Power Supply

Cyparagon · Apr 6, 2011

No, I mean either after or before the regulator itself. It is only to divert some of the heat.

dethlore · Apr 6, 2011

Oh, you're saying put one 3Ω resistor in series before the LM? If I haven't got a 3w resistor, could I just use 3 paralleled 10Ω 1w resistors?

Cyparagon · Apr 7, 2011

Now you're thinking

Bionic-Badger · Apr 7, 2011

You're still wasting a lot of power using resistors and the voltage they drop will vary according to what you set your LM317 current regulation at. Just get some more capable rectifier diodes like the 1N5400 series. The 1N4001 diodes are designed to only tolerate 1A sustained current which is not enough for many 445nm laser designs.

Cyparagon · Apr 7, 2011

You need to drop the voltage with linear regulators. The power is wasted no matter what. Where the heat is dissipated depends on the design, but the total heat will be the same. I suggested resistors because they're good at dissipating heat and their temp can be hundreds of degrees higher than silicon devices (like diodes and transistors and LM317s).

Yes, they will drop less voltage at lower current, but remember power = I²R. When the current is lower, everything generates less heat. If the LM317 can handle the current at 9V, then it can actually handle a lower current at 12V better.

dethlore · Apr 7, 2011

Bionic-Badger said:
You're still wasting a lot of power using resistors and the voltage they drop will vary according to what you set your LM317 current regulation at. Just get some more capable rectifier diodes like the 1N5400 series. The 1N4001 diodes are designed to only tolerate 1A sustained current which is not enough for many 445nm laser designs.

Haha good thought! I actually have some 1N5402 diodes on the way... the 5400s weren't available, but I didn't notice any significant differences. When they get in I'll post some results of trying the different methods we've discussed.

dethlore · Apr 19, 2011

Just to give everyone an update, I've got the 13.8v 25amp power supply behaving and powering an A140 diode quite nicely at 5.6v 800ma.

I ended up using 10 Ohms (1 Ohm 5 Watt, 3x 100 Ohm 2 Watt) before hitting the first LM317 with no resistors between Adj and Out which feeds into another LM317 (no resistance between adj and out again) with output splitting voltage one way to the Capacitor then LD, the other through 12.5 Ohms (8x 100 Ohm 2 Watt). The output is about 5.6v at 800ma. This is by NO means a small driver … but then again, what kind of flashlight is going to have 14v up to 25A??? haha kind of a fun experiment anyways though. I’m going to integrate a switch and a few more circuits so I can basically have my own switching test drivers to run different diodes that have different power needs. Should work great for a bench/lab!

Benm · Apr 19, 2011

Sounds a bit confusing... could you draw a circuit diagram of your final solution?

dethlore · Apr 20, 2011

Made a small tweak to the first resistor and got the actual numbers rather than trying to remember.

I think I could probably take one of these LM317s out of the circuit... but this works so well in dissipating heat.

Sorry for the rough drawing of this schematic.
R1: 1 Ohm 5W
LM1: Regulates Current to 740mA
LM2: Regulates Voltage to 5.25v
R2-R9: 100 Ohm 1W in parallel
C: 10uf 16v
LD: A140 445nm

Toke · Apr 20, 2011

That circuit is not regulating anything.
It looks like you have just strung components together until the current were acceptable.

dethlore · Apr 20, 2011

Toke said:
That circuit is not regulating anything.
It looks like you have just strung components together until the current were acceptable.

Gosh I noticed that when I drew this out...

I tried setting it up how the LM diagrams instructed to, but they just wouldn't give the right results. This setup DOES give me what I want... and maybe it IS just a bunch of stuff strung together, but it's something I can build off of to get functional. Lots of room for improvement.

Toke · Apr 20, 2011

I am trying out a new simulation program called Qucs, it is no problem to draw the circuit I just can't get the simulation function to work, or export the drawing.'

The idea is that on the first LM317 you connect a 100 Ohm from output to adj, and then 600-700 Ohm from adjust to zero. That is a voltage divider that will give a regulated voltage output from the first of app. 1.25*(700/100) = 8.75V.

Of course, using the lm317 like it is supposed to requires that you have some kind of heatsinking for it.

dethlore · Apr 20, 2011

Toke said:
I am trying out a new simulation program called Qucs, it is no problem to draw the circuit I just can't get the simulation function to work, or export the drawing.'

The idea is that on the first LM317 you connect a 100 Ohm from output to adj, and then 600-700 Ohm from adjust to zero. That is a voltage divider that will give a regulated voltage output from the first of app. 1.25*(700/100) = 8.75V.

Of course, using the lm317 like it is supposed to requires that you have some kind of heatsinking for it.

I was thinking last night of changing my setup to something similar to what you are describing, just haven't done it yet. Correct me if I"m wrong, but for the 100 Ohm Adj-Out, would you use a potentiometer so you more easily vary the current?

For a 445nm diode, the battery input should be about 9v in an LM317 system, correct? Just prior to getting to the diode the voltage should be ~5-6v? So wouldn't you want to use 400 Ohms for the voltage divider instead of 700?

Thankfully, I do have a great heatsink on the LM317 right now. I'll have to take a picture of it. I'm using a PhenomII x6 stock CPU heatsink with 80mm fan. Keeps it nice and cool!

Toke · Apr 20, 2011

dethlore said:
I was thinking last night of changing my setup to something similar to what you are describing, just haven't done it yet. Correct me if I"m wrong, but for the 100 Ohm Adj-Out, would you use a potentiometer so you more easily vary the current?

The drawings have the pot in the voltage divider between adj and ground.
In order to adjust VOLTAGE.

For a 445nm diode, the battery input should be about 9v in an LM317 system, correct? Just prior to getting to the diode the voltage should be ~5-6v? So wouldn't you want to use 400 Ohms for the voltage divider instead of 700?

The 9V is fine and that is what you want coming from the first lm317 to the second. The second will then be set up as a current regulator and automatically drop the voltage to whatever drives the set current through the diode.

Thankfully, I do have a great heatsink on the LM317 right now. I'll have to take a picture of it. I'm using a PhenomII x6 stock CPU heatsink with 80mm fan. Keeps it nice and cool!

That is fine, just remember that the lm317 have output to case so you will need insulation if you want them both on the same heatsink.

dethlore · Apr 20, 2011

Toke said:
The drawings have the pot in the voltage divider between adj and ground.
In order to adjust VOLTAGE.

The 9V is fine and that is what you want coming from the first lm317 to the second. The second will then be set up as a current regulator and automatically drop the voltage to whatever drives the set current through the diode.

That is fine, just remember that the lm317 have output to case so you will need insulation if you want them both on the same heatsink.

Right ok - this is what I thought, but wasn't 100% sure. I'll give this a go tonight or tomorrow and let you know how it pans out.

Thanks for your input! :yh:

Toke · Apr 20, 2011

You do have a test load, Right?

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