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ArcticMyst Security by Avery

Driver for 405nm laser build.

Joined
Oct 2, 2010
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Hi there

I am building a 405nm laser (PHR-803T). I want to run it off a 9V battery so I will need a driver.

I was going to build a simplified version of a DDL driver with just a LM317 and a 12 ohm 1W resistor between ADJ and VOUT pins of LM317. This would achieve around 100mA-110mA which I hear is fine if you put the module in a heatsink.

Could I just place a 9V battery + on the VIN, and - on the LD - in conjunction with the DDL driver? How many volts are sent on to the LD, or does this not matter as I know it doesn't matter as much for LEDs as they are current driven (I presume this is the same for LDs).

So my questions.

1. Will the DDL driver work fine with the 1W resistor and LM317 as I have outlined?
2. Will the driver with a 9V battery function the LD perfectly with this setup? (even though I guess life time is short).

Thanks in advance, I look forward to building this.
 





Morgan

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The driver will work in the configuration you mention, (+ to VIN and - to LD-), but you'll have to wait for more epxert opinion on the resistor value.

The problem you will encounter, as I think you're are aware, will be the lifetime of the battery. Those 9V don't last as they don't have the capacity and you'll end up spending a lot on batteries. A better option is some Li-ion rechargeables. The 3.7V versions, when fully charged, provide 4.2V and two should give you a better runtime, less voltage to be dissipated as heat through the driver and for a much better cost.

The voltage put through to the LD is just what is required to maintain the current setting as the LM317 is usually set up as a constant current regulator for our uses. This means any extra voltage is dissipated as heat. For a PHR diode this will be around 5V. So 5V + the dropout of the driver should still be below two 3.7V li-ions.

I hope that helps. Others will provide better info I'm sure...

Good luck and post some pics when you're done!

Don't forget to introduce yourself in the Welcome section if you haven't already but as for me... Welcome to LPF! :wave:

M
:)
 
Joined
Sep 22, 2010
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I' m far from an expert but I have done quite a bit of research here in the last month or two so here's my $0.025 USD.

I'm planning on using a DDL driver as well for my 803T once my host parts from DX arrive. (hopefully this week!) From everything I've read the setup you described will work fine. To figure out the output of the driver use (1.25/n)*1000 where n is the value of the resistor in ohms. With your 12ohm you should get about 104mA. if you have a target mA you can rearrange the above equation and use 1250/mA to get the value of the resistor in ohms. I always double check my results using the original formula just to be safe. I'd recommend testing the driver with a dummy load as well - again just to be safe.


I currently have an LM317 with three 10ohm resistors in series giving me 42mA to drive a 5mW 635nm red. When I actually build it into a host I'll be replacing the 3x10ohm with a single 30 to save space.


Here's a couple thoughts/suggestions:

- As Morgan suggested you may want to consider using rechargeable LiIon batteries. I'll be powering my red with two 3.7v 10440s and the PHR-803T with two 3.7v 10500s. What battery type you can use will depend on what host you use. If you can fit two 18650s in your host they'll give you the best bang for your buck.

- If you go with LiIons spend the extra couple bucks on protected batteries and get a good charger. Cheap LiIons and chargers are just asking for trouble.

- Put a safety diode on the negative line to prevent blowing your diode if you accidentally put the batteries in backwards. installing it on the positive side will cause about a .7v voltage drop which will lessen battery life. Make sure the cathode end of the diode marked with a bar around it is connected to the the host's negative terminal (or the lead going to it) and the anode to the the diode's negative pin (or the lead from it). If you reverse the diode your laser won't work and your laser diode will fry if you accidentally reverse the battery. If you use the 9v this really isn't needed as much since it's keyed but IMO a must otherwise. I'd personally still use one since a 1N4001 cost about quarter a piece digikey or about a buck at your local rat shack which is a small price to save your laser diode. It already has for me at least once so far while testing some other laser diodes.

Here's a pic of the DDL powering my 635 red set up on a breadboard for testing. Full sized can be seen on my flickr page.


DSC_0435 by ltkernelpanic, on Flickr

Good luck with your build!
 
Last edited:

Morgan

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That's a neat little link there Vaporizer, nice one. I've added that to my guide...

M
:)
 
Joined
Aug 6, 2010
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Thanks Morgan. Glad you see it useful.
Some have issues with linking calculators, but it helps newcomers to get the right values without asking and it shows ohms laws that they can learn.
It's actually good for the LM1117 and most of the LM series when used for current regulation and it has a link when using them as voltage regulators.
I checked the values and they are dead on. The wattage also shows what size resistor is needed too.

Mind if I link your tutorial in my sig?
 

Morgan

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Not at all Vaporizer, the more that can see it the better in my view. If you know how to get the link into a title, (I've seen it explained a few times but can't remember where), it would save space in my sig and be a little easier to find. I'd like to just be able to click on the, "I want to build a laser", bit.

goninanbl00d's is worth linking too. I know he won't mind.

(Sorry for the minor threadjack here. It's a good time to do some admin!)

M
:)
 
Joined
Sep 22, 2010
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Excellent link Vaporizer!

bradkirwan - i realized the wording I used to describe the placement of the diode to stop an accidental battery reversal from ruining your LD was wrong. in fact the way I said it was backwards and corrected it. It should be:

LD neg -> anode of 1N4001 (or similar). cathode of 1N4001 (end with the stripe) -> negative connection of the host/battery.

I really shouldn't write long posts when I'm tired.
 




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