Home made LM-317 Driver

[Eudaimonium]

Yes, all four 9mm IR diodes I have have a bluish tint on the window. I think it is an AR coating.

That red dot was for me to remember which pin was positive. I have run it at 360 mA, but only quickly. Just to see if it worked. :yh:
It got a little warm not in a module or heatsink.

best regards

David

And I take it that it's not red?
I know it's an AR coating, but by it's color you can aproximate the color. Blue and violet diodes have yellowish tint, red diodes have bluish, NIR and IR have green , and very far IR have brown.

What did you see any glow from the diode?

 

[Autist]

And I take it that it's not red?
I know it's an AR coating, but by it's color you can aproximate the color. Blue and violet diodes have yellowish tint, red diodes have bluish, NIR and IR have green , and very far IR have brown.

What did you see any glow from the diode?

Hi, sorry, yes they were all a rich red colour at the emitter. But I have no idea how far up the red wavelength scale I can see compared to others.
I did not want to look for long, just to see if they were lasing. You can see the difference as the LD starts to lase. The ambient light was too bright to see a reflection off anything as there was no lens used to focus the output.

regards

David

 

[jmgallego]

The trimmer isn't even getting warm, whereas the 0.5W 2R2 resistors in parallel are getting a bit hot.

Can you tell me a little more about your 2R2 resistors? How many ohms are they, 2.2 ohms?

 

[HIMNL9]

2,2 ohm resistors ..... that in parallel, make 1,1 ohm ..... that, for the LM317, make 1,25/1.1=1136mA (1,136A) ..... plus the part regulated from the trimmer, that must not be too much, with this configuration

But this can easily carry the LM317 to go in overheating protection, cause the package is rated for 1,5W dissipation, usually (can be more, with a huge heatsink you can reach 3,5 to 4 W dissipation, from a TO220 case) .....

Anyway ..... when used without heatsinks, you need to keep dissipated power under the 1,5W, if you don't want that the regulator overheat and go in protection, and the dissipated power is made from: the current, multiplied for the total dropout voltage (that is, the 2,5V of the internal dropout, plus the difference from the input and output voltage) ..... so, if you have, as example, a LD that need 5V (where you need a minimum input of 7,5 / 8V), and you use a 9V input voltage, with a current of 1,136A you have a total power dissipation, from the regulator, of 4*1.136=4,55W ..... a bit too much

 

[jupiter8]

Thanks for those calculations HIMNL9, I've written that down for my future reference. Looks like I need a bigger heatsink on the LM317, I might even get a fan! I'm wondering to myself how these circuits are going to cope with summer here... It's cold right now, will probably make a big difference I expect.

 

[HIMNL9]

Yes, this can also be a problem ..... normal heatsinks efficency depends from a lot of factors, not last the difference of temperature from the heatsink and the air ..... forced airflow can help a lot, in hot ambient conditions .....

You can try a thing, anyway, if your electronic parts shop can help you ..... taking two LM317 from the same production lot (this means, ALL the numbers on the bodies MUST be identicals, not just the part number), hook them on a decent heatsink, and directly parallel them (also better, using two LM117 from the same production lot, if you find them, that are rated for a higher working temperature) ..... this is, anyway, a trial ..... i made it, once, and it worked good for 2A, but is all matter of trials, cause they are not designed for be used in this way .....

 

[jmgallego]

2,2 ohm resistors ..... that in parallel, make 1,1 ohm ..... that, for the LM317, make 1,25/1.1=1136mA (1,136A) ..... plus the part regulated from the trimmer, that must not be too much, with this configuration

But this can easily carry the LM317 to go in overheating protection, cause the package is rated for 1,5W dissipation, usually (can be more, with a huge heatsink you can reach 3,5 to 4 W dissipation, from a TO220 case) .....

Anyway ..... when used without heatsinks, you need to keep dissipated power under the 1,5W, if you don't want that the regulator overheat and go in protection, and the dissipated power is made from: the current, multiplied for the total dropout voltage (that is, the 2,5V of the internal dropout, plus the difference from the input and output voltage) ..... so, if you have, as example, a LD that need 5V (where you need a minimum input of 7,5 / 8V), and you use a 9V input voltage, with a current of 1,136A you have a total power dissipation, from the regulator, of 4*1.136=4,55W ..... a bit too much

Thanks.

Same goes with the diodes, they too will overheat. So this where the LM350 would come handy, to prevent going into protection, and the 1N5402s from going into melt down. However, the heat would still need to be dissipated. (http://laserpointerforums.com/f51/dummy-load-high-current-2a-test-load-52372.html#post736135)