Building my first lpc826 red laser

Hey everyone,

Im making (well, trying to make) my first burning red laser from a lpc 826 diode that I ordered from ebay here.

I made a driver using a lm317, a capacitor, diode and some resistors.
If I put 2 ohms of resistance in the driver I measure about 360mV over the 1ohm resistor in my test circuit.
When I add 1 ohm to get 3 ohms in the driver the multimeter reads about 320-330mV.
Then when I add another ohm I measure about 290mV.

Strangely enough when I compare it with this site the values seem to kind of fit when I used 4ohm. But when I decrease the resistance, the mV does not go up quickly enough.

The resistors I use in the driver part are all 1ohm resistors in series rated for .25W. I dont have enough 1W rated ones so I only use that in the test load part. The resistors in the driver dont seem to get hot though.

Then, when I hook up the diode, it lights up, the diode gets pretty hot
but the focus point of the beam doesnt seem to be hot at all. When I look at PIV plots for the lpc826 it seems that at 300mA it should still give almost 200mw, which, I imagine, should be noticable.

Do you guys have any ideas about my situation? Is my driver faulty because the measurements dont seem to add up?
Or are these measurements normal and is my diode faulty or a fake?

Dear friend, if u use lm317 for lpc826,u have to add 1 registor 3 ohm---> A = 1250/R = 1250/3 = 415mA(good) > 250mW you get

thanhtung said:

Dear friend, if u use lm317 for lpc826,u have to add 1 registor 3 ohm---> A = 1250/R = 1250/3 = 415mA(good) > 250mW you get

Click to expand...

The thing is I read that the amount of mV measured on the test load is roughly equal to the amount of milliamps that go through the diode, and i measure only 320mV.

You will still probably get around 200mW with a standard plastic lens and it will burn quite well.

When I hook up the lpc826 diode it doesnt produce a hot beam at all, but the module does get hot. Do you think the diode was a scam? I bought this one: 660nm 300 400mW CW Red Laser Diode LPC 826 Special OFFER | eBay

Please post some pictures of your set-up, makes it much easier to find faults.

Jonathane said:

When I hook up the lpc826 diode it doesnt produce a hot beam at all, but the module does get hot. Do you think the diode was a scam? I bought this one: 660nm 300 400mW CW Red Laser Diode LPC 826 Special OFFER | eBay

Click to expand...

That wavelength isn't absorbed so well by the skin - try focusing the beam onto a black surface of some sort, like some electrical tape or something else you don't mind burning.

diachi said:

That wavelength isn't absorbed so well by the skin - try focusing the beam onto a black surface of some sort, like some electrical tape or something else you don't mind burning.

Click to expand...

I tried shining it at a matchhead and that didnt catch fire, ill try pointing at some black paper to check it.

Benm said:

Please post some pictures of your set-up, makes it much easier to find faults.

Click to expand...

Makes sense, heres a picture:


I hope you guys can follow, I'm not an electrical engineer, it could be a lot better i guess.

Did you try focusing it on the match head? Generally that'll do it if you have it focused to a point.