Author Topic: simple resistor calculations  (Read 1889 times)

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Offline BANETopic starter

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simple resistor calculations
« on: January 14, 2009, 06:51:34 PM »
Hello, I was trying to do some resistance calculations on some simple circuity, but keep getting unrealistic figures.
If there was a resistor and a standard LED hooked to a battery 5V, the LED was rated for 3v at 150mA; how many oms would the resistor need to have?

I know they have a lot of LED calculators, but I'm looking for the equation. :)

Bane
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Offline HDL_CinC_Dragon

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Re: simple resistor calculations
« Reply #1 on: January 14, 2009, 06:57:24 PM »
13 ohms
« Last Edit: January 14, 2009, 07:05:44 PM by HDL_CinC_Dragon »
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Offline krich

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Re: simple resistor calculations
« Reply #2 on: January 14, 2009, 07:03:20 PM »
It's right there in the LED tutorial:

Equation:

(voltage applied - forward voltage drop) / forward current = resistor value

Example with 6V power source, LED with 1.85V forward voltage and 20mA current:

(6V - 1.85V) / .02A = 207.5 ohms

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Offline BANETopic starter

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Re: simple resistor calculations
« Reply #3 on: January 14, 2009, 07:12:38 PM »
oh, i knew it was something simple :P.  Thanks guys

bane
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