On Tue, 2007-05-29 at 23:46 -0700, Gus Wirth wrote: > Lan Barnes wrote: > > I need a low volt (0.9 V) way low amp LED for a science project. Radio > > Shack is hopeless. > > > > Can anyone remind me of that great hole-in-the-wall components store's > > name or address? > > > There is no such thing as an LED that operates in the visible spectrum > at a voltage less than about 1.2 volts. The lowest voltage LED's are red > (680 nm wavelength) and the voltage climbs as you move up in spectrum. A > blue LED (470 nm wavelength) needs about 3.8 volts to work. > > Typical currents are about 10-20 milliamps for decent visibility on > standard brightness LED's. > > I have a whole bunch of red and green LED's in my parts box. You're > welcome to have a few to play with. > > If you are really limited in the voltage, it might be possible to build > a small inverter to step the voltage up. There used to be a great part > called an LM3909 <http://home.cogeco.ca/~rpaisley4/LM3909.html> that > worked as a voltage pump to flash an LED but they don't make them any > more. You could probably build something out of either a germanium > transistor (0.2 volts saturation) or maybe a specialty FET. I would do > it as a simple transformer coupled oscillator. Of course the efficiency > loss would probably kill your current consumption budget. > > Gus
Newer LEDs are surprisingly bright at low currents. The forward voltage, however, is a hard limit. By sheer coincidence, I used a circuit to get enough voltage for a green LED from only 700mV as proof-of-concept for wine: http://www.kernel-panic.org/Members/cmaier/hamburger-lugnut-log/archive/2007/02/04/both-linuxes-emulate-windows-xp/ (by the way, Plone still doesn't work quite right, *&[EMAIL PROTECTED]) but you'd need an AC waveform for the charge pumps to work. It's not easy at all to build a DC to AC converter that works from 700mV. HTH Christoph -- KPLUG-List@kernel-panic.org http://www.kernel-panic.org/cgi-bin/mailman/listinfo/kplug-list
