RGB led max current - Page 1
Forum section: electronics / beginners

author: Zedy
author_rank: Contributor
timestamp: October 22, 2010, 09:38:10 am
content: hello,Just wondering, if in datasheet for RGB led max current for each colour is 20 mA, does it mean I could pump 20 mA current simultaneously into all 3 colour pins, which would give 60 mA in total.

author: Zero999
author_rank: Super Contributor
timestamp: October 22, 2010, 12:24:34 pm
content: That should be the case but read the whole datasheet to make sure there's no limit such as the power dissipation for the entire package.

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 22, 2010, 06:12:17 pm
content: Quote from: Zedy on October 22, 2010, 09:38:10 amif you are not sure what the datasheet say, u can always check with DMM.

author: Zedy
author_rank: Contributor
timestamp: October 23, 2010, 01:02:58 pm
content: Quote from: shafri on October 22, 2010, 06:12:17 pmHow can I check it?

author: Zero999
author_rank: Super Contributor
timestamp: October 23, 2010, 03:38:40 pm
content: Yes, how do you check the maximum current rating with a DVM? I'd like to know this.

author: djsb
author_rank: Super Contributor
timestamp: October 23, 2010, 03:40:22 pm
content: The current for 1 LED may be 20mA but for all three at once the current may need to be reduced for each one. This is because of the junction temperature of each device influencing each other. I would play it safe and limit the current initially to 15mA per LED and if that works OK build up gradually from there 1mA at a time. You could use a pot in series with a fixed current limit resistor (20mA limit). It's best to take the 20mA as an absolute LIMIT and put LESS THAN 20mA through it.

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 23, 2010, 06:30:06 pm
content: Quote from: Zedy on October 23, 2010, 01:02:58 pmconnect the power supply in series with DMM in A mode to the RGB LED power line.edited: dont forget the resistor!

author: Unknown
author_rank: Unknown
timestamp: October 23, 2010, 06:33:21 pm
content: Quote from: shafri on October 23, 2010, 06:30:06 pmIndeed, just keep increasing the current until the LED starts to release magic smoke. The maximum current is somewhere below the current indicated by the DMM just before the LED died. Use three current sources and DMM's for an RGB LED.

author: allanw
author_rank: Frequent Contributor
timestamp: October 23, 2010, 07:48:04 pm
content: The LED lifetime is increased by running them at lower current and lower temperature. Maximum current it can handle before releasing magic smoke is probably way too high for normal operation, because the lifetime will be significantly reduced if you run it near that current.Are you using 5mm RGB LED's? I've had no problems running them at 20mA each color for long periods of time. Keep in mind that the human eye will barely see a difference between 15mA and 20mA though, so it might just be safer to run them at 15mA if you intend to run them all at max brightness all the time.

author: Zero999
author_rank: Super Contributor
timestamp: October 23, 2010, 09:56:08 pm
content: I think shafri may have forgot that the LED needs a series resistor. I've never tested a component to destruction in an attempt to get the maximum current rating. If you're going to do that, then I'd recommend testing some components with known maximum ratings beforehand. In this case that shouldn't be necessary as it's listed on the datasheet.Generally running components near or at their absolute maximum ratings is a bad idea. In this case if the absolute maximum rating is 20mA, design for 15mA.

author: Unknown
author_rank: Unknown
timestamp: October 23, 2010, 10:22:37 pm
content: Quote from: Hero999 on October 23, 2010, 09:56:08 pmMy reaction was tongue-in-the-cheek, since actually impossible to measure absolute maximum ratings (although my statement about somewhere below the current that killed it is true, you just don't know how much below). Absolute maximum ratings are a guarantee by the manufacturer. It doesn't mean that it will die above that, but it means it will survive below that. Not just today's sample, but next year's sample also. No way to know the manufacturer's limits from just measurements.Quote from: Hero999 on October 23, 2010, 09:56:08 pmAgreed, especially since LED's lifetime usually depends on junction temperature (which for low-power LED's is determined by current). Not sure if 20mA gets the junction close to max sustained temperature or if low-power LED's have other failure modes, though.

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 24, 2010, 02:05:50 am
content: Quote from: alm on October 23, 2010, 06:33:21 pmyup guys. i forgot the resistor!think i'm going to do the same mistake twice! thats how i burnt a LED (no resistor). i got no magic smoke, just a magic dimming effect and dead forever. to find out max rating, u can use 100K potentiometer maybe and turn down bit by bit until the magic smoke. what i understood and try to explain is, the OP try to figure out whether the 20mA is for single color LED or all the RGB alltogether. so he can check each power line, or all of them at onceso, if the supply from battery is 20mA and the LED is not bright enough, then try feed it with 60mA!

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 24, 2010, 02:20:17 am
content: this is some link while googling RGB LEDhttp://www.best-microcontroller-projects.com/rgb-led.html, just for the recordi think the last pic driver is overkill for single RGB LED. and no resistors thereand this one is some "wacko" nerd doing his thing!

author: Zedy
author_rank: Contributor
timestamp: October 24, 2010, 03:22:57 pm
content: Quote from: allanw on October 23, 2010, 07:48:04 pmYes, I am using 5 mm RGB LEd'sThanks for your replays!Accually I need the most brightest light I could get. So, I think I will just test this LED's running on 60 mA (20 mA on each pin), what the normal temperature rise should be? any ideas?And I am ordering this LEd's from china, so I don't have any datasheetI now only maximum current through each colour - 20mA

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 24, 2010, 03:30:45 pm
content: Quote from: Zedy on October 24, 2010, 03:22:57 pmtry to test on lower current first, then move to higher until you satisfy, just to be safe. an order from China is.... expensive!

author: eecfans
author_rank: Newbie
timestamp: November 14, 2010, 11:41:48 am
content: Quote from: Zedy on October 22, 2010, 09:38:10 amI guess they are tri-chip R/G/B led strip that has 4 wires on the PCB board: Red,Green,Blue and "+" Pole. I don't think you need worry about the current, although each color is rated at 20mA, because led strips should be working at constant voltage 12v DC. They will work find as long as you input constant voltage 12v DC, with enough power. Better to confirm again with your seller.

author: eecfans
author_rank: Newbie
timestamp: November 14, 2010, 11:46:41 am
content: I think they are 5mm tri-chip rgb leds that set each color @ 20mA, so you need 60mA. But it is not absoluteley, usually there is a current tolerance range. You'd better confirm again with the seller. Tks.