Whats a safe ma to test out unknown LD's?

Hey guys i'm still fairly new here, i just got my parts for my 317T DDL driver, and after frustratingly trying to build it for 2 days I think i'm ready to test my two DL's.

real quick, why it was frustrating was apparently the person who sent me the Vairable resistor sent me the value of 100k not 100ohm and I couldnt' figure out why my readings were jumping all over hell when i'd wind it up (it would go from 98 to 185 in a fraction of a turn). So for the time being, I've just removed the variable resistor and am running a jumper wire from the middle pin of my 317T to the resistors.

Becuase of this, I want to error on the side of caution, I have 2 LD I've pulled from what I remember to be a 16x DVD burner, i'm not sure which is which (from my posting here http://laserpointerforums.com/f51/there-anyway-do-quick-2-3-second-test-ld-without-driver-74272.html) not that i doubt the advice that was given to me there, but If i didnt want to burn up either diode (not sure if it matters that i'd probably most likely burn the NIR diode if i used the same ma i'd use for the Red diode, which i'm 'hoping' can be around 200ma).

so my question is, what is a safe ma (i.e. resistor value) I can substitue into my design instead of the 2 10's that DDL had mocked up? would 60ma fry the NIR? would that same 60ma even light up the Red one so I could tell which is which? I have a 20ohm resistor i bought just for testing purposes which I believe would give me 60ma with this 317DDL and me using a 9volt battery as the test power source.

Also I know the first thing to do is always drain the capacitor which i've been doing as pratice (the LD's are not even off the shelf yet) but i've noticed after i remove my shorting tool the multimeter starts to read that the volts are slowly climbing back up again.. Is this normal? or am I not shorting it out long enough? It climbs rather slow at about .01 every few seconds.. It seems to have gotten up to .72 before.. I assume that wont be too much if an issue?

oh and if i haven't asked too much already, is it correct that i get a bout 7.2 volts when just hooking up the multi-meter to the postive and negative of the DDL cuircit itself? I've read many threads that say dont worry about the volts, its the current you want to worry about. (when i used the test load and using DDL's recommended 2 10ohm resistors together I set my multi-meter to 2000m under the DC section and the reading comes out at about 240 but slowly starts to drop down to around 215 or so, i attribute this being a not super charged battery, but i still want to make sure i'm donig things right and i assume that is calculated out to 240ma becuase i am using a 1ohm resistor in the test load as described).


thanks in advance!

If you pulled those LDs from 16xburners I would suspect that 200mA is a safe current to drive them at. However you could set it to 150mA just to make sure that they lase as expected.

Regarding the DDL driver - It will only let the voltage through that is actually consumed since the LM317 is a voltage regulator mosfet. What you need to make sure is that the current will not exceed the LDs max, and you should always use a testload prior to hooking up your LD. You will have to use a testload and set it for red since the current will change depending of the voltage draw. I am not sure about the caps and the behaviour you are seeing related to this and will let someone else answer that :beer:

Forget the variable resistors, I hate those things and never use them.

Driver doesn't have to be complicated.


You can easily calculate your needed resistance between OUT and ADJ pins by using a simple Ohm's law
Resistance needed in Ohms = 1.25 Volts / Current desired in Amperes

You can also turn it around,
Current = 1.25 / Resistance

You appear to be measuring the current right because, if you followed that other schematic, you have two 10homs in parallel, which is 5 ohms.
Current = 1.25 / 5
Current = 0.25 amps (or 250 mA)

Thanks guys! I ran a test using the diode, it worked! i picked the right one first try.. I used a single 10ohm to get it down to 125ohm instead of going with 250 as i've read a few posts here that says 16x diodes should probably be around 200 and i don wana push it.. I did not have it in housing or focused, I simply hooked it up and turned it on, it was insanely bright compared to 5mw laser pointers i've had. IT wasn't focused so it was a huge blotch on the wall.

My real problem now is how to get it out of its little heatsink it came attached to (they soldiered it on two sides and it seems to have thick globs which my soldering iron is having a hell of a time trying to melt. its only a 30 watt if i remember correctly and i'm fearful of frying the LD by holding the soldering iron on those soldier points too long).

