Figure out current res.

Discussion in 'The Projects Forum' started by conntaxman, Nov 9, 2012.

  1. conntaxman

    Thread Starter New Member

    Oct 30, 2009
    can someone explain this in different terms. I always have problems reading how to figure the current out.Im planing on use these for different leds.But here is one led i will be using off of a 12 deep cycle battery.spec for led
    10 watt led.
    The last line for the math is the one i mean.
    FV. 9-12
    FC 1000
    and spec for
    ""STCS2 is a BiCMOS constant current source
    Current setting
    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 2 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, RF should be selected according to
    the following equation:
    RF = VFB / ILEDs = 100 mV / 700 mA = 142 mΩ
  2. wayneh


    Sep 9, 2010
    An LED needs a specific current level to provide brightness over a long life. You usually want to set the current level well below the rated maximum current, for instance less than 20mA for an LED rated at 30mA. High power LEDs have an additional concern of heat. Without a heat sink, you cannot get anywhere near the rated maximum.

    Your driver is designed to provide more or less current - whatever it takes - to hold the FB pin at 100mV. So you use Ohm's law V = I*R to calculate the required R in ohms, given I = your LED current in amps and V = 0.1 volt.

    I think your LED will draw about 1A at 10V to produce 10W, but it's not clear. You should verify and again, don't expect it to stay cool without a proper heat sink.