# Cree xm-l2 led related question

#### marcelobm

Joined Nov 18, 2020
19
Hi All,

I have a project for which I chose the xm-l2 led which according to the specs have a maximum current of 3A at 3.18V.

To my understanding, if a component can draw xA it will do it as long as the power supply will be able to deliver it.

In this case, the maximum drawn current at the specified voltage is 300mA.

can someone explain why is that?

#### ericgibbs

Joined Jan 29, 2010
19,135
hi,
How are you driving the LED.?
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#### marcelobm

Joined Nov 18, 2020
19
right now for the test, throw a power supply directly

#### bertus

Joined Apr 5, 2008
22,306
Hello,

Does the power supply have a current limiting function?
If so set a current and raise the voltage.
Leds are current driven elements.

Bertus

#### ericgibbs

Joined Jan 29, 2010
19,135
Hi,
What voltage/current is the power supply to output.?
E

#### marcelobm

Joined Nov 18, 2020
19
The power supply has a maximum supply current of 10A. I tried setting a higher voltage and that indeed increased the current consumption and therefore the brightness of the led. The question is why if the power supply can supply higher currents the led is not drawing them, at the end of the day I planned to power the led from a li-ion cell.

#### ericgibbs

Joined Jan 29, 2010
19,135
If you vary the Voltage output of the power supply does the current follow the plot of published chart.???

#### marcelobm

Joined Nov 18, 2020
19
This is the C/V chart for this specific led

#### ericgibbs

Joined Jan 29, 2010
19,135
Hi marc,
If you vary the Voltage output of the power supply does the current follow the plot of published chart.???

I have already posted the plot in post #2

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#### marcelobm

Joined Nov 18, 2020
19
Sorry I missed you posted the chart, in answer to your question, yes, you can say it follows some what the C/V relation shown in the chart, but of course not at the same values, otherwise I wouldn;t be asking

#### ericgibbs

Joined Jan 29, 2010
19,135
hi,
You will find that most published charts are only 'typical' , so an exact match would be unusual.

Many LED's are powered by a constant current supply, that is set to operate within the specified current range, in order to control the brightness.

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#### marcelobm

Joined Nov 18, 2020
19
Thank you for your reply, the only thing that I find odd or don't understand it I guess is, current is something the circuit draws right, so if the led consumes xA at xV and the power supply can deliver it should do it no?

I understand that the typical chart values might be off, bu I can tell you that I set the power supply to 5.6V and it draw only 1A which is way less than what the chart show.

Thanks again

#### ericgibbs

Joined Jan 29, 2010
19,135
hi,
Reading thru the Cree datasheet, if you are sure that your power supply is not set to a 1Amp current limit and you are applying 5.6Vdc to the LED, I would recommend that you contact Cree for an explanation. [ oy vey.. ]

I assume you have the recommended heatsink fitted.

E

#### Audioguru again

Joined Oct 21, 2019
6,785
The current vs voltage graph shows that one LED typically draws 1A when its forward voltage is a little higher than 2.8V, but your voltage is double 2.8V at 5.6V so you probably have two LEDs in series.

#### marcelobm

Joined Nov 18, 2020
19
I see what you're saying but I definitely don't have 2 in series

I have contacted Cree, maybe they'll be able to explain.

Thanks for all your replies. Will update if I get response from Cree

#### neonstrobe

Joined May 15, 2009
191
The trouble with these types of LED package is that they need soldering on a good thermal board like IMS. Not many have the facilities to surface mount devices. It can be done but needs a hotplate or controlled heat source that can reach solder temperature in the recommended cycle - which is relatively quick.