A130 diode losing output power

Bluefan · Sep 8, 2010

I really can't explain this behaviour. I got a diode from an early groupbuy of scopeguy20 (I think they were A130's) and build it in a nice module. I started with a currect of 630mA and only got 350mW, which is pretty low. but, as I'm using a plastic lens, I may have some losses.
But each time I take the module apart and put it back together, the output changes. And now I run it at 830mA and the output is even lower than before, around 320mW. How could this possibly happen?
I can run the module for tens of minutes without any change, but somehow I did something that lowered the output. Setting the current back at 630mA only lowers the output even more. I've been very carefull with the diode, I left the diode connected to the driver when I took the module apart, so I'm pretty sure it's not ESD. And it runs stable for a long time, so it's not thermal What could it be? The beam profile without a collimating lens still looks perfect.

kiyoukan · Sep 8, 2010

build a lm317 driver and drive it with a 9v and post findings.

chipdouglas · Sep 8, 2010

and by 9v don't use the rectangular 9v. there is definitely not enough current capacity in there.

michael

yobresal · Sep 8, 2010

If you are using a plastic lens you have likely coated the diode window with a thick layer of melted plastic. I would be willing to be that if you unfocussed your laser it would look like a scattered mess of light. You can clean the window of your diode but it is a timely process and will never be as good as new.

If this is not the problem then you are just not using a power supply with enough capacity to power the diode at higher currents.

Coherent Light · Sep 8, 2010

The Acrylic Lens could be melting or burning causing a degradation in output over time.

yobresal beat me to it.

Bluefan · Sep 9, 2010

I checked the lens, still looks perfect. I monitor the current, and it really is as expected. I sometimes run it with an adapter, but usually on my lab power suppy.
I will check if the driver is broken, I hope the diode is OK.

Edit: Even with just a lab psu and a 8ohm resistor I get 425mW at 775mA without a collimating lens. How much power would a slightly dirty diode window absorb? It looks reasonably clean though.

Firefly · Sep 9, 2010

Bluefan said:
I checked the lens, still looks perfect. I monitor the current, and it really is as expected. I sometimes run it with an adapter, but usually on my lab power suppy.
I will check if the driver is broken, I hope the diode is OK.

What's driver do you use?

Bluefan · Sep 9, 2010

I made one myself, but even with just a lab power supply and a 8ohm resistor it has the same behaviour.

Bionic-Badger · Sep 9, 2010

If you are using an acrylic lens, I'd exchange it ASAP. Even if the lens looks "okay" it might melting off into fumes that are coating your diode, and you won't want to steadily add more with use.

Still, it might just be degrading too. See if it continues to degrade without a collimator.

Bluefan · Sep 9, 2010

The thing is, I left it running for 30 minutes at a time, with no degredation. Even the first try was disappointing, 350mW with 630mA. But then I open the module, reseat the diode, adjust the lens and turned up the current to around 800mA. But the output got even slightly lower.

I now run it without a lens, but it's still not performing as expected.

Coherent Light · Sep 9, 2010

You could have a flaky Diode, but I haven't heard of anyone else posting with the symptoms You are describing.:thinking:

oic0 · Sep 9, 2010

A good glass lens is $10 shipped, vs hours of frustration and a ruined diode. Not a hard choice

Bluefan · Sep 10, 2010

oic0 said:
A good glass lens is $10 shipped, vs hours of frustration and a ruined diode. Not a hard choice

I'd be incredibly surprised if the lens, which is still fine, would have changed anything in the diode.

What would the effect of thermal damage be? It's possible it got overheated somehow, I haven't always had it in large heatsinking during testing (but never completey without). I did during the first run, so I don't think it's thermal, but I might be.

Firefly · Sep 10, 2010

that depend if the lens is AR coated or not and maybee your diode burned because the lens is not AR coated or burned because the diode isn't cooled correctly.

Morgan · Sep 10, 2010

^ This is a good point. No AR coating is risking back reflections.

You say you reseated the diode? What module are you using? Are you using the case as a return path? If so you could have added in some resistance to the regulation and this would change the output.

Check ALL your electrical connections first and when absolutely sure they are good, solid and correct you can look for other reasons.

The effects of heat damage or COD would be loss in output but assuming nothing had changed in terms of the diode, from the time you received it, to the time you first powered it, 350mW from 630mA is very low, even with a plastic lens. All other factors excluded I would be looking to the diode itself for an explanation.

M

Bluefan · Sep 10, 2010

There is an insane amount of light per area coming from the front facet which diverges fast. A just as fast diverging reflection won't add much to it, I only lose a bit of power.

I build everything myself, I'm not using the case as return path, just the two pins are connected. Some serie resistance won't change a thing because the current will still go through the diode, and my driver has a very large voltage output range it can provide.

What does surprise me is the voltage across the diode. At 1.2A the voltage starts at 4.4V but drops in roughly a second to 4.15V. I only run it very short at 1.2A, a few second at a time. At lower current the voltage still seems lower than normal for these diodes.

I am carefull to avoid ESD, but maybe nor carefull enough. I can't find any other explanation.

A130 diode losing output power

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