Did a noob thing to my new Cree and have a noob question...

First off, I want to say that nothing good ever happened to me while working on my LED projects after 2:00 am! I was testing the output of my new Cree XR-E that I got from Cutter Electronics and using different optics when the thing just stopped working. Doh! I just want some help to me point out what I exactly did wrong.

I was using a spare Fatman boost circuit that I made into a special enclosure for testing all of my new LEDs to find the Vf of the LED at specified current levels. I would have this hooked up to my meter and using a strategically placed switch, I can measure either the V out (for the Vf of the LED), or the voltage across the 0.1 (or 1?) Ohm resistor on the board for a nice current measurement. I have two lead wires that I would solder to the contacts of the LED (must be soldered because I can fry the Fatman if it is on and the output is open).

I have tested over 45 LEDs successfully (for my LED headlight project) with this setup with no problems of any sort so far. I was doing something differently this time though. I had a simple toggle switch set up so I can switch the negative wire out of the circuit either to the negative wire of the Cree XR-E or the negative wire of a spare u-binned Luxeon K2. The positive wires of both LEDs were soldered to the positive wire of the circuit. I know the Fatman is pretty durable because I know of several times that I had a poor connection and I have turned on the Fatman with no load for fractions of seconds before (I have a momentary switch hooked up between the battery and the circuit by the way). The voltage on the meter will read like 15V for that very brief instance. No problem...

After I finished soldering all of this up, I lit up the K2, then then I tried the Cree to compare, but nothing happened. I switched back and the K2 lit up fine, but I switched to the Cree and nothing. My meter would read the odd 10-15V when I would do this, like there is an open circuit. What the heck? I tried reapplying power briefly to the Cree while wiggling the wires and nothing. I disconnected the Cree and tried three alkaline batteries together (only 4.5V -which I had used with success before), and nothing. I thought the wires were broken so I tried connecting power directly to the contacts and nothing is happening. I was confused and frustated by this point.

I thought maybe the Cree was hooked backwards, but I think I remembered that the positive wire was always soldered to the positive wire coming out of the circuit. I am sure that it was hooked up right, but I am just making this error a possible option. I know that boost circuits can create a too high of a voltage when left open, so I do not know if I applied power to the circuit then to the LED by accident, giving it a short pulse of ~10V or not. That error is another option.

So you know, I had this Fatman hooked up to the Cree by itself without the stupid switch and it was fine. I was testing the Cree out at different current levels and it was spectacular! I tried different optics and stuff without problems, then I wanted to test overall brightness and compare with the K2 and everything went downhill.

Do Cree's have the same two zener protection diodes the the Luxeons have (that I am familiar and used to accidentally messing up)? If so, How would they even be used if the middle heat pad is electrically isolated (unlike the Luxeons)? The bond wires couldn't have been fried. They aren't discolored from heat, but I can hook up my meter to the bare XR-E and have it to the diode testing setting and it tells me it is an open circuit. Is the die itself totally destroyed? I have a LED that looks completely fine but is completely unusable... aye carumba!

See what I mean by a noob like situation and a noob like question? I am just totally confused and frustrated on what I did that destroyed my new and expensive LED (which I ended up paying in Australian bucks because they didn't convert it to USD -a near $10 difference). What should I do? Should I give up on the thing and maybe try getting another, or can I hook it up differently and get it to still work, even without the ESD protection (if it has it)? I have many questions and I understand if many of you don't want to reply because of that. Thanks all for your help. I know that the CPF is awesome.


-Tony

It takes a lot to "fry" an LED, they are generally very robust. You say you haven't hooked it up backwards. Have you tried connecting the Cree to three alkalines directly? Try reversing the connection. If you're using AA alkalines, they are pretty weak and won't do any damage to the Crees no matter which way you connect. Are you connecting to the top part of the LED? Any pictures?

