Delete comment from: Ken Shirriff's blog
Hi,
Fantastic article.
I think the slope on the output of the Apple chargers is probably not a bad thing. It's better for power supplies to have some source resistance, it will naturally limit the output power from the device, and prevent catastrophic overloads.
Also, having this resistance can be good for rejecting noise, or when external sources are coupled onto the same circuit... i.e. if charging a battery ... since it will naturally limit the amount of current that can be drawn from the circuit. It's a sort of backup safety feature. As you draw more current, the voltage will drop more and more, and it's a nice little negative feedback loop.
Perhaps, on the spectrum of safety vs efficiency, the slope of that V-I curve is right in the Goldilocks zone.
It's simple and effective. Not sure if that is the story though, 0-100% of what I said about could be lie(s). Pure speculation.
Oct 15, 2017, 10:33:01 AM
Posted to A dozen USB chargers in the lab: Apple is very good, but not quite the best