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Thread: Electrical Circuit for DIY LED, need input

  1. #61
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    a wire with conductor diameter of 1mm or more can handle 12a. look for awg18 or smaller.
    try to keep the cable length short to reduce cable losses.
    thomas liew

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    Saw this diagram, what is the transistor doing there?

    Baby Steel!

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    What is pin 1, 2, 3? Have not see the spec yet, but my guess is to control the output voltage using PWM. Look like you want to clock/pulse the output.
    -Robert
    Aquascaping is a marriage between Art and Farming
    My Blog: http://aquatic-art.blogspot.com/

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    That image is misleading. Look at the image of the IC in the link below.
    http://en.wikipedia.org/wiki/LM317
    On that page:
    Pin 1 = +VIn
    Pin 2 = +VOut
    Pin 3 = +Adjust

    The LM317 is a linear device. No pulsing here =)

    Use this website to calculate the values if you need. http://diyaudioprojects.com/Technica...age-Regulator/

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    though the pin connections are wrong, the LM317 is connected as a constant current regulator.
    the constant current is set by the 'r' value. maximum current is 1.5A.
    the transistor is use to dim the led using a pulse width modulated signal.
    thomas liew

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    Based on the specs to calculate a constant current with a regulated voltage gives me impossible results so yea.. Just be wary of that. I am still unsure if they can both be achieved at the same time with one IC.

    Also, the LM317 can output more than 1.5A but it is not recommended. It will need serious heat dissipation. Anything above 1A should also be heat sunk. Note that this is load current. Not current available. i.e. Only if the actual current flowing to the load/device is more than 1A should serious thoughts be given to heat dissipation.

  7. #67
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    Re: Electrical Circuit for DIY LED, need input

    Just saw this thread, have u guys tried the buckpuck?
    http://www.luxeonstar.com/buckpuck-7...leads-p-35.php


    JC
    Last edited by solonavi; 23rd Feb 2009 at 23:46.

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    Re: Electrical Circuit for DIY LED, need input

    Correct me... but this buck puck function like a LM317. Spec is also quite similar...

    an LM317 function between 5V (can't go lower anyway) to 32V.. with a resistor 1.8Ω, I get about 694milliamps...

    ONE LM317 - $1
    ONE 1.8Ω (1W) - $0.30

    Considering Labor, equipment and material cost to solder the components. Even without calculator, it should be much cheaper!

    Unless the buck/puck can be connected directly to our home wall socket, but they still need VDC input so not worth the $$$
    Baby Steel!

  9. #69
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    Re: Electrical Circuit for DIY LED, need input

    I believe its more than the LM317 + resistor. Cos it can buck and puck the current that is been supplied. For a LM317 + resistor, we need to change the resistor whenever we want to change the current.

    Moreover, I read that hte LM317 can get very hot especially if its been driven at 1000mA and above. If you are going to the LM317 design, not sure if you have seen this. Quite a few nice design been proposed.
    http://www.instructables.com/id/Circ...h-Power-LED_s/

    Cheers
    JC

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