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Coherent high power diode possibly??

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Alright guys I think I posted about this a while ago but now I understand diodes more I have a question, so I have an 18 watt coherent fap module yes I have laser glasses od5+ but I also have a 300 dollar driver on the way from OPT Lasers. The power supply I have is 5 volts at 20 amps, I was wondering if I could just hook the diode straight to that power supply because the diode is rated at 22 amps and the supply is only 20 amps so technically I wouldn’t be able to hurt the diode just plugging it straight into the 5v 20a supply right? It would draw 20 amps at whatever voltage it would need to run that current correct? And I have a diode on the laser diode so no reverse current or voltage, all I need is a yes or no this will blow it up and I should wait till I get the driver :) Thanks ! Also the supply is a constant 5 volt output so I can’t change that at a constant 20 amps :)
 

Alaskan

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Ouch, no way man, you can't have much more than 2 volts, that 5 volts will kill that diode immediately regardless of it's maximum current capacity.
 
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Okay, my question is though how come I am supposed to put 5 volts into the driver I am getting? It says on the website if the diode has an operating voltage or forward voltage of 2 volts add 3 volts to that and so I would put in 5 volts 20 amps to the linear driver? Why?
 

Alaskan

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Are you serious? You don't understand that and want to power that FAP? You have to be trolling us! 5 volts in, the regulator reduces it to 2 volts, plus or minus a tenth or so, to pull the rated current for full power out of that diode. I have a FAP and looked at that same CC driver too, you don't really need it, I power my 40W FAP directly with a 2.0 volt cyclon lead acid cell batter and no problem. This isn't recommended, but I haven't killed my FAP yet and have used it that way many times. Only thing is, the battery runs down in just 15 minutes :p
 
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Too late for that I already bought that one :) but I do know a lot about lasers I just haven’t really dived deep into the workings of the driver, I know almost everything about lasers though :) Still need to learn about drivers a little more though lol
 

Alaskan

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I thought you were pulling my leg, but now I see you have 80 posts, so not trolling.

Well, all constant current regulators take a higher voltage than the diode is rated for and reduces the voltage to match what the diode needs. At a certain voltage, the diode will pull the full rated current you need (edit: It adjusts the voltage up or down to keep the current constant, has a low value resistor in them to monitor how much current is flowing with a feed back loop tied to a circuit which adjusts the voltage).

For the FAP I have, about 2.1 volts pulls about 50 amps to produce its full rated 40 watts of IR output, my 2.0 volt 25 amp hour lead acid battery is just under that voltage and would run down fairly fast at about 45 amps, or less, of current at that voltage. Because of this, it could not over current the diode because it didn't have the ability to produce enough voltage to do that & would run down before the diode could get too hot to begin pulling too much current.

Trick is to make sure your heat sink is big enough and the battery runs down before it can get too hot to start doing that. As far as I know, all laser diodes will begin to pull too much current if they get too hot, that is why we use constant current regulators because at some point, the current will be so high the device fails. There might be some diodes this won't happen with, but as a rule of thumb you should always use a constant current regulator with a laser diode.

Depends on how much you over voltage them, if the voltage is too high I am fairly confident you can over current most laser diodes and destroy them regardless of having a good heat sink, or destroy it at the rated current if there isn't a heat sink when one is needed.
 
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Thank you so much for that reply, you explained it very nicely and I appreciate that :) now I understand how it works, but for some reason this driver didn’t include reverse polarity protection so will that be a problem or not one that I should worry about too much?
 

paul1598419

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If you hook your supply to the driver backwards it will be the last problem that driver has. Always observe the polarity of your supply and your diode.
 

Cyparagon

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Most power supplies are constant voltage with a current rating. They hold the voltage at their voltage rating, provided the load current is within the current rating. Current output may exceed the rated current, sometimes by a lot. But loading the power supply above the rated current will often either cause the supply to shut down, overheat, or self-destruct.

Laser diodes require the opposite. A constant current power supply - a supply that holds the current at a specified value, provided the load voltage is within the supply's(driver's) rating.
 

lasersbee

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Too late for that I already bought that one :) but I do know a lot about lasers I just haven’t really dived deep into the workings of the driver, I know almost everything about lasers though :) Still need to learn about drivers a little more though lol
It seems these statements may be erroneous.....:whistle:

Jerry
 

CurtisOliver

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There's always something more to learn when it comes to lasers. ;)
Good job Alaskan. :beer:
Those FAP usually take a max of 2.2V. 5V is slightly overkill I might say.
Occasionally you can come across LD Drivers for these FAP's at 10V, but they are meant to run 5 LD's at once.
 
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Wow laserbee you always have something to say don’t you, and also would I need to use the TEC in the fap package or is the big block of metal underneath of it already enough?
 

CurtisOliver

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Preferably you would need the TEC for good run times.
I have a 50W FAP-I but because I have no connector I can't actually run mine with the internal TEC.
If you are going to run that module without the TEC, make sure you invest in a hefty heatsink.
 

DashApple

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If the diode is on a TEC You need to use the TEC other wise heat transfer will be poor .
 
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Alright but what I’m saying is mine comes in the golden box not just the gold diode part, it does have the internal TEC and I also have no connector but underneath the diode it is sitting on what appears to be a large 1 inch thick chunk of some kind of metal that sits on top of the TEC I was wondering if that is enough just for a few minutes of run time?
 

CurtisOliver

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Alright but what I’m saying is mine comes in the golden box not just the gold diode part, it does have the internal TEC and I also have no connector but underneath the diode it is sitting on what appears to be a large 1 inch thick chunk of some kind of metal that sits on top of the TEC I was wondering if that is enough just for a few minutes of run time?
Yes, I know. You have a FAP-I as well. 'I' stands for the integrated package from Coherent. These modules come out of large DPSS systems such as the Verdi. You would need to get specialist connectors and power supplies to run the package as intended which of course would cost you $$$$'s.

With the lower power I'd say it is possible to run it for around a minute without additional cooling I would say, but certainly no longer as you could damage the diode.
 




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