DIY Homemade laser diode driver

[wilheldp]

That's weird because I didn't disconnect and reconnect the diode during that time. I was always careful to fully discharge the cap before I connected the LD to the circuit (even checking it with the meter until it made it to 0.00V.

I thought that the leads connecting would just drain the batteries, but apparently it fried the LD too.

 

[chimo]

ZZZZZZZZZAP!  I think I fried my diode.
Any hope that another circuit component (capacitor, regular diode, resistor, pot, or LM317) failed, or is my LD hosed?  I don't see any other shorts in the circuit, and it appears to be drawing 294 mA (0.98V/3.33ohm).

Likely hosed.

Where did you get 0.98V? Is that measured?
Normally you would have 1.25V across the sense resistor which would give 379mA - certainly enough to fry the diode.

294mA was also enough to fry the diode. These LDs are rated for 130mA DC operating current.

I don't understand the surprise when they burn out when driven at over twice that amount. :-?

 

[wilheldp]

Likely hosed.  

Where did you get 0.98V?  Is that measured?  
Normally you would have 1.25V across the sense resistor which would give 379mA - certainly enough to fry the diode.

294mA was also enough to fry the diode.  These LDs are rated for 130mA DC operating current.

I don't understand the surprise when they burn out when driven at over twice that amount.  :-?

0.98V was measured across the resistor.

Where did you get the 130mA rating? I was driving it higher than that earlier with no issues. In fact, 130mA was hardly making the diode lase, much less getting close to 80mW output.

 

[chimo]

Where did you get the 130mA rating?  I was driving it higher than that earlier with no issues.  In fact, 130mA was hardly making the diode lase, much less getting close to 80mW output.

130mA is the figure from the spec sheet.

 

[toked323]

daedal was great help to me with his circuit if you follow that the right way you will not burn out the diode the pot is for the current you want to go through and be like stableized i think i honestly could not tell you but also make sure you measure your ma's as daedal told me dont try going over 250ma's

 

[Archane]

ok now that i'm finally caught up on all the posts I decided to go out and build DDL's circuit(thanks btw) I couldn't find an lm317t so I got an nte956 which is the same thing just a different company.(yes I checked the spec sheed and pin config soo)

So I built the circuit, but I can't post pics yet as you can see this is my very first post, and i'm have some problems. my setup uses all the same parts ecept I took out the 10 ohm resistor, it was causing the MA to drop alot.

So once it's all hooked up with 2 AAA batteries i'm getting 2.4v on the other end of the nte956 and i'm getting 100ma from the circuit. This is with my pot turned all the way down, if I plug my LD in I get a very dim light but it's "technically" working

now I have figured out that if I put a 3rd battery in the pack it I get about 4v from the circuit and 205ma. and the LD is bright as hell. GREAT! one problem the circuit only works for like 10sec, the NTE956 overheats and I don't know how I can fix this. the LD i'm using seems to eat more juice then the ones eing talked about in here normally. I pulled it from an Acer DVD bruner.

Any ideas?

 

[SenKat]

Archane - add in another 1N4001 type of silicon diode to the positive lead....that will drop your voltage down .6v without affecting the current. Then re-try. Even at 3.4v, you are most likely going to have a short lived laser....

 

[wilheldp]

What current are other people driving their LDs? 130mA sounds really low to me, but apparently 294 is way too high. Before I go blowing up another diode, I would like to get some actual current readings from other successful circuits. Then I'll try different resistors until I get that current with the pot turned all the way down.

 

[Archane]

Ok i'll try that when I get home, now just add it to the + side or should I put it in series with the other diode thats with the cap?

 

[Daedal]

Archane, the NTE has the same dropout voltage as the LM317, and thus, powering it with 2 X AAA batteries gives you around 2.4-2.8V supply... that's barely enough to power up the chip itself. You need to supply this circuit with at least 6V for it to start operating as expected... :-/

The values that you are getting are capacitance values (or so it seems). If you are measuring the voltage across the other side of the chip, make sure to have some load on there first. You will notice the voltage dwindle down to a dead stop when you add a load. I doubt the LM317 would be able to push even 50mA to the other side with a supply this low...

--DDL

 

[Archane]

Ahh ok so it was my misunderstanding. For some dumb reason I looked at the CR123 batteries as 1.5v not 3v. ok so i'm only running it at half power when i'm using 2 AA's gotcha.

The only thing that doesn't explain is why the NTE956 got so damn hot so fast when a load was put on the circuit when I added just one battery. If thats the case when I used 4 AA batteries that thing should be red and glowing when I hook it up. (Bare with me i'm at work and can't test any of this till I get home)

I'll have some pics later on when I get home as well to help see what i'm doing, but I followed DDL's pictures exactly(except for batteries yes we discovered this already )

 

[Daedal]

No worries Archane.

It really is very odd that it would get hot like that... I honestly don't know. Maybe it's just some faulty wiring somewhere? :-?

GL;
DDL

 

[Archane]

well if it is my wiring(believe me i'm not discounting that at all) when I post the pics maybe that will shed some light on it. I tried to follow the picture of your breadboard exactly so that I have a good reliable base to start with.

 

[toked323]

dude archane instead of a pot use a 5ohm resistor or tie the terminals of 2 10ohms together and that will set you at just about 250ma

 

[Archane]

no because without the pot i'm still not getting enough power with 2 AA's I need to either use 4 to get the 6v or get to CR123's

i'm going to rewire it with 4 AA's and readd the 10ohm resistor that I took out so it's exaclty like DDL's original picture, what i'm confused on it in the post he made he uses 6v on the ciruit the way I have it i'll get almost 5v on the other side not 2.5-3 that i'm reading we need.

Maybe the NTE956 doesn't have the same 1.25v drop.....hmmm

 

[Daedal]

Archane,

Check this out:
http://www.nteinc.com/specs/900to999/pdf/nte956.pdf

You can notice these 2 values on the sheet:

When they give current measurements: 2.5V [ch8804] (VIN–VOUT) [ch8804] 40V
When they give Voltage measurements: 3V [ch8804] (VIN–VOUT) [ch8804] 40V

For a stable reference voltage, you need a voltage drop of 3V, and for a stable current adjustment, you need 2.5V.

When you measured the voltage, did you connect the two probed from the DMM to the circuit's corresponding + and - leads? This doesn't give you a correct reading (sorry if you already knew that).

Other than that... their damn 'Data Sheet' means nothing! IT doesn't even give you the pinouts!

Either way... let us know what you get out of it... I would suggest you try and locate an LM317, or give me a few hours to get some kind of something written up about my LM2991 testing

--DDL