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FrozenGate by Avery

Low voltage, HC driver for a coherent FAP module?

A

Arcygenical

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Joined
May 8, 2012
Messages
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Hey guys, long time no post.

I've got a Coherent branded FAP 808nm +/-3mw source, rated for 40w of optical output.
Based on the datasheet it has a Vf of <2.2v for the array.

Its threshold lasing current is ~9a, (mine begins to lase around 8a, but my bench supply fails after 10a, so I can't test far beyond the module's threshold).
It's rated for an If of <53a.

Let's aim for a conservative 55a supply, with an output voltage of 2.15v.

How the hell would you drive this thing, if efficiency wasn't a concern?

Any thoughts on how you could vary the CC output of the driver? I really don't want a 40w 808nm source on 24/7 during testing and alignment.

Any thoughts at all would be very appreciated!
 





A linear regulator for this current @ only a couple volts is gonna generate a lotta heat. Well over 100 watts if you start with a 5V power supply. A switching regulator would be more complex but a lot more efficient.
 
WizardG said:
A linear regulator for this current @ only a couple volts is gonna generate a lotta heat. Well over 100 watts if you start with a 5V power supply. A switching regulator would be more complex but a lot more efficient.
Click to expand...
This was my concern.

I DID say I wasn't super worried about efficiency, but sinking a 100w or so, is a bit outside the realm of reasonability...

This WAS my first idea, though... build a cheap 110vac>3v toroid, rectify it with a low voltage rectifier, clean the hell out of its output, and pump in into a few stages of a low voltage output regulation circuit.

But there has to be a more elegant solution.

Can you point me in the direction of "explain to me like I'm 5" switching regulator theory? I'm assuming this is just a buck converter... but I could be mistaken.
 
Buck converter was pretty much what I had in mind. Maybe parallel a couple of VRMs used for CPUs? Would take a custom PCB but would be pretty efficient. My motherboard can feed my CPU well over 100A @ 1.25 volts so they could handle the load.
 
Also, if anyone's wondering WHY I need a 40w 808nm source, it's to pump into an optical train for 808>1064>532nm light, using some homegrown KDP crystals that I'm cutting and polishing myself.

808nm FAP : > MIRROR [T95% 808nm | R 99% 1064nm] > CRYSTAL [Nd:YVO4] > CRYSTAL [KTP to test, or KDP after proof of concept]

The basics of the optical train.
 
WizardG said:
Buck converter was pretty much what I had in mind. Maybe parallel a couple of VRMs used for CPUs? Would take a custom PCB but would be pretty efficient. My motherboard can feed my CPU well over 100A @ 1.25 volts so they could handle the load.
Click to expand...
Honestly, I could probably just find a 50a output buck converter on amazon for less of the cost of the DIY.
I'm always worried about powering on CC buck converters, due to their horrible tolerances, and possible output spikes on power on/off.

EDIT: I can't find any buck converters rated for a CV of <2.5v, making this a.... bit of a dead end.

I suppose I could take that 2.5v output, and cut it, linearly, to 2.15v... Worst of both worlds, cheap ebay electronics and the efficiency of a linear driver.
 
Last edited:
You should use a switch mode power supply to power any current regulator you use. Power supplies don't get any cheaper than these. I have one for my 1300 mW 532 nm laser that's rated at 75 watts. It's definitely overkill, but only costs $20.
 
Last edited:
Arcygenical said:
Honestly, I could probably just find a 50a output buck converter on amazon for less of the cost of the DIY.
I'm always worried about powering on CC buck converters, due to their horrible tolerances, and possible output spikes on power on/off.

EDIT: I can't find any buck converters rated for a CV of <2.5v, making this a.... bit of a dead end.

I suppose I could take that 2.5v output, and cut it, linearly, to 2.15v... Worst of both worlds, cheap ebay electronics and the efficiency of a linear driver.
Click to expand...

You don't want a CV driver....Period. Any Buck driver that regulates current should work as long as it can provide the necessary power you need.
 
I'm slowly designing a switching power supply for my FAP usage. It's polyphase buck converter downconverting 12V input. It'll be a while though before I'm done, but it's already around $100 in parts. There's a reason big part of verdi is just psu.

