CW Laser diode Drivers - What are the important properties?

[likevvii]

Hello,

I am interested to know what are the important properties of a good laser diode driver.

Are DC step up/down CC/CV power supplies sufficient?
Is ramping up important? How would I incorporate ramping into a standard DC supply?
I hear alot about frequency but what does that actually mean.
I also hear about stability. How do we achieve stability?
What safety measures are usually included in purpose build CW laser drivers?

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My applications:

Continuous wave; No TTL/pulsing required
4W+ blue diode single/arrays
Analog power control.
Voltage requirement can be up to 80V for the arrays if I run them all in series. (array: Nichia nubm31t)
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My intended ideas:

I plan to use a generic, but high quality DC boost or buck driver with CC/CV capabilities. Remove the small pot included and add my own twisty pot for easy analog control.
I still do not know how ramping is achieved and how to incorporate it into a basic DC converter.



Thanks

 

[paul1598419]

Adjustable CC drivers are meant to be set on a dummy load. Using them to change the output power of your laser on the fly in not recommended. You can easily kill your laser diode that way.

 

[Cyparagon]

Simply put, the driver should send the programmed current to the load (no more, no less), regardless of what the input voltage is doing. Overshoot, and oscillations in the output are to be avoided... although some laser diodes are more tolerant to this than others.

As for your other uncertainties about words, you'd need to put them in context.

When it comes to an unknown new potential driver, either verify the performance on an oscilloscope, or take the word of someone else that has done so. "high quality" CC supply is subjective and doesn't mean there is no overshoot or oscillation by default.

Since potentiometers will often intermittently break the wiper contact when turning, this leaves the current setpoint at an undefined state for an unknown amount of time. Depending on the auxiliary circuitry here, this could cause overcurrent, undercurrent, or nothing. Adding capacitance from the wiper contact to a stable reference point (and again, that point will depend on the circuitry) may fix the undefined operation by holding the voltage at this node, but that might be too advanced a project if you're starting from the point of "what's a laser driver". It's best practice to not adjust the current more than necessary with the load active. Not unless you've verified the operation beforehand.

Do you have a DSO?

 

[likevvii]

Hello guys, I apologize for the premature questions. It was very late and I wanted to put a few questions out there before I even did my own searching.

I did some reading and studying on laser drivers and am now a little bit more familiar on this topic.
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I just finished using my DSO to test my only decent driver; the MDP-XP digital power supply performs.
This is the first driver I have actually looked at with my scope; but so far, it seems to be quite good!
I regret not taking a pictures of the triggers I did so you guys can give some input.

Some notes on the waveform based on my memory: ( regret not taking a picture before putting equipment away! )
My settings/set up:
-Nubm44-v2
-lithium battery input
-LD terminals are already connected.
-Voltage set to 10V, current set to 4.5A (I slowly tested up to 10V to see if the overshoot changes)

On the first few ms, voltage would oscillate up and down about 5 times before reaching CC mode and overshoots about 0.2V compared to the final voltage when stabilized.

The next ~50ms? the voltage would drop to about 3V

Finally, at I think ~150ms? the voltage will rise back to optimal at 4.4V
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It seems like the only important thing to watch out for is voltage spikes above nominal?
I forgot to test what happens when the unit is powered on, a little scared to test this now. But before I learned about how sensitive a LD is, I was handling it like what I would do with high powered LEDs. I even did the power on when LD was connected and I'm still good.

What is a good dummy load/replacement so I can test dangerous procedures or mystery drivers?
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I am looking to purchase a multi array driver (nichia nubm31t). I have not had much luck so far. I found 2 candidates:
Astrum LDD480-12A-CW @ astrum-lasers.com/technology-and-components/cw-laser-diode-driver-ldd480-12a-cw-copy
quoted 650USD/pc

Maiman CW 15А 40V SF6060 @ maimanelectronics.com/product-page/high-power-laser-diode-driver-oem-cw-15а-40v-sf6060
listed price: 450USD/pc

requirements:
minimum 30V output each array
minimum 2.5A output each array
5S 4P, 20 diodes in total

At this mega price, I can just buy 4 MDP-XP regulators as drivers for the same price with great reusability purposes.

I really need all your help to recommend me one, or modify/build one. I want current controlling capabilities and hopefully good efficiency because i'm going to pass 200W ;D

 

[Cyparagon]

Okay, but why didn't you measure the current with your DSO? That's the only one that matters and you've somehow forgotten it.

 

[likevvii]

Okay, but why didn't you measure the current with your DSO? That's the only one that matters and you've somehow forgotten it.

Sorry, maybe I misunderstood the actual meaning of DSO. I thought it just meant a typical digital oscilloscope. One that measures only waveforms. Mine doesn't have the ability to measure current.

My power supply does display output current and voltage, so I do have this information.

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To anyone who may come across this post, The MDP-XP digital power supply (only the module, you dont need the "monitor top portion") is basically the only thing I use to test my diodes now. It is extremely versatile and can adjust your output during operation.
Only thing to remember is connect your diode first. If you connect your diode first, even if you set the voltage to a crazy high amount, it will go into current regulation mode before the high voltage can kill your diode. I was not able to measure any spikes even during boot up.

 

[paul1598419]

You measure current the same was as you would with a digital multimeter. Think series resistor. Put it is series and measure across it.

 

[Cyparagon]

[My DSO] doesn't have the ability to measure current.

Not directly. You measure the voltage across a shunt resistor (that you, yourself introduce into the circuit) and apply ohm's law. Google it. Any voltmeter can measure current in this way.