Dissecting a Cree LED Incandecent Bulb Replacement

[MileHigh]

The answer to this mystery is probably quite trivial.  One of the LEDs or the interconnect went open-circuit and the bulb failed.  The power supply in an LED light bulb converts mains power into a current source output.  Look up LED power supplies online and you will see that the vast majority of them are rated in current output and not in voltage output.

When you open-circuit a current output style of power supply the output voltage goes as high as possible.

[e2matrix]

Yes current regulation is very important for LED's but they also need voltage limited.   I can't imagine why there would be a step up to almost 300 volts in a setup like this.   I've never seen an single LED that could tolerate 14.4 volts.   Arrays of LED's often run at higher voltages but they are made up of individual chips that all run around 4 volts more or less.   The highest voltage LED I know of off hand was the old Luxeon V that ran from close to 8 volts.   That's about 10 year old tech and definitely not being used in LED light bulbs as they were very low efficiency compared to today's Cree LED's.    However not knowing the designs they use in all these bulbs I suppose some might have had a circuit that could go that high when open circuited but it seems like a poor design IMO. 

[mondrasek]

@e2matrix, I was not there when the bulb failed.  My wife may have noticed it.  It is in the area where we do laundry and she said she was folding clothes when she "thinks" she saw the lights flicker.  Afterwards she thought the light was a bit dimmer in that area.  The fixture in that area holds two bulbs and only one failed, so that would make sense.  But it is all subjective evidence.  She also has a cold at the moment and may not be a reliable witness.

@MH, that is very interesting info.  So, is there a way to test the converter further?  The bulb assy is rated at 9.5W, so I assume that the converter would regulate down to it's design voltage if given the appropriate load?

I seem to remember having the heating elements from a toaster around somewhere...

And yeah, all this is trivial.  But still something to do on a cold, rainy day.

Thanks,

M.

[TinselKoala]

Sorry, there are many high-power LED chips that use 10-12 volts supply. Yes, it's stupid to put 20 LEDs in series, but we've all seen stupider things from Chinese designers.

http://www.youtube.com/watch?v=BkUGNtYKasU
please read the description on the YT page

http://www.youtube.com/watch?v=j2DFJo90JUA

gahh... where do these people get these musics....

It would be extremely unlikely to have a power supply fault that caused it to produce much higher voltage than normal, rather than simply stopping working at all. I'm not saying it's impossible....

(later)
I found this article which you may find interesting.
http://ledsmagazine.com/features/10/4/1
Turns out the Cree bulb uses a 10series2parallel arrangement, so a single LED failure would knock out half the bulb.

[MileHigh]

Mondrasek:

It will regulate down to it's design _current_.  If you assume that it's a current source output you could short the outputs and then nothing should happen.  Assuming that's true, then you could then connect an ammeter across the outputs and chances are it will read close to 350 mA or 700 mA, which are the standard currents for driving LEDs.

However, I don't recommend that you do this test, it's not worth the fuss and you can't forget that you are very close to mains power and therefore it's dangerous and potentially lethal.

Instead, read up on current sources and LED lights and how they are rated in by current draw and not by voltage.

Cheap and dirty direct from China:

http://www.meanwell.com/product/led/LED.html

MileHigh