[SML] Advancing development of a new flash for antique cameras

[Bruce Cooper]

> I did a little more research, and saw a number of articles from 
> around 10 years ago, from designers seeking to create LED 
> flashes for our phones.  They used a similar approach, but what 
> surprised me was that they were stating they needed to supply 1 
> to 2 amps of current to the LED.  I have never seen LEDs, in a 
> small form factor, perhaps a 5mm through-hole style, which had 
> anywhere near that for a peak current rating.  2x the Max 
> constant current seems to be the norm.
>
> I imagine that the fact that the high current is applied only 
> briefly does permit you to push the envelope, in terms of max 
> current. But, rather than taking a trial-and-error approach, I 
> would prefer to use a LED that gives me the data to support my 
> design.
> Of course, I can put multiples of them in parallel. But, with 
> their resistors, this can start to get bulky fairly quickly.


All LEDs really care about in terms of current is if it overheats the die 
and destroys the semiconductor interface layer bond.  Thus, it is usually 
[*usually*] permissible to drive them with up to 300% of their nominal 
drive current as long as the duty cycle is kept low [<5% on time]. 

Check this PDF link

< 
http://www.cree.com/~/media/Files/Cree/LED%20Components%20and%20Modules/XLamp/XLamp%20Application%20Notes/XLampPulsedCurrent.pdf 
>

 I could get into the physics of it, but suffice to say that heat is 
responsible for >90% of LED deaths in one way or another.

  Use a monostable trigger circuit to limit the total time current can 
flow.  Or a small microcontroller if you swing that way.

My .02 from a former life.

:Bruce Cooper