To Jim Weir

brian whatcott wrote:


Quite so. Moreover, the idea of providing an individual series resistor
to pass about 20 mA works for a good variety of LEDs.
Focussing on the desire to dim a LED, there is no reason (that I know)
not to reduce the current. This has the great advantage over pulse width
modulation that it does not kick up radio interference. There are LED
drive chips on offer now that might suit....

Brian W

Maybe this will help the builder. A current source (rather than a
voltage source) will make the LED brightness varaiable. A typical (red)
LED runs at about 20 mA for full brightness, while dropping about 1.7V
across the LED. Lowering this current dims the LED. The shown circuit
can be set to supply up to about 400 mA, enough for about 20 LEDs. Of
course, he will want to use red LEDs in place of the white ones drawn in
the circuit...

http://radiolocation.tripod.com/LEDd...ampDimmer.html

Scott