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crazyharryoxymoron
Lv 4
crazyharryoxymoron asked in Science & MathematicsEngineering · 1 decade ago

Help with an LED array?

I'm working on an LED array, and I need to figure out how big a current-limiting resistor I need. I have the Shockley diode equation and I figured I'd just use that with Ohm's law and solve the system of equations, but I can't figure out the reverse bias saturation current, I have an equation for it, but it requires a number of values I don't have access to. I'd just use one of the online calculators to figure out my resistance values, but I need more detailed information to build the circuit safely. I only have 1/2 W resistors, and the fewer I cook the happier I am. Anybody have an easier solution? Some way I can make an estimate, average values for different sizes and colors?

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  • billrussell42
    Lv 7
    1 decade ago
    Favorite Answer

    Shockley equation is no help here.

    You have to look the specification for each LED for Vf, and add them together (assuming they are in series) and calculate the resistor voltage by subtracting the sums of the Vfs for the LEDs, and use the LEd current with the resistor voltage to get the resistance.

    If you don't have the Vf, get the part number and look it up online. Or find some similar one and use that Vf

    .

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