Re: LED question for electronics wizards

<ship>

If you want to be more efficient, hook up 2 or 3 LEDS in series. 3 of them
at 3.5 V would be 10.5V, leaving 1.5V across the resistor. The total current
(power) used is the same, but now, instead of heating up a resistor and
lighting 1 LED, we are lighting up 3 LEDs instead of one. I leave finding
the size of the resistor in this case as an exercise for anyone one that
really wants to find out because I gotta go and don't have any more time :(

Here is another thought. Using the math I did, if you had a 12V
battery and 3 LEDS, each 3.5V, then your resistor would be 60 ohm, and
you could use a 1/4 or 1/8 watt resistor. However! If your LEDs turned
out to be 3.0 V and not 3.5, then the current through them would be
50mA, not 25mA. You may be pushing their design limitations and risk
burning them out, and the resistor may get hot depending on the size
your used.

If you want to get fancy, you could build a current regulator and set
it at 25mA. Use this in place of your current limiting resistor. Then
you could use any combination of 1, 2, or 3 LEDs, and the current
would still be properly regulated. An LM317 will do this quite nicely.
The downside of this is that you need to understand a bit about
electronics, or find a friend that does to design it for you. I could
whip one out pretty quickly, but if you don't know a bit about
electronics, you won't know what to do if it's not working, or how to
test that it is indeed working correctly.

.

Relevant Pages

  • Re: Cant get enough current for 1W Luexon LED even without resistor
    ... resistor but still only about 100ma current. ... want to be thinking in terms of voltage. ... life from any high power LED, is to pulse drive it. ... The level of these that some high power LEDs can ...
    (sci.electronics.repair)
  • Help Getting Started - Simple DC Circuit
    ... problems with it and this afternoon it occured to me some simple electronics ... - 30 ea green LEDs ... When everything is lined up right on my mechanical device, ... Does each LED need its own resistor or is one resistor ...
    (sci.electronics.basics)
  • Re: Cant get enough current for 1W Luexon LED even without resistor
    ... Then I tried without the resistor but ... the LED I have to raise the voltage to about 11V and of course I ... LEDs for a long time, and never suffered a problem with a switch-on ... max forward current quoted in specs, is for a short duration pulse. ...
    (sci.electronics.repair)
  • Resistors for LEDs: the real answer
    ... First of all, while non-electronics types refer to the resistor in this use as a "dropping resistor", that's not really technically accurate: whats actually going on is that you're making a voltage divider network with a resistor in series with the LED. ... By putting a resistor in series with the LED, you're dividing the 24 volts between the resistor and the LED, because the whole idea is to make sure that the LED doesn't get too many volts and blow. ... Turning to my handy-dandy Jameco catalog, it appears that most garden-variety LEDs are rated at about 2 volts, some more, some less: close enough to be no never mind. ...
    (rec.models.railroad)
  • Re: Resistors for LEDs: the real answer
    ... while non-electronics types refer to the resistor in this ... whats actually going on is that you're making a voltage divider network ... Obviously, if you just put the poor LED across the 24 volts, ... the great majority of LEDs are rated at 20 mA; ...
    (rec.models.railroad)
Loading