Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Simple Circuit for high power LED

  1. Feb 15, 2012 #1
    What simple circuit that I can design for a 3V high power LED with max current 0.8 amps , I think the component names would help me , I would like to power it on 4.5 to 9 V batteries .Preferably lower voltages. Thanks
  2. jcsd
  3. Feb 15, 2012 #2
    Connect the 9v battery to the led in series with a (9-3)/.8 Ohm resistor.

    On a 4.5v battery use a (4.5-3)/.8 ohm resistor.
  4. Feb 15, 2012 #3
    Just make sure the resistor has suitable power rating - in the above scenario, the resistor is dropping 6 volts at 0.8A, which is 4.8 watts. I'd use at least a 10 watt resistor in that case, and that is going to be a LOT of heat... it would need mounted on a pretty beefy heatsink. The LED will need mounted on a big heatsink too.

    If the OP can do it, it would be better to have more LED's in series rather than burning all that power as heat, or if you want to get more advanced, a buck switching regulator will get you into the 90%+ efficiency range and make the battery last 3 times longer and massively reduce the heat output.
  5. Feb 16, 2012 #4
  6. Feb 18, 2012 #5
    These are voltage regulator ICs that ensure the LED is constant brightness even as the battery voltage drops lower.
    Last edited by a moderator: Feb 21, 2012
  7. Feb 18, 2012 #6
    You may want some size-D or lantern batteries for something that draws this much current. (3) size D alkalines have a nominal voltage of 4.5. That might get you there without wasting too much of your power as heat.
  8. Feb 18, 2012 #7
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook