I would be nervous putting a cheap switching power supply regulator on that diode, they can be noisy with transient voltage spikes riding on the output as well as have huge voltage spikes when first powering them on, or if there were a short interruption to the input the same thing; zap, dead diode, I've done it a few times, but not with a FAP.
I see that big capacitor, maybe you intended on putting that across the output to help smooth out ripples but I'd use one closer to the DC voltage you are using as it will be far smaller for the same amount of capacitance. I don't think this is the right way to power this and not sure putting a capacitor across the laser diode like that is a good idea, maybe it is and I just don't know, but I haven't seen that done before. With three of these regulators in parallel I am concerned things can go haywire fairly fast, that said, I did the same thing for some high power 100 watt RGB LED arrays, but eight of them and it worked for me using isolation diodes between each PS output. But, they weren't sensitive laser diodes either.
Also, my experience with these cheap CC regulators has been poor, I had to try several until I could find a model which would produce enough current because they rate them at an amount of current capacity, but only when having the lowest voltage drop, if they are regulating a higher voltage down to a low voltage, not so good, or if a step up, from a lower voltage to a higher voltage, the current capacity is always far lower than the power handling ability they advertise.
I would stay away from cheap switching regulators at this kind of current level all together and use something else, unless a laboratory design power supply, but that won't guarantee they won't also behave the same way, I have an expensive one which does the same thing when powered on. The fix for this is simply to make sure the wires to the diode are disconnected when powering on, or turning off the power supply. If you don't, too often they produce a huge spike when powering on which will kill that laser diode (that and pray you don't have a blip to your AC power when hooked up to a diode). This problem can also happen to regular non-switching supplies too, it's a challenge to find one which won't do that.
Optlasers makes high current regulators which can run a FAP, that would be a better way to go, but not cheap for a 40 watt FAP. I know, I told you I powered one of my FAP's straight off a 2.0 VDC lead acid battery, but it is a FAP I don't care about, if I had a newer FAP which had lots of life left in it, and all of the fibers good inside that bundle, I wouldn't treat it that way. If you can find a DC power supply designed to run FAP laser diodes that would be ideal, but I haven't found them cheap.
Optlasers high current laser diode drivers:
Opt Laser manufactures high power laser diode controllers. Our laser controllers were designed by experienced engineers and based on branded components.
optlasers.com
If you want to try using that cheap regulator, check it out to make sure you won't have the problems I mentioned. If you want to parallel the outputs of the regulators, some will allow that without an isolation diode between them, some won't. You might need to add that diode and then of course, factor in the voltage drop through that diode. Do you have an O'scope to check the output of that regulator?
Oh, on that FAP thermistor, it looks like a standard unit to me, something Coherent supplied with it. Here's one I just received in the mail this week which came from Coherent this way:
You probably have searched the forum and found this thread by now, but just in case you haven't, this may be of interest:
I'm getting started here on a new project. I hope to make this portable (handheld) !!! A big thanks to Chris from way north for his help. These are the main components. The FAP RED module, a SUPER buck driver from TI and a battery pack to kick ass.... The Pot is for power control and the PB...
laserpointerforums.com
Here is a link to a data sheet for the Texas Instruments 50 amp regulator Mike was trying to use with his FAP:
ptv08t250w, but I don't think he found a way to control the current yet. I also have this same document saved here:
These TI regulators have built-in over current protection, just get one of the models which is designed to run close to the current you want to run (which is still below the maximum current rating of your FAP) and let it fold back (or perhaps stop output) to prevent over current and don't worry about trying to make an adjustable current set point, just make sure the voltage is set low enough the diode won't reach fold back or interruption current limiting, unless the diode gets so hot it starts pulling more current, you probably won't reach it. However, you will need to investigate this idea to be sure my reasoning is sound regarding how it functions, but I believe it will protect the diode from over current that way.
Edit: I found this information regarding overcurrent loads:
Overcurrent Protection:
For protection against load faults, all modules incorporate output overcurrent protection. Applying a load that exceeds the regulator's overcurrent threshold causes the regulated output to shutdown. Following shutdown, a module periodically attempts tor ecover by initiating a soft-start power-up. This is described as a hiccup mode of operation, whereby the module continues in a cycle of successive shutdown and powerup until the load fault is removed. During this period, the average currentf lowing into the fault is significantly reduced. Once the fault is removed, the module automatically recovers and returns to normal operation.
The way I read this, when an over current situation occurs the output is shut down but keeps trying, or "hiccuping" an output until the FAP cools enough to have a higher impedance, or lower current draw, but to reach overcurrent with the 50A module it is far too high at 85 amps to safely run the FAP that way. Choosing a lower current rated TI module which has close to a 50 amp overcurrent threshold (depending upon which FAP you have) such as the PTH08T210W rated for 30 amps continuous appears to be the way to handle this, but perhaps 50 amps is too high for your unit. There are several versions of the TI regulators to choose from, so you probably can find a suitable one with a lower threshold. if running the FAP in intermittent duty cycle, this ought to work out for us, but I wouldn't try it for 100% duty cycle as the module would probably heat up too much.
Here are some 30 amp units on ebay cheap right now:
https://www.ebay.com/itm/5-NEW-Texa...H-MODULE-PIP-7-3-6V-30A-HORZ-T-H/162926589289 - Unfortunately, the drop-out voltage of this regulator is fairly high, so you would need to run a few volts higher into the regulator than you might want to use, if using batteries. The good news is 96% efficiency, so you wouldn't waste enough battery capacity doing so to worry about, just that your pack would need to be larger. I'm assuming you want to run off of batteries though, you probably don't, I'm projecting a bit there, as I do.
One of the things these regulators could be useful for is as a high current pre-regulator to hang another regulator off of, their efficiency is uber high and depending upon what you are using, could be far more efficient to reduce a few volts using one of them first ahead of your adjustable CC regulator.
Download PDF for the 30 amp TI regulator here:
Enough ideas from me now? I've given you everything I've come to see as a poor mans solution as well as good practice, that is, if you use optlasers drivers. Only thing I've left out is collimation.[/COLOR]
If the duty cycle is so short the FAP cannot heat up enough to start pulling more current, then no problem. That is the same thing I observed with my own FAP without a regulator, but my on time was 20+ minutes on a fairly massive but passive heat sink using a lead acid battery which was draining at such a fast rate for its capacity, the input voltage was continually trailing lower and lower.
