Hi. I’m looking to power multiple color changing LED’s on one power source. No controller is needed. What voltage is needed for power supply?
What LEDs are you wanting to power? They all have different requirements and those should be listed in the data sheet. Some LEDs can run on 5 volts without a resistor while others will be destroyed if connected without a resistor.
Check your data sheet and see what it says for forward voltage and maximum current, those numbers will determine what size resistor you need for a given power supply voltage.
We have a tutorial for picking a resistor for your LEDs [here, you might have a look at that too.](Light-Emitting Diodes (LEDs) - SparkFun Learn)
Hi Chris,
Thanks for the prompt response. I’ll be buying the 3mm, 5mm, and 10mm cycling LED’s from Sparkfun. I want to run a couple of them on a single circuit, or parallel circuit, if need be, and want to just be sure about the voltage I’ll need.
Alright.
Current is more important than voltage and you set the current with a resistor. The voltage you use will determine what size resistor you will need.
It looks like you’re going to need at least 3.5 volts and something between 5 and 12 would be ideal. The real question would be what is a convenient voltage for you to use? You might shoot for 6 volts since that’s what you’d get from 4 AA sized batteries and 4 cell battery holders are easy to get.
In the case of 6 volts, we subtract the forward voltage of the LEDs which for the color changing LEDs is about 2.75 volts. That leaves us with 3.25 volts.
Now, the LEDs want to see about 15 mA of current. Ohms law lets us solve for resistance when we know voltage and current. The formula for resistance is R (ohms) = E (volts) / I (current) so if we plug our numbers in:
R = 3.25 volts / 0.015 amp (15mA) and we get 216.66 ohms.
Since 216.66 isn’t an available resistor value, we’re going to use the next closest one and that’s 220 ohms.
So, what you need is a battery holder for 4 AA batteries, your LEDs and then one 220 ohm resistor for each LED.
[PRT-00552 will work for a battery holder.
We only sell 220 ohm resistors in a kit and part number [COM-10969 comes with 25 of them.
Just add 4 AA sized batteries and connect everything together and this should work for you.](https://www.sparkfun.com/products/10969)](https://www.sparkfun.com/products/552)