Thanks for the idea! We'd have the voltage Vce drop plus the emitter resistor drop, then have to get current to power the zener bias circuit. I don't think I can get that whole thing to work on 1V or less. Thanks, though! Harold > Have you considered biasing a BJT with a zener diode to create a crude > current source? It should work from about 1v on up, so long as the Zener > can > handle the current at max voltage. It would consume power at a fairly > large > rate, so probably not great for battery powered projects. > > ----- Original Message ----- > From: "Harold Hallikainen" > To: > Sent: Thursday, June 24, 2004 4:37 PM > Subject: [EE:] Constant current diodes or FETs? > > >> I'm loooking for a two terminal constant current device that could be >> put >> between an LED and a variable DC supply to hold the LED current at 5mA >> as >> the supply varies over a 0-10V range (recognizing we're not going to get >> it at 0V, but I'd like the widest range possible). So far i've found the >> Central Semiconductor CCLM5750 which is a nominal 5.750mA, but it takes >> 4.5V to get 80% of the rated current. Anyone have other ideas? >> >> THANKS! >> >> Harold >> >> >> -- >> FCC Rules Online at http://www.hallikainen.com >> >> -- >> http://www.piclist.com hint: To leave the PICList >> mailto:piclist-unsubscribe-request@mitvma.mit.edu > > -- > http://www.piclist.com hint: To leave the PICList > mailto:piclist-unsubscribe-request@mitvma.mit.edu > -- FCC Rules Online at http://www.hallikainen.com -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu