This has become a thing lately, with Apple changing stuff on everybody. Everyone has an opinion, and most of them suck. I meant to post this about a week or two ago, but I got busy. Internet dick-waving contests really aren't worth my time anymore, but I thought this could be educational for a few people. Hence why I'm not posting it in the iPhone 5 thread. My target audience isn't reading that thread anymore.
So the first question is: Do you know what you're looking at?
If you answered with, "That's the standard DC bias voltage for digital logic," you'd be correct. If you answered with, "That's the input to pin 1 of a USB connector," you'd also be correct. (That's because USB is used for digital logic circuits). But wait! DC stands for direct current. If those three funny green lines are DC, why aren't they flat? Why do they start at zero?
That's because there really is no such thing as DC, even out of a battery. Even if there was, it's not what comes out of your wall. Instead, what we do is take something wiggly (that's a technical term) and make it as close to flat as we possibly can. So, when the notion of power requirements comes up, that isn't just a reference to how many Watts it draws. It also addresses how those Watts are delivered. There's also the fact that some digital logic circuits use 2.5V for their DC bias, and on satellite systems, we've come down to 1.6V due to power constraints.
However, when you design a device for different power requirements, you want to make sure they can't plug in the wrong cord. This is why, for example, a 240V outlet is drastically different from a 120V outlet in North America. I don't think I have to explain how plugging a 120V appliance into a 240V outlet is bad, but I will anyway.
BOOM! With smartphones, things probably won't be that exciting, but it can do a number on your phone. If your device is designed for a tighter voltage ripple, it's a good idea to prevent you from plugging in a sloppier waveform.
As an aside, each of those is made using parts that come on a silicon chip. That means if I wanted to build a lot of them, I'd have to purchase those chips from a manufacturer. It's even possible I might have specifications that aren't currently in production, which would require having a new chip designed.
Expect to see more of this in the future, because USB is sixteen years old. It will probably be on its way out by the time we're having our next presidential election. We love our energy efficiency lately, and we already have sophisticated logic circuits running on lower DC bias voltages.
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