Why isn't my diode putting out more power?

I built a driver with an LM317 and two 10 ohm resistors in parallel (5ohm total resistance), powered by three AAA batteries. That should amount to 250mA, right?  The diode should be putting out almost 200mW!  (It's only rated for about 100mW for continuous use).  But it appears to be only a few times more bright than my red laser pointer, and it will not burn black paper at all.  What could I be doing wrong?  Do I need a fourth AAA battery?  Shouldn't 4.5v be enough?

How much current do you measure to the diode?
Mike

Three AAA batteries will not power the LM317 IT needs 5 volts alone to run so you would need at least 4 aaa batteries BUT 6 Is better. To power reds you really need ~7.2-7.4 volts, blue needs 9 volts.

Like jonrobertd said you need at least 5 AAAs for your laser to run at full power.

Perhaps use three lithium ion 10440's instead? It's 10.8V nominally, and roughly 12.6V at full charge.

I just tried four AAA batteries, and it actually burned dark paper and plastic.  It was able to burn though a black-marked piece of writing paper in about 3-5 seconds.  The diode also got pretty hot, so that's probably as much current as I want to run through it.

I also tried a 9v battery.  I'm pretty sure it was new, but after only about 15 minutes of playing with it, the battery died.  Does the diode really use that much power?

Is it normal for the diode to "die" when it gets too hot, but work perfectly once it cools?  It's done that several times.

Hemlock Mike said:

How much current do you measure to the diode?
Mike

Click to expand...

I don't know. The most fancy piece of electrical equipment I have is my $8 soldering gun. I have no way to measure current. I just guessed that the LM317's 1.25v divided by 5ohms = 250mA. I guess I just didn't have enough voltage, 'cause with the extra battery (6v total), it burned with the same driver.

Greenhorn said:

I just tried four AAA batteries, and it actually burned dark paper and plastic.  It was able to burn though a black-marked piece of writing paper in about 3-5 seconds.  The diode also got pretty hot, so that's probably as much current as I want to run through it.

I also tried a 9v battery.  I'm pretty sure it was new, but after only about 15 minutes of playing with it, the battery died.  Does the diode really use that much power?

Is it normal for the diode to "die" when it gets too hot, but work perfectly once it cools?  It's done that several times.

Click to expand...

Diodes vary widely in characteristics. Sometimes one will die and never work again, another might die when warm and then work fine again after it cools. There's really no way to tell how a diode will react to anything really. They are about the most sensitive electronic devices I know of.

Is there a graph or something to show the mW laser output of a 16x burner vs the mA input?  I'd rather not run mine higher than about 150mW, but I don't know how much current to give it.  For that matter, is there such a graph for a phr-803t?

Greenhorn said:

I just tried four AAA batteries, and it actually burned dark paper and plastic.  It was able to burn though a black-marked piece of writing paper in about 3-5 seconds.  The diode also got pretty hot, so that's probably as much current as I want to run through it.
I also tried a 9v battery.  I'm pretty sure it was new, but after only about 15 minutes of playing with it, the battery died.  Does the diode really use that much power?
Is it normal for the diode to "die" when it gets too hot, but work perfectly once it cools?  It's done that several times.

Click to expand...

9V batteries suck. Their mAh ratings are very low. They won't last long enough.

Diodes don't usually "die and come back." It is much more likely that there is a bad connection in some part of the electronics or a component is failing.

Peace,
dave

Greenhorn said:

I just tried four AAA batteries, and it actually burned dark paper and plastic.  It was able to burn though a black-marked piece of writing paper in about 3-5 seconds.  The diode also got pretty hot, so that's probably as much current as I want to run through it.

I also tried a 9v battery.  I'm pretty sure it was new, but after only about 15 minutes of playing with it, the battery died.  Does the diode really use that much power?

Is it normal for the diode to "die" when it gets too hot, but work perfectly once it cools?  It's done that several times.

[quote author=Hemlock Mike link=1227072347/0#1 date=1227073335]How much current do you measure to the diode?
Mike

Click to expand...

I don't know. The most fancy piece of electrical equipment I have is my $8 soldering gun.  I have no way to measure current.  I just guessed that the LM317's 1.25v divided by 5ohms = 250mA.  I guess I just didn't have enough voltage, 'cause with the extra battery (6v total), it burned with the same driver.[/quote]

I had the same effect on my LM317 DDL driver. It would gradually decrease in power as the regulator got warmer and warmer and then a min or so off, it would be back at 100%. I personally haven't had much luck with the DDL driver, although I have built a few that work I was never really satisfied with their performance. And the LD doesn't really draw as much power as the LM317 I believe is what drains the batteries so quickly, and is what gets so hot. I built mine exactly to the schematic, but I have a feeling that a better/different capacitor might help. I just resorted to buying the rkcstr drivers. You can click "see" in my sig next to diy and see a few of my projects.

Greenhorn said:

I just tried four AAA batteries, and it actually burned dark paper and plastic. It was able to burn though a black-marked piece of writing paper in about 3-5 seconds. The diode also got pretty hot, so that's probably as much current as I want to run through it.

