I need a win - Help me to NOT kill this mystery 635nm diode ?

[rhd]

After (I'm convinced) receiving a DOA $200 diode, I really need a *win* on this next endeavor

I grabbed a used DVR-S201 from eBay. It's an early model 1x DVD burner with a 635nm diode (confirmed - it's one of the few DVD burners known to have a 635nm diode in it)

Challenge is, I have no idea how powerful it is, nor what current to run it at. This is what I need to figure out. At present, my planned approach has been to run it at 20mA, and slowly increase it while monitoring on an LPM for "hiccups". As soon as power output starts to drop, pull it back a bit and use that current.

But, there must be a better way. Can anyone contribute some wisdom here? My goal is both to get the best output I can, and also, to not have this little guy die

 

[joeyss]

I'm guessing this dioide can't go above 50-70mw. I'd turn the current up to it gets to 50 mw on the lpm and then drop it down by 10ma just to be safe. 40-50mw of 635nm is still a bright laser. Also my experiment with a 50-70mw 660nm laser I had indicates they ARE powerful enough to burn noticeably.

 

[anselm]

Cool!!

First thing I would determine is it's lasing threshold, at what current does it jump
from faintly glowing to actual laser light. Note that current once you found it.
Then increase in baby steps, let it run for a few minutes at each setting and
notice how the temperature develops.

Make sure to read voltage ta the diode pins (or driver output) at the different currents.

As to determine a "safe" current, I would plot a graph whith all the mA in vs mW out vs Vf
up until the point I'd chicken out with the current because heat would begin to become
an issue.

Then I'd look for local maxima/minima in the derivative of that function interpolated from that graph from those numbers.:tinfoil:
(points where the 2nd derivative would be = 0)

Remember those 20mW and 40mW diodes have rather low voltage almost more like IR than the DVD diodes,
and they run at ~80ma and ~100ma, respectively.

 

[joeyss]

Also beam pics please.

 

[daguin]

As you are plotting your IP/OP graph, watch for a "kink" or "knee" in the graph. A kink is where the straight line slope "wiggles." A knee is where the slope begins to flatten out.

Keep the current below the kink or knee

Peace,
dave

 

[joeyss]

Also make sure you use a large heatsink for this one. That diode is old we don't need it to go poooooooooooof in 3 minutes.

 

[rhd]

I don't have the ability to test both current and voltage at the same time. If my DMM is in current mode, in series with the diode, I won't be able to test voltage.

My sense though, is that voltage is less crucial to track. Yes?

 

[rhd]

Also, should I assume a typical LOC pinout ?

 

[anselm]

Chinese DMM's are 5$ at the dollar store, near you, not?
I have three, LOL!

Assume away, but I'd rather put the DMM in diode test mode and check which combination
of legs/case and probe polarity has continuity and makes it glow faintly.

Only then would I give it proper voltage and current.:tinfoil:

 

[rhd]

It's lasing at 40mA (the lowest I can feed it with my DIY PSU)

It's fine (visually) up to 55mA.

That's as far as I've gone before moving this game to my LPM, and the next increment range my PSU can do from 55 to 85mA. I'm going to chart properly now.

 

[joeyss]

What are the MW reads at 55 and 85?

 

[RA_pierce]

All of the 635nm diodes I have used were case positive.

Edit: Oops. Looks like you got it lasing already.

 

[rhd]

50mA - 0mW
160mA - 6mW

So far, it's pretty impossible to determine a "curve" because breathing the wrong way increments my LPM. However, at this stage, it's clear that this is not going to be a high powered diode

 

[rhd]

And if I can't get this above 10mW, I won't be sad about toasting it. IE, I'm infinitely adventurous below the 20mW threshold.

 

[rhd]

200mA - it hits 20mW - not warm at all, going to keep going.

 

[rhd]

300 mA - 50mW