XML led won't light on low current.

Flashlight Modding and DIY Parts
1

I have another XML led dedomed. But this one won’t light up at minimum currant on my bench PSU. Normally it goes on at few mA currant but this one need 100mA to light up.

I have put two XML in series, one dedomed and one original and the original XML immediately light up when there is some currant.

To my eyes they have the same brightness at higher currant like 500mA.

Could I have damage the XML ? There is no physical damage visible.

2

Someone will say something about Vf probably, but since I don’t know anything about that I’ll just say “vedy eentedesting”.

3

I doubt it is about vf but my guess is you nicked one of the bond wires on the LED and that is causing this. Not really sure though.

4

Hi Blord,

You’re an expert in lasers and now LED’s as well!

Anyways, this is very curious indeed. As scaru had said, you probably scratched the thin wires in the LED, but I’m not quite sure how that would affect the minimum current required to operate the LED.

At 100mA, how does it compare to a regular LED at 100mA? At what point do they look identical?

Cheers!

5

Yea, these dedoming is somewhat new for me. I am paying learning money now, lost already 3 XML. :)

All wires are accounted for. I think it must be the heat that cripple it. The XML led was heated up without a sink for the dedoming process but I don't have an accurate temperature meter.

It must be overheated beyond repair.

6

You take insanely good macro shots. Good for you! :bigsmile:

7

If it works with higher currents then why trash it?

8

It needs more current to stay at the same brightness level as a normal one. At LPF we called it a zombie. It isn't dead but also not fully 100% life.

9

same happens to my nichia LED. problem is its protection diode shorted. LED light up current over 500mA only.

currents below 500mA flow through diode.

diode damaged due to over rated reverse current. (polarity changed)

I think there is no protection diode in XML. may be die fault.

10

So you do notice the loss of brightness at a normal flashlight current?

11

Blord, your emitter looks fine. Great job leaving only phosphor layer. And great macro shot by the way.

Probably this is a different issue. Maybe ran too hot and desoldered the emitter-star connection? Try to solder new wire on the emitter sides and test if it's working.