Also I'm not going to go any further (in terms of putting the diode into the Aixis housing) untill i get a pair of saftey glasses for the 650nm wavelength . I dont have a ton to spend being unemployed, but I do want to try to get a pair that will at least protect me. seeing how bright the output was just on the wall next to me made me realize they would be a good idea.

Thanks for the help guys! i was glad to see it worked!

I agree with Eud that you can skip the variable resistor however if you want to use your driver as a test psu then it does come in handy. If you are making the driver -> LD as a 1-1 relationship there is no need to put it in there. However you will need to get the calculation correct since there is no way of adjusting the current without it.

Yeah I think I've got the calculations correct. I dont want to push it to 250, (unless it needs that to pop a balloon) I was hoping to keep it at about 200mah and ideally would use a 6 ohm (i bought a 6.2 and 6.1 while at the electronics store) to hit that number.

my biggest problem as I say now is getting the blasted thing out of its stupid little mounting/heatsink housing without frying it..

Use two pliers, grab opposite sides of the heatsink and twist.

Those little heatsinks are made from some aluminium-magnesium compound IIRC, and is quite weak and brittle. Twisting in opposite directionf from two sides almost guarantees nice breaking points without any damage to the diode.

It's the most common used method of diode extraction.

Can you post a picure of the ld with heatsink? I suspect its similar to the heatsink that you extract from a LPC sled, and if so you can use a couple of pliers to twist the heatsink off. If it is similar it will break incredible easy as the aluminum is very fragile. What I actually do myself is use my Dremel multitool and a metal cutting disk and make a slit in the aluminum block. I then hold the block with a plier and use a flatheaded screwdriver to twist it apart.

EDIT: was in a meeting with the browser still open and didnt refresh before I posted, hence the very similar posts from me and Eud :beer:

Have a look at this video: http://laserpointerforums.com/f51/harvesting-loc-lpc-815-diode-45153.html

I am basically doing the same as Moh in that video except that i use a multitool instead of a file. Hope this helps.

Sure! here's a few pics... Please never mind how bad the soldering looks i started trying to cut through it with a knife after a while as i do not own a dremel at this time.. i also tried to peel off the 'cuircuit' tape that was on the diode, but it didnt like that s much so i left half of it on. It's a real mess..

That looks messy. Pry with a little screwdriver between the diode edge and the heatsink. It should popped out.

Is that safe? is the diode housing pretty strong? I'm trying not to kill this poor thing before i get it out.. why they felt they need pea sized drops of solder to hold this thing in at 4 places is beyond me!


so dont try to snap anything in half with 2 pliers then?

Is that solder between the diode and the heatsink ? I thought it was some kind of paste.

okay i think i broke it, i tried to break the peice off with 2 pliers and i did break it out but now i hear it rattle when i shake it, i tink the little glass lense peice inside there is loose now...

** update

I dont think i broke it, but i do think the little lense inside is loose, i got it all out of the housing, and hooked it up again for another quick test, it does still light up so it appears to be working still to some degree.

the problem now is that there is solder residue around the edge and on the flat part so when i insert it into the aixis housing it does not even get close to being flush or almost even fit inside... I cannot melt this older with my old crappy pos radio shack iron its just about dead now I'll post a picture of the iron for laughs. Also a picture of the laser shining onto the wall (without any aixis housing just the diode itself being driven at 125Mah, so i'm asumming 200mah will be considerably brighter if/when i decide to push it that far, but this is just to show it does appear to be working and is pretty bright to me so i dont think i turned it into an LED yet!)

Don't use 200mA on a bare diode. That diode has barely heatsinking and will overheat fast !
Get some fine sandpaper or a sandstone to grind the edge of the diode smooth. It will then fit a module.

Blord said:

Is that solder between the diode and the heatsink ? I thought it was some kind of paste.

Click to expand...

to answer your question, yes it was solder and it seepted down into the side of the diode too it was a REAL mess so in the end i just broke off the old housing with pliers, which cuased me to put 2 little 'bends' in the can housing part of the diode itself, which i think cuased the little peice of glass in there to become a little loose and i think now rattles when i shake it lightly (i'm wondering if this is going to make the diode worthless for focus reasons)