On Sat, 09 Jan 2010 22:16:16 -0600, the renowned Don Foreman
wrote:

On Sun, 10 Jan 2010 00:48:00 +0000, Mark Rand
wrote:

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

They're still available. 48 cents at Digi-Key
http://tinyurl.com/y86xeer

In the UK, Farnell's has 'em:
http://tinyurl.com/y9gk9fx

And they are cheap. But the 2N6027/8 are PUTs, a kind of SCR-like
4-layer thyristor device, not real unijunctions (eg. 2N2646).

But Newark still has the 2N2646 :
http://www.newark.com/jsp/search/pro...FC-GB100000001
http://www.newark.com/multicomp/2n26... iscretes_None

I miss LASCRs (light activated SCRs), SBS (Silicon bilateral
switches), tunnel diodes, germanium transistors, clean air, tuna,
Taiwan.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com