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LM317 Driver problem

Conando

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I made a LM317 Driver circuit for my 1W 445 using a 1 ohm resister instead of a 10 ohm (like the one at Laser driver - It can be done ). I got 500ma on a dummy load. Hook it up to my laser for the first time and it worked OK I am guessing about 200-300mw it didn't seem too powerful. I wanted to make it brighter so I used a .6 ohm and then tried an .3 ohm resister. My dummy load would not go over 500ma. I am using 6 new 1.5 volt alkaline battery's as a power source.
I would like to drive it at 800 or 1000ma. Am I doing something wrong? Could the LM317 be bad?
 



ReNNo

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Don't use lower values than 1ohm.
1ohm resistor will provide 1.25A, that is enough.

What dummy load do you use?
You should try better batteries, like 2x18650, and use big heatsink on LM317.
 

VietTrader

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When you use 1 ohm resistor, you will get 1250mA. You got 500mA because alkaline battery can't provide over 500mA. Try 3x lithium batteries in series (18650 or CR123A will be ok).
 

Coherent Light

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Yea what They ^ said. Most standard Batteries (the one's in the checkout line) cannot deliver the current out required for Laser Diodes unless they are run in Series.
 

lasersbee

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Yea what They ^ said. Most standard Batteries (the one's in the checkout line) cannot deliver the current out required for Laser Diodes unless they are run in Series.
I think you may have meant Parallel if you want more Current
and Series if you want more Voltage from batteries...:evil:


Jerry
 

Coherent Light

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OOoooPPPppppSSSSsssss Yes PARALLEL is what I intended to type. I had a Brain Finger disconnect!
 

ReNNo

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When you use 1 ohm resistor, you will get 1250mA. You got 500mA because alkaline battery can't provide over 500mA. Try 3x lithium batteries in series (18650 or CR123A will be ok).
No, 2x li-ions are OK.
Another battery will just heat up LM317.
 

billg519

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Note also that the LM317 is quite stressed at the levels of current needed for these 445nm diodes. I am using LM350's as they are rated 3A. The LM338 can go 5-7A. The resistor is calculated the same as for the LM317. Test your laser and driver using a bench power supply of some sort, capable of delivering at least 7.5V at several amps. Do not use a resistor below 1 ohm, as this 1 ohm will give 1.25A of drive current to the diode, assuming the batteries can provide this current. The LM series regulators need some voltage overhead to work. If your diode has a forward voltage of 4.5 to 5V at full power, and the regulator needs 2-3V of overhead, you need at least 7.4V (two lithiums in series) to run at full power. Your 6V may not be quite enough. Two good CR123's will be the minimum configuration, 2 x 18350 (two of these will usually fit in a 1 x 18650 host) are a good choice. I have also used helicopter lipo packs rated 7.4V for these blue lasers. If you switch to a boost driver from Dr. Lava, then 1 x 18650 would be perfect.
 
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Conando

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Thanks, you guys are right about the AA batteries not putting out enough current. I solved the problem by using Lithium Ions 2 cells at first but it wasn't enough the current only went up from 500ma to 600ma (not enough voltage I guess), so I went to 3 Lithium Ions and it work great, now I am getting 960ma using 1.3 ohms. But the LM317 gets very hot I would like to switch to a LM338 do any of you have any schematics? Is it exactly the same as LM317?
Thanks.
 

qumefox

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You do have a heatsink on the LM317 right? And what kind of Li-ions are you using? Primaries or rechargables? Rechargable li-ions top out at 4.2v each. 8.4v from two in series should be sufficient to run the driver. If you were using primaries, then you'd need 3, as I don't think 6v from two would cut it.
 
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jayrob

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Also, the Wattage of the resistor should be rated for the amount of current you plan on running...

Using the LM317, 1250mA's would need a 1.5 Watt 1 Ohm resistor. Or 2 Watts...
 
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Leodahsan

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look for electronics simulator program on internet, and the datasheet for the lm317. Most famous lasers drivers (LM317 driver for BLU-RAY laser aren't well built). Look the fairchild datasheet for lm317.
 

Blu lase

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I would like to award all you guys a rep point. I have learnt a lot from reading all you posts and how helpful you are when people a legitament question and don't fool around.

I new nothing about anything when I first joined and I'm gradually picking it up. So I don't know if I can do the above mentioned. But I am for the first time in a long time really happy to be apart of something that I am enjoying.

So thanks to you all
 

Benm

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Thanks, you guys are right about the AA batteries not putting out enough current. I solved the problem by using Lithium Ions 2 cells at first but it wasn't enough the current only went up from 500ma to 600ma (not enough voltage I guess), so I went to 3 Lithium Ions and it work great, now I am getting 960ma using 1.3 ohms. But the LM317 gets very hot I would like to switch to a LM338 do any of you have any schematics? Is it exactly the same as LM317?
Thanks.
It doenst matter which regulator you use - it will still dissipate the same amount of power, and need equal heatsinks to allow continos operation. Using 3 lithium cells the input voltage is about 11 volts. The diode will drop roughly 5, and the current setting resistor another 1.25 volts. At 1 amp, that leaves about 5 watts of power for the regulator to dissipate, which an LM317 can easily handle.

It will require a heatsink to match though - something rated like 10 K/W would suffice if there is free air flow around it. Changing to a LM338 will not make any difference here - running at 1 amp is within the specs of the LM317, as long as you provide heatsinking... and a LM338 will require exactly the same amount of heatsinking to work.

Once you push beyond 1.5 amps you need to replace the LM317 by something more powerful, since its designed not to source more current than that, and it will limit the current if you try to.
 

Bluefan

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There is a variant of the LM317 with a lower voltage drop = less power dissipated, but it will still need a heatsink I think. In this case you already have a working driver, so just add a proper heatsink and you're done.
 

Fivos

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Ha!I have exactly the same problem. I use a lm317 driver with 2x 18650 batteries and the laser draw 600mah. But I don't have a third 18650 battery.I have two cr2 batteries and one hq L16a lihium battery like this: IpShop.Gr | HQ What can I do to power my laser? Should I connect the 2x 18650 with the h L16a battery?
 




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