Power led maximum current - Page 1
Forum section: electronics / beginners

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: December 14, 2014, 08:16:07 am
content: So, first postI'm designing a office light for lighting up my workspace for both studying and doing electronics work, and was looking at a power LED sollution. At the moment I will probbably be using 3 of these 7W power leds:http://be.farnell.com/multicomp/703-0118/led-white-chip-on-copper-7w/dp/2112131However, I am confused about some of the specs. What exactly does the @Test mean? At first glance I thought these leds were 9.5v@350mA, but in the datasheet they also refer to a forward current of 1,05 amps - so I'm confused as to what they really will draw and thus how powerfull my powersource for them needs to be.All help understanding what the datasheets are trying to tell me greatly appreciatedTheUnnamedNewbie

author: Psi
author_rank: Super Contributor
timestamp: December 14, 2014, 08:23:20 am
content: Ignore what farnell says about @test, its incorrect/misleading.Have a look in the datasheet,1000mAh is for PWM at 1/10 duty cycle and max 0.1ms on time.350mA is the maximum current for a constant DC supply.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: December 14, 2014, 08:31:37 am
content: Quote from: Psi on December 14, 2014, 08:23:20 amThanks for the reply! My first designs were based of that 350mA based supply but I wasn't sure anymore since 9.5V at 350mA doesent give me 7W

author: Psi
author_rank: Super Contributor
timestamp: December 14, 2014, 10:05:34 am
content: yeah, the specs on that LED are quite strange.The input current * voltage should equal the LED power.It doesn't even make sense if they meant 7W peak, since 10.5V @ 1A = 10.5W

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: December 14, 2014, 10:11:48 am
content: Thats what got me confused. The data sheet also mentions a 1200smthin mW power dissipation, but I was thinking maybe this was per led on the actual thing (since it has 6 individual leds, and 6*1,2 is pretty close to 7W), but then that brings me back to the current thing, since the actual leds are in 2 parallel groups of 3, either it should be 700mA for the 2 parralel loops or something magic is going on).I guess I might just look at another power led, or order one to do some testing with first and see what I actually measure.

author: Zero999
author_rank: Super Contributor
timestamp: December 14, 2014, 12:50:08 pm
content: Yes it makes no sense.What's your supply voltage? I hope you know you need a constant current source for these.Unless you need a special supply voltage or mounting then why bother making your own LED lamps? It's hardly worth it anymore, unless it's for educational purposes. You can buy a whole LED lamp with the power supply built-in for much less than that.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: December 14, 2014, 05:34:28 pm
content: Quote from: Hero999 on December 14, 2014, 12:50:08 pmI'm fully aware of that. It's just because I can and because it's fun.And yes, I am aware that they need to be powered constant current instead of constant voltage - thanks for reminding me tho.Quote from: AcHmed99 on December 14, 2014, 12:18:09 pmI'll look into other sources and brands as well. I just like ordering from farnell (and RS components but their website is a pain) because I can do so through my university and it's no hassle, just order your parts, go pick them up the next day when I pass it on my way to class.Edit: Decided that I will take a different brand. Bridgelux is actually documented properly and cheaper.

author: IanB
author_rank: Super Contributor
timestamp: December 14, 2014, 05:46:00 pm
content: Quote from: TheUnnamedNewbie on December 14, 2014, 05:34:28 pmThat's good to hear. However a comment in your first post cast doubt on your understanding:Quote from: TheUnnamedNewbie on December 14, 2014, 08:16:07 amWhen powered correctly they do not draw current, they accept whatever current you decide to give them and no more. Therefore your power supply only needs to be as powerful as you want it to be. The LED does not set the power, you do.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: December 14, 2014, 06:17:43 pm
content: Quote from: IanB on December 14, 2014, 05:46:00 pmI meant to power them at full potential. I wouldn't want to pay for extra wattage that I won't use anyways.

author: SeanB
author_rank: Super Contributor
timestamp: December 14, 2014, 06:21:49 pm
content: Power rating of a LED is more a function of the trade off between temperature of the die and lifetime. A 1W chip can be driven to 2W easily, but the lifetime will only be around 1000H at that level, even with the best heatsink. Running it at a lower temperature or lower power which decreases die temperature and you get a much longer life.

author: IanB
author_rank: Super Contributor
timestamp: December 14, 2014, 06:32:44 pm
content: There is also a point of maximum luminous efficiency, which is generally lower than the point of maximum brightness.