Nick writes –
“Here’s great site that tells you the quantity and size of components you need depending on the number of led’s you are planning on using, and what kind of series you are planning on putting them in; it even has an option to build the circuit layout for you based on what you need.” – Link.
- The LED center – Link.
4 thoughts on “Resistor calculator for LEDs”
If you want to drive LED’s and be really barinless about it (outside of the target current through them) use an LM317 voltage regulator as a constent current source. They come in nice little TO-92 packages and only require one resistor to set the current.
The advantage of this type of drive is you are using a true constent current source, so the current through the LED will stay more or less the same id you change the supply voltage and/or change the LED to adifferent color or number of LED’s.
So, in a nutshell, set one of these babies up to give you 15 to 20 ma and you can hit it with 6V from 4 button cells to 36V from a 24V unregulated wall wart and the LED will not see a difference. You can also swap out a white LED for a red LED, and the current through them will still be the same. In fact, you can string up red, white and blue LED’s in series and they will all have the same current going through them (assuming your supply voltage is high enough)
I ha da look at the site, and spotted their circuit for LEDs in parallel. Now, that’ll most likely work, but it’s a poor design. If you connect LEDs in parallel, with a single series resistor, the LED(s) with the lowest voltage drop(s) will take more current than the LED(s) with the higher voltage drop(s). So, your LEDs will vary in brightness, depending on voltage drop, which can be quite widely variable. A better design would be to use individual series resistors.
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