Working with USB 3.1 Help

Thread Starter

awwende

Joined Feb 17, 2009
39
The newest USB standard, 3.1 offers a wide range of power output options:
  • 5V, 900mA (USB 3.0)
  • 5V, 2A
  • 12V, 5A
  • 20V, 5A
  • Existing USB 2.0 power options
Has anyone worked with USB 3.1 and negotiating power? I'm thinking of working on a USB power supply and would like to enable the 20V, 5A power setting and use an adjustable buck regulator for the supply.

Do I need an IC to do the power negotiation (if so, is there one that's readily available from digikey/mouser)?

Or can I do the same thing as the old DIY Apple chargers where you use a resistor voltage divider to enable the full power output from the USB port?

EDIT: I'm not looking for a critique of the idea, but looking for ideas how to do it.
 
Last edited:

Papabravo

Joined Feb 24, 2006
13,924
What does the spec say? Have you downloaded it and read it? That might be a valuable first step. I am familiar with the negotiation process in USB 2.0. It is hard to imagine doing that without a processor and a USB controller.
 

Thread Starter

awwende

Joined Feb 17, 2009
39
Or you just could buy a PC PSU and use it as a power supply.
There's a few problems with PC PSUs but the main reason I don't want to use one is because I would like to be able to plug into my USB on my desktop with a 3.1 port. As 3.1 becomes the standard on laptops, I would like to be able to plug into my laptop and have a portable, light weight supply.
 

spinnaker

Joined Oct 29, 2009
7,835
There's a few problems with PC PSUs but the main reason I don't want to use one is because I would like to be able to plug into my USB on my desktop with a 3.1 port. As 3.1 becomes the standard on laptops, I would like to be able to plug into my laptop and have a portable, light weight supply.
So you are going to risk frying your expensive laptop that may or may not have over current protection for the sake of convenience?
 

Papabravo

Joined Feb 24, 2006
13,924
There's a few problems with PC PSUs but the main reason I don't want to use one is because I would like to be able to plug into my USB on my desktop with a 3.1 port. As 3.1 becomes the standard on laptops, I would like to be able to plug into my laptop and have a portable, light weight supply.
That is possibly the worst idea I've ever heard of.
 

ErnieM

Joined Apr 24, 2011
8,045
I've used my desktop to power small 5V projects off a USB from time to time, certainly during programming. During debug I add a bench supply but still have the PC connected for in circuit debug.

You just try to keep things isolated as possible while generally accumulating good karma.
 

Thread Starter

awwende

Joined Feb 17, 2009
39
So you are going to risk frying your expensive laptop that may or may not have over current protection for the sake of convenience?
In order to fry my expensive laptop, I first need to be able to negotiate the power to get the full power output. Any ideas as to how to get the full power out of a 3.1 port?
 
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