Hello
I need to know about controlling current through LEDs in order to
control the illumination
I've searched, but all I found was of commercial content, I need to
know the theory.
Thank you
PWM is simplest and pretty much the standard these days.
I suppose you could get away with a pot, in series with a fixed
resistor, in series with a LED. That might work for small LEDs,
drawing 20 mA or less. If you go this route, check the power
dissipation of the pot. Otherwise you might build a variable current
source from a regulator IC or a transistor.
To figure the LED's current limiting resistor requirement, subtract
its forward voltage drop from the supply voltage. Then determine the
current you want to push through the LED. The dropping resistor value
will be (V - Vf) / I. (For small LEDs, you'd typically drive them
with 5 to 20 mA. Often less than that will serve you well.)
For manual control, a pot, feeding the ADC input of a Picaxe08M chip,
driving a small LED via its PWM output through a series resistor is
pretty simple and reliable. Just a few lines of simple code makes it
happen.
I guess it all comes down to what you want to do. Change the
brightness of a small indicator LED or control 100 3 watt RGB LEDs to
light a nightclub? Vastly differing requirements.
HTH,
Tom