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LM317 for 445nm laser

Fivos

Fivos

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Hello guys. I'm planning a new 445nm build and I don't wont to put money on a driver. I want to use an LM317 driver with an 1ohm 2 watt resistor. I don't want to power my laser from a pc's power supply because it is not stable and I have destroyed 2 445nm diodes in the past with this power supply. So what batteries can I use to power my laser? Can I use 2x 18650 batteries at 2500ma each (3.7 volt 4.2 full) or it will be two much and will destroy my diode???
 





deluminati

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You've destroyed two 445 diodes with a faulty power supply, but you don't want to spend money on a proper driver?

*does not compute*
 
Gryphon

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Yes, you can run 2 LM317s in parallel with each set at half your desired current.
 
Blord

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Or use the LM338. The beef-up version of the LM317. I don't know about the heat dissipation.
 
Cyparagon

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^1.2A is within the LM317's limits. There's no reason to spend $15 when a $2 chip will suffice.

The lm338 would give off the same amount of heat as an lm317. Two lm317s in parallel would give off the same amount of heat as one lm317. If you use two lm317 in parallel, you only double the area the heat can be emitted while a heat sink can increase surface area 20 times or more. Adding a heat sink is simpler, more effective, and likely cheaper.
 
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sampson

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Cyparagon said:
^1.2A is within the LM317's limits. There's no reason to spend $15 when a $2 chip will suffice.

The lm338 would give off the same amount of heat as an lm317. Two lm317s in parallel would give off the same amount of heat as one lm317. If you use two lm317 in parallel, you only double the area the heat can be emitted while a heat sink can increase surface area 20 times or more. Adding a heat sink is simpler, more effective, and likely cheaper.
Click to expand...

Exactly; You will end up with the exact same amount of waste heat. The LM317 is rated to handle up to 125C. With that being said, I've stress tested for 12 hour cycles at ~105C with no degradation. The LM317 also has thermal shutdown protection; I've tested it, it works (the device simply stops delivering current until the temp reduces to proper operating levels). Unless you're looking for really long duty cycles don't waste too much time here; just sink it and call it good.
 
Fivos

Fivos

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Hey guys I have a good heatsink for my Lm317 but I don't want the pc'c power supply. It has a kind of problem and it hasn't stable power so it burns my lasers..I have destroyed 2 445nm and one 405nm laser. I may use an adaptor.. So if I connect 3 18650 batteries the voltage will be at 12.6 volt. Will the Lm317 give me 4.5 volts at 1 amp or more to kill my diode?
 
midias

midias

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The LM317 will give you current at a set amount and should not kill your diode. If set up properly with filter caps the power supply should not matter. Personally I would go 2 18650s because there will be less for the regulator to dropout and convert into heat.
 
Cheech

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I use a 7 volt 1 amp router wall adapter with the lm317 on most of my builds. The lm317 heats up a bit when used with red diodes.
 
sampson

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midias said:
The LM317 will give you current at a set amount and should not kill your diode. If set up properly with filter caps the power supply should not matter. Personally I would go 2 18650s because there will be less for the regulator to dropout and convert into heat.
Click to expand...

What he said. Two 18650s is perfect for this build; Even at their lowest charge state they will produce slightly more voltage than you need.

If you use the third battery you are going to be making considerably more heat since the LM317 has to dissipate any extra/unused voltage. On top of that, your battery life is probably not going to increase (much).
 
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