Author Topic: USB Power supply, 5V or 5.12V ?  (Read 1352 times)

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Offline smbakerTopic starter

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USB Power supply, 5V or 5.12V ?
« on: December 12, 2018, 12:04:25 am »
I have a usb power supply project that I'm planning on building. I can trim it out to supply exactly 5V, or I can go a little bit higher, for example 5.12V.

Knowing that there's usually a healthy cable voltage drop in even most decent USB cables, let alone your typical crappy cable, I'm thinking that 5.12V seems like the reasonable choice. I also see that there's lots of 5.1V power supplies on the market, and that they're often recommened for, for example, rasbperry pi.

This power supply will be used for powering projects, as well as charging iphones and similar devices.

Thoughts on 5V vs 5.1V?

Scott
 

Offline james_s

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Re: USB Power supply, 5V or 5.12V ?
« Reply #1 on: December 12, 2018, 12:39:52 am »
You're splitting hairs here. 5.12V is well within the tolerance for USB and won't hurt anything. Given cables will all have some drop, it's probably not a bad idea to err a little on the high side.
 

Online DaJMasta

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Re: USB Power supply, 5V or 5.12V ?
« Reply #2 on: December 12, 2018, 01:59:10 am »
5.1V or so is probably fine, for reasons mentioned.  That said, if you want to charge phones and things using higher than normal USB currents, you need the appropriate IC to negotiate that protocol, and often have to supply higher voltages.
 

Offline bson

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Re: USB Power supply, 5V or 5.12V ?
« Reply #3 on: December 12, 2018, 06:18:02 am »
Aim a little high; it's common for USB devices to have a Schottky diode on VBUS.
 

Online TERRA Operative

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Re: USB Power supply, 5V or 5.12V ?
« Reply #4 on: December 12, 2018, 01:26:19 pm »
The USB spec allows up to 5.25V (5V +/-5%), so 5.12V will be perfectly fine (and help allow for voltage losses through cables and connectors and reverse polarity protection diodes etc).

https://en.wikipedia.org/wiki/USB See the right hand sidebar for details.
Where does all this test equipment keep coming from?!?

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