589nm Laser / Powersource Modification

Hello everyone. When I thought about getting a 589nm laser I was not sure about the output power. A nice bright 589nm has a truly beautiful beam (in my opinion) but is not really practical in daily use. I was thinking about getting a 5mW laser but got a 50mW because the price / power ratio.
So now I build a little circuit to adjust the input power. I is using a variable step down regulator. First I wantet to build a variable current source but I had way to much ripple on th output. Now, using a variable voltage source everything works fine. The only thing that is not perfect ist the switch of the Spartan host itself. Maybe I will modify it sometime too. I am quite happy now to have a more eye safe and more mode and output power stable laser . If I turn the converter up to 2.25V I get the full output power and the laser is more efficient due the step down regulator.
I added some pictures in the attachments.

That's interesting, did you use a readily available step down?

Nice buck

Atomicrox said:

That's interesting, did you use a readily available step down?

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I used a ST1S31, mainly because I can solder it by hand. It isn't that expensive too. However the filtering of the noise was a bit of a challenge.

Be careful, those drivers and diodes get hot and don't dump heat well. They're easy to destroy varying the voltage and the noise will destroy the diode. Filter it to he extreme or it'll die fast.

Are you saying they can be killed by underdriving (like, say, using a lower voltage batt) or because it's a buck driver?

Mr Kaiser, perhaps you're missing the topology used here: Buck voltage regulator followed by a LDO current regulator. The noise of the first stage will be resolved by the second.

I did. And you're not wrong...but it does fix it in a kind patch or band-aid fashion.

I made an incorrect assumption when I posted that so don't worry about it. I skimmed it in a hurry since I'm at work. Creative idea. My bad! :beer: and no lowering the voltage using that shouldn't be a big deal. I don't think the driver in these would mind much. They're actually surprisingly flexible voltage-wise.

What if the laser had a (current) buck driver instead of a linear? Could I still power it up safely with a previous stage (voltage) buck?

Probably^. But that would be pointless. You lose efficiency for no reason. Just vary the current of the existing driver. I'd recommend varying the current of the existing driver in this case, too, but that would involve tapping into the current sense loop, and that might not be as efficient, seeing as it's linear. Ideally you'd replace the driver with a buck regulator instead of adding a regulator.

Cyparagon said:

Probably^. But that would be pointless. You lose efficiency for no reason. Just vary the current of the existing driver. I'd recommend varying the current of the existing driver in this case, too, but that would involve tapping into the current sense loop, and that might not be as efficient, seeing as it's linear. Ideally you'd replace the driver with a buck regulator instead of adding a regulator.

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If this is a spartan, there is a current adjust trim pot on the driver. IIRC clockwise is decreasing. just don't forget where it was set originally and don't turn it up past about 1.7A or so and don't run it without a heatsink. honestly CNI already overdrives them a bit, and they get really hot pretty fast. though I don't recommend taking these apart. it's quite a chore without tearing up the parts.