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Math for led calculations

Discussion in 'LEDs and Optoelectronics' started by conntaxman, Mar 12, 2013.

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  1. conntaxman

    conntaxman

    89
    0
    Jun 17, 2011
    Im tring to figure out how to do the math for using it in a cir.here's what it is.
    http://www.mouser.com/ds/2/389/CD00156614-115578.pdf
    The Current setting. ----FOR A ----stcs1phr
    The current is set with an external sensing resistor connected to the FB pin. The feedback
    voltage is 100 mV, then a low resistor value can be chosen reducing power dissipation. A
    value between 1 mA and 1.5 A can be set according to the resistor value, the resulting
    output current has a tolerance of ± 10 %.
    For instance, should one need a 700 mA LEDs current, R
    F
    should be selected according to
    the following equation:
    RF=VFB/ILEDS=100MV/700MA=142MΩ
    ------------------
    here is the spec for a 10watt led that im going to use.
    and power it by a 12 car battery.[VF]9-12 [IF]1000MA
    .
    To figure the amps out is it 12 divied by 1000 =.012
    what dose RF AND VFB,I think vfb = forward voltage ,
    don't know what RF stands for.
    tks
    John
     
  2. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    Feedback resistor. You need to choose a resistor that drops 100mV at the desired current. At 1000mA that would be

    V = I R
    0.1 = 1 R or R = .1 Ohm

    Bob
     
  3. duke37

    duke37

    5,364
    771
    Jan 9, 2011
    100MV at 700MA is quite enormous. Do you have your own generating station!

    I do not follow your calculations. I do not see what current your leds take, perhaps it is 1A, The feedback resistor has to give 100mV. R = V/I = 0.1/1 = 0.1ohm.

    Rfb = Feedback resistance
    Vfb = Feedback voltage
    RF = radio frequency
     
  4. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    MV = Megavolts mV = millivolts
    MA = Megamps mA = milliamps

    What's 9 orders of magnitude between friends?

    Bob
     
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