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Author Topic: 5v to Uno thru USB.... what voltage tolerance?  (Read 581 times)
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Hi all,

I'm in the process of converting an ATX PSU into a lab supply. It of course has a 5v output: I'm not exactly sure how precise that is. I was thinking of using it to supply Uno through the USB by hacking a cable. What actual voltage is ok through the USB?

I do have a nice regulator like this which I could easily use to make sure the 5v is in fact 5v. Beauty of that regulator is that the input can be below or above the output, so I'm good no matter what. The regulator's 300mA is enough, since the whole point of the PSU is to be able to supply all other equipment - servos etc- without going through the Uno. Even with a few loaded IO pins at 40mA each, I think I'll be good.

Alternatively I could regulate the PSU 5v up to 7v - that's a bit easier since I can simply jam a wire into Uno's Vin. Of course that seems a bit Irish since the Uno will regulate it back down to 5v again..

As an aside, there are loads of Instructables on using an ATX PSU on the bench; I like this example.

Thoughts please?

Jim
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I believe the USB standard for USB voltage states an acceptable range of 4.75 to 5.25. The regulated 5 volt output from your ATX PSU should be just fine as that is what normally powers the USB ports on PCs.

Lefty

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As long as there is a proper load on your 5V rail, then it should be well within regulation for USB.  After all, where do you think the Vusb for your USB port comes from?
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that is what normally powers the USB ports on PCs.

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where do you think the Vusb for your USB port comes from

Yes indeed, that thought struck me after I posted and was out in the car....

I have a power resistor on the 5v line in accord with what most of the Instructables say.... without it it won't provide VDC anyhoo.

Regarding a connection, I suppose easiest would be to buy a cable and chop the other end off to connect inside the ATX PSU?

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I'm not exactly sure how precise that is.

Most will be within 100mv, +/-. Sometimes within 200mv, +/-.

Alternatively, you can use a to220 5v regulator on the +12v output.

Switching regulators aren't that great if you are dealing with analog signals.
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Regarding a connection, I suppose easiest would be to buy a cable and chop the other end off to connect inside the ATX PSU?

..... which I have since done, works a treat  smiley-cool
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