3 ms·
I'm aware. The potential "dumps" current into the load proportional to its voltage. (A constant current supply would raise the voltage to achieve the requested
by R0b0t1 6y ago
I'm aware. The potential "dumps" current into the load proportional to its voltage. (A constant current supply would raise the voltage to achieve the requested current but the USB bus is not a constant current supply. There are multiple ways your yes-but is annoying and unhelpful.)
The main concern behind negotiation seems to be safety of the user and safety of the power supply. Detecting a safe load means detecting a not-short.
The basis for the 5V power negotiation on USB is extremely silly. The power supply is already current limited, protecting you from shorts, and the supply voltage is ~5V, quite far from anything dangerous.
- lxgr 6y ago> The basis for the 5V power negotiation on USB is extremely silly. This may be true for wall chargers but not devices capable of supplying power to peripherals while on battery power themselves. For example, an external hard drive should not have to figure out that a large tablet can power it, while a phone won't, though trial and error, by attempting to spin up the disks multiple times.
- R0b0t1 6y agoTrue, but opt-in seems to do what users expect most of the time. Enough device expose their full power without negotiation that there are workarounds like sleeping a USB port instead of relying on power negotiation. Devices are going to misbehave anyway, it's probably more important to default to a reasonable level of mostly works.