Go Down

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

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...)

Go Up