Getting a steady 5v from a PSU... Molex??

[azibux1]

Better in the respect that the PC PSU will likely have a lot less ripple and be massively more efficient provided you have some decent load going through it. From the datasheet the LM2596 has an efficiency of around 72%, this would go on top of your PC PSU's efficiency at whatever load you have on it.

One possible benefit you might see on 5.12v vs 5.00v would be if you are using the Arduino's analogue outputs to measure something and you need the accuracy to be super high, otherwise who cares about 0.1v.

What sort of load on the 12v and 5v are you planning anyway?

If I needed 5v or 12v near my PC and it wasn't an audio circuit, then I would use my PC power supply. PC SMPS are fantastic compared with a crappy LM2596 circuit from China.

Ahh right, makes sense

It won't be involving any audio so that's good

To answer your question, there isn't going to be much load at all really, will that be a problem?

There will be 2 - 4 (probably just 2 though) 120mm case fans and the arduino

Case fans will be on the 12v and Arduino on the 5v

If the (lack of) load will be a problem (I'll wait for your answer on this please), would I be best off splicing into just one of the 12v cables and adding a resistor in between it and ground. And the same for 5v? Would you be able to suggest a resistor please if that's necessary?

Thanks!

 

[Tealc]

The efficiency of a PC SMPS apparently isn't wonderful down low as they are made for 20,50 and 100% duty. 3 fans and an Arduino will use less than 10W probably and that's in standby power usage territory. The PSU will have to power its own fan as well so that will add a watt or two.

You might be better off with a different power supply. You can get 12v/5v supplies that look a bit like laptop power bricks and they'll run passive and they can come with a Molex on the end. They might not be as good as a PC SMPS but should be more than adequate for any project and I've used them. Arduino isn't that fussy and the other chip isn't fussy as it has its own regulation.

What would be the point in having a resistor to ground? All it would do is dissipate heat and waste energy. You can get <50 Ohm >5W resistors that would burn some energy for you and make some heat but I wouldn't do that.

It used to be the case that PSUs required some load to function and start up but generally these days they'll run with a minimal load. Using just the 12v is pointless in modern PSUs as the 5v is derived usually from the 12v rail. If you were using your existing PC power supply modded to power something outside the case then go for it but for a standalone project an ATX PSU is overkill.

What are you planning anyway?

 

[Rroff]

Ahh sorry I only just realised that

I kind of like the idea of being able to precisely control it. And it makes my project look that little bit cooler haha

Are there any downsides to using the LM2596?

EDIT: Ahh just saw this, LM2596 might have no effect then:

Ooops the buck-boost modules I use handle equal voltage never occurred to me the buck ones might not :S