On Mon, 4 Nov 2002, Jai Dhar wrote:

*>>From what I see of your post, are you not suggesting the 'recommended' setup
*>from National on the LM317 datasheet? (check out www.national.com). I'm just
*>not sure if what you told me is something that I should be applying to my
*>design or not, considering I planned on having a 240 ohm resistor there
*>already (as recommended per the datasheet), and either using a digital pot for
*>adjusting the current to the adj pin, or some other method (which is what I
*>have been asking, but I think I have it answered). I hope I am not mistaking
*>your post.

The usual way to interface a AD to a 317 is to use an opamp. The opamp
will drive the ADJ pin of the 317, the out-adj resistor will be higher
than 240Ohms (probably 2k2) and the opamp will be connected as dc
amplifier with feedback from out. This way you can control a 40V supply
with a 0-5V standard AD. The 317 becomes a high quality pass transistor
with SOA and current limit (like a LM195 but different) with the opamp
doing the regulation. Pick an opamp with a lot of input voltage range
(rail to rail preferrably). This is not so easy.

The standard application of the 317 is not directly suitable for
electronic control imho. Unless you find a mosfet transistor and map its
individual characteristic probably. The circuit would not be reproducible.

hope this helps,

Peter

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