How do you polish home grown crystals?
 
atomd said:
I'm slowly designing a switching power supply for my FAP usage. It's polyphase buck converter downconverting 12V input. It'll be a while though before I'm done, but it's already around $100 in parts. There's a reason big part of verdi is just psu.

How do you polish home grown crystals?
Click to expand...

You should be able to buy a switched mode PS much cheaper than you can build one. Do you really need one that outputs +12 volts? I would go for the lowest voltage you can get by with. It's the current that makes these work well. If you go with a SEPIC driver you can get away with just a +5 volt supply.
 
atomd said:
It's polyphase buck converter downconverting 12V input.
Click to expand...
Seems very reasonable.
Make a thread about it and just ignore all the hate and silly discussions that somehow always break out here.

One could also do 5V in to have lower step-down ratio - possible higher efficiency.
A SMPS with 5V will cost the same as a 12V one.

I would do DC/DC U source + Linear CC stage.
If you dont need to modulate quickly you could also do for a DCDC only topology.
Using a INA186 or so amplifier to generate a feedback signal for the step-down stage. I did that for much lower currents before and it worked flawlessly.
You ABSOLUTELY NEED to compensate the feedback network properly to eliminate oscillations and maybe even use an additional LC filter to lower the ripple.
A multi phase setup will be very good in that regard.


paul1598419 said:
.. If you go with a SEPIC driver ...
Click to expand...

sure..
 
paul1598419 said:
You don't want a CV driver....Period. Any Buck driver that regulates current should work as long as it can provide the necessary power you need.
Click to expand...

paul1598419 said:
You should use a switch mode power supply to power any current regulator you use. Power supplies don't get any cheaper than these. I have one for my 1300 mW 532 nm laser that's rated at 75 watts. It's definitely overkill, but only costs $20.
Click to expand...


Yep. Not driving the damn thing without CC output.

I've got a buck converter that outputs 1.2v to VCC, up to 20a, with a CC pot coming from Amazon today. Although it's only offering half the amperage necessary to drive the array, it's a step up from the ~10a CC bench supply I've been using to test threshold lasing.

I'll be powering it with a 12v, 15a SMPS to start, with a decent filtering stage into the CC/CV buck, to prevent ripple going where I don't want it to.

We'll move onto something more elegant in the future, if I get results in the direction I'm looking for.

Wish me luck.

And thank you!
 
Arcygenical said:
Yep. Not driving the damn thing without CC output.

I've got a buck converter that outputs 1.2v to VCC, up to 20a, with a CC pot coming from Amazon today. Although it's only offering half the amperage necessary to drive the array, it's a step up from the ~10a CC bench supply I've been using to test threshold lasing.

I'll be powering it with a 12v, 15a SMPS to start, with a decent filtering stage into the CC/CV buck, to prevent ripple going where I don't want it to.

We'll move onto something more elegant in the future, if I get results in the direction I'm looking for.

Wish me luck.

And thank you!
Click to expand...
Luck!
 
farbe2 said:
Seems very reasonable.
Make a thread about it and just ignore all the hate and silly discussions that somehow always break out here.

One could also do 5V in to have lower step-down ratio - possible higher efficiency.
A SMPS with 5V will cost the same as a 12V one.

I would do DC/DC U source + Linear CC stage.
If you dont need to modulate quickly you could also do for a DCDC only topology.
Using a INA186 or so amplifier to generate a feedback signal for the step-down stage. I did that for much lower currents before and it worked flawlessly.
You ABSOLUTELY NEED to compensate the feedback network properly to eliminate oscillations and maybe even use an additional LC filter to lower the ripple.
A multi phase setup will be very good in that regard.




sure..
Click to expand...
Linear stage is just wasteful. I'm thinking about a simple, polyphase, current mode converter. Current measurement is already used for balancing, so no need to do current mode -> voltage loop -> current measurement.

Considering that some people here want to use cheap chinese buck converter, no LC filtering is needed 😊.
Jokes aside, I'm more or a less copying Verdi internal topology, together with linear noise cancelation. I'm just changing two high power phases for more, lower power phases. Slightly cheaper and much more efficient conversion.

I was considering 5V input, but 12V input allows for much lower input currents, which simplifies things like input protection. Also for 5V input I had to go for custom stackup ⇒ $$$.
 
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