Odd driver problem

So the LM317 was dissipating 1.9Watts. ((12-4.35) x 0.25)

matt09 said:

Thanks for all your replys, it turns out I had blown the first LD, but I now have the 2nd working fine in an Aixiz module, apart from tha fact it won't burn anything even though focussed within a milimeter or two :S

Regarding the PSU, I was only using the adapter to test it and wasn't planning on using it as a permenant power source. I was running at about 12v into the regulator and yes, I believe it is a cheapo unregulated one. I forgot about the voltage drop etc and was thinking it would only be pushing 250ma x 3v but of course this is only the output so thanks for setting that straight.
I'm using the 12v rail of from my pc for testing now hehe  

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@Igor... You don't need to put any regulator before the 317. As long as you are running at least 6 volts into it, the current going to the diode will remain constant no matter what the input voltage is...above 6 volts. Also if you were to do this you would need at least a 6 volt voltage regulator for this application.

@Matt:
Sorry you lost the diode but it is good you have another one. To calculate the resistor needed for the diode using the 317, take the sense voltage and divide it by the current you need. The sense voltage is 1.25 volts. So if you want to run 250ma's into your diode, 1.25/.250 = 5ohms. I do recommend at least a half watt resistor. ALWAYS put a test load on your circuit before connecting the LD to it.

The following link will take you to a website I found that explains in much detail how the LM317 works as a current regulator.

http://users.pandora.be/davshomepage/current-source.htm

Thanks for all the help, I'll get the circuit all sorted tomorrow and might leave a pot in there. The current source seemed a little unstable even though the diode wasn't getting too warm with surges up to > 270 ma but I was quick to rip off the wires at that point. I think the regulator was overheating and going unstable, not good. Does anyone know why it won't burn anything :-[ I thought anything above 150mw for a red meant burning ?

If there is nothing wrong with the LM317, then current going to the load should drop since it is thermally protected.

It should burn like crazy. Try something black..like a floppy disk, tape..or a piece of a dark colored trash bag. You said you were focused within a couple of mm's. Try focusing it at around a foot away and see what happens.

Gazoo said:

@Igor... You don't need to put any regulator before the 317. As long as you are running at least 6 volts into it, the current going to the diode will remain constant no matter what the input voltage is...above 6 volts. Also if you were to do this you would need at least a 6 volt voltage regulator for this application.

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Yeah, i forgot it needs 6V in this application.. In one of the devices i had to develope, i used the LM317 AFTER the LM7805, but there it was controlling the current going through an array of LEDs, and those have a lower voltage drop...


But there is something else that i would like to know about that regulator..

You say if it's used in current regulation mode, the current will always be the same, as long as the imput voltage is above 6V..

But what happens if you give it more than 6V.. The current through the LD will still be the same, but the voltage on the LD will be higher, right?

Therefor the power going through the LD will also be higher, since it doesn't only depend on the current.. (P=U*I)

That's why i would like to first regulate the voltage and THEN the current in my next project, so that as the battery voltage drops, the power will stay the same all the time, untill the voltage drops too low for the voltage regulator to still give out 6V..

Of course, if you're doing stuff on your table, you can use a PSU and allways have a regulated voltage anyway..  But i'm into small and portable, that's why i would like to regulate both the voltage AND the current, for constant power AND max efficiency, over the entire capacity of the batteries..


If i'm missing something, please tell me.

Just a thought on it not burning, have you increased the aperture by cutting out at the back of the lens holder of your Aixiz module?

Regards rog8811

rog8811 said:

Just a thought on it not burning, have you increased the aperture by cutting out at the back of the lens holder of your Aixiz module?
Regards rog8811

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So the Aixiz modules also need some modifications for better efficiency? Is there a link with pics on how to do this, or is it gonna be obvious once i finally get them? Is there some drilling involved or are you talking about some plastics?

For now i'm using the optics scavanged from a cheap laser pointer and hoped the aixiz modules would be MUCH better...

Try this one.....
http://www.laserpointerforums.com/forums/YaBB.pl?num=1190476363

Regards rog8811

rog8811 said:

Try this one.....
Regards rog8811

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Thanks!

Good to know!

Thanks for the continuted help, I'm very impressed with the members of this forum, it's one of the best i've come across I now have the LD burning and have cut away the plastic, I'm trying to burn right through a floppy disk at the moment hehe.

IgorT, in this circuit, the voltage is fixed at 3 volts regardless of the input voltage providing it remains within the limits of the regulator, hense P stays the same as V and I are constant.

matt09 said:

IgorT, in this circuit, the voltage is fixed at 3 volts regardless of the input voltage providing it remains within the limits of the regulator, hense P stays the same as V and I are constant.

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Thanks! That's exactly what i wanted to know.. Maybe i was asking the wrong way before (if all else fails, blame it on the language barrier ). I should have just built and tested it. But when ordering the components, they gave me the small 317s instead of the big ones, so i had to improvise... I would have to solder 4 of the small ones in parallel to get to the current my LD is currently eating up..