Crap I forgot some of the details. I did try the 4.5V battery pack and nothing happened again. I connected it to the bottom two contacts as well as the top two. I even switched polarity with the battery pack on both sides and nothing happened.

When I had the Cree XR-E attached to the Fatman circuit, I did have it soldered to the top two contacts. I did this so I wouldn't foul up the bottom with solder in case I wanted to epoxy this thing down on a smooth surface later. The XR-E was pressed against the provided hex board made for the LED that came from Cutter electronics and I used simple thermal paste. It was pressed on by some solid wire. The wire was soldered to one contact, then over the pad on top of the LED, to the other contact. I put pressure on this wire with a small knife then re-soldered. I then put a little solder on the wire over the LED to make good contact with the pad. I did this to both sides and it worked pretty well before. Some say that they have accidentally bridged the solder over to the ring, but I made sure that didn't happen to me. It looked relatively clean. Lastly, I had the hex star attached to a small heatsink and it was held in place with some tape.


-Tony

When you connect "directly" to the pads, are you making sure you really have good contact? Is there any flux residue that would inhibit making a good connection? Use alcohol to remove excess flux or scratch up a good area nice and shiny to ensure you are making metal to metal contact. The connection to the LED is made at the top and connections to the bottom pads are made through vias if that helps any. If you can't get it to work this way, then I can only assume it's toast for whatever reason. How much did these Cree's cost from Cutter? Email me if you're looking for some P4 Cree's. I think I can get you a couple for probably more reasonable prices.

Well, I checked the pads with my meter (with the continuity feature), and the top and bottom pads are still connected. I got a good joint when I soldered the power wires to the pads. I have a few technical questions now.

What is the name for that little connection where you have a two-sided or multiple layer circuit board, and there is a hole where a trace from one side/layer is electrically connected to another trace on a different side/layer? I was always wondering what it was called. Also, what physically happens to the LED die when hooked in reverse polarity past the breakdown voltage? Why does it have to stop working even if it isn't mutilated or burned? Does a chemical change or something happen on the atomic level? This just bugs me. I hate wasting good LEDs as we all do.

Anyway, I payed 11.50 ("9.06USD") for the P3 XR-E. I guess I should have left a note on the Paypal payment thing to have them convert the price from AUS to USD. According to XE.com, 1 USD = 1.269 AUS, so I wasted only $6 and not $10 as I thought I did. I ordered the optic and hex star for it, also, so that and the shipping and Paypal fees is why I payed about $28 total. Now I am going to order my next from CPF somewhere. CM, a message is sent...

Thanks again all for your help and concern. I bet many can relate to my problems with failing LEDs! :scowl:


-Tony

If you want you can send me your busted Cree lamp also it really shouldn't do much of anything the hooked up backwards. Sounds like a failure.

First, you don't sound like a noobie.

Second, you said you were testing optics. did you allow a metal reflector contact the two leads on top of the Cree platform? That could cause an instant "poof".

Bernie

*

PTH (Plated Through Hole) is a little more accurate than Via, but both work interchangeably in circuit board lingo.

Thanks. A PTH (Plated Through Hole) or via. Interesting! 65535, I going to have to say no. Sorry. I will use this thing as a dummy during mock ups and stuff. I have plans to remove the dome and ring of the XR-E to get a more Lambertian beam pattern that would work better with reflectors. I see plenty of people on CPF doing this in a safe manner (I even found instructions) so I will test on this first on the dummy, then my new good XR-E later (when I get it).

No, it wasn't my optics causing problems, because I had the XR-E mounted to the heatsink and hooked up to the Fatman circuit (way before) testing the optics, then later, I decided to compare brightnesses, which caused me the problems. And yeah, I suppose I know my way around working with LEDs, but I felt that I sort of reverted back to a noob state. I knew I did something wrong, but I couldn't figure out what exactly that was that cause the odd failure. Arghh! Thanks for you help, again. I appreciate the ideas and efforts!


-Tony