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Old 07-04-2015, 11:38 PM #1
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Default Optimal current for 300mW 808nm diode

Recently I bought a few 300mW 808nm diodes from China, but I have a bit of a problem - I don't know the current I am supposed to drive it with. I asked the seller if they had any datasheet for those, so far no response.

Then I took this guide Cheap burning laser tutorial as a reference, as it is also dealing with a "burning grade" laser. It describes carefully increasing the current until the brightness no longer increases or observing the pattern of the uncollimated light. Since my diode is 808nm I am using the following setup: driver circuit, diode, a webcam without IR filter and a screen are placed inside a cupboard with the door closed, USB cable from camera and wires for potentiometer and multimeter are coming out.

With the whole thing in place I started slowly increasing the current by turning the potentiometer. At first there was nothing and then light appeared and slowly intensified on the screen as expected. But then many things happened at once - the light deformed from a main thick line to a more dispersed diffraction-like pattern, and I immediately tuned down the potentiometer. I wasn't properly paying attention to the multimeter but I think there was some 400-500 mA running through at some point. Upon reviewing the circuit it turned out the potentiometer was behaving erratically - its resistance went quickly down by putting a bit more pressure on it. During next attempt the diode did not seem to be as bright any more, but I'm not sure.

So the question is - how could I find out what is the proper current for this diode? There are a few options I can think of:
1) try again observing changes in the brightness or deformations of the pattern (is it reliable?)
2) assume a maximum current (is there a standard for 300mW 808nm ones? I have seen mentions from 300 to 400mA but that seems like a big difference)
3) assume an efficiency % for converting current to light and divide 300mW by that % to get total dissipated power, which I could observe with voltmeter and ammeter (what might the % be?)
4) sacrifice a diode to see how much current they can handle.


Any help would be appreciated.


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Old 07-06-2015, 12:17 PM #2
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Default Re: Optimal current for 300mW 808nm diode

Yeah you burned the diode out.

That is literally the worst possible "setup procedure" I have ever heard of. Because of this, I hate potentiometers and drivers that incorporate them. They are never reliable, ever.

Use this schematic for future:


300mW IR diode requires what, aprox 350mA?

1.25 / 0.35 = 3.5 ohms (as close to this as possible). Solder on the resistors that make up your total capacitance, and forget the potentiometer tweaking.
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Old 07-06-2015, 12:23 PM #3
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Default Re: Optimal current for 300mW 808nm diode

You really need a LPM and a good source to slowly adjust in even increments (say 40-50ma) at a time.

Record the increase. There will be a point of diminishing returns (less power per increment) Look for the best efficiency and you can probably go SLIGHTLY above that. Much higher and you risk damaging the diode. There will always be a difference from diode to diode. Usually there is a range that is OK and efficient for most of them.

My guess however, it since you bought 808nm diodes and only have 3 posts, that you don't have an LPM???

I would suggest you first start with something visible and a known diode from the forums.
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