Old 09-16-2015, 01:44 PM #1
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Default 808nm 300mW Battery driven questions

Hi Folks! this is my first post here on this forum.
I hope that you will have mercy for me asking some basic questions since i havent really found the right answers yet on google and this forum.

The storry:

Ive ordered and received a cheapo 808nm 300mw
2.2V Diode Typ: TO18(5.6mm).
There was no data sheet or pinout given with my purchase.
The photo of the article shows 8809880 but is not printed on the actual diode i have received. But i think it is the same.
When i google the 8809880 i get this promising pdf:
http://www.eqphotonics.de/cms/cms/up...-300m-1-PD.pdf

If i interpret it correctly pin 2 is +
and pin 1 is - (negative) for the LD.

I measure 132kOhm from pin2 to pin1 (is that too much?)
and infinite resistence from pin1 to pin2 (that should be fine)

From pin 3 (photodiode?) i measure infinite resistance to everything else.

My plan:

I want to build a driver for the Laserdiode powered by 3xAA Batteries @ 1.5v
each eaqualing to 4,5v.

LM317T ,diodes, resistors and caps are at my hands as well.

My problem:

I havent understood yet if the pin3 of the diode is relevant or not.
Reading the pdf and researching on the net it is connected to a photodiode which saves the LD from frying and is possibly prohibiting th LD from emitting if not connected.

My questions:
-Is pin3 relevant for my plan? (id like to leave it out if possible and use this schematics: http://laserpointerforums.com/f42/di...ver-26339.html)

-Are 3xAA Batteries giving 4,5v sufficient for driving the diode at full power?

-Is my diode faulty since i can only measure infinite resistance from pin3 to anything else an vice versa?


WELL i hope i expressed myself good enough for you to understand.

I thinks this is a very common diode and some of you have allready worked on it.

hope to hear from you soon,

ogee!


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Old 09-16-2015, 01:56 PM #2
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Default Re: 808nm 300mW Battery driven questions

I wouldn't recommend you to make a 808nm laser as your first build. It is nearly invisible and might cause you to blind someone by accident. Amyway, a welcome post in the welcome section would be nice
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Old 09-16-2015, 02:07 PM #3
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Default Re: 808nm 300mW Battery driven questions

Quote:
Originally Posted by marcuspeh View Post
I wouldn't recommend you to make a 808nm laser as your first build. It is nearly invisible and might cause you to blind someone by accident. Amyway, a welcome post in the welcome section would be nice
Thx 4 your concerns but i have Goggles and live in a rural area.
So safety is garanteed.
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Old 09-16-2015, 02:46 PM #4
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Default Re: 808nm 300mW Battery driven questions

Hi,
Did you first go to the welcome section so we know a little more about you. considering this is your 1st post I'm assuming you didn't ,but if you did i missed it. Anyway welcome to LPF your questions can be answered if you READ through the forums everything is covered here .
Use the search bar its magical like a crystal ball.
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Old 09-16-2015, 03:08 PM #5
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Default Re: 808nm 300mW Battery driven questions

There are much better options out there than LM317, but it's fine if you're just doing it for the experience. If you wanted to design it properly, you'd want to consider the battery voltage as it drains. Alkalines do not stay at 1.5V under load, and their voltage drops significantly as they drain. Design for 0.8-1.6V (per cell) is ideal, but design for 1.1V-1.6V is close enough. LM317 needs about 3.5V minimum dropout voltage, so your voltage supply needs to be at least 5.5V. This means 5 cells in series if you want to actually use the capacity in your alkalines. Be sure to heat sink the IC. Too hot to touch is too hot to operate reliably.
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Old 09-16-2015, 03:28 PM #6
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Default Re: 808nm 300mW Battery driven questions

Quote:
Originally Posted by ogee View Post
My questions:
-Is pin3 relevant for my plan? (id like to leave it out if possible and use this schematics: http://laserpointerforums.com/f42/di...ver-26339.html)

-Are 3xAA Batteries giving 4,5v sufficient for driving the diode at full power?

-Is my diode faulty since i can only measure infinite resistance from pin3 to anything else an vice versa?
Pin 3 could be disconnected, connected to case or a photodiode. Either way you can disregard it.

Infinite resistance may be normal depending on what pin 3 is attached to and how it is attached.

As others have said, maybe think about using more AA batteries with an LM317 or use Li-Ion.

If you hook it all up and only see a dim red output **DON'T** look into it, that's all you'll be able to see at 808nm. Even at 20 WATTS all you'll see is a dull red. Test if it's working either with an LPM or a black piece of tape, which should start to smoke in the beam at 300mW.
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Old 09-17-2015, 01:22 AM #7
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Default Re: 808nm 300mW Battery driven questions

Doesn't sound like best of ideas to me overall. The LM317 driving it from 3 alkaline cells is not very reliable (it could work, but could fail, it is far out of spec). The combination with nearly invisible output light its not a good one either.

If this is your first build, i would suggest using a DVD writer red diode. Those are very inexpensive, handle about the same amount of current as the diode you propose, but have a properly visible output that would deter you from accidentily looking into it, or hitting yourself with a reflection from a window etc.
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Old 09-18-2015, 11:31 AM #8
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Default Re: 808nm 300mW Battery driven questions

At first let me thank you all for your concerns and helpful tips.
Since i have no other LDs other than some from old DVD burners i still tend to go for this build.

Thing is that i have a little trouble understanding the drivers logic.
If i understand correctly, 1 LM317 is sufficiant for current regulation and the voltage reching the LD regulates itself?

But how do i calculate the resistor and cap?
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Old 09-19-2015, 02:04 AM #9
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Default Re: 808nm 300mW Battery driven questions

The LM317 circuit basically relies on putting 1.25 volts over a resistor. You can calculate what current is required to do so for the resistors value, and this also is the output current.

Keep in mind that the LM317 is just a widely available voltage regulator IC, and not very well suited to this task. It takes 3 volts across it plus the 1.25 volts to operate within specification. This requires a battery voltage 4.25 volts over the laser diode voltage drop to work reliably. In your case you'd need at least 4 alkaline batteries, and even with that it would only reliably with fresh batteries.

If your source of laser diodes are dvd burners you should, however, have access to 650 nm laser diodes. Given the low price of those i'd stick with them for a bit, and leave the cd burner diodes alone.

I don't want to discourage you from experimenting building lasers, but as a beginner just start with visible ones. I've lit cigs with lasers, which i'm perfectly comfortable doing, but something like a 300 mW 808 or 780 nm laser still scares the hell out of me: it is something you can hardly see but will damage your eyes on touch. And since it's hardly visible it could be burning away at your retina without you even noticing it.
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Old 09-19-2015, 02:47 PM #10
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Default Re: 808nm 300mW Battery driven questions

How about a LPC-836? At least you would be able to see the beam.
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Old 09-20-2015, 05:10 AM #11
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Default Re: 808nm 300mW Battery driven questions

Might be easier to just convert a perfectly good 532nm DPSS pointer to a IR laser pointer, if you can get a lens with a short enough focal length and modify the pointer to take it.

http://laserpointerforums.com/f40/co...ser-91151.html
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