With a led across a fan connected to a rheostat or linear controller, you get a much better dim if you hook a few diodes in series with the led. Raise the Vf of the series (taking diodes as about 0.65v each) to just under the minimum fan voltage, with a resistor calculated to limit current to about 10mA at 12v. (Use a low If, brightness changes over about 10mA are less obvious.) The extra Vf greatly exaggerates the fall in led current with voltage. Five 1N4001 diodes and 470R on a blue Kingbright L934MBC led gave me: At controller max (10.9v) led drop - 3.0v diode drop - 3.4v resistor drop - 4.5v If - 10.9mA At min (5.1v) led drop - 2.4v diode drop - 2.6v (must get the meter checked ) resistor drop - 0.1v If - 0.2mA
Textbook claim, but a slight fallacy, the germanium Vf goes up fast to over 0.6v with a few mA flowing. Lowest drop at led currents is with Schottky silicon.
Awesome, thanks for the info, I was hoping someone would come up with a way for LED's to dim in a nice fashion. Its hard to just use a resistor to make a LED dimmable with a variable Vf.
Haha..military field manuals: "In case of enemy attack, follow following circuit diagram for safety..."
You're right at the low currents you get off an aerial (antenna), and that's where the germanium are best used. And the graph I found was in a 1980 book
