lab-style power supply
> using multiple 317s.  Several in parallel for increased output.  One
> for the negative-voltage-driven current source that permits voltages
> below 1.25V.  Maybe one as the regulation element in a switching pre-
> regulator.  Probably because of that eBay deal I got on a box of
> 317s... :-)
>=20
> BillW

LM317's have some disadvantages for a lab supply:

1) Minimum output of 1.25v unless you can have a regulated, negative
rail you can use to pull the reference pin below ground.
2) To add any kind of variable current limiting means adding a bunch of
extra components
3) Not easy to add remote sense.

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