On Fri, 08 Jan 2010 23:45:09 -0600, Don Foreman
wrote:


After thinking about that some today, I'm leaning toward a dirt-simple
hysteretic switching current regulator comprised of a 220 uH inductor
(35 cents at AxMan), MCP6022 opamp, MOSFET, Schottky diode, sense
resistor and voltage reference. Maybe 2 more resistors to get a 0.5
volt ref from a 1.23V bandgap device. All bench stock. I sometimes
build such simple circuits "in air", no circuit board. Just solder
the various parts together with perhaps a bit of hookup wire and then
pot the lot in epoxy on top of the wallwart xfmr that supplies the
low-voltage line-isolated DC.


Where did all those nice unijunction transistors of yesteryear go :-(


Mark Rand
RTFM