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Topic: Control very high power LED (Read 1 time) previous topic - next topic

fungus


Since it is just a prototype to find out how large of an area I can cover with a 100W IR led, I just need to make it work for a few minutes at the time. I'm not too concerned with durability etc. If anybody has a really simple solution, that would be perfect...


For power: A 20V power supply and a big resistor

(or lots of smaller resistors in parallel to soak up the Watts...)

Use a MOSFET to switch it but drive the gate high/low with a second transistor.
No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

Docedison

I don't think... short of radioisotopes that you could have picked a more dangerous project... AND a First one Yet... I just looked at the calendar and we're not even close to April First. 100 mW of IR power is enough to cause blindness and the IR "Beam" is invisible. 25W focused is enough to cut thin sheet metal.
THIS IS EXTREMELY DANGEROUS AND ILLEGAL IN A BUNCH OF DIFFERENT PLACES...

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afremont

Can you cite a reference to that?  100mW from an IR LED will not cause blindness as far as I know, now from a laser diode that's different.  1 ordinary IR LED from Sparkfun can dissipate 90mW.  Most TV remote controls have more output than that.  I have a remote control transmitter from a piece of heavy construction equipment.  The transmitter has more than 50 IR LEDs on it, and they ain't 90mW sparkfun LEDs.
Experience, it's what you get when you were expecting something else.

fungus

#18
Feb 27, 2013, 04:53 pm Last Edit: Feb 27, 2013, 04:56 pm by fungus Reason: 1

Can you cite a reference to that?  100mW from an IR LED will not cause blindness as far as I know


He said 100W...

Imagine a 100W LED on your desk but you can't see the light coming from it so your pupils don't react and you don't turn your head away from away from it.

Eye damage is definitely possible if you're close to one of these and/or look directly at it.
No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

afremont

No, docedison said 100mW would cause blindness.  I'd like some evidence of that.
Experience, it's what you get when you were expecting something else.

fungus


No, docedison said 100mW would cause blindness.  I'd like some evidence of that.


It might be possible.

eg. I wouldn't like to stare into a normal 20mA white LED at close range for any period of time.

No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

afremont

I could easily believe that a laser diode could do it though at less than 100mW even.  There's a really huge difference between coherent light from a LASER diode and ordinary LED light. 

Still, 100W of IR is not something to be shining in peoples eyes continuously.  OTOH, emergency vehicles do it all the time with the traffic light changers that give them a green light.  Allot of the vehicles use a xenon strobe to generate the level of IR they want, kinda like the traffic light cameras.  Others use an IR filter so that it's not visible, yet the light is just as bright.  But these devices are strobing and rarely encountered. 

Night vision security cameras have dozens of IR LEDs in them shining continuously at night and I've never heard of anyone being harmed by them. 
Experience, it's what you get when you were expecting something else.

cordvision

I absolutely aware of the potential dangers, which is why I'm in the process of getting IR safety glasses. It's not a laser, but a normal IR LED.
It's similar to what you can see here: http://www.alibaba.com/product-gs/513452759/100W_IR_LED_850_860nm.html

So far this seems to be the simplest solution: "Use a MOSFET to switch it but drive the gate high/low with a second transistor".
Will this work?


Any more suggestions on how to make a simple prototype?

fungus


So far this seems to be the simplest solution: "Use a MOSFET to switch it but drive the gate high/low with a second transistor".
Will this work?


Yes, but it's not as easy as it sounds. Switching 3.5A at 38kHz needs careful selection of parts and getting the math right. The MOSFET will overheat if you don't.


Any more suggestions on how to make a simple prototype?


Maybe a TIP150 is better suited for high frequencies. It eliminates all the MOSFET switching speed problems and you end up with a simple heatsinking problem - much easier to solve if you're not an expert. If it gets too hot you can just run two of them (or more) in parallel.

You still need to find a way to regulate the current, too. You can use a resistor if you're not worried about power efficiency but when you do the math you end up with numbers like "1 Ohm, 50W". Such resistors do exist (eg. http://www.ebay.com/itm/400310239042 ) but when you see devices like that you should wonder if your cunning plan needs a revisit. There's usually a better way.

What exactly is it you're trying to do? A 38kHz IR signal is obviously for a remote control, but 100W? Are you trying to switch a TV on from half a mile away? A small radio transceiver would do it better. Are you trying to flood a football stadium? The light from a few dozen smaller LEDs would probably disperse better (LEDs are quite directional) and cause less lawsuits for eye damage.


No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

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