So you got your laser working with your second LD? What was the last problem you had to overcome? Was it the problem with not enough light getting to the lense?

Nice to hear.. I also just finished my first laser a couple of days ago (after killing two LDs and a lot of help from members of this forum) and this one looks very durable and strong.. And i don't even have the aixiz modules yet, just some improvised crap for focusing..

What i wanted to say is, i know how you feel now that it's working..


BTW: A few questions:
- What did you set the current to? Mine is doing 320mA when the LiPo is full and 230mA when it's almost empty.. In both cases it can light a match immediately.
- Do you know how warm your LD gets? At 320mA mine goes to 40°C after 4 minutes.. But i think this is a good result, and my heatsinks are doing their job.. I'll attach a pic, so you can see how my improvised cooling works..


Have fun!


Igor

The problem was that killed it being an idiot and not thinking that I would be zapping it with the fully charged capacitor when connecting the LD with the circuit already on and the cap at the regulator end.

320ma sounds very high, other forum members who know more than me will be able to confirm this but I would take it down. I just tried to light a match with mine and couldn't from any distance :'( not sure why.

matt09 said:

320ma sounds very high, other forum members who know more than me will be able to confirm this but I would take it down. I just tried to light a match with mine and couldn't from any distance   :'( not sure why.

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Did you paint the match black first? If you have a red match and a red laser, most of the light is getting reflected.. That's why it looks red in the first place (cos it reflects only red light)..

I need to paint my matches black first, to make sure all the light is getting absorbed.. Black doesn't reflect much..

But with my lousy optical assembly it's hard to do focusing right.. I'm hoping it get's better with the Aixiz modules & lenses..


Oh, and 320mA is a bit much without active cooling.. I just lowered it a little, to 280mA, so it wouldn't warm up that fast..

But for my next project, i'll use a tiny Peltier TEC (15x15mm), mounted through the enclosure. It will pump the heat away from the LD, to the outside of the enclosure, and there i'll have a heatsink attached (maybe with a small fan) to dissipate the heat.

That way i'll be able to drive my next laser harder, without worrying about overheating.. But for now it seems the LDs i have are pretty durable..


BTW: I thought i read you have a working laser now. I was asking what the problem was that prevented this one from burning.. Did you have to modify the aixiz lense holder (bigger hole)? If it's burning plastics, it should light a match, just make it black first..


One more question.. What is the current going through your LD when you're trying to burn stuff?



EDIT: I just tried my laser on an old floppy disk and it burns it very quickly.. Wow!

I didn't to begin with and realised that some light was being reflected, however I read that the red safety matches could be lit with only 160ma, without colouring them black. Are you able to light matches without colouring them?

I actually don't know why it is now burning and it wasn't yesterday, I got it burning just before i enlarged the lens holder so I don't really know if that helped or not, it seemed pretty similar after.

I have upped the current to 280ma now but don't keep it on long unless a fan is placed ontop. When I come up with a case mount idea i'll do something similar to yours and have two motherboard chipset heatsinks either side or something.

matt09 said:

I didn't to begin with and realised that some light was being reflected, however I read that the red safety matches could be lit with only 160ma, without colouring them black. Are you able to light matches without colouring them?

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No, i'm not yet able to light matches without making them at least a little bit darker yet.. But i have some weird matches anyway..
But as i said before, i have very lousy optics right now.. A lot of light is getting lost due to the distande between the LD and the lense being too big. And the lense itself is not that good.. A lot of the light is also getting spread out from the beam and making a star like pattern on the wall.. So there is much to be improoved and i hope the Aixiz modules do the trick..

What are safety matches? What's different about them?

Actually matches would have to be at least a little bit dark to ignite from a red laser beam.. Otherwise they reflect the most of it..

A green laser on the other hand would not reflect from a red match head AT ALL (theoretically) and all of the energy would get absorbed..

I have an idea.. Get green matches.. Or just paint the red ones black. Or green. Did you try this? Did it ignite?

matt09 said:

I actually don't know why it is now burning and it wasn't yesterday, I got it burning just before i enlarged the lens holder so I don't really know if that helped or not, it seemed pretty similar after.

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What distance did you focus the beam to? I used some smoke to make the beam visible, and put the match at it's narrowest point..

matt09 said:

I have upped the current to 280ma now but don't keep it on long unless a fan is placed ontop. When I come up with a case mount idea i'll do something similar to yours and have two motherboard chipset heatsinks either side or something.

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And i have lowered the current to 280mA now.. It looks the same, burns the same, but heats up much more slowly..

If you really want to drive your laser hard, i'd suggest some active cooling.. I already bought a peltier and intend to use it next time.. They're pretty cheap.. Mine costed 11€.

But you can also use some heatsinks with fins and provide some sort of airflow.. I was thinking of using a tiny pager motor with a tiny tail rotor (from a miniature helicopter) to dissipate more heat..

Of course with a peltier you can even go bellow the room temperature. But it's best not to overdo it, to prevent condensation...

BTW: Is your lense clean? Do you have any scratches on it? When you point it at the wall, do you get a dot only, or some spread pattern?