Newbie advice

[**DONOTDELETE**]

I'm a bit baffled....I just completed the Zetex AA minimag mod shown on the site, http://www.5thcolumn.org/zetex/project/. I started doing some tests to see if the circuit actually worked, since I've never worked with SMD's and surely thought I messed something up during construction. I had everything hard wired, I plugged the power leads to the minimag socket and to my surprise, it worked beautifully! I ran it for over 5 minutes...very little heat and no failures.

Believing all was well, I worked on trimming the board down a little bit more so I could pack it into the minimag's head. After doing so, I went to do another test run before installing it. This time though, I had the board plugged into the socket and I then connected the Luxeon to the output leads......a faint blink and then darkness.

After that, the Luxeon would light no more. I hooked up a Nichia white to the circuit and it lit up fine. How did I kill my Luxeon??? Does anyone have an idea on what might have caused it? I have a funny feeling that hooking it up to a already live circuit might have had something to do with it, but I'm not sure. I'm ordering another one and I want to prevent another expensive mishap. Any advice would be appreciated.

Thanks for your wisdom,

A rusty electronics hobbiest and LED freak

 

[remuen]

Welcome on board!

In the thread ZLT+ additional construction tips and solutions to problems you will find a lot of informations about possible problems and how to solve or even better how to avoid them.

 

[bikeNomad]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by analogkid:
After doing so, I went to do another test run before installing it. This time though, I had the board plugged into the socket and I then connected the Luxeon to the output leads......a faint blink and then darkness.

After that, the Luxeon would light no more. I hooked up a Nichia white to the circuit and it lit up fine. How did I kill my Luxeon??? Does anyone have an idea on what might have caused it? I have a funny feeling that hooking it up to a already live circuit might have had something to do with it, but I'm not sure. I'm ordering another one and I want to prevent another expensive mishap. Any advice would be appreciated.<HR></BLOCKQUOTE>


We discussed this problem at some length a while back. What's happening is that with no load your circuit charges up the output capacitor to a high voltage. Then when you connect it to the LS, most of the energy stored in the cap is dumped into the LED, in addition to the current that is still being generated by the circuit.

So you gave your LED a massive peak current infusion, limited only by the internal resistance of the LED chip itself (and the ESR of the output cap). Since the dynamic resistance of the LS is about an ohm, if you charged the cap to (say) 16V, then you'd be dumping a peak current of over 10A into the LED. Unfortunately, they're rated for maximum peak currents of 0.5A.

Solutions to this problem include using Zener diodes (with a voltage just above the normal voltage across the LS) across the output.

Sorry. If it makes you feel any better, I toasted one with a current-limited bench power supply (its output cap was charged up...).

 

[jeff1500]

Would this happen with a circuit that regulated voltage instead of current?

 

[**DONOTDELETE**]

Thanks, bikeNomad. That's an "oops" that I won't do again. I should have known better. Many years ago I used to build photoflash circuits and had full understanding of the power of a charged cap.

Poor LS.....it didn't even stand a chance.