alt Hacker NewsYou could run on 5V with a boost voltage converter to 12V. For extra credit, you could run the USB-PD off 5V, negotiate 12V and only then switch it to the load.
You could run on 5V with a boost voltage converter to 12V. For extra credit, you could run the USB-PD off 5V, negotiate 12V and only then switch it to the load.
If I need 12V/1A, then that suggests I need 5V/2.4A even with 100% efficiency. Without negotiating anything, a device shouldn't draw more than 5V/0.5A.
That's not to say that a boost converter doesn't have value, but it still leaves a gap where there could be confusion.
The confusion or complexity even multiplies if the device has additional USB-C for data transfer. In that case, you either have to mark one port as being the "power in" port, or you have to support power in and data out on all the ports, which gets complicated and expensive.
It would be a great move by the USB IF to think through this sort of thing more carefully. Right now the USB-c connector is so overloaded in terms of power, display modes, thunderbolt, speeds, etc. that it's very hard to predict whether two USB-c devices will connect and at what power or speed and with what capabilities. For power, it would be helpful to require supplies to have a standardized status LED so that e.g. green means that the supply is providing the highest power allowed by the device (not the supply), yellow means there's been a compromise, and red suggests an error condition.