I also tried a 9v battery. I'm pretty sure it was new, but after only about 15 minutes of playing with it, the battery died. Does the diode really use that much power?

Is it normal for the diode to "die" when it gets too hot, but work perfectly once it cools? It's done that several times.

[quote author=Hemlock Mike link=1227072347/0#1 date=1227073335]How much current do you measure to the diode?
Mike

Click to expand...

I don't know. The most fancy piece of electrical equipment I have is my $8 soldering gun. I have no way to measure current. I just guessed that the LM317's 1.25v divided by 5ohms = 250mA. I guess I just didn't have enough voltage, 'cause with the extra battery (6v total), it burned with the same driver.[/quote]


Now try with 5 or 6 aaa, I guarantee you will get even more power out of it.

Your build is exactly what my first build was like. lm317 4xaaa and a 16x burner diode, I thought the power great but it started decreasing the second the batteries sagged. So i replaced the batteries with 2xCR123 batts which give around 8v when fully charged. The difference in beam visibility is amazing. You will be surprised how much more power you can get from these red diodes.

brtaman said:

Now try with 5 or 6 aaa, I guarantee you will get even more power out of it.

Your build is exactly what my first build was like. lm317 4xaaa and a 16x burner diode, I thought the power great but it started decreasing the second the batteries sagged. So i replaced the batteries with 2xCR123 batts which give around 8v when fully charged. The difference in beam visibility is amazing. You will be surprised how much more power you can get from these red diodes.

Click to expand...

So while 6v may be enough to power the diode, once the batteries begin decreasing in voltage the laser will quickly lose power even if the batteries still have plenty of juice left?

But anyway, with what I have now, the diode gets pretty hot within about 15-20 seconds.  I'm afraid that if I give it any more current it'll burn out. I suppose once I install one in an aixiz module it'll do better since the module will act as a heat sink.

Ace82 said:

And the LD doesn't really draw as much power as the LM317 I believe is what drains the batteries so quickly, and is what gets so hot.

Click to expand...

If the LM317 uses so much voltage and current, is there anything else that would do the same job with less wasted power?  What do ordinary IIIb lasers like my green Executive use?  They run on only 2 AAA batteries and fit in a tiny space.  They clearly don't use an LM317 or anything like that.

Oh yeah, another question.  I know that AAA batteries put out something like 1.2 watts max.  How do I know what wattage rating I need for my resistors?  Is it determined by the battery's output, or the actual current that is put through the diode?  For example, if I ran my diode under 250mA (which I would, of course), would 1/4watt resistors work?  I'm currently using 1/2watt resistors, and they seem to work fine. But they're kind of large, and it would be nice to use the smaller 1/4watt resistors.

Green pointers usually use custom drivers based on surface-mount technology to keep them tiny. I'm sort of new to the forum, but the only place I know of on here to get similar driver to what is installed in a green pointer is the rkcstr driver. More info on this can be had by searching this forum.

Greenhorn said:

[quote author=brtaman link=1227072347/0#10 date=1227117156]
Now try with 5 or 6 aaa, I guarantee you will get even more power out of it.

Your build is exactly what my first build was like. lm317 4xaaa and a 16x burner diode, I thought the power great but it started decreasing the second the batteries sagged. So i replaced the batteries with 2xCR123 batts which give around 8v when fully charged. The difference in beam visibility is amazing. You will be surprised how much more power you can get from these red diodes.

Click to expand...

So while 6v may be enough to power the diode, once the batteries begin decreasing in voltage the laser will quickly lose power even if the batteries still have plenty of juice left?

But anyway, with what I have now, the diode gets pretty hot within about 15-20 seconds. I'm afraid that if I give it any more current it'll burn out. I suppose once I install one in an aixiz module it'll do better since the module will act as a heat sink.

Ace82 said:

And the LD doesn't really draw as much power as the LM317 I believe is what drains the batteries so quickly, and is what gets so hot.

Click to expand...

If the LM317 uses so much voltage and current, is there anything else that would do the same job with less wasted power? What do ordinary IIIb lasers like my green Executive use? They run on only 2 AAA batteries and fit in a tiny space. They clearly don't use an LM317 or anything like that.[/quote]


Oh if thats the case then I would keep the diode usage to a minimum, I didn't realize that you are still waiting to receive the module to put the diode in. Yeah the LM317 isn't the most efficient component, but its does the job well, a reason that it is so popular. As elektrofeak already stated drivers in greenie's are smd drivers with a lower dropout than the L317 another reason that they can run off only 2aaa cells is the fact that a pump diode only uses around 1.8v.

If you want a nice low drop-out driver (1v dropout) I suggest checking out the groove driver, a little smd soldering but its really fun to put the thing together it outputs up to 500ma. Both drlava and Kenom sell these kits for a little over 5bucks, they are a good deal. I think that Kenom has quite a few left over from the Kryton GB, so I would contact him.

Thanks
brtaman

If the LM317 gets hot, it internally starts shutting down with its protection circuit. You may need to HS the regulator.
Most of the resistors can be 1/4 watt. Use ohm's law and the power law to figure what is needed.

When I kill a LD -- it stays dead

Mike