On Sat, Oct 13, 2007 at 08:08:39AM -0400, Bob Paddock wrote: > On Friday 12 October 2007 11:48:12 am John Doty wrote: > > On Oct 12, 2007, at 7:20 AM, Randall Nortman wrote: > > > So I have a 42VDC supply that I want to feed into a linear regulator. > > > But almost all linear regulators want 40V absolute maximum, and the > > > ones that have higher maximums are not reliably stocked anywhere. > > > > What's wrong with an LM317HV? > > They have a tendency to explode in my experience with them. > The TI TL783 does not.
I came across the TL783 in my first-pass search, and was initially excited, until I checked distribution and found that stocking of this part is spotty, especially in the package I'd be interested in (TO-263). Anyway, I decided that I am not going to worry about output shorts. My 42V calculation is a worst-case estimate, including a fair margin for Murphy's Law. That's only 2V above the rated max. On top of that, an output short is highly unlikely in my situation -- the closest thing likely to happen is a 150 Ohm load, which would limit current to 160mA, well within the regulator's limits. Unfortunately, that makes the load -- an 0805 resistor -- dissipate almost 4W, which is of course going to do bad things to it. If it fails short, I'm in trouble, but then I'm still assuming that my worst-case voltage is present at the same time that somebody sticks a wire in the wrong hole. I'm not flying planes here -- I'll take that risk. (Famous last words) Post-mortem analysis: Operator error. Device operated outside of specified bounds. Recommend immediate apologies to designer. P.S. Too bad about burning that house down -- stuff happens, right? -- Randall _______________________________________________ geda-user mailing list [email protected] http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
