Re: Luxeon emitter forward voltage question


Ian Stirling wrote:

RHRRC <h.lewis@xxxxxxxxxxxxxxx> wrote:
The datasheet(s) for the Luxeon 1 emitters gives the change in forward
voltage with temperature at -2mV/degC.
I have just measured 2 samples and found this to be -1.7mV/degC.
Both samples gave very similar results (a lot closer than experimetal
error) and were measured over the range of -17degC to +68degC with a
current of 80uA. The leds were soaked overnight at temperature, the

uA?
I would not be comfortable with measuring at a current of much under
80mA.
There are non-linearities in there.

Make an op-amp rectifier feeding a capacitor.
Now, dump in 100mA for 1ms into the luxeon.
Measure the voltage on the capacitor, and reset.

Thanks for the response

I thought that I could remember Lumileds using 1ma but cannot turn up a
reference to this fact.
Are you sure about your numbers - throwing around 250uJ at a junction
with such a low thermal mass at a rate of 250 mJ.s seems excessive for
what is needed to be achieved.
I was hoping that keeping the rate low (~200uJ.s) even though there was
a long (up to 2 secs) duration would keep self heating effects small.

Do you have further details on the non linearities of the thermal coeff
of Vf at low currents?

Regards

.

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