Computer PSU + DDL Question

[whatsupadrian]

OK so today i took apart an old ATX PSU. Its a 300 watt PSU. It has output of 3.3v @ 28A Max, 5v @ 30A Max, and 12v @ 15A Max. I want to use it to power 2 PHR Blue Rays. I plan on making a DDL circuit for each diode. My questions.... Are CPU PSUs stable as far as the voltage/current? Also using the 12v source what resistor would I use on the LM317T to get a the brightest laser but with a decent life expectancy(no POT).

Thank you.

 

[Alexizupinhea]

1. Someone can correct me if I'm wrong but, as long as you use the capacitor (like in the DDL), you should be fine in terms of spikes, and as for stability, I think the PSUs are pretty stable (aren't computer parts sensitive to voltage?)

2. For the PHR, I'd recommend 125mA or lower, but thats just what I use. There are plenty of other ppl who go higher, but I don't think it's worth it. Most people (I'm afraid to say this generalization) usually recommend 120mA (as far as I've seen), so I use 125mA just as a convenience since w/ the DDL you would need a simple 10ohm resistor for 125mA. If you choose a lower mA, just use the formula 1.25V/x where x is the current (remember to convert to Amps, so 125mA would equal .125Amps). If you did that you would get 10ohm!. Or, you could use the same formula 1.25V/x where x is the resistance. So, if you have a 10ohm resistor, 1.25/10 equals .125Amps, or 125mA.

The above equation works because the LM317 uses a reference voltage of 1.25V to set the current. And yeah, I also don't like working with pots, they annoy the sh*t out of me when trying to set the current for a driver.

 

[whatsupadrian]

Answered my questions. Perfect. Thank you very much. I really don't see the point of pots unless your looking to adjust or fine tuning. Its just an expensive resistor in most cases.

 

[ElektroFreak]

^Pots are great if they're multi-turn.. They're usually way too sensitive if they're single-turn. I enjoy being able to adapt any driver to any diode.

PC PSUs work wonderfully. They tend to be very well filtered, since they're used with digital components, and they provide ample current for nearly every kind of diode you'll use as a hobbyist. I use them in all my scanners since I can power every part of it from one source.

 

[Alexizupinhea]

Yeah, I don't use pots but tht's because 1. I don't have multi-turn pots, only single turn (which can get VERY frustrating.... as said, they are VERY sensitive if single turn), but also, I just don't like setting up a test load. It's pure laziness lol... I'll spend ours on a single laser, but for some reason I hate the idea of spending 5 min. on a test load.

 

[whatsupadrian]

ok well i got it all wired up and everything and the voltage regulator gets real warm over time. Got it heatsinked so its all good now. thanks

 

[Cyparagon]

You should be able to drive a diode with simply a current limiting resistor in series. ATX supplies are already regulated.