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Old 12-17-2011, 11:41 PM #1
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Question Need a little help with projec

First i would like to say that i have been reading and searching this forum for weeks trying to gather all the info i need, and i am thankful for such a great site. Now i have been experimenting with lasers for a long time, but i have decided to go all in and build a 1w 445nm laser. I have ordered the diode in an aixiz module, and have built a DDL driver using the lm338 instead of lm317. From my research i believe they are pretty much the same, aside from higher current handling. I have built the curcuit in a somewhat weird way, as i have used 10x 10ohm 1/2w resistors, and 5 of them are permanantly hooked up, and the other 5 are mounted to the board but not attached at one end unless jumpers are added so i can slowly step up my power. As far as current goes i am getting almost exactly what i should be +/- 10ma. Now i know the diodes are current regulated, but i am worried about my voltage. Using 2x 18650's in series my input voltage is 7.4 and my output is about 6v. Is that to high for the diode? I used a small DC motor as a dummy load and the voltage drops to almost 2v when pushing 1A. Can a motor be used as a dummy load? The reason i used a motor is because i built the standard dummy load shown in many tutorials here and my results where even more boggling. When building the dummy load, for some reason i was not getting near the .7v drop per diode, and instead of 6 diodes i had to use 9 to get 4.5v drop. When testing with this dummy load, across the resistor(1ohm 10w) i only got about 8Ma, and across the diodes(in4001) i got the same 6v. Anyone know whats going on here? Thank you in advance for the help!


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Old 12-17-2011, 11:52 PM #2
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Default Re: Need a little help with projec

Powering the DDL driver with two 18650 batteries in series should work fine. The excess voltage will be dump in the LM317 as heat. That is why you need to heatsink it especially at high current and ample voltage. More voltage means more heat.

The voltage drop over in4001 change with the current. It is not a constant 0.7V, it varies over a range of voltages. Normally four in4001 should work as a testload. They also need heatsink at 1A as they can be really hot at this current. Better use 3A diodes as testload like I have in the picture..

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Old 12-18-2011, 12:38 PM #3
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Default Re: Need a little help with projec

That explains a lot, thanks! When you say the excess voltage is dumped as heat, does that mean the laser diode will only take the 4.5v it needs, so a reading of 6v is alright?
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Old 12-18-2011, 02:15 PM #4
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Default Re: Need a little help with projec

To test the voltage that goes to the diode, you need again a test load.

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Old 12-18-2011, 03:05 PM #5
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Default Re: Need a little help with projec

Just put your ammeter on the output. It's more trouble than it's worth to try to match the voltage of the laser diode. It's a constant current driver.
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Old 12-18-2011, 07:53 PM #6
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Default Re: Need a little help with projec

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Originally Posted by laserholic View Post
That explains a lot, thanks! When you say the excess voltage is dumped as heat, does that mean the laser diode will only take the 4.5v it needs, so a reading of 6v is alright?
Too keep it simple - yes that's exactly what's he saying.

You have an input of around 8.4 Volts with fully charged lithium ion cells (each is at 4.2 V), and with about 1 Ampere (considering the battery sagging at high current), you've got around 8 Watts of input power.

You need to power your diode at 4.5 V and 1 Amp, so that's 4.5 Watts.

The 3.5 Watts of difference is being dissipated at the regulator chip as heat. And that's a lot of heat - you really want to provide some sort of heatsinking to the driver.
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Old 12-20-2011, 02:01 AM #7
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Default Re: Need a little help with projec

Ok i understand now, thanks for the help guys. With the heatsink, and the way i have the resistors set up to be adjustable, plus 2x 18650's it is going to be too big for the host i was hoping to use. I am going to keep this as a bench/test supply setup but I went ahead and ordered a microboost V5 (And a nice pair of 445nm goggles) so i can run on a single 18650 in a "hand held" setup. Ill probably take some pics of the build and beamshots to share with the community.
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Old 12-20-2011, 09:23 AM #8
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Default Re: Need a little help with projec

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Originally Posted by laserholic View Post
Ok i understand now, thanks for the help guys. With the heatsink, and the way i have the resistors set up to be adjustable, plus 2x 18650's it is going to be too big for the host i was hoping to use. I am going to keep this as a bench/test supply setup but I went ahead and ordered a microboost V5 (And a nice pair of 445nm goggles) so i can run on a single 18650 in a "hand held" setup. Ill probably take some pics of the build and beamshots to share with the community.
An alternative to 18650 batteries, can be a battery cell known as "18350".

It's as wide as the original 18650 cell, but long just a pinch over half of it.

So in short, you can fit two 18350 cells, into one 18650 tube. They are some beefy batteries and will provide quite a current for your 445nm diode, I believe those batteries can give you up to 1.5 A with no complications.

Here's a link to ones I found on DX:
UltraFire 18350 3.7V 1200mAh Batteries (Pair) - Free Shipping - DealExtreme
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Old 12-20-2011, 01:07 PM #9
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Default Re: Need a little help with projec

Quote:
Originally Posted by Eudaimonium View Post
An alternative to 18650 batteries, can be a battery cell known as "18350".

It's as wide as the original 18650 cell, but long just a pinch over half of it.

So in short, you can fit two 18350 cells, into one 18650 tube. They are some beefy batteries and will provide quite a current for your 445nm diode, I believe those batteries can give you up to 1.5 A with no complications.

Here's a link to ones I found on DX:
UltraFire 18350 3.7V 1200mAh Batteries (Pair) - Free Shipping - DealExtreme
Awesome! Good to know about these, these will come in handy for some laser builds, and some of my high power flashlights. Im gonna order a couple of pairs. Thanks again!
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