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By Leoman456
#206589
I’ve decided to buy the slow cycling RGB LED ( 3mm version) (COM-11448) but I’m a bit unsure of something. I know typical LEDs usually require a current limiting resistor to prevent LED burnout from excessive current draw, but based on this LED datasheet, the application circuit shows a battery connected directly to the LED without a series resistor. Additionally, it has a typical VDD voltage of 4.5V. So I ask: Would this type of LED be able to handle a 3V (or possibly 4.5V ) directly without current limiting resistor? Or should I add a 68 ohm (or 150 ohm for 4.5V case) resistor in series just in case? Thanks.
User avatar
By TS-Mark
#206611
Hi Leoman456,

My guess is this LED may have an internal resistor(s) but it's always good practice to start your circuit with a resistor in series and then adjust that value to get the performance you want. Either of those resistor values should work just fine. I usually start with a 330ohm resistor and adjust from there but that's just because I have a bunch of them readily available.
By n1ist
#206628
That LED has an integrated circuit built in to it that does the color cycling. It either has output resistors or current sources to limit the LED current.
From the data sheet, the supply voltage is between 2 and 5v, with the typical being 4.5v. So it is intended to be powered from 2 or 3 AA/AAA batteries in series, without any external series resistors.
/mike
User avatar
By Leoman456
#206633
n1ist wrote: Wed Aug 07, 2019 7:47 am That LED has an integrated circuit built in to it that does the color cycling. It either has output resistors or current sources to limit the LED current.
From the data sheet, the supply voltage is between 2 and 5v, with the typical being 4.5v. So it is intended to be powered from 2 or 3 AA/AAA batteries in series, without any external series resistors.
/mike
I was thinking the same thing. Thanks a bunch!
User avatar
By Leoman456
#206785
Hey folks, I bought a few of these and tested them. These results may be helpful to those who plan to use them.

I used a regulated DC power supply, resistors, and multimeter to measure voltage and current readings.
Circuit: DC supply to series resistor in series with LED.
Note: VLED and ILED changes based on color its cycling through.

With Vsupply of 3V and Series resistor of 330 ohm (322.5 actually): VLED=2.11V to 2.72V, Imax=2.72mA, dim lighting

With Vsupply of 4.5V and series resistor of 330 ohm (322.5 actually): VLED=2.43V to 3.05V, Imax=6.42mA, dim lighting

With Vsupply of 3V and series resistor of 100 ohm (98.6 actually): VLED=2.418V to 2.84V, Imax=6.15mA, dim lighting

With Vsupply of 4.5V and series resistor of 100 ohm (98.6 actually): VLED=2.88V to 3.441V, Imax=15.97mA, fairly good brightness

With Vsupply of 3V and series resistor of 68 ohm (66.4 actually): VLED=2.510V to 2.872V, Imax=7.66mA, fairly bright

With Vsupply of 3V and series resistor of 33 ohm (32.7 actually): VLED=2.672V to 2.935V, Imax=10.94mA, fairly bright

With Vsupply of 3V and series resistor of 22 ohm (21.8 actually): VLED=2..746V to 2.959V, Imax=12.33mA, fairly bright

With Vsupply of 3V and no series resistor: VLED =3V, Imax=17.88mA, bright lighting

With Vsupply of 4.5V and no series resistor: VLED=4.5V, Imax=76.5mA, very bright, Exceeds 225mW of power!!!

Additionally I asked the company that created the LED, they mentioned that 3V directly to LED is ok but not 4.5V. Also 2V directly to LED is not recommended.

I recommend using some series resistor to keep LED current in control and establish desired brightness.
User avatar
By TS-Mark
#206799
Thanks so much for sharing these test results. I'm sure this will come in handy for other users of these cycling LEDs. Let us know if you have any other questions about this LED or other SparkFun products and tutorials and we would be happy to help.