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Topic: LED photostrobe Alpha test (Read 3 times) previous topic - next topic

Udo Klein

Reducing the pulse length from 10ms to 10us means 1/1000 of the light output all other things staying the same. Or with other words: 100W for 10ms is 1J while 100W for 10us is only 1mJ. If you want to get 1J during 10us this translates to 100kW. This is the reason why high speed photography is usually not approached with LEDs.

You might want to consider some focusing lenses to compensate for that. Or consider xenon flashes.
Check out my experiments http://blog.blinkenlight.net

focalist

#6
Apr 15, 2012, 09:13 pm Last Edit: Apr 15, 2012, 11:08 pm by focalist Reason: 1


The core emitter has arrived... 3500 lumens of 3000K, a fifty watt warm white LED array.  Eighteen bucks.

Guys, understand.. I know the physics I am facing.. But I am also depending upon the inverse square of the distance from the source.  I am not lighting a room.. At best a field of a few square feet... And I already have the Fresnel lens for focusing this behemoth.  This is an exercise in "let's see if I can make this work somehow".... And I do have a few tricks in reserve, including having harvested a dozen xenon flash units from disposable cameras.  They are perfect for some things when triggered through a simple optoisolator.  It is important to keep in mind that I am not trying to make something that's a normal use flash.. It'd be cool as hell for milkdrop photography, or a feeding hummingbird for example.. Very close, macro even.  The power decreases by the SQUARE of the distance, so I believe that I have a fighting chance at getting at least some limited success with over 100 watts of LED's.  Note that stage professional PAR cans are now 100w LED arrays already...that's replacing carbon arc in some cases.

http://www.ebay.com/itm/Blizzard-Lighting-ProPar-TRI-36-x-3-watt-Tri-Color-RGB-LED-DMX-Par-Can-/110844578515?pt=LH_DefaultDomain_0&hash=item19ceda0ad3#ht_2032wt_759

That is a professinal stage flood, LED... Five hundred bucks.  I am cautiously hopeful seeing these products.

I really am caught up with the 'If I can get this working at any level, it would be a very cool tool' thing.  If it doesn't pan out as a strobe, it's still a solid state floodlight that is a consistent color every time.. That alone is worth the cost of the parts.. The total on this now.. Hmm.. Like thirty bucks.

It will probably be several days until I can hook it up, in any case.. Gotta now look at the best way to feed that LED.  It'll be PWM'd with MOSFETS, but I will be taking a little time looking for a good current regulator setup for it... Though I understand there is a variation on LM317 thing with a feedback loop, that easily can do. 

It's got to limit at 2.5-3amps at 16-18v, anyone got a particulary cheap and easy solution (I love LM317 regulators.. and I have a bunch...but current sources couldn't run tandem due to tbe feedback circuit, right?  If they can, easy enough to tandem the little beasts.. Three would be plenty, an amp each...)
When the testing is complete there will be... cake.

jwatte

How about an LM350 for 3A? Still needs a fair bit of heat sinking. Or an LM338. Still needs heat sinking. If you want to get rid of that, you have to go with a switcher, which ends up requiring potentially bulky inductors, but perhaps that's not a problem.

focalist

#8
Apr 16, 2012, 12:53 am Last Edit: Apr 16, 2012, 02:47 am by focalist Reason: 1
I'm not sure if the current rating applies when you are wiring it as a current source rather than voltage regulator... The current rating is load max when operating as a voltage regulator.  In the spec sheet for LM317, a circuit for a 1A current source is given, but I have no idea what kind of load is on the regulator when operating as a current source.  It could even be that in that configuration it can carry more current, even..

If they can be used in parallel (Kirchoffs apply here?), then I'd just run three and call it good... I believe it is possible to run them side by side as voltage regulators, but in current regulation 'mode' I'll either need to research (or just try it).
When the testing is complete there will be... cake.

jwatte

I think the current rating is the same. As far as I understand it, a "current regulator" really just is a voltage regulator with feedback, which makes it very similar to an adjustable voltage regulator.

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