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high output leds

bobroanbobroan Posts: 37
edited 2005-12-27 01:03 in General Discussion
Has anyone constructed circuits using very high output LEDs (1 watt)

I purchased a CREE 7090 LED from all electronics because it can supply a lot of brightness (1 watt).· I thought, rather naively, that it would hook up just like a normal LED.· Not so.· First, it can take up to 350 ma at 4 volts, so I know i can't hook it right to the Stamp, but I figure I can get around that by using something like a ULN 2803.· But I wonder if I need to do anything else besides put it in series with a resistor, which, following an appendix in the "elements of digital logic" book I have calculated at 3 ohms (which seems kind of small).

thanks for any ideas about how to proceed?

bob
·

Comments

  • LightfootLightfoot Posts: 228
    edited 2005-12-19 17:47
    You need to build a power supply that supplies 350ma at 4 volts. Use a power mosfet to switch it on and off with your stamp. There are bipolar transistors that will work, however this is a less efficient way of switching it.

    Post Edited (Lightfoot) : 12/19/2005 5:55:28 PM GMT
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-12-19 18:02
    Bob,

    ·· 3 ohms sounds about right if the forward voltage is 4 volts, the supply voltage is 5 volts and the desired current is 350 mA.· Please be sure this isn't the max allowed, but the normal amount.· If your power supply already provides 400 mA or more, you can drive the LED using an ULN2003, ULN2803 or a MOSFET.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • ElectronegativityElectronegativity Posts: 311
    edited 2005-12-19 18:37
    Hi Borbroan, the STP16C596 is a driver that is designed to control up to 16 high brightness LEDs.

    350 mA would be no problem and it is programmable through a serial pin.

    I have attached the data sheet and an application note that I recieved from the company (ST Microelectronics)

    You can buy them at Mouser.com

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    I wonder if this wire is hot...
    pdf
    pdf
    LEDs Array Reference Design.pdf
    1M
    pdf
    pdf
    STP16C596.pdf
    556K
  • nick bernardnick bernard Posts: 329
    edited 2005-12-19 19:31
    P = I^2 * R
    a 3 ohm resistor dissipates ~.4 watts @ 350mA. i recommend a 1W resistor for the ckt if you go with that design.

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    engineer, fireman, bowler, father, WoW addict [noparse];)[/noparse]
  • Paul BakerPaul Baker Posts: 6,351
    edited 2005-12-19 20:33
    The question on how to drive Luxeons comes up occasionally on these forums, here are·the threads I could readily find:
    http://forums.parallax.com/showthread.php?p=518640
    http://forums.parallax.com/showthread.php?p=545868
    ·

    Luxeons are constant current devices, and Luxeon sells special driver pucks for care-free driving thier modules, they even have one that accepts a PWM control signal to adjust the brightness. While your LED may not be luxeon, it is the same current/output as the Luxeons.

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    ·1+1=10

    Post Edited (Paul Baker) : 12/19/2005 8:37:55 PM GMT
  • bobroanbobroan Posts: 37
    edited 2005-12-27 01:03
    Thanks for all your help.· I might have expected that it can get complicated!· However, it seems to me, from reading the messages, that there are a number of ways to light this 1 watt LED.· The simplest, and perhaps crudest and least efficient, is to put it in series with a 3 ohm, 1 watt resistor and drive that circuit with a uln 2803.

    Other, probably more efficient and ultimately more flexible, solutions involve dedicated driver chips as part of larger circuits.

    As a beginner with fairly crude needs at the moment, I will opt with the simplest method if my interpretation of these responses is correct and it will work.

    thanks again

    bob
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