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powering white LED array from a car battery

Discussion in 'Electronic Design' started by [email protected], Apr 22, 2007.

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  1. Guest

    hi,
    i need to build a LED light source using an array of LED's. (about
    100). the supply voltaeg is 12DC(from a car battery). i tried powering
    multiples of 3 series LEDs (without any resisters) , but the intensity
    of LED's were not uniform. many LED's were destroyed when powered
    continuously.

    i need to know the reason for this and the proper way way to do this.

    thank you
     
  2. D from BC

    D from BC Guest

    ewwwww :(
    Sorry..I can only provide a table of contents.

    1) LED Binning
    2) LED temp coefficient
    3) current limiting methods active and passive
    4) car system voltage
    5) heat sinking?
    6) LED spec variation
    7) LED series parallel combinations
    8) Maximum drive DC and pulse
    D from BC
     
  3. http://led.linear1.org/led.wiz
     
  4. default

    default Guest

    You should be posting basic questions to the basic newsgroup - this
    isn't Google you just went through google to get to usenet.

    Lurk and learn

    White leds typically require 20 milliamps at three point something
    volts. You need to limit the current or the leds burn up. You limit
    current by adding a resistor in series with three or four leds for 12
    volts.

    For instance my 12 volt application was using 56 white leds in series
    strings of four each - the 12 volt battery was putting out ~14.8 volts
    when charging (when the engine was running)

    The leds I used required 3.2 volts each X 4 = 12.8 volts for each
    string minus 14.8 volts for the battery left 2 volts at 20 milliamps
    to dissipate in the resistor. Ohms law says that I need to divide .02
    amps into 2 volts for the proper resistor or ~100 ohms. Fourteen 100
    ohm 1/4 watt resistors in series with 4 leds each for 56 leds total.

    Your choice of led and the voltage and current it requires and your
    actual battery voltage will determine the correct resistor - a 12 volt
    battery is usually ~12.6 at rest and 13.8-15 when the motor is
    running.
     
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